import fs from "node:fs/promises";
import { posix as path } from "node:path";
import { fsCachePath } from "../../utils/runtimeChecks.js";

const copied = new Set();
const dirsCreated = new Set();

export async function saveAndCopyAsset(
  hash,
  image,
  buffer,
  outDir,
  assetsDir,
  assetPath,
  isSsrBuild
) {
  // Use Set for O(1) lookup instead of O(n) array search
  if (copied.has(assetPath)) return;

  const src = fsCachePath + hash;
  const dest = path.join(outDir, isSsrBuild ? "/client" : "", assetPath);
  const destDir = path.dirname(dest);

  // Check if destination already exists and is valid (skip copy)
  try {
    const stats = await fs.stat(dest);
    if (stats.size > 0) {
      copied.add(assetPath);
      console.log(`[skip] ${assetPath} (already exists)`);
      return;
    }
  } catch {
    // File doesn't exist, continue with copy
  }

  // Ensure destination directory exists (but only create once per unique dir)
  if (!dirsCreated.has(destDir)) {
    await fs.mkdir(destDir, { recursive: true });
    dirsCreated.add(destDir);
  }

  // Try hardlink first (instant, no disk usage), fallback to copy
  let linked = false;
  try {
    await fs.link(src, dest);
    linked = true;
  } catch (linkError) {
    // Hardlink failed, try copy
    try {
      await fs.copyFile(src, dest);
    } catch (copyError) {
      if (copyError.code === "ENOENT") {
        // Source doesn't exist, regenerate from buffer/image
        const imageBuffer = buffer || (await image.toBuffer());
        await Promise.all([
          fs.writeFile(src, imageBuffer),
          fs.writeFile(dest, imageBuffer)
        ]);
        console.log(`[regen] ${src} -> ${dest}`);
      } else {
        throw copyError;
      }
    }
  }

  copied.add(assetPath);
}

// Helper to pre-create directories in batch (call before processing)
export async function preCreateDirectories(assetPaths, outDir, isSsrBuild) {
  const uniqueDirs = new Set(
    assetPaths.map(assetPath => 
      path.dirname(path.join(outDir, isSsrBuild ? "/client" : "", assetPath))
    )
  );
  
  await Promise.all(
    [...uniqueDirs].map(dir => fs.mkdir(dir, { recursive: true }))
  );
  uniqueDirs.forEach(dir => dirsCreated.add(dir));
}