/**
 * ─────────────────────────────────────────────
 *  SPB Git — Personal Git Platform
 * ─────────────────────────────────────────────
 *  Author  : Simon-Pierre Boucher
 *  Contact : contact@spboucher.ai
 *  File    : src/lib/cache.mjs
 *  Purpose : Filesystem cache keyed by <repo>@<sha> — busted on push
 *  License : MIT © Simon-Pierre Boucher
 * ─────────────────────────────────────────────
 */

import {
  readFileSync, writeFileSync, mkdirSync, rmSync, existsSync,
  readdirSync, statSync, renameSync,
} from 'node:fs';
import { join, dirname } from 'node:path';
import { randomBytes } from 'node:crypto';
import { safeJoin } from './util.mjs';

/**
 * Content cache under `cacheDir`. Layout:
 *   <cacheDir>/repos/<repo>/<sha>/<kind>          per-commit artifacts
 *   <cacheDir>/global/<kind>                       cross-repo artifacts (search index, heatmap)
 * Push hooks call {@link Cache#bustRepo} which nukes the repo subtree.
 */
export class Cache {
  /** @param {string} cacheDir */
  constructor(cacheDir) {
    this.root = cacheDir;
  }

  /** @param {...string} segments @returns {string} */
  path(...segments) {
    const cleaned = segments.map((s) => String(s).replaceAll('/', '_'));
    return safeJoin(this.root, ...cleaned);
  }

  /** Per-repo, per-commit key. @returns {string} */
  repoPath(repo, sha, kind) {
    return safeJoin(this.root, 'repos', repo, sha, kind.replaceAll('/', '_'));
  }

  /** @returns {Buffer|null} */
  getBuffer(path) {
    try {
      return readFileSync(path);
    } catch {
      return null;
    }
  }

  /** @returns {any|null} */
  getJSON(path) {
    const buf = this.getBuffer(path);
    if (buf === null) return null;
    try {
      return JSON.parse(buf.toString('utf8'));
    } catch {
      return null;
    }
  }

  /** Atomic write (tmp + rename). */
  set(path, data) {
    mkdirSync(dirname(path), { recursive: true });
    const tmp = `${path}.${randomBytes(4).toString('hex')}.tmp`;
    writeFileSync(tmp, data);
    renameSync(tmp, path);
  }

  setJSON(path, value) {
    this.set(path, JSON.stringify(value));
  }

  /**
   * Read-through helper for JSON artifacts.
   * @param {string} path
   * @param {() => Promise<any>|any} compute
   */
  async remember(path, compute) {
    const hit = this.getJSON(path);
    if (hit !== null) return hit;
    const value = await compute();
    if (value !== undefined) this.setJSON(path, value);
    return value;
  }

  /** Drop every cached artifact for a repo (all shas). @param {string} repo */
  bustRepo(repo) {
    rmSync(safeJoin(this.root, 'repos', repo), { recursive: true, force: true });
    rmSync(safeJoin(this.root, 'global'), { recursive: true, force: true });
  }

  /** @returns {{files: number, bytes: number}} recursive cache footprint */
  footprint() {
    let files = 0;
    let bytes = 0;
    const walk = (dir) => {
      let entries;
      try {
        entries = readdirSync(dir);
      } catch {
        return;
      }
      for (const entry of entries) {
        const full = join(dir, entry);
        let st;
        try {
          st = statSync(full);
        } catch {
          continue;
        }
        if (st.isDirectory()) walk(full);
        else {
          files += 1;
          bytes += st.size;
        }
      }
    };
    if (existsSync(this.root)) walk(this.root);
    return { files, bytes };
  }
}