package syncapi

import (
	"cmp"
	"context"
	"encoding/json"
	"fmt"
	"slices"

	"github.com/dariuszjaniak/warp/server/internal/matrix/event"
	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// The receipt types the Client-Server API defines.
const (
	// ReceiptRead is public: everybody in the room sees it.
	ReceiptRead = "m.read"

	// ReceiptReadPrivate is the user's own, and is reported only back to
	// them. It exists so that a user can mark a room read without telling
	// the room they read it.
	ReceiptReadPrivate = "m.read.private"

	// ReceiptFullyRead is not a receipt at all: it is the read marker, and
	// is stored as the room account data type m.fully_read. It is named
	// here because POST /read_markers takes all three in one body.
	ReceiptFullyRead = "m.fully_read"
)

// requireJoined refuses a caller who is not in the room.
//
// Every write in this file is a claim about a room — "I am typing in it",
// "I have read this far" — rather than data belonging to the caller, so
// being in the room is the condition for all of them.
func (s *API) requireJoined(ctx context.Context, roomID, userID string) error {
	membership, err := s.rooms.Membership(ctx, roomID, userID)
	if err != nil {
		return err
	}
	if membership != event.MembershipJoin {
		return errForbiddenf("%s is not joined to %s", userID, roomID)
	}
	return nil
}

// ReceiptRequest is POST /rooms/{roomID}/receipt/{receiptType}/{eventID}.
type ReceiptRequest struct {
	RoomID string

	// User is the full user ID sending the receipt.
	User string

	ReceiptType string
	EventID     string

	// ThreadID is the thread the receipt is for, or empty for the room's
	// main timeline. Threads are PLAN.md phase 10; the value is stored so
	// that a client that sends one gets it back, rather than having its
	// threaded receipt silently collapse onto the main timeline's.
	ThreadID string
}

// SetReceipt records a read receipt.
func (s *API) SetReceipt(ctx context.Context, req ReceiptRequest) error {
	switch req.ReceiptType {
	case ReceiptRead, ReceiptReadPrivate, ReceiptFullyRead:
	default:
		return errInvalidParamf("%q is not a receipt type this server accepts", req.ReceiptType)
	}

	if err := s.requireJoined(ctx, req.RoomID, req.User); err != nil {
		return err
	}

	// The spec routes m.fully_read through this endpoint too, and it is
	// account data rather than a receipt — but it is still a claim about a
	// room the caller has to be in, which is why the check above comes
	// first.
	if req.ReceiptType == ReceiptFullyRead {
		return s.setFullyRead(ctx, req.RoomID, req.User, req.EventID)
	}

	_, moved, err := s.store.SetReceipt(ctx, storage.Receipt{
		RoomID:      req.RoomID,
		UserID:      req.User,
		ReceiptType: req.ReceiptType,
		ThreadID:    req.ThreadID,
		EventID:     req.EventID,
		TimestampMS: s.nowMS(),
	})
	if err != nil {
		return err
	}

	// Nothing moved means the user had already read further, and there is
	// nothing for anybody to be woken about.
	if !moved {
		return nil
	}
	// A private receipt concerns only its sender; a public one is part of
	// the room's ephemeral stream and everybody in it wants it.
	if req.ReceiptType == ReceiptReadPrivate {
		s.notifier.NotifyUser(req.User)
		return nil
	}
	s.notifier.NotifyRoom(req.RoomID)
	return nil
}

// ReadMarkersRequest is POST /rooms/{roomID}/read_markers.
type ReadMarkersRequest struct {
	RoomID string
	User   string

	// FullyRead is the event up to which the user has read, stored as the
	// room account data m.fully_read. It is where a client draws the
	// "unread from here" line, which is a different thing from a receipt:
	// the line stays where the user left it even as they scroll past.
	FullyRead string

	// Read and ReadPrivate are ordinary receipts, sent in the same request
	// because a client moving the marker almost always moves both.
	Read        string
	ReadPrivate string
}

// SetReadMarkers implements the read markers endpoint: up to three
// independent writes from one request.
//
// They are not atomic, and cannot usefully be: the marker is account data
// and the receipts are the receipt stream, which are two streams with two
// positions. A failure partway through leaves the earlier writes in place,
// which is the same state a client would reach by sending them separately
// and losing its connection — and which the next call corrects.
func (s *API) SetReadMarkers(ctx context.Context, req ReadMarkersRequest) error {
	if err := s.requireJoined(ctx, req.RoomID, req.User); err != nil {
		return err
	}

	if req.FullyRead != "" {
		if err := s.setFullyRead(ctx, req.RoomID, req.User, req.FullyRead); err != nil {
			return err
		}
	}
	for _, receipt := range []struct {
		receiptType string
		eventID     string
	}{
		{ReceiptRead, req.Read},
		{ReceiptReadPrivate, req.ReadPrivate},
	} {
		if receipt.eventID == "" {
			continue
		}
		if err := s.SetReceipt(ctx, ReceiptRequest{
			RoomID:      req.RoomID,
			User:        req.User,
			ReceiptType: receipt.receiptType,
			EventID:     receipt.eventID,
		}); err != nil {
			return err
		}
	}
	return nil
}

// setFullyRead writes the read marker as room account data.
func (s *API) setFullyRead(ctx context.Context, roomID, userID, eventID string) error {
	localpart, ok := s.localpartOf(userID)
	if !ok {
		return errForbiddenf("%s is not a user of this server", userID)
	}
	content, err := json.Marshal(map[string]string{"event_id": eventID})
	if err != nil {
		return fmt.Errorf("marshalling the read marker: %w", err)
	}
	if err := s.accounts.SetAccountData(ctx, localpart, roomID, ReceiptFullyRead, content); err != nil {
		return err
	}
	s.notifier.NotifyUser(userID)
	return nil
}

// receiptsEvent builds the m.receipt EDU of one room.
//
// The shape is the spec's, and it is an awkward one: a map of event ID to
// receipt type to user ID to the receipt's data. It is nested that way
// because a client's job is to answer "who has read up to this event",
// which this shape makes a lookup and a flat list would make a scan.
func receiptsEvent(receipts []storage.Receipt) *EphemeralEvent {
	if len(receipts) == 0 {
		return nil
	}

	type receiptData struct {
		TS       int64  `json:"ts"`
		ThreadID string `json:"thread_id,omitempty"`
	}
	content := map[string]map[string]map[string]receiptData{}
	for _, r := range receipts {
		byType, ok := content[r.EventID]
		if !ok {
			byType = map[string]map[string]receiptData{}
			content[r.EventID] = byType
		}
		byUser, ok := byType[r.ReceiptType]
		if !ok {
			byUser = map[string]receiptData{}
			byType[r.ReceiptType] = byUser
		}
		byUser[r.UserID] = receiptData{TS: r.TimestampMS, ThreadID: r.ThreadID}
	}

	body, err := json.Marshal(content)
	if err != nil {
		// Every value here is a string or an integer, so this cannot
		// happen; dropping the EDU beats failing the sync if it does.
		return nil
	}
	return &EphemeralEvent{Type: "m.receipt", Content: body}
}

// roomReceipts reads the receipts a user is entitled to see in a set of
// rooms, between two positions.
//
// Private receipts are filtered here rather than in SQL: the query is the
// same one the public receipts come from, and a WHERE clause that had to
// name the asking user would turn one query per sync into two.
func (s *API) roomReceipts(ctx context.Context, userID string, roomIDs []string, from, to int64) (map[string][]storage.Receipt, error) {
	if len(roomIDs) == 0 {
		return nil, nil
	}
	receipts, err := s.store.Receipts(ctx, roomIDs, from, to)
	if err != nil {
		return nil, err
	}
	// An initial sync also wants the user's own receipts however old they
	// are: a client that has just logged in has to know where it had read
	// up to, and that receipt was set long before this sync's window.
	if from == 0 {
		own, err := s.store.ReceiptsForUser(ctx, userID, roomIDs)
		if err != nil {
			return nil, err
		}
		receipts = append(receipts, own...)
	}

	out := map[string][]storage.Receipt{}
	seen := map[storage.Receipt]struct{}{}
	for _, r := range receipts {
		if r.ReceiptType == ReceiptReadPrivate && r.UserID != userID {
			continue
		}
		if _, dup := seen[r]; dup {
			// The user's own receipts can arrive from both reads above.
			continue
		}
		seen[r] = struct{}{}
		out[r.RoomID] = append(out[r.RoomID], r)
	}
	for roomID := range out {
		slices.SortFunc(out[roomID], func(a, b storage.Receipt) int {
			return cmp.Compare(a.StreamPos, b.StreamPos)
		})
	}
	return out, nil
}