import cacache from 'cacache';
import { Readable } from 'stream';
import { KeyTimeout } from './key_timeout.js';

function getBodyAndMetaKeys(key) {
  return [`${key}body`, `${key}meta`];
}

export class FileSystemCache {
  constructor(options = {}) {
    this.ttl = options.ttl;
    this.keyTimeout = new KeyTimeout();
    this.cacheDirectory = options.cacheDirectory || '.cache';
  }

  async get(key) {
    const [, metaKey] = getBodyAndMetaKeys(key);

    const metaInfo = await cacache.get.info(this.cacheDirectory, metaKey);

    if (!metaInfo) {
      return undefined;
    }

    const metaBuffer = await cacache.get.byDigest(this.cacheDirectory, metaInfo.integrity);
    const metaData = JSON.parse(metaBuffer);
    const { bodyStreamIntegrity, bodyStreamLength } = metaData;
    delete metaData.bodyStreamIntegrity;
    delete metaData.bodyStreamLength;

    const bodyStream = bodyStreamLength > 0
      ? cacache.get.stream.byDigest(this.cacheDirectory, bodyStreamIntegrity)
      : Readable.from(Buffer.alloc(0));

    return {
      bodyStream,
      metaData,
    };
  }

  remove(key) {
    const [bodyKey, metaKey] = getBodyAndMetaKeys(key);

    this.keyTimeout.clearTimeout(key);

    return Promise.all([
      cacache.rm.entry(this.cacheDirectory, bodyKey),
      cacache.rm.entry(this.cacheDirectory, metaKey),
    ]);
  }

  async set(key, bodyStream, metaData, bodyStreamLength) {
    const [bodyKey, metaKey] = getBodyAndMetaKeys(key);
    const metaCopy = { ...metaData, bodyStreamLength };

    this.keyTimeout.clearTimeout(key);

    if (bodyStreamLength > 0) {
      metaCopy.bodyStreamIntegrity = await new Promise((fulfill, reject) => {
        bodyStream.pipe(cacache.put.stream(this.cacheDirectory, bodyKey))
          .on('integrity', (i) => fulfill(i))
          .on('error', (e) => {
            reject(e);
          });
      });
    }

    const metaBuffer = Buffer.from(JSON.stringify(metaCopy));
    await cacache.put(this.cacheDirectory, metaKey, metaBuffer);

    if (typeof this.ttl === 'number') {
      this.keyTimeout.updateTimeout(key, this.ttl, () => this.remove(key));
    }
  }
}