// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreTypes.h"
#include "Containers/StringView.h"
#include "DerivedDataBuildKey.h"
#include "DerivedDataBuildPolicy.h"
#include "DerivedDataRequest.h"
#include "Templates/Function.h"
#include "Templates/UniquePtr.h"

namespace UE::DerivedData { class FBuildAction; }
namespace UE::DerivedData { class FBuildDefinition; }
namespace UE::DerivedData { class FBuildOutput; }
namespace UE::DerivedData { class FBuildSession; }
namespace UE::DerivedData { class FOptionalBuildInputs; }
namespace UE::DerivedData { class FPayload; }
namespace UE::DerivedData { struct FBuildActionCompleteParams; }
namespace UE::DerivedData { struct FBuildCompleteParams; }
namespace UE::DerivedData { struct FBuildPayloadCompleteParams; }

namespace UE::DerivedData
{

using FOnBuildComplete = TUniqueFunction<void (FBuildCompleteParams&& Params)>;
using FOnBuildActionComplete = TUniqueFunction<void (FBuildActionCompleteParams&& Params)>;
using FOnBuildPayloadComplete = TUniqueFunction<void (FBuildPayloadCompleteParams&& Params)>;

} // UE::DerivedData

namespace UE::DerivedData::Private
{

class IBuildSessionInternal
{
public:
	virtual ~IBuildSessionInternal() = default;
	virtual FStringView GetName() const = 0;
	virtual FRequest Build(
		const FBuildDefinition& Definition,
		EBuildPolicy Policy,
		EPriority Priority,
		FOnBuildComplete&& OnComplete) = 0;
	virtual FRequest BuildAction(
		const FBuildAction& Action,
		const FOptionalBuildInputs& Inputs,
		EBuildPolicy Policy,
		EPriority Priority,
		FOnBuildActionComplete&& OnComplete) = 0;
	virtual FRequest BuildPayload(
		const FBuildPayloadKey& Payload,
		EBuildPolicy Policy,
		EPriority Priority,
		FOnBuildPayloadComplete&& OnComplete) = 0;
};

FBuildSession CreateBuildSession(IBuildSessionInternal* Session);

} // UE::DerivedData::Private

namespace UE::DerivedData
{

/**
 * A build session is the main point to the build scheduler.
 *
 * The purpose of a session is to group together related builds that use the same input resolver,
 * such as grouping builds by target platform. A request to build one definition can lead to more
 * builds being scheduled if the definition references payloads from other builds as inputs.
 */
class FBuildSession
{
public:
	/** Returns the name by which to identify this session for logging and profiling. */
	inline FStringView GetName() const
	{
		return Session->GetName();
	}

	/**
	 * Asynchronous request to execute a build according to the policy.
	 *
	 * The callback will always be called, and may be called from an arbitrary thread.
	 *
	 * @param Definition   The build function to execute and references to its inputs.
	 * @param Policy       Flags to control the behavior of the request. See EBuildPolicy.
	 * @param Priority     A priority to consider when scheduling the request. See EPriority.
	 * @param OnComplete   A callback invoked when the build completes or is canceled.
	 */
	inline FRequest Build(
		const FBuildDefinition& Definition,
		EBuildPolicy Policy,
		EPriority Priority,
		FOnBuildComplete&& OnComplete)
	{
		return Session->Build(Definition, Policy, Priority, MoveTemp(OnComplete));
	}

	/**
	 * Asynchronous request to execute a build according to the policy.
	 *
	 * The callback will always be called, and may be called from an arbitrary thread.
	 *
	 * @param Action       The build function to execute and references to its inputs.
	 * @param Inputs       The build inputs referenced by the action, if it has any.
	 * @param Policy       Flags to control the behavior of the request. See EBuildPolicy.
	 * @param Priority     A priority to consider when scheduling the request. See EPriority.
	 * @param OnComplete   A callback invoked when the build completes or is canceled.
	 */
	inline FRequest BuildAction(
		const FBuildAction& Action,
		const FOptionalBuildInputs& Inputs,
		EBuildPolicy Policy,
		EPriority Priority,
		FOnBuildActionComplete&& OnComplete)
	{
		return Session->BuildAction(Action, Inputs, Policy, Priority, MoveTemp(OnComplete));
	}

	/**
	 * Asynchronous request to execute a build according to the policy and return one payload.
	 *
	 * The callback will always be called, and may be called from an arbitrary thread.
	 *
	 * @param Payload      The key identifying the build definition and the payload to return.
	 * @param Policy       Flags to control the behavior of the request. See EBuildPolicy.
	 * @param Priority     A priority to consider when scheduling the request. See EPriority.
	 * @param OnComplete   A callback invoked when the build completes or is canceled.
	 */
	inline FRequest BuildPayload(
		const FBuildPayloadKey& Payload,
		EBuildPolicy Policy,
		EPriority Priority,
		FOnBuildPayloadComplete&& OnComplete)
	{
		return Session->BuildPayload(Payload, Policy, Priority, MoveTemp(OnComplete));
	}

private:
	friend FBuildSession Private::CreateBuildSession(Private::IBuildSessionInternal* Session);

	/** Construct a build session. Use IBuild::CreateSession(). */
	inline explicit FBuildSession(Private::IBuildSessionInternal* InSession)
		: Session(InSession)
	{
	}

	TUniquePtr<Private::IBuildSessionInternal> Session;
};

/** Parameters for the completion callback for build requests. */
struct FBuildCompleteParams
{
	/** Key for the build request that completed or was canceled. */
	FBuildKey Key;

	/**
	 * Output for the build request that completed or was canceled.
	 *
	 * The name, function, and diagnostics are always populated.
	 *
	 * The payloads are populated when Status is Ok, but with null data if skipped by the policy.
	 */
	FBuildOutput&& Output;

	/** Status of the build request. */
	EStatus Status = EStatus::Error;
};

/** Parameters for the completion callback for build action requests. */
struct FBuildActionCompleteParams
{
	/** Key for the build action request that completed or was canceled. */
	FBuildActionKey Key;

	/**
	 * Output for the build action request that completed or was canceled.
	 *
	 * The name, function, and diagnostics are always populated.
	 *
	 * The payloads are populated when Status is Ok, but with null data if skipped by the policy.
	 */
	FBuildOutput&& Output;

	/** Status of the build request. */
	EStatus Status = EStatus::Error;
};

/** Parameters for the completion callback for build payload requests. */
struct FBuildPayloadCompleteParams
{
	/** Key for the build request that completed or was canceled. See Payload for ID. */
	FBuildKey Key;

	/**
	 * Payload from the build payload request that completed or was canceled.
	 *
	 * The ID is always populated.
	 * The hash and size are populated when Status is Ok.
	 * The data is populated when Status is Ok and the data was not skipped by the policy.
	 */
	FPayload&& Payload;

	/** Status of the build request. */
	EStatus Status = EStatus::Error;
};

} // UE::DerivedData