"""
GPX file processing utilities for extracting route statistics
"""

import xml.etree.ElementTree as ET
import math
import os
from typing import Dict, Optional, Tuple


def calculate_distance(lat1: float, lon1: float, lat2: float, lon2: float) -> float:
    """
    Calculate the great circle distance between two points on the earth (specified in decimal degrees)
    Returns distance in kilometers
    """
    # Convert decimal degrees to radians
    lat1, lon1, lat2, lon2 = map(math.radians, [lat1, lon1, lat2, lon2])
    
    # Haversine formula
    dlat = lat2 - lat1
    dlon = lon2 - lon1
    a = math.sin(dlat/2)**2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon/2)**2
    c = 2 * math.asin(math.sqrt(a))
    
    # Radius of earth in kilometers
    r = 6371
    
    return c * r


def extract_gpx_statistics(file_path: str) -> Optional[Dict]:
    """
    Extract statistics from a GPX file
    
    Returns:
        Dictionary with keys: total_distance, elevation_gain, max_elevation, 
        min_elevation, total_points, or None if file cannot be processed
    """
    if not os.path.exists(file_path):
        return None
    
    try:
        # Parse GPX file
        tree = ET.parse(file_path)
        root = tree.getroot()
        
        # Handle GPX namespace
        namespace = {'gpx': 'http://www.topografix.com/GPX/1/1'}
        if not root.tag.endswith('gpx'):
            # Try without namespace
            namespace = {}
        
        # Find track points
        track_points = []
        
        # Look for track points in tracks
        tracks = root.findall('.//gpx:trk', namespace) if namespace else root.findall('.//trk')
        for track in tracks:
            segments = track.findall('.//gpx:trkseg', namespace) if namespace else track.findall('.//trkseg')
            for segment in segments:
                points = segment.findall('.//gpx:trkpt', namespace) if namespace else segment.findall('.//trkpt')
                for point in points:
                    lat = float(point.get('lat'))
                    lon = float(point.get('lon'))
                    
                    # Get elevation if available
                    ele_elem = point.find('gpx:ele', namespace) if namespace else point.find('ele')
                    elevation = float(ele_elem.text) if ele_elem is not None and ele_elem.text else 0.0
                    
                    track_points.append({
                        'lat': lat,
                        'lon': lon,
                        'elevation': elevation
                    })
        
        # Also look for waypoints if no track points found
        if not track_points:
            waypoints = root.findall('.//gpx:wpt', namespace) if namespace else root.findall('.//wpt')
            for point in waypoints:
                lat = float(point.get('lat'))
                lon = float(point.get('lon'))
                
                ele_elem = point.find('gpx:ele', namespace) if namespace else point.find('ele')
                elevation = float(ele_elem.text) if ele_elem is not None and ele_elem.text else 0.0
                
                track_points.append({
                    'lat': lat,
                    'lon': lon,
                    'elevation': elevation
                })
        
        if not track_points:
            return {
                'total_distance': 0.0,
                'elevation_gain': 0.0,
                'max_elevation': 0.0,
                'min_elevation': 0.0,
                'total_points': 0
            }
        
        # Calculate statistics
        total_distance = 0.0
        elevation_gain = 0.0
        elevations = [point['elevation'] for point in track_points if point['elevation'] > 0]
        
        # Calculate distance and elevation gain
        for i in range(1, len(track_points)):
            current = track_points[i]
            previous = track_points[i-1]
            
            # Distance
            distance = calculate_distance(
                previous['lat'], previous['lon'],
                current['lat'], current['lon']
            )
            total_distance += distance
            
            # Elevation gain (only uphill)
            if current['elevation'] > 0 and previous['elevation'] > 0:
                elevation_diff = current['elevation'] - previous['elevation']
                if elevation_diff > 0:
                    elevation_gain += elevation_diff
        
        # Elevation statistics
        max_elevation = max(elevations) if elevations else 0.0
        min_elevation = min(elevations) if elevations else 0.0
        
        return {
            'total_distance': round(total_distance, 2),
            'elevation_gain': round(elevation_gain, 1),
            'max_elevation': round(max_elevation, 1),
            'min_elevation': round(min_elevation, 1),
            'total_points': len(track_points)
        }
        
    except Exception as e:
        print(f"Error processing GPX file {file_path}: {e}")
        return None


def process_gpx_file(gpx_file_record) -> bool:
    """
    Process a GPXFile record and update its statistics
    
    Args:
        gpx_file_record: GPXFile model instance
        
    Returns:
        True if processing was successful, False otherwise
    """
    from flask import current_app
    
    # Build file path
    if gpx_file_record.post.media_folder:
        file_path = os.path.join(
            current_app.root_path, 'static', 'media', 'posts',
            gpx_file_record.post.media_folder, 'gpx', gpx_file_record.filename
        )
    else:
        file_path = os.path.join(
            current_app.root_path, 'static', 'uploads', 'gpx', gpx_file_record.filename
        )
    
    # Extract statistics
    stats = extract_gpx_statistics(file_path)
    if stats is None:
        return False
    
    # Update the record
    gpx_file_record.total_distance = stats['total_distance']
    gpx_file_record.elevation_gain = stats['elevation_gain']
    gpx_file_record.max_elevation = stats['max_elevation']
    gpx_file_record.min_elevation = stats['min_elevation']
    gpx_file_record.total_points = stats['total_points']
    
    return True