'use strict'

const crypto = require('crypto')
const {
  appendFile,
  mkdir,
  readFile,
  readdir,
  rm,
  writeFile,
} = require('fs/promises')
const Minipass = require('minipass')
const path = require('path')
const ssri = require('ssri')
const uniqueFilename = require('unique-filename')

const contentPath = require('./content/path')
const hashToSegments = require('./util/hash-to-segments')
const indexV = require('../package.json')['cache-version'].index
const moveFile = require('@npmcli/move-file')

module.exports.NotFoundError = class NotFoundError extends Error {
  constructor (cache, key) {
    super(`No cache entry for ${key} found in ${cache}`)
    this.code = 'ENOENT'
    this.cache = cache
    this.key = key
  }
}

module.exports.compact = compact

async function compact (cache, key, matchFn, opts = {}) {
  const bucket = bucketPath(cache, key)
  const entries = await bucketEntries(bucket)
  const newEntries = []
  // we loop backwards because the bottom-most result is the newest
  // since we add new entries with appendFile
  for (let i = entries.length - 1; i >= 0; --i) {
    const entry = entries[i]
    // a null integrity could mean either a delete was appended
    // or the user has simply stored an index that does not map
    // to any content. we determine if the user wants to keep the
    // null integrity based on the validateEntry function passed in options.
    // if the integrity is null and no validateEntry is provided, we break
    // as we consider the null integrity to be a deletion of everything
    // that came before it.
    if (entry.integrity === null && !opts.validateEntry) {
      break
    }

    // if this entry is valid, and it is either the first entry or
    // the newEntries array doesn't already include an entry that
    // matches this one based on the provided matchFn, then we add
    // it to the beginning of our list
    if ((!opts.validateEntry || opts.validateEntry(entry) === true) &&
      (newEntries.length === 0 ||
        !newEntries.find((oldEntry) => matchFn(oldEntry, entry)))) {
      newEntries.unshift(entry)
    }
  }

  const newIndex = '\n' + newEntries.map((entry) => {
    const stringified = JSON.stringify(entry)
    const hash = hashEntry(stringified)
    return `${hash}\t${stringified}`
  }).join('\n')

  const setup = async () => {
    const target = uniqueFilename(path.join(cache, 'tmp'), opts.tmpPrefix)
    await mkdir(path.dirname(target), { recursive: true })
    return {
      target,
      moved: false,
    }
  }

  const teardown = async (tmp) => {
    if (!tmp.moved) {
      return rm(tmp.target, { recursive: true, force: true })
    }
  }

  const write = async (tmp) => {
    await writeFile(tmp.target, newIndex, { flag: 'wx' })
    await mkdir(path.dirname(bucket), { recursive: true })
    // we use @npmcli/move-file directly here because we
    // want to overwrite the existing file
    await moveFile(tmp.target, bucket)
    tmp.moved = true
  }

  // write the file atomically
  const tmp = await setup()
  try {
    await write(tmp)
  } finally {
    await teardown(tmp)
  }

  // we reverse the list we generated such that the newest
  // entries come first in order to make looping through them easier
  // the true passed to formatEntry tells it to keep null
  // integrity values, if they made it this far it's because
  // validateEntry returned true, and as such we should return it
  return newEntries.reverse().map((entry) => formatEntry(cache, entry, true))
}

module.exports.insert = insert

async function insert (cache, key, integrity, opts = {}) {
  const { metadata, size } = opts
  const bucket = bucketPath(cache, key)
  const entry = {
    key,
    integrity: integrity && ssri.stringify(integrity),
    time: Date.now(),
    size,
    metadata,
  }
  try {
    await mkdir(path.dirname(bucket), { recursive: true })
    const stringified = JSON.stringify(entry)
    // NOTE - Cleverness ahoy!
    //
    // This works because it's tremendously unlikely for an entry to corrupt
    // another while still preserving the string length of the JSON in
    // question. So, we just slap the length in there and verify it on read.
    //
    // Thanks to @isaacs for the whiteboarding session that ended up with
    // this.
    await appendFile(bucket, `\n${hashEntry(stringified)}\t${stringified}`)
  } catch (err) {
    if (err.code === 'ENOENT') {
      return undefined
    }

    throw err
  }
  return formatEntry(cache, entry)
}

module.exports.find = find

async function find (cache, key) {
  const bucket = bucketPath(cache, key)
  try {
    const entries = await bucketEntries(bucket)
    return entries.reduce((latest, next) => {
      if (next && next.key === key) {
        return formatEntry(cache, next)
      } else {
        return latest
      }
    }, null)
  } catch (err) {
    if (err.code === 'ENOENT') {
      return null
    } else {
      throw err
    }
  }
}

module.exports.delete = del

function del (cache, key, opts = {}) {
  if (!opts.removeFully) {
    return insert(cache, key, null, opts)
  }

  const bucket = bucketPath(cache, key)
  return rm(bucket, { recursive: true, force: true })
}

module.exports.lsStream = lsStream

function lsStream (cache) {
  const indexDir = bucketDir(cache)
  const stream = new Minipass({ objectMode: true })

  // Set all this up to run on the stream and then just return the stream
  Promise.resolve().then(async () => {
    const buckets = await readdirOrEmpty(indexDir)
    await Promise.all(buckets.map(async (bucket) => {
      const bucketPath = path.join(indexDir, bucket)
      const subbuckets = await readdirOrEmpty(bucketPath)
      await Promise.all(subbuckets.map(async (subbucket) => {
        const subbucketPath = path.join(bucketPath, subbucket)

        // "/cachename/<bucket 0xFF>/<bucket 0xFF>./*"
        const subbucketEntries = await readdirOrEmpty(subbucketPath)
        await Promise.all(subbucketEntries.map(async (entry) => {
          const entryPath = path.join(subbucketPath, entry)
          try {
            const entries = await bucketEntries(entryPath)
            // using a Map here prevents duplicate keys from showing up
            // twice, I guess?
            const reduced = entries.reduce((acc, entry) => {
              acc.set(entry.key, entry)
              return acc
            }, new Map())
            // reduced is a map of key => entry
            for (const entry of reduced.values()) {
              const formatted = formatEntry(cache, entry)
              if (formatted) {
                stream.write(formatted)
              }
            }
          } catch (err) {
            if (err.code === 'ENOENT') {
              return undefined
            }
            throw err
          }
        }))
      }))
    }))
    stream.end()
    return stream
  }).catch(err => stream.emit('error', err))

  return stream
}

module.exports.ls = ls

async function ls (cache) {
  const entries = await lsStream(cache).collect()
  return entries.reduce((acc, xs) => {
    acc[xs.key] = xs
    return acc
  }, {})
}

module.exports.bucketEntries = bucketEntries

async function bucketEntries (bucket, filter) {
  const data = await readFile(bucket, 'utf8')
  return _bucketEntries(data, filter)
}

function _bucketEntries (data, filter) {
  const entries = []
  data.split('\n').forEach((entry) => {
    if (!entry) {
      return
    }

    const pieces = entry.split('\t')
    if (!pieces[1] || hashEntry(pieces[1]) !== pieces[0]) {
      // Hash is no good! Corruption or malice? Doesn't matter!
      // EJECT EJECT
      return
    }
    let obj
    try {
      obj = JSON.parse(pieces[1])
    } catch (_) {
      // eslint-ignore-next-line no-empty-block
    }
    // coverage disabled here, no need to test with an entry that parses to something falsey
    // istanbul ignore else
    if (obj) {
      entries.push(obj)
    }
  })
  return entries
}

module.exports.bucketDir = bucketDir

function bucketDir (cache) {
  return path.join(cache, `index-v${indexV}`)
}

module.exports.bucketPath = bucketPath

function bucketPath (cache, key) {
  const hashed = hashKey(key)
  return path.join.apply(
    path,
    [bucketDir(cache)].concat(hashToSegments(hashed))
  )
}

module.exports.hashKey = hashKey

function hashKey (key) {
  return hash(key, 'sha256')
}

module.exports.hashEntry = hashEntry

function hashEntry (str) {
  return hash(str, 'sha1')
}

function hash (str, digest) {
  return crypto
    .createHash(digest)
    .update(str)
    .digest('hex')
}

function formatEntry (cache, entry, keepAll) {
  // Treat null digests as deletions. They'll shadow any previous entries.
  if (!entry.integrity && !keepAll) {
    return null
  }

  return {
    key: entry.key,
    integrity: entry.integrity,
    path: entry.integrity ? contentPath(cache, entry.integrity) : undefined,
    size: entry.size,
    time: entry.time,
    metadata: entry.metadata,
  }
}

function readdirOrEmpty (dir) {
  return readdir(dir).catch((err) => {
    if (err.code === 'ENOENT' || err.code === 'ENOTDIR') {
      return []
    }

    throw err
  })
}
