namespace DataBoss.Data

{

using System;

using System.Collections.Generic;

using System.Data;

using System.Linq;

public static class DbObjectQuery

{

public static DbObjectQuery<IDbCommand, IDataReader> Create(Func<IDbCommand> getCommand) =>

new(getCommand, x => x.ExecuteReader());

public static DbObjectQuery<IDbCommand, IDataReader> Create(Func<IDbCommand> getCommand, bool bufferResult) =>

new(getCommand, x => x.ExecuteReader(), bufferResult: bufferResult);

internal static Func<TReader, TOutput> NewFuncConverter<TReader, TFun, TOutput> (TReader reader, object state)

where TReader : IDataReader

where TFun : Delegate

=> new FuncConverter<TReader, TFun, TOutput>(reader, (TFun)state).Materialize;

internal class FuncConverter<TReader, TFun, TOutput>

where TReader : IDataReader

where TFun : Delegate

{

readonly Func<TReader, TFun, TOutput> trampoline;

readonly TFun fun;

public FuncConverter(TReader reader, TFun fun) {

this.trampoline = (Func<TReader, TFun, TOutput>)ConverterFactory.Default.CompileTrampoline(reader, fun);

this.fun = fun;

}

public TOutput Materialize(TReader reader) => trampoline(reader, fun);

}

}

public readonly struct DbObjectQuery<TCommand, TReader>

where TCommand : IDbCommand

where TReader: IDataReader

{

readonly Func<TCommand> getCommand;

readonly Func<TCommand, TReader> executeReader;

readonly bool bufferResult;

public DbObjectQuery(Func<TCommand> getCommand, Func<TCommand, TReader> executeReader, bool bufferResult = false) {

this.getCommand = getCommand;

this.executeReader = executeReader;

this.bufferResult = bufferResult;

}

public IEnumerable<TResult> Read<TResult>() =>

BufferOrNot(MakeEnumerable(GetReader<TResult>, null));

public IEnumerable<TOutput> Read<TFun, TOutput>(TFun fun) where TFun : Delegate =>

BufferOrNot(MakeEnumerable<TFun, TOutput>(fun));

IEnumerable<T> BufferOrNot<T>(IEnumerable<T> xs) => bufferResult ? xs.ToList() : xs;

static Func<TReader, T> GetReader<T>(TReader reader, object state) =>

state is not ConverterCollection customConversions

? ConverterFactory.Default.GetConverter<TReader, T>(reader).Compiled

: ConverterFactory.GetConverter<TReader, T>(reader, customConversions).Compiled;

public DbCommandEnumerable<TCommand, TReader, TOutput> Read<TOutput>(ConverterCollection converters) => MakeEnumerable(GetConverter<TOutput>, converters);

static Func<TReader, TOutput> GetConverter<TOutput>(TReader reader, object state) =>

ObjectReader.GetConverter<TReader, TOutput>(reader, (ConverterCollection)state);

public DbCommandEnumerable<TCommand, TReader, TOutput> MakeEnumerable<TOutput>(Func<TReader, object, Func<TReader, TOutput>> converterFactory, object state) =>

new(getCommand, executeReader, converterFactory, state);

public DbCommandEnumerable<TCommand, TReader, TOutput> MakeEnumerable<TFun, TOutput>(TFun fun) where TFun : Delegate =>

new(getCommand, executeReader, DbObjectQuery.NewFuncConverter<TReader, TFun,TOutput>, fun);

public List<TOutput> ReadWithRetry<TOutput>(RetryStrategy retry) => MakeEnumerable(GetReader<TOutput>, null).ToList(retry);

public List<TOutput> ReadWithRetry<TOutput>(RetryStrategy retry, ConverterCollection converters) => MakeEnumerable(GetReader<TOutput>, converters).ToList(retry);

public TOutput Single<TOutput>() where TOutput : new() =>

MakeEnumerable(GetReader<TOutput>, null).Single();

}

}