// Copyright (C) 2024 Leah Neukirchen
//
// based on mautrix-go example code:
//
// Copyright (C) 2017 Tulir Asokan
// Copyright (C) 2018-2020 Luca Weiss
// Copyright (C) 2023 Tulir Asokan
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

package main

import (
	"context"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"time"

	"k8s.io/klog"
	"maunium.net/go/mautrix"
	"maunium.net/go/mautrix/event"
	"maunium.net/go/mautrix/id"
)

var folks map[string]struct{}

type JSONTop struct {
	Users []JSONUser `json:"users"`
}

type JSONUser struct {
	Login string `json:"login"`
}

func ircquote(s string) string {
	if len(s) < 1 {
		return s // bad luck, V
	}

	ZWJ := "\u200d"
	return s[0:1] + ZWJ + s[1:]
}

func listFmt(list []string) string {
	var listQuoted []string
	for _, l := range list {
		listQuoted = append(listQuoted, ircquote(l))
	}
	return "[ " + strings.Join(listQuoted, " ") + " ]"
}

func update(ctx context.Context) (string, error) {
	req, err := http.NewRequestWithContext(ctx, "GET", flagBackendURL, nil)
	if err != nil {
		return "", err
	}
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		return "", err
	}
	defer res.Body.Close()

	var users JSONTop

	if res.StatusCode != 200 {
		return "", fmt.Errorf("unexpected API status code %d", res.StatusCode)
	}
	if err := json.NewDecoder(res.Body).Decode(&users); err != nil {
		return "", fmt.Errorf("could not decode API response: %v", err)
	}

	var left []string
	var arrived []string
	var unchanged []string

	newFolks := make(map[string]struct{})
	for _, user := range users.Users {
		newFolks[user.Login] = struct{}{}
		if _, ok := folks[user.Login]; !ok {
			arrived = append(arrived, user.Login)
		} else {
			unchanged = append(unchanged, user.Login)
		}
	}
	for user, _ := range folks {
		if _, ok := newFolks[user]; !ok {
			left = append(left, user)
		}
	}

	folks = newFolks

	// no change
	if len(arrived) == 0 && len(left) == 0 {
		return "", nil
	}

	var parts []string
	if len(arrived) > 0 {
		parts = append(parts, fmt.Sprintf("arrived: %s", listFmt(arrived)))
	}
	if len(left) > 0 {
		parts = append(parts, fmt.Sprintf("left: %s", listFmt(left)))
	}
	if len(unchanged) > 0 {
		adjective := "also"
		if len(left) > 0 && len(arrived) == 0 {
			adjective = "still"
		}
		parts = append(parts, fmt.Sprintf("%s there: %s", adjective, listFmt(unchanged)))
	}

	return strings.Join(parts, "; "), nil
}

var (
	flagMatrixHomeserver   = "matrix.org"
	flagMatrixUsername     = "@fafomo:matrix.org"
	flagMatrixPasswordFile = "password.txt"
	flagMatrixRoom         string
	flagBackendURL         string
)

func main() {
	flag.StringVar(&flagMatrixHomeserver, "matrix_homeserver", flagMatrixHomeserver, "Address of Matrix homeserver")
	flag.StringVar(&flagMatrixUsername, "matrix_username", flagMatrixUsername, "Matrix login username")
	flag.StringVar(&flagMatrixPasswordFile, "matrix_password_file", flagMatrixPasswordFile, "Path to file containing matrix login password")
	flag.StringVar(&flagMatrixRoom, "matrix_room", flagMatrixRoom, "Matrix room MXID")
	flag.StringVar(&flagBackendURL, "backend_url", flagBackendURL, "Checkinator (backend) addresss")
	flag.Parse()

	for _, s := range []struct {
		value string
		name  string
	}{
		{flagMatrixHomeserver, "matrix_homeserver"},
		{flagMatrixUsername, "matrix_username"},
		{flagMatrixPasswordFile, "matrix_password_file"},
		{flagMatrixRoom, "matrix_room"},
		{flagBackendURL, "backend_url"},
	} {
		if s.value == "" {
			klog.Exitf("-%s must be set", s.name)
		}
	}

	startCtx, startCtxC := context.WithTimeout(context.Background(), 20*time.Second)
	defer startCtxC()

	if _, err := update(startCtx); err != nil {
		klog.Exitf("Initial update failed: %v", err)
	}

	client, err := mautrix.NewClient(flagMatrixHomeserver, id.UserID(flagMatrixUsername), "")
	if err != nil {
		klog.Exitf("NewClient failed: %v", err)
	}

	passwordBytes, err := os.ReadFile(flagMatrixPasswordFile)
	if err != nil {
		klog.Exitf("Could not read password file: %v", err)
	}
	password := strings.TrimSpace(string(passwordBytes))

	klog.Infof("Logging in...")

	login, err := client.Login(startCtx, &mautrix.ReqLogin{
		Type:       mautrix.AuthTypePassword,
		Identifier: mautrix.UserIdentifier{Type: mautrix.IdentifierTypeUser, User: flagMatrixUsername},
		Password:   password,
	})
	if err != nil {
		klog.Exitf("Failed to log in: %v", err)
	}

	client.AccessToken = login.AccessToken

	syncer := client.Syncer.(*mautrix.DefaultSyncer)
	syncer.OnEventType(event.EventMessage, func(ctx context.Context, evt *event.Event) {
		klog.V(1).Infof("Sender: %s, type: %s, id: %s, body: %q", evt.Sender, evt.Type, evt.ID, evt.Content.AsMessage().Body)
	})

	klog.Infof("Now running...")

	ctx, ctxC := signal.NotifyContext(context.Background(), os.Interrupt)
	defer ctxC()

	// Run Matrix sync process in the background.
	syncDone := make(chan struct{})
	go func() {
		err = client.SyncWithContext(ctx)
		defer close(syncDone)
		if err != nil && !errors.Is(err, ctx.Err()) {
			klog.Exitf("Sync failed: %v", err)
		}
	}()

	// Update space members every minute.
	ticker := time.NewTicker(60 * time.Second)
process:
	for {
		select {
		case <-ticker.C:
			ctx, _ := context.WithTimeout(ctx, 5*time.Second)

			message, err := update(ctx)
			if err != nil {
				klog.Errorf("Update failed: %v", err)
			} else if message != "" {
				klog.Infof("Sent update: %s\n", message)
				_, err := client.SendText(ctx, id.RoomID(flagMatrixRoom), message)
				if err != nil {
					klog.Errorf("Failed to send event: %v\n", err)
				}
			}

		case <-ctx.Done():
			break process
		}
	}

	klog.Infof("Waiting for graceful sync before exiting...")
	<-syncDone
	klog.Infof("Done.")
}