'use strict';

/**
 * Operator callback functions.
 *
 * @type {Object}
 */
var OPERATORS = {
	'!': function( a ) {
		return ! a;
	},
	'*': function( a, b ) {
		return a * b;
	},
	'/': function( a, b ) {
		return a / b;
	},
	'%': function( a, b ) {
		return a % b;
	},
	'+': function( a, b ) {
		return a + b;
	},
	'-': function( a, b ) {
		return a - b;
	},
	'<': function( a, b ) {
		return a < b;
	},
	'<=': function( a, b ) {
		return a <= b;
	},
	'>': function( a, b ) {
		return a > b;
	},
	'>=': function( a, b ) {
		return a >= b;
	},
	'==': function( a, b ) {
		return a === b;
	},
	'!=': function( a, b ) {
		return a !== b;
	},
	'&&': function( a, b ) {
		return a && b;
	},
	'||': function( a, b ) {
		return a || b;
	},
	'?:': function( a, b, c ) {
		if ( a ) {
			throw b;
		}

		return c;
	},
};

/**
 * Given an array of postfix terms and operand variables, returns the result of
 * the postfix evaluation.
 *
 * @example
 *
 * ```js
 * import evaluate from '@tannin/evaluate';
 *
 * // 3 + 4 * 5 / 6 ⇒ '3 4 5 * 6 / +'
 * const terms = [ '3', '4', '5', '*', '6', '/', '+' ];
 *
 * evaluate( terms, {} );
 * // ⇒ 6.333333333333334
 * ```
 *
 * @param {string[]} postfix   Postfix terms.
 * @param {Object}   variables Operand variables.
 *
 * @return {*} Result of evaluation.
 */
function evaluate( postfix, variables ) {
	var stack = [],
		i, j, args, getOperatorResult, term, value;

	for ( i = 0; i < postfix.length; i++ ) {
		term = postfix[ i ];

		getOperatorResult = OPERATORS[ term ];
		if ( getOperatorResult ) {
			// Pop from stack by number of function arguments.
			j = getOperatorResult.length;
			args = Array( j );
			while ( j-- ) {
				args[ j ] = stack.pop();
			}

			try {
				value = getOperatorResult.apply( null, args );
			} catch ( earlyReturn ) {
				return earlyReturn;
			}
		} else if ( variables.hasOwnProperty( term ) ) {
			value = variables[ term ];
		} else {
			value = +term;
		}

		stack.push( value );
	}

	return stack[ 0 ];
}

module.exports = evaluate;
