package main

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"path/filepath"
	"sync"
	"time"
)

const (
	// daemonAgentDirName is the directory of the root agent in the data
	// directory.
	daemonAgentDirName = "agent"

	// daemonClientEvents is the number of events that can wait for a slow
	// client before the daemon drops it.
	daemonClientEvents = 1024
)

// daemon runs "onechat daemon": it owns the root agent and its files and serves
// the clients on the Unix socket in the data directory until ctx ends. When
// telegram.json exists, it also runs the Telegram bot. It holds the lock of the
// token file, so it is the only process that refreshes the tokens.
func daemon(ctx context.Context, out io.Writer) (err error) {
	dir, err := dataDir()
	if err != nil {
		return err
	}

	// Check the socket path before the daemon writes a file, so that a data
	// directory with a long path stays empty.
	socket := filepath.Join(dir, socketFileName)
	err = checkSocketPath(socket)
	if err != nil {
		return err
	}

	config, err := loadConfig(dir)
	if err != nil {
		return err
	}

	botSettings, hasBot, err := loadTelegramConfig(dir)
	if err != nil {
		return err
	}

	tokens, err := lockTokens(dir)
	if err != nil {
		return err
	}

	defer func() {
		err = errors.Join(err, tokens.Close())
	}()

	address, auth, err := modelEndpoint(config, dir)
	if err != nil {
		return err
	}

	agent, err := openAgent(filepath.Join(dir, daemonAgentDirName))
	if err != nil {
		return err
	}

	client := newModelClient(address, auth, agent.CacheKey(), filepath.Join(agent.dir, "usage.jsonl"))
	memory, err := openMemory(ctx, agent.dir, time.Now, newCompactor(client, agent.Prompt, config.Compactor))
	if err != nil {
		return err
	}

	defer func() {
		err = errors.Join(err, memory.Close())
	}()

	listener, err := daemonListenSocket(socket)
	if err != nil {
		return err
	}

	_, err = fmt.Fprintf(out, "onechat: %s on %s, %s at %s effort, in %s\n", agent.config.Name, listener.Addr(), agent.config.Model, agent.config.Effort, agent.config.Workdir)
	if err != nil {
		return errors.Join(err, listener.Close())
	}

	var telegram *TelegramBot
	if hasBot {
		telegram = newTelegramBot(newTelegramAPI(telegramAPIURL, botSettings.Token), botSettings.Owner, filepath.Join(agent.dir, telegramOffsetFileName), log.New(out, "telegram: ", log.LstdFlags))
		_, err = fmt.Fprintln(out, "onechat: the Telegram bot waits for messages of its owner")
		if err != nil {
			return errors.Join(err, listener.Close())
		}
	}

	return daemonServe(ctx, listener, telegram, func(notify func(Event)) (*TurnLoop, error) {
		return newTurnLoop(agent, memory, client, time.Now, notify)
	})
}

// DaemonHub holds the connected clients and sends each event to all of them.
type DaemonHub struct {
	mutex   sync.Mutex
	clients map[*DaemonClient]bool
	workers sync.WaitGroup
}

// Accept serves each client of listener until the listener closes. A new
// client gets a ready event with the name of the agent, and a busy event when a
// turn runs.
func (h *DaemonHub) Accept(ctx context.Context, listener net.Listener, l *TurnLoop) {
	for {
		conn, err := listener.Accept()
		if err != nil {
			return
		}

		client := &DaemonClient{
			conn:   conn,
			events: make(chan Event, daemonClientEvents),
		}

		h.mutex.Lock()
		h.clients[client] = true
		h.mutex.Unlock()

		h.workers.Add(2)
		go h.write(client)
		go h.read(ctx, client, l)

		h.Send(client, Event{
			Kind: "ready",
			Text: l.agent.config.Name,
		})

		if l.Busy() {
			h.Send(client, Event{
				Kind: "busy",
			})
		}
	}
}

// write sends the events of client as JSON lines until its channel closes.
func (h *DaemonHub) write(client *DaemonClient) {
	defer h.workers.Done()

	encoder := json.NewEncoder(client.conn)
	for event := range client.events {
		err := encoder.Encode(event)
		if err != nil {
			h.drop(client)
		}
	}
}

// read runs the requests of client until it closes its connection.
func (h *DaemonHub) read(ctx context.Context, client *DaemonClient, l *TurnLoop) {
	defer h.workers.Done()
	defer h.drop(client)

	scanner := bufio.NewScanner(client.conn)
	scanner.Buffer(make([]byte, 64*1024), socketRequestBytes)
	for ctx.Err() == nil && scanner.Scan() {
		var request SocketRequest
		err := json.Unmarshal(scanner.Bytes(), &request)
		if err == nil {
			err = daemonRunRequest(l, request)
		}

		if err != nil {
			h.Send(client, Event{
				Kind: "error",
				Text: err.Error(),
			})
		}
	}
}

// Send gives event to one client, or drops the client when its events do not
// fit.
func (h *DaemonHub) Send(client *DaemonClient, event Event) {
	h.mutex.Lock()
	defer h.mutex.Unlock()

	h.send(client, event)
}

// drop removes client and closes its connection.
func (h *DaemonHub) drop(client *DaemonClient) {
	h.mutex.Lock()
	defer h.mutex.Unlock()

	h.remove(client)
}

// send gives event to client. The caller holds the mutex.
func (h *DaemonHub) send(client *DaemonClient, event Event) {
	if !h.clients[client] {
		return
	}

	select {
	case client.events <- event:
	default:
		h.remove(client)
	}
}

// remove removes client, closes its connection, and ends its writer. The
// caller holds the mutex.
func (h *DaemonHub) remove(client *DaemonClient) {
	delete(h.clients, client)
	client.once.Do(func() {
		close(client.events)
		_ = client.conn.Close()
	})
}

// Broadcast gives event to every client.
func (h *DaemonHub) Broadcast(event Event) {
	h.mutex.Lock()
	defer h.mutex.Unlock()

	for client := range h.clients {
		h.send(client, event)
	}
}

// CloseAll drops every client and waits for their readers and writers.
func (h *DaemonHub) CloseAll() {
	h.mutex.Lock()
	for client := range h.clients {
		h.remove(client)
	}
	h.mutex.Unlock()

	h.workers.Wait()
}

// DaemonClient is one connected client. Its events wait in a channel for the
// writer, so a slow client does not stop the agent.
type DaemonClient struct {
	conn   net.Conn
	events chan Event
	once   sync.Once
}

// daemonListenSocket listens on the Unix socket at path, with mode 0600. The
// caller owns the chat, so a socket file at path is left from a daemon that
// ended, and daemonListenSocket removes it.
func daemonListenSocket(path string) (net.Listener, error) {
	err := checkSocketPath(path)
	if err != nil {
		return nil, err
	}

	err = os.Remove(path)
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return nil, fmt.Errorf("remove old socket: %w", err)
	}

	listener, err := net.Listen("unix", path)
	if err != nil {
		return nil, fmt.Errorf("listen on socket: %w", err)
	}

	err = os.Chmod(path, 0o600)
	if err != nil {
		return nil, errors.Join(fmt.Errorf("set socket mode: %w", err), listener.Close())
	}

	return listener, nil
}

// daemonServe runs the loop that start makes and serves the clients of listener
// until ctx ends or the loop fails. It closes listener. When bot is not nil, it
// runs the bot too, and a failure of the bot stops the agent.
func daemonServe(ctx context.Context, listener net.Listener, bot *TelegramBot, start func(notify func(Event)) (*TurnLoop, error)) error {
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	hub := &DaemonHub{
		clients: make(map[*DaemonClient]bool),
	}

	notify := hub.Broadcast
	if bot != nil {
		notify = func(event Event) {
			hub.Broadcast(event)
			bot.Notify(event)
		}
	}

	l, err := start(notify)
	if err != nil {
		return errors.Join(err, listener.Close())
	}

	var workers sync.WaitGroup
	workers.Add(1)
	go func() {
		defer workers.Done()

		hub.Accept(ctx, listener, l)
	}()

	var botErr error
	if bot != nil {
		workers.Add(1)
		go func() {
			defer workers.Done()

			botErr = bot.Run(ctx, l)
			cancel()
		}()
	}

	err = l.Run(ctx)
	if errors.Is(err, context.Canceled) {
		err = nil
	}

	cancel()
	err = errors.Join(err, listener.Close())
	hub.CloseAll()
	workers.Wait()

	return errors.Join(err, botErr)
}

// daemonRunRequest runs one request of a client.
func daemonRunRequest(l *TurnLoop, request SocketRequest) error {
	switch request.Type {
	case "send":
		if request.Text == "" {
			return errors.New("empty message")
		}

		_, err := l.Submit(terminalSource, request.Text)

		return err
	case "interrupt":
		if !l.Interrupt() {
			return errors.New("no turn runs")
		}

		return nil
	default:
		return fmt.Errorf("unknown request %q", request.Type)
	}
}