import fsSyncOriginal from 'fs'
import fsPromisesOriginal from 'fs/promises'
import crypto from 'crypto'
import path from 'path'
import os from 'os'

export default class FSCache {
  constructor(options = {}, fsSync, fsPromises) {
    this.fsSync = fsSync || fsSyncOriginal
    this.fsPromises = fsPromises || fsPromisesOriginal

    this.id = crypto.randomBytes(15).toString('base64').replace(/\//g, '-')
    this.prefix = (options.ns || options.prefix || '') + '-'
    this.hash_alg = options.hash_alg || 'md5'
    this.cache_dir = options.cache_dir || path.join(os.tmpdir(), this.id)
    this.ttl = options.ttl || 0

    // Verify hash algorithm is supported on this system
    crypto.createHash(this.hash_alg)

    this.fsSync.mkdirSync(this.cache_dir, { recursive: true })
  }

  _checkIsExpired(parsed, now) {
    return parsed.ttl != null && now > parsed.ttl
  }

  _parseCacheData(data, fallback, overwrite = {}) {
    let parsed = JSON.parse(data)
    if (this._checkIsExpired(parsed, new Date().getTime())) {
      return fallback || null
    }
    return parsed.content
  }

  _parseSetData(key, data, overwrite = {}) {
    if (!(overwrite.ttl ?? this.ttl)) {
      return JSON.stringify({ key: key, content: data })
    }
    return JSON.stringify({
      key: key,
      content: data,
      ttl: new Date().getTime() + (overwrite.ttl || this.ttl) * 1000,
    })
  }

  hash(name) {
    return path.join(this.cache_dir, this.prefix + crypto.hash(this.hash_alg, name))
  }

  get(name, fallback, opts) {
    return this.fsPromises.readFile(this.hash(name), { encoding: 'utf8' })
    .then(
      data => this._parseCacheData(data, fallback, opts),
      err => (fallback)
    )
  }

  getSync(name, fallback, opts) {
    let data;

    try {
      data = this.fsSync.readFileSync(this.hash(name), { encoding: 'utf8' })
    } catch {
      return fallback
    }
    return this._parseCacheData(data, fallback, opts)
  }

  set(name, data, orgOpts = {}) {
    let opts = typeof orgOpts === 'number' ? { ttl: orgOpts } : orgOpts

    try {
      return this.fsPromises.writeFile(
        this.hash(name),
        this._parseSetData(name, data, opts),
        { encoding: opts.encoding || 'utf8' }
      )
    } catch (err) {
      return Promise.reject(err)
    }
  }

  async setMany(items, options) {
    for (let item of items) {
      await this.set(item.key, item.content ?? item.value, options)
    }
  }

  save(items, options) {
    return this.setMany(items, options)
  }

  setSync(name, data, orgOpts = {}) {
    let opts = typeof orgOpts === 'number' ? { ttl: orgOpts } : orgOpts

    this.fsSync.writeFileSync(
      this.hash(name),
      this._parseSetData(name, data, opts),
      { encoding: opts.encoding || 'utf8' }
    )
  }

  setManySync(items, options) {
    for (let item of items) {
      this.setSync(item.key, item.content ?? item.value, options)
    }
  }

  saveSync(items, options) {
    return this.setManySync(items, options)
  }

  remove(name) {
    return this.fsPromises.rm(this.hash(name), { force: true })
  }

  removeSync(name) {
    return this.fsSync.rmSync(this.hash(name), { force: true })
  }

  async clear() {
    for (let file of await this.fsPromises.readdir(this.cache_dir)) {
      if (!file.startsWith(this.prefix)) continue
      await this.fsPromises.rm(path.join(this.cache_dir, file), { force: true })
    }
  }

  clearSync() {
    for (let file of this.fsSync.readdirSync(this.cache_dir)) {
      if (!file.startsWith(this.prefix)) continue
      this.fsSync.rmSync(path.join(this.cache_dir, file), { force: true })
    }
  }

  async getAll() {
    let out = []
    let now = new Date().getTime()
    for (let file of await this.fsPromises.readdir(this.cache_dir)) {
      if (!file.startsWith(this.prefix)) continue
      let data = await this.fsPromises.readFile(path.join(this.cache_dir, file), { encoding: 'utf8' })
      let entry = JSON.parse(data)
      if (entry.content && !this._checkIsExpired(entry, now)) {
        out.push(entry)
      }
    }
    return out
  }

  load() {
    return this.getAll().then(res => {
      return {
        files: res.map(entry => ({ path: this.hash(entry.key), value: entry.content, key: entry.key }))
      }
    })
  }
}