using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using TransportGame.Model;
using TransportGame.Model.Road;
using TransportGame.Utils;
using Vector2 = TransportGame.Model.Vector2;

namespace TransportGame.Generator
{
    public class RoadGenerator
    {
        class RoadGeneratorSegment
        {
            public RoadNode Terminal1;
            public Vector2 Terminal2Pos;
            public RoadNode Terminal2;
            public bool Highway;
            public int Time;

            public RoadGeneratorSegment(RoadNode term1, Vector2 term2pos, bool highway, int time = 0)
            {
                Terminal1 = term1;
                Terminal2Pos = term2pos;
                Highway = highway;
                Time = time;
            }

            public override string ToString()
            {
                string str = String.Format("(gensegment, {0}->", Terminal1);

                if (Terminal2 == null)
                    str += Terminal2Pos.ToString();
                else str += Terminal2.ToString();

                str += ", ";
                if (Highway)
                    str += "highway, ";
                str += String.Format("time={0})", Time);

                return str;
            }
        }

        QuadTree<RoadNode> qtree;
        List<RoadGeneratorSegment> queue;

        System.Random random = new System.Random();
        Map map;

        const float HighwaySegmentLength = 60;
        const float DefaultBranchPopulationTreshold = 0.12f;
        const float DefaultBranchProbability = 0.2f;
        const float DefaultSegmentLength = 24;
        const float SteepnessLimit = 10;
        const float SlopeLimit = (float)Math.PI / 6;
        const float RoadSegmentAngleLimit = (float)Math.PI / 4;
        const float RoadSnapDistance = 19;
        const float MinNodeDistance = 12;
        const int MaximumRandomStraightAngle = 45; // in degrees
        const int MaximumBranchAngleVariation = 12; // in degrees
        const float HighwayBranchPopulationTreshold = .4f; // 0..1
        const float HighwayBranchProbability = .01f;
        const int HighwayBranchDelay = 3;
        const int MaximumIntersectingRoads = 5;

        public RoadGenerator()
        {
        }

        public void Initialize(Map map)
        {
            this.map = map;
            map.RoadNetwork = new RoadNetwork();
            qtree = new QuadTree<RoadNode>(0, 0, map.Width, map.Height);
            queue = new List<RoadGeneratorSegment>();

            // Generate positions
            Vector2 center = new Vector2(map.Width / 2, map.Height / 2);
            int maxDistanceFromCenter = map.Width / 3;

            Vector2 p0, p1, p2; // p2 goes in opposite direction

            do
            {
                // Generate point close to center of the map
                float gen_x = random.Next(-maxDistanceFromCenter, maxDistanceFromCenter) + random.NextSingle();
                float gen_y = random.Next(-maxDistanceFromCenter, maxDistanceFromCenter) + random.NextSingle();

                p0 = center + new Vector2(gen_x, gen_y);

                // Generate a random direction
                Vector2 dir = Vector2.FromDegrees(random.Next(360)) * (HighwaySegmentLength / 2);
                p1 = p0 + dir;
                p2 = p0 - dir;

            } while (IsObstacle(p0) || IsObstacle(p1) || IsObstacle(p2));

            // Create root node
            var node0 = map.RoadNetwork.CreateNode(p0);
            qtree.Add(node0);

            // Create & enqueue segments
            queue.Add(new RoadGeneratorSegment(node0, p1, true));
            queue.Add(new RoadGeneratorSegment(node0, p2, true));
        }

        public void Step()
        {
            var segment = queue.OrderBy(x => x.Time).First();
            queue.Remove(segment);

            // Check local constraints
            if (CheckLocalConstraints(segment))
            {
                RoadSegment createdSegment;

                // Finish to create segment
                if (segment.Terminal2 != null)
                    createdSegment = map.RoadNetwork.CreateArticulationSegment(segment.Terminal1, segment.Terminal2);

                else
                    createdSegment = map.RoadNetwork.CreateArticulationSegment(segment.Terminal1, segment.Terminal2Pos);

                qtree.Add(createdSegment.Terminal2);
                createdSegment.LanesTo1 = createdSegment.LanesTo2 = (segment.Highway) ? 3 : 1;

                // Use global goals to get new segments
                foreach (var newSegment in GlobalGoals(createdSegment))
                {
                    newSegment.Time += segment.Time + 1;
                    queue.Add(newSegment);
                }
            }
        }

        private bool IsObstacle(Vector2 p)
        {
            return !map.IsInside(p.X, p.Y) || map.IsWater(p.X, p.Y) || map.GetSteepness(p.X, p.Y) > SteepnessLimit;
        }

        public void Generate(Map map)
        {
            Initialize(map);

            int iterationCount = (map.Width * map.Height) / 512;

            for (int i = 0; i < iterationCount && queue.Count > 0; i++)
                Step();
        }

        private IEnumerable<RoadGeneratorSegment> GlobalGoals(RoadSegment segment)
        {
            Vector2 prevPos = segment.Terminal2.Position;
            Vector2 dir = (segment.Terminal2.Position - segment.Terminal1.Position).Normalized;
            bool highway = (segment.LanesTo1 >= 3);
            bool highwayBranched = false;

            // Going straight
            Vector2 straight = prevPos + dir * ((highway) ? HighwaySegmentLength : DefaultSegmentLength);
            float straightPopulation = map.GetPopulation(straight);

            // Highways...
            if (highway)
            {
                Vector2 randomStraight = prevPos + HighwaySegmentLength * dir.RotateDeg(random.Next(-MaximumRandomStraightAngle, MaximumRandomStraightAngle));
                float randomPopulation = map.GetPopulation(randomStraight);

                if (randomPopulation > straightPopulation)
                    yield return new RoadGeneratorSegment(segment.Terminal2, randomStraight, highway);
                else
                    yield return new RoadGeneratorSegment(segment.Terminal2, straight, highway);

                // Branch highway
                if (Math.Max(straightPopulation, randomPopulation) > HighwayBranchPopulationTreshold)
                {
                    if (random.NextSingle() < HighwayBranchProbability)
                    {
                        Vector2 leftBranch = prevPos + HighwaySegmentLength * dir.RotateDeg(-90 + random.Next(-MaximumBranchAngleVariation, MaximumBranchAngleVariation));
                        yield return new RoadGeneratorSegment(segment.Terminal2, leftBranch, highway, HighwayBranchDelay);

                        highwayBranched = true;
                    }
                    if (random.NextSingle() < HighwayBranchProbability)
                    {
                        Vector2 rightBranch = prevPos + HighwaySegmentLength * dir.RotateDeg(90 + random.Next(-MaximumBranchAngleVariation, MaximumBranchAngleVariation));
                        yield return new RoadGeneratorSegment(segment.Terminal2, rightBranch, highway, HighwayBranchDelay);

                        highwayBranched = true;
                    }
                }

                // Don't allow more branches
                if (highwayBranched)
                    yield break;
            }

            else if (random.NextSingle() < straightPopulation)
                yield return new RoadGeneratorSegment(segment.Terminal2, straight, false);

            // Branch normal road
            if (straightPopulation > DefaultBranchPopulationTreshold)
            {
                if (random.NextSingle() < DefaultBranchProbability * straightPopulation)
                {
                    Vector2 leftBranch = prevPos + HighwaySegmentLength * dir.RotateDeg(-90 + random.Next(-MaximumBranchAngleVariation, MaximumBranchAngleVariation));
                    yield return new RoadGeneratorSegment(segment.Terminal2, leftBranch, false, (highway) ? HighwayBranchDelay : 0);
                }
                if (random.NextSingle() < DefaultBranchProbability * straightPopulation)
                {
                    Vector2 rightBranch = prevPos + HighwaySegmentLength * dir.RotateDeg(90 + random.Next(-MaximumBranchAngleVariation, MaximumBranchAngleVariation));
                    yield return new RoadGeneratorSegment(segment.Terminal2, rightBranch, false, (highway) ? HighwayBranchDelay : 0);
                }
            }
        }

        private bool CheckLocalConstraints(RoadGeneratorSegment segment)
        {
            // Constraint #1: check for obstacles
            if (IsObstacle(segment.Terminal2Pos))
                return false;

            // Constraint #2: slope
            float segmentLength = (segment.Highway) ? HighwaySegmentLength : DefaultSegmentLength;
            float levelDiff = map.GetHeight((int)segment.Terminal1.X, (int)segment.Terminal1.Y) -
                map.GetHeight((int)segment.Terminal2Pos.X, (int)segment.Terminal2Pos.Y);
            float sinSlope = Math.Abs(levelDiff) / segmentLength;

            if (Math.Asin(sinSlope) > SlopeLimit)
                return false;

            // Constraint #3: Number of intersecting roads
            if (segment.Terminal1.ArticulationSegmentIds.Count > MaximumIntersectingRoads)
                return false;

            // Constraint #4: intersections & snapping
            Rectangle queryArea = new Rectangle(
                Math.Min(segment.Terminal1.X, segment.Terminal2Pos.X) - 3 * HighwaySegmentLength,
                Math.Min(segment.Terminal1.Y, segment.Terminal2Pos.Y) - 3 * HighwaySegmentLength,
                Math.Max(segment.Terminal1.X, segment.Terminal2Pos.X) + 3 * HighwaySegmentLength,
                Math.Max(segment.Terminal1.Y, segment.Terminal2Pos.Y) + 3 * HighwaySegmentLength);

            IEnumerable<int> segmentIds = Enumerable.Empty<int>();

            // Look for nearby segments
            foreach (var node in qtree.Query(queryArea))
            {
                if (node == segment.Terminal1)
                    continue;

                // Too close to another node in the area
                if ((node.Position - segment.Terminal2Pos).LengthSq < MinNodeDistance * MinNodeDistance)
                    return false;

                segmentIds = segmentIds.Concat(node.ArticulationSegmentIds);
            }

            // Filter & sort the segments by distance
            segmentIds = segmentIds.Distinct().OrderBy(id =>
            {
                var seg = map.RoadNetwork.ArticulationSegments[id];
                var line = new LineSegment(seg.Terminal1.Position, seg.Terminal2.Position);
                return LineSegment.Distance(line, segment.Terminal2Pos);
            });

            foreach (var segmentId in segmentIds)
            {
                var other = map.RoadNetwork.ArticulationSegments[segmentId];
                var line1 = new LineSegment(segment.Terminal1.Position, segment.Terminal2Pos);
                var line2 = new LineSegment(other.Terminal1.Position, other.Terminal2.Position);

                Vector2? inters = LineSegment.Intersect(line1, line2);

                // Case #1: there is an intersection with another segment. We cut the rest of the segment
                if (inters.HasValue && inters.Value != segment.Terminal1.Position)
                {
                    // Check angle between segments
                    float cos = Vector2.Dot((line1.P1 - line1.P0).Normalized, (line2.P1 - line2.P0).Normalized);
                    if (Math.Abs(Math.Acos(cos)) < RoadSegmentAngleLimit)
                        return false;

                    // Split segment
                    var newNode = map.RoadNetwork.SplitArticulationSegment(other, inters.Value);
                    segment.Terminal2Pos = inters.Value;
                    segment.Terminal2 = newNode;
                    return true;
                }

                // Case #2: no intersection, but the point is close enough to an existing intersection
                if ((segment.Terminal2Pos - other.Terminal2.Position).LengthSq <= RoadSnapDistance * RoadSnapDistance)
                {
                    // Check angle between intersecting segments
                    foreach (var intersSeg in other.Terminal2.ArticulationSegments)
                    {
                        float cos = Vector2.Dot((line1.P1 - line1.P0).Normalized, (intersSeg.Terminal2.Position - intersSeg.Terminal1.Position).Normalized);
                        if (Math.Abs(Math.Acos(cos)) < RoadSegmentAngleLimit)
                            return false;
                    }

                    segment.Terminal2Pos = other.Terminal2.Position;
                    segment.Terminal2 = other.Terminal2;
                    return true;
                }

                //// TODO: Case #3: the point is close enough to an existing road segment
                //float dist = LineSegment.Distance(line2, segment.Terminal2Pos);
                //if (dist < RoadSnapDistance)
                //{
                //    float proj0 = (float)Math.Sqrt((line2.P0 - segment.Terminal2Pos).LengthSq - dist * dist);
                //    float percent = proj0 / 
                //}
            }

            return true;
        }
    }
}