/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2021-2022, Ideas On Board
 *
 * agc.cpp - AGC/AEC mean-based control algorithm
 */

#include "agc.h"

#include <algorithm>
#include <chrono>
#include <cmath>

#include <libcamera/base/log.h>
#include <libcamera/base/utils.h>

#include <libcamera/ipa/core_ipa_interface.h>

#include "libipa/histogram.h"

/**
 * \file agc.h
 */

namespace libcamera {

using namespace std::literals::chrono_literals;

namespace ipa::rkisp1::algorithms {

/**
 * \class Agc
 * \brief A mean-based auto-exposure algorithm
 */

LOG_DEFINE_CATEGORY(RkISP1Agc)

/* Limits for analogue gain values */
static constexpr double kMinAnalogueGain = 1.0;
static constexpr double kMaxAnalogueGain = 8.0;

/* \todo Honour the FrameDurationLimits control instead of hardcoding a limit */
static constexpr utils::Duration kMaxShutterSpeed = 60ms;

/* Number of frames to wait before calculating stats on minimum exposure */
static constexpr uint32_t kNumStartupFrames = 10;

/* Target value to reach for the top 2% of the histogram */
static constexpr double kEvGainTarget = 0.5;

/*
 * Relative luminance target.
 *
 * It's a number that's chosen so that, when the camera points at a grey
 * target, the resulting image brightness is considered right.
 *
 * \todo Why is the value different between IPU3 and RkISP1 ?
 */
static constexpr double kRelativeLuminanceTarget = 0.4;

Agc::Agc()
	: frameCount_(0), numCells_(0), numHistBins_(0), filteredExposure_(0s)
{
}

/**
 * \brief Configure the AGC given a configInfo
 * \param[in] context The shared IPA context
 * \param[in] configInfo The IPA configuration data
 *
 * \return 0
 */
int Agc::configure(IPAContext &context, const IPACameraSensorInfo &configInfo)
{
	/* Configure the default exposure and gain. */
	context.frameContext.agc.gain = std::max(context.configuration.agc.minAnalogueGain, kMinAnalogueGain);
	context.frameContext.agc.exposure = 10ms / context.configuration.sensor.lineDuration;

	/*
	 * According to the RkISP1 documentation:
	 * - versions < V12 have RKISP1_CIF_ISP_AE_MEAN_MAX_V10 entries,
	 * - versions >= V12 have RKISP1_CIF_ISP_AE_MEAN_MAX_V12 entries.
	 */
	if (context.configuration.hw.revision < RKISP1_V12) {
		numCells_ = RKISP1_CIF_ISP_AE_MEAN_MAX_V10;
		numHistBins_ = RKISP1_CIF_ISP_HIST_BIN_N_MAX_V10;
	} else {
		numCells_ = RKISP1_CIF_ISP_AE_MEAN_MAX_V12;
		numHistBins_ = RKISP1_CIF_ISP_HIST_BIN_N_MAX_V12;
	}

	/*
	 * Define the measurement window for AGC as a centered rectangle
	 * covering 3/4 of the image width and height.
	 */
	context.configuration.agc.measureWindow.h_offs = configInfo.outputSize.width / 8;
	context.configuration.agc.measureWindow.v_offs = configInfo.outputSize.height / 8;
	context.configuration.agc.measureWindow.h_size = 3 * configInfo.outputSize.width / 4;
	context.configuration.agc.measureWindow.v_size = 3 * configInfo.outputSize.height / 4;

	/* \todo Use actual frame index by populating it in the frameContext. */
	frameCount_ = 0;
	return 0;
}

/**
 * \brief Apply a filter on the exposure value to limit the speed of changes
 * \param[in] exposureValue The target exposure from the AGC algorithm
 *
 * The speed of the filter is adaptive, and will produce the target quicker
 * during startup, or when the target exposure is within 20% of the most recent
 * filter output.
 *
 * \return The filtered exposure
 */
utils::Duration Agc::filterExposure(utils::Duration exposureValue)
{
	double speed = 0.2;

	/* Adapt instantly if we are in startup phase. */
	if (frameCount_ < kNumStartupFrames)
		speed = 1.0;

	/*
	 * If we are close to the desired result, go faster to avoid making
	 * multiple micro-adjustments.
	 * \todo Make this customisable?
	 */
	if (filteredExposure_ < 1.2 * exposureValue &&
	    filteredExposure_ > 0.8 * exposureValue)
		speed = sqrt(speed);

	filteredExposure_ = speed * exposureValue +
			    filteredExposure_ * (1.0 - speed);

	LOG(RkISP1Agc, Debug) << "After filtering, exposure " << filteredExposure_;

	return filteredExposure_;
}

/**
 * \brief Estimate the new exposure and gain values
 * \param[inout] frameContext The shared IPA frame Context
 * \param[in] yGain The gain calculated on the current brightness level
 * \param[in] iqMeanGain The gain calculated based on the relative luminance target
 */
void Agc::computeExposure(IPAContext &context, double yGain, double iqMeanGain)
{
	IPASessionConfiguration &configuration = context.configuration;
	IPAFrameContext &frameContext = context.frameContext;

	/* Get the effective exposure and gain applied on the sensor. */
	uint32_t exposure = frameContext.sensor.exposure;
	double analogueGain = frameContext.sensor.gain;

	/* Use the highest of the two gain estimates. */
	double evGain = std::max(yGain, iqMeanGain);

	utils::Duration minShutterSpeed = configuration.agc.minShutterSpeed;
	utils::Duration maxShutterSpeed = std::min(configuration.agc.maxShutterSpeed,
						   kMaxShutterSpeed);

	double minAnalogueGain = std::max(configuration.agc.minAnalogueGain,
					  kMinAnalogueGain);
	double maxAnalogueGain = std::min(configuration.agc.maxAnalogueGain,
					  kMaxAnalogueGain);

	/* Consider within 1% of the target as correctly exposed. */
	if (utils::abs_diff(evGain, 1.0) < 0.01)
		return;

	/* extracted from Rpi::Agc::computeTargetExposure. */

	/* Calculate the shutter time in seconds. */
	utils::Duration currentShutter = exposure * configuration.sensor.lineDuration;

	/*
	 * Update the exposure value for the next computation using the values
	 * of exposure and gain really used by the sensor.
	 */
	utils::Duration effectiveExposureValue = currentShutter * analogueGain;

	LOG(RkISP1Agc, Debug) << "Actual total exposure " << currentShutter * analogueGain
			      << " Shutter speed " << currentShutter
			      << " Gain " << analogueGain