/**
 * @module adaptive-expressions
 */
/**
 * Copyright (c) Microsoft Corporation. All rights reserved.
 * Licensed under the MIT License.
 */

import { Expression } from '../expression';
import { EvaluateExpressionDelegate, ExpressionEvaluator } from '../expressionEvaluator';
import { ExpressionType } from '../expressionType';
import { FunctionUtils } from '../functionUtils';
import { ReturnType } from '../returnType';

/**
 * Return a collection that has all the items from the specified collections.
 * To appear in the result, an item can appear in any collection passed to this function.
 * If one or more items have the same name, the last item with that name appears in the result.
 */
export class Union extends ExpressionEvaluator {
    /**
     * Initializes a new instance of the [Union](xref:adaptive-expressions.Union) class.
     */
    constructor() {
        super(ExpressionType.Union, Union.evaluator(), ReturnType.Array, Union.validator);
    }

    /**
     * @private
     */
    private static evaluator(): EvaluateExpressionDelegate {
        return FunctionUtils.apply((args: any[]): any => {
            let result: any[] = [];
            for (const arg of args) {
                result = result.concat(arg);
            }

            return Array.from(new Set(result));
        }, FunctionUtils.verifyList);
    }

    /**
     * @private
     */
    private static validator(expression: Expression): void {
        FunctionUtils.validateArityAndAnyType(expression, 1, Number.MAX_SAFE_INTEGER, ReturnType.Array);
    }
}