package transport

import (
	"encoding/json"
	"fmt"
)

// ExtractMessage extracts a message from a byte buffer with length prefix format
// Format: "length\nmessage_data"
func ExtractMessage(buffer []byte) (*Message, []byte, error) {
	// Look for length prefix (format: "length\nmessage_data")
	newlineIndex := -1
	for i, b := range buffer {
		if b == '\n' {
			newlineIndex = i
			break
		}
	}

	if newlineIndex == -1 {
		return nil, buffer, nil // No complete length prefix yet
	}

	// Parse length
	lengthStr := string(buffer[:newlineIndex])
	var messageLength int
	if _, err := fmt.Sscanf(lengthStr, "%d", &messageLength); err != nil {
		return nil, nil, fmt.Errorf("invalid length prefix: %s", lengthStr)
	}

	// Check if we have the complete message
	messageStart := newlineIndex + 1
	messageEnd := messageStart + messageLength
	if len(buffer) < messageEnd {
		return nil, buffer, nil // Incomplete message
	}

	// Extract and parse message
	messageData := buffer[messageStart:messageEnd]
	var msg Message
	if err := json.Unmarshal(messageData, &msg); err != nil {
		return nil, nil, fmt.Errorf("failed to unmarshal message: %w", err)
	}

	// Return message and remaining buffer
	remaining := buffer[messageEnd:]
	return &msg, remaining, nil
}