package pushserver

import (
	"context"
	"encoding/json"
	"errors"
	"strconv"

	"github.com/dariuszjaniak/warp/server/internal/roomserver"
	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// Receipt types that move the counts. A private receipt is still the
// user saying they have read up to here; it is private from other users,
// not from the user's own badge.
const (
	receiptRead        = "m.read"
	receiptReadPrivate = "m.read.private"

	// threadMain is the thread ID of a receipt for the main timeline.
	threadMain = "main"
)

// ReceiptSet is told about a read receipt a local user set, and clears
// their notifications in the room up to the event it names.
//
// Notifications are filed by thread, and a receipt reads the part of the
// room it is for: thread_id "main" the main timeline, a thread root's ID
// that thread, and no thread_id the whole room. Reading one thread leaves
// the main timeline and the other threads unread, and a client that does
// not know about threads sends unthreaded receipts and keeps clearing the
// room as a whole, as before threads.
func (a *API) ReceiptSet(ctx context.Context, userID, roomID, receiptType, threadID, eventID string) {
	if receiptType != receiptRead && receiptType != receiptReadPrivate {
		return
	}
	thread := receiptThread(threadID)
	pos, err := a.rooms.EventPosition(ctx, roomID, userID, eventID)
	if err != nil {
		// A receipt for an event this server does not have — or one the
		// user cannot see — reads nothing.
		if !errors.Is(err, roomserver.ErrNoSuchEvent) && !errors.Is(err, roomserver.ErrForbidden) {
			a.log.Warn("locating a receipt's event failed",
				"user_id", userID, "room_id", roomID, "event_id", eventID, "error", err)
		}
		return
	}
	if err := a.markRead(ctx, userID, roomID, thread, pos); err != nil {
		a.log.Warn("clearing notifications on a receipt failed",
			"user_id", userID, "room_id", roomID, "error", err)
	}
}

// receiptThread is the part of a room a receipt's thread_id reads, as the
// store names it.
func receiptThread(threadID string) string {
	switch threadID {
	case "":
		return storage.AllThreads
	case threadMain:
		return storage.ThreadMain
	}
	return threadID
}

// markRead clears a user's notifications in a room, or in one thread of
// it, up to a position, and wakes their syncs if the counts moved.
func (a *API) markRead(ctx context.Context, userID, roomID, thread string, upTo int64) error {
	_, moved, err := a.store.MarkNotificationsRead(ctx, userID, roomID, thread, upTo)
	if err != nil {
		return err
	}
	if moved {
		a.notifyUsers(userID)
	}
	return nil
}

// NotificationCounts reads a user's unread counts in the given rooms.
func (a *API) NotificationCounts(ctx context.Context, userID string, roomIDs []string) (map[string]storage.NotificationCounts, error) {
	return a.store.NotificationCounts(ctx, userID, roomIDs)
}

// ThreadNotificationCounts reads a user's unread counts in the given rooms
// per thread, with the main timeline under storage.ThreadMain.
func (a *API) ThreadNotificationCounts(ctx context.Context, userID string, roomIDs []string) (map[string]map[string]storage.NotificationCounts, error) {
	return a.store.ThreadNotificationCounts(ctx, userID, roomIDs)
}

// NotificationCountChanges lists the rooms whose counts for a user moved
// in a window of the notification stream.
func (a *API) NotificationCountChanges(ctx context.Context, userID string, from, to int64) ([]string, error) {
	return a.store.NotificationCountChanges(ctx, userID, from, to)
}

// Notification is one entry of GET /notifications.
type Notification struct {
	Actions    []json.RawMessage      `json:"actions"`
	Event      roomserver.ClientEvent `json:"event"`
	ProfileTag string                 `json:"profile_tag,omitempty"`
	Read       bool                   `json:"read"`
	RoomID     string                 `json:"room_id"`
	TS         int64                  `json:"ts"`
}

// NotificationsRequest is GET /notifications.
type NotificationsRequest struct {
	UserID string

	// From is the next_token of an earlier page, or empty for the newest.
	From string

	Limit         int
	OnlyHighlight bool
}

// Limits on a page of notifications.
const (
	DefaultNotificationsLimit = 20
	MaxNotificationsLimit     = 100
)

// ErrInvalidFrom is a from token that is not one this server handed out.
var ErrInvalidFrom = errors.New("invalid pagination token")

// Notifications pages through a user's notifications, newest first. It
// returns the page and the token for the next one, which is empty at the
// end.
func (a *API) Notifications(ctx context.Context, req NotificationsRequest) ([]Notification, string, error) {
	var before int64
	if req.From != "" {
		var err error
		if before, err = strconv.ParseInt(req.From, 10, 64); err != nil || before <= 0 {
			return nil, "", ErrInvalidFrom
		}
	}
	limit := req.Limit
	if limit <= 0 {
		limit = DefaultNotificationsLimit
	}
	limit = min(limit, MaxNotificationsLimit)

	stored, err := a.store.Notifications(ctx, req.UserID, before, limit, req.OnlyHighlight)
	if err != nil {
		return nil, "", err
	}

	out := make([]Notification, 0, len(stored))
	for _, n := range stored {
		ev, err := a.rooms.Event(ctx, n.RoomID, req.UserID, n.EventID)
		switch {
		case errors.Is(err, roomserver.ErrNoSuchEvent), errors.Is(err, roomserver.ErrNoSuchRoom),
			errors.Is(err, roomserver.ErrForbidden):
			// Purged, or no longer the user's to see: the notification
			// has nothing left to show.
			continue
		case err != nil:
			return nil, "", err
		}
		var actions []json.RawMessage
		if err := json.Unmarshal(n.Actions, &actions); err != nil {
			actions = []json.RawMessage{}
		}
		out = append(out, Notification{
			Actions: actions,
			Event:   ev,
			Read:    n.Read,
			RoomID:  n.RoomID,
			TS:      n.TimestampMS,
		})
	}

	var next string
	if len(stored) == limit {
		next = strconv.FormatInt(stored[len(stored)-1].ID, 10)
	}
	return out, next, nil
}