import { createHash } from 'node:crypto';
import { availableParallelism } from 'node:os';
import { readFile, readdir, stat, writeFile } from 'node:fs/promises';
import { dirname, join, relative, resolve } from 'node:path';
import process from 'node:process';
import { fileURLToPath } from 'node:url';
import { Worker } from 'node:worker_threads';
import { hasUtf8Bom } from './eu4_han_convert/src/codec.js';

const PROFILE = 'compatible';
const MANIFEST_VERSION = 1;
const repositoryRoot = resolve(dirname(fileURLToPath(import.meta.url)), '..');
const sourceRoot = join(repositoryRoot, 'localisation_source');
const encodedRoot = join(repositoryRoot, 'localisation');
const manifestPath = join(repositoryRoot, 'localisation_manifest.json');
const codecPath = join(repositoryRoot, 'tools', 'eu4_han_convert', 'src', 'codec.js');

function hash(buffer) {
  return createHash('sha256').update(buffer).digest('hex');
}

async function listLocalisationFiles(root) {
  const files = [];

  async function visit(directory) {
    const entries = await readdir(directory, { withFileTypes: true });
    for (const entry of entries) {
      const path = join(directory, entry.name);
      if (entry.isDirectory()) await visit(path);
      else if (entry.isFile() && entry.name.endsWith('.yml')) {
        files.push(relative(root, path).replaceAll('\\', '/'));
      }
    }
  }

  await visit(root);
  return files.sort();
}

async function pathExists(path) {
  try {
    await stat(path);
    return true;
  } catch (error) {
    if (error.code === 'ENOENT') return false;
    throw error;
  }
}

async function readManifest() {
  if (!await pathExists(manifestPath)) return null;
  return JSON.parse(await readFile(manifestPath, 'utf8'));
}

async function getPipeline() {
  return {
    version: MANIFEST_VERSION,
    profile: PROFILE,
    codecSha256: hash(await readFile(codecPath)),
  };
}

function isCurrentManifest(manifest, pipeline) {
  return manifest
    && manifest.version === pipeline.version
    && manifest.profile === pipeline.profile
    && manifest.codecSha256 === pipeline.codecSha256;
}

function compareFileSets(sourceFiles, encodedFiles) {
  const sourceSet = new Set(sourceFiles);
  const encodedSet = new Set(encodedFiles);
  return {
    missing: sourceFiles.filter((path) => !encodedSet.has(path)),
    extra: encodedFiles.filter((path) => !sourceSet.has(path)),
  };
}

function assertSameFileSet(sourceFiles, encodedFiles) {
  const { missing, extra } = compareFileSets(sourceFiles, encodedFiles);
  if (missing.length || extra.length) {
    throw new Error([
      ...missing.map((path) => `missing encoded file: ${path}`),
      ...extra.map((path) => `missing source file: ${path}`),
    ].join('\n'));
  }
}

async function mapConcurrent(items, concurrency, worker) {
  const results = new Array(items.length);
  let nextIndex = 0;

  async function run() {
    while (nextIndex < items.length) {
      const index = nextIndex;
      nextIndex += 1;
      results[index] = await worker(items[index]);
    }
  }

  await Promise.all(
    Array.from(
      { length: Math.min(concurrency, Math.max(items.length, 1)) },
      () => run(),
    ),
  );
  return results;
}

class CodecPool {
  constructor(size) {
    this.queue = [];
    this.nextId = 0;
    this.workers = Array.from({ length: size }, () => {
      const state = {
        worker: new Worker(new URL('./localisation_worker.mjs', import.meta.url)),
        active: null,
      };
      state.worker.on('message', (message) => {
        if (message.error) state.active.reject(new Error(message.error));
        else state.active.resolve(Buffer.from(message.output));
        state.active = null;
        this.dispatch();
      });
      state.worker.on('error', (error) => {
        if (state.active) state.active.reject(error);
        state.active = null;
        this.dispatch();
      });
      return state;
    });
  }

  run(operation, input) {
    return new Promise((resolveJob, rejectJob) => {
      this.queue.push({
        id: this.nextId,
        operation,
        input,
        resolve: resolveJob,
        reject: rejectJob,
      });
      this.nextId += 1;
      this.dispatch();
    });
  }

  dispatch() {
    for (const state of this.workers) {
      if (state.active || !this.queue.length) continue;
      state.active = this.queue.shift();
      state.worker.postMessage({
        id: state.active.id,
        operation: state.active.operation,
        input: state.active.input,
      });
    }
  }

  async close() {
    await Promise.all(this.workers.map(({ worker }) => worker.terminate()));
  }
}

async function writeManifest(pipeline, entries) {
  const manifest = {
    ...pipeline,
    files: Object.fromEntries(
      Object.entries(entries).sort(([left], [right]) => left.localeCompare(right)),
    ),
  };
  await writeFile(manifestPath, `${JSON.stringify(manifest, null, 2)}\n`, 'utf8');
}

async function build(concurrency, codecPool) {
  const sourceFiles = await listLocalisationFiles(sourceRoot);
  const encodedFiles = await listLocalisationFiles(encodedRoot);
  const { extra } = compareFileSets(sourceFiles, encodedFiles);
  if (extra.length) {
    throw new Error(extra.map((path) => `missing source file: ${path}`).join('\n'));
  }

  const encodedSet = new Set(encodedFiles);
  const pipeline = await getPipeline();
  const previous = await readManifest();
  const previousFiles = isCurrentManifest(previous, pipeline) ? previous.files : {};

  const results = await mapConcurrent(sourceFiles, concurrency, async (path) => {
    const sourceBuffer = await readFile(join(sourceRoot, path));
    const sourceSha256 = hash(sourceBuffer);
    const outputPath = join(encodedRoot, path);
    const outputBuffer = encodedSet.has(path) ? await readFile(outputPath) : null;
    const encodedSha256 = outputBuffer ? hash(outputBuffer) : null;
    const previousEntry = previousFiles[path];

    if (
      previousEntry
      && previousEntry.sourceSha256 === sourceSha256
      && previousEntry.encodedSha256 === encodedSha256
    ) {
      return { path, entry: previousEntry, rebuilt: false };
    }

    const expected = await codecPool.run('encode', sourceBuffer);
    const rebuilt = !outputBuffer || !outputBuffer.equals(expected);
    if (rebuilt) await writeFile(outputPath, expected);

    return {
      path,
      rebuilt,
      entry: {
        sourceSha256,
        encodedSha256: hash(expected),
      },
    };
  });

  await writeManifest(
    pipeline,
    Object.fromEntries(results.map(({ path, entry }) => [path, entry])),
  );
  const rebuilt = results.filter((result) => result.rebuilt).length;
  process.stdout.write(
    `Localisation build complete: ${rebuilt} rebuilt, ${sourceFiles.length - rebuilt} reused, ${concurrency} workers.\n`,
  );
}

async function check(concurrency, codecPool) {
  const sourceFiles = await listLocalisationFiles(sourceRoot);
  const encodedFiles = await listLocalisationFiles(encodedRoot);
  assertSameFileSet(sourceFiles, encodedFiles);

  const pipeline = await getPipeline();
  const manifest = await readManifest();
  const manifestCurrent = isCurrentManifest(manifest, pipeline);
  const results = await mapConcurrent(sourceFiles, concurrency, async (path) => {
    const sourceBuffer = await readFile(join(sourceRoot, path));
    const encodedBuffer = await readFile(join(encodedRoot, path));
    if (!hasUtf8Bom(encodedBuffer)) throw new Error(`missing UTF-8 BOM: ${path}`);

    const sourceSha256 = hash(sourceBuffer);
    const encodedSha256 = hash(encodedBuffer);
    const entry = manifestCurrent ? manifest.files[path] : null;
    if (
      entry
      && entry.sourceSha256 === sourceSha256
      && entry.encodedSha256 === encodedSha256
    ) {
      return false;
    }

    const expected = await codecPool.run('encode', sourceBuffer);
    if (!encodedBuffer.equals(expected)) {
      throw new Error(`encoded localisation is out of date: ${path}`);
    }
    return true;
  });

  if (!manifestCurrent || results.some(Boolean)) {
    throw new Error('localisation_manifest.json is out of date; run the build command');
  }

  process.stdout.write(
    `Localisation check complete: ${sourceFiles.length} verified, 0 re-encoded, ${concurrency} workers.\n`,
  );
}

async function source(concurrency, codecPool) {
  const encodedFiles = await listLocalisationFiles(encodedRoot);
  const sourceFiles = await listLocalisationFiles(sourceRoot);
  const { missing } = compareFileSets(sourceFiles, encodedFiles);
  if (missing.length) {
    throw new Error(missing.map((path) => `missing encoded file: ${path}`).join('\n'));
  }

  const sourceSet = new Set(sourceFiles);
  const pipeline = await getPipeline();
  const previous = await readManifest();
  const previousFiles = isCurrentManifest(previous, pipeline) ? previous.files : {};

  const results = await mapConcurrent(encodedFiles, concurrency, async (path) => {
    const encodedBuffer = await readFile(join(encodedRoot, path));
    if (!hasUtf8Bom(encodedBuffer)) throw new Error(`missing UTF-8 BOM: ${path}`);

    const encodedSha256 = hash(encodedBuffer);
    const outputPath = join(sourceRoot, path);
    const sourceBuffer = sourceSet.has(path) ? await readFile(outputPath) : null;
    const sourceSha256 = sourceBuffer ? hash(sourceBuffer) : null;
    const previousEntry = previousFiles[path];

    if (previousEntry) {
      const sourceChanged = previousEntry.sourceSha256 !== sourceSha256;
      const encodedChanged = previousEntry.encodedSha256 !== encodedSha256;
      if (sourceChanged && encodedChanged) throw new Error(`localisation conflict: ${path}`);
      if (sourceChanged) throw new Error(`readable source is newer; run the build command: ${path}`);
      if (!encodedChanged) return { path, entry: previousEntry, decoded: false };
    }

    const decodedBuffer = await codecPool.run('decode', encodedBuffer);
    await writeFile(outputPath, decodedBuffer);
    return {
      path,
      decoded: true,
      entry: {
        sourceSha256: hash(decodedBuffer),
        encodedSha256,
      },
    };
  });

  await writeManifest(
    pipeline,
    Object.fromEntries(results.map(({ path, entry }) => [path, entry])),
  );
  const decoded = results.filter((result) => result.decoded).length;
  process.stdout.write(
    `Localisation source sync complete: ${decoded} decoded, ${encodedFiles.length - decoded} reused, ${concurrency} workers.\n`,
  );
}

function parseArguments(arguments_) {
  const command = arguments_[0] ?? 'build';
  if (!['build', 'source'].includes(command)) {
    throw new TypeError(`unknown command: ${command} (use node tools/validate.mjs for checking)`);
  }

  const jobsIndex = arguments_.indexOf('--jobs');
  const defaultJobs = Math.min(Math.max(availableParallelism() - 1, 1), 8);
  const concurrency = jobsIndex === -1 ? defaultJobs : Number(arguments_[jobsIndex + 1]);
  if (!Number.isInteger(concurrency) || concurrency < 1) {
    throw new TypeError('--jobs requires a positive integer');
  }

  return { command, concurrency };
}

const { command, concurrency } = parseArguments(process.argv.slice(2));
const codecPool = new CodecPool(concurrency);

try {
  if (command === 'build') await build(concurrency, codecPool);
  else await source(concurrency, codecPool);
} catch (error) {
  process.stderr.write(`${error.message}\n`);
  process.exitCode = 1;
} finally {
  await codecPool.close();
}