import { existsSync } from "node:fs";
import { readdir, readFile } from "node:fs/promises";
import { join, relative, resolve } from "node:path";
import type {
	CollectionConfig,
	CollectionEntry,
	ContentSchema,
	LoadedFile,
	ResolvedConfig,
} from "../contracts/index.ts";
import { Service } from "../decorators/Service.ts";

/** Validates the frontmatter of an entry against the schema of a collection. */
export function validateFrontmatter(
	schema: ContentSchema | undefined,
	frontmatter: Record<string, unknown>,
): string[] {
	if (!schema) return [];
	const errors: string[] = [];

	for (const field of schema.required ?? []) {
		const value = frontmatter[field];
		if (value === undefined || value === "") {
			errors.push(`${field} is required`);
		}
	}

	for (const [field, allowed] of Object.entries(schema.enum ?? {})) {
		const value = frontmatter[field];
		if (value === undefined) continue;
		if (!allowed.includes(String(value))) {
			errors.push(`${field} must be one of ${allowed.join(", ")}`);
		}
	}

	for (const [field, length] of Object.entries(schema.maxLength ?? {})) {
		const value = frontmatter[field];
		if (value === undefined) continue;
		if (String(value).length > length) {
			errors.push(`${field} must be at most ${length} characters`);
		}
	}

	return errors;
}

/** Registry of the content collections of a project. */
export class ContentRegistry {
	private readonly collections = new Map<string, CollectionEntry[]>();

	constructor(private readonly config: ResolvedConfig) {}

	/** Loads every collection of the project. */
	async load(): Promise<void> {
		for (const collection of this.config.collections ?? []) {
			this.collections.set(
				collection.name,
				await this.loadCollection(collection),
			);
		}
	}

	/** Entries of a collection. */
	entries<T extends Record<string, unknown> = Record<string, unknown>>(
		name: string,
	): CollectionEntry<T>[] {
		return (this.collections.get(name) ?? []) as CollectionEntry<T>[];
	}

	/** A single entry of a collection. */
	get<T extends Record<string, unknown> = Record<string, unknown>>(
		name: string,
		id: string,
	): CollectionEntry<T> | undefined {
		return this.entries<T>(name).find((entry) => entry.id === id);
	}

	/** Names of the loaded collections. */
	names(): string[] {
		return [...this.collections.keys()];
	}

	private async loadCollection(
		collection: CollectionConfig,
	): Promise<CollectionEntry[]> {
		const dir = resolve(this.config.root, collection.dir);
		if (!existsSync(dir)) return [];

		const loader =
			typeof collection.loader === "string"
				? this.config.loaders[collection.loader]
				: collection.loader;
		if (!loader) {
			throw new Error(
				`Unknown loader "${collection.loader}" of the collection "${collection.name}"`,
			);
		}

		const files = await listCollectionFiles(dir, loader.extensions);
		const entries: CollectionEntry[] = [];

		for (const file of files.sort()) {
			const path = join(dir, file);
			const source = await readFile(path, "utf8");
			const loaded: LoadedFile = await loader.load({
				path,
				relativePath: relative(this.config.root, path).replace(/\\/g, "/"),
				source,
			});

			const errors = validateFrontmatter(collection.schema, loaded.data);
			if (errors.length > 0) {
				throw new Error(
					`Invalid frontmatter in ${relative(this.config.root, path)}:\n${errors
						.map((error) => `  - ${error}`)
						.join("\n")}`,
				);
			}

			const id = file.replace(/\.[^.]+$/, "").replace(/\\/g, "/");
			entries.push({
				id,
				path: relative(this.config.root, path).replace(/\\/g, "/"),
				frontmatter: loaded.data,
				body: loaded.content ?? "",
				content: source,
			});
		}

		return entries;
	}
}

async function listCollectionFiles(dir: string, extensions: string[], prefix = ""): Promise<string[]> {
	const files: string[] = [];
	for (const entry of await readdir(dir, { withFileTypes: true })) {
		const relativePath = join(prefix, entry.name);
		if (entry.isDirectory()) files.push(...(await listCollectionFiles(join(dir, entry.name), extensions, relativePath)));
		else if (extensions.some((extension) => entry.name.endsWith(extension))) files.push(relativePath);
	}
	return files.sort();
}

/** Service exposing the content collections to the controllers. */
@Service()
export class ContentService {
	constructor(private readonly registry: ContentRegistry) {}

	/** Entries of a collection. */
	list<T extends Record<string, unknown> = Record<string, unknown>>(
		name: string,
	): CollectionEntry<T>[] {
		return this.registry.entries<T>(name);
	}

	/** A single entry of a collection. */
	get<T extends Record<string, unknown> = Record<string, unknown>>(
		name: string,
		id: string,
	): CollectionEntry<T> | undefined {
		return this.registry.get<T>(name, id);
	}
}