const Stack = require("./Stack");
const ComputerParameterMode = require('./ComputerParameterMode');

/**
 * An Intcode Computer for the Advent of Code 2019 challenge
 *
 * @author Apis Necros
 */
module.exports = class Computer {
    constructor(stack) {
        this.stack = new Stack(stack);
        this.OPCODES = {
            ADD: 1,
            MULTIPLY: 2,
            OUTPUT: 4,
            HALT: 99,
        };

        this.paramMode = ComputerParameterMode.POSITION_MODE;
    }

    /**
     * Run the computer
     *
     * Runs opcodes on the stack until either the a HALT command is
     * encountered, or an error is thrown.
     * @returns {void}
     */
    Run() {
        // eslint-disable-next-line no-empty
        while (this.Execute(this.stack.Get()) === true) { }
    }

    /**
     * Execute a call using the provided opcode
     *
     * @param {number} opcode A opcode to execute
     * @returns {boolean} False if the opcode was HALT, otherwise true
     */
    Execute(opcode) {
        // console.log(`DEBUG: opcode: ${opcode}`)
        let status = true;
        switch (opcode) {
            case this.OPCODES.ADD: {
                const operandLeft = this.stack.Next().Get();
                const operandRight = this.stack.Next().Get();
                const position = this.stack.Next().Get();

                this.Operation_Add(operandLeft, operandRight, position);
                break;
            }
            case this.OPCODES.MULTIPLY: {
                const operandLeft = this.stack.Next().Get();
                const operandRight = this.stack.Next().Get();
                const position = this.stack.Next().Get();

                this.Operation_Multiply(operandLeft, operandRight, position);
                break;
            }
            case this.OPCODES.OUTPUT: {
                const outputPosition = this.stack.Next().Get();

                this.Operation_Output(outputPosition);
                break;
            }
            case this.OPCODES.HALT:
                status = false;
                break;
            default:
                throw Error(`Opcode ${opcode} not found`);
        }

        this.stack.Next();

        return status;
    }

    /**
     * Execute the Add opcode
     *
     * Adds two numbers and stores the result at the provided position
     * on the stack.
     *
     * @param {number} operandLeft The first operand
     * @param {number} operandRight The second operand
     * @param {number} outputPosition The position on the stack to place the result
     * @returns {void}
     */
    Operation_Add(operandLeft, operandRight, outputPosition) {
        const newValue = operandLeft + operandRight;
        this.stack.Put(outputPosition, newValue);
    }

    /**
     * Execute the Multiply opcode
     *
     * Multiplies two numbers and stores the result at the provided
     * position on the stack.
     *
     * @param {number} operandLeft The first operand
     * @param {number} operandRight The second operand
     * @param {number} outputPosition The position on the stack to place the result
     * @returns {void}
     */
    Operation_Multiply(operandLeft, operandRight, outputPosition) {
        const newValue = operandLeft * operandRight;
        this.stack.Put(outputPosition, newValue);
    }

    /**
     * Execute the OUTPUT opcode
     *
     * @param {number} outputPosition The memory address of the value to output
     */
    Operation_Output(outputPosition) {
        console.log(this.stack.Get(outputPosition));
    }

    /**
     * Outputs the computer's stack to the console
     * @returns {void}
     */
    DumpMemory() {
        console.log(this.stack.Dump());
    }
};

/**
 * Check whether the value at a specific spot in a number is non-zero
 *
 * Similar to the bitwise & operator, checks a "place" in a decimal number
 * to see if it has a non-zero value.
 *
 * @example
 * const test = 107;
 * console.log(DecimalPlaceIsNonZero(test, 1)) // true
 * console.log(DecimalPlaceIsNonZero(test, 2)) // false
 * console.log(DecimalPlaceIsNonZero(test, 3)) // true
 *
 * @param {number} input The number to check
 * @param {number} place The power of 10 to check against
 * @returns {boolean} Whether the value in that number's place is non-zero
 */
function DecimalPlaceIsNonZero(input, place) {
    return !!Math.floor((input % 10**place) / 10**(place - 1));
}