import { NODE, NodeTarget } from "./element-common.js";
import { ENV } from "./env.js";
import { createText } from "./internals/create-text.js";
import { createMapArrayState, MapArrayFn, mapArrayUpdate } from "./internals/map-array.js";
import { $, capture, Expression, get, isolate, memo, Signal, teardown, TeardownHook, watch } from "./signals.js";
import type { Component, Content, Falsy } from "./types.js";
import type { Attach, For, Index, Nest, Show } from "./view-jsx.js";

/**
 * Internal utility to create placeholder comments.
 */
function createPlaceholder(env: typeof globalThis): Node {
	return env.document.createComment("g");
}

/**
 * Internal utility to create an arbitrary parent node.
 */
function createParent(env: typeof globalThis): Node {
	return env.document.createDocumentFragment();
}

/**
 * Internal shorthand for creating the boundary comment of an empty view.
 */
function empty(setBoundary: ViewSetBoundaryFn, env: typeof globalThis): void {
	const node = createPlaceholder(env);
	setBoundary(node, node);
}

/**
 * Internal shorthand for using the children of a node as boundary.
 */
function use(setBoundary: ViewSetBoundaryFn, node: Node, env: typeof globalThis): void {
	if (node.firstChild === null) {
		empty(setBoundary, env);
	} else {
		setBoundary(node.firstChild, node.lastChild!);
	}
}

/**
 * Render arbitrary content.
 *
 * Supported content types are:
 * + Null and undefined (not displayed).
 * + Arbitrarily nested arrays/fragments of content.
 * + DOM nodes. Children will be removed from document fragments.
 * + {@link View Views}.
 * + Anything created with rvx's jsx runtime.
 * + Anything else is displayed as text.
 *
 * @param content The content to render.
 * @returns A view instance or the `content` parameter itself if its already a view.
 *
 * @example
 * ```tsx
 * import { $, render } from "rvx";
 *
 * // Not displayed:
 * render(null);
 * render(undefined);
 *
 * // Arbitrarily nested arrays/fragments of content:
 * render([["Hello"], " World!"]);
 * render(<>{<>"Hello"</>}{" World!"}</>);
 *
 * // DOM nodes:
 * render(<h1>Hello World!</h1>);
 * render(document.createElement("input"));
 * render(document.createTextNode("Hello World!"));
 * render(someTemplate.content.cloneNode(true));
 *
 * // Views:
 * render(render("Hello World!"));
 * render(when(true, () => "Hello World!"));
 * render(<Show when={true}>{() => "Hello World!"}</Show>);
 *
 * // Text:
 * render("Hello World!");
 * render(() => "Hello World!");
 * render(42);
 * render($(42));
 * ```
 */
export function render(content: Content): View {
	if (content instanceof View) {
		return content;
	}
	return new View(setBoundary => {
		const env = ENV.current;
		if (Array.isArray(content)) {
			const flat = content.flat(Infinity) as Content[];
			if (flat.length > 1) {
				const parent = createParent(env);
				for (let i = 0; i < flat.length; i++) {
					let part = flat[i];
					if (part === null || part === undefined) {
						parent.appendChild(createPlaceholder(env));
					} else if (typeof part === "object") {
						if (NODE in part) {
							part = (part as NodeTarget)[NODE];
						}
						if (part instanceof env.Node) {
							if (part.nodeType === 11 && part.childNodes.length === 0) {
								parent.appendChild(createPlaceholder(env));
							} else {
								parent.appendChild(part);
							}
						} else if (part instanceof View) {
							part.appendTo(parent);
							if (i === 0) {
								part.setBoundaryOwner((first, _last) => setBoundary(first, undefined));
							} else if (i === flat.length - 1) {
								part.setBoundaryOwner((_first, last) => setBoundary(undefined, last));
							}
						} else {
							parent.appendChild(createText(part, env));
						}
					} else {
						parent.appendChild(createText(part, env));
					}
				}
				use(setBoundary, parent, env);
				return;
			}
			content = flat[0];
		}
		if (content === null || content === undefined) {
			empty(setBoundary, env);
		} else if (typeof content === "object") {
			if (NODE in content) {
				content = (content as NodeTarget)[NODE];
			}
			if (content instanceof env.Node) {
				if (content.nodeType === 11) {
					use(setBoundary, content, env);
				} else {
					setBoundary(content, content);
				}
			} else if (content instanceof View) {
				setBoundary(content.first, content.last);
				content.setBoundaryOwner(setBoundary);
			} else {
				const text = createText(content, env);
				setBoundary(text, text);
			}
		} else {
			const text = createText(content, env);
			setBoundary(text, text);
		}
	});
}

/**
 * Render arbitrary content and append it to the specified parent until the current lifecycle is disposed.
 *
 * @param parent The parent node.
 * @param content The content to render. See {@link render} for supported types.
 * @returns The view instance.
 *
 * @example
 * ```tsx
 * import { mount } from "rvx";
 *
 * mount(
 *   document.body,
 *   <h1>Hello World!</h1>
 * );
 * ```
 *
 * Since the content is removed when the current lifecycle is disposed, this can also be used to temporarily append
 * content to different elements while some component is rendered:
 * ```tsx
 * import { mount, Content } from "rvx";
 *
 * function Popover(props: { text: Content, children: Content }) {
 *   const visible = $(false);
 *
 *   mount(
 *     document.body,
 *     <Show when={visible}>
 *       {props.children}
 *     </Show>
 *   );
 *
 *   return <button on:click={() => { visible.value = !visible.value; }}>
 *     {props.text}
 *   </button>;
 * }
 *
 * mount(
 *   document.body,
 *   <Popover text="Click me!">
 *     Hello World!
 *   </Popover>
 * );
 * ```
 */
export function mount(parent: Node, content: Content): View {
	const view = render(content);
	view.appendTo(parent);
	teardown(() => view.detach());
	return view;
}

/**
 * A function that is called when the view boundary may have been changed.
 */
export interface ViewBoundaryOwner {
	/**
	 * @param first The current first node.
	 * @param last The current last node.
	 */
	(first: Node, last: Node): void;
}

/**
 * A function that must be called after the view boundary has been changed.
 */
export interface ViewSetBoundaryFn {
	/**
	 * @param first The first node if changed.
	 * @param last The last node if changed.
	 */
	(first: Node | undefined, last: Node | undefined): void;
}

interface UninitViewProps {
	/**
	 * The current first node of this view.
	 *
	 * + This may be undefined while the view is not fully initialized.
	 * + This property is not reactive.
	 */
	get first(): Node | undefined;

	/**
	 * The current last node of this view.
	 *
	 * + This may be undefined while the view is not fully initialized.
	 * + This property is not reactive.
	 */
	get last(): Node | undefined;
}

export type UninitView = UninitViewProps & Omit<View, keyof UninitViewProps>;

/**
 * A function that is called once to initialize a view instance.
 *
 * View creation will fail if no first or last node has been set during initialization.
 */
export interface ViewInitFn {
	/**
	 * @param setBoundary A function that must be called after the view boundary has been changed.
	 * @param self The current view itself. This can be used to keep track of the current boundary and parent nodes.
	 */
	(setBoundary: ViewSetBoundaryFn, self: UninitView): void;
}

/**
 * Represents a sequence of at least one DOM node.
 *
 * Consumers of the view API need to guarantee that:
 * + The sequence of nodes is not modified from the outside.
 * + If there are multiple nodes, all nodes must have a common parent node at all time.
 */
export class View {
	#first!: Node;
	#last!: Node;
	#owner: ViewBoundaryOwner | undefined;

	/**
	 * Create a new view.
	 *
	 * View implementations need to guarantee that:
	 * + The view doesn't break when the parent node is replaced or when a view consisting of only a single node is detached from its parent.
	 * + The boundary is updated immediately after the first or last node has been updated.
	 * + If there are multiple nodes, all nodes remain in the current parent.
	 * + If there are multiple nodes, the initial nodes must have a common parent.
	 */
	constructor(init: ViewInitFn) {
		init((first, last) => {
			if (first) {
				this.#first = first;
			}
			if (last) {
				this.#last = last;
			}
			this.#owner?.(this.#first, this.#last);
		}, this);
		if (!this.#first || !this.#last) {
			// View boundary was not completely initialized:
			throw new Error("G1");
		}
	}

	/**
	 * The current first node of this view.
	 *
	 * Note, that this property is not reactive.
	 */
	get first(): Node {
		return this.#first;
	}

	/**
	 * The current last node of this view.
	 *
	 * Note, that this property is not reactive.
	 */
	get last(): Node {
		return this.#last;
	}

	/**
	 * The current parent node or undefined if there is none.
	 *
	 * Note, that this property is not reactive.
	 */
	get parent(): Node | undefined {
		return this.#first?.parentNode ?? undefined;
	}

	/**
	 * Set the boundary owner for this view until the current lifecycle is disposed.
	 *
	 * @throws An error if there currently is a boundary owner.
	 */
	setBoundaryOwner(owner: ViewBoundaryOwner): void {
		if (this.#owner !== undefined) {
			// View already has a boundary owner:
			throw new Error("G2");
		}
		this.#owner = owner;
		teardown(() => this.#owner = undefined);
	}

	/**
	 * Append all nodes of this view to the specified parent.
	 *
	 * @param parent The parent to append to.
	 */
	appendTo(parent: Node): void {
		let node = this.#first;
		const last = this.#last;
		for (;;) {
			const next = node.nextSibling;
			parent.appendChild(node);
			if (node === last) {
				break;
			}
			node = next!;
		}
	}

	/**
	 * Insert all nodes of this view before a reference child of the specified parent.
	 *
	 * @param parent The parent to insert into.
	 * @param ref The reference child to insert before. If this is null, the nodes are appended to the parent.
	 */
	insertBefore(parent: Node, ref: Node | null): void {
		if (ref === null) {
			return this.appendTo(parent);
		}
		let node = this.#first;
		const last = this.#last;
		for (;;) {
			const next = node.nextSibling;
			parent.insertBefore(node, ref);
			if (node === last) {
				break;
			}
			node = next!;
		}
	}

	/**
	 * Detach all nodes of this view from the current parent if there is one.
	 *
	 * If there are multiple nodes, they are moved into a new document fragment to allow the view implementation to stay alive.
	 *
	 * @returns The single removed node or the document fragment they have been moved into.
	 */
	detach(): Node | DocumentFragment {
		const first = this.#first;
		const last = this.#last;
		if (first === last) {
			first.parentNode?.removeChild(first);
			return first;
		} else {
			const fragment = ENV.current.document.createDocumentFragment();
			this.appendTo(fragment);
			return fragment;
		}
	}
}

/**
 * Get an iterator over all current top level nodes of a view.
 *
 * @param view The view.
 * @returns The iterator.
 *
 * @example
 * ```tsx
 * import { render, viewNodes } from "rvx";
 *
 * const view = render(<>
 *   <h1>Hello World!</h1>
 * </>);
 *
 * for (const node of viewNodes(view)) {
 *   console.log(node);
 * }
 * ```
 */
export function * viewNodes(view: View): IterableIterator<Node> {
	let node = view.first;
	for (;;) {
		const next = node.nextSibling!;
		yield node;
		if (node === view.last) {
			break;
		}
		node = next;
	}
}

const _nestDefault = ((component: Component | null | undefined) => component?.()) as Component<unknown>;

/**
 * Watch an expression and render content from its result.
 *
 * + If an error is thrown during initialization, the error is re-thrown.
 * + If an error is thrown during a signal update, the previously rendered content is kept in place and the error is re-thrown.
 * + Content returned from the component can be directly reused within the same `nest` instance.
 *
 * See {@link Nest `<Nest>`} when using JSX.
 *
 * @param expr The expression to watch.
 * @param component The component to render with the expression result. If the expression returns a component, null or undefined, this can be omitted.
 *
 * @example
 * ```tsx
 * import { $, nest, e } from "rvx";
 *
 * const count = $(0);
 *
 * // Using the expression result in a component:
 * nest(count, count => {
 *   switch (count) {
 *     case 0: return e("h1").append("Hello World!");
 *     case 1: return "Something else...";
 *   }
 * })
 *
 * // Or directly returning a component from the expression:
 * nest(() => {
 *   switch (count.value) {
 *     case 0: return () => e("h1").append("Hello World!");
 *     case 1: return () => "Something else...";
 *   }
 * })
 * ```
 */
export function nest(expr: Expression<Component | null | undefined>): View;
export function nest<T>(expr: Expression<T>, component: Component<T>): View;
export function nest(expr: Expression<unknown>, component: Component<unknown> = _nestDefault): View {
	return new View((setBoundary, self) => {
		watch(expr, value => {
			const last: Node | undefined = self.last;
			const parent = last?.parentNode;
			let view: View;
			if (parent) {
				const anchor = last.nextSibling;
				self.detach();
				view = render(component(value));
				view.insertBefore(parent, anchor);
			} else {
				view = render(component(value));
			}
			setBoundary(view.first, view.last);
			view.setBoundaryOwner(setBoundary);
		});
	});
}

/**
 * Render conditional content.
 *
 * + Content is only re-rendered if the expression result is not strictly equal to the previous one. If this behavior is undesired, use {@link nest} instead.
 * + If an error is thrown by the expression or component during initialization, the error is re-thrown.
 * + If an error is thrown by the expression or component during a signal update, the previously rendered content is kept and the error is re-thrown.
 *
 * See {@link Show `<Show>`} when using JSX.
 *
 * @param condition The condition to watch.
 * @param truthy The component to render when the condition result is truthy.
 * @param falsy An optional component to render when the condition is falsy.
 *
 * @example
 * ```tsx
 * import { $, when, e } from "rvx";
 *
 * const message = $<null | string>("Hello World!");
 *
 * when(message, value => e("h1").append(value), () => "No message...")
 * ```
 */
export function when<T>(condition: Expression<T | Falsy>, truthy: Component<T>, falsy?: Component): View {
	return nest(memo(condition), value => value ? truthy(value) : falsy?.());
}

export interface ForContentFn<T> {
	/**
	 * @param value The value.
	 * @param index An expression to get the current index.
	 * @returns The content.
	 */
	(value: T, index: () => number): Content;
}

/**
 * Render content for each value in an iterable.
 *
 * Errors thrown by the component or while updating an index result in undefined behavior.
 *
 * See {@link For `<For>`} for use with JSX.
 *
 * @param each The expression to watch. Note, that signals accessed during iteration will also trigger updates.
 * @param component The component to render for each value.
 *
 * @example
 * ```tsx
 * import { $, forEach, e } from "rvx";
 *
 * const items = $([1, 2, 3]);
 *
 * forEach(items, value => e("li").append(value))
 * ```
 */
export function forEach<T>(each: Expression<Iterable<T>>, component: ForContentFn<T>): View {
	return new View(setBoundary => {
		const env = ENV.current;
		const first = createPlaceholder(env);
		setBoundary(first, first);
		const mapFn: MapArrayFn<T, View> = (input, index) => render(component(input, index));
		const state = createMapArrayState<T, View>();
		watch(() => {
			const update = mapArrayUpdate<T, View>(state, get(each), mapFn);
			if (update !== null) {
				let parent = first.parentNode as Node | null;
				if (parent === null) {
					parent = createParent(env);
					parent.appendChild(first);
				}
				for (let i = 0; i < update.p.length; i++) {
					const entry = update.p[i];
					if (entry.r) {
						entry.o.detach();
					}
				}
				let prev = update.s > 0 ? state[update.s - 1].o.last : first;
				for (let i = 0; i < update.n.length; i++) {
					const view = update.n[i].o;
					if (prev.nextSibling !== view.first) {
						view.insertBefore(parent, prev.nextSibling);
					}
					prev = view.last;
				}
				if (update.e === state.length) {
					setBoundary(undefined, prev);
				}
			}
		});
	});
}

export interface IndexContentFn<T> {
	/**
	 * @param value An expression to get the current value.
	 * @param index The index.
	 * @returns The content.
	 */
	(value: () => T, index: number): Content;
}

/**
 * Render content for each index in an iterable.
 *
 * Errors thrown by the component or while updating a value result in undefined behavior.
 *
 * See {@link Index `<Index>`} when using JSX.
 *
 * @param each The expression to watch. Note, that signals accessed during iteration will also trigger updates.
 * @param component The component to render for each index.
 *
 * @example
 * ```tsx
 * import { $, indexEach, e } from "rvx";
 *
 * const items = $([1, 2, 3]);
 *
 * indexEach(items, value => e("li").append(value))
 * ```
 */
export function indexEach<T>(each: Expression<Iterable<T>>, component: IndexContentFn<T>): View {
	return new View((setBoundary, self) => {
		interface Instance {
			/** input value */
			i: Signal<T>;
			/** view */
			v: View;
			/** dispose */
			d: TeardownHook;
		}

		const env = ENV.current;
		const state: Instance[] = [];

		const first = createPlaceholder(env);
		setBoundary(first, first);

		teardown(() => {
			for (let i = state.length - 1; i >= 0; i--) {
				state[i].d();
			}
		});

		watch(() => {
			let parent = first.parentNode as Node | null;
			if (!parent) {
				parent = createParent(env);
				parent.appendChild(first);
			}

			let index = 0;
			for (const value of get(each)) {
				if (index < state.length) {
					const instance = state[index];
					instance.i.value = value;
				} else {
					const signal = $(value);
					let view!: View;
					const dispose = isolate(capture, () => {
						view = render(component(() => signal.value, index));
					});
					state.push({
						i: signal,
						v: view,
						d: dispose,
					});
					const prev = index > 0 ? state[index - 1].v.last : first;
					view.insertBefore(parent, prev.nextSibling);
				}
				index++;
			}
			while (state.length > index) {
				const instance = state.pop()!;
				instance.d();
				instance.v.detach();
			}
			const last = state.length > 0 ? state[state.length - 1].v.last : first;
			if (self.last !== last) {
				setBoundary(undefined, last);
			}
		});
	});
}

/**
 * A wrapper that can be used for moving and reusing views.
 */
export class MovableView {
	#view: View;
	#target: Signal<View | void> = $();

	constructor(view: View) {
		this.#view = view;
	}

	/**
	 * Create a new view that contains the wrapped view until it is moved again or detached.
	 *
	 * If the lifecycle in which `move` is called is disposed, the created view no longer updates its boundary and nodes may be silently removed.
	 */
	move: Component<void, View> = () => {
		this.#target.value = undefined;
		const target = this.#target = $(this.#view);
		return nest(target, v => v);
	};

	/**
	 * Detach content from the currently active view.
	 */
	detach(): void {
		this.#target.value = undefined;
	}
}

/**
 * Render and wrap arbitrary content so that it can be moved and reused.
 */
export function movable(content: Content): MovableView {
	return new MovableView(render(content));
}

/**
 * Attach or detach content depending on an expression.
 *
 * Content is kept alive when detached.
 *
 * See {@link Attach `<Attach>`} when using JSX.
 *
 * @param condition The condition to watch.
 * @param content The content to attach when the condition result is truthy.
 *
 * @example
 * ```tsx
 * import { $, attach } from "rvx";
 *
 * const showMessage = $(true);
 *
 * attachWhen(showMessage, e("h1").append("Hello World!"))
 * ```
 */
export function attachWhen(condition: Expression<boolean>, content: Content): View {
	return nest(condition, value => value ? content : undefined);
}