// Map a stored comment anchor back onto its SOURCE markdown so an agent can read
// comments from the CLI with the relevant slice of the file in hand.
//
// The viewer anchors comments to RENDERED text ({quote, prefix, suffix}; see
// manifest.ts) and re-finds the quote in the live DOM. The CLI has no DOM, so we
// approximate the same match against a normalized copy of the source: strip the
// inline/block markdown syntax the renderer would have dropped, collapse
// whitespace (paragraphs render as one line), and search for the quote. From the
// matched line range we return the enclosing markdown block (the paragraph / list
// / blockquote the quote sits in, blank-line delimited) plus the nearest heading
// for orientation — that block is the editable unit handed back to the agent.

import type { Comment } from "./manifest.ts";

export interface LocatedComment extends Comment {
  /** True when the quote was found in the source. */
  matched: boolean;
  /** 1-based source line where the quote starts; null when unmatched. */
  line: number | null;
  /** 1-based source line where the quote ends; null when unmatched. */
  endLine: number | null;
  /** Nearest enclosing heading text (orientation only); null if none / unmatched. */
  heading: string | null;
  /** The markdown block (paragraph/list/quote) the quote sits in; null when unmatched. */
  context: string | null;
  /** 1-based source line range of `context` (inclusive); null when unmatched. */
  contextLines: [number, number] | null;
}

const HEADING_RE = /^\s{0,3}(#{1,6})\s+(.*?)\s*#*\s*$/;

/** Strip inline markdown the renderer collapses to plain text.
 * HTML comments are deliberately NOT stripped here: the markdown renderer keeps
 * them visible (painted muted, see .md-comment), so a quote can legitimately
 * contain one and must still match this projection. buildHtmlIndex blanks them
 * because a real browser hides them — that divergence is intentional. */
function stripInline(s: string): string {
  return s
    .replace(/\[\[([^\]|]+)(?:\|([^\]]+))?\]\]/g, (_, name, alias) => (alias ?? name).trim()) // wikilinks → display text
    .replace(/!\[([^\]]*)\]\([^)]*\)/g, "$1") // images → alt
    .replace(/\[([^\]]*)\]\([^)]*\)/g, "$1") // links → text
    .replace(/`([^`]+)`/g, "$1") // inline code
    .replace(/\*\*([^*]+)\*\*/g, "$1")
    .replace(/__([^_]+)__/g, "$1")
    .replace(/\*([^*]+)\*/g, "$1")
    .replace(/_([^_]+)_/g, "$1")
    .replace(/~~([^~]+)~~/g, "$1");
}

/** Strip leading block markers (heading hashes, blockquote, list bullets). */
function stripBlock(line: string): string {
  return line
    .replace(/^\s{0,3}#{1,6}\s+/, "")
    .replace(/^\s*>\s?/, "")
    .replace(/^\s*([-*+]|\d+[.)])\s+/, "");
}

const isFence = (line: string) => /^\s*(```|~~~)/.test(line);
const collapseWs = (s: string) => s.replace(/\s+/g, " ");
const normWs = (s: string) => collapseWs(s).trim();

/** A source file parsed once: lines, per-line fenced-code state, and a
 * whitespace-collapsed/syntax-stripped projection with a char→line map. Built
 * with `buildIndex` so a file with many comments pays the parse cost only once. */
export interface SourceIndex {
  /** Which projection built this — markdown and html strip different syntax and
   * disagree on what a "block" is, so every consumer has to branch on it. */
  kind: "markdown" | "html";
  lines: string[];
  /** Per-line "inside a fenced code block" flag (so `#` in code isn't a heading). */
  inFence: boolean[];
  /** Rendered-text projection: hit positions resolve to lines via `lineOf`. */
  text: string;
  lineOf: number[];
}

/** Pick the projection from the file's extension. The viewer anchors comments to
 * whatever it rendered, so the CLI has to un-render the same language. */
export function buildIndexFor(filePath: string, source: string): SourceIndex {
  return /\.html?$/i.test(filePath) ? buildHtmlIndex(source) : buildIndex(source);
}

export function buildIndex(source: string): SourceIndex {
  const lines = source.split(/\r?\n/);
  const inFence: boolean[] = [];
  let fence = false;
  for (let i = 0; i < lines.length; i++) {
    inFence[i] = fence;
    if (isFence(lines[i]!)) fence = !fence;
  }
  // Project to rendered text + char→line map: strip markdown outside fences,
  // keep fenced lines verbatim, collapse all whitespace (paragraphs render as
  // one line, so a line/paragraph break becomes a single space between words).
  return {
    kind: "markdown",
    lines,
    inFence,
    ...project(lines, (raw, i) =>
      isFence(raw) ? null : inFence[i] ? raw : stripInline(stripBlock(raw)),
    ),
  };
}

/** Collapse a per-line render into the flat rendered text plus its char→line map.
 * Both projections share it so locateComment's lineOf lookup can only ever mean one
 * thing. `render` returns null for a line that renders to nothing (a fence marker). */
function project(
  lines: string[],
  render: (raw: string, i: number) => string | null,
): { text: string; lineOf: number[] } {
  const chars: string[] = [];
  const lineOf: number[] = [];
  let lastSpace = true;
  lines.forEach((raw, idx) => {
    const str = render(raw, idx);
    if (str == null) return;
    for (const ch of str) {
      if (/\s/.test(ch)) {
        if (lastSpace) continue;
        chars.push(" ");
        lineOf.push(idx + 1);
        lastSpace = true;
      } else {
        chars.push(ch);
        lineOf.push(idx + 1);
        lastSpace = false;
      }
    }
    // A line end is a word boundary in the rendered text (so is a tag boundary,
    // which the html projection has already turned into a space).
    if (!lastSpace) {
      chars.push(" ");
      lineOf.push(idx + 1);
      lastSpace = true;
    }
  });
  return { text: chars.join(""), lineOf };
}

const HTML_HEADING_RE = /<h[1-6][^>]*>([\s\S]*?)<\/h[1-6]>/i;
const HTML_HEADING_OPEN = /<h([1-6])\b[^>]*>/i;
/** How many lines a heading may span. Formatters and generated pages routinely put
 * the text on its own line, so matching within one line misses those entirely. */
const HTML_HEADING_SPAN = 8;
const ENTITIES: Record<string, string> = {
  amp: "&", lt: "<", gt: ">", quot: '"', apos: "'", nbsp: " ",
};
/** Decode the entities a browser would have turned back into text — the anchor was
 * captured from the RENDERED page, so its quote holds the character, not the entity. */
function decodeEntities(s: string): string {
  return s.replace(/&(#x?[0-9a-f]+|[a-z]+);/gi, (m, ref: string) => {
    if (ref[0] === "#") {
      const code = ref[1]?.toLowerCase() === "x" ? parseInt(ref.slice(2), 16) : parseInt(ref.slice(1), 10);
      // Out-of-range is not merely un-decodable: fromCodePoint THROWS, and this
      // runs during `scratch ui`/`export` render, so one bad reference would take
      // the whole command down instead of leaving the entity as written.
      return Number.isFinite(code) && code > 0 && code <= 0x10ffff
        ? String.fromCodePoint(code)
        : m;
    }
    return ENTITIES[ref.toLowerCase()] ?? m;
  });
}

/** Project an HTML source to the text a browser would render: drop script/style
 * bodies and comments (never displayed), drop tags, decode entities, collapse
 * whitespace. Line-accurate because the blanking is length-preserving per line —
 * every kept char keeps the source line it came from.
 *
 * Limitation worth knowing: text a script GENERATES is not in the source, so a
 * comment anchored to it cannot be located here and reports as unmatched. */
export function buildHtmlIndex(source: string): SourceIndex {
  const lines = source.split(/\r?\n/);
  // Blank out non-rendered regions in the FULL text first (they span lines), keeping
  // newlines so the line numbering below still lines up with the original.
  const keepNewlines = (m: string) => m.replace(/[^\n]/g, " ");
  const cleaned = source
    .replace(/<!--[\s\S]*?-->/g, keepNewlines)
    .replace(/<(script|style)\b[^>]*>[\s\S]*?<\/\1\s*>/gi, keepNewlines)
    .replace(/<[^>]*>/g, keepNewlines);
  return {
    kind: "html",
    lines,
    inFence: lines.map(() => false),
    ...project(cleaned.split(/\r?\n/), decodeEntities),
  };
}

/** Nearest heading text at or above a 1-based source line (orientation only). */
export function headingFor(idx: SourceIndex, line: number): { heading: string | null; level: number } {
  for (let i = Math.min(line, idx.lines.length) - 1; i >= 0; i--) {
    if (idx.inFence[i]) continue;
    if (idx.kind === "html") {
      const open = idx.lines[i]!.match(HTML_HEADING_OPEN);
      if (open) {
        // Match forward from the opening tag, not within its line — a closing tag
        // on a later line is the common shape in generated markup.
        const h = idx.lines.slice(i, i + HTML_HEADING_SPAN).join("\n").match(HTML_HEADING_RE);
        const text = h ? normWs(decodeEntities(h[1]!.replace(/<[^>]*>/g, " "))) : "";
        if (text) return { heading: text, level: Number(open[1]) };
      }
      continue;
    }
    const m = idx.lines[i]!.match(HEADING_RE);
    if (m) return { heading: m[2]!.trim(), level: m[1]!.length };
  }
  return { heading: null, level: 0 };
}

/** The markdown block (paragraph / list / blockquote) covering a 1-based line
 * range — expanded outward to the surrounding blank lines, the natural editable
 * unit. Headings and fence markers act as hard boundaries. */
export function blockFor(
  idx: SourceIndex,
  startLine: number,
  endLine: number,
): { text: string; lines: [number, number] } {
  const { lines, inFence } = idx;
  // HTML has no blank-line block structure — indentation and newlines are free —
  // so the matched lines ARE the unit. In practice a text run sits inside one
  // element on one line, which is exactly what an agent needs to edit.
  if (idx.kind === "html") {
    const s = Math.max(0, startLine - 1);
    const e = Math.min(endLine, lines.length) - 1;
    return { text: lines.slice(s, e + 1).join("\n").trim(), lines: [s + 1, e + 1] };
  }
  const blank = (i: number) => lines[i]!.trim() === "";
  const bound = (i: number) => !inFence[i] && (isFence(lines[i]!) || HEADING_RE.test(lines[i]!));
  let s = startLine - 1;
  let e = Math.min(endLine, lines.length) - 1;
  while (s > 0 && !blank(s - 1) && !bound(s - 1)) s--;
  while (e < lines.length - 1 && !blank(e + 1) && !bound(e + 1)) e++;
  return { text: lines.slice(s, e + 1).join("\n").trim(), lines: [s + 1, e + 1] };
}

// Find a quote in the projection, disambiguating multiple matches by how many
// chars of prefix/suffix match contiguously outward from the quote's boundary
// (ties keep the first hit). Mirrors the viewer's cmtFindAnchor so the CLI and
// the rendered view resolve the same occurrence. Returns -1 when not found.
function findQuote(text: string, q: string, prefix: string, suffix: string): number {
  if (!q) return -1;
  const hits: number[] = [];
  for (let i = text.indexOf(q); i !== -1; i = text.indexOf(q, i + 1)) hits.push(i);
  if (hits.length <= 1) return hits[0] ?? -1;
  let best = hits[0]!;
  let bestScore = -1;
  for (const h of hits) {
    const before = text.slice(Math.max(0, h - prefix.length), h);
    const after = text.slice(h + q.length, h + q.length + suffix.length);
    let score = 0;
    for (let k = 1; k <= before.length; k++) {
      if (prefix[prefix.length - k] === before[before.length - k]) score++;
      else break;
    }
    for (let k = 0; k < after.length; k++) {
      if (suffix[k] === after[k]) score++;
      else break;
    }
    if (score > bestScore) {
      bestScore = score;
      best = h;
    }
  }
  return best;
}

/** One comment flattened for an agent: the human comment + quoted text + where it
 * anchors in the source. The shape `scratch comments --json` emits and the viewer
 * copies (Ctrl+Alt+C), so both stay byte-identical. */
export interface CommentItem {
  id: string;
  file: string;
  comment: string;
  quote: string;
  matched: boolean;
  line: number | null;
  section_heading: string | null;
  context: string | null;
  context_lines: string | null;
}

/** Resolve a file's comments into agent-friendly items: parse the source once,
 * locate each comment's quote, and flatten. Shared by the CLI (`cmdComments`) and
 * the viewer's copy-comments shortcut so their output matches exactly. */
export function toCommentItems(filePath: string, source: string, comments: Comment[]): CommentItem[] {
  const index = buildIndexFor(filePath, source); // parse once, reuse for all the file's comments
  return comments.map((c) => {
    const r = locateComment(index, c);
    return {
      id: c.id,
      file: filePath,
      comment: c.body,
      quote: c.anchor.quote.replace(/\s+/g, " ").trim(),
      matched: r.matched,
      line: r.line,
      section_heading: r.heading,
      context: r.context,
      context_lines: r.contextLines ? `${r.contextLines[0]}-${r.contextLines[1]}` : null,
    };
  });
}

const UNMATCHED = { matched: false, line: null, endLine: null, heading: null, context: null, contextLines: null } as const;

/** Locate a comment's quote in a parsed source and resolve its enclosing block. */
export function locateComment(idx: SourceIndex, comment: Comment): LocatedComment {
  const { text, lineOf } = idx;
  // Prefix/suffix keep their boundary whitespace (only inner runs collapse) — the
  // space adjacent to the quote is what disambiguates between occurrences.
  // An html projection already dropped every tag, so the markdown syntax-stripper
  // would only corrupt the quote (underscores, asterisks and backticks are literal
  // text in an author's page).
  const strip = idx.kind === "html" ? (s: string) => s : stripInline;
  const prefix = collapseWs(strip(comment.anchor.prefix ?? ""));
  const suffix = collapseWs(strip(comment.anchor.suffix ?? ""));
  let q = normWs(strip(comment.anchor.quote));
  let at = findQuote(text, q, prefix, suffix);
  if (at === -1 && comment.anchor.quote) {
    // Fallback: the quote may have already been plain (e.g. code) — try as-is.
    q = normWs(comment.anchor.quote);
    at = findQuote(text, q, prefix, suffix);
  }
  if (at === -1) return { ...comment, ...UNMATCHED };
  const line = lineOf[at]!;
  const endLine = lineOf[Math.min(at + q.length - 1, lineOf.length - 1)]!;
  const block = blockFor(idx, line, endLine);
  return {
    ...comment,
    matched: true,
    line,
    endLine,
    heading: headingFor(idx, line).heading,
    context: block.text,
    contextLines: block.lines,
  };
}