daizong.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

func main() {
	inFileName, outFileName, err := filenamesFromCmd()

	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

	if inFileName == "" || outFileName == "" {
		fmt.Println("inFileName or outFileName is null")
		os.Exit(1)
	}

	inFile, outFile := os.Stdin, os.Stdout

	if inFile, err = os.Open(inFileName); err != nil {
		log.Fatal(err)
	}
	defer inFile.Close()

	if outFile, err = os.OpenFile(outFileName, os.O_WRONLY, 0644); err != nil {
		log.Fatal(err)
	}
	defer outFile.Close()

	if err = americanise(inFile, outFile); err != nil {
		log.Fatal(err)
	}
}

func filenamesFromCmd() (inFilename, outFileName string, err error) {
	inFilename = ""
	outFileName = ""
	argsLen := len(os.Args)

	if argsLen > 1 && (os.Args[1] == "-h" || os.Args[1] == "--help") {
		err = fmt.Errorf("usage: %s [<]infile.txt [>]outfile.txt",
			filepath.Base(os.Args[0]))
		return "", "", err
	}

	if argsLen > 1 {
		inFilename = os.Args[1]
	}
	if argsLen > 2 {
		outFileName = os.Args[2]
	} else {
		outFileName = inFilename
	}
	return inFilename, outFileName, nil
}

func americanise(inFile io.Reader, outFile io.Writer) (err error) {
	reader := bufio.NewReader(inFile)
	writer := bufio.NewWriter(outFile)


	var replacer func(string) string
	if replacer, err = makeReplacer("british-american.txt"); err != nil {
		return err
	}

	wordRegexp := regexp.MustCompile("[A-Za-z]+")
	eof := false

	for !eof {
		var line string
		line, err = reader.ReadString('\n')
		if err == io.EOF {
			err = nil
			eof = true
		} else if err != nil {
			return err
		}

		line = wordRegexp.ReplaceAllStringFunc(line, replacer)
		fmt.Println(line)
		if _, err = writer.WriteString(line); err != nil {
			return err
		}
	}

    err = writer.Flush()

	return err
}

func makeReplacer(filename string) (func(string) string, error) {
	rawBytes, err := ioutil.ReadFile(filename)
	if err != nil {
		return nil, err
	}

	text := string(rawBytes)

	lines := strings.Split(text, "\n")
	usOfBritish := make(map[string]string)
	for _, line := range lines {
		fileds := strings.Fields(line)
		if len(fileds) == 2 {
			usOfBritish[fileds[0]] = fileds[1]
		}
	}

	replacer := func(word string) string {
		if usWord, isFound := usOfBritish[word]; isFound {
			return usWord
		}
		return word
	}

	return replacer, nil
}