'use strict'

const fs = require('fs')
const fsp = require('fs').promises
const path = require('path')

// accessSync instead of existsSync: same answer, one syscall fewer.
function pathExists(p) {
  try {
    fs.accessSync(p)
    return true
  } catch {
    return false
  }
}

// Returns a non-existing path in `base` named `name` (or `name (2)`, `name (3)`...).
function dedupeDir(base, name) {
  const candidate = path.join(base, name)
  if (!fs.existsSync(candidate)) return candidate
  let n = 2
  while (fs.existsSync(path.join(base, `${name} (${n})`))) n++
  return path.join(base, `${name} (${n})`)
}

// Events are rate limited to ~10/s; `force` pushes the final value through.
const PROGRESS_MIN_MS = 100

function progressGate(emit) {
  let last = 0
  let pending = null
  let timer = null
  const flush = () => {
    timer = null
    if (!pending) return
    last = Date.now()
    const data = pending
    pending = null
    emit(data)
  }
  const push = (data, force) => {
    pending = data
    const wait = PROGRESS_MIN_MS - (Date.now() - last)
    if (force || wait <= 0) {
      if (timer) clearTimeout(timer)
      flush()
    } else if (!timer) {
      timer = setTimeout(flush, wait)
      if (timer.unref) timer.unref()
    }
  }
  push.done = () => {
    if (timer) clearTimeout(timer)
    flush()
  }
  return push
}

// Run `fn` over `items` with at most `limit` in flight, results in order.
async function mapLimit(items, limit, fn) {
  const out = new Array(items.length)
  let next = 0
  const workers = Array.from({ length: Math.min(limit, items.length) }, async () => {
    while (next < items.length) {
      const i = next++
      out[i] = await fn(items[i], i)
    }
  })
  await Promise.all(workers)
  return out
}

// What a tree copy will move. Symlinks are recreated, not read. `skipDir`
// leaves out one directory name (redistributables).
async function treeSize(root) {
  let files = 0
  let bytes = 0
  // a symlinked root is the whole tree; never measure through it
  let rootStat = null
  try {
    rootStat = await fsp.lstat(root)
  } catch {
    return { files, bytes }
  }
  if (!rootStat.isDirectory()) return { files: 1, bytes: rootStat.isSymbolicLink() ? 0 : rootStat.size }
  const walk = async dir => {
    let entries
    try {
      entries = await fsp.readdir(dir, { withFileTypes: true })
    } catch {
      return
    }
    for (const entry of entries) {
      const full = path.join(dir, entry.name)
      if (entry.isSymbolicLink()) {
        files++
      } else if (entry.isDirectory()) {
        await walk(full)
      } else if (entry.isFile()) {
        files++
        try {
          bytes += (await fsp.stat(full)).size
        } catch {}
      }
    }
  }
  await walk(root)
  return { files, bytes }
}

// Copy a tree with symlinks recreated and permissions carried (copyFile
// drops both); reports cumulative { done, bytes } through onProgress.
async function copyTree(src, dst, onProgress) {
  let done = 0
  let bytes = 0
  const gate = onProgress ? progressGate(onProgress) : null
  const tick = () => {
    if (gate) gate({ done, bytes }, false)
  }
  const walk = async (from, to) => {
    let entries
    try {
      entries = await fsp.readdir(from, { withFileTypes: true })
    } catch {
      return
    }
    await fsp.mkdir(to, { recursive: true })
    for (const entry of entries) {
      const s = path.join(from, entry.name)
      const d = path.join(to, entry.name)
      if (entry.isSymbolicLink()) {
        let target = null
        try {
          target = await fsp.readlink(s)
        } catch {}
        if (!target) continue
        try {
          await fsp.symlink(target, d)
        } catch {}
        done++
        tick()
      } else if (entry.isDirectory()) {
        await walk(s, d)
      } else if (entry.isFile()) {
        let size = 0
        try {
          size = (await fsp.stat(s)).size
        } catch {}
        try {
          await fsp.copyFile(s, d)
          await fsp.chmod(d, (await fsp.stat(s)).mode & 0o777)
        } catch {}
        done++
        bytes += size
        tick()
      }
    }
  }
  await walk(src, dst)
  if (gate) gate({ done, bytes }, true)
  return { done, bytes }
}

// Imported trees come from media that lose permissions (archives, FAT, a
// read-only backup drive), and copyFile keeps whatever the source had: every
// node gets owner rwx and `x` mirrored from `r`, so the app can run its own
// binaries and write its own files.
async function chmodTree(root) {
  const desired = mode => mode | 0o700 | ((mode & 0o444) >> 2)
  let files = 0
  let dirs = 0
  const walk = async dir => {
    let entries
    try {
      entries = await fsp.readdir(dir, { withFileTypes: true })
    } catch {
      return
    }
    for (const entry of entries) {
      const full = path.join(dir, entry.name)
      if (entry.isSymbolicLink()) continue
      if (entry.isDirectory()) {
        await walk(full)
      } else if (!entry.isFile()) {
        continue
      }
      try {
        const before = (await fsp.stat(full)).mode & 0o7777
        const after = desired(before)
        if (after !== before) {
          await fsp.chmod(full, after)
          if (entry.isDirectory()) dirs++
          else files++
        }
      } catch {}
    }
  }
  await walk(root)
  return { files, dirs }
}

// One file, streamed, with byte progress: copyFile says nothing until a
// multi-gigabyte copy is over. The bytes land on a .part name and are renamed
// at the end, so nothing can ever read a half-written document.
async function copyFileProgress(src, dst, onProgress) {
  const stat = await fsp.stat(src)
  if (!stat.isFile()) throw new Error('not a file: ' + src)
  const gate = onProgress ? progressGate(onProgress) : null
  await fsp.mkdir(path.dirname(dst), { recursive: true })
  const part = dst + '.part'
  let bytes = 0
  try {
    await new Promise((resolve, reject) => {
      const input = fs.createReadStream(src)
      const output = fs.createWriteStream(part)
      const fail = err => {
        input.destroy()
        output.destroy()
        reject(err)
      }
      input.on('error', fail)
      output.on('error', fail)
      input.on('data', chunk => {
        bytes += chunk.length
        if (gate) gate({ done: 0, bytes }, false)
      })
      output.on('finish', resolve)
      input.pipe(output)
    })
    await fsp.chmod(part, stat.mode & 0o777)
    await fsp.rename(part, dst)
  } catch (err) {
    try {
      await fsp.rm(part, { force: true })
    } catch {}
    throw err
  }
  if (gate) {
    gate({ done: 1, bytes: stat.size }, true)
    gate.done()
  }
  return { files: 1, bytes: stat.size }
}

// Delete deepest-first with progress through onProgress; symlinks are
// unlinked, never followed.
async function removeTree(root, onProgress) {
  let files = 0
  let dirs = 0
  let bytes = 0
  const gate = onProgress ? progressGate(onProgress) : null
  const tick = () => {
    if (gate) gate({ files, dirs, bytes }, false)
  }
  // a symlinked root is removed as itself, never walked through
  let rootStat = null
  try {
    rootStat = await fsp.lstat(root)
  } catch {
    return { files, dirs, bytes }
  }
  if (!rootStat.isDirectory()) {
    files = 1
    bytes = rootStat.isSymbolicLink() ? 0 : rootStat.size
    try {
      await fsp.unlink(root)
    } catch {}
    if (gate) gate({ files, dirs, bytes }, true)
    return { files, dirs, bytes }
  }
  const walk = async dir => {
    let entries
    try {
      entries = await fsp.readdir(dir, { withFileTypes: true })
    } catch {
      return false
    }
    for (const entry of entries) {
      const full = path.join(dir, entry.name)
      if (entry.isDirectory()) {
        await walk(full)
        try {
          await fsp.rmdir(full)
        } catch {}
        dirs++
        tick()
        continue
      }
      let size = 0
      try {
        const st = await fsp.lstat(full)
        size = st.isFile() ? st.size : 0
      } catch {}
      try {
        await fsp.unlink(full)
      } catch {}
      files++
      bytes += size
      tick()
    }
    try {
      await fsp.rmdir(dir)
      dirs++
    } catch {}
    return true
  }
  await walk(root)
  if (gate) gate({ files, dirs, bytes }, true)
  return { files, dirs, bytes }
}

module.exports = { pathExists, dedupeDir, copyTree, copyFileProgress, treeSize, removeTree, chmodTree, progressGate, mapLimit }