using Microsoft.AspNetCore.Mvc.Diagnostics;
using MongoDB.Bson;
using MongoDB.Bson.Serialization;
using MongoDB.Driver;
using Salmon.Core;
using System;
using System.Collections;
using System.Security.Cryptography;

namespace Salmon.Web.Data;

public class MongoDbInterface
    : Salmon.Core.Depth.Persistence
{
    private enum Constraint
    {
        Equal,
        NotEqual,
        Greater,
        GreaterOrEqual,
        Less,
        LessOrEqual
    }

    public MongoClient Client { get; private set; }
    public IMongoDatabase Database { get; private set; }

    public const string TripletsCollectionName = "Triplets";
    public const string EventsCollectionName = "Events";

    public IMongoCollection<BsonDocument> TripletsCollection { get; private set; }
    public IMongoCollection<BsonDocument> EventsCollection { get; private set; }

    public MongoDbInterface(IConfiguration conf)
    {
        var connectionStr = conf["Persistence:ConnectionString"];
        if (connectionStr is null)
            throw new Exception("Cannot create persistence module without connection string.");

        Client = new (connectionStr);
        Database = Client.GetDatabase("Salmon");

        TripletsCollection = Database.GetCollection<BsonDocument>(TripletsCollectionName);
        EventsCollection = Database.GetCollection<BsonDocument>(EventsCollectionName);
    }

    public async Task<bool> Test()
    {
        var databases = Client.ListDatabasesAsync().Result;
        await databases.MoveNextAsync();

        try
        {
            bool b = Client.Cluster.Description.Servers.Single().State == MongoDB.Driver.Core.Servers.ServerState.Connected;
            return true;
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Mongodb connection test failed: {ex}");
            return false;
        }
    }

    public override async Task<object?> GetLastValue(string subject, string predicate)
    {
        var filter = Builders<BsonDocument>.Filter.And(new[]
        {
            Builders<BsonDocument>.Filter.Eq("Subject", subject),
            Builders<BsonDocument>.Filter.Eq("Predicate", predicate)
        });
        var sort = Builders<BsonDocument>.Sort.Ascending("When");

        using (var cursor = await TripletsCollection.FindAsync(filter, new()
        {
            Sort = sort,
            Limit = 1
        }))
        {
            if (!await cursor.MoveNextAsync())
                return null;

            var batch = cursor.Current;
            foreach(var i in batch)
            {
                if (!i.Contains("Object"))
                    throw new Exception("Response value doesn't have any Object field");

                return DeserializeRawValue(i["Object"]);
            }

            return null;
        }

    }

    protected override async Task RegisterStateChange(string subject, string predicate, DateTime when, object? value)
    {
        await TripletsCollection.InsertOneAsync(
            new BsonDocument(new[]
            {
                new KeyValuePair<string, object>("Subject", subject),
                new KeyValuePair<string, object>("Predicate", predicate),
                new KeyValuePair<string, object>("When", when),
                new KeyValuePair<string, object>("Object", value)
            }
        ));
    }

    public override async IAsyncEnumerable<Triplet> GetState()
    {
        var src = TripletsCollection
            .Aggregate()
            .Group(new BsonDocument
            {
                { "_id", new BsonDocument
                    {
                        { "Subject", "$Subject" },
                        { "Predicate", "$Predicate" }
                    } },
                { "Subject", new BsonDocument("$first", "$Subject") },
                { "Predicate", new BsonDocument("$first", "$Predicate") },
                { "When", new BsonDocument("$first", "$When") },
                { "Object", new BsonDocument("$first", "$Object") }
            });

        using (var cursor = await src.ToCursorAsync())
        {
            if (!await cursor.MoveNextAsync())
                yield break;

            var batch = cursor.Current;
            foreach (var i in batch)
            {
                if (!i.Contains("Subject"))
                    throw new Exception("Response value doesn't have any Subject field");
                
                if (!i.Contains("Predicate"))
                    throw new Exception("Response value doesn't have any Predicate field");

                if (!i.Contains("Object"))
                    throw new Exception("Response value doesn't have any Object field");

                if (!i.Contains("When"))
                    throw new Exception("Response value doesn't have any When field");

                yield return new Triplet
                {
                    key = i[1].AsString,
                    predicate = i[2].AsString,
                    LastFlush = i[3].ToUniversalTime(),
                    value = DeserializeRawValue(i[4]),

                };
            }
        }
    }

    static private object? DeserializeRawValue(BsonValue v)
    {
        if (v.IsBsonNull)
            return null;

        if (v.IsBoolean)
            return v.AsBoolean;

        if (v.IsString)
            return v.AsString;

        if (v.IsValidDateTime)
            return v.ToUniversalTime();

        if (v.IsInt32)
            return v.AsInt32;

        if (v.IsInt64)
            return v.AsInt64;

        if (v.IsDouble)
            return v.AsDouble;

        if (v.IsDecimal128)
            return v.AsDecimal128;

        throw new NotImplementedException();
    }

    static private BsonValue SerializeRawValue(object? value)
    {
        if (value == null)
            return BsonNull.Value;

        if (value is bool) return (bool)value;
        if (value is string) return (string)value;
        if (value is DateTime) return (DateTime)value;

        if (value is byte) return (byte)value;
        if (value is short) return (short)value;
        if(value is ushort) return (ushort)value;
        if (value is int) return (int)value;
        if(value is uint) return (uint)value;
        if (value is long) return (long)value;

        if(value is float) return (float)value;
        if(value is double) return (double)value;
        if(value is decimal) return (decimal)value;

        throw new NotImplementedException();
    }

    public override async Task RegisterEvent(Event e)
    {
        var properties = new BsonDocument();
        foreach (var kv in e.Properties)
            properties.Add(kv.Key, SerializeRawValue(kv.Value));

        var bson = new BsonDocument(new[]
            {
                new KeyValuePair<string, object>("_id", e.UniqueId),
                new KeyValuePair<string, object>("Thrower", e.ThrowerId),
                new KeyValuePair<string, object>("Type", e.Type),
                new KeyValuePair<string, object>("When", e.When),
                new KeyValuePair<string, object>("Properties", properties),
            });

        await EventsCollection.InsertOneAsync(bson);
    }

    public override Task<Event?> GetEvent(string id)
    {
        throw new NotImplementedException();
    }

    private Event EventFromBson(BsonDocument bson)
    {
        Event ret = new(bson["_id"].AsString, bson["Thrower"].AsString, bson["Type"].AsString, bson["When"].ToUniversalTime());
        foreach (var kv in bson["Properties"].AsBsonDocument)
            ret.Properties.Add(kv.Name, kv.Value);

        return ret;
    }

    private bool isMainProperty(string name)
    {
        if (name == "Type")
            return true;

        return false;
    }

    public override async IAsyncEnumerable<Event> GetEvents(string? subject = null, DateTime? from = null, DateTime? to = null, int? limit = null, int? offset = null, Dictionary<string, object>? filters = null)
    {
        var conditions = new List<FilterDefinition<BsonDocument>>();

        if (subject is not null)
            conditions.Add(Builders<BsonDocument>.Filter.Eq("Thrower", subject));

        if(filters is not null)
        {
            Func<Constraint, string, object, FilterDefinition<BsonDocument>> createFilter = (Constraint c, string property, object value) =>
            {
                if (c == Constraint.Equal)
                    return Builders<BsonDocument>.Filter.Eq(property, value);
                else if (c == Constraint.NotEqual)
                    return Builders<BsonDocument>.Filter.Not(Builders<BsonDocument>.Filter.Eq(property, value));
                else if (c == Constraint.Less)
                    return Builders<BsonDocument>.Filter.Lt(property, value);
                else if (c == Constraint.LessOrEqual)
                    return Builders<BsonDocument>.Filter.Lte(property, value);                
                else if (c == Constraint.Greater)
                    return Builders<BsonDocument>.Filter.Gt(property, value);
                else if (c == Constraint.GreaterOrEqual)
                    return Builders<BsonDocument>.Filter.Gte(property, value);

                throw new NotImplementedException();
            };

            foreach (var f in filters)
            {
                string property;
                Constraint constraint;
                if (f.Key.StartsWith("!"))
                {
                    property = f.Key.Substring(1);
                    constraint = Constraint.NotEqual;
                }
                else if (f.Key.StartsWith("<"))
                {
                    property = f.Key.Substring(1);
                    constraint = Constraint.Less;
                }
                else if (f.Key.StartsWith("<="))
                {
                    property = f.Key.Substring(2);
                    constraint = Constraint.LessOrEqual;
                }
                else if (f.Key.StartsWith(">"))
                {
                    property = f.Key.Substring(1);
                    constraint = Constraint.Greater;
                }
                else if (f.Key.StartsWith(">="))
                {
                    property = f.Key.Substring(2);
                    constraint = Constraint.GreaterOrEqual;
                }
                else
                {
                    property = f.Key;
                    constraint = Constraint.Equal;
                }

                bool isMain = isMainProperty(property);
                if (isMain)
                    conditions.Add(createFilter(constraint, property, f.Value));
                else
                    conditions.Add(Builders<BsonDocument>.Filter.Eq("Properties", createFilter(constraint, property, f.Value)));
            }
        }



        FilterDefinition<BsonDocument> filter = conditions.Count > 0
                                              ? Builders<BsonDocument>.Filter.And(conditions)
                                              : FilterDefinition<BsonDocument>.Empty;
        var sort = Builders<BsonDocument>.Sort.Descending("When");

        using (var cursor = await EventsCollection.FindAsync(filter, new()
        {
            Sort = sort,
            Limit = limit,
        }))
        {
            if (!await cursor.MoveNextAsync())
                yield break;

            var batch = cursor.Current;
            foreach (var i in batch)
            {
                yield return EventFromBson(i);
            }
        }
    }
}