import {
	PERMISSION_DECISION_CODE_SNAPSHOT_DENIED,
	PERMISSION_EFFECT_ALLOW,
	PERMISSION_EFFECT_DENY,
	PERMISSION_EFFECT_INDETERMINATE,
	PERMISSION_FALLBACK_DENY
} from '$libs/perm';
import { HTTP_CONTENT_TYPE_JSON, HTTP_HEADER_CONTENT_TYPE, HTTP_METHOD_POST } from '$libs/http';
import { permissionDecisionKey } from './keys.ts';
import {
	LOGGER_CATEGORY,
	PERMISSION_CLIENT_DEFAULT_CACHE_TTL_MS,
	PERMISSION_CLIENT_PATH_BATCH,
	PERMISSION_CLIENT_PATH_CHECK,
	PERMISSION_CLIENT_PATH_EXPLAIN,
	PERMISSION_CLIENT_PATH_WHAT,
	PERMISSION_ERROR_MSG_REQUEST_FAILED_PREFIX,
	PERMISSION_HTTP_CREDENTIALS_INCLUDE,
	PERMISSION_LOG_MSG_REMOTE_BATCH_FAILED,
	PERMISSION_LOG_MSG_REMOTE_CHECK_FAILED,
	PERMISSION_LOG_MSG_REMOTE_WHAT_FAILED,
	PERMISSION_REQUEST_FIELD_ACTION,
	PERMISSION_REQUEST_FIELD_CHECKS,
	PERMISSION_REQUEST_FIELD_CONTEXT,
	PERMISSION_REQUEST_FIELD_RESOURCE,
	PERMISSION_RESPONSE_FIELD_ACTIONS,
	PERMISSION_RESPONSE_FIELD_DECISIONS,
	PERMISSION_SNAPSHOT_GLOBAL_POLICY
} from './consts.ts';
import type {
	PermissionClient,
	PermissionClientBatchInput,
	PermissionClientCheckInput,
	PermissionClientOptions,
	PermissionSnapshot
} from './types.ts';
import type { ExplainResult, PermissionDecision } from '$libs/perm';

interface CacheEntry {
	readonly decision: PermissionDecision;
	readonly expiresAt: number;
}

function now(): number {
	return Date.now();
}

function joinUrl(base: string, path: string): string {
	return `${base.replace(/\/$/, '')}/${path.replace(/^\//, '')}`;
}

async function postJson<T>(
	options: PermissionClientOptions,
	path: string,
	body: unknown
): Promise<T> {
	const url = joinUrl(options.endpoint, path);
	if (options.http) {
		const response = await options.http.post(url, { body: body as Record<string, unknown> });
		if (response.ok) return response.value as T;
		throw new Error(`${PERMISSION_ERROR_MSG_REQUEST_FAILED_PREFIX}${url}`);
	}

	const fetcher = options.fetcher ?? fetch.bind(globalThis);
	const response = await fetcher(url, {
		method: HTTP_METHOD_POST,
		headers: { [HTTP_HEADER_CONTENT_TYPE]: HTTP_CONTENT_TYPE_JSON },
		credentials: PERMISSION_HTTP_CREDENTIALS_INCLUDE,
		body: JSON.stringify(body)
	});

	if (!response.ok) {
		throw new Error(
			`${PERMISSION_ERROR_MSG_REQUEST_FAILED_PREFIX}${response.status} ${response.statusText}`
		);
	}

	return (await response.json()) as T;
}

export function createPermissionClient(options: PermissionClientOptions): PermissionClient {
	const cacheTtlMs = options.cacheTtlMs ?? PERMISSION_CLIENT_DEFAULT_CACHE_TTL_MS;
	const cache = new Map<string, CacheEntry>();
	const pending = new Map<string, Promise<PermissionDecision>>();
	const listeners = new Set<(snapshot: PermissionSnapshot) => void>();
	let currentSnapshot: PermissionSnapshot = options.initialSnapshot ?? { decisions: {} };

	function emit(): void {
		for (const listener of listeners) listener(currentSnapshot);
	}

	function decisionKey(input: PermissionClientCheckInput): string {
		return permissionDecisionKey(input);
	}

	function snapshotStillValid(snapshot: PermissionSnapshot): boolean {
		return snapshot.expiresAt === undefined || Date.parse(snapshot.expiresAt) > now();
	}

	function readSnapshotDecision(input: PermissionClientCheckInput): PermissionDecision | undefined {
		if (!snapshotStillValid(currentSnapshot)) return undefined;
		const key = decisionKey(input);
		const direct = currentSnapshot.decisions?.[key];
		if (direct) return direct;
		const global = currentSnapshot.global?.[input.action];
		if (typeof global === 'boolean') {
			return global
				? { effect: PERMISSION_EFFECT_ALLOW, policy: PERMISSION_SNAPSHOT_GLOBAL_POLICY }
				: {
						effect: PERMISSION_EFFECT_DENY,
						code: PERMISSION_DECISION_CODE_SNAPSHOT_DENIED,
						reason: PERMISSION_SNAPSHOT_GLOBAL_POLICY
					};
		}
		return global;
	}

	function setCached(input: PermissionClientCheckInput, decision: PermissionDecision): void {
		const key = decisionKey(input);
		const ttl =
			decision.effect === PERMISSION_EFFECT_ALLOW && decision.ttl ? decision.ttl : cacheTtlMs;
		cache.set(key, { decision, expiresAt: now() + ttl });
		currentSnapshot = {
			...currentSnapshot,
			decisions: {
				...(currentSnapshot.decisions ?? {}),
				[key]: decision
			}
		};
		emit();
	}

	async function check(input: PermissionClientCheckInput): Promise<PermissionDecision> {
		const key = decisionKey(input);
		const cached = cache.get(key);
		if (cached && cached.expiresAt > now()) return cached.decision;

		const snapshotDecision = readSnapshotDecision(input);
		if (snapshotDecision) {
			cache.set(key, { decision: snapshotDecision, expiresAt: now() + cacheTtlMs });
			return snapshotDecision;
		}

		const inFlight = pending.get(key);
		if (inFlight) return inFlight;

		const request = postJson<PermissionDecision>(options, PERMISSION_CLIENT_PATH_CHECK, {
			[PERMISSION_REQUEST_FIELD_ACTION]: input.action,
			[PERMISSION_REQUEST_FIELD_RESOURCE]: input.resource,
			[PERMISSION_REQUEST_FIELD_CONTEXT]: input.context
		})
			.then((decision) => {
				setCached(input, decision);
				return decision;
			})
			.catch((error) => {
				options.onError?.(error);
				options.logger?.error?.(LOGGER_CATEGORY, PERMISSION_LOG_MSG_REMOTE_CHECK_FAILED, {
					error,
					context: { input }
				});
				return {
					effect: PERMISSION_EFFECT_INDETERMINATE,
					reason: PERMISSION_LOG_MSG_REMOTE_CHECK_FAILED,
					fallback: PERMISSION_FALLBACK_DENY,
					errors: [error]
				} satisfies PermissionDecision;
			})
			.finally(() => {
				pending.delete(key);
			});
		pending.set(key, request);
		return request;
	}

	async function batch(
		input: PermissionClientBatchInput
	): Promise<Record<string, PermissionDecision>> {
		try {
			const result = await postJson<{ decisions: Record<string, PermissionDecision> }>(
				options,
				PERMISSION_CLIENT_PATH_BATCH,
				{ [PERMISSION_REQUEST_FIELD_CHECKS]: input.checks }
			);
			for (const item of input.checks) {
				const key = decisionKey(item);
				const decision = result[PERMISSION_RESPONSE_FIELD_DECISIONS][key];
				if (decision) setCached(item, decision);
			}
			return result[PERMISSION_RESPONSE_FIELD_DECISIONS];
		} catch (error) {
			options.onError?.(error);
			options.logger?.error?.(LOGGER_CATEGORY, PERMISSION_LOG_MSG_REMOTE_BATCH_FAILED, {
				error,
				context: { input }
			});
			const decisions: Record<string, PermissionDecision> = {};
			for (const item of input.checks) {
				decisions[decisionKey(item)] = {
					effect: PERMISSION_EFFECT_INDETERMINATE,
					reason: PERMISSION_LOG_MSG_REMOTE_BATCH_FAILED,
					fallback: PERMISSION_FALLBACK_DENY,
					errors: [error]
				};
			}
			return decisions;
		}
	}

	async function what(input: {
		readonly resource?: PermissionClientCheckInput['resource'];
		readonly actions?: readonly string[];
		readonly context?: PermissionClientCheckInput['context'];
	}): Promise<Record<string, PermissionDecision>> {
		try {
			const result = await postJson<{ actions: Record<string, PermissionDecision> }>(
				options,
				PERMISSION_CLIENT_PATH_WHAT,
				input
			);
			for (const [action, decision] of Object.entries(result[PERMISSION_RESPONSE_FIELD_ACTIONS])) {
				setCached({ action, resource: input.resource, context: input.context }, decision);
			}
			return result[PERMISSION_RESPONSE_FIELD_ACTIONS];
		} catch (error) {
			options.onError?.(error);
			options.logger?.error?.(LOGGER_CATEGORY, PERMISSION_LOG_MSG_REMOTE_WHAT_FAILED, {
				error,
				context: { input }
			});
			return {};
		}
	}

	async function explain(input: PermissionClientCheckInput): Promise<ExplainResult | null> {
		try {
			return await postJson<ExplainResult>(options, PERMISSION_CLIENT_PATH_EXPLAIN, input);
		} catch (error) {
			options.onError?.(error);
			return null;
		}
	}

	function hydrate(snapshot: PermissionSnapshot): void {
		currentSnapshot = snapshot;
		cache.clear();
		for (const [key, decision] of Object.entries(snapshot.decisions ?? {})) {
			cache.set(key, { decision, expiresAt: now() + cacheTtlMs });
		}
		emit();
	}

	function invalidate(scope?: string): void {
		if (!scope) {
			cache.clear();
			currentSnapshot = { ...currentSnapshot, decisions: {} };
			emit();
			return;
		}
		for (const key of [...cache.keys()]) if (key.includes(scope)) cache.delete(key);
		const decisions = { ...(currentSnapshot.decisions ?? {}) };
		for (const key of Object.keys(decisions)) if (key.includes(scope)) delete decisions[key];
		currentSnapshot = { ...currentSnapshot, decisions };
		emit();
	}

	return {
		check,
		async can(input) {
			return (await check(input)).effect === PERMISSION_EFFECT_ALLOW;
		},
		batch,
		what,
		explain,
		hydrate,
		snapshot: () => currentSnapshot,
		invalidate,
		subscribe(listener) {
			listeners.add(listener);
			listener(currentSnapshot);
			return () => listeners.delete(listener);
		},
		decisionKey
	};
}