package api

import (
	"encoding/json"
	"net/http"
	"strconv"
	"strings"
	"time"

	"messenger/internal/realtime"
	"messenger/internal/store"
)

type conversationJSON struct {
	ID          int64        `json:"id"`
	Type        string       `json:"type"`
	Name        string       `json:"name"`
	Avatar      string       `json:"avatar"`
	CreatedAt   time.Time    `json:"created_at"`
	LastMessage *messageJSON `json:"last_message,omitempty"`
	UnreadCount int64        `json:"unread_count"`
}

type memberJSON struct {
	User     userJSON  `json:"user"`
	Role     string    `json:"role"`
	JoinedAt time.Time `json:"joined_at"`
}

type messageJSON struct {
	ID             int64          `json:"id"`
	ConversationID int64          `json:"conversation_id"`
	SenderID       int64          `json:"sender_id"`
	Body           string         `json:"body"`
	Reactions      []reactionJSON `json:"reactions"`
	Media          *mediaJSON     `json:"media,omitempty"`
	CreatedAt      time.Time      `json:"created_at"`
	EditedAt       *time.Time     `json:"edited_at,omitempty"`
	DeletedAt      *time.Time     `json:"deleted_at,omitempty"`
}

type reactionJSON struct {
	Emoji  string `json:"emoji"`
	UserID int64  `json:"user_id"`
}

func toMessageJSON(m *store.Message) messageJSON {
	return messageJSON{
		ID:             m.ID,
		ConversationID: m.ConversationID,
		SenderID:       m.SenderID,
		Body:           m.Body,
		Reactions:      []reactionJSON{},
		CreatedAt:      m.CreatedAt,
		EditedAt:       m.EditedAt,
		DeletedAt:      m.DeletedAt,
	}
}

func attachReactions(msgs []messageJSON, reactions []store.Reaction) {
	byMessage := make(map[int64][]reactionJSON)
	for _, r := range reactions {
		byMessage[r.MessageID] = append(byMessage[r.MessageID], reactionJSON{Emoji: r.Emoji, UserID: r.UserID})
	}
	for i := range msgs {
		if rs, ok := byMessage[msgs[i].ID]; ok {
			msgs[i].Reactions = rs
		}
	}
}

func (h *apiHandler) listConversations(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	summaries, err := h.store.ListConversationsForUser(r.Context(), userID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	out := make([]conversationJSON, 0, len(summaries))
	for _, s := range summaries {
		item := conversationJSON{
			ID:          s.ID,
			Type:        s.Type,
			Name:        s.Name,
			Avatar:      s.Avatar,
			CreatedAt:   s.CreatedAt,
			UnreadCount: s.UnreadCount,
		}
		if s.LastMessage != nil {
			msg := toMessageJSON(s.LastMessage)
			item.LastMessage = &msg
		}
		out = append(out, item)
	}
	writeJSON(w, http.StatusOK, out)
}

type createConversationRequest struct {
	Type      string  `json:"type"`
	UserID    int64   `json:"user_id"`
	Name      string  `json:"name"`
	MemberIDs []int64 `json:"member_ids"`
}

func (h *apiHandler) createConversation(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	var req createConversationRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}

	if req.Type == "group" || req.Name != "" {
		h.createGroup(w, r, userID, req)
		return
	}

	if req.UserID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid user_id")
		return
	}
	if req.UserID == userID {
		writeError(w, http.StatusBadRequest, "cannot chat with yourself")
		return
	}
	conv, err := h.store.CreateDM(r.Context(), userID, req.UserID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	writeJSON(w, http.StatusCreated, conversationJSON{
		ID: conv.ID, Type: conv.Type, Name: conv.Name, Avatar: conv.Avatar, CreatedAt: conv.CreatedAt,
	})
}

func (h *apiHandler) createGroup(w http.ResponseWriter, r *http.Request, userID int64, req createConversationRequest) {
	name := strings.TrimSpace(req.Name)
	if name == "" || len(name) > 64 {
		writeError(w, http.StatusBadRequest, "name must be 1-64 chars")
		return
	}
	for _, uid := range req.MemberIDs {
		if uid == userID {
			continue
		}
		if _, err := h.store.GetUserByID(r.Context(), uid); err != nil {
			writeError(w, http.StatusBadRequest, "invalid member_id")
			return
		}
	}
	conv, err := h.store.CreateGroup(r.Context(), userID, name, req.MemberIDs)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	h.hub.Subscribe(userID, conv.ID)
	for _, uid := range req.MemberIDs {
		if uid == userID {
			continue
		}
		h.hub.Subscribe(uid, conv.ID)
		h.hub.SendToUser(uid, realtime.EventConversationAdded, realtime.ConversationChanged{ConversationID: conv.ID})
	}
	writeJSON(w, http.StatusCreated, conversationJSON{
		ID: conv.ID, Type: conv.Type, Name: conv.Name, Avatar: conv.Avatar, CreatedAt: conv.CreatedAt,
	})
}

func (h *apiHandler) listMembers(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil || convID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid conversation id")
		return
	}
	if member, err := h.store.IsMember(r.Context(), convID, userID); err != nil || !member {
		writeError(w, http.StatusForbidden, "not a member")
		return
	}
	members, err := h.store.ListMembers(r.Context(), convID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	out := make([]memberJSON, 0, len(members))
	for _, m := range members {
		out = append(out, memberJSON{User: toUserJSON(&m.User), Role: m.Role, JoinedAt: m.JoinedAt})
	}
	writeJSON(w, http.StatusOK, out)
}

func (h *apiHandler) addMember(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil || convID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid conversation id")
		return
	}
	if member, err := h.store.IsMember(r.Context(), convID, userID); err != nil || !member {
		writeError(w, http.StatusForbidden, "not a member")
		return
	}
	conv, err := h.store.GetConversationByID(r.Context(), convID)
	if err != nil {
		writeError(w, http.StatusNotFound, "conversation not found")
		return
	}
	if conv.Type != "group" {
		writeError(w, http.StatusBadRequest, "only groups support members")
		return
	}
	var req struct {
		UserID int64 `json:"user_id"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || req.UserID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid user_id")
		return
	}
	if _, err := h.store.GetUserByID(r.Context(), req.UserID); err != nil {
		writeError(w, http.StatusNotFound, "user not found")
		return
	}
	if err := h.store.AddMember(r.Context(), convID, req.UserID); err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	h.hub.Subscribe(req.UserID, convID)
	h.hub.SendToUser(req.UserID, realtime.EventConversationAdded, realtime.ConversationChanged{ConversationID: convID})
	h.hub.PublishMemberChanged(convID, req.UserID, true)
	writeJSON(w, http.StatusCreated, map[string]string{"status": "ok"})
}

func (h *apiHandler) removeMember(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil || convID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid conversation id")
		return
	}
	targetID, err := strconv.ParseInt(r.PathValue("user_id"), 10, 64)
	if err != nil || targetID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid user_id")
		return
	}

	requesterRole, err := h.store.MemberRole(r.Context(), convID, userID)
	if err != nil {
		writeError(w, http.StatusForbidden, "not a member")
		return
	}
	targetRole, err := h.store.MemberRole(r.Context(), convID, targetID)
	if err != nil {
		writeError(w, http.StatusNotFound, "member not found")
		return
	}
	if targetRole == "owner" {
		writeError(w, http.StatusBadRequest, "cannot remove the owner")
		return
	}
	if userID != targetID && requesterRole != "owner" {
		writeError(w, http.StatusForbidden, "only the owner can remove others")
		return
	}

	if err := h.store.RemoveMember(r.Context(), convID, targetID); err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	h.hub.Unsubscribe(targetID, convID)
	h.hub.SendToUser(targetID, realtime.EventConversationRemoved, realtime.ConversationChanged{ConversationID: convID})
	h.hub.PublishMemberChanged(convID, targetID, false)
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (h *apiHandler) listMessages(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil || convID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid conversation id")
		return
	}
	member, err := h.store.IsMember(r.Context(), convID, userID)
	if err != nil || !member {
		writeError(w, http.StatusForbidden, "not a member")
		return
	}

	limit := 50
	if v := r.URL.Query().Get("limit"); v != "" {
		if n, err := strconv.Atoi(v); err == nil && n > 0 && n <= 100 {
			limit = n
		}
	}
	var before int64
	if v := r.URL.Query().Get("before"); v != "" {
		before, _ = strconv.ParseInt(v, 10, 64)
	}

	messages, err := h.store.ListMessages(r.Context(), convID, before, limit)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	out := make([]messageJSON, 0, len(messages))
	msgIDs := make([]int64, 0, len(messages))
	mediaIDs := make(map[int64]struct{})
	for i := range messages {
		out = append(out, toMessageJSON(&messages[i]))
		msgIDs = append(msgIDs, messages[i].ID)
		if messages[i].MediaID != nil {
			mediaIDs[*messages[i].MediaID] = struct{}{}
		}
	}
	reactions, err := h.store.ReactionsForMessages(r.Context(), msgIDs)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	attachReactions(out, reactions)

	mediaByID := make(map[int64]mediaJSON)
	for id := range mediaIDs {
		m, err := h.store.GetMediaByID(r.Context(), id)
		if err == nil {
			mediaByID[id] = toMediaJSON(m)
		}
	}
	for i := range out {
		for j := range messages {
			if messages[j].ID == out[i].ID && messages[j].MediaID != nil {
				if md, ok := mediaByID[*messages[j].MediaID]; ok {
					out[i].Media = &md
				}
				break
			}
		}
	}
	writeJSON(w, http.StatusOK, out)
}

type sendMessageRequest struct {
	Body    string `json:"body"`
	TempID  string `json:"temp_id"`
	MediaID *int64 `json:"media_id,omitempty"`
}

func (h *apiHandler) sendMessage(w http.ResponseWriter, r *http.Request) {
	userID, _ := userIDFrom(r.Context())
	convID, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil || convID <= 0 {
		writeError(w, http.StatusBadRequest, "invalid conversation id")
		return
	}
	member, err := h.store.IsMember(r.Context(), convID, userID)
	if err != nil || !member {
		writeError(w, http.StatusForbidden, "not a member")
		return
	}

	var req sendMessageRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "invalid json")
		return
	}
	if req.Body == "" && req.MediaID == nil {
		writeError(w, http.StatusBadRequest, "body or media_id is required")
		return
	}
	if len(req.Body) > 4000 {
		writeError(w, http.StatusBadRequest, "body too long (max 4000)")
		return
	}

	var attached *store.Media
	if req.MediaID != nil {
		attached, err = h.store.GetMediaByID(r.Context(), *req.MediaID)
		if err != nil || attached.UploaderID != userID {
			writeError(w, http.StatusBadRequest, "invalid media_id")
			return
		}
	}

	msg, err := h.store.InsertMessage(r.Context(), convID, userID, req.Body, req.MediaID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	wsEvent := realtime.MessageCreated{
		TempID:         req.TempID,
		ConversationID: convID,
		MessageID:      msg.ID,
		SenderID:       userID,
		Body:           msg.Body,
		CreatedAt:      msg.CreatedAt,
	}
	if attached != nil {
		wsEvent.MediaID = &attached.ID
		info := toRealtimeMedia(attached)
		wsEvent.Media = &info
	}
	h.hub.PublishMessageCreated(convID, wsEvent)

	out := toMessageJSON(msg)
	if attached != nil {
		md := toMediaJSON(attached)
		out.Media = &md
	}
	writeJSON(w, http.StatusCreated, out)
}

func toRealtimeMedia(m *store.Media) realtime.MediaInfo {
	return realtime.MediaInfo{
		ID:          m.ID,
		Filename:    m.Filename,
		ContentType: m.ContentType,
		Size:        m.Size,
		URL:         "/api/v1/media/" + strconv.FormatInt(m.ID, 10),
	}
}