package main

import (
	"fmt"
	"io/fs"
	"log"
	"maps"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"time"

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

const VERSION string = "v0.1.0"

var opts struct {
	Version   bool     `short:"v" long:"version" description:"Displays version info and exits"`
	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"`
	Checksum  bool     `short:"c" long:"checksum" description:"Use checksum to determine when file(s) are changed instead of modification time (only used when -i is specified)"`
	Interval  string   `short:"i" long:"interval" description:"Use this time interval (ex. 5m30s, 1s) between filesystem checks instead of using kernel events"`
}

func validateFiles(files []string) error {
	if len(files) <= 0 {
		fmt.Println("listen: at least one file (-f) is required")
		return flags.ErrCommandRequired
	}

	for _, file := range 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
		}
	}

	return nil
}

func listen(files map[string]bool, condition string, cksum bool, interval string, command []string) {
	// catch ^C
	quit := make(chan bool)
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt)

	// main loop
	if interval == "" {
		watcher, err := fsnotify.NewWatcher()
		if err != nil {
			log.Fatal(err)
		}

		for key := range files {
			watcher.Add(key)
		}

		go func() {
			for {
				trigger := false
				select {
				case event, ok := <-watcher.Events:
					if !ok {
						return
					}
					fmt.Println(event)

					for key := range files {
						if event.Has(fsnotify.Write) && event.Name == key {
							if condition == "any" {
								trigger = true
								break
							}
							files[key] = true
						}
					}

					if condition == "all" {
						trigger = true
						for value := range maps.Values(files) {
							if !value {
								trigger = false
								break
							}
						}
					}

				case _, ok := <-watcher.Errors:
					if !ok {
						return
					}
				}

				if trigger {
					if len(command) >= 1 {
						exec.Command(command[0], command[1:]...)
					} else {
						quit <- true
					}
				}
			}
		}()

	} else {
		go func() {
			for {
				fmt.Printf("running")
				time.Sleep(1 * time.Second)
			}

		}()

	}

	select {
	case <-c:
	case <-quit:
	}

}

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

	if err == nil {
		if opts.Version {
			fmt.Printf("listen %s\n", VERSION)
		} else if err := validateFiles(opts.Files); err == nil {
			var filesMap map[string]bool = make(map[string]bool)
			success := true
			for _, file := range opts.Files {
				abs, err := filepath.Abs(file)
				if err == nil {
					filesMap[abs] = false
				} else {
					success = false
				}
			}

			if success {
				listen(filesMap, opts.Condition, opts.Checksum, opts.Interval, remaining)
			}
		}
	}
}