// packer - a simple CLI tool to find and zip file corresponding to a given regex
// find + zip linux CLI works too
package main

import (
	"archive/zip"
	"fmt"
	"github.com/akamensky/argparse"
	"io"
	"log"
	"os"
	fp "path/filepath"
	re "regexp"
)

// parseArguments - get needed arguments to launch the `packer`
// returns 3 strings :
// * regex
// * outputPath
// * directory
func parseArguments() (string, string, string, error) {
	parser := argparse.NewParser("packer", "packer - zip file where filenames match with a regex")
	var err error

	regex := parser.String("r", "regex", &argparse.Options{Required: true, Help: "filename Regex"})
	outputPath := parser.String("o", "output-path", &argparse.Options{Required: true, Help: "zip output path (including zip name)"})
	directory := parser.String("d", "directory", &argparse.Options{Required: false, Help: "root directory to check files", Default: "."})

	parseError := parser.Parse(os.Args)
	if parseError != nil {
		err = fmt.Errorf("parsing error: %s", parseError)
	}

	return *regex, *directory, *outputPath, err
}

// buildRegex - build POSIX regex from a string
// WARN: lookahead and lookbehind are not supported
func buildRegex(regex string) (*re.Regexp, error) {
	rc, err := re.CompilePOSIX(regex)
	return rc, err
}

// walkFilteredDir - walk into a directory and its subdirectories and find files that match a regex
func walkDirFiltered(directory string, regex re.Regexp) ([]string, error) {
	var files []string
	err := fp.Walk(directory,
		func(path string, info os.FileInfo, err error) error {
			if err != nil {
				return err
			}
			if !info.IsDir() && regex.MatchString(path) {
				log.Println("file found :", path)
				files = append(files, path)
			}
			return err
		})
	return files, err
}

// getFilesFromDirectoryPath - wrapper calling `walkDirFiltered()`
func getFilesFromDirectoryPath(directory string, regex re.Regexp) ([]string, error) {
	files, err := walkDirFiltered(directory, regex)
	return files, err
}

// writeFileContent - write file content into zipped file
// chunking is used to avoid memory errors with large files
func writeFileContent(f *os.File, zf io.Writer) (err error) {
	const chunkSize = 4
	b := make([]byte, chunkSize)

	for {
		_, err := f.Read(b)
		if err != nil {
			if err != io.EOF {
				continue
			}
			break
		}
		zf.Write(b)
	}

	return err
}

// generateZip - create a zip archive
// * outputPath: zip archive full path
// * filePaths: files path
func generateZip(outputPath string, filepaths []string) (err error) {

	// create a zipfile from `outputPath`
	zipPath, err := os.Create(outputPath)
	if err != nil {
		return err
	}
	defer zipPath.Close()

	// create a new zip archive from `zipPath`
	w := zip.NewWriter(zipPath)

	for _, filepath := range filepaths {
		// open matching regex file
		f, err := os.Open(filepath)
		if err != nil {
			log.Println("[ERROR] :", err)
			continue
		}

		// create a zipped file
		zf, err := w.Create(filepath)
		if err != nil {
			log.Println("[ERROR] :", err)
			f.Close()
			continue
		}

		// write file content into zipped file
		err = writeFileContent(f, zf)

		// clean up opened file
		f.Close()
	}

	// make sure to check the error on Close.
	err = w.Close()

	return err
}

func main() {

	// parse arguments
	regex, directory, outputPath, err := parseArguments()
	if err != nil {
		log.Fatal("error while parsing args : ", err)
	}

	// build regex from string
	rc, err := buildRegex(regex)
	if err != nil {
		log.Fatal("error while compiling regex : '", regex, "'\nWARN: lookahead and lookbehind not implemented")
	}

	// deferencing Regexp pointer
	rd := *rc

	// walk into directory
	log.Printf("looking for file '%s' in '%s' ...", rd.String(), directory)
	files, err := getFilesFromDirectoryPath(directory, rd)

	// generating zip archive
	log.Printf("files found : %d", len(files))
	generateZip(outputPath, files)

	log.Printf("zip archive generated in %s", outputPath)
}