//! `textDocument/rename` — server-side rename with cross-document link
//! rewriting.
//!
//! Phase 13 implementation:
//! 1. Resolve the rename target — cursor on a wikilink renames the linked
//!    page; otherwise rename the current file.
//! 2. Build the new URI from the wiki root + the user-supplied path.
//! 3. For every page in the wiki's index with an outgoing link to the
//!    old page name, read its source via the Phase 11 closed-doc loader
//!    so cached spans are validated against current text, then emit a
//!    `TextEdit` that swaps the `[[old]]` for `[[new]]` while preserving
//!    anchors and descriptions.
//! 4. Add the `RenameFile` op last so the builder emits it before content
//!    edits in `documentChanges` ordering.

use std::path::Path;

use tower_lsp::lsp_types::{Url, WorkspaceEdit};

use crate::edits::{op_rename, text_edit_replace, WorkspaceEditBuilder};
use crate::index::page_name_from_uri;
use crate::Backend;

/// Compute the `WorkspaceEdit` for renaming `target_uri` to `new_name`.
///
/// Returns `None` when:
///   - the URI doesn't belong to any registered wiki,
///   - the new URI couldn't be built from the wiki root + new_name,
///   - the new URI is the same as the old one.
pub(crate) async fn compute_rename(
    backend: &Backend,
    target_uri: Url,
    new_name: String,
    utf8: bool,
) -> Option<WorkspaceEdit> {
    let wiki = backend.wiki_for_uri(&target_uri)?;
    let old_name = page_name_from_uri(&target_uri, Some(&wiki.config.root));
    let new_uri = build_new_uri(&wiki.config.root, &new_name, &wiki.config.file_extension)?;
    if new_uri == target_uri {
        return None;
    }

    let mut builder = WorkspaceEditBuilder::new();
    builder.file_op(op_rename(target_uri.clone(), new_uri));

    // Snapshot the backlinks so the index read lock is released before we
    // await any disk I/O.
    let backlinks = {
        let idx = wiki.index.read().ok()?;
        idx.backlinks_for(&old_name).to_vec()
    };

    for bl in backlinks {
        let Ok(snapshot) = backend.read_or_open(&bl.source_uri).await else {
            continue;
        };
        let start = bl.source_span.start.offset.min(snapshot.text.len());
        let end = bl.source_span.end.offset.min(snapshot.text.len());
        if start >= end {
            continue;
        }
        let original = &snapshot.text[start..end];
        if let Some(new_link) = rewrite_wikilink_target(original, &new_name) {
            let edit = text_edit_replace(bl.source_span, new_link, &snapshot.text, utf8);
            builder.edit(bl.source_uri.clone(), edit);
        }
    }

    if builder.is_empty() {
        None
    } else {
        Some(builder.build())
    }
}

/// Build `<root>/<new_name>(<ext>)` as a `file://` URL.
pub fn build_new_uri(root: &Path, new_name: &str, ext: &str) -> Option<Url> {
    let mut path = root.to_path_buf();
    for part in new_name.split(['/', '\\']) {
        if !part.is_empty() {
            path.push(part);
        }
    }
    let path_str = path.to_string_lossy().to_string();
    let with_ext = if path_str.ends_with(ext) {
        path_str
    } else {
        format!("{path_str}{ext}")
    };
    Url::from_file_path(with_ext).ok()
}

/// Rewrite a `[[...]]` source segment so the path portion becomes
/// `new_path`, keeping any `#anchor` and `|description` parts intact.
///
/// Returns `None` if `segment` doesn't look like a wikilink (starts with
/// `[[`, ends with `]]`).
pub fn rewrite_wikilink_target(segment: &str, new_path: &str) -> Option<String> {
    if !segment.starts_with("[[") || !segment.ends_with("]]") || segment.len() < 4 {
        return None;
    }
    let inner = &segment[2..segment.len() - 2];
    let (path_part, description) = match inner.find('|') {
        Some(i) => (&inner[..i], Some(&inner[i + 1..])),
        None => (inner, None),
    };
    let anchor = path_part.find('#').map(|i| &path_part[i + 1..]);

    let mut out = String::with_capacity(segment.len());
    out.push_str("[[");
    out.push_str(new_path);
    if let Some(a) = anchor {
        out.push('#');
        out.push_str(a);
    }
    if let Some(d) = description {
        out.push('|');
        out.push_str(d);
    }
    out.push_str("]]");
    Some(out)
}