using System;

using System.Collections.Generic;

using System.Data;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

namespace DataBoss.Data

{

public abstract class DbObjectReader<TCommand, TReader>

where TCommand : IDbCommand

where TReader : IDataReader

{

static readonly Regex FormatEx = new Regex(@"(@[A-Za-z_]+)");

static readonly Func<TCommand, TReader> ExecuteReader = Lambdas.Func<TCommand, TReader>(nameof(IDbCommand.ExecuteReader));

readonly Func<TCommand> newCommand;

public DbObjectReader(Func<TCommand> newCommand) {

this.newCommand = newCommand;

}

public TimeSpan? CommandTimeout = TimeSpan.FromSeconds(30);

public IEnumerable<T> Read<T>(string command) => Query(command, new { }).Read<T>();

public IEnumerable<T> Read<T>(string command, ConverterCollection converters) => Query(command, new { }).Read<T>(converters);

public T Single<T>(string command) => Read<T>(command).Single();

public DbObjectQuery<TCommand, TReader> Query<T>(string command, T args) =>

new DbObjectQuery<TCommand, TReader>(() => {

var cmd = CreateCommand();

cmd.CommandType = CommandType.Text;

cmd.CommandText = command;

AddParameters(cmd, args);

return cmd;

}, ExecuteReader);

public DbObjectQuery<TCommand, TReader> Query<T, T2>(string command, IEnumerable<T> args, Func<T, T2> toArg) =>

new DbObjectQuery<TCommand, TReader>(() => {

var q = new StringBuilder();

var cmd = CreateCommand();

var format = FormatEx.Replace(command, "$1$${0}");

using (var item = args.GetEnumerator())

for (var n = 0; item.MoveNext(); ++n) {

var first = cmd.Parameters.Count;

AddParameters(cmd, toArg(item.Current));

for (var i = first; i != cmd.Parameters.Count; ++i)

((IDbDataParameter)cmd.Parameters[i]).ParameterName += "$" + n;

q.AppendFormat(format, n);

q.AppendLine();

}

cmd.CommandText = q.ToString();

return cmd;

}, ExecuteReader);

public abstract void AddParameters<T>(TCommand cmd, T args);

TCommand CreateCommand() {

var cmd = newCommand();

cmd.CommandTimeout = CommandTimeout.HasValue ? (int)CommandTimeout.Value.TotalSeconds : 0;

return cmd;

}

}

}