listen/main.go

package main

import (
	"crypto/sha256"
	"fmt"
	"io"
	"io/fs"
	"log"
	"os"
	"path/filepath"
	"time"

	flags "github.com/jessevdk/go-flags"
)

const VERSION string = "v0.4.0"

type Options struct {
	Version    bool     `short:"v" long:"version" description:"Displays version info and exits"`
	Quiet      bool     `short:"q" long:"quiet" description:"Suppresses status messages (stderr lines beginning with '&')"`
	Files      []string `short:"f" long:"file" description:"File(s) to listen to (watch)" value-name:"FILE"`
	Condition  string   `short:"w" long:"when" description:"If multiple files are specified, choose if any file or all files specified are needed to trigger COMMAND" default:"any" choice:"any" choice:"all"`
	NoChecksum bool     `short:"x" long:"no-checksum" description:"Do not calculate checksum as an additional check for file changes (see MODES section in man page for more info)"`
	Interval   string   `short:"i" long:"interval" description:"Use this time interval (ex. 5m30s, 1s) between filesystem checks instead of watching kernel events. If the interval is effectively 0 (the default), kernel events are used" default:"0s"`
	RunFirst   bool     `short:"r" long:"run" description:"Runs COMMAND (if specified) before starting listen"`
}

func validateArgs(opts Options, commandLen int) error {
	// file checks
	if len(opts.Files) <= 0 {
		fmt.Println("listen: at least one file (-f) is required")
		return flags.ErrCommandRequired
	}

	for _, file := range opts.Files {
		info, err := os.Stat(file)
		if err != nil {
			fmt.Printf("listen: %s\n", err)
			return err
		}

		if info.IsDir() {
			fmt.Printf("listen: %s: not a file\n", file)
			return fs.ErrInvalid
		}

		_, err = os.Open(file)
		if err != nil {
			fmt.Printf("listen: %s\n", err)
			return err
		}
	}

	// interval checks
	if _, err := time.ParseDuration(opts.Interval); err != nil {
		fmt.Printf("listen: %s\n", err)
		return err
	}

	// run first check
	if commandLen < 1 && opts.RunFirst {
		fmt.Println("listen: -r cannot be specified without a command")
		return flags.ErrInvalidChoice
	}

	return nil
}

func setup(opts Options, command []string) int {
	var filesMap map[string]bool = make(map[string]bool)
	var cksumMap map[string][]byte = make(map[string][]byte)
	var intervalMap map[string]time.Time = make(map[string]time.Time)
	intervalDuration, _ := time.ParseDuration(opts.Interval)
	success := true
	for _, file := range opts.Files {
		hasher := sha256.New()
		f, err := os.Open(file)
		if err != nil {
			success = false
			break
		}
		defer f.Close()

		s, err := os.Stat(file)
		if err != nil {
			success = false
			break
		}

		if _, err := io.Copy(hasher, f); err != nil {
			log.Fatal(err)
		}

		abs, err := filepath.Abs(file)
		if err == nil {
			filesMap[abs] = false
			cksumMap[abs] = hasher.Sum(nil)
			intervalMap[abs] = s.ModTime()
		} else {
			success = false
			break
		}
	}

	if success {
		l := Listen{filesMap, cksumMap, intervalMap, opts.Condition, opts.NoChecksum, intervalDuration, command, opts.Quiet, opts.RunFirst}
		return l.Run()
	}

	return -1
}

func main() {
	ret := 0
	opts := Options{}
	parser := flags.NewParser(&opts, flags.Default)
	parser.Usage = "[OPTIONS] -- [COMMAND]"
	remaining, err := parser.Parse()

	defer func() {
		if err := recover(); err != nil {
			switch ret {
			case -1:
				os.Exit(5)
			default:
				os.Exit(ret)
			}
		}
	}()

	if err == nil {
		if opts.Version {
			fmt.Printf("listen %s\n", VERSION)
		} else if err := validateArgs(opts, len(remaining)); err == nil {
			ret = setup(opts, remaining)
			if ret != 0 {
				panic(ret)
			}
		}
	}

}