// Visualize debug information from hamnet70.
//
// This program is a HTTP server which reads JSON messages (one per line) from
// a FIFO filled by hamnet70 and passes them to the browser via WebSocket.
// Concurrent browser sessions and reconnects are supported. This binary is
// standalone and can be used without the static/ directory.

package main

import (
	"bufio"
	"embed"
	"io/fs"
	"log"
	"net/http"
	"os"
	"sync"
	"time"

	"golang.org/x/net/websocket"
)

//go:embed static/*
var static embed.FS

func main() {
	if len(os.Args) != 2 && len(os.Args) != 3 {
		log.SetFlags(0)
		log.Fatalf("usage: %s <fifo> [<json-dup-prefix>]", os.Args[0])
	}

	var mutex sync.Mutex
	listeners := make(map[*chan string]struct{})

	go func() {
		for {
			path := os.Args[1]
			var dupPath string
			if len(os.Args) == 3 {
				dupPath = os.Args[2] + "." + time.Now().Format(time.RFC3339)
			}

			fh, err := os.Open(path)
			if err != nil {
				log.Fatal(err)
			}
			var dupFh *os.File
			if dupPath != "" {
				dupFh, err = os.Create(dupPath)
				if err != nil {
					log.Fatal(err)
				}
			}

			r := bufio.NewReader(fh)
			for {
				line, err := r.ReadString('\n')
				if err != nil {
					log.Printf("read %q: %v", path, err)
					break
				}

				// Duplicate JSON input to a file so it can be replayed later
				// if necessary
				if dupFh != nil {
					_, err = dupFh.WriteString(line)
					if err != nil {
						log.Fatalf("write %q: %v", dupPath, err)
					}
				}

				// Send to all listeners
				mutex.Lock()
				for x := range listeners {
					*x <- line
				}
				mutex.Unlock()
			}

			err = fh.Close()
			if err != nil {
				log.Fatalf("close %q: %v", path, err)
			}
			if dupFh != nil {
				err = dupFh.Close()
				if err != nil {
					log.Fatalf("close %q: %v", dupPath, err)
				}
			}
		}
	}()

	// Use existing "./static/" directory for quick changes
	var staticFS http.FileSystem
	_, err := os.Stat("static")
	if err == nil {
		staticFS = http.Dir("static")
	} else {
		x, err := fs.Sub(static, "static")
		if err != nil {
			log.Fatal(err)
		}
		staticFS = http.FS(x)
	}
	http.Handle("/", http.FileServer(staticFS))

	http.Handle("/events", websocket.Handler(func(conn *websocket.Conn) {
		// Register new listener for this connection
		ch := make(chan string, 512) // buffer up to x number of messages
		mutex.Lock()
		listeners[&ch] = struct{}{}
		mutex.Unlock()
		defer func() {
			mutex.Lock()
			delete(listeners, &ch)
			mutex.Unlock()
		}()

		for {
			x := <-ch
			err := websocket.Message.Send(conn, x)
			if err != nil {
				log.Printf("Websocket error: %v", err)
				break
			}
		}
	}))

	err = http.ListenAndServe("localhost:8080", nil)
	if err != nil {
		log.Fatal(err)
	}
}

// vi: set noet ts=4 sw=4 sts=4: