import { writable, derived } from 'svelte/store';
import type { Session, SessionMetadata } from '$lib/types/api';
import type { SessionListItem } from '$lib/types/client';
import { apiClient } from '$lib/services/api';
import { STORAGE_KEY_ACTIVE_SESSION } from '$lib/utils/constants';
import { getItem, setItem, removeItem } from '$lib/services/storage';

/**
 * Session store managing user's chat sessions
 * Handles session list, active session, and CRUD operations
 */

interface SessionState {
	sessions: SessionListItem[]; // List of user sessions (metadata only)
	activeSession: Session | null; // Currently loaded session with full messages
	loading: boolean;
	error: string | null;
}

function createInitialState(): SessionState {
	return {
		sessions: [],
		activeSession: null,
		loading: false,
		error: null
	};
}

// Create the session store
function createSessionStore() {
	const { subscribe, set, update } = writable<SessionState>(createInitialState());

	return {
		subscribe,

		/**
		 * Load all sessions for current user
		 */
		async loadSessions() {
			update((state) => ({ ...state, loading: true, error: null }));

			try {
				const sessions = await apiClient.listSessions();

				// Convert to SessionListItem format (convert Unix timestamps to ISO strings)
				const sessionList: SessionListItem[] = sessions.map((s) => ({
					id: s.id,
					title: s.title,
					last_interaction: new Date(s.last_interaction * 1000).toISOString(),
					message_count: s.message_count,
					is_reference: s.is_reference,
					is_active: false
				}));

				update((state) => ({
					...state,
					sessions: sessionList,
					loading: false
				}));
			} catch (err) {
				const errorMessage = err instanceof Error ? err.message : 'Failed to load sessions';
				update((state) => ({
					...state,
					loading: false,
					error: errorMessage
				}));
			}
		},

		/**
		 * Create a new session
		 */
		async createSession(title: string): Promise<string | null> {
			update((state) => ({ ...state, loading: true, error: null }));

			try {
				const response = await apiClient.createSession(title);
				const newSessionId = response.session_id;

				// Add to session list
				const newSession: SessionListItem = {
					id: newSessionId,
					title,
					last_interaction: new Date().toISOString(),
					message_count: 0,
					is_reference: false,
					is_active: false
				};

				update((state) => ({
					...state,
					sessions: [newSession, ...state.sessions],
					loading: false
				}));

				return newSessionId;
			} catch (err) {
				const errorMessage = err instanceof Error ? err.message : 'Failed to create session';
				update((state) => ({
					...state,
					loading: false,
					error: errorMessage
				}));
				return null;
			}
		},

		/**
		 * Load a specific session with messages
		 */
		async loadSession(sessionId: string) {
			update((state) => ({ ...state, loading: true, error: null }));

			try {
				const session = await apiClient.getSession(sessionId);

				// Mark as active in session list
				update((state) => ({
					...state,
					sessions: state.sessions.map((s) => ({
						...s,
						is_active: s.id === sessionId
					})),
					activeSession: session,
					loading: false
				}));

				// Persist active session ID
				setItem(STORAGE_KEY_ACTIVE_SESSION, sessionId);
			} catch (err) {
				const errorMessage = err instanceof Error ? err.message : 'Failed to load session';
				update((state) => ({
					...state,
					loading: false,
					error: errorMessage
				}));
			}
		},

		/**
		 * Delete a session
		 */
		async deleteSession(sessionId: string): Promise<boolean> {
			update((state) => ({ ...state, loading: true, error: null }));

			try {
				await apiClient.deleteSession(sessionId);

				update((state) => {
					const newState = {
						...state,
						sessions: state.sessions.filter((s) => s.id !== sessionId),
						loading: false
					};

					// Clear active session if it was deleted
					if (state.activeSession?.id === sessionId) {
						newState.activeSession = null;
						removeItem(STORAGE_KEY_ACTIVE_SESSION);
					}

					return newState;
				});

				return true;
			} catch (err) {
				const errorMessage = err instanceof Error ? err.message : 'Failed to delete session';
				update((state) => ({
					...state,
					loading: false,
					error: errorMessage
				}));
				return false;
			}
		},

		/**
		 * Update session reference flag
		 */
		async updateSessionReference(sessionId: string, isReference: boolean): Promise<boolean> {
			update((state) => ({ ...state, loading: true, error: null }));

			try {
				await apiClient.updateSession(sessionId, isReference);

				update((state) => ({
					...state,
					sessions: state.sessions.map((s) =>
						s.id === sessionId ? { ...s, is_reference: isReference } : s
					),
					activeSession:
						state.activeSession?.id === sessionId
							? { ...state.activeSession, is_reference: isReference }
							: state.activeSession,
					loading: false
				}));

				return true;
			} catch (err) {
				const errorMessage = err instanceof Error ? err.message : 'Failed to update session';
				update((state) => ({
					...state,
					loading: false,
					error: errorMessage
				}));
				return false;
			}
		},

		/**
		 * Clear active session
		 */
		clearActive() {
			update((state) => ({
				...state,
				activeSession: null
			}));
			removeItem(STORAGE_KEY_ACTIVE_SESSION);
		},

		/**
		 * Send a message to the active session
		 */
		async sendMessage(
			sessionId: string,
			content: string,
			mode: string
		): Promise<boolean> {
			update((state) => ({ ...state, loading: true, error: null }));

			try {
				const response = await apiClient.sendMessage(sessionId, {
					mode: mode as any,
					message: content,
					save_to_memory: mode === 'memorize'
				});

				// Update active session with new message
				update((state) => {
					if (state.activeSession?.id === sessionId) {
						return {
							...state,
							activeSession: {
								...state.activeSession,
								messages: [
									...state.activeSession.messages,
									{
										mode: mode as any,
										content,
										created_at: new Date().toISOString()
									}
								],
								last_interaction: new Date().toISOString()
							},
							sessions: state.sessions.map((s) =>
								s.id === sessionId
									? {
											...s,
											message_count: s.message_count + 1,
											last_interaction: new Date().toISOString()
										}
									: s
							),
							loading: false
						};
					}
					return { ...state, loading: false };
				});

				return true;
			} catch (err) {
				const errorMessage = err instanceof Error ? err.message : 'Failed to send message';
				update((state) => ({
					...state,
					loading: false,
					error: errorMessage
				}));
				return false;
			}
		},

		/**
		 * Clear error
		 */
		clearError() {
			update((state) => ({ ...state, error: null }));
		}
	};
}

export const sessionStore = createSessionStore();

// Derived stores
export const activeSessions = derived(sessionStore, ($session) => $session.sessions);

export const activeSession = derived(sessionStore, ($session) => $session.activeSession);

export const sessionCount = derived(sessionStore, ($session) => $session.sessions.length);

export const isLoading = derived(sessionStore, ($session) => $session.loading);

export const sessionError = derived(sessionStore, ($session) => $session.error);