// Concurrent render of N BannerSpecs through a single Chromium instance.
// One browser, multiple isolated contexts, capped at min(N, 3). Failures
// for one spec do not stop the others — they accumulate in the errors
// list. Font + GSAP bytes are read once at the top so renderToZip never
// hits disk for them.

import fs from 'node:fs';
import path from 'node:path';
import { createRequire } from 'node:module';
import { fileURLToPath } from 'node:url';
import { chromium } from 'playwright';
import type { BannerSpec } from '@banner-studio/types';
import { renderToZip } from './render-to-zip.js';

export interface RenderManyArgs {
  specs: BannerSpec[];
  outputDir: string;
  concurrency?: number;
  /**
   * Absolute path to the repository root, used to locate
   * infra/fonts/Inter-*.ttf and node_modules/gsap/dist/gsap.min.js.
   * Defaults to the caller's CWD if omitted.
   */
  repoRoot?: string;
  /**
   * Optional callback to override the per-spec output path. Returns
   * `{ subdir, filename }` (filename without `.zip`). If omitted, falls
   * back to the renderToZip default (`<campaign>/<version>.zip`).
   *
   * Multi-size exports use this to group by feed row:
   *   `({ spec }) => ({ subdir: \`row-\${i+1}\`, filename: spec.artboards[0]!.artboard_id })`
   */
  pathFor?: (spec: BannerSpec, index: number) => { subdir: string; filename: string };
}

export interface ExportedItem {
  version_id: string;
  zip_path: string;
  bytes: number;
}

export interface ExportError {
  version_id?: string;
  error: string;
}

export interface RenderManyResult {
  exported: ExportedItem[];
  errors: ExportError[];
}

function resolveGsapSourcePath(repoRoot: string): string {
  // pnpm puts the real package under a content-addressed folder, NOT at the
  // top-level node_modules. Resolve through Node's module resolver, anchored
  // on this file — render-worker declares gsap in its own package.json, so
  // this createRequire sees it via pnpm's nested node_modules. Anchoring on
  // the repo root fails because gsap isn't installed there.
  try {
    const here = fileURLToPath(import.meta.url);
    const req = createRequire(here);
    return req.resolve('gsap/dist/gsap.min.js');
  } catch {
    // Fall through to a best-effort path. With pnpm this is almost certainly
    // wrong, but it's only hit if the import.meta.url anchor failed entirely.
    return path.join(repoRoot, 'node_modules', 'gsap', 'dist', 'gsap.min.js');
  }
}

async function runWithConcurrency<T, R>(
  items: T[],
  limit: number,
  fn: (item: T, index: number) => Promise<R>
): Promise<R[]> {
  const results: R[] = new Array(items.length);
  let next = 0;
  const worker = async () => {
    while (true) {
      const i = next++;
      if (i >= items.length) return;
      results[i] = await fn(items[i]!, i);
    }
  };
  const workers: Promise<void>[] = [];
  for (let i = 0; i < Math.min(limit, items.length); i++) {
    workers.push(worker());
  }
  await Promise.all(workers);
  return results;
}

export async function renderMany({
  specs,
  outputDir,
  concurrency,
  repoRoot,
  pathFor
}: RenderManyArgs): Promise<RenderManyResult> {
  const exported: ExportedItem[] = [];
  const errors: ExportError[] = [];

  if (specs.length === 0) return { exported, errors };

  const root = repoRoot ?? process.cwd();
  const fontsDir = path.join(root, 'infra', 'fonts');
  let interRegular: Buffer;
  let interBold: Buffer;
  let gsapSource: string;
  try {
    interRegular = fs.readFileSync(path.join(fontsDir, 'Inter-Regular.ttf'));
    interBold = fs.readFileSync(path.join(fontsDir, 'Inter-Bold.ttf'));
    gsapSource = fs.readFileSync(resolveGsapSourcePath(root), 'utf8');
  } catch (err) {
    return {
      exported,
      errors: [
        {
          error: `Failed to load required assets (fonts/gsap): ${
            err instanceof Error ? err.message : String(err)
          }`
        }
      ]
    };
  }

  fs.mkdirSync(outputDir, { recursive: true });

  const browser = await chromium.launch({ headless: true });
  try {
    const limit = concurrency ?? Math.min(specs.length, 3);
    await runWithConcurrency(specs, limit, async (spec, idx) => {
      try {
        const override = pathFor ? pathFor(spec, idx) : undefined;
        const result = await renderToZip({
          spec,
          outputDir,
          browser,
          gsapSource,
          interRegular,
          interBold,
          ...(override ? { subdir: override.subdir, filename: override.filename } : {})
        });
        exported.push({
          version_id: spec.version_id,
          zip_path: result.zip_path,
          bytes: result.bytes
        });
      } catch (err) {
        errors.push({
          version_id: spec.version_id,
          error: err instanceof Error ? err.message : String(err)
        });
      }
    });
  } finally {
    await browser.close();
  }

  return { exported, errors };
}