// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package pandora.l2cap;

import "google/protobuf/any.proto";
import "google/protobuf/empty.proto";
import "pandora/host.proto";

option java_outer_classname = "L2CAPProto";

// L2CAP (Logical Link Control and Adaptation Protocol) services for managing channels
// and data communication over ACL connections. This protocol is essential for
// creating multiplexed data channels over the underlying ACL connections in Bluetooth.
service L2CAP {
  // Establish an L2CAP channel on an ACL connection.
  rpc Connect(ConnectRequest) returns (ConnectResponse);
  // Await and accept an incoming L2CAP channel on an existing ACL connection.
  // Every incoming L2CAP channel connection request not handled by this
  // method should be rejected.
  rpc WaitConnection(WaitConnectionRequest) returns (WaitConnectionResponse);
  // Disconnect an established L2CAP channel.
  rpc Disconnect(DisconnectRequest) returns (DisconnectResponse);
  // Await an established L2CAP channel's termination.
  rpc WaitDisconnection(WaitDisconnectionRequest) returns (WaitDisconnectionResponse);
  // Fetch data received from an active L2CAP channel.
  // Packets are yielded until the stream is closed, packets are dropped otherwise.
  rpc Receive(ReceiveRequest) returns (stream ReceiveResponse);
  // Send data over an L2CAP channel to a connected device.
  rpc Send(SendRequest) returns (SendResponse);
}

// Potential reasons for command rejections in the L2CAP protocol.
enum CommandRejectReason {
  // The command wasn't understood by the receiver.
  COMMAND_NOT_UNDERSTOOD = 0;
  // The received signal exceeds the allowed MTU (Maximum Transmission Unit).
  SIGNAL_MTU_EXCEEDED = 1;
  // The received command includes an invalid Channel Identifier (CID).
  INVALID_CID_IN_REQUEST = 2;
}

// A Token representing a unique L2CAP channel for data communication.
message Channel {
  // Opaque value filled by the gRPC server, must not be modified nor crafted.
  google.protobuf.Any cookie = 1;
}

// Fixed channel, represented by a `Connection` and a Fixed Channel Identifier (CID).
message FixedChannel {
  // Specifies the underlying ACL connection, either BR/EDR (Basic Rate/Enhanced Data Rate) or BLE.
  Connection connection = 1;
  // Fixed Channel Identifier (CID). Represents the unique identifier for the fixed channel.
  // Available CIDs are:
  // - 0x0001: L2CAP Signaling Channel
  // - 0x0002: Connectionless Channel
  // - 0x0003: AMP Manager Protocol
  // - 0x0004: Attribute Protocol (ATT) for BLE
  // - 0x0005: L2CAP Signaling Channel for BLE
  // - 0x0006: Security Manager Protocol for BLE
  // - 0x0007: Security Manager Protocol for BR/EDR
  // - CIDs in the range of 0x0007 to 0x003F are reserved for standardization purposes.
  uint32 cid = 2;
}

// Request for establishing an L2CAP connection-oriented channel, 
// where data is transmitted with acknowledgment.
message ConnectionOrientedChannelRequest {
  // Protocol/Service Multiplexer (PSM) for identifying the upper-layer protocol.
  uint32 psm = 1;
  // Defines the maximum size of data payload (in bytes) that can be sent in a single packet.
  uint32 mtu = 2;
}

// Request for establishing a credit-based L2CAP channel, 
// typically used in BLE (Bluetooth Low Energy) when precise flow control is required.
message CreditBasedChannelRequest {
  // Simplified Protocol/Service Multiplexer (sPSM) for identifying the upper-layer protocol in BLE.
  uint32 spsm = 1;
  // Defines the maximum size of data payload (in bytes) that can be sent in a single packet.
  uint32 mtu = 2;
  // Maximum size of the PDU (Protocol Data Unit) payload.
  uint32 mps = 3;
  // Initial credits given for flow control, defining the number of PDUs the sender can transmit.
  uint32 initial_credit = 4;
}

// Request of the `Connect` method.
message ConnectRequest {
  // Specifies the underlying ACL connection, either BR/EDR (Basic Rate/Enhanced Data Rate) or BLE.
  Connection connection = 1;
  // Defines the type and specifics of the channel to establish.
  oneof type {
    // Request a connection-oriented channel.
    ConnectionOrientedChannelRequest basic = 2;
    // Request a BLE credit-based channel.
    CreditBasedChannelRequest le_credit_based = 3;
    // Request an enhanced credit-based channel.
    CreditBasedChannelRequest enhanced_credit_based = 4;
  }
}

// Response of the `Connect` method.
message ConnectResponse {
  oneof result {
    // Error details if the connection failed.
    CommandRejectReason error = 1;
    // Details of the established channel on success.
    Channel channel = 2;
  }
}

// Request of the `WaitConnection` method.
message WaitConnectionRequest {
  // Specifies the underlying ACL connection, either BR/EDR or BLE.
  Connection connection = 1;
  // Defines the type and specifics of the channel to wait and accept.
  oneof type {
    // Accept connection-oriented channels.
    ConnectionOrientedChannelRequest basic = 2;
    // Accept BLE credit-based channels.
    CreditBasedChannelRequest le_credit_based = 3;
    // Accept enhanced credit-based channels.
    CreditBasedChannelRequest enhanced_credit_based = 4;
  }
}

// Response of the `WaitConnection` method.
message WaitConnectionResponse {
  oneof result {
    CommandRejectReason error = 1;
    Channel channel = 2;
  }
}

// Request of the `Disconnect` method.
message DisconnectRequest {
  // Specifies the channel to disconnect.
  Channel channel = 1;
}

// Response of the `Disconnect` method.
message DisconnectResponse {
  oneof result {
    CommandRejectReason error = 1;
    google.protobuf.Empty success = 2;
  }
}

// Request of the `WaitDisconnection` method.
message WaitDisconnectionRequest {
  // Specifies the channel to await disconnection.
  Channel channel = 1;
}

// Response of the `WaitDisconnection` method.
message WaitDisconnectionResponse {
  oneof result {
    CommandRejectReason error = 1;
    google.protobuf.Empty success = 2;
  }
}

// Request of the `Receive` method.
message ReceiveRequest {
  // Specifies the channel to fetch data from.
  oneof source {
    // Fetch data from a dynamic channel.
    Channel channel = 1;
    // Fetch data from a fixed channel.
    FixedChannel fixed_channel = 2;
  }
}

// Response of the `Receive` method.
message ReceiveResponse {
  // Contains the data received from the channel.
  bytes data = 1;
}

// Request of the `Send` method.
message SendRequest {
  // Specifies the channel to send data over.
  oneof sink {
    // Send data over a dynamic channel.
    Channel channel = 1;
    // Send data over a fixed channel.
    FixedChannel fixed_channel = 2;
  }
  // Data to be sent over the specified channel.
  bytes data = 3;
}

// Response of the `Send` method.
message SendResponse {
  oneof result {
    CommandRejectReason error = 1;
    google.protobuf.Empty success = 2;
  }
}