#include <gtest/gtest.h>

#include <cstdint>
#include <span>

#include "esphome/components/modbus/modbus.h"

namespace esphome::modbus::testing {

namespace {

// Exposes the protected tx queue and waiting-for-response slot so tests can drive the
// no-response path without a UART: force_send_front() mimics send_next_frame_() moving the
// front frame in flight, timeout_waiting() mimics the loop() no-response timeout handling.
class NoResponseProbeHub : public ModbusClientHub {
 public:
  size_t queued_frames() const { return this->tx_buffer_.size(); }
  const ModbusDeviceCommand &front() const { return this->tx_buffer_.front(); }
  bool waiting() const { return this->waiting_for_response_.has_value(); }
  const ModbusDeviceCommand &waiting_command() const {
    EXPECT_TRUE(this->waiting_for_response_.has_value());
    return *this->waiting_for_response_;  // NOLINT(bugprone-unchecked-optional-access)
  }

  void force_send_front() {
    this->waiting_for_response_ = std::move(this->tx_buffer_.front());
    this->tx_buffer_.pop_front();
  }
  // Drives the real unexpected-frame branch in process_modbus_server_frame().
  void receive_frame_for_test(uint8_t address, std::span<const uint8_t> pdu) {
    this->process_modbus_server_frame(address, pdu);
  }
  void timeout_waiting() {
    if (this->waiting_for_response_.has_value())
      this->notify_no_response_(*this->waiting_for_response_);
    this->waiting_for_response_.reset();
  }
};

// A device with a scripted answer to on_no_response().
class RetryingDevice : public ModbusClientDevice {
 public:
  RetryingDevice(ModbusClientHub *hub, uint8_t address, bool retry) : ModbusClientDevice(hub, address), retry_(retry) {}
  bool on_no_response() override {
    this->no_response_count_++;
    return this->retry_;
  }
  int no_response_count_{0};

 protected:
  bool retry_{false};
};

// A device that clears its own queued traffic from inside the no-response callback, then asks for a retry.
class ClearingRetryDevice : public ModbusClientDevice {
 public:
  ClearingRetryDevice(ModbusClientHub *hub, uint8_t address) : ModbusClientDevice(hub, address) {}
  bool on_no_response() override {
    this->no_response_count_++;
    this->clear_tx_queue_for_device();  // detaches this device from the waiting slot mid-callback
    return true;                        // and still requests a retry
  }
  int no_response_count_{0};
};

constexpr uint8_t READ_PDU[] = {0x03, 0x01, 0x00, 0x00, 0x02};  // read 2 holding registers at 0x100

StaticVector<uint8_t, MAX_PDU_SIZE> read_pdu() {
  StaticVector<uint8_t, MAX_PDU_SIZE> pdu;
  pdu.assign(READ_PDU, READ_PDU + sizeof(READ_PDU));
  return pdu;
}

}  // namespace

// A device that requests a retry gets the frame the hub was holding re-queued on its behalf,
// byte-identical and still routed to the same device.
TEST(ModbusClientHubNoResponse, RetryRequeuesWaitingFrame) {
  NoResponseProbeHub hub;
  RetryingDevice device(&hub, 0x02, /*retry=*/true);

  device.send_pdu(read_pdu());
  ASSERT_EQ(hub.queued_frames(), 1u);
  hub.force_send_front();
  ASSERT_EQ(hub.queued_frames(), 0u);
  ASSERT_TRUE(hub.waiting());

  hub.timeout_waiting();

  EXPECT_EQ(device.no_response_count_, 1);
  EXPECT_FALSE(hub.waiting());
  ASSERT_EQ(hub.queued_frames(), 1u);
  const ModbusDeviceCommand &requeued = hub.front();
  EXPECT_EQ(requeued.device, &device);
  // address + PDU + CRC
  ASSERT_EQ(requeued.frame.size(), sizeof(READ_PDU) + 3);
  EXPECT_EQ(requeued.frame.address(), 0x02);
  ASSERT_EQ(requeued.frame.pdu().size(), sizeof(READ_PDU));
  EXPECT_EQ(0, memcmp(requeued.frame.pdu().data(), READ_PDU, sizeof(READ_PDU)));
}

// A device that declines the retry has the frame dropped.
TEST(ModbusClientHubNoResponse, NoRetryDropsWaitingFrame) {
  NoResponseProbeHub hub;
  RetryingDevice device(&hub, 0x02, /*retry=*/false);

  device.send_pdu(read_pdu());
  hub.force_send_front();

  hub.timeout_waiting();

  EXPECT_EQ(device.no_response_count_, 1);
  EXPECT_FALSE(hub.waiting());
  EXPECT_EQ(hub.queued_frames(), 0u);
}

// After the device is detached from the waiting frame (e.g. clear_tx_queue_for_device on
// destruction), a timeout must not deliver a callback or re-queue anything.
TEST(ModbusClientHubNoResponse, DetachedDeviceIsNotNotified) {
  NoResponseProbeHub hub;
  {
    RetryingDevice device(&hub, 0x02, /*retry=*/true);
    device.send_pdu(read_pdu());
    hub.force_send_front();
    // device destructor clears its queue entries, including the waiting frame's device pointer
  }
  ASSERT_TRUE(hub.waiting());
  EXPECT_EQ(hub.waiting_command().device, nullptr);

  hub.timeout_waiting();

  EXPECT_FALSE(hub.waiting());
  EXPECT_EQ(hub.queued_frames(), 0u);
}

// An unexpected frame interrupts the transaction: the retry is re-queued immediately, but the
// waiting entry survives as an interrupted shell (device detached) that keeps tx blocked until the
// send-wait timeout clears it - without a second no-response callback or a duplicate requeue.
TEST(ModbusClientHubNoResponse, RetryBehindInterruptedShell) {
  NoResponseProbeHub hub;
  RetryingDevice device(&hub, 0x02, /*retry=*/true);

  device.send_pdu(read_pdu());
  hub.force_send_front();

  // A frame from the wrong address (0x07, expected 0x02) hits the unexpected-frame branch.
  const uint8_t stray_pdu[] = {0x03, 0x04, 0x00, 0x2A, 0x01, 0x00};
  hub.receive_frame_for_test(0x07, stray_pdu);

  EXPECT_EQ(device.no_response_count_, 1);
  ASSERT_EQ(hub.queued_frames(), 1u);  // exactly one requeue...
  EXPECT_EQ(hub.front().device, &device);
  ASSERT_TRUE(hub.waiting());  // ...while the shell stays in the waiting slot
  EXPECT_TRUE(hub.waiting_command().interrupted);
  EXPECT_EQ(hub.waiting_command().device, nullptr);

  // The send-wait timeout clears the shell without a second callback or another requeue.
  hub.timeout_waiting();
  EXPECT_FALSE(hub.waiting());
  EXPECT_EQ(device.no_response_count_, 1);
  EXPECT_EQ(hub.queued_frames(), 1u);
}

// A callback that detaches the device (clear_tx_queue_for_device()) wins over its own retry request:
// no orphaned frame with a null device is re-queued.
TEST(ModbusClientHubNoResponse, MidCallbackClearCancelsRetry) {
  NoResponseProbeHub hub;
  ClearingRetryDevice device(&hub, 0x02);

  device.send_pdu(read_pdu());
  hub.force_send_front();
  hub.timeout_waiting();

  EXPECT_EQ(device.no_response_count_, 1);
  EXPECT_EQ(hub.queued_frames(), 0u);  // the retry was not re-queued for a detached device
  EXPECT_FALSE(hub.waiting());
}

namespace {
// Overrides only the DEPRECATED on_modbus_* names: the new-name default implementations must forward, so
// external devices written against the old names keep working through the deprecation window.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
class LegacyNameDevice : public ModbusClientDevice {
 public:
  LegacyNameDevice(ModbusClientHub *hub, uint8_t address) : ModbusClientDevice(hub, address) {}
  void on_modbus_not_sent() override { this->legacy_not_sent_++; }
  bool on_modbus_no_response() override {
    this->legacy_no_response_++;
    return false;
  }
  int legacy_not_sent_{0};
  int legacy_no_response_{0};
};
#pragma GCC diagnostic pop
}  // namespace

TEST(ModbusClientHubCompat, LegacyCallbackNamesStillForward) {
  NoResponseProbeHub hub;
  LegacyNameDevice device(&hub, 0x02);

  const uint8_t read[] = {0x03, 0x00, 0x10, 0x00, 0x01};
  device.send_pdu(read);
  hub.force_send_front();
  hub.timeout_waiting();  // no reply -> on_no_response -> forwards to on_modbus_no_response
  EXPECT_EQ(device.legacy_no_response_, 1);

  device.send_pdu(std::span<const uint8_t>());  // empty PDU refused -> on_not_sent -> forwards
  EXPECT_EQ(device.legacy_not_sent_, 1);
}

// The send_pdu() capacity bound: a PDU larger than MAX_PDU_SIZE would build a frame past the RTU
// 256-byte limit, so it is refused up front and signalled like any other failed send.
TEST(ModbusClientHub, OversizedPduIsRefusedWithNotSent) {
  NoResponseProbeHub hub;
  LegacyNameDevice device(&hub, 0x02);
  std::vector<uint8_t> big(MAX_PDU_SIZE + 1, 0x41);
  device.send_pdu(big);
  EXPECT_EQ(device.legacy_not_sent_, 1);  // on_not_sent, observed via the legacy forward
  EXPECT_TRUE(hub.tx_buffer_empty());
}

// --- ModbusDevice compatibility shim ------------------------------------------------------------
// External components written against the pre-2026.8 API subclass ModbusDevice and override the
// old callbacks; the shim adapts the span-based hooks back to those signatures.
namespace {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
class LegacyApiDevice : public ModbusDevice {
 public:
  LegacyApiDevice(ModbusClientHub *hub, uint8_t address) : ModbusDevice(hub, address) {}
  void on_modbus_data(const std::vector<uint8_t> &data) override { this->last_data_ = data; }
  void on_modbus_error(uint8_t function_code, uint8_t exception_code) override {
    this->last_error_fc_ = function_code;
    this->last_error_code_ = exception_code;
  }
  std::vector<uint8_t> last_data_;
  int last_error_fc_{-1};
  int last_error_code_{-1};
};
#pragma GCC diagnostic pop
}  // namespace

TEST(ModbusDeviceShim, LegacyCallbacksReceiveTheOldShapes) {
  NoResponseProbeHub hub;
  LegacyApiDevice device(&hub, 0x02);

  // Read response: on_modbus_data() historically received the payload after the function code and
  // the byte-count byte, as an owning vector.
  const uint8_t read_req[] = {0x03, 0x00, 0x10, 0x00, 0x02};
  device.send_pdu(read_req);
  hub.force_send_front();
  const uint8_t response[] = {0x03, 0x04, 0x00, 0x2A, 0x01, 0x00};
  hub.receive_frame_for_test(0x02, response);
  const std::vector<uint8_t> expected{0x00, 0x2A, 0x01, 0x00};
  EXPECT_EQ(device.last_data_, expected);

  // Write echo: no byte-count byte, so the payload is everything after the function code.
  const uint8_t write_req[] = {0x06, 0x00, 0x10, 0x00, 0x2A};
  device.send_pdu(write_req);
  hub.force_send_front();
  hub.receive_frame_for_test(0x02, write_req);  // single-write responses echo the request
  const std::vector<uint8_t> expected_echo{0x00, 0x10, 0x00, 0x2A};
  EXPECT_EQ(device.last_data_, expected_echo);

  // Exception response: on_modbus_error() received the masked function code and the exception code.
  device.send_pdu(read_req);
  hub.force_send_front();
  const uint8_t error[] = {0x83, 0x02};
  hub.receive_frame_for_test(0x02, error);
  EXPECT_EQ(device.last_error_fc_, 0x03);
  EXPECT_EQ(device.last_error_code_, 0x02);
}

}  // namespace esphome::modbus::testing