package main

import (
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"flag"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
)

func main() {
	fromFile := flag.String("from-file", "", "Load results file from <path>")
	toFile := flag.String("to-file", "", "Save results to <path>")
	flag.Parse()

	var filesMap filesMap
	if *fromFile != "" {

		byteValue, _ := ioutil.ReadFile(*fromFile)

		// we unmarshal our byteArray which contains our
		// jsonFile's content into 'users' which we defined above
		json.Unmarshal(byteValue, &filesMap)
	} else {
		filesMap = newFilesMap()

		for _, path := range os.Args[1:] {
			filepath.Walk(path, func(path string, info os.FileInfo, err error) error {
				filesMap.Add(path, info)
				return nil
			})
		}
	}

	if *toFile != "" && *fromFile == "" {
		json, _ := json.MarshalIndent(filesMap.FilesBySize, "", "  ")
		ioutil.WriteFile(*toFile, json, 644)
	}
}

type filesMap struct {
	FilesBySize map[int64]map[string][]*fileEntry
}

func (fm *filesMap) Add(path string, info os.FileInfo) error {
	if info.IsDir() {
		return nil
	}

	fileInfo := &fileEntry{
		Path: path,
		Size: info.Size(),
	}

	filesByHash := fm.FilesBySize[fileInfo.Size]

	// first file with same size
	// => create new map for size
	if filesByHash == nil {
		filesByHash = map[string][]*fileEntry{}
		fm.FilesBySize[fileInfo.Size] = filesByHash
		filesByHash[""] = []*fileEntry{fileInfo}
		return nil
	}

	// second file with same size
	// => calculate hashes for all entries
	if _, hasEmptyHash := filesByHash[""]; hasEmptyHash {
		err := appendByFileHash(filesByHash, fileInfo)
		err2 := appendByFileHash(filesByHash, filesByHash[""][0])

		delete(filesByHash, "")

		if err != nil {
			return err
		}

		return err2
	}

	// for later files always append by hash
	return appendByFileHash(filesByHash, fileInfo)
}

func appendByFileHash(filesByHash map[string][]*fileEntry, fileInfo *fileEntry) error {
	hash, err := calculateHash(fileInfo.Path)

	if err != nil {
		return err
	}

	if _, ok := filesByHash[hash]; ok {
		filesByHash[hash] = append(filesByHash[hash], fileInfo)
	} else {
		filesByHash[hash] = []*fileEntry{fileInfo}
	}
	return nil
}

func newFilesMap() filesMap {
	return filesMap{
		FilesBySize: map[int64]map[string][]*fileEntry{},
	}
}

type fileEntry struct {
	Path string
	Size int64
}

func calculateHash(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}

	return base64.RawStdEncoding.EncodeToString(h.Sum(nil)), nil
}