using System;
using System.Data.Common;
using System.Diagnostics.CodeAnalysis;
using System.Reflection;
using Npgsql.Logging;

namespace Npgsql;

/// <summary>
/// A factory to create instances of various Npgsql objects.
/// </summary>
[Serializable]
public sealed class NpgsqlFactory : DbProviderFactory, IServiceProvider
{
    /// <summary>
    /// Gets an instance of the <see cref="NpgsqlFactory"/>.
    /// This can be used to retrieve strongly typed data objects.
    /// </summary>
    public static readonly NpgsqlFactory Instance = new();

    NpgsqlFactory() {}

    /// <summary>
    /// Returns a strongly typed <see cref="DbCommand"/> instance.
    /// </summary>
    public override DbCommand CreateCommand() => new NpgsqlCommand();

    /// <summary>
    /// Returns a strongly typed <see cref="DbConnection"/> instance.
    /// </summary>
    public override DbConnection CreateConnection() => new NpgsqlConnection();

    /// <summary>
    /// Returns a strongly typed <see cref="DbParameter"/> instance.
    /// </summary>
    public override DbParameter CreateParameter() => new NpgsqlParameter();

    /// <summary>
    /// Returns a strongly typed <see cref="DbConnectionStringBuilder"/> instance.
    /// </summary>
    public override DbConnectionStringBuilder CreateConnectionStringBuilder() => new NpgsqlConnectionStringBuilder();

    /// <summary>
    /// Returns a strongly typed <see cref="DbCommandBuilder"/> instance.
    /// </summary>
    public override DbCommandBuilder CreateCommandBuilder() => new NpgsqlCommandBuilder();

    /// <summary>
    /// Returns a strongly typed <see cref="DbDataAdapter"/> instance.
    /// </summary>
    public override DbDataAdapter CreateDataAdapter() => new NpgsqlDataAdapter();

#if !NETSTANDARD2_0
    /// <summary>
    /// Specifies whether the specific <see cref="DbProviderFactory"/> supports the <see cref="DbDataAdapter"/> class.
    /// </summary>
    public override bool CanCreateDataAdapter => true;

    /// <summary>
    /// Specifies whether the specific <see cref="DbProviderFactory"/> supports the <see cref="DbCommandBuilder"/> class.
    /// </summary>
    public override bool CanCreateCommandBuilder => true;
#endif

#if NET6_0_OR_GREATER
    /// <inheritdoc/>
    public override bool CanCreateBatch => true;

    /// <inheritdoc/>
    public override DbBatch CreateBatch() => new NpgsqlBatch();

    /// <inheritdoc/>
    public override DbBatchCommand CreateBatchCommand() => new NpgsqlBatchCommand();
#endif

    #region IServiceProvider Members

    /// <summary>
    /// Gets the service object of the specified type.
    /// </summary>
    /// <param name="serviceType">An object that specifies the type of service object to get.</param>
    /// <returns>A service object of type serviceType, or null if there is no service object of type serviceType.</returns>
    [RequiresUnreferencedCode("Legacy EF5 method, not trimming-safe.")]
    public object? GetService(Type serviceType)
    {
        if (serviceType == null)
            throw new ArgumentNullException(nameof(serviceType));

        // In legacy Entity Framework, this is the entry point for obtaining Npgsql's
        // implementation of DbProviderServices. We use reflection for all types to
        // avoid any dependencies on EF stuff in this project. EF6 (and of course EF Core) do not use this method.

        if (serviceType.FullName != "System.Data.Common.DbProviderServices")
            return null;

        // User has requested a legacy EF DbProviderServices implementation. Check our cache first.
        if (_legacyEntityFrameworkServices != null)
            return _legacyEntityFrameworkServices;

        // First time, attempt to find the EntityFramework5.Npgsql assembly and load the type via reflection
        var assemblyName = typeof(NpgsqlFactory).GetTypeInfo().Assembly.GetName();
        assemblyName.Name = "EntityFramework5.Npgsql";
        Assembly npgsqlEfAssembly;
        try {
            npgsqlEfAssembly = Assembly.Load(new AssemblyName(assemblyName.FullName));
        } catch {
            return null;
        }

        Type? npgsqlServicesType;
        if ((npgsqlServicesType = npgsqlEfAssembly.GetType("Npgsql.NpgsqlServices")) == null ||
            npgsqlServicesType.GetProperty("Instance") == null)
            throw new Exception("EntityFramework5.Npgsql assembly does not seem to contain the correct type!");

        return _legacyEntityFrameworkServices = npgsqlServicesType
            .GetProperty("Instance", BindingFlags.Public | BindingFlags.Static)!
            .GetMethod!.Invoke(null, new object[0]);
    }

    static object? _legacyEntityFrameworkServices;

    #endregion
}