//! `workspace/executeCommand` dispatcher.
//!
//! Phase 13 introduced the router + `nuwiki.file.delete`. Phase 14 added
//! the cheap surgical edits — checkbox toggle/cycle/reject, heading
//! promote/demote, "next task" navigation. Phase 15 layers on the
//! generation + workspace-query commands: `toc.generate`,
//! `links.generate`, `workspace.checkLinks`, `workspace.findOrphans`.
//!
//! Every command resolves to either a `WorkspaceEdit` (the server then
//! calls `apply_edit`) or a JSON `Value` (returned to the client) — see
//! `CommandOutcome` below. `ops::*` are the pure functions the dispatcher
//! wraps; they're `pub` so tests and future tooling can drive them
//! without spinning up a Backend.

use serde::Deserialize;
use serde_json::Value;
use std::sync::atomic::Ordering;
use tower_lsp::lsp_types::{Position as LspPosition, Url, WorkspaceEdit};

use crate::edits::{op_delete, WorkspaceEditBuilder};
use crate::nav;
use crate::Backend;

/// Result of a single executeCommand dispatch.
pub enum CommandOutcome {
    /// Push to the client via `workspace/applyEdit`.
    Edit(WorkspaceEdit),
    /// Return verbatim as the executeCommand response.
    Value(Value),
}

/// All commands the server advertises in `ExecuteCommandOptions.commands`.
/// Keep in lock-step with the match arms in `execute`.
pub const COMMANDS: &[&str] = &[
    "nuwiki.file.delete",
    "nuwiki.list.toggleCheckbox",
    "nuwiki.list.cycleCheckbox",
    "nuwiki.list.rejectCheckbox",
    "nuwiki.list.nextTask",
    "nuwiki.heading.addLevel",
    "nuwiki.heading.removeLevel",
    "nuwiki.toc.generate",
    "nuwiki.links.generate",
    "nuwiki.workspace.checkLinks",
    "nuwiki.workspace.findOrphans",
    "nuwiki.diary.openToday",
    "nuwiki.diary.openYesterday",
    "nuwiki.diary.openTomorrow",
    "nuwiki.diary.openIndex",
    "nuwiki.diary.generateIndex",
    "nuwiki.diary.next",
    "nuwiki.diary.prev",
    "nuwiki.diary.listEntries",
    "nuwiki.diary.openForDate",
    "nuwiki.tags.search",
    "nuwiki.tags.generateLinks",
    "nuwiki.tags.rebuild",
    "nuwiki.export.currentToHtml",
    "nuwiki.export.allToHtml",
    "nuwiki.export.allToHtmlForce",
    "nuwiki.export.browse",
    "nuwiki.export.rss",
    "nuwiki.wiki.listAll",
    "nuwiki.wiki.select",
    "nuwiki.wiki.openIndex",
    "nuwiki.wiki.tabOpenIndex",
    "nuwiki.wiki.gotoPage",
];

pub(crate) async fn execute(
    backend: &Backend,
    command: &str,
    args: Vec<Value>,
) -> Result<Option<CommandOutcome>, String> {
    match command {
        "nuwiki.file.delete" => file_delete(args).map(|opt| opt.map(CommandOutcome::Edit)),
        "nuwiki.list.toggleCheckbox" => {
            Ok(list_checkbox(backend, args, ops::toggle_state)?.map(CommandOutcome::Edit))
        }
        "nuwiki.list.cycleCheckbox" => {
            Ok(list_checkbox(backend, args, ops::cycle_state)?.map(CommandOutcome::Edit))
        }
        "nuwiki.list.rejectCheckbox" => {
            Ok(list_checkbox(backend, args, ops::reject_state)?.map(CommandOutcome::Edit))
        }
        "nuwiki.list.nextTask" => {
            list_next_task(backend, args).map(|opt| opt.map(CommandOutcome::Value))
        }
        "nuwiki.heading.addLevel" => {
            Ok(heading_change_level(backend, args, 1)?.map(CommandOutcome::Edit))
        }
        "nuwiki.heading.removeLevel" => {
            Ok(heading_change_level(backend, args, -1)?.map(CommandOutcome::Edit))
        }
        "nuwiki.toc.generate" => toc_generate(backend, args).map(|o| o.map(CommandOutcome::Edit)),
        "nuwiki.links.generate" => {
            links_generate(backend, args).map(|o| o.map(CommandOutcome::Edit))
        }
        "nuwiki.workspace.checkLinks" => {
            workspace_check_links(backend, args).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.workspace.findOrphans" => {
            workspace_find_orphans(backend, args).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.diary.openToday" => diary_open_relative(backend, args, RelativeDay::Today)
            .map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.diary.openYesterday" => diary_open_relative(backend, args, RelativeDay::Yesterday)
            .map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.diary.openTomorrow" => diary_open_relative(backend, args, RelativeDay::Tomorrow)
            .map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.diary.openIndex" => {
            diary_open_index(backend, args).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.diary.generateIndex" => {
            diary_generate_index(backend, args).map(|o| o.map(CommandOutcome::Edit))
        }
        "nuwiki.diary.next" => {
            diary_step(backend, args, true).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.diary.prev" => {
            diary_step(backend, args, false).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.diary.listEntries" => {
            diary_list(backend, args).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.diary.openForDate" => {
            diary_open_for_date(backend, args).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.tags.search" => tags_search(backend, args).map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.tags.generateLinks" => {
            tags_generate_links(backend, args).map(|o| o.map(CommandOutcome::Edit))
        }
        "nuwiki.tags.rebuild" => tags_rebuild(backend, args).map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.export.currentToHtml" => {
            export_current(backend, args, false).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.export.allToHtml" => {
            export_all(backend, args, false).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.export.allToHtmlForce" => {
            export_all(backend, args, true).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.export.browse" => {
            export_current(backend, args, true).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.export.rss" => export_rss(backend, args).map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.wiki.listAll" => wiki_list_all(backend).map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.wiki.select" => wiki_list_all(backend).map(|o| o.map(CommandOutcome::Value)),
        "nuwiki.wiki.openIndex" => {
            wiki_open_index(backend, args, false).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.wiki.tabOpenIndex" => {
            wiki_open_index(backend, args, true).map(|o| o.map(CommandOutcome::Value))
        }
        "nuwiki.wiki.gotoPage" => {
            wiki_goto_page(backend, args).map(|o| o.map(CommandOutcome::Value))
        }
        other => Err(format!("unknown nuwiki command: {other}")),
    }
}

#[derive(Deserialize)]
struct PosArgs {
    uri: Url,
    position: LspPosition,
}

fn parse_pos(args: Vec<Value>) -> Result<PosArgs, String> {
    let raw = args
        .into_iter()
        .next()
        .ok_or_else(|| "missing { uri, position } argument".to_string())?;
    serde_json::from_value(raw).map_err(|e| format!("invalid args: {e}"))
}

fn file_delete(args: Vec<Value>) -> Result<Option<WorkspaceEdit>, String> {
    #[derive(Deserialize)]
    struct Args {
        uri: Url,
    }
    let raw = args
        .into_iter()
        .next()
        .ok_or_else(|| "nuwiki.file.delete: missing arguments".to_string())?;
    let parsed: Args = serde_json::from_value(raw)
        .map_err(|e| format!("nuwiki.file.delete: invalid args — {e}"))?;
    let mut builder = WorkspaceEditBuilder::new();
    builder.file_op(op_delete(parsed.uri));
    Ok(Some(builder.build()))
}

fn list_checkbox(
    backend: &Backend,
    args: Vec<Value>,
    mutate: fn(&str) -> Option<&'static str>,
) -> Result<Option<WorkspaceEdit>, String> {
    let p = parse_pos(args)?;
    let doc = match backend.documents.get(&p.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let (line, col) = nav::lsp_to_byte_pos(p.position, &doc.text, utf8);
    Ok(ops::checkbox_edit(
        &doc.text, &doc.ast, &p.uri, line, col, utf8, mutate,
    ))
}

fn list_next_task(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    let p = parse_pos(args)?;
    let doc = match backend.documents.get(&p.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let (line, col) = nav::lsp_to_byte_pos(p.position, &doc.text, utf8);
    let Some(loc) = ops::next_task(&doc.ast, &p.uri, &doc.text, line, col, utf8) else {
        return Ok(None);
    };
    serde_json::to_value(loc)
        .map(Some)
        .map_err(|e| format!("nuwiki.list.nextTask: serialization failed — {e}"))
}

fn heading_change_level(
    backend: &Backend,
    args: Vec<Value>,
    delta: i32,
) -> Result<Option<WorkspaceEdit>, String> {
    let p = parse_pos(args)?;
    let doc = match backend.documents.get(&p.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let (line, col) = nav::lsp_to_byte_pos(p.position, &doc.text, utf8);
    Ok(ops::heading_change_level(
        &doc.text, &doc.ast, &p.uri, line, col, utf8, delta,
    ))
}

#[derive(Deserialize)]
struct UriArg {
    uri: Url,
}

fn parse_uri_arg(args: Vec<Value>) -> Result<UriArg, String> {
    let raw = args
        .into_iter()
        .next()
        .ok_or_else(|| "missing { uri } argument".to_string())?;
    serde_json::from_value(raw).map_err(|e| format!("invalid args: {e}"))
}

#[derive(Deserialize, Default)]
struct OptionalUriArg {
    #[serde(default)]
    uri: Option<Url>,
}

fn parse_optional_uri_arg(args: Vec<Value>) -> Result<OptionalUriArg, String> {
    match args.into_iter().next() {
        Some(v) => serde_json::from_value(v).map_err(|e| format!("invalid args: {e}")),
        None => Ok(OptionalUriArg::default()),
    }
}

fn toc_generate(backend: &Backend, args: Vec<Value>) -> Result<Option<WorkspaceEdit>, String> {
    let p = parse_uri_arg(args)?;
    let doc = match backend.documents.get(&p.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    Ok(ops::toc_edit(&doc.text, &doc.ast, &p.uri, utf8))
}

fn links_generate(backend: &Backend, args: Vec<Value>) -> Result<Option<WorkspaceEdit>, String> {
    let p = parse_uri_arg(args)?;
    let doc = match backend.documents.get(&p.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let wiki = match backend.wiki_for_uri(&p.uri) {
        Some(w) => w,
        None => return Ok(None),
    };
    let current_page = crate::index::page_name_from_uri(&p.uri, Some(&wiki.config.root));
    let pages = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        idx.page_names()
    };
    Ok(ops::links_edit(
        &doc.text,
        &doc.ast,
        &p.uri,
        &current_page,
        &pages,
        utf8,
    ))
}

fn workspace_check_links(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let wiki = match p.uri.as_ref().and_then(|u| backend.wiki_for_uri(u)) {
        Some(w) => w,
        None => match backend.default_wiki() {
            Some(w) => w,
            None => return Ok(Some(serde_json::json!([]))),
        },
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let idx = wiki
        .index
        .read()
        .map_err(|_| "index lock poisoned".to_string())?;
    let broken = ops::collect_workspace_broken_links(backend, &idx, utf8);
    Ok(Some(serde_json::to_value(broken).map_err(|e| {
        format!("nuwiki.workspace.checkLinks: serialization failed — {e}")
    })?))
}

#[derive(Clone, Copy)]
enum RelativeDay {
    Today,
    Yesterday,
    Tomorrow,
}

fn resolve_diary_wiki(backend: &Backend, uri: Option<&Url>) -> Option<crate::wiki::Wiki> {
    if let Some(u) = uri {
        if let Some(w) = backend.wiki_for_uri(u) {
            return Some(w);
        }
    }
    backend.default_wiki()
}

fn diary_open_relative(
    backend: &Backend,
    args: Vec<Value>,
    rel: RelativeDay,
) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let Some(wiki) = resolve_diary_wiki(backend, p.uri.as_ref()) else {
        return Ok(None);
    };
    let today = nuwiki_core::date::DiaryDate::today_utc();
    let date = match rel {
        RelativeDay::Today => today,
        RelativeDay::Yesterday => today.prev_day(),
        RelativeDay::Tomorrow => today.next_day(),
    };
    let Some(uri) = crate::diary::uri_for_date(&wiki.config, &date) else {
        return Ok(None);
    };
    Ok(Some(serde_json::json!({
        "uri": uri,
        "date": date.format(),
    })))
}

fn diary_open_index(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let Some(wiki) = resolve_diary_wiki(backend, p.uri.as_ref()) else {
        return Ok(None);
    };
    let Some(uri) = crate::diary::index_uri(&wiki.config) else {
        return Ok(None);
    };
    Ok(Some(serde_json::json!({ "uri": uri })))
}

fn diary_generate_index(
    backend: &Backend,
    args: Vec<Value>,
) -> Result<Option<WorkspaceEdit>, String> {
    let p = parse_optional_uri_arg(args)?;
    let Some(wiki) = resolve_diary_wiki(backend, p.uri.as_ref()) else {
        return Ok(None);
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let Some(index_uri) = crate::diary::index_uri(&wiki.config) else {
        return Ok(None);
    };
    let body = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        crate::diary::render_index_body(&wiki.config, &idx)
    };
    Ok(Some(ops::diary_generate_index_edit(
        backend, &index_uri, &body, utf8,
    )))
}

fn diary_step(backend: &Backend, args: Vec<Value>, forward: bool) -> Result<Option<Value>, String> {
    let p = parse_uri_arg(args)?;
    let Some(wiki) = backend.wiki_for_uri(&p.uri) else {
        return Ok(None);
    };
    // Pivot date: the current page's `diary_date` when it's an entry,
    // otherwise today — matches vimwiki's "navigate from whatever date
    // I'm currently viewing".
    let pivot = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        idx.page(&p.uri)
            .and_then(|page| page.diary_date)
            .unwrap_or_else(nuwiki_core::date::DiaryDate::today_utc)
    };
    let next = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        if forward {
            crate::diary::next_entry(&idx, &pivot)
        } else {
            crate::diary::prev_entry(&idx, &pivot)
        }
    };
    match next {
        None => Ok(None),
        Some(entry) => Ok(Some(serde_json::to_value(&entry).map_err(|e| {
            format!("nuwiki.diary.next/prev: serialization failed — {e}")
        })?)),
    }
}

fn diary_list(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    #[derive(Deserialize, Default)]
    struct Args {
        #[serde(default)]
        uri: Option<Url>,
        #[serde(default)]
        year: Option<i32>,
        #[serde(default)]
        month: Option<u8>,
    }
    let parsed: Args = match args.into_iter().next() {
        Some(v) => serde_json::from_value(v).map_err(|e| format!("invalid args: {e}"))?,
        None => Args::default(),
    };
    let Some(wiki) = resolve_diary_wiki(backend, parsed.uri.as_ref()) else {
        return Ok(Some(serde_json::json!([])));
    };
    let entries = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        crate::diary::list_entries_filtered(&idx, parsed.year, parsed.month)
    };
    Ok(Some(serde_json::to_value(&entries).map_err(|e| {
        format!("nuwiki.diary.listEntries: serialization failed — {e}")
    })?))
}

fn diary_open_for_date(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    #[derive(Deserialize)]
    struct Args {
        date: String,
        #[serde(default)]
        uri: Option<Url>,
    }
    let raw = args
        .into_iter()
        .next()
        .ok_or_else(|| "nuwiki.diary.openForDate: missing { date } argument".to_string())?;
    let parsed: Args = serde_json::from_value(raw)
        .map_err(|e| format!("nuwiki.diary.openForDate: invalid args — {e}"))?;
    let Some(date) = nuwiki_core::date::DiaryDate::parse(&parsed.date) else {
        return Err(format!(
            "nuwiki.diary.openForDate: '{}' is not a YYYY-MM-DD date",
            parsed.date
        ));
    };
    let Some(wiki) = resolve_diary_wiki(backend, parsed.uri.as_ref()) else {
        return Ok(None);
    };
    let Some(uri) = crate::diary::uri_for_date(&wiki.config, &date) else {
        return Ok(None);
    };
    Ok(Some(
        serde_json::json!({ "uri": uri, "date": date.format() }),
    ))
}

fn tags_search(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    #[derive(Deserialize, Default)]
    struct Args {
        #[serde(default)]
        uri: Option<Url>,
        #[serde(default)]
        query: Option<String>,
    }
    let parsed: Args = match args.into_iter().next() {
        Some(v) => serde_json::from_value(v).map_err(|e| format!("invalid args: {e}"))?,
        None => Args::default(),
    };
    let Some(wiki) = resolve_diary_wiki(backend, parsed.uri.as_ref()) else {
        return Ok(Some(serde_json::json!([])));
    };
    let hits = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        ops::tag_hits(&idx, parsed.query.as_deref().unwrap_or(""))
    };
    Ok(Some(serde_json::to_value(&hits).map_err(|e| {
        format!("nuwiki.tags.search: serialization failed — {e}")
    })?))
}

fn tags_generate_links(
    backend: &Backend,
    args: Vec<Value>,
) -> Result<Option<WorkspaceEdit>, String> {
    #[derive(Deserialize)]
    struct Args {
        uri: Url,
        #[serde(default)]
        tag: Option<String>,
    }
    let raw = args
        .into_iter()
        .next()
        .ok_or_else(|| "nuwiki.tags.generateLinks: missing { uri } argument".to_string())?;
    let parsed: Args = serde_json::from_value(raw)
        .map_err(|e| format!("nuwiki.tags.generateLinks: invalid args — {e}"))?;
    let doc = match backend.documents.get(&parsed.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let utf8 = backend.use_utf8.load(Ordering::Relaxed);
    let Some(wiki) = backend.wiki_for_uri(&parsed.uri) else {
        return Ok(None);
    };
    let snapshot = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        ops::tag_pages_snapshot(&idx)
    };
    Ok(ops::tag_links_edit(
        &doc.text,
        &doc.ast,
        &parsed.uri,
        parsed.tag.as_deref(),
        &snapshot,
        utf8,
    ))
}

fn tags_rebuild(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let Some(wiki) = resolve_diary_wiki(backend, p.uri.as_ref()) else {
        return Ok(None);
    };
    let registry = std::sync::Arc::clone(&backend.registry);
    let root = wiki.config.root.clone();
    if root.as_os_str().is_empty() {
        return Ok(Some(
            serde_json::json!({ "pages": 0, "reason": "no wiki root configured" }),
        ));
    }
    let Some(plugin) = registry.get("vimwiki") else {
        return Err("vimwiki syntax plugin missing".to_string());
    };
    let files = crate::index::walk_wiki_files(&root);
    let total = files.len();
    let mut indexed = 0usize;
    let mut idx = wiki
        .index
        .write()
        .map_err(|_| "index lock poisoned".to_string())?;
    // Drop pages whose files no longer exist. Collect first to avoid mutating
    // during iteration.
    let stale: Vec<Url> = idx
        .pages_by_uri
        .keys()
        .filter(|u| match u.to_file_path() {
            Ok(p) => !p.exists(),
            Err(_) => true,
        })
        .cloned()
        .collect();
    for u in &stale {
        idx.remove(u);
    }
    for path in files {
        let Ok(text) = std::fs::read_to_string(&path) else {
            continue;
        };
        let ast = plugin.parse(&text);
        let Ok(uri) = Url::from_file_path(&path) else {
            continue;
        };
        idx.upsert(uri, &ast);
        indexed += 1;
    }
    Ok(Some(serde_json::json!({
        "pages": indexed,
        "files_seen": total,
        "stale_removed": stale.len(),
    })))
}

// ===== Phase 18: multi-wiki picker commands =====

fn wiki_list_all(backend: &Backend) -> Result<Option<Value>, String> {
    let wikis = backend.wikis_snapshot();
    let rows: Vec<Value> = wikis
        .iter()
        .enumerate()
        .map(|(i, w)| {
            serde_json::json!({
                "id": i,
                "name": w.config.name,
                "root": w.config.root,
                "syntax": w.config.syntax,
                "file_extension": w.config.file_extension,
            })
        })
        .collect();
    Ok(Some(serde_json::json!(rows)))
}

fn resolve_wiki_selector(backend: &Backend, sel: Option<&Value>) -> Option<crate::wiki::Wiki> {
    let wikis = backend.wikis_snapshot();
    let Some(sel) = sel else {
        return wikis.into_iter().next();
    };
    if let Some(idx) = sel.as_u64() {
        return wikis.into_iter().nth(idx as usize);
    }
    if let Some(name) = sel.as_str() {
        // Numeric strings are also accepted so the picker UI can pass
        // back whatever it received without coercing.
        if let Ok(idx) = name.parse::<usize>() {
            if let Some(w) = wikis.get(idx).cloned() {
                return Some(w);
            }
        }
        return wikis.into_iter().find(|w| w.config.name == name);
    }
    None
}

fn wiki_open_index(
    backend: &Backend,
    args: Vec<Value>,
    tab: bool,
) -> Result<Option<Value>, String> {
    #[derive(Deserialize, Default)]
    struct Args {
        #[serde(default)]
        wiki: Option<Value>,
    }
    let parsed: Args = match args.into_iter().next() {
        Some(v) => serde_json::from_value(v).map_err(|e| format!("invalid args: {e}"))?,
        None => Args::default(),
    };
    let Some(wiki) = resolve_wiki_selector(backend, parsed.wiki.as_ref()) else {
        return Ok(None);
    };
    let index_path = wiki
        .config
        .root
        .join(format!("index{}", wiki.config.file_extension));
    let Ok(uri) = Url::from_file_path(&index_path) else {
        return Ok(None);
    };
    Ok(Some(serde_json::json!({
        "uri": uri,
        "name": wiki.config.name,
        "tab": tab,
    })))
}

fn wiki_goto_page(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    #[derive(Deserialize)]
    struct Args {
        page: String,
        #[serde(default)]
        wiki: Option<Value>,
    }
    let raw = args
        .into_iter()
        .next()
        .ok_or_else(|| "nuwiki.wiki.gotoPage: missing { page } argument".to_string())?;
    let parsed: Args = serde_json::from_value(raw)
        .map_err(|e| format!("nuwiki.wiki.gotoPage: invalid args — {e}"))?;
    let Some(wiki) = resolve_wiki_selector(backend, parsed.wiki.as_ref()) else {
        return Ok(None);
    };
    // Prefer an indexed page first (canonical URI from the workspace
    // index), then fall back to building the path from the page name.
    let uri = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        idx.pages_by_name.get(&parsed.page).cloned()
    };
    let uri = uri.unwrap_or_else(|| {
        // Build `<root>/<page>.wiki` directly. `page` may contain
        // forward-slashes for subdirs.
        let mut path = wiki.config.root.clone();
        for seg in parsed.page.split('/') {
            if !seg.is_empty() {
                path.push(seg);
            }
        }
        let path = path.with_extension(wiki.config.file_extension.trim_start_matches('.'));
        Url::from_file_path(path)
            .unwrap_or_else(|_| Url::parse("file:///nonexistent").expect("constant url"))
    });
    Ok(Some(serde_json::json!({
        "uri": uri,
        "page": parsed.page,
        "wiki": wiki.config.name,
    })))
}

// ===== Phase 17: HTML export commands =====

fn export_current(
    backend: &Backend,
    args: Vec<Value>,
    return_open_url: bool,
) -> Result<Option<Value>, String> {
    let p = parse_uri_arg(args)?;
    let doc = match backend.documents.get(&p.uri) {
        Some(d) => d,
        None => return Ok(None),
    };
    let Some(wiki) = backend.wiki_for_uri(&p.uri) else {
        return Ok(None);
    };
    let cfg = &wiki.config;
    if doc.ast.metadata.nohtml {
        return Ok(Some(serde_json::json!({
            "exported": [],
            "skipped": [{"uri": p.uri, "reason": "nohtml"}],
        })));
    }
    let name = crate::index::page_name_from_uri(&p.uri, Some(&cfg.root));
    let outcome = match crate::commands::export_ops::write_page(&doc.ast, &name, cfg) {
        Ok(o) => o,
        Err(e) => return Err(format!("nuwiki.export.currentToHtml: {e}")),
    };
    let css = crate::commands::export_ops::ensure_css(cfg).map_err(|e| e.to_string())?;
    let mut body = serde_json::json!({
        "exported": [outcome.to_json()],
        "css_path": css.path,
        "css_created": css.created,
    });
    if return_open_url {
        if let Ok(url) = Url::from_file_path(&outcome.output_path) {
            body["browse"] = serde_json::json!(url);
        }
    }
    Ok(Some(body))
}

fn export_all(backend: &Backend, args: Vec<Value>, force: bool) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let Some(wiki) = resolve_diary_wiki(backend, p.uri.as_ref()) else {
        return Ok(None);
    };
    let cfg = wiki.config.clone();
    if cfg.root.as_os_str().is_empty() {
        return Ok(Some(serde_json::json!({
            "exported": [],
            "reason": "no wiki root configured",
        })));
    }
    let registry = std::sync::Arc::clone(&backend.registry);
    let Some(plugin) = registry.get("vimwiki") else {
        return Err("vimwiki syntax plugin missing".to_string());
    };
    let files = crate::index::walk_wiki_files(&cfg.root);
    let mut exported: Vec<serde_json::Value> = Vec::new();
    let mut skipped: Vec<serde_json::Value> = Vec::new();
    for path in &files {
        let Ok(uri) = Url::from_file_path(path) else {
            continue;
        };
        let name = crate::index::page_name_from_uri(&uri, Some(&cfg.root));
        if crate::export::is_excluded(&cfg.html.exclude_files, &name) {
            skipped.push(serde_json::json!({"uri": uri, "reason": "excluded"}));
            continue;
        }
        let (text, ast) = match backend.documents.get(&uri) {
            Some(d) => (d.text.clone(), d.ast.clone()),
            None => {
                let Ok(text) = std::fs::read_to_string(path) else {
                    continue;
                };
                let ast = plugin.parse(&text);
                (text, ast)
            }
        };
        let _ = text;
        if ast.metadata.nohtml {
            skipped.push(serde_json::json!({"uri": uri, "reason": "nohtml"}));
            continue;
        }
        let out_path = crate::export::output_path_for(&cfg.html, &name);
        if !force {
            // Compare modification times. Skip when the HTML is newer than
            // the source. Cheap and matches vimwiki's incremental behaviour.
            if let (Ok(src_meta), Ok(html_meta)) =
                (std::fs::metadata(path), std::fs::metadata(&out_path))
            {
                let src_mtime = src_meta.modified().ok();
                let out_mtime = html_meta.modified().ok();
                if let (Some(s), Some(o)) = (src_mtime, out_mtime) {
                    if o >= s {
                        skipped.push(serde_json::json!({"uri": uri, "reason": "up-to-date"}));
                        continue;
                    }
                }
            }
        }
        match crate::commands::export_ops::write_page(&ast, &name, &cfg) {
            Ok(outcome) => exported.push(outcome.to_json()),
            Err(e) => skipped.push(serde_json::json!({"uri": uri, "reason": e.to_string()})),
        }
    }
    let css = crate::commands::export_ops::ensure_css(&cfg).map_err(|e| e.to_string())?;
    Ok(Some(serde_json::json!({
        "exported": exported,
        "skipped": skipped,
        "files_seen": files.len(),
        "css_path": css.path,
        "css_created": css.created,
        "forced": force,
    })))
}

fn export_rss(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let Some(wiki) = resolve_diary_wiki(backend, p.uri.as_ref()) else {
        return Ok(None);
    };
    let entries = {
        let idx = wiki
            .index
            .read()
            .map_err(|_| "index lock poisoned".to_string())?;
        crate::diary::list_entries(&idx)
    };
    let out_path = crate::commands::export_ops::write_rss(&wiki.config, &entries)
        .map_err(|e| format!("nuwiki.export.rss: {e}"))?;
    Ok(Some(serde_json::json!({
        "rss_path": out_path,
        "entries": entries.len(),
    })))
}

fn workspace_find_orphans(backend: &Backend, args: Vec<Value>) -> Result<Option<Value>, String> {
    let p = parse_optional_uri_arg(args)?;
    let wiki = match p.uri.as_ref().and_then(|u| backend.wiki_for_uri(u)) {
        Some(w) => w,
        None => match backend.default_wiki() {
            Some(w) => w,
            None => return Ok(Some(serde_json::json!([]))),
        },
    };
    let idx = wiki
        .index
        .read()
        .map_err(|_| "index lock poisoned".to_string())?;
    let orphans = ops::find_orphans(&idx);
    Ok(Some(serde_json::to_value(orphans).map_err(|e| {
        format!("nuwiki.workspace.findOrphans: serialization failed — {e}")
    })?))
}

// ===== Pure operations =====

pub mod ops {
    use super::*;
    use crate::edits::text_edit_replace;
    use nuwiki_core::ast::{
        BlockNode, BlockquoteNode, CheckboxState, DocumentNode, HeadingNode, ListItemNode,
        ListNode, Span,
    };
    use tower_lsp::lsp_types::Location;

    /// Toggle ` ↔ X. Mid-states (`.`, `o`, `O`) snap forward to `X`.
    /// Rejected (`-`) reverts to empty.
    pub fn toggle_state(current: &str) -> Option<&'static str> {
        match current {
            "[ ]" => Some("[X]"),
            "[X]" => Some("[ ]"),
            "[.]" | "[o]" | "[O]" => Some("[X]"),
            "[-]" => Some("[ ]"),
            _ => None,
        }
    }

    /// `[ ]` → `[.]` → `[o]` → `[O]` → `[X]` → `[ ]`. `[-]` → `[ ]`.
    pub fn cycle_state(current: &str) -> Option<&'static str> {
        match current {
            "[ ]" => Some("[.]"),
            "[.]" => Some("[o]"),
            "[o]" => Some("[O]"),
            "[O]" => Some("[X]"),
            "[X]" => Some("[ ]"),
            "[-]" => Some("[ ]"),
            _ => None,
        }
    }

    /// Toggle the `[-]` "rejected" state.
    pub fn reject_state(current: &str) -> Option<&'static str> {
        match current {
            "[-]" => Some("[ ]"),
            _ => Some("[-]"),
        }
    }

    pub fn checkbox_edit(
        text: &str,
        ast: &DocumentNode,
        uri: &Url,
        line: u32,
        col: u32,
        utf8: bool,
        mutate: fn(&str) -> Option<&'static str>,
    ) -> Option<WorkspaceEdit> {
        let item = find_list_item_at(ast, line, col)?;
        let cb_span = find_checkbox_span(text, item.span)?;
        let cur = &text[cb_span.start.offset..cb_span.end.offset];
        let new = mutate(cur)?;
        let mut b = WorkspaceEditBuilder::new();
        b.edit(
            uri.clone(),
            text_edit_replace(cb_span, new.to_string(), text, utf8),
        );
        Some(b.build())
    }

    pub fn next_task(
        ast: &DocumentNode,
        uri: &Url,
        text: &str,
        line: u32,
        _col: u32,
        utf8: bool,
    ) -> Option<Location> {
        // Walk in source order; first task at line > cursor wins. Wraps to
        // the start of the document if nothing found after cursor — matches
        // vimwiki's `gnt`.
        let mut items: Vec<&ListItemNode> = Vec::new();
        for block in &ast.children {
            collect_list_items(block, &mut items);
        }
        let is_unfinished = |it: &&ListItemNode| match it.checkbox {
            Some(CheckboxState::Done) | Some(CheckboxState::Rejected) => false,
            Some(_) | None => it.checkbox.is_some(),
        };
        let after = items
            .iter()
            .find(|it| it.span.start.line > line && is_unfinished(it));
        let chosen = after.or_else(|| items.iter().find(|it| is_unfinished(it)))?;
        let span = chosen.span;
        Some(Location {
            uri: uri.clone(),
            range: crate::edits::text_edit_replace(span, String::new(), text, utf8).range,
        })
    }

    fn collect_list_items<'a>(block: &'a BlockNode, out: &mut Vec<&'a ListItemNode>) {
        match block {
            BlockNode::List(ListNode { items, .. }) => {
                for it in items {
                    out.push(it);
                    if let Some(sub) = &it.sublist {
                        for sub_it in &sub.items {
                            collect_list_items_from_item(sub_it, out);
                        }
                    }
                }
            }
            BlockNode::Blockquote(BlockquoteNode { children, .. }) => {
                for c in children {
                    collect_list_items(c, out);
                }
            }
            _ => {}
        }
    }

    fn collect_list_items_from_item<'a>(item: &'a ListItemNode, out: &mut Vec<&'a ListItemNode>) {
        out.push(item);
        if let Some(sub) = &item.sublist {
            for sub_it in &sub.items {
                collect_list_items_from_item(sub_it, out);
            }
        }
    }

    pub fn heading_change_level(
        text: &str,
        ast: &DocumentNode,
        uri: &Url,
        line: u32,
        _col: u32,
        utf8: bool,
        delta: i32,
    ) -> Option<WorkspaceEdit> {
        let heading = find_heading_at(ast, line)?;
        let current = heading.level as i32;
        let new_level = (current + delta).clamp(1, 6) as u8;
        if new_level == heading.level {
            return None;
        }
        let new_text = rewrite_heading_with_level(text, heading.span, new_level)?;
        let mut b = WorkspaceEditBuilder::new();
        b.edit(
            uri.clone(),
            text_edit_replace(heading.span, new_text, text, utf8),
        );
        Some(b.build())
    }

    fn find_heading_at(ast: &DocumentNode, line: u32) -> Option<&HeadingNode> {
        for block in &ast.children {
            if let BlockNode::Heading(h) = block {
                if h.span.start.line == line {
                    return Some(h);
                }
            }
        }
        None
    }

    /// Rewrite a heading's source so it has `new_level` `=`s on each side.
    /// Returns `None` if the source doesn't have a balanced `=` ... `=`
    /// shape (defensive — the lexer should guarantee this, but we don't
    /// crash if the buffer was edited mid-flight).
    pub fn rewrite_heading_with_level(text: &str, span: Span, new_level: u8) -> Option<String> {
        if !(1..=6).contains(&new_level) {
            return None;
        }
        let segment = &text[span.start.offset..span.end.offset];
        let leading_ws = segment
            .bytes()
            .take_while(|b| *b == b' ' || *b == b'\t')
            .count();
        let after_ws = &segment[leading_ws..];
        let opening = after_ws.bytes().take_while(|b| *b == b'=').count();
        let trimmed_end = after_ws.trim_end_matches([' ', '\t']).len();
        let trailing = after_ws[..trimmed_end]
            .bytes()
            .rev()
            .take_while(|b| *b == b'=')
            .count();
        if opening == 0 || trailing == 0 || opening != trailing {
            return None;
        }
        let middle = &after_ws[opening..trimmed_end - trailing];
        let trailing_ws = &after_ws[trimmed_end..];

        let mut out = String::with_capacity(segment.len() + 2);
        out.push_str(&segment[..leading_ws]);
        for _ in 0..new_level {
            out.push('=');
        }
        out.push_str(middle);
        for _ in 0..new_level {
            out.push('=');
        }
        out.push_str(trailing_ws);
        Some(out)
    }

    /// Find the `[X]` (or other checkbox) substring within a list item's
    /// source span. Returns a span covering exactly the 3-byte run.
    pub fn find_checkbox_span(text: &str, item_span: Span) -> Option<Span> {
        let start = item_span.start.offset;
        let end = item_span.end.offset.min(text.len());
        if start >= end {
            return None;
        }
        let segment = &text[start..end];
        let bytes = segment.as_bytes();
        let mut i = 0;
        while i + 2 < bytes.len() {
            if bytes[i] == b'['
                && bytes[i + 2] == b']'
                && matches!(bytes[i + 1], b' ' | b'.' | b'o' | b'O' | b'X' | b'-')
            {
                let abs_start = start + i;
                let cb_start = nuwiki_core::ast::Position {
                    line: item_span.start.line,
                    column: item_span.start.column + i as u32,
                    offset: abs_start,
                };
                let cb_end = nuwiki_core::ast::Position {
                    line: item_span.start.line,
                    column: item_span.start.column + (i + 3) as u32,
                    offset: abs_start + 3,
                };
                return Some(Span::new(cb_start, cb_end));
            }
            i += 1;
        }
        None
    }

    /// Find the list item whose source line contains `line`. Descends into
    /// sublists; returns the deepest match so editing the inner item works
    /// when the user's cursor sits there.
    pub fn find_list_item_at(ast: &DocumentNode, line: u32, col: u32) -> Option<&ListItemNode> {
        for block in &ast.children {
            if let Some(it) = item_in_block(block, line, col) {
                return Some(it);
            }
        }
        None
    }

    fn item_in_block(block: &BlockNode, line: u32, col: u32) -> Option<&ListItemNode> {
        match block {
            BlockNode::List(l) => l.items.iter().find_map(|it| item_in_list(it, line, col)),
            BlockNode::Blockquote(BlockquoteNode { children, .. }) => {
                children.iter().find_map(|c| item_in_block(c, line, col))
            }
            _ => None,
        }
    }

    fn item_in_list(item: &ListItemNode, line: u32, col: u32) -> Option<&ListItemNode> {
        // Prefer the deepest match: try sublists first.
        if let Some(sub) = &item.sublist {
            for sub_it in &sub.items {
                if let Some(found) = item_in_list(sub_it, line, col) {
                    return Some(found);
                }
            }
        }
        if (item.span.start.line..=item.span.end.line).contains(&line) {
            return Some(item);
        }
        let _ = col;
        None
    }

    // ===== Phase 15: TOC + Links generation, workspace queries =====

    use serde::Serialize;

    pub const TOC_HEADING: &str = "Contents";
    pub const LINKS_HEADING: &str = "Generated Links";

    use crate::diagnostics::classify_outgoing;
    use crate::edits::text_edit_insert;
    use crate::index::WorkspaceIndex;
    use nuwiki_core::ast::Position as AstPosition;

    /// One heading entry used to render the TOC.
    struct TocItem {
        level: u8,
        title: String,
        anchor: String,
    }

    /// Build a heading + nested list TOC for the current document. The TOC
    /// itself (any existing `= Contents =` heading on the page) is skipped
    /// so re-generation is idempotent.
    pub fn build_toc_text(items: &[(u8, String, String)], heading_name: &str) -> String {
        let mut out = String::new();
        out.push_str("= ");
        out.push_str(heading_name);
        out.push_str(" =\n");
        if items.is_empty() {
            return out;
        }
        let min_level = items.iter().map(|(l, _, _)| *l).min().unwrap_or(1);
        for (level, title, anchor) in items {
            let depth = level.saturating_sub(min_level) as usize;
            for _ in 0..depth {
                out.push_str("  ");
            }
            out.push_str("- [[#");
            out.push_str(anchor);
            out.push('|');
            out.push_str(title);
            out.push_str("]]\n");
        }
        out
    }

    /// Build a flat list of wikilinks to every page (sorted), optionally
    /// excluding `current_page`.
    pub fn build_links_text(pages: &[String], heading_name: &str, exclude: Option<&str>) -> String {
        let mut out = String::new();
        out.push_str("= ");
        out.push_str(heading_name);
        out.push_str(" =\n");
        for name in pages {
            if Some(name.as_str()) == exclude {
                continue;
            }
            out.push_str("- [[");
            out.push_str(name);
            out.push_str("]]\n");
        }
        out
    }

    /// Locate an existing section whose level-1 heading matches
    /// `heading_name` case-insensitively. Returns the offset range covering
    /// `[heading start .. (immediately-following list end | heading end)]`
    /// plus the start `AstPosition` for emitting an LSP range from a
    /// synthesised span.
    pub fn find_section_range(
        ast: &DocumentNode,
        heading_name: &str,
    ) -> Option<(AstPosition, AstPosition)> {
        let needle = heading_name.to_ascii_lowercase();
        for (i, block) in ast.children.iter().enumerate() {
            let BlockNode::Heading(h) = block else {
                continue;
            };
            if h.level != 1 {
                continue;
            }
            let title = heading_title(h).to_ascii_lowercase();
            if title != needle {
                continue;
            }
            let start = h.span.start;
            let end = match ast.children.get(i + 1) {
                Some(BlockNode::List(list)) => list.span.end,
                _ => h.span.end,
            };
            return Some((start, end));
        }
        None
    }

    fn heading_title(h: &nuwiki_core::ast::HeadingNode) -> String {
        crate::diagnostics::heading_text(&h.children)
    }

    fn collect_toc_items(ast: &DocumentNode, toc_heading: &str) -> Vec<TocItem> {
        let mut out = Vec::new();
        let needle = toc_heading.to_ascii_lowercase();
        for block in &ast.children {
            let BlockNode::Heading(h) = block else {
                continue;
            };
            let title = heading_title(h);
            if h.level == 1 && title.to_ascii_lowercase() == needle {
                // skip the TOC's own heading
                continue;
            }
            let anchor = crate::index::slugify(&title);
            out.push(TocItem {
                level: h.level,
                title,
                anchor,
            });
        }
        out
    }

    /// Produce a `WorkspaceEdit` that replaces or inserts the TOC for the
    /// given document. Returns `None` if the document has no headings at
    /// all (other than possibly a pre-existing TOC heading).
    pub fn toc_edit(
        text: &str,
        ast: &DocumentNode,
        uri: &Url,
        utf8: bool,
    ) -> Option<WorkspaceEdit> {
        let items = collect_toc_items(ast, TOC_HEADING);
        if items.is_empty() {
            return None;
        }
        let triples: Vec<(u8, String, String)> = items
            .into_iter()
            .map(|it| (it.level, it.title, it.anchor))
            .collect();
        let new_text = build_toc_text(&triples, TOC_HEADING);
        let mut b = WorkspaceEditBuilder::new();
        match find_section_range(ast, TOC_HEADING) {
            Some((start, end)) => {
                let span = Span::new(start, end);
                b.edit(uri.clone(), text_edit_replace(span, new_text, text, utf8));
            }
            None => {
                let with_sep = format!("{new_text}\n");
                b.edit(
                    uri.clone(),
                    text_edit_insert(
                        LspPosition {
                            line: 0,
                            character: 0,
                        },
                        with_sep,
                    ),
                );
            }
        }
        Some(b.build())
    }

    /// Produce a `WorkspaceEdit` that replaces or inserts the
    /// auto-generated links section for the given document.
    pub fn links_edit(
        text: &str,
        ast: &DocumentNode,
        uri: &Url,
        current_page: &str,
        all_pages: &[String],
        utf8: bool,
    ) -> Option<WorkspaceEdit> {
        if all_pages.is_empty() {
            return None;
        }
        let new_text = build_links_text(all_pages, LINKS_HEADING, Some(current_page));
        let mut b = WorkspaceEditBuilder::new();
        match find_section_range(ast, LINKS_HEADING) {
            Some((start, end)) => {
                let span = Span::new(start, end);
                b.edit(uri.clone(), text_edit_replace(span, new_text, text, utf8));
            }
            None => {
                let with_sep = format!("{new_text}\n");
                b.edit(
                    uri.clone(),
                    text_edit_insert(
                        LspPosition {
                            line: 0,
                            character: 0,
                        },
                        with_sep,
                    ),
                );
            }
        }
        Some(b.build())
    }

    // ===== Workspace queries =====

    #[derive(Debug, Serialize)]
    pub struct BrokenLinkEntry {
        pub uri: Url,
        pub range: tower_lsp::lsp_types::Range,
        pub kind: &'static str,
        pub message: String,
    }

    /// Walk every indexed page and classify each outgoing link against the
    /// workspace index. Open documents (held in `backend.documents`) use
    /// live text for LSP range conversion; closed pages fall back to the
    /// stored span coordinates verbatim (they're already in line/column form).
    pub(crate) fn collect_workspace_broken_links(
        backend: &Backend,
        index: &WorkspaceIndex,
        utf8: bool,
    ) -> Vec<BrokenLinkEntry> {
        let mut out = Vec::new();
        for page in index.pages_by_uri.values() {
            for link in &page.outgoing {
                let Some(broken) = classify_outgoing(link, &page.uri, index, &page.name) else {
                    continue;
                };
                let range = match backend.documents.get(&page.uri) {
                    Some(doc) => crate::to_lsp_range(&link.span, &doc.text, utf8),
                    None => no_text_range(&link.span),
                };
                out.push(BrokenLinkEntry {
                    uri: page.uri.clone(),
                    range,
                    kind: broken.tag(),
                    message: broken.message(),
                });
            }
        }
        out.sort_by(|a, b| {
            (a.uri.as_str(), a.range.start.line, a.range.start.character).cmp(&(
                b.uri.as_str(),
                b.range.start.line,
                b.range.start.character,
            ))
        });
        out
    }

    #[derive(Debug, Serialize)]
    pub struct OrphanEntry {
        pub uri: Url,
        pub name: String,
    }

    /// A page is an orphan when no other indexed page links to it. The
    /// current convention is to surface every orphan and let the client
    /// filter out the index page if it wants to.
    pub fn find_orphans(index: &WorkspaceIndex) -> Vec<OrphanEntry> {
        let mut out: Vec<OrphanEntry> = index
            .pages_by_uri
            .values()
            .filter(|p| index.backlinks_for(&p.name).is_empty())
            .map(|p| OrphanEntry {
                uri: p.uri.clone(),
                name: p.name.clone(),
            })
            .collect();
        out.sort_by(|a, b| a.name.cmp(&b.name));
        out
    }

    fn no_text_range(span: &Span) -> tower_lsp::lsp_types::Range {
        tower_lsp::lsp_types::Range {
            start: LspPosition {
                line: span.start.line,
                character: span.start.column,
            },
            end: LspPosition {
                line: span.end.line,
                character: span.end.column,
            },
        }
    }

    /// Re-exported AST link walker so tests can drive it without depending
    /// on the diagnostics module's internals.
    pub use crate::diagnostics::collect_wiki_links;

    // ===== Phase 16: diary helpers =====

    use crate::edits::op_create;

    /// Build the `WorkspaceEdit` that materialises the diary index page.
    ///
    /// Decision tree:
    /// - If the index URI is open in `backend.documents`, the live text is
    ///   the source of truth: emit a single full-document `TextEdit`
    ///   replacing it with `body`.
    /// - If the index file exists on disk but isn't open: same full-doc
    ///   replace, span computed from the on-disk bytes.
    /// - If neither: a `CreateFile` op + an insert at `0:0`.
    pub(crate) fn diary_generate_index_edit(
        backend: &Backend,
        index_uri: &Url,
        body: &str,
        utf8: bool,
    ) -> WorkspaceEdit {
        let mut b = WorkspaceEditBuilder::new();
        if let Some(doc) = backend.documents.get(index_uri) {
            let span = whole_doc_span(&doc.text);
            b.edit(
                index_uri.clone(),
                text_edit_replace(span, body.to_string(), &doc.text, utf8),
            );
            return b.build();
        }
        if let Ok(path) = index_uri.to_file_path() {
            if let Ok(existing) = std::fs::read_to_string(&path) {
                let span = whole_doc_span(&existing);
                b.edit(
                    index_uri.clone(),
                    text_edit_replace(span, body.to_string(), &existing, utf8),
                );
                return b.build();
            }
        }
        // File does not exist — create it and insert the body. The text
        // edit applies *after* CreateFile via the builder's ordering.
        b.file_op(op_create(index_uri.clone()));
        b.edit(
            index_uri.clone(),
            crate::edits::text_edit_insert(
                LspPosition {
                    line: 0,
                    character: 0,
                },
                body.to_string(),
            ),
        );
        b.build()
    }

    // ===== Tag ops (Phase 12 commands) =====
    //
    // SPEC §12.3 calls for three tag-driven commands beyond the indexing
    // that Phase 12 already shipped. `tag_hits` powers `nuwiki.tags.search`;
    // `tag_links_edit` powers `nuwiki.tags.generateLinks`; the rebuild
    // command is a direct re-walk of the wiki root in the dispatcher.

    use crate::index::TagOccurrence;
    use nuwiki_core::ast::TagScope;

    /// One row returned by `nuwiki.tags.search`. Serialised as
    /// `{ name, uri, range, scope, page }` so editors can render either a
    /// flat hit list or a per-tag tree.
    #[derive(Debug, Clone, serde::Serialize)]
    pub struct TagHit {
        pub name: String,
        pub uri: Url,
        pub range: tower_lsp::lsp_types::Range,
        pub scope: &'static str,
        pub page: String,
    }

    fn scope_tag(s: TagScope) -> &'static str {
        match s {
            TagScope::File => "file",
            TagScope::Heading(_) => "heading",
            TagScope::Standalone => "standalone",
        }
    }

    /// Filter every indexed tag by a case-insensitive substring match. An
    /// empty query returns everything (sorted by name, then by page).
    pub fn tag_hits(index: &WorkspaceIndex, query: &str) -> Vec<TagHit> {
        let needle = query.to_ascii_lowercase();
        let mut out: Vec<TagHit> = Vec::new();
        for (name, occs) in &index.tags_by_name {
            if !needle.is_empty() && !name.to_ascii_lowercase().contains(&needle) {
                continue;
            }
            for occ in occs {
                let page = index
                    .pages_by_uri
                    .get(&occ.uri)
                    .map(|p| p.name.clone())
                    .unwrap_or_default();
                out.push(TagHit {
                    name: name.clone(),
                    uri: occ.uri.clone(),
                    range: no_text_range(&occ.span),
                    scope: scope_tag(occ.scope),
                    page,
                });
            }
        }
        out.sort_by(|a, b| {
            a.name
                .cmp(&b.name)
                .then_with(|| a.page.cmp(&b.page))
                .then_with(|| a.range.start.line.cmp(&b.range.start.line))
        });
        out
    }

    /// Snapshot of `tag → sorted [page names]` taken under the index read
    /// lock so the dispatcher can release the lock before computing the
    /// edit.
    pub fn tag_pages_snapshot(
        index: &WorkspaceIndex,
    ) -> std::collections::BTreeMap<String, Vec<String>> {
        let mut by_tag: std::collections::BTreeMap<String, std::collections::BTreeSet<String>> =
            std::collections::BTreeMap::new();
        for (name, occs) in &index.tags_by_name {
            for occ in occs {
                if let Some(page) = index.pages_by_uri.get(&occ.uri) {
                    by_tag
                        .entry(name.clone())
                        .or_default()
                        .insert(page.name.clone());
                }
            }
        }
        by_tag
            .into_iter()
            .map(|(k, v)| (k, v.into_iter().collect()))
            .collect()
    }

    /// Render a `= Tag: <name> =` section listing every page tagged with
    /// `name`. When `tag` is `None` the section becomes a "Tag Index"
    /// covering every tag, headed `== <tag> ==` per group — matches
    /// `:VimwikiGenerateTagLinks` (no arg) variant.
    pub fn build_tag_links_text(
        pages_by_tag: &std::collections::BTreeMap<String, Vec<String>>,
        tag: Option<&str>,
    ) -> Option<String> {
        match tag {
            Some(t) => {
                let pages = pages_by_tag.get(t)?;
                if pages.is_empty() {
                    return None;
                }
                let mut out = format!("= Tag: {t} =\n");
                for p in pages {
                    out.push_str(&format!("- [[{p}]]\n"));
                }
                Some(out)
            }
            None => {
                if pages_by_tag.is_empty() {
                    return None;
                }
                let mut out = String::from("= Tags =\n");
                for (name, pages) in pages_by_tag {
                    out.push_str(&format!("\n== {name} ==\n"));
                    for p in pages {
                        out.push_str(&format!("- [[{p}]]\n"));
                    }
                }
                Some(out)
            }
        }
    }

    /// Heading name used to locate an existing tag-links section so
    /// re-generation is idempotent.
    fn tag_section_heading(tag: Option<&str>) -> String {
        match tag {
            Some(t) => format!("Tag: {t}"),
            None => "Tags".to_string(),
        }
    }

    /// Build a `WorkspaceEdit` that replaces an existing `Tag: <name>`
    /// section (case-insensitive match on the h1 title) or inserts at the
    /// top of the document when no such section exists. Returns `None`
    /// when there are no matching tagged pages.
    pub fn tag_links_edit(
        text: &str,
        ast: &DocumentNode,
        uri: &Url,
        tag: Option<&str>,
        pages_by_tag: &std::collections::BTreeMap<String, Vec<String>>,
        utf8: bool,
    ) -> Option<WorkspaceEdit> {
        let body = build_tag_links_text(pages_by_tag, tag)?;
        let heading = tag_section_heading(tag);
        let mut b = WorkspaceEditBuilder::new();
        match find_section_range(ast, &heading) {
            Some((start, end)) => {
                let span = Span::new(start, end);
                b.edit(uri.clone(), text_edit_replace(span, body, text, utf8));
            }
            None => {
                let with_sep = format!("{body}\n");
                b.edit(
                    uri.clone(),
                    text_edit_insert(
                        LspPosition {
                            line: 0,
                            character: 0,
                        },
                        with_sep,
                    ),
                );
            }
        }
        Some(b.build())
    }

    // Keep the import live for downstream use even when the local module
    // doesn't reference it directly.
    #[allow(dead_code)]
    fn _retain_tag_occurrence_import(_o: &TagOccurrence) {}

    fn whole_doc_span(text: &str) -> Span {
        let bytes = text.as_bytes();
        let mut line = 0u32;
        let mut last_nl = 0usize;
        for (i, b) in bytes.iter().enumerate() {
            if *b == b'\n' {
                line += 1;
                last_nl = i + 1;
            }
        }
        let column = (bytes.len() - last_nl) as u32;
        Span::new(
            AstPosition {
                line: 0,
                column: 0,
                offset: 0,
            },
            AstPosition {
                line,
                column,
                offset: bytes.len(),
            },
        )
    }
}

/// Disk-touching helpers for the Phase 17 `nuwiki.export.*` commands.
/// Kept out of `ops` because everything here is side-effecting — pure
/// rendering / templating lives in [`crate::export`].
pub mod export_ops {
    use std::path::{Path, PathBuf};

    use nuwiki_core::ast::DocumentNode;
    use nuwiki_core::date::DiaryDate;

    use crate::config::WikiConfig;
    use crate::diary::DiaryEntry;
    use crate::export::{
        css_path, fallback_template, is_excluded, output_path_for, render_page_html, template_for,
        DEFAULT_CSS,
    };

    /// Per-page result of `write_page`. Serialised back to the client as
    /// `{ uri, output_path, page }`.
    pub struct PageExport {
        pub page: String,
        pub output_path: PathBuf,
        pub source_uri: Option<tower_lsp::lsp_types::Url>,
    }

    impl PageExport {
        pub fn to_json(&self) -> serde_json::Value {
            serde_json::json!({
                "page": self.page,
                "output_path": self.output_path,
                "uri": self.source_uri,
            })
        }
    }

    /// CSS write outcome — `created = true` when we just put a default
    /// stylesheet on disk; false when one already existed.
    pub struct CssOutcome {
        pub path: PathBuf,
        pub created: bool,
    }

    /// Render `doc` and write the result to `<html_path>/<name>.html`.
    /// Reads the template from disk (primary → fallback → built-in
    /// fallback). Creates any missing parent directories.
    pub fn write_page(
        doc: &DocumentNode,
        name: &str,
        cfg: &WikiConfig,
    ) -> std::io::Result<PageExport> {
        if is_excluded(&cfg.html.exclude_files, name) {
            return Err(std::io::Error::new(
                std::io::ErrorKind::InvalidInput,
                format!("excluded by exclude_files: {name}"),
            ));
        }
        let template_source = template_for(&cfg.html, doc);
        let template = load_template(&template_source)
            .unwrap_or_else(|| fallback_template(&cfg.html.css_name));
        let html = render_page_html(
            doc,
            Some(template),
            name,
            DiaryDate::today_utc(),
            &cfg.html,
            std::collections::HashMap::new(),
        )?;
        let out_path = output_path_for(&cfg.html, name);
        if let Some(parent) = out_path.parent() {
            std::fs::create_dir_all(parent)?;
        }
        std::fs::write(&out_path, html)?;
        let source_uri = tower_lsp::lsp_types::Url::from_file_path(
            cfg.root.join(format!("{name}{}", cfg.file_extension)),
        )
        .ok();
        Ok(PageExport {
            page: name.to_string(),
            output_path: out_path,
            source_uri,
        })
    }

    /// Two-tier template load. Returns the resolved template body, or
    /// `None` if neither file exists — caller falls back to the built-in
    /// template.
    fn load_template(src: &crate::export::TemplateSource) -> Option<String> {
        if let Some(p) = src.primary.as_ref() {
            if let Ok(text) = std::fs::read_to_string(p) {
                return Some(text);
            }
        }
        std::fs::read_to_string(&src.fallback).ok()
    }

    /// Ensure `<html_path>/<css_name>` exists. Writes the built-in
    /// [`DEFAULT_CSS`] when missing. No-op when it's already there.
    pub fn ensure_css(cfg: &WikiConfig) -> std::io::Result<CssOutcome> {
        let path = css_path(&cfg.html);
        if path.exists() {
            return Ok(CssOutcome {
                path,
                created: false,
            });
        }
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)?;
        }
        std::fs::write(&path, DEFAULT_CSS)?;
        Ok(CssOutcome {
            path,
            created: true,
        })
    }

    /// Write `<html_path>/rss.xml` listing the wiki's diary entries
    /// newest-first. The feed is intentionally minimal — just enough to
    /// validate against RSS 2.0 parsers — since the diary URLs are file:
    /// scheme and won't survive remote consumption anyway.
    pub fn write_rss(cfg: &WikiConfig, entries: &[DiaryEntry]) -> std::io::Result<PathBuf> {
        let mut sorted: Vec<&DiaryEntry> = entries.iter().collect();
        sorted.sort_by(|a, b| b.date.cmp(&a.date));
        let mut xml = String::from(
            r#"<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0"><channel>
"#,
        );
        xml.push_str(&format!("<title>{}</title>\n", xml_escape(&cfg.name)));
        xml.push_str("<description>nuwiki diary</description>\n");
        for e in sorted {
            xml.push_str("<item>");
            xml.push_str(&format!("<title>{}</title>", e.date.format()));
            xml.push_str(&format!("<link>{}</link>", e.uri.as_str()));
            xml.push_str(&format!("<guid>{}</guid>", e.uri.as_str()));
            xml.push_str("</item>\n");
        }
        xml.push_str("</channel></rss>\n");

        let path = rss_path(cfg);
        if let Some(parent) = path.parent() {
            std::fs::create_dir_all(parent)?;
        }
        std::fs::write(&path, xml)?;
        Ok(path)
    }

    fn rss_path(cfg: &WikiConfig) -> PathBuf {
        cfg.html.html_path.join("rss.xml")
    }

    fn xml_escape(s: &str) -> String {
        let mut out = String::with_capacity(s.len());
        for ch in s.chars() {
            match ch {
                '&' => out.push_str("&amp;"),
                '<' => out.push_str("&lt;"),
                '>' => out.push_str("&gt;"),
                '"' => out.push_str("&quot;"),
                _ => out.push(ch),
            }
        }
        out
    }

    /// Re-export so the dispatcher doesn't have to know about the export
    /// module's path manipulation primitives.
    #[allow(dead_code)]
    pub fn _silence_unused(_: &Path) {}
}