package main

import (
	"bufio"
	"crypto/md5"
	"errors"
	"fmt"
	"hash"
	"io"
	"os"
	"strings"

	"github.com/alexflint/go-arg"
	common "source.heropunch.io/tomo/go-coreutils"
)

var ImproperlyFormattedErr = errors.New("improperly formatted line")

func printSumForFile(filename string, sumFunc func(io.Reader) (hash.Hash, error)) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	h, err := sumFunc(file)
	if err != nil {
		return err
	}

	printHash(h, filename)
	return nil
}

func printSumForStdin(sumFunc func(io.Reader) (hash.Hash, error)) {
	h, err := sumFunc(os.Stdin)
	if err != nil {
		common.PrintToStderr(err)
		os.Exit(1)
	}
	printHash(h, "<stdin>")
	os.Exit(0)
}

func md5sum(r io.Reader) (hash.Hash, error) {
	h := md5.New()
	if _, err := io.Copy(h, r); err != nil {
		return nil, err
	}
	return h, nil
}

func printHash(h hash.Hash, filename string) {
	fmt.Printf("%x  %v\n", h.Sum(nil), filename)
}

func checkSumForFile(filename string) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	return checkSums(file)
}

func checkSums(r io.Reader) error {
	scanner := bufio.NewScanner(r)

	for scanner.Scan() {
		err := checkMD5Sum(scanner.Text())
		if err != nil {
			return err
		}
	}
	return scanner.Err()
}

func checkMD5Sum(line string) error {
	s := strings.SplitN(line, "  ", 2)
	hash := s[0]
	filename := s[1]

	if filename == "" {
		return ImproperlyFormattedErr
	}

	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	h, err := md5sum(file)
	if err != nil {
		return err
	}
	result := "OK"
	if fmt.Sprintf("%x", h.Sum(nil)) != hash {
		result = "FAILED"
	}
	fmt.Printf("%s: %s\n", filename, result)

	return nil
}

func main() {
	var args struct {
		Check bool     `arg:"-c"`
		Files []string `arg:"positional"`
	}

	arg.MustParse(&args)

	exitCode := 0
	if len(args.Files) == 0 {
		if !args.Check {
			printSumForStdin(md5sum)
		} else {
			fmt.Println("Checking from stdin")
		}
	}

	for _, filename := range args.Files {
		if !args.Check {
			err := printSumForFile(filename, md5sum)
			if err != nil {
				common.PrintToStderr(err)
				exitCode = 1
			}
		} else {
			err := checkSumForFile(filename)
			if err != nil {
				common.PrintToStderr(err)
				exitCode = 1
			}
		}
	}

	os.Exit(exitCode)
}