package store

import (
	"context"
	"errors"
	"fmt"
	"time"

	"go.mongodb.org/mongo-driver/v2/bson"
	"go.mongodb.org/mongo-driver/v2/mongo"
	"go.mongodb.org/mongo-driver/v2/mongo/options"

	"bountyboard/internal/ulid"
)

// Conversation per §4.6.
type Conversation struct {
	ID             string    `bson:"_id" json:"id"`
	Kind           string    `bson:"kind" json:"kind"` // dm | group | project
	CustomerID     string    `bson:"customerId,omitempty" json:"customerId,omitempty"`
	Title          string    `bson:"title,omitempty" json:"title,omitempty"`
	CreatorID      string    `bson:"creatorId,omitempty" json:"creatorId,omitempty"`
	ParticipantIDs []string  `bson:"participantIds" json:"participantIds"`
	LastMessageAt  time.Time `bson:"lastMessageAt" json:"lastMessageAt"`
	CreatedAt      time.Time `bson:"createdAt" json:"createdAt"`
}

// MessageAttachment per §4.6.
type MessageAttachment struct {
	FileID   string `bson:"fileId" json:"fileId"`
	Name     string `bson:"name" json:"name"`
	MimeType string `bson:"mimeType" json:"mimeType"`
	Size     int64  `bson:"size" json:"size"`
	IsImage  bool   `bson:"isImage" json:"isImage"`
}

type ReadReceipt struct {
	UserID string    `bson:"userId" json:"userId"`
	At     time.Time `bson:"at" json:"at"`
}

type Message struct {
	ID             string              `bson:"_id" json:"id"`
	ConversationID string              `bson:"conversationId" json:"conversationId"`
	SenderID       string              `bson:"senderId" json:"senderId"`
	Body           string              `bson:"body" json:"body"` // sanitized rich text
	Attachments    []MessageAttachment `bson:"attachments" json:"attachments"`
	ReadBy         []ReadReceipt       `bson:"readBy" json:"readBy"`
	EditedAt       *time.Time          `bson:"editedAt" json:"editedAt"`
	DeletedAt      *time.Time          `bson:"deletedAt" json:"deletedAt"`
}

func (c *Conversation) HasParticipant(userID string) bool {
	for _, id := range c.ParticipantIDs {
		if id == userID {
			return true
		}
	}
	return false
}

// FindOrCreateDM returns the unique dm between two users, creating it on
// first contact (§4.6: participantIds is the dm unique key).
func (s *Store) FindOrCreateDM(ctx context.Context, a, b string) (*Conversation, error) {
	var conv Conversation
	err := s.DB.Collection("conversations").FindOne(ctx, bson.M{
		"kind":           "dm",
		"participantIds": bson.M{"$all": []string{a, b}, "$size": 2},
	}).Decode(&conv)
	if err == nil {
		return &conv, nil
	}
	if !errors.Is(err, mongo.ErrNoDocuments) {
		return nil, fmt.Errorf("find dm: %w", err)
	}
	conv = Conversation{
		ID: ulid.New(), Kind: "dm", ParticipantIDs: []string{a, b},
		LastMessageAt: time.Now().UTC(), CreatedAt: time.Now().UTC(),
	}
	if _, err := s.DB.Collection("conversations").InsertOne(ctx, conv); err != nil {
		return nil, fmt.Errorf("create dm: %w", err)
	}
	return &conv, nil
}

func (s *Store) CreateConversation(ctx context.Context, c *Conversation) error {
	c.ID = ulid.New()
	c.CreatedAt = time.Now().UTC()
	c.LastMessageAt = c.CreatedAt
	if _, err := s.DB.Collection("conversations").InsertOne(ctx, c); err != nil {
		return fmt.Errorf("create conversation: %w", err)
	}
	return nil
}

func (s *Store) ConversationByID(ctx context.Context, id string) (*Conversation, error) {
	var c Conversation
	err := s.DB.Collection("conversations").FindOne(ctx, bson.M{"_id": id}).Decode(&c)
	if errors.Is(err, mongo.ErrNoDocuments) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("find conversation: %w", err)
	}
	return &c, nil
}

// AddParticipant adds a user to a conversation (idempotent via $addToSet).
func (s *Store) AddParticipant(ctx context.Context, convID, userID string) error {
	_, err := s.DB.Collection("conversations").UpdateOne(ctx,
		bson.M{"_id": convID},
		bson.M{"$addToSet": bson.M{"participantIds": userID}})
	if err != nil {
		return fmt.Errorf("add participant: %w", err)
	}
	return nil
}

// RemoveParticipant removes a user from a conversation.
func (s *Store) RemoveParticipant(ctx context.Context, convID, userID string) error {
	_, err := s.DB.Collection("conversations").UpdateOne(ctx,
		bson.M{"_id": convID},
		bson.M{"$pull": bson.M{"participantIds": userID}})
	if err != nil {
		return fmt.Errorf("remove participant: %w", err)
	}
	return nil
}

func (s *Store) ListConversations(ctx context.Context, userID string) ([]Conversation, error) {
	cur, err := s.DB.Collection("conversations").Find(ctx,
		bson.M{"participantIds": userID},
		options.Find().SetSort(bson.D{{Key: "lastMessageAt", Value: -1}}).SetLimit(100))
	if err != nil {
		return nil, fmt.Errorf("list conversations: %w", err)
	}
	out := []Conversation{}
	if err := cur.All(ctx, &out); err != nil {
		return nil, fmt.Errorf("decode conversations: %w", err)
	}
	return out, nil
}

// UnreadCounts returns per-conversation unread message counts for the user.
func (s *Store) UnreadCounts(ctx context.Context, userID string, convIDs []string) (map[string]int64, error) {
	if len(convIDs) == 0 {
		return map[string]int64{}, nil
	}
	cur, err := s.DB.Collection("messages").Aggregate(ctx, mongo.Pipeline{
		{{Key: "$match", Value: bson.M{
			"conversationId": bson.M{"$in": convIDs},
			"senderId":       bson.M{"$ne": userID},
			"deletedAt":      nil,
			"readBy.userId":  bson.M{"$ne": userID},
		}}},
		{{Key: "$group", Value: bson.M{"_id": "$conversationId", "n": bson.M{"$sum": 1}}}},
	})
	if err != nil {
		return nil, fmt.Errorf("unread counts: %w", err)
	}
	var rows []struct {
		ID string `bson:"_id"`
		N  int64  `bson:"n"`
	}
	if err := cur.All(ctx, &rows); err != nil {
		return nil, fmt.Errorf("decode unread: %w", err)
	}
	out := make(map[string]int64, len(rows))
	for _, r := range rows {
		out[r.ID] = r.N
	}
	return out, nil
}

// InsertMessage stores the message and bumps the conversation timestamp.
func (s *Store) InsertMessage(ctx context.Context, m *Message) error {
	m.ID = ulid.New()
	if m.Attachments == nil {
		m.Attachments = []MessageAttachment{}
	}
	m.ReadBy = []ReadReceipt{{UserID: m.SenderID, At: time.Now().UTC()}}
	if _, err := s.DB.Collection("messages").InsertOne(ctx, m); err != nil {
		return fmt.Errorf("insert message: %w", err)
	}
	_, err := s.DB.Collection("conversations").UpdateOne(ctx,
		bson.M{"_id": m.ConversationID},
		bson.M{"$set": bson.M{"lastMessageAt": time.Now().UTC()}})
	if err != nil {
		return fmt.Errorf("bump conversation: %w", err)
	}
	return nil
}

// ListMessages returns up to limit messages older than cursor (ULID order),
// newest last.
func (s *Store) ListMessages(ctx context.Context, convID, cursor string, limit int) ([]Message, error) {
	if limit <= 0 || limit > 100 {
		limit = 50
	}
	q := bson.M{"conversationId": convID}
	if cursor != "" {
		q["_id"] = bson.M{"$lt": cursor}
	}
	cur, err := s.DB.Collection("messages").Find(ctx, q,
		options.Find().SetSort(bson.D{{Key: "_id", Value: -1}}).SetLimit(int64(limit)))
	if err != nil {
		return nil, fmt.Errorf("list messages: %w", err)
	}
	out := []Message{}
	if err := cur.All(ctx, &out); err != nil {
		return nil, fmt.Errorf("decode messages: %w", err)
	}
	// reverse to chronological order
	for i, j := 0, len(out)-1; i < j; i, j = i+1, j-1 {
		out[i], out[j] = out[j], out[i]
	}
	return out, nil
}

// MarkConversationRead adds a read receipt to every unread message.
func (s *Store) MarkConversationRead(ctx context.Context, convID, userID string) (int64, error) {
	res, err := s.DB.Collection("messages").UpdateMany(ctx,
		bson.M{
			"conversationId": convID,
			"readBy.userId":  bson.M{"$ne": userID},
		},
		bson.M{"$push": bson.M{"readBy": ReadReceipt{UserID: userID, At: time.Now().UTC()}}})
	if err != nil {
		return 0, fmt.Errorf("mark read: %w", err)
	}
	return res.ModifiedCount, nil
}

// UserCanAccessChatFile checks the file is attached to a message in one of
// the user's conversations.
func (s *Store) UserCanAccessChatFile(ctx context.Context, userID, fileID string) (bool, error) {
	var msg Message
	err := s.DB.Collection("messages").FindOne(ctx,
		bson.M{"attachments.fileId": fileID}).Decode(&msg)
	if errors.Is(err, mongo.ErrNoDocuments) {
		return false, nil
	}
	if err != nil {
		return false, fmt.Errorf("find file message: %w", err)
	}
	conv, err := s.ConversationByID(ctx, msg.ConversationID)
	if err != nil {
		return false, err
	}
	return conv.HasParticipant(userID), nil
}