"use strict";

const cnst = (x) => () => x;

const pi = cnst(Math.PI);
const e = cnst(Math.E);

const variable = (name) => (x, y, z) => {
    if (name === "x") return x;
    if (name === "y") return y;
    if (name === "z") return z;
}

const add = (a, b) => (...args) => a(...args) + b(...args);

const subtract = (a, b) => (...args) => a(...args) - b(...args);

const multiply = (a, b) => (...args) => a(...args) * b(...args);

const divide = (a, b) => (...args) => a(...args) / b(...args);

const negate = (a) => (...args) => (-1) * a(...args);

const avg5 = (a, b, c, d, e) => (...args) => {
    return (a(...args) + b(...args) + c(...args) + d(...args) + e(...args)) / 5;
}

const med3 = (a, b, c) => (...args) => {
    let arr = [a(...args), b(...args), c(...args)];
    arr = arr.sort((a, b) => a - b);
    return arr[1];
}

const  operations = [ 'negate', '+', '-', '*', '/', 'med3', 'avg5' ];

const operationToArity = {
    'negate': 1,
    '+' : 2,
    '-' : 2,
    '*' : 2,
    '/' : 2,
    'med3' : 3,
    'avg5' : 5
};

const operationToFunction = {
    'negate': negate,
    '+' : add,
    '-' : subtract,
    '*' : multiply,
    '/' : divide,
    'med3' : med3,
    'avg5' : avg5
};

const parse = function(expression) {
    let stack = [];
    let tokens = expression.split(' ').filter((word) => word !== '');
    for (let token of tokens) {
        let arity = token in operationToArity ? operationToArity[token] : 0;
        let args = [];
        for (let i = 0; i < arity; i++) {
            args.push(stack.pop());
        }
        args = args.reverse();
        stack.push(makeOperation(token, ...args));
    }
    return stack.pop();
}

const makeOperation = function (token, ...args) {
    switch (token) {
        case 'negate': return negate(...args);
        case "+": return add(...args);
        case "-": return subtract(...args);
        case "*": return multiply(...args);
        case "/": return divide(...args);
        case 'med3': return med3(...args);
        case 'avg5': return avg5(...args);
        case "x": return variable("x");
        case "y": return variable("y");
        case "z": return variable("z");
        case 'pi': return pi;
        case 'e': return e;
    }
    return cnst(Number.parseInt(token));
}