#include "resampler.h"

#include <math.h>
#include <stdlib.h>
#include <string.h>

/* Copyright (C) 2004-2008 Shay Green.
   Copyright (C) 2015-2022 Christopher Snowhill. This module is free software; you
can redistribute it and/or modify it under the terms of the GNU Lesser
General Public License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version. This
module 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 Lesser General Public License for more
details. You should have received a copy of the GNU Lesser General Public
License along with this module; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */

#undef PI
#define PI 3.1415926535897932384626433832795029

enum { imp_scale = 0x7FFF };
typedef int16_t imp_t;
typedef int32_t imp_off_t; /* for max_res of 512 and impulse width of 32, end offsets must be 32 bits */

#if RESAMPLER_BITS == 16
typedef int32_t intermediate_t;
#elif RESAMPLER_BITS == 32
typedef int64_t intermediate_t;
#endif

static void gen_sinc(double rolloff, int width, double offset, double spacing, double scale,
                     int count, imp_t *out) {
	double const maxh = 256;
	double const step = PI / maxh * spacing;
	double const to_w = maxh * 2 / width;
	double const pow_a_n = pow(rolloff, maxh);
	double angle = (count / 2 - 1 + offset) * -step;
	scale /= maxh * 2;

	while(count--) {
		double w;
		*out++ = 0;
		w = angle * to_w;
		if(fabs(w) < PI) {
			double rolloff_cos_a = rolloff * cos(angle);
			double num = 1 - rolloff_cos_a -
			             pow_a_n * cos(maxh * angle) +
			             pow_a_n * rolloff * cos((maxh - 1) * angle);
			double den = 1 - rolloff_cos_a - rolloff_cos_a + rolloff * rolloff;
			double sinc = scale * num / den - scale;

			out[-1] = (imp_t)(cos(w) * sinc + sinc);
		}
		angle += step;
	}
}

enum { width = 64 };
enum { stereo = 2 };
enum { max_res = 512 };
enum { min_width = (width < 4 ? 4 : width) };
enum { adj_width = min_width / 4 * 4 + 2 };
enum { write_offset = adj_width * stereo };

enum { buffer_size = 128 };

typedef struct _resampler {
	int width_;
	int rate_;
	int inptr;
	int infilled;
	int outptr;
	int outfilled;

	int latency;

	imp_t const *imp;
	imp_t impulses[max_res * (adj_width + 2 * (sizeof(imp_off_t) / sizeof(imp_t)))];
	sample_t buffer_in[buffer_size * stereo * 2];
	sample_t buffer_out[buffer_size * stereo];
} resampler;

void *resampler_create() {
	resampler *r = (resampler *)malloc(sizeof(resampler));
	if(r) resampler_clear(r);
	return r;
}

void *resampler_dup(void *_r) {
	resampler *r = (resampler *)_r;
	resampler *t = (resampler *)malloc(sizeof(resampler));
	if(r && t) {
		memcpy(t, r, sizeof(resampler));
		t->imp = t->impulses + (r->imp - r->impulses);
	} else if(t) {
		resampler_clear(t);
	}
	return t;
}

void resampler_destroy(void *r) {
	free(r);
}

void resampler_clear(void *_r) {
	resampler *r = (resampler *)_r;
	r->width_ = adj_width;
	r->inptr = 0;
	r->infilled = 0;
	r->outptr = 0;
	r->outfilled = 0;
	r->latency = 0;
	r->imp = r->impulses;

	resampler_set_rate(r, 1.0);
}

void resampler_set_rate(void *_r, double new_factor) {
	resampler *rs = (resampler *)_r;

	double const rolloff = 0.999;
	double const gain = 1.0;

	int step;
	double fraction;

	double filter;
	double pos = 0.0;

	imp_t *out;

	int n;

	/* determine number of sub-phases that yield lowest error */
	double ratio_ = 0.0;
	int res = -1;
	{
		double least_error = 2;
		double pos = 0;
		int r;
		for(r = 1; r <= max_res; r++) {
			double nearest, error;
			pos += new_factor;
			nearest = floor(pos + 0.5);
			error = fabs(pos - nearest);
			if(error < least_error) {
				res = r;
				ratio_ = nearest / res;
				least_error = error;
			}
		}
	}
	rs->rate_ = ratio_;

	/* how much of input is used for each output sample */
	step = stereo * (int)floor(ratio_);
	fraction = fmod(ratio_, 1.0);

	filter = (ratio_ < 1.0) ? 1.0 : 1.0 / ratio_;
	/*int input_per_cycle = 0;*/
	out = rs->impulses;
	for(n = res; --n >= 0;) {
		int cur_step;

		gen_sinc(rolloff, (int)(rs->width_ * filter + 1) & ~1, pos, filter,
		         (double)(imp_scale * gain * filter), (int)rs->width_, out);
		out += rs->width_;

		cur_step = step;
		pos += fraction;
		if(pos >= 0.9999999) {
			pos -= 1.0;
			cur_step += stereo;
		}

		((imp_off_t *)out)[0] = (cur_step - rs->width_ * 2 + 4) * sizeof(sample_t);
		((imp_off_t *)out)[1] = 2 * sizeof(imp_t) + 2 * sizeof(imp_off_t);
		out += 2 * (sizeof(imp_off_t) / sizeof(imp_t));
		/*input_per_cycle += cur_step;*/
	}
	/* last offset moves back to beginning of impulses*/
	((imp_off_t *)out)[-1] -= (char *)out - (char *)rs->impulses;

	rs->imp = rs->impulses;
}

int resampler_get_free(void *_r) {
	resampler *r = (resampler *)_r;
	return buffer_size * stereo - r->infilled;
}

int resampler_get_min_fill(void *_r) {
	resampler *r = (resampler *)_r;
	const int min_needed = write_offset + stereo;
	const int latency = r->latency ? 0 : adj_width;
	int min_free = min_needed - r->infilled - latency;
	return min_free < 0 ? 0 : min_free;
}

void resampler_write_pair(void *_r, sample_t ls, sample_t rs) {
	resampler *r = (resampler *)_r;

	if(!r->latency) {
		int i;
		for(i = 0; i < adj_width / 2; ++i) {
			r->buffer_in[r->inptr + 0] = 0;
			r->buffer_in[r->inptr + 1] = 0;
			r->buffer_in[buffer_size * stereo + r->inptr + 0] = 0;
			r->buffer_in[buffer_size * stereo + r->inptr + 1] = 0;
			r->inptr = (r->inptr + stereo) % (buffer_size * stereo);
			r->infilled += stereo;
		}
		r->latency = 1;
	}

	if(r->infilled < buffer_size * stereo) {
		r->buffer_in[r->inptr + 0] = ls;
		r->buffer_in[r->inptr + 1] = rs;
		r->buffer_in[buffer_size * stereo + r->inptr + 0] = ls;
		r->buffer_in[buffer_size * stereo + r->inptr + 1] = rs;
		r->inptr = (r->inptr + stereo) % (buffer_size * stereo);
		r->infilled += stereo;
	}
}

#ifdef _MSC_VER
#define restrict __restrict
#endif

static const sample_t *resampler_inner_loop(resampler *r, sample_t **out_,
                                            sample_t const *out_end, sample_t const in[], int in_size) {
	in_size -= write_offset;
	if(in_size > 0) {
		sample_t *restrict out = *out_;
		sample_t const *const in_end = in + in_size;
		imp_t const *imp = r->imp;

		do {
			/* accumulate in extended precision*/
			int pt = imp[0];
			int n;
			intermediate_t l = (intermediate_t)pt * (intermediate_t)(in[0]);
			intermediate_t r = (intermediate_t)pt * (intermediate_t)(in[1]);
			if(out >= out_end)
				break;
			for(n = (adj_width - 2) / 2; n; --n) {
				pt = imp[1];
				l += (intermediate_t)pt * (intermediate_t)(in[2]);
				r += (intermediate_t)pt * (intermediate_t)(in[3]);

				/* pre-increment more efficient on some RISC processors*/
				imp += 2;
				pt = imp[0];
				r += (intermediate_t)pt * (intermediate_t)(in[5]);
				in += 4;
				l += (intermediate_t)pt * (intermediate_t)(in[0]);
			}
			pt = imp[1];
			l += (intermediate_t)pt * (intermediate_t)(in[2]);
			r += (intermediate_t)pt * (intermediate_t)(in[3]);

			/* these two "samples" after the end of the impulse give the
			 * proper offsets to the next input sample and next impulse */
			in = (sample_t const *)((char const *)in + ((imp_off_t *)(&imp[2]))[0]); /* some negative value */
			imp = (imp_t const *)((char const *)imp + ((imp_off_t *)(&imp[2]))[1]); /* small positive or large negative */

			out[0] = (sample_t)(l >> 15);
			out[1] = (sample_t)(r >> 15);
			out += 2;
		} while(in < in_end);

		r->imp = imp;
		*out_ = out;
	}
	return in;
}

#undef restrict

static int resampler_wrapper(resampler *r, sample_t out[], int *out_size,
                             sample_t const in[], int in_size) {
	sample_t *out_ = out;
	int result = resampler_inner_loop(r, &out_, out + *out_size, in, in_size) - in;

	*out_size = out_ - out;
	return result;
}

static void resampler_fill(resampler *r) {
	while(!r->outfilled && r->infilled) {
		int writepos = (r->outptr + r->outfilled) % (buffer_size * stereo);
		int writesize = (buffer_size * stereo) - writepos;
		int inread;
		if(writesize > (buffer_size * stereo - r->outfilled))
			writesize = buffer_size * stereo - r->outfilled;
		inread = resampler_wrapper(r, &r->buffer_out[writepos], &writesize, &r->buffer_in[buffer_size * stereo + r->inptr - r->infilled], r->infilled);
		r->infilled -= inread;
		r->outfilled += writesize;
		if(!inread)
			break;
	}
}

int resampler_get_avail(void *_r) {
	resampler *r = (resampler *)_r;
	if(r->outfilled < stereo && r->infilled >= r->width_)
		resampler_fill(r);
	return r->outfilled;
}

static void resampler_read_pair_internal(resampler *r, sample_t *ls, sample_t *rs, int advance) {
	if(r->outfilled < stereo)
		resampler_fill(r);
	if(r->outfilled < stereo) {
		*ls = 0;
		*rs = 0;
		return;
	}
	*ls = r->buffer_out[r->outptr + 0];
	*rs = r->buffer_out[r->outptr + 1];
	if(advance) {
		r->outptr = (r->outptr + 2) % (buffer_size * stereo);
		r->outfilled -= stereo;
	}
}

void resampler_read_pair(void *_r, sample_t *ls, sample_t *rs) {
	resampler *r = (resampler *)_r;
	resampler_read_pair_internal(r, ls, rs, 1);
}

void resampler_peek_pair(void *_r, sample_t *ls, sample_t *rs) {
	resampler *r = (resampler *)_r;
	resampler_read_pair_internal(r, ls, rs, 0);
}