import fs from "node:fs";
import path from "node:path";

const SKIP_FOLDERS = new Set(["_templates", "prds"]);
const SKIP_FILES = new Set(["README.md", "_state.json"]);

/**
 * Walk the `docs/work/` tree starting at `workRoot` and return a structured
 * state object. Each epic folder must contain `_epic.md`; each story
 * subfolder must contain `_story.md`.
 *
 * Returns:
 * {
 *   updated_at: ISO string,
 *   epics: {
 *     <epic-id>: {
 *       status: "todo" | "in-progress" | "done",
 *       title: string,
 *       stories: {
 *         <story-id>: {
 *           status: "todo" | "in-progress" | "done",
 *           title: string,
 *           ac_total: number,    // total checkboxes in Tasks section
 *           ac_completed: number, // - [x] checkboxes
 *         }
 *       }
 *     }
 *   }
 * }
 */
export function buildState(workRoot) {
  const state = {
    updated_at: new Date().toISOString(),
    epics: {},
  };

  if (!fs.existsSync(workRoot)) return state;

  for (const entry of fs.readdirSync(workRoot)) {
    if (SKIP_FOLDERS.has(entry) || SKIP_FILES.has(entry)) continue;
    const epicDir = path.join(workRoot, entry);
    if (!fs.statSync(epicDir).isDirectory()) continue;
    const epicFile = path.join(epicDir, "_epic.md");
    if (!fs.existsSync(epicFile)) continue;

    const epicMeta = parseFrontmatter(epicFile);
    const epicEntry = {
      status: epicMeta.status ?? "todo",
      title: epicMeta.title ?? entry,
      stories: {},
    };

    for (const sub of fs.readdirSync(epicDir)) {
      const subPath = path.join(epicDir, sub);
      if (!fs.statSync(subPath).isDirectory()) continue;
      const storyFile = path.join(subPath, "_story.md");
      if (!fs.existsSync(storyFile)) continue;
      const storyMeta = parseFrontmatter(storyFile);
      const storyContent = fs.readFileSync(storyFile, "utf8");
      const { total, completed } = countTaskCheckboxes(storyContent);
      epicEntry.stories[storyMeta.id ?? sub] = {
        status: storyMeta.status ?? "todo",
        title: storyMeta.title ?? sub,
        ac_total: total,
        ac_completed: completed,
      };
    }

    state.epics[epicMeta.id ?? entry] = epicEntry;
  }

  return state;
}

/**
 * Read a markdown file's YAML frontmatter (between leading `---` delimiters)
 * and return a flat object of string-valued keys. Numeric / bool values are
 * left as strings; this is enough for our needs (status, id, title fields).
 */
export function parseFrontmatter(filePath) {
  const src = fs.readFileSync(filePath, "utf8");
  const match = src.match(/^---\n([\s\S]+?)\n---/);
  if (!match) return {};
  const out = {};
  for (const line of match[1].split("\n")) {
    const m = line.match(/^([\w-]+):\s*(.*)$/);
    if (!m) continue;
    let value = m[2].trim();
    if (value.startsWith('"') && value.endsWith('"')) value = value.slice(1, -1);
    if (value.startsWith("'") && value.endsWith("'")) value = value.slice(1, -1);
    out[m[1]] = value;
  }
  return out;
}

/**
 * Count `- [x]` and `- [ ]` checkboxes inside the file's `## Tasks` section.
 * Returns { total, completed }.
 */
export function countTaskCheckboxes(content) {
  const lines = content.split("\n");
  let inTasks = false;
  let total = 0;
  let completed = 0;
  for (const line of lines) {
    if (line.startsWith("## ")) {
      inTasks = /^##\s+Tasks\b/i.test(line);
      continue;
    }
    if (!inTasks) continue;
    const m = line.match(/^[\s>-]*\[(.)\]/);
    if (m) {
      total++;
      if (m[1] === "x" || m[1] === "X") completed++;
    }
  }
  return { total, completed };
}