import 'dart:async';
import 'dart:math';

import 'package:flutter/material.dart';
import 'package:latlong2/latlong.dart';

import '../models/directions.dart';
import '../utils/geometry_utils.dart';

/// Maximum distance the user can be from the line before recalculating the directions
const maxDistanceFromLine = 100;

class DirectionsInstruction extends StatefulWidget {
  final Directions directions;
  final Stream<LatLng> currentPositionStream;
  final StreamController<int> currentWaypointIndexController;
  final bool Function(LatLng) recalculateDirections;

  const DirectionsInstruction({
    required this.directions,
    required this.currentPositionStream,
    required this.currentWaypointIndexController,
    required this.recalculateDirections,
    Key? key,
  }) : super(key: key);

  @override
  State<DirectionsInstruction> createState() => _DirectionsInstructionState();
}

class _DirectionsInstructionState extends State<DirectionsInstruction> {
  /// The current step the user is in the directions
  int _currentSegmentIndex = 0;
  /// Next waypoint the user has to pass
  int _nextWaypointIndex = 0;
  late StreamSubscription<LatLng> _currentPositionSubscription;

  /// Line the user is currently following, defined by the previous and next waypoints
  Segment get _currentLine {
    final startLine = widget.directions.waypointsCoordinates[max(0, _nextWaypointIndex - 1)];
    final endLine = widget.directions.waypointsCoordinates[_nextWaypointIndex];
    return Segment(start: startLine, end: endLine);
  }

  @override
  initState() {
    super.initState();
    _currentPositionSubscription = widget.currentPositionStream.listen(_handleCurrentPositionUpdates);
  }

  @override
  void dispose() {
    _currentPositionSubscription.cancel();
    super.dispose();
  }

  void _handleCurrentPositionUpdates(currentPosition) {
    _updateDirectionsFromCurrentPosition(currentPosition);
    _updateWaypointFromCurrentPosition(currentPosition);
  }

  void _updateWaypointFromCurrentPosition(LatLng currentPosition) {
    final nextWaypointIndex = _getNextWaypointIndex(currentPosition);
    widget.currentWaypointIndexController.add(nextWaypointIndex);
    setState(() {
      _nextWaypointIndex = nextWaypointIndex;
      _currentSegmentIndex = _getNewSegmentIndex(nextWaypointIndex);
    });
  }

  /// Get new directions if the user is too far from the current segment
  void _updateDirectionsFromCurrentPosition(LatLng currentPosition) {
    var distanceFromCurrentSegment = DistanceUtils.distToSegment(currentPosition, _currentLine);
    if (distanceFromCurrentSegment > maxDistanceFromLine) {
      // If we could recalculate the directions, we reset the segment and waypoint to zero
      if (widget.recalculateDirections(currentPosition)) {
        setState(() {
          _currentSegmentIndex = 0;
          _nextWaypointIndex = 0;
        });
      }
    }
  }

  num _getDistanceFromWaypoint(LatLng currentPosition, int waypointIndex) {
    final currentWaypoint = widget.directions.waypointsCoordinates[waypointIndex];
    return DistanceUtils.distBetweenTwoPoints(currentPosition, currentWaypoint);
  }

  int _getNewSegmentIndex(int nextWaypointIndex) {
    final currentSegment = widget.directions.segments[_currentSegmentIndex];
    var newSegmentIndex = _currentSegmentIndex;
    if (nextWaypointIndex > currentSegment.waypoints[1]) {
      newSegmentIndex++;
    } else if (nextWaypointIndex <= currentSegment.waypoints[0]) {
      newSegmentIndex--;
    }
    return max(0, min(newSegmentIndex, widget.directions.segments.length - 1));
  }

  int _getNextWaypointIndex(LatLng currentPosition) {
    final parameterProjection = DistanceUtils.getParameterFromProjection(currentPosition, _currentLine);
    final distanceFromNextWaypoint = _getDistanceFromWaypoint(currentPosition, _nextWaypointIndex);
    final distanceFromNextNextWaypoint = _nextWaypointIndex < widget.directions.waypointsCoordinates.length - 1
        ? _getDistanceFromWaypoint(currentPosition, _nextWaypointIndex + 1)
        : double.infinity;

    final isProjectedPointOnCurrentSegment = parameterProjection > 0 && parameterProjection < 1;

    // Approaching the next waypoint while following the line
    // We want to detect it before passing the waypoint
    if (distanceFromNextWaypoint < 3 && isProjectedPointOnCurrentSegment) {
      return _nextWaypointIndex + 1;
    }
    // Went back past previous waypoint
    if (parameterProjection < 0) {
      return max(0, _nextWaypointIndex - 1);
    }
    // Not closely following the line, but still went past next waypoint
    if (distanceFromNextWaypoint > distanceFromNextNextWaypoint || parameterProjection > 1) {
      return _nextWaypointIndex + 1;
    }
    return _nextWaypointIndex;
  }

  @override
  Widget build(BuildContext context) {
    final segments = widget.directions.segments;
    return Column(
      children: [
        SizedBox(height: MediaQuery.of(context).size.height * 0.05),
        Text(
          "${segments[_currentSegmentIndex + 1].instruction} in ${segments[_currentSegmentIndex].distance.round()}m",
          style: const TextStyle(fontSize: 25),
        ),
        if (_currentSegmentIndex < segments.length - 2)
          Text(
            "Next: ${segments[_currentSegmentIndex + 2].instruction}",
            style: const TextStyle(fontSize: 20),
          ),
      ],
    );
  }
}