package com.example.service.base;

import com.example.dto.dialogflow.base.DetectIntentRequestDTO;
import com.example.dto.dialogflow.base.DetectIntentResponseDTO;
import com.example.exception.DialogflowClientException;
import com.example.mapper.conversation.DialogflowRequestMapper;
import com.example.mapper.conversation.DialogflowResponseMapper;
import com.google.api.gax.rpc.ApiException;
import com.google.cloud.dialogflow.cx.v3.DetectIntentRequest;
import com.google.cloud.dialogflow.cx.v3.QueryParameters;
import com.google.cloud.dialogflow.cx.v3.SessionName;
import com.google.cloud.dialogflow.cx.v3.SessionsClient;
import com.google.cloud.dialogflow.cx.v3.SessionsSettings;
import java.io.IOException;
import java.util.Objects;
import javax.annotation.PreDestroy;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
import reactor.core.publisher.Mono;
import reactor.util.retry.Retry;

/**
 * Service for interacting with the Dialogflow CX API to detect user DetectIntent.
 * It encapsulates the low-level API calls, handling request mapping from DTOs,
 * managing the `SessionsClient`, and translating API responses into DTOs,
 * all within a reactive programming context.
 */
@Service
@Qualifier("dialogflowClientService")
public class DialogflowClientService implements IntentDetectionService {

    private static final Logger logger = LoggerFactory.getLogger(
        DialogflowClientService.class
    );

    private final String dialogflowCxProjectId;
    private final String dialogflowCxLocation;
    private final String dialogflowCxAgentId;

    private final DialogflowRequestMapper dialogflowRequestMapper;
    private final DialogflowResponseMapper dialogflowResponseMapper;
    private SessionsClient sessionsClient;

    public DialogflowClientService(
        @org.springframework.beans.factory.annotation.Value(
            "${dialogflow.cx.project-id}"
        ) String dialogflowCxProjectId,
        @org.springframework.beans.factory.annotation.Value(
            "${dialogflow.cx.location}"
        ) String dialogflowCxLocation,
        @org.springframework.beans.factory.annotation.Value(
            "${dialogflow.cx.agent-id}"
        ) String dialogflowCxAgentId,
        DialogflowRequestMapper dialogflowRequestMapper,
        DialogflowResponseMapper dialogflowResponseMapper
    ) throws IOException {
        this.dialogflowCxProjectId = dialogflowCxProjectId;
        this.dialogflowCxLocation = dialogflowCxLocation;
        this.dialogflowCxAgentId = dialogflowCxAgentId;
        this.dialogflowRequestMapper = dialogflowRequestMapper;
        this.dialogflowResponseMapper = dialogflowResponseMapper;

        try {
            String regionalEndpoint = String.format(
                "%s-dialogflow.googleapis.com:443",
                dialogflowCxLocation
            );
            SessionsSettings sessionsSettings = SessionsSettings.newBuilder()
                .setEndpoint(regionalEndpoint)
                .build();
            this.sessionsClient = SessionsClient.create(sessionsSettings);
            logger.info(
                "Dialogflow CX SessionsClient initialized successfully for endpoint: {}",
                regionalEndpoint
            );
            logger.info(
                "Dialogflow CX SessionsClient initialized successfully for agent - Test Agent version: {}",
                dialogflowCxAgentId
            );
        } catch (IOException e) {
            logger.error(
                "Failed to create Dialogflow CX SessionsClient: {}",
                e.getMessage(),
                e
            );
            throw e;
        }
    }

    @PreDestroy
    public void closeSessionsClient() {
        if (sessionsClient != null) {
            sessionsClient.close();
            logger.info("Dialogflow CX SessionsClient closed.");
        }
    }

    @Override
    public Mono<DetectIntentResponseDTO> detectIntent(
        String sessionId,
        DetectIntentRequestDTO request
    ) {
        Objects.requireNonNull(
            sessionId,
            "Dialogflow session ID cannot be null."
        );
        Objects.requireNonNull(
            request,
            "Dialogflow request DTO cannot be null."
        );

        logger.info("Initiating detectIntent for session: {}", sessionId);

        DetectIntentRequest.Builder detectIntentRequestBuilder;
        try {
            detectIntentRequestBuilder =
                dialogflowRequestMapper.mapToDetectIntentRequestBuilder(
                    request
                );
            logger.debug(
                "Obtained partial DetectIntentRequest.Builder from mapper for session: {}",
                sessionId
            );
        } catch (IllegalArgumentException e) {
            logger.error(
                " Failed to map DTO to partial Protobuf request for session {}: {}",
                sessionId,
                e.getMessage()
            );
            return Mono.error(
                new IllegalArgumentException(
                    "Invalid Dialogflow request input: " + e.getMessage()
                )
            );
        }

        SessionName sessionName = SessionName.newBuilder()
            .setProject(dialogflowCxProjectId)
            .setLocation(dialogflowCxLocation)
            .setAgent(dialogflowCxAgentId)
            .setSession(sessionId)
            .build();
        detectIntentRequestBuilder.setSession(sessionName.toString());
        logger.debug(
            "Set session path {} on the request builder for session: {}",
            sessionName.toString(),
            sessionId
        );

        QueryParameters.Builder queryParamsBuilder;
        if (detectIntentRequestBuilder.hasQueryParams()) {
            queryParamsBuilder = detectIntentRequestBuilder
                .getQueryParams()
                .toBuilder();
        } else {
            queryParamsBuilder = QueryParameters.newBuilder();
        }

        detectIntentRequestBuilder.setQueryParams(queryParamsBuilder.build());

        // Build the final DetectIntentRequest Protobuf object
        DetectIntentRequest detectIntentRequest =
            detectIntentRequestBuilder.build();
        return Mono.fromCallable(() -> {
            logger.debug(
                "Calling Dialogflow CX detectIntent for session: {}",
                sessionId
            );
            return sessionsClient.detectIntent(detectIntentRequest);
        })
            .retryWhen(
                reactor.util.retry.Retry.backoff(
                    3,
                    java.time.Duration.ofSeconds(1)
                )
                    .filter(throwable -> {
                        if (throwable instanceof ApiException apiException) {
                            com.google.api.gax.rpc.StatusCode.Code code =
                                apiException.getStatusCode().getCode();
                            boolean isRetryable =
                                code ==
                                    com.google.api.gax.rpc.StatusCode.Code.INTERNAL ||
                                code ==
                                com.google.api.gax.rpc.StatusCode.Code.UNAVAILABLE;
                            if (isRetryable) {
                                logger.warn(
                                    "Retrying Dialogflow CX call for session {} due to transient error: {}",
                                    sessionId,
                                    code
                                );
                            }
                            return isRetryable;
                        }
                        return false;
                    })
                    .doBeforeRetry(retrySignal ->
                        logger.debug(
                            "Retry attempt #{} for session {}",
                            retrySignal.totalRetries() + 1,
                            sessionId
                        )
                    )
                    .onRetryExhaustedThrow((retrySpec, retrySignal) -> {
                        logger.error(
                            "Dialogflow CX retries exhausted for session {}",
                            sessionId
                        );
                        return retrySignal.failure();
                    })
            )
            .onErrorMap(ApiException.class, e -> {
                String statusCode = e.getStatusCode().getCode().name();
                String message = e.getMessage();
                String detailedLog = message;

                if (
                    e.getCause() instanceof
                        io.grpc.StatusRuntimeException grpcEx
                ) {
                    detailedLog = String.format(
                        "Status: %s, Message: %s, Trailers: %s",
                        grpcEx.getStatus().getCode(),
                        grpcEx.getStatus().getDescription(),
                        grpcEx.getTrailers()
                    );
                }

                logger.error(
                    "Dialogflow CX API error for session {}: details={}",
                    sessionId,
                    detailedLog,
                    e
                );

                return new DialogflowClientException(
                    "Dialogflow CX API error: " + statusCode + " - " + message,
                    e
                );
            })
            .map(dfResponse ->
                this.dialogflowResponseMapper.mapFromDialogflowResponse(
                    dfResponse,
                    sessionId
                )
            );
    }
}