/**
 * YAML frontmatter → Meta callout (opt-in via --frontmatter-as-callout).
 *
 * Parses a leading `---\n…\n---` block as a minimal YAML subset and renders
 * a blockquote "Meta" callout that lark-hirono's normalize pass later
 * converts to a Feishu callout.
 *
 * Supported value forms: bare string, quoted string, ISO date, flow-style
 * array (`[a, b, c]`). Block-style arrays and nested maps are rejected
 * with a clear error — consumers with richer frontmatter should
 * preprocess it themselves.
 */

// ─── Types ──────────────────────────────────────────────────────────────

export interface ParsedFrontmatter {
  /** Document body with the `---…---` block stripped. */
  body: string;
  /** Rendered Meta callout (blockquote) — null when no frontmatter was present. */
  callout: string | null;
  /** Raw key/value pairs in parse order. */
  data: Record<string, string | string[]>;
}

// Built-in key order; anything else falls through alphabetically.
const KEY_ORDER = [
  "type",
  "created",
  "updated",
  "raw_source",
  "tags",
  "refs",
  "tier",
  "source_count",
  "highlights",
];

// ─── Parser ─────────────────────────────────────────────────────────────

const FENCE_RE = /^---\r?\n([\s\S]*?)\r?\n---\r?\n?/;

function parseValue(raw: string): string | string[] {
  const v = raw.trim();
  if (v === "") return "";
  // Flow-style array: [a, b, c]
  if (v.startsWith("[") && v.endsWith("]")) {
    const inner = v.slice(1, -1).trim();
    if (inner === "") return [];
    return inner.split(",").map((item) => stripQuotes(item.trim()));
  }
  // Quoted scalar
  return stripQuotes(v);
}

function stripQuotes(s: string): string {
  if ((s.startsWith('"') && s.endsWith('"')) || (s.startsWith("'") && s.endsWith("'"))) {
    return s.slice(1, -1);
  }
  return s;
}

function formatLabel(key: string): string {
  const spaced = key.replace(/_/g, " ");
  return spaced.charAt(0).toUpperCase() + spaced.slice(1);
}

function formatValue(v: string | string[]): string {
  if (Array.isArray(v)) return v.join(", ");
  return v;
}

function renderCallout(data: Record<string, string | string[]>): string {
  const keys = Object.keys(data);
  if (keys.length === 0) return "";

  const rows: string[] = ["> **Meta**"];
  const seen = new Set<string>();
  for (const key of KEY_ORDER) {
    if (key in data) {
      rows.push(`> - **${formatLabel(key)}**: ${formatValue(data[key])}`);
      seen.add(key);
    }
  }
  for (const key of keys.sort()) {
    if (!seen.has(key)) {
      rows.push(`> - **${formatLabel(key)}**: ${formatValue(data[key])}`);
    }
  }
  return rows.join("\n");
}

/**
 * Parse a leading YAML frontmatter block.
 *
 * If no frontmatter is present: returns `{ body: md, callout: null, data: {} }`.
 * If malformed (block-style list, nested map, non-`key: value` line): throws.
 */
export function parseFrontmatter(md: string): ParsedFrontmatter {
  const match = md.match(FENCE_RE);
  if (!match) return { body: md, callout: null, data: {} };

  const raw = match[1];
  const data: Record<string, string | string[]> = {};

  for (const rawLine of raw.split(/\r?\n/)) {
    const line = rawLine.trimEnd();
    if (line.trim() === "") continue;
    // Block-list continuation ("- item") without a preceding array context is unsupported.
    if (/^\s*-\s/.test(line)) {
      throw new Error(
        `frontmatter: block-style list not supported (found "${line.trim()}"). ` +
          `Use flow syntax: tags: [a, b, c]`
      );
    }
    const kv = line.match(/^(\w[\w-]*)\s*:\s*(.*)$/);
    if (!kv) {
      throw new Error(`frontmatter: cannot parse line "${line}"`);
    }
    const [, key, valueStr] = kv;
    data[key] = parseValue(valueStr);
  }

  const body = md.slice(match[0].length).replace(/^\n+/, "");
  const callout = renderCallout(data);
  return { body, callout: callout || null, data };
}