import revHash from 'rev-hash'
import { readFileSync, statSync } from 'fs'
import { resolve } from 'path'

/**
 * Calculate the rev hash for a file
 *
 * @param {string} file The path to the file to hash
 * @returns {string}
 */
function hashFile (file) {
  return revHash(readFileSync(file))
}

/**
 * Calculate the rev hashes for a list of files
 *
 * @generator
 * @param {string[]} files The files to hash
 * @param {string}   base  A base path prepended to each file (ignored if a file path is absolute)
 * @yields {string}
 */
function* hashFileList (files, base = '/') {
  for (const file of files) {
    yield [ file, hashFile(resolve(base, file)) ]
  }
}

/**
 * Profile a list of files to compare against a later state
 *
 * @param {string[]} files The files to profile
 * @param {string}   base  A base path prepended to each file (ignored if a file path is absolute)
 * @return {object}
 */
export function profile (files, base = '/') {
  const map = {}
  for (const [ file, hash ] of hashFileList(files, base)) {
    map[file] = [
      statSync(resolve(base, file)).size,
      hash
    ]
  }
  return map
}

/**
 * 
 * @param {string[]} files  The files to profile
 * @param {hashes}   object A the file list characteristics generated earlier by profile()
 * @param {string}   base   A base path prepended to each file (ignored if a file path is absolute)
 * @return {object}
 */
export function diff (files, hashes, base = '/') {
  // Detect new files
  for (const file of files) {
    if (!(file in hashes)) {
      return { type: 'added', file }
    }
  }

  // Detect missing files
  for (const file in hashes) {
    if (!files.includes(file)) {
      return { type: 'removed', file }
    }
  }

  // Check sizes
  for (const file of files) {
    if (statSync(resolve(base, file)).size !== hashes[file][0]) {
      return { type: 'changed', file }
    }
  }

  // Check contents
  for (const [ file, hash ] of hashFileList(files, base)) {
    if (hash !== hashes[file][1]) {
      return { type: 'changed', file }
    }
  }

  return null
}