// Copyright (C) 2014 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.

package scanner

import (
	"errors"
	"os"
	"path/filepath"

	"github.com/syncthing/syncthing/lib/protocol"
	"github.com/syncthing/syncthing/lib/sync"
)

// The parallel hasher reads FileInfo structures from the inbox, hashes the
// file to populate the Blocks element and sends it to the outbox. A number of
// workers are used in parallel. The outbox will become closed when the inbox
// is closed and all items handled.

func newParallelHasher(dir string, blockSize, workers int, outbox, inbox chan protocol.FileInfo, counter Counter, done, cancel chan struct{}) {
	wg := sync.NewWaitGroup()
	wg.Add(workers)

	for i := 0; i < workers; i++ {
		go func() {
			hashFiles(dir, blockSize, outbox, inbox, counter, cancel)
			wg.Done()
		}()
	}

	go func() {
		wg.Wait()
		if done != nil {
			close(done)
		}
		close(outbox)
	}()
}

func HashFile(path string, blockSize int, counter Counter) ([]protocol.BlockInfo, error) {
	fd, err := os.Open(path)
	if err != nil {
		l.Debugln("open:", err)
		return nil, err
	}
	defer fd.Close()

	// Get the size and modtime of the file before we start hashing it.

	fi, err := fd.Stat()
	if err != nil {
		l.Debugln("stat before:", err)
		return nil, err
	}
	size := fi.Size()
	modTime := fi.ModTime()

	// Hash the file. This may take a while for large files.

	blocks, err := Blocks(fd, blockSize, size, counter)
	if err != nil {
		l.Debugln("blocks:", err)
		return nil, err
	}

	// Recheck the size and modtime again. If they differ, the file changed
	// while we were reading it and our hash results are invalid.

	fi, err = fd.Stat()
	if err != nil {
		l.Debugln("stat after:", err)
		return nil, err
	}
	if size != fi.Size() || !modTime.Equal(fi.ModTime()) {
		return nil, errors.New("file changed during hashing")
	}

	return blocks, nil
}

func hashFiles(dir string, blockSize int, outbox, inbox chan protocol.FileInfo, counter Counter, cancel chan struct{}) {
	for {
		select {
		case f, ok := <-inbox:
			if !ok {
				return
			}

			if f.IsDirectory() || f.IsDeleted() {
				panic("Bug. Asked to hash a directory or a deleted file.")
			}

			blocks, err := HashFile(filepath.Join(dir, f.Name), blockSize, counter)
			if err != nil {
				l.Debugln("hash error:", f.Name, err)
				continue
			}

			f.Blocks = blocks

			// The size we saw when initially deciding to hash the file
			// might not have been the size it actually had when we hashed
			// it. Update the size from the block list.

			f.Size = 0
			for _, b := range blocks {
				f.Size += int64(b.Size)
			}

			select {
			case outbox <- f:
			case <-cancel:
				return
			}

		case <-cancel:
			return
		}
	}
}