using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Threading.Tasks;
using Newtonsoft.Json;

namespace Tapeti.Flow.SQL
{
    /// <inheritdoc />
    /// <summary>
    /// IFlowRepository implementation for SQL server.
    /// </summary>
    /// <remarks>
    /// Assumes the following table layout (table name configurable and may include schema):
    /// create table Flow
    /// (
    ///     FlowID uniqueidentifier not null,
    ///     CreationTime datetime2(3) not null,
    ///     StateJson nvarchar(max) null,
    ///     constraint PK_Flow primary key clustered(FlowID)
    /// );
    /// </remarks>
    public class SqlConnectionFlowRepository : IFlowRepository
    {
        private readonly string connectionString;
        private readonly string tableName;


        /// <inheritdoc />
        public SqlConnectionFlowRepository(string connectionString, string tableName = "Flow")
        {
            this.connectionString = connectionString;
            this.tableName = tableName;
        }


        /// <inheritdoc />
        public async Task<List<KeyValuePair<Guid, T>>> GetStates<T>()
        {
            using (var connection = await GetConnection())
            {
                var flowQuery = new SqlCommand($"select FlowID, StateJson from {tableName}", connection);
                var flowReader = await flowQuery.ExecuteReaderAsync();

                var result = new List<KeyValuePair<Guid, T>>();

                while (await flowReader.ReadAsync())
                {
                    var flowID = flowReader.GetGuid(0);
                    var stateJson = flowReader.GetString(1);

                    var state = JsonConvert.DeserializeObject<T>(stateJson);
                    result.Add(new KeyValuePair<Guid, T>(flowID, state));
                }

                return result;
            }

        }

        /// <inheritdoc />
        public async Task CreateState<T>(Guid flowID, T state, DateTime timestamp)
        {
            using (var connection = await GetConnection())
            {
                var query = new SqlCommand($"insert into {tableName} (FlowID, StateJson, CreationTime)" +
                                            "values (@FlowID, @StateJson, @CreationTime)",
                                            connection);

                var flowIDParam = query.Parameters.Add("@FlowID", SqlDbType.UniqueIdentifier);
                var stateJsonParam = query.Parameters.Add("@StateJson", SqlDbType.NVarChar);
                var creationTimeParam = query.Parameters.Add("@CreationTime", SqlDbType.DateTime2);

                flowIDParam.Value = flowID;
                stateJsonParam.Value = JsonConvert.SerializeObject(state);
                creationTimeParam.Value = timestamp;

                await query.ExecuteNonQueryAsync();
            }
        }

        /// <inheritdoc />
        public async Task UpdateState<T>(Guid flowID, T state)
        {
            using (var connection = await GetConnection())
            {
                var query = new SqlCommand($"update {tableName} set StateJson = @StateJson where FlowID = @FlowID", connection);

                var flowIDParam = query.Parameters.Add("@FlowID", SqlDbType.UniqueIdentifier);
                var stateJsonParam = query.Parameters.Add("@StateJson", SqlDbType.NVarChar);

                flowIDParam.Value = flowID;
                stateJsonParam.Value = JsonConvert.SerializeObject(state);

                await query.ExecuteNonQueryAsync();
            }
        }

        /// <inheritdoc />
        public async Task DeleteState(Guid flowID)
        {
            using (var connection = await GetConnection())
            {
                var query = new SqlCommand($"delete from {tableName} where FlowID = @FlowID", connection);

                var flowIDParam = query.Parameters.Add("@FlowID", SqlDbType.UniqueIdentifier);
                flowIDParam.Value = flowID;

                await query.ExecuteNonQueryAsync();
            }
        }


        private async Task<SqlConnection> GetConnection()
        {
            var connection = new SqlConnection(connectionString);
            await connection.OpenAsync();

            return connection;
        }
    }
}