package com.cfdeployer.service;

import com.cfdeployer.model.UploadSession;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Service;
import org.springframework.web.multipart.MultipartFile;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.file.Files;
import java.nio.file.Path;
import java.time.LocalDateTime;
import java.util.Comparator;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;

@Service
@Slf4j
public class ChunkedUploadService {

    @Value("${cf.upload.session.timeout-minutes:30}")
    private int sessionTimeoutMinutes;

    private final Map<String, UploadSession> activeSessions = new ConcurrentHashMap<>();

    public String createUploadSession(String requestJson) throws IOException {
        String sessionId = UUID.randomUUID().toString();
        Path workingDir = Files.createTempDirectory("cf-upload-" + sessionId);

        UploadSession session = new UploadSession(sessionId, requestJson, workingDir);
        activeSessions.put(sessionId, session);

        log.info("Created upload session: {} at {}", sessionId, workingDir);
        return sessionId;
    }

    public synchronized void uploadChunk(String sessionId, String fileType, String fileName,
                                        int chunkIndex, int totalChunks, MultipartFile chunk) throws IOException {
        UploadSession session = activeSessions.get(sessionId);
        if (session == null) {
            throw new IllegalArgumentException("Upload session not found or expired: " + sessionId);
        }

        session.updateLastAccessed();

        // Get or create file upload state
        UploadSession.FileUploadState fileState = session.getFileStates()
                .computeIfAbsent(fileType, k -> {
                    String targetFileName = fileType.equals("manifest") ? "manifest.yml" : fileName;
                    Path targetPath = session.getWorkingDirectory().resolve(targetFileName);
                    return new UploadSession.FileUploadState(fileName, totalChunks, targetPath);
                });

        // Validate total chunks consistency
        if (fileState.getTotalChunks() != totalChunks) {
            throw new IllegalArgumentException(
                    String.format("Total chunks mismatch for %s: expected %d, got %d",
                            fileType, fileState.getTotalChunks(), totalChunks));
        }

        // Write chunk to file using sequential append mode
        // This supports variable chunk sizes - chunks MUST be uploaded in order (0, 1, 2, ...)
        Path targetPath = fileState.getTargetPath();

        // Verify chunks are uploaded in order
        if (chunkIndex != fileState.getReceivedChunkCount()) {
            throw new IllegalArgumentException(
                    String.format("Chunks must be uploaded in order. Expected chunk %d but received %d",
                            fileState.getReceivedChunkCount(), chunkIndex));
        }

        try (var inputStream = chunk.getInputStream();
             var outputStream = Files.newOutputStream(targetPath,
                     java.nio.file.StandardOpenOption.CREATE,
                     java.nio.file.StandardOpenOption.APPEND)) {

            // Stream chunk data in smaller buffers to reduce memory pressure
            byte[] buffer = new byte[8192]; // 8KB buffer
            int bytesRead;
            long totalWritten = 0;

            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
                totalWritten += bytesRead;
            }

            log.debug("Appended chunk {} ({} bytes) to {}",
                    chunkIndex, totalWritten, targetPath.getFileName());
        }

        fileState.markChunkReceived(chunkIndex);
        log.info("Session {}: Received chunk {}/{} for {} ({} bytes)",
                sessionId, chunkIndex + 1, totalChunks, fileType, chunk.getSize());

        if (fileState.isComplete()) {
            log.info("Session {}: File {} upload completed ({} chunks)",
                    sessionId, fileType, totalChunks);
        }
    }

    public UploadSession getSession(String sessionId) {
        UploadSession session = activeSessions.get(sessionId);
        if (session != null) {
            session.updateLastAccessed();
        }
        return session;
    }

    public boolean isSessionReady(String sessionId) {
        UploadSession session = activeSessions.get(sessionId);
        if (session == null) {
            return false;
        }

        // Check if both jarFile and manifest are complete
        UploadSession.FileUploadState jarState = session.getFileStates().get("jarFile");
        UploadSession.FileUploadState manifestState = session.getFileStates().get("manifest");

        return jarState != null && jarState.isComplete() &&
               manifestState != null && manifestState.isComplete();
    }

    public void deleteSession(String sessionId) {
        UploadSession session = activeSessions.remove(sessionId);
        if (session != null) {
            cleanupSessionDirectory(session);
            log.info("Deleted upload session: {}", sessionId);
        }
    }

    @Scheduled(fixedRate = 300000) // Run every 5 minutes
    public void cleanupExpiredSessions() {
        LocalDateTime expirationTime = LocalDateTime.now().minusMinutes(sessionTimeoutMinutes);
        int cleanedCount = 0;

        for (Map.Entry<String, UploadSession> entry : activeSessions.entrySet()) {
            if (entry.getValue().getLastAccessedAt().isBefore(expirationTime)) {
                deleteSession(entry.getKey());
                cleanedCount++;
            }
        }

        if (cleanedCount > 0) {
            log.info("Cleaned up {} expired upload sessions", cleanedCount);
        }
    }

    private void cleanupSessionDirectory(UploadSession session) {
        try {
            Path workingDir = session.getWorkingDirectory();
            if (Files.exists(workingDir)) {
                Files.walk(workingDir)
                        .sorted(Comparator.reverseOrder())
                        .forEach(path -> {
                            try {
                                Files.delete(path);
                            } catch (IOException e) {
                                log.warn("Failed to delete file: {}", path, e);
                            }
                        });
                log.debug("Cleaned up session directory: {}", workingDir);
            }
        } catch (IOException e) {
            log.warn("Failed to clean up session directory for session: {}", session.getSessionId(), e);
        }
    }

    public int getActiveSessionCount() {
        return activeSessions.size();
    }
}