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

/**
 * 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,
            HALT: 99,
        };
    }

    /**
     * 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().GetUsingStackValue();
                const operandRight = this.stack.Next().GetUsingStackValue();
                const position = this.stack.Next().Get();

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

                this.Operation_Multiply(operandLeft, operandRight, position);
                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);
    }

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