import { dirname, isAbsolute, join, resolve } from "node:path";
import { existsSync } from "node:fs";
import { readFile } from "node:fs/promises";
import type { ViewDescriptor } from "../core/router.ts";
import type { RequestContext } from "../contracts/typegen/http/request.ts";
import type { RenderedView } from "../contracts/typegen/http/response.ts";
import type { ViewPath, ViewPropsOf } from "../contracts/typegen/views.ts";
import type { DeferredChunk } from "../contracts/typegen/http/response.ts";
import { TemplateEngine, type RenderContext } from "./engine/runtime.ts";
import { compileCss, styleTag } from "./css/index.ts";
import type { TemplateContext } from "../core/context.ts";
import type {
	ComponentDefinition,
	ComponentRegistry,
	ServerComponent,
} from "./components.ts";
import type { MuddleHooks } from "./hooks.ts";

/**
 * Fluent, type generated view api.
 *
 * The props of a template are declared inside the template itself, the
 * generator turns them into a contract and the builder only accepts the props
 * of the selected template.
 */

export interface ViewsOptions {
	context?: TemplateContext;
	/** Directory holding the templates. */
	viewsDir: string;
	/** Root directory of the project, template paths are resolved against it. */
	root?: string;
	/** Directory holding the components, defaults to `viewsDir/components`. */
	componentsDir?: string;
	/** Server components registered on creation. */
	components?: ComponentRegistry;
	globalLayouts?: string[];
	/** Contextual hooks shared by Spug rendering and STCSS component styles. */
	hooks?: MuddleHooks;
}

export interface SpugComponentOptions {
	template?: string;
	style?: string | string[];
	deferred?: boolean;
}

/** Options of a single render. */
export interface RenderOptions {
	/** Route parameters handed to the template. */
	params?: Record<string, string>;
	/** Additional locals handed to the template. */
	locals?: Record<string, unknown>;
}

/** Result of a render. */
export interface RenderResult {
	/** Html of the shell. */
	html: string;
	/** Chunks rendered after the shell. */
	deferred: DeferredChunk[];
}

export class ViewBuilder<P extends ViewPath = ViewPath> {
	private readonly state: {
		props: Record<string, unknown>;
		params: Record<string, string>;
		locals: Record<string, unknown>;
	};

	constructor(
		private readonly views: Views,
		private readonly path: P,
		props: Record<string, unknown> = {},
		params: Record<string, string> = {},
		locals: Record<string, unknown> = {},
	) {
		this.state = {
			props: { ...props },
			params: { ...params },
			locals: { ...locals },
		};
	}

	/** Sets the props of the template. */
	with(props: ViewPropsOf<P>): this {
		Object.assign(this.state.props, props);
		return this;
	}

	/** Sets the route parameters handed to the template. */
	params(params: Record<string, string>): this {
		Object.assign(this.state.params, params);
		return this;
	}

	/** Sets additional locals handed to the template. */
	locals(locals: Record<string, unknown>): this {
		Object.assign(this.state.locals, locals);
		return this;
	}

	/** Renders the template and awaits the deferred components. */
	async render(): Promise<string> {
		const result = await this.renderResult();
		const deferred = await Promise.all(
			result.deferred.map((chunk) => chunk.content),
		);
		if (deferred.length === 0) return result.html;
		const appended = deferred
			.map(
				(html, index) =>
					`<div data-muddle-deferred="${result.deferred[index]?.id ?? index}">${html}</div>`,
			)
			.join("");
		return `${result.html}${appended}`;
	}

	/** Renders the template and returns the deferred chunks separately. */
	async renderResult(): Promise<RenderResult> {
		const context: RenderContext = {
			locals: { ...this.state.locals, ...this.state.props },
			params: this.state.params,
			deferred: [],
		};
		const html = await this.views.engine.render(
			this.path,
			context.locals,
			context,
		);
		return { html, deferred: context.deferred };
	}

	/**
	 * Renders the template as a stream.
	 *
	 * The shell is sent first, the deferred components follow as soon as they
	 * are rendered. No javascript is required, the browser renders the chunks
	 * while they arrive.
	 */
	async renderStream(): Promise<ReadableStream<Uint8Array>> {
		const { html, deferred } = await this.renderResult();
		const encoder = new TextEncoder();
		return new ReadableStream<Uint8Array>({
			async start(controller) {
				controller.enqueue(encoder.encode(html));
				for (const chunk of deferred) {
					const content = await chunk.content;
					controller.enqueue(
						encoder.encode(
							`<div data-muddle-deferred="${chunk.id}">${content}</div>`,
						),
					);
				}
				controller.close();
			},
		});
	}
}

export class Views {
	readonly engine: TemplateEngine;
	readonly components: ComponentRegistry;
	private readonly hooks?: MuddleHooks;

	constructor(options: ViewsOptions) {
		this.hooks = options.hooks;
		this.components = options.components ?? new Map();
		for (const [name, component] of options.context?.imports ?? []) this.components.set(name, { name, component: component as ServerComponent, deferred: false });
		this.engine = new TemplateEngine({
			viewsDir: options.viewsDir,
			componentsDir: options.componentsDir,
			root: options.root,
			components: this.components,
			globalLayouts: options.globalLayouts,
			hooks: options.hooks,
		});
	}

	/** Registers a server component. */
	component(
		name: string,
		component: ServerComponent,
		options: { deferred?: boolean } = {},
	): this {
		const definition: ComponentDefinition = {
			name,
			component,
			deferred: options.deferred === true,
		};
		this.components.set(name, definition);
		return this;
	}

	/** Registers a component rendered by a SPUG template and optional STCSS files. */
	spugComponent(name: string, options: SpugComponentOptions = {}): this {
		const template = options.template ?? name;
		const styles = Array.isArray(options.style) ? options.style : options.style ? [options.style] : [];
		return this.component(name, {
			render: async (props) => {
				const html = await this.engine.renderComponent(template, props);
				const css = await Promise.all(styles.map(async (style) => {
					const path = resolve(this.componentsDir, style);
					return existsSync(path) ? compileCss(await readFile(path, "utf8"), { hooks: this.hooks }) : "";
				}));
				return `${css.filter(Boolean).map(styleTag).join("")}${html}`;
			},
		}, { deferred: options.deferred });
	}

	/** Starts a fluent render of a template. */
	view<P extends ViewPath>(path: P): ViewBuilder<P> {
		return new ViewBuilder<P>(this, path);
	}

	/** Renders a template with the given props. */
	async render<P extends ViewPath>(
		path: P,
		props: ViewPropsOf<P>,
		options: RenderOptions = {},
	): Promise<string> {
		const builder = this.view(path).with(props);
		if (options.params) builder.params(options.params);
		if (options.locals) builder.locals(options.locals);
		return builder.render();
	}

	/**
	 * Renders a template by its path on disk.
	 *
	 * Used by the `@View()` decorator, therefore the path is resolved relative
	 * to the project.
	 */
	async renderFile(
		path: string,
		props: Record<string, unknown> = {},
		options: RenderOptions = {},
	): Promise<string> {
		const context: RenderContext = {
			locals: { ...options.locals, ...props },
			params: options.params ?? {},
			deferred: [],
		};
		const html = await this.engine.render(path, context.locals, context);
		const deferred = await Promise.all(
			context.deferred.map((chunk) => chunk.content),
		);
		if (deferred.length === 0) return html;
		const appended = deferred
			.map(
				(html, index) =>
					`<div data-muddle-deferred="${context.deferred[index]?.id ?? index}">${html}</div>`,
			)
			.join("");
		return `${html}${appended}`;
	}

	/**
	 * Renders a view descriptor of a route.
	 *
	 * The descriptor of a `@View()` decorator carries an absolute path, the
	 * descriptor of a controller carries the key of a view.
	 */
	async renderDescriptor(
		descriptor: ViewDescriptor,
		context: RequestContext,
	): Promise<string | RenderedView> {
		const props = (descriptor.props ?? {}) as Record<string, unknown>;
		if (isAbsolute(descriptor.template)) {
			const html = await this.renderFile(descriptor.template, props, {
				params: context.params,
				locals: { ...context.locals },
			});
			return html;
		}
		const builder = this.view(
			descriptor.template as Parameters<Views["view"]>[0],
		).with(props as never);
		builder.params(context.params);
		builder.locals(context.locals);
		return builder.renderResult();
	}

	/** Directory of the templates. */
	get viewsDir(): string {
		return this.engine.viewsDir;
	}

	/** Directory of the components. */
	get componentsDir(): string {
		return this.engine.componentsDir;
	}
}

/** Creates the views of a project. */
export function createViews(options: ViewsOptions): Views {
	return new Views(options);
}

/** Resolves a template path relative to the views directory. */
export function resolveTemplatePath(viewsDir: string, path: string): string {
	return join(resolve(viewsDir), dirname(path), path);
}