/**
 * Low-level interface to programmer's I2C USB class.
 *
 * See //dc/hbj11/flasher/bluepill/src/i2c.rs for more information.
 */

const ControlInRequest = Object.freeze({
  'GetStatus': 1,
});

const ControlOutRequest = Object.freeze({
  'SetLED': 1,
  'ReadI2C': 2,
  'ReadBuffer': 3,
  'WriteI2C': 4,
  'SetWritePointer': 5,
});

export const Status = Object.freeze({
  'Idle': 0,
  'InvalidArgument': 1,
  'Ack': 2,
  'Nack': 3,
  'BusError': 4,
});

export const StatusFromU8 = function(u8) {
  for (const label of Object.keys(Status)) {
    let val = Status[label];
    if (val === u8) {
      return label;
    }
  }
};

/**
 * Low-level interface to programmer's I2C USB class. Thinly wraps available
 * USB transfers.
 */
export class USBI2CClassInterface {
  /**
   * @param {USBDevice} usb - The WebUSB device that backs this USB class.
   */
  constructor(device) {
    this.usb = device;
    this.BUFFER_SIZE = 1024;
    this.PACKET_SIZE = 64;
  }

  /**
   * Open this programmer via WebUSB and finds all required endpoints.
   */
  async open() {
    await this.usb.open();
    await this.usb.selectConfiguration(1);
    await this.usb.claimInterface(0);

    let eps = this.usb.configuration.interfaces[0].alternate.endpoints;
    this.bulk_out = null;
    this.bulk_in = null;
    for (const ep of eps) {
        if (ep.direction == "out" && ep.type == "bulk") {
            this.bulk_out = ep;
        }
        if (ep.direction == "in" && ep.type == "bulk") {
            this.bulk_in = ep;
        }
    }
    if (this.bulk_out === null) {
      throw new Error("Could not find bulk out endpoint");
    }
    if (this.bulk_in === null) {
      throw new Error("Could not find bulk in endpoint");
    }
  }

  /**
   * Performs a USB Control OUT request to the I2C class.
   * @param {number} request - Request number for transfer (0-255).
   * @param {number} value - Value for transfer (0-65535).
   * @returns {Promise<USBOutTransferResult>} The underlying WebUSB transfer result.
   */
  async controlOut(request, value) {
    return await this.usb.controlTransferOut({
      requestType: "vendor",
      recipient: "interface",
      request: request,
      value: value,
      index: 0,
    });
  }

  /**
   * Read status from programmer.
   * @returns {Status} The status of the programmer.
   */
  async getStatus() {
    let res = await this.usb.controlTransferIn({
      requestType: "vendor",
      recipient: "interface",
      request: ControlInRequest.GetStatus,
      value: 0,
      index: 0
    }, 1);
    if (res.data.byteLength < 1) {
      throw new Error('returned data too short')
    }
    return res.data.getInt8(0);
  }

  /**
   * Sends SetLED control OUT request.
   */
  async setLED(on) {
    return await this.controlOut(ControlOutRequest.SetLED, on ? 1 : 0);
  }

  /**
   * Sends ReadI2C control OUT request.
   */
  async readI2C(addr, length) {
    return await this.controlOut(ControlOutRequest.ReadI2C, (length << 8) | addr);
  }

  /**
   * Sends ReadBuffer control OUT request.
   */
  async readBuffer(addr, length) {
    return await this.controlOut(ControlOutRequest.ReadBuffer, (length << 8) | addr);
  }

  /**
   * Sends WriteI2C control OUT request.
   */
  async writeI2C(addr, length) {
    return await this.controlOut(ControlOutRequest.WriteI2C, (length << 8) | addr);
  }

  /**
   * Sends SetWritePointer control OUT request.
   */
  async setWritePointer(addr) {
    return await this.controlOut(ControlOutRequest.SetWritePointer, addr);
  }

  /**
   * Requets bulk IN data.
   */
  async bulkIn(length) {
      return await this.usb.transferIn(this.bulk_in.endpointNumber, length);
  }

  /**
   * Sends bulk OUT data.
   */
  async bulkOut(data) {
      return await this.usb.transferOut(this.bulk_out.endpointNumber, data);
  }
}