'use strict';

const Stampit = require('stampit');
const Put     = require('put');

module.exports = Stampit()
    .init(function () {
        const FC = 4;

        let init = () => this.addResponseHandler(FC, onResponse);

        let onResponse = (unitId, pdu, cb) => {
            let fc = pdu.readUInt8(0);

            if (fc !== FC) {
                cb(`ReadInputRegisters: Invalid FC ${fc}`);
            } else {
                let byteCount   = pdu.readUInt8(1);

                let resp = {
                    unitId,
                    fc:         fc,
                    byteCount:  byteCount,
                    payload:    pdu.slice(2),
                    register:   []
                };
                const registerCount = byteCount / 2;

                for (let i = 0; i < registerCount; i++) {
                    resp.register.push(pdu.readUInt16BE(2 + (i * 2)));
                }

                cb && cb(null, resp);
            }
        };

        this.readInputRegisters = (unitId, start, quantity) => {
            return new Promise((resolve, reject) => {
                let pdu = Put().word8be(FC).word16be(start).word16be(quantity).buffer();

                this.queueRequest(unitId, FC, pdu, (err, resp) => {
                    if (err) {
                        reject(err);
                    } else {
                        resolve(resp);
                    }
                });
            });
        };
        init();
    
    });