package main

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"

	"maunium.net/go/mautrix"
	"maunium.net/go/mautrix/crypto/cryptohelper"
	"maunium.net/go/mautrix/event"
	"maunium.net/go/mautrix/id"
)

type MatrixClient struct {
	HomeserverURL string
	AccessToken   string
	RoomID        string
	Limit         int
	TimeLocation  *time.Location
	httpClient    *http.Client
	crypto        *cryptohelper.CryptoHelper
	cryptoClient  *mautrix.Client
	syncOnce      sync.Once
}

func newMatrixClientFromEnv() *MatrixClient {
	hs := strings.TrimRight(readEnv("MATRIX_HOMESERVER_URL", ""), "/")
	token := readEnv("MATRIX_ACCESS_TOKEN", "")
	roomID := readEnv("MATRIX_ROOM_ID", "")
	if hs == "" || token == "" || roomID == "" {
		return nil
	}

	limit := mustInt(readEnv("MATRIX_LIMIT", "25"), 25)
	if limit < 1 {
		limit = 1
	}
	if limit > 100 {
		limit = 100
	}

	m := &MatrixClient{
		HomeserverURL: hs,
		AccessToken:   token,
		RoomID:        roomID,
		Limit:         limit,
		httpClient: &http.Client{
			Timeout: 8 * time.Second,
		},
	}
	locName := strings.TrimSpace(readEnv("MATRIX_TIMEZONE", "Europe/Berlin"))
	if loc, err := time.LoadLocation(locName); err == nil {
		m.TimeLocation = loc
	} else {
		m.TimeLocation = time.Local
	}

	if readEnv("MATRIX_ENABLE_CRYPTO", "1") != "0" {
		m.crypto, m.cryptoClient = initMatrixCrypto(hs, token)
		m.startCryptoSync()
	}
	return m
}

func initMatrixCrypto(hs, token string) (*cryptohelper.CryptoHelper, *mautrix.Client) {
	cli, err := mautrix.NewClient(hs, "", token)
	if err != nil {
		return nil, nil
	}

	if whoami, err := cli.Whoami(context.Background()); err == nil && whoami != nil {
		cli.SetCredentials(whoami.UserID, token)
		cli.DeviceID = whoami.DeviceID
	}

	storePath := readEnv("MATRIX_CRYPTO_STORE_PATH", "/tmp/farmcal-matrix-crypto.db")
	pickleKey := []byte(readEnv("MATRIX_PICKLE_KEY", token))

	helper, err := cryptohelper.NewCryptoHelper(cli, pickleKey, storePath)
	if err != nil {
		return nil, nil
	}
	if err = helper.Init(context.Background()); err != nil {
		return nil, nil
	}
	return helper, cli
}

func (m *MatrixClient) startCryptoSync() {
	if m.cryptoClient == nil || m.crypto == nil {
		return
	}
	m.syncOnce.Do(func() {
		go func() {
			_ = m.cryptoClient.SyncWithContext(context.Background())
		}()
	})
}

func (m *MatrixClient) FetchRecentMessages(ctx context.Context) ([]MatrixMessage, error) {
	endpoint := fmt.Sprintf(
		"%s/_matrix/client/v3/rooms/%s/messages?dir=b&limit=%d",
		m.HomeserverURL,
		url.PathEscape(m.RoomID),
		m.Limit,
	)

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Authorization", "Bearer "+m.AccessToken)

	resp, err := m.httpClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, errors.New("matrix messages failed: " + strconv.Itoa(resp.StatusCode))
	}

	var messagesResp struct {
		Chunk []json.RawMessage `json:"chunk"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&messagesResp); err != nil {
		return nil, err
	}
	if len(messagesResp.Chunk) == 0 {
		return []MatrixMessage{}, nil
	}

	out := make([]MatrixMessage, 0, len(messagesResp.Chunk))
	for i := len(messagesResp.Chunk) - 1; i >= 0; i-- {
		ev := &event.Event{}
		if err := json.Unmarshal(messagesResp.Chunk[i], ev); err != nil {
			continue
		}
		ev.RoomID = id.RoomID(m.RoomID)
		msg, ok := m.mapEventToMessage(ctx, ev)
		if ok {
			out = append(out, msg)
		}
	}
	return out, nil
}

func (m *MatrixClient) mapEventToMessage(ctx context.Context, ev *event.Event) (MatrixMessage, bool) {
	ts := m.formatTimestamp(ev.Timestamp)
	sender := shortMatrixSender(string(ev.Sender))

	switch ev.Type {
	case event.EventMessage:
		if body, ok := extractBody(ev); ok {
			return MatrixMessage{Sender: sender, Body: body, Timestamp: ts}, true
		}
		return MatrixMessage{}, false
	case event.EventEncrypted:
		if m.crypto != nil {
			decrypted, err := m.crypto.Decrypt(ctx, ev)
			if errors.Is(err, cryptohelper.NoSessionFound) {
				content := ev.Content.AsEncrypted()
				m.crypto.RequestSession(ctx, ev.RoomID, content.SenderKey, content.SessionID, ev.Sender, content.DeviceID)
				waitCtx, cancel := context.WithTimeout(ctx, 8*time.Second)
				if m.crypto.WaitForSession(waitCtx, ev.RoomID, content.SenderKey, content.SessionID, 7*time.Second) {
					decrypted, err = m.crypto.Decrypt(ctx, ev)
				}
				cancel()
			}
			if err == nil && decrypted != nil {
				if body, ok := extractBody(decrypted); ok {
					return MatrixMessage{Sender: sender, Body: body, Timestamp: ts}, true
				}
			}
		}
		return MatrixMessage{Sender: sender, Body: "[Verschlüsselte Nachricht]", Timestamp: ts}, true
	default:
		return MatrixMessage{}, false
	}
}

func (m *MatrixClient) formatTimestamp(tsMillis int64) string {
	loc := m.TimeLocation
	if loc == nil {
		loc = time.Local
	}
	return time.UnixMilli(tsMillis).In(loc).Format("02.01.2006 15:04")
}

func extractBody(ev *event.Event) (string, bool) {
	if ev == nil {
		return "", false
	}
	_ = ev.Content.ParseRaw(ev.Type)
	msg := ev.Content.AsMessage()
	if msg.MsgType != event.MsgText && msg.MsgType != event.MsgNotice {
		return "", false
	}
	body := strings.TrimSpace(msg.Body)
	if body == "" {
		return "", false
	}
	return body, true
}

func shortMatrixSender(sender string) string {
	s := strings.TrimSpace(sender)
	if s == "" {
		return sender
	}
	if strings.HasPrefix(s, "@") {
		s = strings.TrimPrefix(s, "@")
	}
	if idx := strings.Index(s, ":"); idx > 0 {
		return s[:idx]
	}
	return s
}