/*
 * Brickworks
 *
 * Copyright (C) 2022-2024 Orastron Srl unipersonale
 *
 * Brickworks is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3 of the License.
 *
 * Brickworks is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Brickworks.  If not, see <http://www.gnu.org/licenses/>.
 *
 * File author: Stefano D'Angelo
 */

/*!
 *  module_type {{{ dsp }}}
 *  version {{{ 1.1.1 }}}
 *  requires {{{ bw_common }}}
 *  description {{{
 *    Post-filter to decolorate oscillator waveshapers when antialiasing is on.
 *
 *    This <a href="https://en.wikipedia.org/wiki/Linear_time-invariant_system"
 *    target="_blank">linear time-invariant filter</a> can be added in series of
 *    oscillator waveshapers that use PolyBLEP antialiasing
 *    (i.e., [bw_osc_saw](bw_osc_saw), [bw_osc_pulse](bw_osc_pulse),
 *    [bw_osc_tri](bw_osc_tri)) to compensate for high-frequency attenuation.
 *  }}}
 *  changelog {{{
 *    <ul>
 *      <li>Version <strong>1.1.1</strong>:
 *        <ul>
 *          <li>Added debugging check in
 *              <code>bw_osc_filt_process_multi()</code> to ensure that buffers
 *              used for both input and output appear at the same channel
 *              indices.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>1.1.0</strong>:
 *        <ul>
 *          <li>Now using <code>BW_NULL</code> and
 *              <code>BW_CXX_NO_ARRAY</code>.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>1.0.0</strong>:
 *        <ul>
 *          <li>Added initial input value to
 *              <code>bw_osc_filt_reset_state()</code>.</li>
 *          <li>Added <code>bw_osc_filt_reset_state_multi()</code> and updated C++
 *              API in this regard.</li>
 *          <li>Now <code>bw_osc_filt_reset_state()</code> returns the initial
 *              output value.</li>
 *          <li>Added overloaded C++ <code>reset()</code> functions taking
 *              arrays as arguments.</li>
 *          <li><code>bw_osc_filt_process()</code> and
 *              <code>bw_osc_filt_process_multi()</code> now use
 *              <code>size_t</code> to count samples and channels.</li>
 *          <li>Added more <code>const</code> and <code>BW_RESTRICT</code>
 *              specifiers to input arguments and implementation.</li>
 *          <li>Moved C++ code to C header.</li>
 *          <li>Added overloaded C++ <code>process()</code> function taking
 *              C-style arrays as arguments.</li>
 *          <li>Changed implementation topology to use less memory.</li>
 *          <li>Removed usage of reserved identifiers.</li>
 *          <li>Added debugging code.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>0.6.0</strong>:
 *        <ul>
 *          <li>Removed dependency on bw_config.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>0.5.0</strong>:
 *        <ul>
 *          <li>Added <code>bw_osc_filt_process_multi()</code>.</li>
 *          <li>Added C++ wrapper.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>0.2.0</strong>:
 *        <ul>
 *          <li>Refactored API.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>0.1.0</strong>:
 *        <ul>
 *          <li>First release.</li>
 *        </ul>
 *      </li>
 *    </ul>
 *  }}}
 */

#ifndef BW_OSC_FILT_H
#define BW_OSC_FILT_H

#include <bw_common.h>

#ifdef __cplusplus
extern "C" {
#endif

/*! api {{{
 *    #### bw_osc_filt_state
 *  ```>>> */
typedef struct bw_osc_filt_state bw_osc_filt_state;
/*! <<<```
 *    Internal state and related.
 *
 *    #### bw_osc_filt_reset()
 *  ```>>> */
static inline float bw_osc_filt_reset_state(
	bw_osc_filt_state * BW_RESTRICT state,
	float                           x_0);
/*! <<<```
 *    Resets the given `state` to its initial values using the given initial
 *    input value `x_0`.
 *
 *    Returns the corresponding initial output value.
 *
 *    #### bw_osc_filt_reset_state_multi()
 *  ```>>> */
static inline void bw_osc_filt_reset_state_multi(
	bw_osc_filt_state * BW_RESTRICT const * BW_RESTRICT state,
	const float *                                       x_0,
	float *                                             y_0,
	size_t                                              n_channels);
/*! <<<```
 *    Resets each of the `n_channels` `state`s to its initial values using the
 *    corresponding initial input value in the `x_0` array.
 *
 *    The corresponding initial output values are written into the `y_0` array,
 *    if not `BW_NULL`.
 *
 *    #### bw_osc_filt_process1()
 *  ```>>> */
static inline float bw_osc_filt_process1(
	bw_osc_filt_state * BW_RESTRICT state,
	float                           x);
/*! <<<```
 *    Processes one input sample `x` using and updating `state`. Returns the
 *    corresponding output sample.
 *
 *    #### bw_osc_filt_process()
 *  ```>>> */
static inline void bw_osc_filt_process(
	bw_osc_filt_state * BW_RESTRICT state,
	const float *                   x,
	float *                         y,
	size_t                          n_samples);
/*! <<<```
 *    Processes the first `n_samples` of the input buffer `x` and fills the
 *    first `n_samples` of the output buffer `y`, while using and updating
 *    `state`.
 *
 *    #### bw_osc_filt_process_multi()
 *  ```>>> */
static inline void bw_osc_filt_process_multi(
	bw_osc_filt_state * BW_RESTRICT const * BW_RESTRICT state,
	const float * const *                               x,
	float * const *                                     y,
	size_t                                              n_channels,
	size_t                                              n_samples);
/*! <<<```
 *    Processes the first `n_samples` of the `n_channels` input buffers `x` and
 *    fills the first `n_samples` of the `n_channels` output buffers `y`, while
 *    using and updating each of the `n_channels` `state`s.
 *
 *    #### bw_osc_filt_state_is_valid()
 *  ```>>> */
static inline char bw_osc_filt_state_is_valid(
	const bw_osc_filt_state * BW_RESTRICT state);
/*! <<<```
 *    Tries to determine whether `state` is valid and returns non-`0` if it
 *    seems to be the case and `0` if it is certainly not. False positives are
 *    possible, false negatives are not.
 *
 *    `state` must at least point to a readable memory block of size greater
 *    than or equal to that of `bw_osc_filt_state`.
 *  }}} */

#ifdef __cplusplus
}
#endif

/*** Implementation ***/

/* WARNING: This part of the file is not part of the public API. Its content may
 * change at any time in future versions. Please, do not use it directly. */

#ifdef __cplusplus
extern "C" {
#endif

struct bw_osc_filt_state {
#ifdef BW_DEBUG_DEEP
	uint32_t	hash;
#endif

	// States
	float		z1;
};

static inline float bw_osc_filt_reset_state(
		bw_osc_filt_state * BW_RESTRICT state,
		float                           x_0) {
	BW_ASSERT(state != BW_NULL);
	BW_ASSERT(bw_is_finite(x_0));

	state->z1 = 0.f;
	const float y = x_0;

#ifdef BW_DEBUG_DEEP
	state->hash = bw_hash_sdbm("bw_osc_filt_state");
#endif
	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
	BW_ASSERT(bw_is_finite(y));

	return y;
}

static inline void bw_osc_filt_reset_state_multi(
		bw_osc_filt_state * BW_RESTRICT const * BW_RESTRICT state,
		const float *                                       x_0,
		float *                                             y_0,
		size_t                                              n_channels) {
	BW_ASSERT(state != BW_NULL);
#ifndef BW_NO_DEBUG
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = i + 1; j < n_channels; j++)
			BW_ASSERT(state[i] != state[j]);
#endif
	BW_ASSERT(x_0 != BW_NULL);

	if (y_0 != BW_NULL)
		for (size_t i = 0; i < n_channels; i++)
			y_0[i] = bw_osc_filt_reset_state(state[i], x_0[i]);
	else
		for (size_t i = 0; i < n_channels; i++)
			bw_osc_filt_reset_state(state[i], x_0[i]);

	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
}

static inline float bw_osc_filt_process1(
		bw_osc_filt_state * BW_RESTRICT state,
		float                           x) {
	BW_ASSERT(state != BW_NULL);
	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
	BW_ASSERT(bw_is_finite(x));

	const float y = 1.371308261611209f * x + state->z1;
	state->z1 = 0.08785458027104826f * x - 4.591628418822578e-1f * y;

	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
	BW_ASSERT(bw_is_finite(y));

	return y;
}

static inline void bw_osc_filt_process(
		bw_osc_filt_state * BW_RESTRICT state,
		const float *                   x,
		float *                         y,
		size_t                          n_samples) {
	BW_ASSERT(state != BW_NULL);
	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
	BW_ASSERT(x != BW_NULL);
	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
	BW_ASSERT(y != BW_NULL);

	for (size_t i = 0; i < n_samples; i++)
		y[i] = bw_osc_filt_process1(state, x[i]);

	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
}

static inline void bw_osc_filt_process_multi(
		bw_osc_filt_state * BW_RESTRICT const * BW_RESTRICT state,
		const float * const *                               x,
		float * const *                                     y,
		size_t                                              n_channels,
		size_t                                              n_samples) {
	BW_ASSERT(state != BW_NULL);
#ifndef BW_NO_DEBUG
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = i + 1; j < n_channels; j++)
			BW_ASSERT(state[i] != state[j]);
#endif
	BW_ASSERT(x != BW_NULL);
	BW_ASSERT(y != BW_NULL);
#ifndef BW_NO_DEBUG
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = i + 1; j < n_channels; j++)
			BW_ASSERT(y[i] != y[j]);
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = 0; j < n_channels; j++)
			BW_ASSERT(i == j || x[i] != y[j]);
#endif

	for (size_t i = 0; i < n_channels; i++)
		bw_osc_filt_process(state[i], x[i], y[i], n_samples);
}

static inline char bw_osc_filt_state_is_valid(
	const bw_osc_filt_state * BW_RESTRICT state) {
	BW_ASSERT(state != BW_NULL);

#ifdef BW_DEBUG_DEEP
	if (state->hash != bw_hash_sdbm("bw_osc_filt_state"))
		return 0;
#endif

	return bw_is_finite(state->z1);
}

#ifdef __cplusplus
}

#ifndef BW_CXX_NO_ARRAY
# include <array>
#endif

namespace Brickworks {

/*** Public C++ API ***/

/*! api_cpp {{{
 *    ##### Brickworks::OscFilt
 *  ```>>> */
template<size_t N_CHANNELS>
class OscFilt {
public:
	OscFilt();
	
	void reset(
		float               x0 = 0.f,
		float * BW_RESTRICT y0 = nullptr);

#ifndef BW_CXX_NO_ARRAY
	void reset(
		float                                       x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0);
#endif

	void reset(
		const float * x0,
		float *       y0 = nullptr);

#ifndef BW_CXX_NO_ARRAY
	void reset(
		std::array<float, N_CHANNELS>               x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr);
#endif

	void process(
		const float * const * x,
		float * const *       y,
		size_t                nSamples);

#ifndef BW_CXX_NO_ARRAY
	void process(
		std::array<const float *, N_CHANNELS> x,
		std::array<float *, N_CHANNELS>       y,
		size_t                                nSamples);
#endif
/*! <<<...
 *  }
 *  ```
 *  }}} */

/*** Implementation ***/

/* WARNING: This part of the file is not part of the public API. Its content may
 * change at any time in future versions. Please, do not use it directly. */

private:
	bw_osc_filt_state		states[N_CHANNELS];
	bw_osc_filt_state * BW_RESTRICT	statesP[N_CHANNELS];
};

template<size_t N_CHANNELS>
inline OscFilt<N_CHANNELS>::OscFilt() {
	for (size_t i = 0; i < N_CHANNELS; i++)
		statesP[i] = states + i;
}

template<size_t N_CHANNELS>
inline void OscFilt<N_CHANNELS>::reset(
		float               x0,
		float * BW_RESTRICT y0) {
	if (y0 != nullptr)
		for (size_t i = 0; i < N_CHANNELS; i++)
			y0[i] = bw_osc_filt_reset_state(states + i, x0);
	else
		for (size_t i = 0; i < N_CHANNELS; i++)
			bw_osc_filt_reset_state(states + i, x0);
}

#ifndef BW_CXX_NO_ARRAY
template<size_t N_CHANNELS>
inline void OscFilt<N_CHANNELS>::reset(
		float                                       x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
	reset(x0, y0 != nullptr ? y0->data() : nullptr);
}
#endif

template<size_t N_CHANNELS>
inline void OscFilt<N_CHANNELS>::reset(
		const float * x0,
		float *       y0) {
	bw_osc_filt_reset_state_multi(statesP, x0, y0, N_CHANNELS);
}

#ifndef BW_CXX_NO_ARRAY
template<size_t N_CHANNELS>
inline void OscFilt<N_CHANNELS>::reset(
		std::array<float, N_CHANNELS>               x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
	reset(x0.data(), y0 != nullptr ? y0->data() : nullptr);
}
#endif

template<size_t N_CHANNELS>
inline void OscFilt<N_CHANNELS>::process(
		const float * const * x,
		float * const *       y,
		size_t                nSamples) {
	bw_osc_filt_process_multi(statesP, x, y, N_CHANNELS, nSamples);
}

#ifndef BW_CXX_NO_ARRAY
template<size_t N_CHANNELS>
inline void OscFilt<N_CHANNELS>::process(
		std::array<const float *, N_CHANNELS> x,
		std::array<float *, N_CHANNELS>       y,
		size_t                                nSamples) {
	process(x.data(), y.data(), nSamples);
}
#endif

}
#endif

#endif