//
//  pool-import
//
//  Copyright (C) 2016 Christian Pointner <equinox@helsinki.at>
//
//  This file is part of pool-import.
//
//  pool-import is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  any later version.
//
//  pool-import is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with pool-import. If not, see <http://www.gnu.org/licenses/>.
//

package main

import (
	"encoding/base64"
	"io"
	"log"
	"os"
	"path/filepath"
	"strings"
	"sync"

	"golang.org/x/crypto/blake2b"
)

type FileMap map[string]string

func (m FileMap) Merge(m2 FileMap) {
	for key, value := range m2 {
		m[key] = value
	}
}

type MusicDir struct {
	root     string
	stdlog   *log.Logger
	filesMtx sync.Mutex
	Files    FileMap
}

func handleEntry(C chan<- string, path string, info os.FileInfo, err error, stdlog *log.Logger) error {
	if err != nil {
		return err
	}
	if info.IsDir() {
		stdlog.Printf("entering directory: %s", path)
		return nil
	}
	if !info.Mode().IsRegular() {
		stdlog.Printf(" - skipping (special file):  %s", info.Name())
		return nil
	}
	switch strings.ToLower(filepath.Ext(path)) {
	case ".flac":
		fallthrough
	case ".ogg":
		fallthrough
	case ".wav":
		fallthrough
	case ".mp3":
		fallthrough
	case ".aac":
		fallthrough
	case ".mp4":
		fallthrough
	case ".m4a":
		C <- path
	default:
		stdlog.Printf(" - skipping (unknown extension):  %s", info.Name())
	}
	return nil
}

func computeHash(path string) (string, error) {
	hash, err := blake2b.New256(nil)
	if err != nil {
		return "", err
	}
	file, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer file.Close()
	if _, err := io.Copy(hash, file); err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(hash.Sum(nil)), nil
}

func (d *MusicDir) collectHashes(C <-chan string, numThreads int) (wg *sync.WaitGroup) {
	wg = &sync.WaitGroup{}

	for i := 0; i < numThreads; i++ {
		wg.Add(1)
		go func(num int) {
			defer wg.Done()
			for {
				file, ok := <-C
				if !ok {
					return
				}
				if hash, err := computeHash(file); err != nil {
					d.stdlog.Printf(" - skipping (%v):  %s", err, filepath.Base(file))
				} else {
					d.stdlog.Printf(" - hashed:  %s", filepath.Base(file))
					d.filesMtx.Lock()
					d.Files[hash] = file
					d.filesMtx.Unlock()
				}
			}
		}(i)
	}
	return
}

func (d *MusicDir) ComputeHashes() (err error) {
	C := make(chan string, 10)

	wg := d.collectHashes(C, 4) // TODO: make number of hashing threads configurable

	err = filepath.Walk(d.root, func(path string, info os.FileInfo, err error) error {
		return handleEntry(C, path, info, err, d.stdlog)
	})
	close(C)

	if err != nil {
		return
	}

	wg.Wait()
	return
}

func NewMusicDir(root string, stdlog *log.Logger) (dir *MusicDir) {
	dir = &MusicDir{root: root, stdlog: stdlog}
	dir.Files = make(map[string]string)
	return
}