using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Diagnostics.CodeAnalysis;

using Npgsql.BackendMessages;

namespace Npgsql

{

/// <summary>

/// Represents a single SQL statement within Npgsql.

///

/// Instances aren't constructed directly; users should construct an <see cref="NpgsqlCommand"/>

/// object and populate its <see cref="NpgsqlCommand.CommandText"/> property as in standard ADO.NET.

/// Npgsql will analyze that property and construct instances of <see cref="NpgsqlStatement"/>

/// internally.

///

/// Users can retrieve instances from <see cref="NpgsqlDataReader.Statements"/>

/// and access information about statement execution (e.g. affected rows).

/// </summary>

public sealed class NpgsqlStatement

{

/// <summary>

/// The SQL text of the statement.

/// </summary>

public string SQL { get; set; } = string.Empty;

/// <summary>

/// Specifies the type of query, e.g. SELECT.

/// </summary>

public StatementType StatementType { get; internal set; }

/// <summary>

/// The number of rows affected or retrieved.

/// </summary>

/// <remarks>

/// See the command tag in the CommandComplete message,

/// https://www.postgresql.org/docs/current/static/protocol-message-formats.html

/// </remarks>

public uint Rows => (uint)LongRows;

/// <summary>

/// The number of rows affected or retrieved.

/// </summary>

/// <remarks>

/// See the command tag in the CommandComplete message,

/// https://www.postgresql.org/docs/current/static/protocol-message-formats.html

/// </remarks>

public ulong LongRows { get; internal set; }

/// <summary>

/// For an INSERT, the object ID of the inserted row if <see cref="Rows"/> is 1 and

/// the target table has OIDs; otherwise 0.

/// </summary>

public uint OID { get; internal set; }

/// <summary>

/// The input parameters sent with this statement.

/// </summary>

public List<NpgsqlParameter> InputParameters

{

get => _inputParameters ??= _ownedInputParameters ??= new();

internal set => _inputParameters = value;

}

List<NpgsqlParameter>? _ownedInputParameters;

List<NpgsqlParameter>? _inputParameters;

/// <summary>

/// The RowDescription message for this query. If null, the query does not return rows (e.g. INSERT)

/// </summary>

internal RowDescriptionMessage? Description

{

get => PreparedStatement == null ? _description : PreparedStatement.Description;

set

{

if (PreparedStatement == null)

_description = value;

else

PreparedStatement.Description = value;

}

}

RowDescriptionMessage? _description;

/// <summary>

/// If this statement has been automatically prepared, references the <see cref="PreparedStatement"/>.

/// Null otherwise.

/// </summary>

internal PreparedStatement? PreparedStatement

{

get => _preparedStatement != null && _preparedStatement.State == PreparedState.Unprepared

? _preparedStatement = null

: _preparedStatement;

set => _preparedStatement = value;

}

PreparedStatement? _preparedStatement;

internal bool IsPreparing;

/// <summary>

/// Holds the server-side (prepared) statement name. Empty string for non-prepared statements.

/// </summary>

internal string StatementName => PreparedStatement?.Name ?? "";

/// <summary>

/// Whether this statement has already been prepared (including automatic preparation).

/// </summary>

internal bool IsPrepared => PreparedStatement?.IsPrepared == true;

internal void Reset()

{

SQL = string.Empty;

StatementType = StatementType.Select;

_description = null;

LongRows = 0;

OID = 0;

PreparedStatement = null;

if (ReferenceEquals(_inputParameters, _ownedInputParameters))

InputParameters.Clear();

else if (_inputParameters is not null)

_inputParameters = null; // We're pointing at a user's NpgsqlParameterCollection

Debug.Assert(_inputParameters is null || _inputParameters.Count == 0);

Debug.Assert(_ownedInputParameters is null || _ownedInputParameters.Count == 0);

}

internal void ApplyCommandComplete(CommandCompleteMessage msg)

{

StatementType = msg.StatementType;

LongRows = msg.Rows;

OID = msg.OID;

}

/// <summary>

/// Returns the SQL text of the statement.

/// </summary>

public override string ToString() => SQL ?? "<none>";

}

}