SP24

const START_OFFSET = 7;

/**
 * @property {string} fields[].name
 * @property {int} fields[].length
 */
export default class BufferCodec {

    constructor(options) {
        Object.assign(this, options);
    }

    createEncoder() {
        let offset = START_OFFSET;

        let code = `const buffer = Buffer.allocUnsafe(${size});`;

        for (let {length, name} of this.fields) {
            if (length > 6) {
                code += `${name}: buffer.subarray(${offset}, ${length}),`
            } else {
                code += `${name}: buffer.readUIntBE(${offset}, ${length}),`;
            }
            offset += length;
        }
        code += "};";

        return new Function('buffer', code);
    }

    createDecoder() {
        let offset = START_OFFSET;
        let code = "return {";

        for (let {length, name} of this.fields) {
            if (length > 6) {
                code += `${name}: buffer.subarray(${offset}, ${length}),`
            } else {
                code += `${name}: buffer.readUIntBE(${offset}, ${length}),`;
            }
            offset += length;
        }
        code += "};";

        return new Function('buffer', code);
    }
}