//! Diagnostic sources beyond parse-time `ErrorNode`s.
//!
//! The `nuwiki.link` source emits broken-link warnings. Walks
//! every `WikiLinkNode` in the AST and emits one diagnostic per:
//!   - `Wiki` target that doesn't resolve to a page in the workspace index,
//!   - `Wiki`/`AnchorOnly` target with an anchor that matches neither a
//!     heading nor a `:tag:` on the target page,
//!   - `File`/`Local` target whose resolved path doesn't exist on disk.
//!
//! Interwiki, Diary, Raw, and external links are not diagnosed —
//! interwiki resolution and diary handling live elsewhere, and we
//! don't fetch URLs.

use std::path::PathBuf;

use tower_lsp::lsp_types::{Diagnostic, DiagnosticSeverity, Url};

use nuwiki_core::ast::{
    BlockNode, BlockquoteNode, DocumentNode, InlineNode, LinkKind, ListItemNode, ListNode,
    TableNode, WikiLinkNode,
};

use crate::config::LinkSeverity;
use crate::index::{OutgoingLink, WorkspaceIndex};
use crate::to_lsp_range;

pub const LINK_SOURCE: &str = "nuwiki.link";

/// Convert a [`LinkSeverity`] to its LSP counterpart. `Off` returns `None`
/// so callers can short-circuit before walking the document.
pub fn severity_to_lsp(s: LinkSeverity) -> Option<DiagnosticSeverity> {
    match s {
        LinkSeverity::Off => None,
        LinkSeverity::Hint => Some(DiagnosticSeverity::HINT),
        LinkSeverity::Warning => Some(DiagnosticSeverity::WARNING),
        LinkSeverity::Error => Some(DiagnosticSeverity::ERROR),
    }
}

/// Walk the AST and collect every `WikiLinkNode` in source order.
pub fn collect_wiki_links(ast: &DocumentNode) -> Vec<&WikiLinkNode> {
    let mut out = Vec::new();
    for block in &ast.children {
        walk_block(block, &mut out);
    }
    out
}

fn walk_block<'a>(block: &'a BlockNode, out: &mut Vec<&'a WikiLinkNode>) {
    match block {
        BlockNode::Heading(h) => walk_inlines(&h.children, out),
        BlockNode::Paragraph(p) => walk_inlines(&p.children, out),
        BlockNode::Blockquote(BlockquoteNode { children, .. }) => {
            for c in children {
                walk_block(c, out);
            }
        }
        BlockNode::List(ListNode { items, .. }) => {
            for item in items {
                walk_list_item(item, out);
            }
        }
        BlockNode::DefinitionList(dl) => {
            for item in &dl.items {
                if let Some(t) = &item.term {
                    walk_inlines(t, out);
                }
                for d in &item.definitions {
                    walk_inlines(d, out);
                }
            }
        }
        BlockNode::Table(TableNode { rows, .. }) => {
            for row in rows {
                for cell in &row.cells {
                    walk_inlines(&cell.children, out);
                }
            }
        }
        _ => {}
    }
}

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

fn walk_inlines<'a>(inlines: &'a [InlineNode], out: &mut Vec<&'a WikiLinkNode>) {
    for n in inlines {
        match n {
            InlineNode::WikiLink(w) => {
                out.push(w);
                if let Some(d) = &w.description {
                    walk_inlines(d, out);
                }
            }
            InlineNode::Bold(b) => walk_inlines(&b.children, out),
            InlineNode::Italic(i) => walk_inlines(&i.children, out),
            InlineNode::BoldItalic(bi) => walk_inlines(&bi.children, out),
            InlineNode::Strikethrough(s) => walk_inlines(&s.children, out),
            InlineNode::Superscript(s) => walk_inlines(&s.children, out),
            InlineNode::Subscript(s) => walk_inlines(&s.children, out),
            InlineNode::Color(c) => walk_inlines(&c.children, out),
            InlineNode::ExternalLink(e) => {
                if let Some(d) = &e.description {
                    walk_inlines(d, out);
                }
            }
            _ => {}
        }
    }
}

/// Classification of why a single wikilink is broken. Returned by
/// [`classify_link`] so callers (diagnostics + `nuwiki.workspace.checkLinks`)
/// share the same logic.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum BrokenLinkKind {
    /// Target page doesn't exist in the workspace index.
    MissingPage(String),
    /// Page exists but the `#anchor` doesn't match any heading or `:tag:`.
    MissingAnchor { page: String, anchor: String },
    /// `file:` / `local:` target whose resolved path isn't on disk.
    MissingFile(PathBuf),
}

impl BrokenLinkKind {
    pub fn message(&self) -> String {
        match self {
            BrokenLinkKind::MissingPage(p) => format!("broken wikilink: page '{p}' not in wiki"),
            BrokenLinkKind::MissingAnchor { page, anchor } => {
                format!("broken anchor: '#{anchor}' not found on page '{page}'")
            }
            BrokenLinkKind::MissingFile(p) => {
                format!("broken file link: '{}' not found", p.display())
            }
        }
    }

    /// Short machine-readable kind, used in the `checkLinks` JSON output so
    /// editors can colour-code or filter.
    pub fn tag(&self) -> &'static str {
        match self {
            BrokenLinkKind::MissingPage(_) => "missing-page",
            BrokenLinkKind::MissingAnchor { .. } => "missing-anchor",
            BrokenLinkKind::MissingFile(_) => "missing-file",
        }
    }
}

/// Inspect one wikilink and return `Some(_)` when it's broken. The `uri`
/// is the source document's URI — required for `file:` / `local:`
/// resolution. `source_page` is the source's name in the index (used by
/// `AnchorOnly` links to look up the current page's headings/tags).
pub fn classify_link(
    link: &WikiLinkNode,
    uri: Option<&Url>,
    index: &WorkspaceIndex,
    source_page: &str,
) -> Option<BrokenLinkKind> {
    match link.target.kind {
        LinkKind::Wiki => {
            let path = link.target.path.as_deref()?;
            match index.page_for_wiki_target(path, source_page, link.target.is_absolute) {
                None => Some(BrokenLinkKind::MissingPage(path.to_string())),
                Some(page) => {
                    if let Some(anchor) = &link.target.anchor {
                        if anchor_resolves_on(page, anchor) {
                            None
                        } else {
                            Some(BrokenLinkKind::MissingAnchor {
                                page: path.to_string(),
                                anchor: anchor.clone(),
                            })
                        }
                    } else {
                        None
                    }
                }
            }
        }
        LinkKind::AnchorOnly => {
            let anchor = link.target.anchor.as_deref()?;
            let page = index.page_by_name(source_page)?;
            if anchor_resolves_on(page, anchor) {
                None
            } else {
                Some(BrokenLinkKind::MissingAnchor {
                    page: source_page.to_string(),
                    anchor: anchor.to_string(),
                })
            }
        }
        LinkKind::File | LinkKind::Local => {
            let path = link.target.path.as_deref()?;
            let resolved = resolve_file_path(uri, index, path, link.target.is_absolute)?;
            if resolved.exists() {
                None
            } else {
                Some(BrokenLinkKind::MissingFile(resolved))
            }
        }
        LinkKind::Interwiki | LinkKind::Diary | LinkKind::Raw => None,
    }
}

fn anchor_resolves_on(page: &crate::index::IndexedPage, anchor: &str) -> bool {
    page.find_heading_by_anchor(anchor).is_some() || page.tags.iter().any(|t| t.name == anchor)
}

/// Same classification as [`classify_link`] but driven from the cached
/// [`OutgoingLink`] data so workspace-wide checks don't have to re-parse
/// every page. The on-disk `File`/`Local` check is performed when the
/// source URI is available.
pub fn classify_outgoing(
    link: &OutgoingLink,
    source_uri: &Url,
    index: &WorkspaceIndex,
    source_page: &str,
) -> Option<BrokenLinkKind> {
    match link.kind {
        LinkKind::Wiki => {
            let path = link.target_page.as_deref()?;
            match index.page_for_wiki_target(path, source_page, link.is_absolute) {
                None => Some(BrokenLinkKind::MissingPage(path.to_string())),
                Some(page) => {
                    if let Some(anchor) = &link.anchor {
                        if anchor_resolves_on(page, anchor) {
                            None
                        } else {
                            Some(BrokenLinkKind::MissingAnchor {
                                page: path.to_string(),
                                anchor: anchor.clone(),
                            })
                        }
                    } else {
                        None
                    }
                }
            }
        }
        LinkKind::AnchorOnly => {
            let anchor = link.anchor.as_deref()?;
            let page = index.page_by_name(source_page)?;
            if anchor_resolves_on(page, anchor) {
                None
            } else {
                Some(BrokenLinkKind::MissingAnchor {
                    page: source_page.to_string(),
                    anchor: anchor.to_string(),
                })
            }
        }
        LinkKind::File | LinkKind::Local => {
            let path = link.target_page.as_deref()?;
            let resolved = resolve_file_path(Some(source_uri), index, path, link.is_absolute)?;
            if resolved.exists() {
                None
            } else {
                Some(BrokenLinkKind::MissingFile(resolved))
            }
        }
        LinkKind::Interwiki | LinkKind::Diary | LinkKind::Raw => None,
    }
}

/// Flatten heading inlines down to a plain string. Used by `commands::ops`
/// to match heading text against the configured TOC/Links section name.
pub fn heading_text(inlines: &[InlineNode]) -> String {
    let mut s = String::new();
    push_inline_text(inlines, &mut s);
    s.trim().to_string()
}

fn push_inline_text(inlines: &[InlineNode], out: &mut String) {
    for n in inlines {
        match n {
            InlineNode::Text(t) => out.push_str(&t.content),
            InlineNode::Bold(b) => push_inline_text(&b.children, out),
            InlineNode::Italic(i) => push_inline_text(&i.children, out),
            InlineNode::BoldItalic(bi) => push_inline_text(&bi.children, out),
            InlineNode::Strikethrough(s) => push_inline_text(&s.children, out),
            InlineNode::Code(c) => out.push_str(&c.content),
            InlineNode::Superscript(s) => push_inline_text(&s.children, out),
            InlineNode::Subscript(s) => push_inline_text(&s.children, out),
            InlineNode::Color(c) => push_inline_text(&c.children, out),
            InlineNode::WikiLink(w) => match &w.description {
                Some(d) => push_inline_text(d, out),
                None => {
                    if let Some(p) = &w.target.path {
                        out.push_str(p);
                    }
                }
            },
            InlineNode::ExternalLink(e) => match &e.description {
                Some(d) => push_inline_text(d, out),
                None => out.push_str(&e.url),
            },
            _ => {}
        }
    }
}

/// Resolve a `file:` / `local:` link target to an absolute path.
///
/// - Absolute (parsed `//path` or `is_absolute`): used as-is.
/// - Otherwise: joined with the source file's parent directory.
/// - If we don't have a URI to anchor relative paths against, falls back
///   to the wiki root from the index.
fn resolve_file_path(
    uri: Option<&Url>,
    index: &WorkspaceIndex,
    path: &str,
    is_absolute: bool,
) -> Option<PathBuf> {
    let candidate = PathBuf::from(path);
    if is_absolute || candidate.is_absolute() {
        return Some(candidate);
    }
    if let Some(uri) = uri {
        if let Ok(base) = uri.to_file_path() {
            if let Some(parent) = base.parent() {
                return Some(parent.join(&candidate));
            }
        }
    }
    index.root.as_ref().map(|r| r.join(&candidate))
}

/// `nuwiki.link` diagnostics for a single document.
pub fn link_health(
    ast: &DocumentNode,
    text: &str,
    uri: Option<&Url>,
    index: &WorkspaceIndex,
    source_page: &str,
    severity: LinkSeverity,
    utf8: bool,
) -> Vec<Diagnostic> {
    let Some(sev) = severity_to_lsp(severity) else {
        return Vec::new();
    };
    let mut out = Vec::new();
    for link in collect_wiki_links(ast) {
        if let Some(kind) = classify_link(link, uri, index, source_page) {
            out.push(Diagnostic {
                range: to_lsp_range(&link.span, text, utf8),
                severity: Some(sev),
                source: Some(LINK_SOURCE.into()),
                message: kind.message(),
                code: Some(tower_lsp::lsp_types::NumberOrString::String(
                    kind.tag().to_string(),
                )),
                ..Diagnostic::default()
            });
        }
    }
    out
}