const Types = {
    Simple: 0x80,
    ANSI_EXTD: 0x91
};

const ElementTypes = {
    UINT8: 0x28,
    UINT16: 0x29,
    UINT32: 0x2a
};

/**
 * Builds EPATH Data Segment
 *
 * @param data
 * @param ANSI - Declare if ANSI Extended or Simple
 * @returns Segment
 */
const build = (data: string | Buffer, ANSI: boolean = true): Buffer => {
    if (!(typeof data === "string" || Buffer.isBuffer(data)))
        throw new Error("Data Segment Data Must be a String or Buffer");

    // Build Element Segment If Int
    if (!isNaN(Number(data))) return elementBuild(Number(data));

    // Build symbolic segment by default
    return symbolicBuild(data, ANSI);
};

/**
 * Builds EPATH Symbolic Segment
 *
 * @param data
 * @param ANSI - Declare if ANSI Extended or Simple
 * @returns Segment
 */
const symbolicBuild = (data: string | Buffer, ANSI: boolean): Buffer => {
    // Initialize Buffer
    let buf = Buffer.alloc(2);

    // Write Appropriate Segment Byte
    buf.writeUInt8(ANSI ? Types.ANSI_EXTD : Types.Simple, 0);

    // Write Appropriate Length
    buf.writeUInt8(ANSI ? data.length : Math.ceil(data.length / 2), 1);

    // Append Data
    buf = Buffer.concat([buf, Buffer.from(data)]);

    // Add Pad Byte if Odd Length
    if (buf.length % 2 === 1) buf = Buffer.concat([buf, Buffer.alloc(1)]); // Pad Odd Length Strings

    return buf;
};

/**
 * Builds EPATH Element Segment
 *
 * @param data
 * @returns Segment
 */
const elementBuild = (data: number): Buffer => {
    // Get Element Length - Data Access 2 - IOI Segments - Element Segments
    let type: number;
    let dataBuf: Buffer;

    if (data < 256) {
        type = ElementTypes.UINT8; // UNIT8 x28 xx
        dataBuf = Buffer.alloc(1);
        dataBuf.writeUInt8(data);
    } else if (data < 65536) {
        type = ElementTypes.UINT16; // UINT16 x29 00 xx xx
        dataBuf = Buffer.alloc(3);
        dataBuf.writeUInt16LE(Number(data), 1);
    } else {
        type = ElementTypes.UINT32; // UINT32 x2a 00 xx xx xx xx
        dataBuf = Buffer.alloc(5);
        dataBuf.writeUInt32LE(Number(data), 1);
    }

    // Initialize Buffer
    let buf = Buffer.alloc(1);

    // Write Appropriate Segment Byte
    buf.writeUInt8(type, 0);

    // Append Data
    buf = Buffer.concat([buf, dataBuf]);

    return buf;
};

export { Types, build };