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";

    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++)
            {
                var filter = Builders<BsonDocument>.Filter.And(
                    Builders<BsonDocument>.Filter.Eq("coord.x", x),
                    Builders<BsonDocument>.Filter.Eq("coord.y", y)
                );

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

                try
                {
                    var result = await _locations.UpdateOneAsync(filter, update, new UpdateOptions { IsUpsert = true });
                    if (result.UpsertedId is not null)
                        generatedCount += 1;
                }
                catch (MongoWriteException ex) when (ex.WriteError.Category == ServerErrorCategory.DuplicateKey)
                {
                    // Another request or service instance created it first.
                }
            }
        }

        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()
            },
            Resources = MapVisibleLocationResources(document)
        };
    }

    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;
    }
}