A go program to convert all relative imports to absolute imports in a Typescript/Javascript codebase

rel_to_abs.go

package main

import (
	"bufio"
	"bytes"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"regexp"
)

var filename = flag.String("f", "", "filename")
var overwrite = flag.Bool("w", false, "overwrite")
var out io.Writer

func main() {
	flag.Parse()
	f, err := os.Open(*filename)
	if os.IsNotExist(err) {
		panic(err)
	}
	defer f.Close()
	b := &bytes.Buffer{}
	if *overwrite {
		out = b
	} else {
		out = os.Stdout
	}

	scanner := bufio.NewScanner(f)
	// optionally, resize scanner's capacity for lines over 64K, see next example
	for scanner.Scan() {
		_, err := out.Write([]byte(HandleLine(scanner.Text(), *filename) + "\n"))
		if err != nil {
			panic(err)
		}
	}

	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}

	if *overwrite {
		f2, err := os.OpenFile(*filename, os.O_WRONLY, 0)
		if err != nil {
			panic(err)
		}
		err = f2.Truncate(0)
		if err != nil {
			panic(err)
		}
		_, err = f2.Write(b.Bytes())
		if err != nil {
			panic(err)
		}
	}
}

var matchLine = regexp.MustCompile("(?P<prefix>.* from )[\"'](?P<path>.*)[\"'];")
var matchLine2 = regexp.MustCompile("(?P<prefix>import )[\"'](?P<path>.*)[\"'];")
var suffix = regexp.MustCompile("\\.[tj]sx?|\\.css|\\.gif|\\.png|\\.svg$")

func HandleLine(in, filename string) string {
	if !matchLine.MatchString(in) && !matchLine2.MatchString(in) {
		return in
	}

	subMatches := []string{}
	if matchLine.MatchString(in) {
		subMatches = matchLine.FindStringSubmatch(in)
	}
	if matchLine2.MatchString(in) {
		subMatches = matchLine2.FindStringSubmatch(in)
	}

	absPath := filepath.Join(filename, "../"+subMatches[2])
	if suffix.MatchString(absPath) && exists(absPath) {
		return fmt.Sprintf("%s\"%s\";", subMatches[1], absPath)
	}
	//add suffix and see if it exists
	for _, tSuffix := range []string{"ts", "js", "tsx", "jsx", "css", "png", "gif", "svg"} {
		if exists(absPath + "." + tSuffix) {
			return fmt.Sprintf("%s\"%s\";", subMatches[1], absPath)
		}
	}

	//Couldn't find the file
	return in
}

func exists(path string) bool {
	_, err := os.Stat(path)
	return !errors.Is(err, os.ErrNotExist)
}