/*
 * alaw.h
 * Copyright (c) 2025 Christopher Herb
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#pragma once

#include <cmath>
#include <cstdint>

#include "lut.h"

namespace trnr {

constexpr float A_LAW_A = 87.6f;
constexpr float A_LAW_LN_A = 4.474f;

constexpr int32_t A_LAW_A_Q15 = static_cast<int32_t>(A_LAW_A * (1 << 15));
constexpr int32_t A_LAW_LN_A_Q15 = static_cast<int32_t>(A_LAW_LN_A * (1 << 15));
constexpr int32_t ONE_LN_A_Q15 = (1 << 15) + A_LAW_LN_A_Q15;

// Threshold in Q15: 1/A ≈ 0.0114 → 373 in Q15
constexpr int32_t ENCODE_THRESHOLD_Q15 = static_cast<int32_t>((1.0f / A_LAW_A) * (1 << 15));
// Threshold in Q15: 1/(1+ln(A)) ≈ 0.183 → 5996 in Q15
constexpr int32_t DECODE_THRESHOLD_Q15 = static_cast<int32_t>((1.0f / (1.0f + A_LAW_LN_A)) * (1 << 15));

inline float alaw_encode(float input)
{
	float sign = (input >= 0.0f) ? 1.0f : -1.0f;
	float abs_sample = std::fabs(input);

	float output;
	if (abs_sample < (1.0f / A_LAW_A)) {
		output = sign * (A_LAW_A * abs_sample) / (1.0f + std::log(A_LAW_A));
	} else {
		output =
			sign * (1.0f + std::log(A_LAW_A * abs_sample)) / (1.0f + std::log(A_LAW_A));
	}

	return output;
}

inline float alaw_decode(float input)
{
	float sign = (input >= 0.0f) ? 1.0f : -1.0f;
	float abs_comp = std::fabs(input);

	float sample;
	if (abs_comp < (1.0f / (1.0f + std::log(A_LAW_A)))) {
		sample = sign * (abs_comp * (1.0f + std::log(A_LAW_A))) / A_LAW_A;
	} else {
		sample = sign * std::exp(abs_comp * (1.0f + std::log(A_LAW_A)) - 1.0f) / A_LAW_A;
	}

	return sample;
}

inline int16_t alaw_encode_fixed(int16_t input)
{
	int32_t sign = (input >= 0) ? 1 : -1;
	int32_t abs_sample = std::abs(input);
	int32_t output;

	if (abs_sample < ENCODE_THRESHOLD_Q15) {
		// Linear region: y = A*x / (1 + ln(A))
		// A_Q15 * x_Q15 / ONE_LN_A_Q15 where ONE_LN_A_Q15 is already scaled by 32768
		output = (int32_t)(((int64_t)A_LAW_A_Q15 * abs_sample) / ONE_LN_A_Q15);
	} else {
		// Logarithmic region: y = (1 + ln(A*x)) / (1 + ln(A))
		// Scale Q15 sample to log table input range [4, 4096]
		int32_t log_input = std::max(4, abs_sample >> 3);
		int32_t log_x_q15 = fixed_log(log_input);
		
		// ln(A*x) = ln(A) + ln(x) in Q15
		int32_t log_ax_q15 = A_LAW_LN_A_Q15 + log_x_q15;
		
		// y = (1 + ln(A*x)) / (1 + ln(A))
		// numerator in Q15, denominator is ONE_LN_A_Q15 (which is (1+ln(A))*32768)
		int64_t numerator = ((int64_t)1 << 15) + log_ax_q15;
		output = (int32_t)((numerator << 15) / ONE_LN_A_Q15);
	}

	output *= sign;
	
	// Clamp to int16 range
	if (output > 32767) output = 32767;
	if (output < -32768) output = -32768;
	return static_cast<int16_t>(output);
}

inline int16_t alaw_decode_fixed(int16_t input)
{
	int32_t sign = (input >= 0) ? 1 : -1;
	int32_t abs_comp = std::abs(input);
	int32_t sample;

	if (abs_comp < DECODE_THRESHOLD_Q15) {
		// Linear region: x = y * (1 + ln(A)) / A
		sample = (int32_t)(((int64_t)abs_comp * ONE_LN_A_Q15) / A_LAW_A_Q15);
	} else {
		// Logarithmic region: x = exp(y * (1 + ln(A)) - 1) / A
		// exp_arg_q12 = ((y_q15 * ONE_LN_A_Q15 * 8192) / (32768*32768*9)) - 910
		// Computing in 64-bit to avoid overflow
		int64_t temp = (((int64_t)abs_comp * ONE_LN_A_Q15) * 8192LL) / (32768LL * 32768LL * 9LL) - 910;
		int32_t exp_arg_q12 = (int32_t)temp;
		
		// Clamp to valid range
		if (exp_arg_q12 < 0) exp_arg_q12 = 0;
		if (exp_arg_q12 > 4096) exp_arg_q12 = 4096;
		
		int32_t exp_val_q15 = fixed_exp(exp_arg_q12);
		sample = (int32_t)(((int64_t)exp_val_q15 << 15) / A_LAW_A_Q15);
	}

	sample *= sign;
	if (sample > 32767) sample = 32767;
	if (sample < -32768) sample = -32768;
	return static_cast<int16_t>(sample);
}

} // namespace trnr