/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
'use strict';

import {TPromise} from 'vs/base/common/winjs.base';
import {TypeConstraint, validateConstraints} from 'vs/base/common/types';
import {ServicesAccessor, createDecorator, ServiceIdentifier} from 'vs/platform/instantiation/common/instantiation';

export const ICommandService = createDecorator<ICommandService>('commandService');

export interface ICommandService {
	serviceId: ServiceIdentifier<any>;
	executeCommand<T>(commandId: string, ...args: any[]): TPromise<T>;
	executeCommand(commandId: string, ...args: any[]): TPromise<any>;
	isKnownCommand(commandId: string): boolean;
}

export interface ICommandsMap {
	[id: string]: ICommand;
}

export interface ICommandHandler {
	(accessor: ServicesAccessor, ...args: any[]): void;
}

export interface ICommand {
	handler: ICommandHandler;
	description?: ICommandHandlerDescription;
}

export interface ICommandHandlerDescription {
	description: string;
	args: { name: string; description?: string; constraint?: TypeConstraint; }[];
	returns?: string;
}

export interface ICommandRegistry {
	registerCommand(id: string, command: ICommandHandler): void;
	registerCommand(id: string, command: ICommand): void;
	getCommand(id: string): ICommand;
	getCommands(): ICommandsMap;
}

function isCommand(thing: any): thing is ICommand {
	return typeof thing === 'object'
		&& typeof (<ICommand>thing).handler === 'function'
		&& (!(<ICommand>thing).description || typeof (<ICommand>thing).description === 'object');
}

export const CommandsRegistry: ICommandRegistry = new class implements ICommandRegistry {

	private _commands: { [id: string]: ICommand } = Object.create(null);

	registerCommand(id: string, commandOrDesc: ICommandHandler | ICommand): void {
		// if (this._commands[id] !== void 0) {
		// 	throw new Error(`command already exists: '${id}'`);
		// }
		if (!commandOrDesc) {
			throw new Error(`invalid command`);
		}

		if (!isCommand(commandOrDesc)) {
			// simple handler
			this._commands[id] = { handler: commandOrDesc };

		} else {
			const {handler, description} = commandOrDesc;
			if (description) {
				// add argument validation if rich command metadata is provided
				const constraints: TypeConstraint[] = [];
				for (let arg of description.args) {
					constraints.push(arg.constraint);
				}
				this._commands[id] = {
					description,
					handler(accessor, ...args: any[]) {
						validateConstraints(args, constraints);
						return handler(accessor, ...args);
					}
				};
			} else {
				// add as simple handler
				this._commands[id] = { handler };
			}
		}
	}

	getCommand(id: string): ICommand {
		return this._commands[id];
	}

	getCommands(): ICommandsMap {
		return this._commands;
	}
};

export const NullCommandService: ICommandService = {
	serviceId: undefined,
	executeCommand() {
		return TPromise.as(undefined);
	},
	isKnownCommand() {
		return false;
	}
};