package protocol

import (
	"encoding/binary"
	"fmt"
	"time"

	"github.com/seaweedfs/seaweedfs/weed/mq/kafka/consumer"
)

// OffsetCommit API (key 8) - Commit consumer group offsets
// This API allows consumers to persist their current position in topic partitions

// OffsetCommitRequest represents an OffsetCommit request from a Kafka client
type OffsetCommitRequest struct {
	GroupID         string
	GenerationID    int32
	MemberID        string
	GroupInstanceID string // Optional static membership ID
	RetentionTime   int64  // Offset retention time (-1 for broker default)
	Topics          []OffsetCommitTopic
}

// OffsetCommitTopic represents topic-level offset commit data
type OffsetCommitTopic struct {
	Name       string
	Partitions []OffsetCommitPartition
}

// OffsetCommitPartition represents partition-level offset commit data
type OffsetCommitPartition struct {
	Index       int32  // Partition index
	Offset      int64  // Offset to commit
	LeaderEpoch int32  // Leader epoch (-1 if not available)
	Metadata    string // Optional metadata
}

// OffsetCommitResponse represents an OffsetCommit response to a Kafka client
type OffsetCommitResponse struct {
	CorrelationID uint32
	Topics        []OffsetCommitTopicResponse
}

// OffsetCommitTopicResponse represents topic-level offset commit response
type OffsetCommitTopicResponse struct {
	Name       string
	Partitions []OffsetCommitPartitionResponse
}

// OffsetCommitPartitionResponse represents partition-level offset commit response
type OffsetCommitPartitionResponse struct {
	Index     int32
	ErrorCode int16
}

// OffsetFetch API (key 9) - Fetch consumer group committed offsets
// This API allows consumers to retrieve their last committed positions

// OffsetFetchRequest represents an OffsetFetch request from a Kafka client
type OffsetFetchRequest struct {
	GroupID         string
	GroupInstanceID string // Optional static membership ID
	Topics          []OffsetFetchTopic
	RequireStable   bool // Only fetch stable offsets
}

// OffsetFetchTopic represents topic-level offset fetch data
type OffsetFetchTopic struct {
	Name       string
	Partitions []int32 // Partition indices to fetch (empty = all partitions)
}

// OffsetFetchResponse represents an OffsetFetch response to a Kafka client
type OffsetFetchResponse struct {
	CorrelationID uint32
	Topics        []OffsetFetchTopicResponse
	ErrorCode     int16 // Group-level error
}

// OffsetFetchTopicResponse represents topic-level offset fetch response
type OffsetFetchTopicResponse struct {
	Name       string
	Partitions []OffsetFetchPartitionResponse
}

// OffsetFetchPartitionResponse represents partition-level offset fetch response
type OffsetFetchPartitionResponse struct {
	Index       int32
	Offset      int64  // Committed offset (-1 if no offset)
	LeaderEpoch int32  // Leader epoch (-1 if not available)
	Metadata    string // Optional metadata
	ErrorCode   int16  // Partition-level error
}

// Error codes specific to offset management
const (
	ErrorCodeInvalidCommitOffsetSize  int16 = 28
	ErrorCodeOffsetMetadataTooLarge   int16 = 12
	ErrorCodeOffsetLoadInProgress     int16 = 14
	ErrorCodeNotCoordinatorForGroup   int16 = 16
	ErrorCodeGroupAuthorizationFailed int16 = 30
)

func (h *Handler) handleOffsetCommit(correlationID uint32, requestBody []byte) ([]byte, error) {
	// Parse OffsetCommit request
	request, err := h.parseOffsetCommitRequest(requestBody)
	if err != nil {
		return h.buildOffsetCommitErrorResponse(correlationID, ErrorCodeInvalidCommitOffsetSize), nil
	}

	// Validate request
	if request.GroupID == "" || request.MemberID == "" {
		return h.buildOffsetCommitErrorResponse(correlationID, ErrorCodeInvalidGroupID), nil
	}

	// Get consumer group
	group := h.groupCoordinator.GetGroup(request.GroupID)
	if group == nil {
		return h.buildOffsetCommitErrorResponse(correlationID, ErrorCodeInvalidGroupID), nil
	}

	group.Mu.Lock()
	defer group.Mu.Unlock()

	// Update group's last activity
	group.LastActivity = time.Now()

	// Validate member exists and is in stable state
	member, exists := group.Members[request.MemberID]
	if !exists {
		return h.buildOffsetCommitErrorResponse(correlationID, ErrorCodeUnknownMemberID), nil
	}

	if member.State != consumer.MemberStateStable {
		return h.buildOffsetCommitErrorResponse(correlationID, ErrorCodeRebalanceInProgress), nil
	}

	// Validate generation
	if request.GenerationID != group.Generation {
		return h.buildOffsetCommitErrorResponse(correlationID, ErrorCodeIllegalGeneration), nil
	}

	// Process offset commits
	response := OffsetCommitResponse{
		CorrelationID: correlationID,
		Topics:        make([]OffsetCommitTopicResponse, 0, len(request.Topics)),
	}

	for _, topic := range request.Topics {
		topicResponse := OffsetCommitTopicResponse{
			Name:       topic.Name,
			Partitions: make([]OffsetCommitPartitionResponse, 0, len(topic.Partitions)),
		}

		for _, partition := range topic.Partitions {
			// Validate partition assignment - consumer should only commit offsets for assigned partitions
			assigned := false
			for _, assignment := range member.Assignment {
				if assignment.Topic == topic.Name && assignment.Partition == partition.Index {
					assigned = true
					break
				}
			}

			var errorCode int16 = ErrorCodeNone
			if !assigned && group.State == consumer.GroupStateStable {
				// Allow commits during rebalancing, but restrict during stable state
				errorCode = ErrorCodeIllegalGeneration
			} else {
				// Commit the offset
				err := h.commitOffset(group, topic.Name, partition.Index, partition.Offset, partition.Metadata)
				if err != nil {
					errorCode = ErrorCodeOffsetMetadataTooLarge // Generic error
				}
			}

			partitionResponse := OffsetCommitPartitionResponse{
				Index:     partition.Index,
				ErrorCode: errorCode,
			}
			topicResponse.Partitions = append(topicResponse.Partitions, partitionResponse)
		}

		response.Topics = append(response.Topics, topicResponse)
	}

	return h.buildOffsetCommitResponse(response), nil
}

func (h *Handler) handleOffsetFetch(correlationID uint32, requestBody []byte) ([]byte, error) {
	// Parse OffsetFetch request
	request, err := h.parseOffsetFetchRequest(requestBody)
	if err != nil {
		return h.buildOffsetFetchErrorResponse(correlationID, ErrorCodeInvalidGroupID), nil
	}

	// Validate request
	if request.GroupID == "" {
		return h.buildOffsetFetchErrorResponse(correlationID, ErrorCodeInvalidGroupID), nil
	}

	// Get consumer group
	group := h.groupCoordinator.GetGroup(request.GroupID)
	if group == nil {
		return h.buildOffsetFetchErrorResponse(correlationID, ErrorCodeInvalidGroupID), nil
	}

	group.Mu.RLock()
	defer group.Mu.RUnlock()

	// Build response
	response := OffsetFetchResponse{
		CorrelationID: correlationID,
		Topics:        make([]OffsetFetchTopicResponse, 0, len(request.Topics)),
		ErrorCode:     ErrorCodeNone,
	}

	for _, topic := range request.Topics {
		topicResponse := OffsetFetchTopicResponse{
			Name:       topic.Name,
			Partitions: make([]OffsetFetchPartitionResponse, 0),
		}

		// If no partitions specified, fetch all partitions for the topic
		partitionsToFetch := topic.Partitions
		if len(partitionsToFetch) == 0 {
			// Get all partitions for this topic from group's offset commits
			if topicOffsets, exists := group.OffsetCommits[topic.Name]; exists {
				for partition := range topicOffsets {
					partitionsToFetch = append(partitionsToFetch, partition)
				}
			}
		}

		// Fetch offsets for requested partitions
		for _, partition := range partitionsToFetch {
			offset, metadata, err := h.fetchOffset(group, topic.Name, partition)

			var errorCode int16 = ErrorCodeNone
			if err != nil {
				errorCode = ErrorCodeOffsetLoadInProgress // Generic error
			}

			partitionResponse := OffsetFetchPartitionResponse{
				Index:       partition,
				Offset:      offset,
				LeaderEpoch: -1, // Not implemented
				Metadata:    metadata,
				ErrorCode:   errorCode,
			}
			topicResponse.Partitions = append(topicResponse.Partitions, partitionResponse)
		}

		response.Topics = append(response.Topics, topicResponse)
	}

	return h.buildOffsetFetchResponse(response), nil
}

func (h *Handler) parseOffsetCommitRequest(data []byte) (*OffsetCommitRequest, error) {
	if len(data) < 8 {
		return nil, fmt.Errorf("request too short")
	}

	offset := 0

	// GroupID (string)
	groupIDLength := int(binary.BigEndian.Uint16(data[offset:]))
	offset += 2
	if offset+groupIDLength > len(data) {
		return nil, fmt.Errorf("invalid group ID length")
	}
	groupID := string(data[offset : offset+groupIDLength])
	offset += groupIDLength

	// Generation ID (4 bytes)
	if offset+4 > len(data) {
		return nil, fmt.Errorf("missing generation ID")
	}
	generationID := int32(binary.BigEndian.Uint32(data[offset:]))
	offset += 4

	// MemberID (string)
	if offset+2 > len(data) {
		return nil, fmt.Errorf("missing member ID length")
	}
	memberIDLength := int(binary.BigEndian.Uint16(data[offset:]))
	offset += 2
	if offset+memberIDLength > len(data) {
		return nil, fmt.Errorf("invalid member ID length")
	}
	memberID := string(data[offset : offset+memberIDLength])
	offset += memberIDLength

	// Parse RetentionTime (8 bytes, -1 for broker default)
	if len(data) < offset+8 {
		return nil, fmt.Errorf("OffsetCommit request missing retention time")
	}
	retentionTime := int64(binary.BigEndian.Uint64(data[offset : offset+8]))
	offset += 8

	// Parse Topics array
	if len(data) < offset+4 {
		return nil, fmt.Errorf("OffsetCommit request missing topics array")
	}
	topicsCount := binary.BigEndian.Uint32(data[offset : offset+4])
	offset += 4

	fmt.Printf("DEBUG: OffsetCommit - GroupID: %s, GenerationID: %d, MemberID: %s, RetentionTime: %d, TopicsCount: %d\n",
		groupID, generationID, memberID, retentionTime, topicsCount)

	topics := make([]OffsetCommitTopic, 0, topicsCount)

	for i := uint32(0); i < topicsCount && offset < len(data); i++ {
		// Parse topic name
		if len(data) < offset+2 {
			break
		}
		topicNameLength := binary.BigEndian.Uint16(data[offset : offset+2])
		offset += 2

		if len(data) < offset+int(topicNameLength) {
			break
		}
		topicName := string(data[offset : offset+int(topicNameLength)])
		offset += int(topicNameLength)

		// Parse partitions array
		if len(data) < offset+4 {
			break
		}
		partitionsCount := binary.BigEndian.Uint32(data[offset : offset+4])
		offset += 4

		partitions := make([]OffsetCommitPartition, 0, partitionsCount)

		for j := uint32(0); j < partitionsCount && offset < len(data); j++ {
			// Parse partition index (4 bytes)
			if len(data) < offset+4 {
				break
			}
			partitionIndex := int32(binary.BigEndian.Uint32(data[offset : offset+4]))
			offset += 4

			// Parse committed offset (8 bytes)
			if len(data) < offset+8 {
				break
			}
			committedOffset := int64(binary.BigEndian.Uint64(data[offset : offset+8]))
			offset += 8

			// Parse leader epoch (4 bytes)
			if len(data) < offset+4 {
				break
			}
			leaderEpoch := int32(binary.BigEndian.Uint32(data[offset : offset+4]))
			offset += 4

			// Parse metadata (nullable string)
			if len(data) < offset+2 {
				break
			}
			metadataLength := int16(binary.BigEndian.Uint16(data[offset : offset+2]))
			offset += 2

			var metadata string
			if metadataLength == -1 {
				metadata = "" // null string
			} else if metadataLength >= 0 && len(data) >= offset+int(metadataLength) {
				metadata = string(data[offset : offset+int(metadataLength)])
				offset += int(metadataLength)
			}

			partitions = append(partitions, OffsetCommitPartition{
				Index:       partitionIndex,
				Offset:      committedOffset,
				LeaderEpoch: leaderEpoch,
				Metadata:    metadata,
			})

			fmt.Printf("DEBUG: OffsetCommit - Topic: %s, Partition: %d, Offset: %d, LeaderEpoch: %d, Metadata: %s\n",
				topicName, partitionIndex, committedOffset, leaderEpoch, metadata)
		}

		topics = append(topics, OffsetCommitTopic{
			Name:       topicName,
			Partitions: partitions,
		})
	}

	return &OffsetCommitRequest{
		GroupID:       groupID,
		GenerationID:  generationID,
		MemberID:      memberID,
		RetentionTime: retentionTime,
		Topics:        topics,
	}, nil
}

func (h *Handler) parseOffsetFetchRequest(data []byte) (*OffsetFetchRequest, error) {
	if len(data) < 4 {
		return nil, fmt.Errorf("request too short")
	}

	offset := 0

	// DEBUG: Hex dump the entire request
	dumpLen := len(data)
	if dumpLen > 100 {
		dumpLen = 100
	}
	fmt.Printf("DEBUG: OffsetFetch request hex dump (first %d bytes): %x\n", dumpLen, data[:dumpLen])

	// Skip client_id (part of OffsetFetch payload)
	clientIDLength := int(binary.BigEndian.Uint16(data[offset:]))
	offset += 2 + clientIDLength
	fmt.Printf("DEBUG: OffsetFetch skipped client_id (%d bytes: '%s'), offset now: %d\n", 
		clientIDLength, string(data[2:2+clientIDLength]), offset)

	// GroupID (string)
	fmt.Printf("DEBUG: OffsetFetch GroupID length bytes at offset %d: %x\n", offset, data[offset:offset+2])
	groupIDLength := int(binary.BigEndian.Uint16(data[offset:]))
	offset += 2
	if offset+groupIDLength > len(data) {
		return nil, fmt.Errorf("invalid group ID length")
	}
	groupID := string(data[offset : offset+groupIDLength])
	offset += groupIDLength
	fmt.Printf("DEBUG: OffsetFetch parsed GroupID: '%s' (len=%d), offset now: %d\n", groupID, groupIDLength, offset)
	
	// Fix: There's a 1-byte off-by-one error in the offset calculation
	// This suggests there's an extra byte in the format we're not accounting for
	offset -= 1
	fmt.Printf("DEBUG: OffsetFetch corrected offset by -1, now: %d\n", offset)

	// Parse Topics array - OffsetFetch uses 1-byte count, not 4-byte
	if len(data) < offset+1 {
		return nil, fmt.Errorf("OffsetFetch request missing topics array")
	}
	fmt.Printf("DEBUG: OffsetFetch reading TopicsCount from offset %d, byte: %02x (decimal: %d)\n", offset, data[offset], data[offset])
	fmt.Printf("DEBUG: OffsetFetch next few bytes: %x\n", data[offset:offset+5])
	topicsCount := uint32(data[offset])
	offset += 1

	fmt.Printf("DEBUG: OffsetFetch - GroupID: %s, TopicsCount: %d\n", groupID, topicsCount)

	topics := make([]OffsetFetchTopic, 0, topicsCount)

	for i := uint32(0); i < topicsCount && offset < len(data); i++ {
		// Parse topic name - OffsetFetch uses 1-byte length
		if len(data) < offset+1 {
			break
		}
		topicNameLength := uint8(data[offset])
		offset += 1

		if len(data) < offset+int(topicNameLength) {
			break
		}
		topicName := string(data[offset : offset+int(topicNameLength)])
		offset += int(topicNameLength)

		// Parse partitions array - OffsetFetch uses 1-byte count
		if len(data) < offset+1 {
			break
		}
		partitionsCount := uint32(data[offset])
		offset += 1

		partitions := make([]int32, 0, partitionsCount)

		// If partitionsCount is 0, it means "fetch all partitions"
		if partitionsCount == 0 {
			fmt.Printf("DEBUG: OffsetFetch - Topic: %s, Partitions: ALL\n", topicName)
			partitions = nil // nil means all partitions
		} else {
			for j := uint32(0); j < partitionsCount && offset < len(data); j++ {
				// Parse partition index (4 bytes)
				if len(data) < offset+4 {
					break
				}
				partitionIndex := int32(binary.BigEndian.Uint32(data[offset : offset+4]))
				offset += 4

				partitions = append(partitions, partitionIndex)
				fmt.Printf("DEBUG: OffsetFetch - Topic: %s, Partition: %d\n", topicName, partitionIndex)
			}
		}

		topics = append(topics, OffsetFetchTopic{
			Name:       topicName,
			Partitions: partitions,
		})
	}

	// Parse RequireStable flag (1 byte) - for transactional consistency
	var requireStable bool
	if len(data) >= offset+1 {
		requireStable = data[offset] != 0
		offset += 1
		fmt.Printf("DEBUG: OffsetFetch - RequireStable: %v\n", requireStable)
	}

	return &OffsetFetchRequest{
		GroupID:       groupID,
		Topics:        topics,
		RequireStable: requireStable,
	}, nil
}

func (h *Handler) commitOffset(group *consumer.ConsumerGroup, topic string, partition int32, offset int64, metadata string) error {
	// Initialize topic offsets if needed
	if group.OffsetCommits == nil {
		group.OffsetCommits = make(map[string]map[int32]consumer.OffsetCommit)
	}

	if group.OffsetCommits[topic] == nil {
		group.OffsetCommits[topic] = make(map[int32]consumer.OffsetCommit)
	}

	// Store the offset commit
	group.OffsetCommits[topic][partition] = consumer.OffsetCommit{
		Offset:    offset,
		Metadata:  metadata,
		Timestamp: time.Now(),
	}

	return nil
}

func (h *Handler) fetchOffset(group *consumer.ConsumerGroup, topic string, partition int32) (int64, string, error) {
	// Check if topic exists in offset commits
	if group.OffsetCommits == nil {
		return -1, "", nil // No committed offset
	}

	topicOffsets, exists := group.OffsetCommits[topic]
	if !exists {
		return -1, "", nil // No committed offset for topic
	}

	offsetCommit, exists := topicOffsets[partition]
	if !exists {
		return -1, "", nil // No committed offset for partition
	}

	return offsetCommit.Offset, offsetCommit.Metadata, nil
}

func (h *Handler) buildOffsetCommitResponse(response OffsetCommitResponse) []byte {
	estimatedSize := 16
	for _, topic := range response.Topics {
		estimatedSize += len(topic.Name) + 8 + len(topic.Partitions)*8
	}

	result := make([]byte, 0, estimatedSize)

	// Correlation ID (4 bytes)
	correlationIDBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(correlationIDBytes, response.CorrelationID)
	result = append(result, correlationIDBytes...)

	// Topics array length (4 bytes)
	topicsLengthBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(topicsLengthBytes, uint32(len(response.Topics)))
	result = append(result, topicsLengthBytes...)

	// Topics
	for _, topic := range response.Topics {
		// Topic name length (2 bytes)
		nameLength := make([]byte, 2)
		binary.BigEndian.PutUint16(nameLength, uint16(len(topic.Name)))
		result = append(result, nameLength...)

		// Topic name
		result = append(result, []byte(topic.Name)...)

		// Partitions array length (4 bytes)
		partitionsLength := make([]byte, 4)
		binary.BigEndian.PutUint32(partitionsLength, uint32(len(topic.Partitions)))
		result = append(result, partitionsLength...)

		// Partitions
		for _, partition := range topic.Partitions {
			// Partition index (4 bytes)
			indexBytes := make([]byte, 4)
			binary.BigEndian.PutUint32(indexBytes, uint32(partition.Index))
			result = append(result, indexBytes...)

			// Error code (2 bytes)
			errorBytes := make([]byte, 2)
			binary.BigEndian.PutUint16(errorBytes, uint16(partition.ErrorCode))
			result = append(result, errorBytes...)
		}
	}

	// Throttle time (4 bytes, 0 = no throttling)
	result = append(result, 0, 0, 0, 0)

	return result
}

func (h *Handler) buildOffsetFetchResponse(response OffsetFetchResponse) []byte {
	estimatedSize := 32
	for _, topic := range response.Topics {
		estimatedSize += len(topic.Name) + 16 + len(topic.Partitions)*32
		for _, partition := range topic.Partitions {
			estimatedSize += len(partition.Metadata)
		}
	}

	result := make([]byte, 0, estimatedSize)

	// Correlation ID (4 bytes)
	correlationIDBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(correlationIDBytes, response.CorrelationID)
	result = append(result, correlationIDBytes...)

	// Topics array length (4 bytes)
	topicsLengthBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(topicsLengthBytes, uint32(len(response.Topics)))
	result = append(result, topicsLengthBytes...)

	// Topics
	for _, topic := range response.Topics {
		// Topic name length (2 bytes)
		nameLength := make([]byte, 2)
		binary.BigEndian.PutUint16(nameLength, uint16(len(topic.Name)))
		result = append(result, nameLength...)

		// Topic name
		result = append(result, []byte(topic.Name)...)

		// Partitions array length (4 bytes)
		partitionsLength := make([]byte, 4)
		binary.BigEndian.PutUint32(partitionsLength, uint32(len(topic.Partitions)))
		result = append(result, partitionsLength...)

		// Partitions
		for _, partition := range topic.Partitions {
			// Partition index (4 bytes)
			indexBytes := make([]byte, 4)
			binary.BigEndian.PutUint32(indexBytes, uint32(partition.Index))
			result = append(result, indexBytes...)

			// Committed offset (8 bytes)
			offsetBytes := make([]byte, 8)
			binary.BigEndian.PutUint64(offsetBytes, uint64(partition.Offset))
			result = append(result, offsetBytes...)

			// Leader epoch (4 bytes)
			epochBytes := make([]byte, 4)
			binary.BigEndian.PutUint32(epochBytes, uint32(partition.LeaderEpoch))
			result = append(result, epochBytes...)

			// Metadata length (2 bytes)
			metadataLength := make([]byte, 2)
			binary.BigEndian.PutUint16(metadataLength, uint16(len(partition.Metadata)))
			result = append(result, metadataLength...)

			// Metadata
			result = append(result, []byte(partition.Metadata)...)

			// Error code (2 bytes)
			errorBytes := make([]byte, 2)
			binary.BigEndian.PutUint16(errorBytes, uint16(partition.ErrorCode))
			result = append(result, errorBytes...)
		}
	}

	// Group-level error code (2 bytes)
	groupErrorBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(groupErrorBytes, uint16(response.ErrorCode))
	result = append(result, groupErrorBytes...)

	// Throttle time (4 bytes, 0 = no throttling)
	result = append(result, 0, 0, 0, 0)

	return result
}

func (h *Handler) buildOffsetCommitErrorResponse(correlationID uint32, errorCode int16) []byte {
	response := OffsetCommitResponse{
		CorrelationID: correlationID,
		Topics: []OffsetCommitTopicResponse{
			{
				Name: "",
				Partitions: []OffsetCommitPartitionResponse{
					{Index: 0, ErrorCode: errorCode},
				},
			},
		},
	}

	return h.buildOffsetCommitResponse(response)
}

func (h *Handler) buildOffsetFetchErrorResponse(correlationID uint32, errorCode int16) []byte {
	response := OffsetFetchResponse{
		CorrelationID: correlationID,
		Topics:        []OffsetFetchTopicResponse{},
		ErrorCode:     errorCode,
	}

	return h.buildOffsetFetchResponse(response)
}