listen/listen.go

package main

import (
	"crypto/sha256"
	"fmt"
	"io"
	"log"
	"maps"
	"os"
	"os/exec"
	"os/signal"
	"runtime"
	"slices"
	"time"

	color "github.com/fatih/color"
	"github.com/fsnotify/fsnotify"
)

type Listen struct {
	FileMap     map[string]bool
	CksumMap    map[string][]byte
	IntervalMap map[string]time.Time
	Condition   string
	Cksum       bool
	Interval    time.Duration
	Command     []string
	Quiet       bool
	RunFirst    bool
}

func printStatus(msg string) {
	c := color.New(color.FgWhite)
	if runtime.GOOS == "windows" {
		c.Fprintf(color.Output, "%s", msg)
	} else {
		c.Fprintf(os.Stderr, "%s", msg)
	}
}

func cksumCheck(l Listen, k string, t *bool) bool {
	hasher := sha256.New()
	f, err := os.Open(k)
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()

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

	if !slices.Equal(l.CksumMap[k], hasher.Sum(nil)) {
		l.CksumMap[k] = hasher.Sum(nil)
		if l.Condition == "any" {
			*t = true
			return true
		}

		l.FileMap[k] = true
	}
	return false

}

func allCheck(l Listen) bool {
	for value := range maps.Values(l.FileMap) {
		if !value {
			return false
		}
	}

	return true
}

func runTrigger(l Listen, f string, r bool, quit chan bool) bool {
	if !l.Quiet && !r {
		if l.Condition == "any" {
			printStatus(fmt.Sprintf("& File %s modified. ", f))
		} else {
			printStatus("& All files have been modified. ")
		}
	}

	if len(l.Command) >= 1 {
		if !l.Quiet {
			printStatus("Running command...\n")
		}

		cmd := exec.Command(l.Command[0], l.Command[1:]...)
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
		if err := cmd.Start(); err != nil {
			log.Fatalln(err)
		}

		if err := cmd.Wait(); err != nil {
			if rc, ok := err.(*exec.ExitError); ok {
				if !l.Quiet {
					color.New(color.FgYellow).Fprintf(os.Stderr, "& WARNING: Command exited with code %d.\n", rc.ExitCode())
				}
			}
		}

		if !l.Quiet {
			printStatus("& Returned to listening...\n")
		}
	} else {
		if !l.Quiet {
			fmt.Println()
		}

		quit <- true
		return true
	}

	return false
}

func loopFsnotify(l Listen, quit chan bool) {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		log.Fatal(err)
	}

	defer watcher.Close()
	for key := range l.FileMap {
		watcher.Add(key)
	}

	for {
		var renameAdd []string = []string{}
		fileMod := ""
		trigger := false
		select {
		case event, ok := <-watcher.Events:
			if !ok {
				return
			}

			for key := range l.FileMap {
				if event.Name == key {
					if l.Cksum {
						// return value indicates a break is needed
						if cksumCheck(l, key, &trigger) {
							fileMod = key
							break
						}
					} else {
						if event.Has(fsnotify.Write) {
							if l.Condition == "any" {
								fileMod = key
								trigger = true
								break
							}

							l.FileMap[key] = true
						} else if event.Has(fsnotify.Rename) {
							// we need to rewatch file
							// sleeping small amount to allow CREATE event to propogate
							time.Sleep(10 * time.Millisecond)
							// ... then adding to a list to allow additional time
							renameAdd = append(renameAdd, key)
							if l.Condition == "any" {
								fileMod = key
								trigger = true
								break
							}

							l.FileMap[key] = true
						}
					}
				}
			} // end for

			if l.Condition == "all" {
				trigger = allCheck(l)
			}
		// end case event
		case _, ok := <-watcher.Errors:
			if !ok {
				return
			}
		} // end switch
		// end case errors

		if trigger {
			if runTrigger(l, fileMod, false, quit) {
				return
			}
		} // end if trigger

		for _, value := range renameAdd {
			err := watcher.Add(value)
			if err != nil {
				fmt.Println(err)
			}
		}
	} // end for
}

func loopInterval(l Listen, quit chan bool) {
	for {
		time.Sleep(l.Interval)
		fileMod := ""
		trigger := false

		for key := range l.FileMap {
			if l.Cksum {
				// return value indicates a break is needed
				if cksumCheck(l, key, &trigger) {
					fileMod = key
					break
				}
			} else {
				s, err := os.Stat(key)
				if err != nil {
					log.Fatal()
				}

				if l.IntervalMap[key] != s.ModTime() {
					l.IntervalMap[key] = s.ModTime()
					if l.Condition == "any" {
						fileMod = key
						trigger = true
						break
					}

					l.FileMap[key] = true
				}

			}
		} // end for key

		if l.Condition == "all" {
			trigger = allCheck(l)
		}

		if trigger {
			if runTrigger(l, fileMod, false, quit) {
				return
			}
		} // end if trigger

	}
}

func startMessage(l Listen) {
	printStatus(fmt.Sprintf("& listen %s\n", VERSION))
	printStatus("& This program is free software, and comes with ABSOLUTELY NO WARRANTY.\n")
	printStatus("& Run 'listen --license' for details.\n")
	printStatus("&\n")
	if len(l.Command) >= 1 {
		printStatus("& This command will run:\n")
		printStatus("&   ")
		for _, value := range l.Command {
			printStatus(value + " ")
		}

		fmt.Println()
		printStatus("& When ")
	} else {
		printStatus("& listen will exit when ")
	}

	if l.Cksum {
		printStatus("the checksum of ")
	}

	if len(l.FileMap) >= 2 {
		if l.Condition == "any" {
			printStatus("any of ")
		} else {
			printStatus("all ")
		}

		printStatus("these files have ")
	} else {
		printStatus("this file has ")
	}

	if l.Cksum {
		printStatus("changed:\n")
	} else {
		printStatus("been modified:\n")
	}

	for key := range l.FileMap {
		printStatus(fmt.Sprintf("&   %s\n", key))
	}
}

func (l Listen) Run() {
	// catch ^C
	quit := make(chan bool)
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt)

	if !l.Quiet {
		startMessage(l)
	}

	if l.RunFirst {
		if !l.Quiet {
			printStatus("& -r option specified. ")
		}
		runTrigger(l, "", true, quit)
	} else {
		printStatus("& Starting now...\n")
	}

	// start main loop
	if l.Interval == time.Duration(0*time.Second) {
		go loopFsnotify(l, quit)
	} else {
		go loopInterval(l, quit)
	}

	select {
	case <-c:
		fmt.Println()
	case <-quit:
	}

	if !l.Quiet {
		printStatus("& Exiting...\n")
	}

}