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.parse_json = options.parse_json ?? true
    this.prefix = options.prefix ? options.prefix + '-' : ''
    this.hash_alg = options.hash_alg || 'md5'
    this.cache_dir = options.cache_dir || path.join(os.tmpdir(), this.id)

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

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

  _parseCacheData(data, overwrite = {}) {
    return overwrite.parse_json ?? this.parse_json ? JSON.parse(data) : data
  }

  _parseSetData(data, overwrite = {}) {
    return overwrite.parse_json ?? this.parse_json ? JSON.stringify(data) : data
  }

  hash(name) {
    return crypto.hash(this.hash_alg, name)
  }

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

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

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

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

  setSync(name, data, opts = {}) {
    this.fsSync.writeFileSync(
      path.join(this.cache_dir, this.hash(name)),
      this._parseSetData(data, opts),
      { encoding: opts.encoding || 'utf8' }
    )
  }
}