using CharacterApi.Models;
using MongoDB.Bson;
using MongoDB.Driver;

namespace CharacterApi.Services;

public class CharacterStore
{
    private readonly IMongoCollection<Character> _col;
    private readonly IMongoCollection<BsonDocument> _locations;
    private const string CoordIndexName = "coord_x_1_coord_y_1";
    private const int WorldSeed = 1729;
    private static readonly string[] BiomeOrder = ["plains", "forest", "wetlands", "rocky", "desert"];
    private static readonly Dictionary<string, BiomeDefinition> Biomes = new()
    {
        ["plains"] = new BiomeDefinition(
            "plains",
            3.0,
            new Dictionary<string, double>
            {
                ["forest"] = 1.7,
                ["wetlands"] = 0.9,
                ["rocky"] = 0.8,
                ["desert"] = 0.4
            },
            new[]
            {
                new ResourceRule("grass", 180, 420, 12),
                new ResourceRule("wood", 25, 90, 3),
                new ResourceRule("stone", 10, 40, 2)
            }),
        ["forest"] = new BiomeDefinition(
            "forest",
            3.4,
            new Dictionary<string, double>
            {
                ["plains"] = 1.6,
                ["wetlands"] = 1.3,
                ["rocky"] = 0.5,
                ["desert"] = 0.1
            },
            new[]
            {
                new ResourceRule("wood", 220, 520, 6),
                new ResourceRule("grass", 90, 220, 8),
                new ResourceRule("stone", 15, 45, 2)
            }),
        ["wetlands"] = new BiomeDefinition(
            "wetlands",
            3.1,
            new Dictionary<string, double>
            {
                ["forest"] = 1.5,
                ["plains"] = 1.1,
                ["rocky"] = 0.2,
                ["desert"] = 0.05
            },
            new[]
            {
                new ResourceRule("grass", 260, 600, 15),
                new ResourceRule("wood", 40, 120, 4)
            }),
        ["rocky"] = new BiomeDefinition(
            "rocky",
            3.0,
            new Dictionary<string, double>
            {
                ["plains"] = 1.2,
                ["forest"] = 0.6,
                ["desert"] = 1.1,
                ["wetlands"] = 0.1
            },
            new[]
            {
                new ResourceRule("stone", 220, 540, 8),
                new ResourceRule("wood", 10, 40, 2),
                new ResourceRule("grass", 20, 70, 4)
            }),
        ["desert"] = new BiomeDefinition(
            "desert",
            3.2,
            new Dictionary<string, double>
            {
                ["rocky"] = 1.4,
                ["plains"] = 0.8,
                ["forest"] = 0.1,
                ["wetlands"] = 0.05
            },
            new[]
            {
                new ResourceRule("stone", 80, 220, 5),
                new ResourceRule("grass", 5, 25, 2)
            })
    };

    public sealed record VisibleLocationResult(List<VisibleLocation> Locations, int GeneratedCount);

    public CharacterStore(IConfiguration cfg)
    {
        var cs = cfg["MongoDB:ConnectionString"] ?? "mongodb://127.0.0.1:27017";
        var dbName = cfg["MongoDB:DatabaseName"] ?? "GameDb";
        var client = new MongoClient(cs);
        var db = client.GetDatabase(dbName);
        _col = db.GetCollection<Character>("Characters");
        _locations = db.GetCollection<BsonDocument>("Locations");
        EnsureLocationCoordIndexes();

        var ownerIndex = Builders<Character>.IndexKeys.Ascending(c => c.OwnerUserId);
        _col.Indexes.CreateOne(new CreateIndexModel<Character>(ownerIndex));
    }

    public Task CreateAsync(Character character) => _col.InsertOneAsync(character);

    public Task<List<Character>> GetForOwnerAsync(string ownerUserId) =>
        _col.Find(c => c.OwnerUserId == ownerUserId).ToListAsync();

    public async Task<Character?> GetByIdAsync(string id) =>
        await _col.Find(c => c.Id == id).FirstOrDefaultAsync();

    public async Task<bool> UpdateCoordAsync(string id, Coord coord)
    {
        var filter = Builders<Character>.Filter.Eq(c => c.Id, id);
        var update = Builders<Character>.Update.Set(c => c.Coord, coord);
        var result = await _col.UpdateOneAsync(filter, update);
        return result.ModifiedCount > 0 || result.MatchedCount > 0;
    }

    public Task<List<VisibleLocation>> GetVisibleLocationsAsync(Character character)
    {
        return GetVisibleLocationsInternalAsync(character, ensureGenerated: false);
    }

    public async Task<VisibleLocationResult> GetOrCreateVisibleLocationsAsync(Character character)
    {
        var generatedCount = await EnsureVisibleLocationsExistAsync(character);
        var locations = await GetVisibleLocationsInternalAsync(character, ensureGenerated: true);
        return new VisibleLocationResult(locations, generatedCount);
    }

    private async Task<List<VisibleLocation>> GetVisibleLocationsInternalAsync(Character character, bool ensureGenerated)
    {
        var radius = character.VisionRadius > 0 ? character.VisionRadius : 3;
        var minX = character.Coord.X - radius;
        var maxX = character.Coord.X + radius;
        var minY = character.Coord.Y - radius;
        var maxY = character.Coord.Y + radius;

        var filter = Builders<BsonDocument>.Filter.And(
            Builders<BsonDocument>.Filter.Gte("coord.x", minX),
            Builders<BsonDocument>.Filter.Lte("coord.x", maxX),
            Builders<BsonDocument>.Filter.Gte("coord.y", minY),
            Builders<BsonDocument>.Filter.Lte("coord.y", maxY)
        );

        var documents = await _locations.Find(filter).ToListAsync();
        return documents.Select(MapVisibleLocation).ToList();
    }

    private async Task<int> EnsureVisibleLocationsExistAsync(Character character)
    {
        var radius = character.VisionRadius > 0 ? character.VisionRadius : 3;
        var generatedCount = 0;

        for (var x = character.Coord.X - radius; x <= character.Coord.X + radius; x++)
        {
            for (var y = character.Coord.Y - radius; y <= character.Coord.Y + radius; y++)
            {
                if (await EnsureLocationStateAsync(x, y))
                    generatedCount += 1;
            }
        }

        return generatedCount;
    }

    private static string DefaultLocationName(int x, int y)
    {
        if (x == 0 && y == 0)
            return "Origin";
        return $"Location {x},{y}";
    }

    private static VisibleLocation MapVisibleLocation(BsonDocument document)
    {
        var coord = document.GetValue("coord", new BsonDocument()).AsBsonDocument;
        var idValue = document.GetValue("_id", BsonNull.Value);
        string? id = null;
        if (!idValue.IsBsonNull)
        {
            id = idValue.BsonType == BsonType.ObjectId
                ? idValue.AsObjectId.ToString()
                : idValue.ToString();
        }

        return new VisibleLocation
        {
            Id = id,
            Name = document.GetValue("name", "").AsString,
            Coord = new LocationCoord
            {
                X = coord.GetValue("x", 0).ToInt32(),
                Y = coord.GetValue("y", 0).ToInt32()
            },
            BiomeKey = document.GetValue("biomeKey", "plains").AsString,
            Resources = MapVisibleLocationResources(document)
        };
    }

    private async Task<bool> EnsureLocationStateAsync(int x, int y)
    {
        var filter = Builders<BsonDocument>.Filter.And(
            Builders<BsonDocument>.Filter.Eq("coord.x", x),
            Builders<BsonDocument>.Filter.Eq("coord.y", y)
        );

        var existing = await _locations.Find(filter).FirstOrDefaultAsync();
        if (existing is not null)
        {
            await BackfillLocationStateAsync(existing);
            return false;
        }

        var biomeKey = await DetermineBiomeKeyAsync(x, y);
        var update = Builders<BsonDocument>.Update
            .SetOnInsert("_id", ObjectId.GenerateNewId())
            .SetOnInsert("name", DefaultLocationName(x, y))
            .SetOnInsert("coord", new BsonDocument
            {
                { "x", x },
                { "y", y }
            })
            .SetOnInsert("biomeKey", biomeKey)
            .SetOnInsert("resources", BuildResourcesDocument(biomeKey, x, y))
            .SetOnInsert("createdUtc", DateTime.UtcNow);

        try
        {
            var result = await _locations.UpdateOneAsync(filter, update, new UpdateOptions { IsUpsert = true });
            return result.UpsertedId is not null;
        }
        catch (MongoWriteException ex) when (ex.WriteError.Category == ServerErrorCategory.DuplicateKey)
        {
            return false;
        }
    }

    private async Task BackfillLocationStateAsync(BsonDocument document)
    {
        var coord = document.GetValue("coord", new BsonDocument()).AsBsonDocument;
        var x = coord.GetValue("x", 0).ToInt32();
        var y = coord.GetValue("y", 0).ToInt32();

        var updates = new List<UpdateDefinition<BsonDocument>>();
        var biomeKey = document.GetValue("biomeKey", BsonNull.Value).IsBsonNull
            ? await DetermineBiomeKeyAsync(x, y)
            : document.GetValue("biomeKey", "plains").AsString;

        if (!document.Contains("biomeKey"))
            updates.Add(Builders<BsonDocument>.Update.Set("biomeKey", biomeKey));
        if (!document.Contains("resources"))
            updates.Add(Builders<BsonDocument>.Update.Set("resources", BuildResourcesDocument(biomeKey, x, y)));

        if (updates.Count == 0)
            return;

        var id = document.GetValue("_id").AsObjectId;
        await _locations.UpdateOneAsync(
            Builders<BsonDocument>.Filter.Eq("_id", id),
            Builders<BsonDocument>.Update.Combine(updates));
    }

    private async Task<string> DetermineBiomeKeyAsync(int x, int y)
    {
        if (x == 0 && y == 0)
            return "plains";

        var neighbors = await LoadNeighborBiomeKeysAsync(x, y);
        var baseBiome = DetermineBaseBiomeKey(x, y);
        if (neighbors.Count == 0)
            return baseBiome;

        var dominantNeighbor = neighbors
            .GroupBy(key => key)
            .OrderByDescending(group => group.Count())
            .ThenBy(group => group.Key)
            .First().Key;

        var bestBiome = baseBiome;
        var bestScore = double.NegativeInfinity;
        foreach (var candidate in BiomeOrder)
        {
            var score = candidate == baseBiome ? 2.5 : 0.35;
            if (candidate == dominantNeighbor)
                score += 1.8;

            foreach (var neighbor in neighbors)
            {
                if (!Biomes.TryGetValue(neighbor, out var neighborDefinition))
                    continue;

                if (candidate == neighbor)
                    score += neighborDefinition.ContinuationWeight;
                else if (neighborDefinition.TransitionWeights.TryGetValue(candidate, out var transitionWeight))
                    score += transitionWeight;
            }

            score += StableNoise(x, y, StableHash(candidate)) * 0.25;
            if (score > bestScore)
            {
                bestScore = score;
                bestBiome = candidate;
            }
        }

        return bestBiome;
    }

    private async Task<List<string>> LoadNeighborBiomeKeysAsync(int x, int y)
    {
        var coords = new[]
        {
            (x - 1, y),
            (x + 1, y),
            (x, y - 1),
            (x, y + 1)
        };

        var filters = coords.Select(coord =>
            Builders<BsonDocument>.Filter.And(
                Builders<BsonDocument>.Filter.Eq("coord.x", coord.Item1),
                Builders<BsonDocument>.Filter.Eq("coord.y", coord.Item2)))
            .ToList();
        var filter = Builders<BsonDocument>.Filter.Or(filters);
        var neighbors = await _locations.Find(filter).ToListAsync();

        return neighbors
            .Where(doc => doc.Contains("biomeKey"))
            .Select(doc => doc.GetValue("biomeKey", "plains").AsString)
            .Where(key => !string.IsNullOrWhiteSpace(key))
            .ToList();
    }

    private static string DetermineBaseBiomeKey(int x, int y)
    {
        var temperature = StableNoise(x, y, 101);
        var moisture = StableNoise(x, y, 202);
        var ruggedness = StableNoise(x, y, 303);

        if (ruggedness > 0.74)
            return "rocky";
        if (moisture > 0.72 && temperature < 0.75)
            return "wetlands";
        if (moisture > 0.56)
            return "forest";
        if (moisture < 0.22 && temperature > 0.58)
            return "desert";
        return "plains";
    }

    private static BsonArray BuildResourcesDocument(string biomeKey, int x, int y)
    {
        if (!Biomes.TryGetValue(biomeKey, out var biome))
            biome = Biomes["plains"];

        var resources = new BsonArray();
        foreach (var rule in biome.ResourceRules)
        {
            var roll = StableNoise(x, y, StableHash(rule.ItemKey));
            var quantity = rule.MinQuantity + (int)Math.Round(roll * (rule.MaxQuantity - rule.MinQuantity));
            if (quantity <= 0)
                continue;

            resources.Add(new BsonDocument
            {
                { "itemKey", rule.ItemKey },
                { "remainingQuantity", quantity },
                { "gatherQuantity", rule.GatherQuantity }
            });
        }

        return resources;
    }

    private static double StableNoise(int x, int y, int salt)
    {
        var value = Math.Sin((x * 12.9898) + (y * 78.233) + ((WorldSeed + salt) * 0.1597)) * 43758.5453;
        return value - Math.Floor(value);
    }

    private static int StableHash(string value)
    {
        unchecked
        {
            var hash = 23;
            foreach (var c in value)
                hash = (hash * 31) + c;
            return hash;
        }
    }

    private static List<VisibleLocationResource> MapVisibleLocationResources(BsonDocument document)
    {
        if (!document.TryGetValue("resources", out var resourcesValue) || resourcesValue.BsonType != BsonType.Array)
            return [];

        var results = new List<VisibleLocationResource>();
        foreach (var value in resourcesValue.AsBsonArray)
        {
            if (value.BsonType != BsonType.Document)
                continue;

            var resource = value.AsBsonDocument;
            results.Add(new VisibleLocationResource
            {
                ItemKey = resource.GetValue("itemKey", "").AsString,
                RemainingQuantity = resource.GetValue("remainingQuantity", 0).ToInt32(),
                GatherQuantity = resource.GetValue("gatherQuantity", 1).ToInt32()
            });
        }

        return results;
    }

    private void EnsureLocationCoordIndexes()
    {
        var indexes = _locations.Indexes.List().ToList();
        foreach (var index in indexes)
        {
            var name = index.GetValue("name", "").AsString;
            if (name == "_id_")
                continue;

            var keyDoc = index.GetValue("key", new BsonDocument()).AsBsonDocument;
            if (IsLegacyCoordIndex(keyDoc) || IsUnexpectedCoordIndex(keyDoc))
                _locations.Indexes.DropOne(name);
        }

        var coordIndex = new BsonDocument
        {
            { "coord.x", 1 },
            { "coord.y", 1 }
        };
        var coordIndexOptions = new CreateIndexOptions { Unique = true, Name = CoordIndexName };
        _locations.Indexes.CreateOne(new CreateIndexModel<BsonDocument>(coordIndex, coordIndexOptions));
    }

    private static bool IsLegacyCoordIndex(BsonDocument keyDoc) =>
        keyDoc.ElementCount == 2 &&
        keyDoc.TryGetValue("Coord.X", out var xValue) &&
        xValue.IsInt32 && xValue.AsInt32 == 1 &&
        keyDoc.TryGetValue("Coord.Y", out var yValue) &&
        yValue.IsInt32 && yValue.AsInt32 == 1;

    private static bool IsUnexpectedCoordIndex(BsonDocument keyDoc)
    {
        var hasLower = keyDoc.Contains("coord.x") || keyDoc.Contains("coord.y");
        var hasUpper = keyDoc.Contains("Coord.X") || keyDoc.Contains("Coord.Y");
        return hasUpper || (hasLower && !(keyDoc.Contains("coord.x") && keyDoc.Contains("coord.y")));
    }

    public async Task<bool> DeleteForOwnerAsync(string id, string ownerUserId, bool allowAnyOwner)
    {
        var filter = Builders<Character>.Filter.Eq(c => c.Id, id);
        if (!allowAnyOwner)
        {
            filter = Builders<Character>.Filter.And(
                filter,
                Builders<Character>.Filter.Eq(c => c.OwnerUserId, ownerUserId)
            );
        }

        var result = await _col.DeleteOneAsync(filter);
        return result.DeletedCount > 0;
    }

    private sealed record ResourceRule(string ItemKey, int MinQuantity, int MaxQuantity, int GatherQuantity);

    private sealed record BiomeDefinition(
        string Key,
        double ContinuationWeight,
        Dictionary<string, double> TransitionWeights,
        IReadOnlyList<ResourceRule> ResourceRules);
}