// @ts-check
/** @typedef { import('estree').BaseNode} BaseNode */

/** @typedef {{
	skip: () => void;
	remove: () => void;
	replace: (node: BaseNode) => void;
}} WalkerContext */

class WalkerBase {
	constructor() {
		/** @type {boolean} */
		this.should_skip = false;

		/** @type {boolean} */
		this.should_remove = false;

		/** @type {BaseNode | null} */
		this.replacement = null;

		/** @type {WalkerContext} */
		this.context = {
			skip: () => (this.should_skip = true),
			remove: () => (this.should_remove = true),
			replace: (node) => (this.replacement = node)
		};
	}

	/**
	 *
	 * @param {any} parent
	 * @param {string} prop
	 * @param {number} index
	 * @param {BaseNode} node
	 */
	replace(parent, prop, index, node) {
		if (parent) {
			if (index !== null) {
				parent[prop][index] = node;
			} else {
				parent[prop] = node;
			}
		}
	}

	/**
	 *
	 * @param {any} parent
	 * @param {string} prop
	 * @param {number} index
	 */
	remove(parent, prop, index) {
		if (parent) {
			if (index !== null) {
				parent[prop].splice(index, 1);
			} else {
				delete parent[prop];
			}
		}
	}
}

// @ts-check

/** @typedef { import('estree').BaseNode} BaseNode */
/** @typedef { import('./walker.js').WalkerContext} WalkerContext */

/** @typedef {(
 *    this: WalkerContext,
 *    node: BaseNode,
 *    parent: BaseNode,
 *    key: string,
 *    index: number
 * ) => void} SyncHandler */

class SyncWalker extends WalkerBase {
	/**
	 *
	 * @param {SyncHandler} enter
	 * @param {SyncHandler} leave
	 */
	constructor(enter, leave) {
		super();

		/** @type {SyncHandler} */
		this.enter = enter;

		/** @type {SyncHandler} */
		this.leave = leave;
	}

	/**
	 *
	 * @param {BaseNode} node
	 * @param {BaseNode} parent
	 * @param {string} [prop]
	 * @param {number} [index]
	 * @returns {BaseNode}
	 */
	visit(node, parent, prop, index) {
		if (node) {
			if (this.enter) {
				const _should_skip = this.should_skip;
				const _should_remove = this.should_remove;
				const _replacement = this.replacement;
				this.should_skip = false;
				this.should_remove = false;
				this.replacement = null;

				this.enter.call(this.context, node, parent, prop, index);

				if (this.replacement) {
					node = this.replacement;
					this.replace(parent, prop, index, node);
				}

				if (this.should_remove) {
					this.remove(parent, prop, index);
				}

				const skipped = this.should_skip;
				const removed = this.should_remove;

				this.should_skip = _should_skip;
				this.should_remove = _should_remove;
				this.replacement = _replacement;

				if (skipped) return node;
				if (removed) return null;
			}

			for (const key in node) {
				const value = node[key];

				if (typeof value !== "object") {
					continue;
				} else if (Array.isArray(value)) {
					for (let i = 0; i < value.length; i += 1) {
						if (value[i] !== null && typeof value[i].type === 'string') {
							if (!this.visit(value[i], node, key, i)) {
								// removed
								i--;
							}
						}
					}
				} else if (value !== null && typeof value.type === "string") {
					this.visit(value, node, key, null);
				}
			}

			if (this.leave) {
				const _replacement = this.replacement;
				const _should_remove = this.should_remove;
				this.replacement = null;
				this.should_remove = false;

				this.leave.call(this.context, node, parent, prop, index);

				if (this.replacement) {
					node = this.replacement;
					this.replace(parent, prop, index, node);
				}

				if (this.should_remove) {
					this.remove(parent, prop, index);
				}

				const removed = this.should_remove;

				this.replacement = _replacement;
				this.should_remove = _should_remove;

				if (removed) return null;
			}
		}

		return node;
	}
}

// @ts-check

/** @typedef { import('estree').BaseNode} BaseNode */
/** @typedef { import('./walker').WalkerContext} WalkerContext */

/** @typedef {(
 *    this: WalkerContext,
 *    node: BaseNode,
 *    parent: BaseNode,
 *    key: string,
 *    index: number
 * ) => Promise<void>} AsyncHandler */

class AsyncWalker extends WalkerBase {
	/**
	 *
	 * @param {AsyncHandler} enter
	 * @param {AsyncHandler} leave
	 */
	constructor(enter, leave) {
		super();

		/** @type {AsyncHandler} */
		this.enter = enter;

		/** @type {AsyncHandler} */
		this.leave = leave;
	}

	/**
	 *
	 * @param {BaseNode} node
	 * @param {BaseNode} parent
	 * @param {string} [prop]
	 * @param {number} [index]
	 * @returns {Promise<BaseNode>}
	 */
	async visit(node, parent, prop, index) {
		if (node) {
			if (this.enter) {
				const _should_skip = this.should_skip;
				const _should_remove = this.should_remove;
				const _replacement = this.replacement;
				this.should_skip = false;
				this.should_remove = false;
				this.replacement = null;

				await this.enter.call(this.context, node, parent, prop, index);

				if (this.replacement) {
					node = this.replacement;
					this.replace(parent, prop, index, node);
				}

				if (this.should_remove) {
					this.remove(parent, prop, index);
				}

				const skipped = this.should_skip;
				const removed = this.should_remove;

				this.should_skip = _should_skip;
				this.should_remove = _should_remove;
				this.replacement = _replacement;

				if (skipped) return node;
				if (removed) return null;
			}

			for (const key in node) {
				const value = node[key];

				if (typeof value !== "object") {
					continue;
				} else if (Array.isArray(value)) {
					for (let i = 0; i < value.length; i += 1) {
						if (value[i] !== null && typeof value[i].type === 'string') {
							if (!(await this.visit(value[i], node, key, i))) {
								// removed
								i--;
							}
						}
					}
				} else if (value !== null && typeof value.type === "string") {
					await this.visit(value, node, key, null);
				}
			}

			if (this.leave) {
				const _replacement = this.replacement;
				const _should_remove = this.should_remove;
				this.replacement = null;
				this.should_remove = false;

				await this.leave.call(this.context, node, parent, prop, index);

				if (this.replacement) {
					node = this.replacement;
					this.replace(parent, prop, index, node);
				}

				if (this.should_remove) {
					this.remove(parent, prop, index);
				}

				const removed = this.should_remove;

				this.replacement = _replacement;
				this.should_remove = _should_remove;

				if (removed) return null;
			}
		}

		return node;
	}
}

// @ts-check

/** @typedef { import('estree').BaseNode} BaseNode */
/** @typedef { import('./sync.js').SyncHandler} SyncHandler */
/** @typedef { import('./async.js').AsyncHandler} AsyncHandler */

/**
 *
 * @param {BaseNode} ast
 * @param {{
 *   enter?: SyncHandler
 *   leave?: SyncHandler
 * }} walker
 * @returns {BaseNode}
 */
function walk(ast, { enter, leave }) {
	const instance = new SyncWalker(enter, leave);
	return instance.visit(ast, null);
}

/**
 *
 * @param {BaseNode} ast
 * @param {{
 *   enter?: AsyncHandler
 *   leave?: AsyncHandler
 * }} walker
 * @returns {Promise<BaseNode>}
 */
async function asyncWalk(ast, { enter, leave }) {
	const instance = new AsyncWalker(enter, leave);
	return await instance.visit(ast, null);
}

export { asyncWalk, walk };