'use strict'

// Sender-side hashing: walk sync units into a manifest of dirs, links, files.
// Factory over the path guards and hash store, one per launcher state.

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

function createManifestBuilder({ filesPath, filesRoot, hash, mapLimit, concurrency }) {
  // Targets inside the launcher data travel relative (the mirrored layout is
  // the same on both machines); outside targets stay as they are.
  function portableLinkTarget(linkAbs, target) {
    if (typeof target !== 'string' || !target || !path.isAbsolute(target)) return target
    const rel = path.relative(path.dirname(linkAbs), target)
    if (!rel || path.isAbsolute(rel)) return target
    const root = path.resolve(filesRoot)
    const resolved = path.resolve(path.dirname(linkAbs), rel)
    if (resolved !== root && !resolved.startsWith(root + path.sep)) return target
    return rel
  }

  // Walk without following symlinks (dosdevices etc. are part of the sync).
  // Iterative, with one directory's stat/readlink calls in flight together.
  // `emit` (optional) streams dirs and links out while the walk continues;
  // file entries only land in `out` (their digest comes later).
  async function scanTree(abs, rel, out, mtimes, emit) {
    const queue = [[abs, rel]]
    while (queue.length) {
      const [dirAbs, dirRel] = queue.pop()
      let entries
      try {
        entries = await fsp.readdir(dirAbs, { withFileTypes: true })
      } catch {
        continue
      }
      const dirs = []
      const leaves = []
      for (const entry of entries) {
        const relChild = `${dirRel}/${entry.name}`
        if (entry.isDirectory()) {
          const record = { path: relChild, type: 'dir' }
          out.push(record)
          if (emit) await emit(record)
          dirs.push([path.join(dirAbs, entry.name), relChild])
        } else {
          leaves.push(entry)
        }
      }
      await mapLimit(leaves, concurrency, async entry => {
        const absChild = path.join(dirAbs, entry.name)
        const relChild = `${dirRel}/${entry.name}`
        if (entry.isSymbolicLink()) {
          let target = ''
          try {
            target = await fsp.readlink(absChild)
          } catch {}
          const record = { path: relChild, type: 'link', target: portableLinkTarget(absChild, target) }
          out.push(record)
          if (emit) await emit(record)
          return
        }
        let st
        try {
          st = await fsp.stat(absChild)
        } catch {
          return
        }
        if (!st.isFile()) return
        // mode travels with the file
        out.push({ path: relChild, type: 'file', size: st.size, mode: st.mode & 0o777, hash: null })
        // mtimes are machine-local: kept out of the manifest
        if (mtimes) mtimes.set(relChild, st.mtimeMs || 0)
      })
      queue.push(...dirs)
    }
  }

  // Manifest of one unit, streamed: `handlers` may carry onEntry (a Promise
  // per entry, awaited - backpressure), onTotal and onProgress. File entries
  // go out as their digests finish, so the receiver compares while this side
  // is still hashing; hashing itself stays parallel, a batch at a time.
  async function buildManifestStream(roots, force, handlers) {
    const onEntry = handlers && handlers.onEntry
    const onTotal = handlers && handlers.onTotal
    const onProgress = handlers && handlers.onProgress
    const entries = []
    const mtimes = new Map()
    for (const rel of roots) {
      const abs = filesPath(rel)
      if (!abs) continue
      let st
      try {
        st = await fsp.lstat(abs)
      } catch {
        continue
      }
      if (st.isSymbolicLink()) {
        let target = ''
        try {
          target = await fsp.readlink(abs)
        } catch {}
        const record = { path: rel, type: 'link', target: portableLinkTarget(abs, target) }
        entries.push(record)
        if (onEntry) await onEntry(record)
      } else if (st.isDirectory()) {
        const record = { path: rel, type: 'dir' }
        entries.push(record)
        if (onEntry) await onEntry(record)
        await scanTree(abs, rel, entries, mtimes, onEntry)
      } else if (st.isFile()) {
        entries.push({ path: rel, type: 'file', size: st.size, mode: st.mode & 0o777, hash: null })
        mtimes.set(rel, st.mtimeMs || 0)
      }
    }
    const files = entries.filter(e => e.type === 'file')
    // total size is known before hashing: the receiver sizes its compare bar
    // from this, the sender's popup from onProgress
    const totalBytes = files.reduce((sum, entry) => sum + (entry.size || 0), 0)
    if (onTotal) await onTotal(totalBytes)
    let done = 0
    let hashed = 0
    // one batch hashes with the whole disk queue behind it; its entries go
    // on the wire in order before the next batch starts
    for (let i = 0; i < files.length; i += concurrency) {
      const batch = files.slice(i, i + concurrency)
      if (!force) {
        await Promise.all(batch.map(async entry => {
          const abs = filesPath(entry.path)
          try {
            // unchanged size + mtime: the cached digest still holds
            const mtimeMs = mtimes.get(entry.path) || 0
            entry.hash = abs
              ? await hash.cachedHash(entry.path, abs, entry.size, mtimeMs, bytes => {
                hashed += bytes
                if (onProgress) onProgress(done, files.length, hashed, totalBytes)
              })
              : null
          } catch {
            entry.hash = null
          }
        }))
      }
      for (const entry of batch) {
        done++
        if (!entry.hash) hashed += entry.size || 0 // nothing read: still report the file as passed over
        if (onProgress) onProgress(done, files.length, hashed, totalBytes)
        if (onEntry) await onEntry(entry)
      }
    }
    hash.save()
    return entries
  }

  // Buffering variant for callers that want the whole manifest first.
  async function buildManifest(roots, force, onProgress) {
    const entries = []
    await buildManifestStream(roots, force, {
      onProgress,
      onEntry: entry => { entries.push(entry) }
    })
    return entries
  }

  return { buildManifest, buildManifestStream, scanTree, portableLinkTarget }
}

module.exports = { createManifestBuilder }