import {
	ADOPT_REASON_INVARIANT_FAILED,
	ADOPT_REASON_VALIDATION_FAILED,
	DEFAULT_BROADCAST_CHANNEL,
	ENGINE_METHOD_ADOPT,
	ENGINE_METHOD_ADOPT_SERVER,
	ENGINE_METHOD_CLEAR_LOCAL,
	ENGINE_METHOD_REFRESH,
	ENGINE_METHOD_REVOKE,
	EVENT_ADOPTED,
	EVENT_ADOPTED_SERVER,
	EVENT_EXPIRED,
	EVENT_EXTERNAL_CHANGED,
	EVENT_INITIAL_SESSION,
	EVENT_REFRESHED,
	EVENT_REFRESH_FAILED,
	EVENT_REVOKED,
	FIELD_ACTOR,
	FIELD_CREDENTIAL,
	FIELD_DATA,
	FIELD_USER,
	IDENTITY_ANONYMOUS,
	IDENTITY_IDENTIFIED,
	IDENTITY_NONE,
	REFRESH_STATUS_EXPIRED,
	REFRESH_STATUS_FAILED,
	REFRESH_STATUS_REFRESHED,
	REFRESH_STATUS_SKIPPED,
	REVOKE_REASON_MISSING_REVOKE_URL,
	REVOKE_REASON_NETWORK_ERROR,
	REVOKE_REASON_NO_SESSION,
	REVOKE_REASON_SERVER_REJECTED,
	REVOKE_SCOPE_GLOBAL,
	REVOKE_SCOPE_LOCAL,
	SESSION_DIAGNOSTIC_EVENTS,
	SKIP_REASON_NO_REFRESH_FN,
	SKIP_REASON_NO_SESSION,
	SKIP_REASON_STALE_GENERATION,
	adoptServerErrorMessage,
	disposedErrorMessage
} from './consts.ts';
import { createSessionDiagnostics, emitSessionDiagnostic } from './diagnostics.ts';
import { SessDisposedError, SessInvalidSessionError } from './errors.ts';
import {
	freezeSession,
	readField,
	sameSnapshot,
	toError
} from './session-helpers.ts';
import {
	createSessionBroadcastSync,
	hydrateSessionStorage,
	wireSessionStorageSync
} from './session-sync.ts';
import { checkSessionInvariants, validateSessionCandidate } from './session-validation.ts';
import type {
	AdoptResultField,
	EngineSession,
	EngineSessionOptions,
	RefreshResult,
	RevokeOptions,
	RevokeResult,
	Session,
	SessionActor,
	SessionChange,
	SessionIdentityState,
	SessionListener
} from './types.ts';

function refreshValidationDiagnosticEvent(field: AdoptResultField) {
	switch (field) {
		case FIELD_USER:
			return SESSION_DIAGNOSTIC_EVENTS.REFRESH_USER_SCHEMA_FAILED;
		case FIELD_CREDENTIAL:
			return SESSION_DIAGNOSTIC_EVENTS.REFRESH_CREDENTIAL_SCHEMA_FAILED;
		case FIELD_DATA:
			return SESSION_DIAGNOSTIC_EVENTS.REFRESH_DATA_SCHEMA_FAILED;
		case FIELD_ACTOR:
			return SESSION_DIAGNOSTIC_EVENTS.REFRESH_ACTOR_SCHEMA_FAILED;
	}
}

/**
 * Build a fresh `EngineSession`. Runes-free — safe to import from server-only
 * modules. The Active wrapper layers reactive state on top.
 *
 * Internally maintains:
 * - State cell (Session or null)
 * - `generation` counter incremented on every adopt/revoke/external change
 *   (guards stale refresh from any source)
 * - `refreshing` slot that dedupes concurrent `refresh()`
 * - Listener set with synchronous `INITIAL_SESSION` dispatch on subscribe
 * - Optional storage sync
 * - Optional `BroadcastChannel` (event + generation only — never tokens)
 */
export function createEngineSession<TUser, TCredential = undefined, TData = undefined>(
	options: EngineSessionOptions<TUser, TCredential, TData>
): EngineSession<TUser, TCredential, TData> {
	const { schemas, storage, onRefresh, onRevoke, logger } = options;
	const diagnostics = createSessionDiagnostics(logger);

	type Snap = Session<TUser, TCredential, TData>;

	let snapshot: Snap | null = null;
	let generation = 0;
	let refreshing: Promise<RefreshResult<TUser, TCredential, TData>> | null = null;
	let disposed = false;

	const listeners = new Set<SessionListener<TUser, TCredential, TData>>();
	const detachers: Array<() => void> = [];

	// ── Storage sync ────────────────────────────────────────────────────────

	if (storage !== undefined) {
		const promoted = hydrateSessionStorage<TUser, TCredential, TData>(storage, diagnostics);
		if (promoted !== null) snapshot = promoted;

		const detachStorage = wireSessionStorageSync<TUser, TCredential, TData>({
			storage,
			diagnostics,
			warnNoOnChange: logger !== undefined,
			applyExternalChange: (next) => {
				if (next !== null || snapshot !== null) applyExternalChange(next);
			}
		});
		if (detachStorage !== undefined) detachers.push(detachStorage);
	}

	// ── Cross-tab broadcast (event + generation only, never tokens) ─────────

	const channelName = options.broadcastChannel ?? DEFAULT_BROADCAST_CHANNEL;
	const broadcastSync = createSessionBroadcastSync<
		TUser,
		TCredential,
		TData,
		SessionChange<TUser, TCredential, TData>['event']
	>({
		channelName,
		storage,
		applyExternalChange: (next) => {
			if (next !== null || snapshot !== null) applyExternalChange(next);
		}
	});
	if (broadcastSync !== undefined) detachers.push(() => broadcastSync.detach());

	function broadcast(event: SessionChange<TUser, TCredential, TData>['event']): void {
		broadcastSync?.post(event, generation);
	}

	// ── State helpers ───────────────────────────────────────────────────────

	function computeIdentity(s: Snap | null): SessionIdentityState {
		if (s === null) return IDENTITY_NONE;
		return s.user === null ? IDENTITY_ANONYMOUS : IDENTITY_IDENTIFIED;
	}

	/**
	 * Apply a snapshot that came from outside this engine (storage event,
	 * BroadcastChannel). Dedups against the current snapshot so a storage
	 * event + a broadcast event for the same change only fire one
	 * `EXTERNAL_CHANGED`. Increments `generation` so refresh promises
	 * started before the external change cannot resurrect an old snapshot.
	 */
	function applyExternalChange(next: Snap | null): void {
		const prev = snapshot;
		if (sameSnapshot(prev, next)) return;
		const fromIdentity = computeIdentity(prev);
		generation += 1;
		snapshot = next;
		const toIdentity = computeIdentity(next);
		dispatch({
			event: EVENT_EXTERNAL_CHANGED,
			current: next,
			previous: prev,
			generation,
			identity: { from: fromIdentity, to: toIdentity }
		});
	}

	function persist(value: Snap | null): void {
		if (storage === undefined) return;
		try {
			if (value === null) {
				storage.adapter.removeItem(storage.key);
			} else {
				storage.adapter.setItem(storage.key, JSON.stringify(value));
			}
		} catch (err) {
			emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.STORAGE_PERSIST_FAILED, {
				error: toError(err)
			});
		}
	}

	function dispatch(change: SessionChange<TUser, TCredential, TData>): void {
		for (const listener of listeners) {
			try {
				listener(change);
			} catch (err) {
				emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.LISTENER_THREW, {
					error: toError(err),
					event: change.event
				});
			}
		}
	}

	function commitAdoption(
		next: Snap,
		event: typeof EVENT_ADOPTED | typeof EVENT_ADOPTED_SERVER | typeof EVENT_REFRESHED
	): void {
		const prev = snapshot;
		const fromIdentity = computeIdentity(prev);
		generation += 1;
		snapshot = next;
		persist(next);
		const toIdentity = computeIdentity(next);
		dispatch({
			event,
			current: next,
			previous: prev,
			generation,
			identity: { from: fromIdentity, to: toIdentity }
		});
		broadcast(event);
	}

	function commitRevocation(
		event: typeof EVENT_REVOKED | typeof EVENT_EXPIRED,
		revoke?: RevokeResult
	): void {
		const prev = snapshot;
		const fromIdentity = computeIdentity(prev);
		generation += 1;
		snapshot = null;
		persist(null);
		dispatch({
			event,
			current: null,
			previous: prev,
			generation,
			identity: { from: fromIdentity, to: IDENTITY_NONE },
			revoke
		});
		broadcast(event);
	}

	// ── Public API ──────────────────────────────────────────────────────────

	function ensureLive(method: string): void {
		if (disposed) {
			const message = disposedErrorMessage(method);
			emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.DISPOSED_ACCESS, {
				method
			});
			throw new SessDisposedError(message);
		}
	}

	const engine: EngineSession<TUser, TCredential, TData> = {
		get current() {
			return snapshot;
		},
		get generation() {
			return generation;
		},
		get identity() {
			return computeIdentity(snapshot);
		},

		async adopt(input) {
			ensureLive(ENGINE_METHOD_ADOPT);

			const invariant = checkSessionInvariants(input);
			if (invariant !== null) {
				return { ok: false, reason: ADOPT_REASON_INVARIANT_FAILED, invariant };
			}

			const validated = await validateSessionCandidate(input, schemas);
			if (!validated.ok) {
				return {
					ok: false,
					reason: ADOPT_REASON_VALIDATION_FAILED,
					field: validated.field,
					issues: validated.issues
				};
			}

			const next = validated.session;
			commitAdoption(next, EVENT_ADOPTED);
			return { ok: true, session: next };
		},

		adoptServer(input) {
			ensureLive(ENGINE_METHOD_ADOPT_SERVER);
			const invariant = checkSessionInvariants(input);
			if (invariant !== null) {
				const message = adoptServerErrorMessage(invariant);
				emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.ADOPT_SERVER_INVALID, {
					invariant
				});
				throw new SessInvalidSessionError(invariant, message);
			}
			const next = freezeSession<TUser, TCredential, TData>({
				user: input.user,
				credential: readField<TCredential | undefined>(input, FIELD_CREDENTIAL),
				data: readField<TData | undefined>(input, FIELD_DATA),
				actor: readField<SessionActor | undefined>(input, FIELD_ACTOR),
				issuedAt: input.issuedAt,
				expiresAt: input.expiresAt
			});
			commitAdoption(next, EVENT_ADOPTED_SERVER);
			return next;
		},

		async refresh() {
			ensureLive(ENGINE_METHOD_REFRESH);

			if (refreshing !== null) return refreshing;
			if (snapshot === null) {
				return { status: REFRESH_STATUS_SKIPPED, reason: SKIP_REASON_NO_SESSION };
			}
			if (onRefresh === undefined) {
				return { status: REFRESH_STATUS_SKIPPED, reason: SKIP_REASON_NO_REFRESH_FN };
			}

			const startedAt = generation;
			const current = snapshot;

			refreshing = (async (): Promise<RefreshResult<TUser, TCredential, TData>> => {
				try {
					const next = await onRefresh(current, { logger });

					if (startedAt !== generation) {
						return {
							status: REFRESH_STATUS_SKIPPED,
							reason: SKIP_REASON_STALE_GENERATION
						};
					}

					if (next === null) {
						commitRevocation(EVENT_EXPIRED);
						return { status: REFRESH_STATUS_EXPIRED };
					}

					const invariant = checkSessionInvariants(next);
					if (invariant !== null) {
						emitSessionDiagnostic(
							diagnostics,
							SESSION_DIAGNOSTIC_EVENTS.REFRESH_INVARIANT_VIOLATED,
							{ invariant }
						);
						return {
							status: REFRESH_STATUS_FAILED,
							error: new TypeError(invariant),
							session: current
						};
					}

					const validated = await validateSessionCandidate(next, schemas);
					if (!validated.ok) {
						emitSessionDiagnostic(
							diagnostics,
							refreshValidationDiagnosticEvent(validated.field),
							{ error: validated.issues }
						);
						return {
							status: REFRESH_STATUS_FAILED,
							error: validated.issues,
							session: current
						};
					}

					if (startedAt !== generation) {
						return {
							status: REFRESH_STATUS_SKIPPED,
							reason: SKIP_REASON_STALE_GENERATION
						};
					}

					commitAdoption(validated.session, EVENT_REFRESHED);
					return { status: REFRESH_STATUS_REFRESHED, session: validated.session };
				} catch (err) {
					if (startedAt !== generation) {
						return {
							status: REFRESH_STATUS_SKIPPED,
							reason: SKIP_REASON_STALE_GENERATION
						};
					}
					emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.REFRESH_TRANSIENT_FAILURE, {
						error: toError(err)
					});
					dispatch({
						event: EVENT_REFRESH_FAILED,
						current: snapshot,
						previous: snapshot,
						generation,
						identity: {
							from: computeIdentity(snapshot),
							to: computeIdentity(snapshot)
						},
						error: err
					});
					return { status: REFRESH_STATUS_FAILED, error: err, session: current };
				} finally {
					refreshing = null;
				}
			})();

			return refreshing;
		},

		async revoke(opts: RevokeOptions = {}) {
			ensureLive(ENGINE_METHOD_REVOKE);

			if (snapshot === null) {
				return {
					localRevoked: true,
					globalRevoked: false,
					scope: REVOKE_SCOPE_LOCAL,
					reason: REVOKE_REASON_NO_SESSION
				};
			}

			// Default to global when an `onRevoke` handler is configured —
			// cookie-auth apps almost always want the server-side cookie
			// cleared along with the local snapshot.
			const requestedScope =
				opts.scope ?? (onRevoke !== undefined ? REVOKE_SCOPE_GLOBAL : REVOKE_SCOPE_LOCAL);
			let result: RevokeResult;

			if (requestedScope === REVOKE_SCOPE_GLOBAL) {
				if (onRevoke === undefined) {
					result = {
						localRevoked: true,
						globalRevoked: false,
						scope: REVOKE_SCOPE_LOCAL,
						reason: REVOKE_REASON_MISSING_REVOKE_URL
					};
					emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.REVOKE_GLOBAL_NO_HANDLER, {
						error: REVOKE_REASON_MISSING_REVOKE_URL
					});
				} else {
					try {
						const ok = await onRevoke(snapshot, { logger });
						if (ok) {
							result = {
								localRevoked: true,
								globalRevoked: true,
								scope: REVOKE_SCOPE_GLOBAL
							};
						} else {
							result = {
								localRevoked: true,
								globalRevoked: false,
								scope: REVOKE_SCOPE_LOCAL,
								reason: REVOKE_REASON_SERVER_REJECTED
							};
							emitSessionDiagnostic(
								diagnostics,
								SESSION_DIAGNOSTIC_EVENTS.REVOKE_GLOBAL_SERVER_REJECTED,
								{ error: REVOKE_REASON_SERVER_REJECTED }
							);
						}
					} catch (err) {
						result = {
							localRevoked: true,
							globalRevoked: false,
							scope: REVOKE_SCOPE_LOCAL,
							reason: REVOKE_REASON_NETWORK_ERROR
						};
						emitSessionDiagnostic(
							diagnostics,
							SESSION_DIAGNOSTIC_EVENTS.REVOKE_GLOBAL_HANDLER_FAILED,
							{ error: toError(err) }
						);
					}
				}
			} else {
				result = {
					localRevoked: true,
					globalRevoked: false,
					scope: REVOKE_SCOPE_LOCAL
				};
			}

			commitRevocation(EVENT_REVOKED, result);
			return result;
		},

		clearLocal() {
			ensureLive(ENGINE_METHOD_CLEAR_LOCAL);
			const result: RevokeResult =
				snapshot === null
					? {
							localRevoked: true,
							globalRevoked: false,
							scope: REVOKE_SCOPE_LOCAL,
							reason: REVOKE_REASON_NO_SESSION
						}
					: {
							localRevoked: true,
							globalRevoked: false,
							scope: REVOKE_SCOPE_LOCAL
						};
			if (snapshot !== null) commitRevocation(EVENT_REVOKED, result);
			return result;
		},

		onChange(listener) {
			if (disposed) return () => {};
			listeners.add(listener);
			try {
				const identity = computeIdentity(snapshot);
				listener({
					event: EVENT_INITIAL_SESSION,
					current: snapshot,
					previous: snapshot,
					generation,
					identity: { from: identity, to: identity }
				});
			} catch (err) {
				emitSessionDiagnostic(diagnostics, SESSION_DIAGNOSTIC_EVENTS.LISTENER_THREW, {
					error: toError(err),
					event: EVENT_INITIAL_SESSION
				});
			}
			return () => listeners.delete(listener);
		},

		dispose() {
			if (disposed) return;
			disposed = true;
			for (const detach of detachers) {
				try {
					detach();
				} catch {
					// best-effort
				}
			}
			listeners.clear();
		}
	};

	return engine;
}