/*
 * melisma - extensible and scriptable audio engine
 * Copyright (C) 2026  Ludvig Gunne Lindström
 *
 * This program 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, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <stdlib.h>
#include <lauxlib.h>
#include "melisma.h"
#include "mutil.h"

#define DELAY_TYPENAME "delay"

#define MAX_DELAY         2.00f
#define DEFAULT_DELAY     0.25f
#define DEFAULT_GAIN      1.00f
#define DEFAULT_FEEDBACK  0.25f
#define DEFAULT_WETDRYMIX 0.50f

#define CLAMP(v,min,max) ((v)<(min)?(min):((v)>(max)?(max):(v)))

struct delay
{
	ml_channel *out;
	float       feedback;
	float       gain;
	float       wetdrymix;
	float       delay;
	size_t      len;
	size_t      write;
	float      *buffer;
};

static void proc(const ml_proc_args *args)
{
	struct delay *dl = args->userp;

	size_t sr = ml_sample_rate();
	size_t offset = sr*dl->delay;

	const float *in = args->in[0];
	float *out = args->out[0];

	size_t read;
	float dry,wet;

	for (size_t i = 0; i < args->nframes; i++)
	{
		read = dl->write + dl->len - offset;

		if (read >= dl->len)
		{
			read -= dl->len;
		}

		dry = in[i];
		wet = dl->buffer[read]*dl->gain;

		out[i] = wet*dl->wetdrymix + dry*(1 - dl->wetdrymix);
		dl->buffer[dl->write++] = dry + wet*dl->feedback;

		if (dl->write == dl->len)
		{
			dl->write = 0;
		}
	}
}

static void clamp(struct delay *dl)
{
	dl->delay = CLAMP(dl->delay,0,MAX_DELAY);
	dl->gain = CLAMP(dl->gain,0,1);
	dl->feedback = CLAMP(dl->feedback,0,1);
	dl->wetdrymix = CLAMP(dl->wetdrymix,0,1);
}

static int l_init(lua_State *s)
{
	ml_channel *src = mutil_get_channel(s,1);

	struct delay *dl = calloc(1,sizeof(*dl));

	dl->delay = DEFAULT_DELAY;
	dl->gain = DEFAULT_GAIN;
	dl->feedback = DEFAULT_FEEDBACK;
	dl->wetdrymix = DEFAULT_WETDRYMIX;

	size_t sr = ml_sample_rate();
	dl->len = sr*MAX_DELAY;
	dl->buffer = calloc(1,dl->len*sizeof(dl->buffer[0]));

	clamp(dl);

	ml_node *node = ml_create_node(proc,dl);
	ml_label_node(node,"delay");
	ml_channel *dst = ml_add_input(node);
	ml_connect(src,dst);

	dl->out = ml_add_output(node);

	*(void**) lua_newuserdata(s,sizeof(void*)) = dl;
	luaL_setmetatable(s,DELAY_TYPENAME);

	return 1;
}

static int l_out(lua_State *s)
{
	struct delay *dl = *(void**) luaL_checkudata(s,1,DELAY_TYPENAME);
	*(void**) lua_newuserdata(s,sizeof(void*)) = dl->out;
	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
	return 1;
}

static int l_delay(lua_State *s)
{
	struct delay *dl = *(void**) luaL_checkudata(s,1,DELAY_TYPENAME);
	float v = luaL_checknumber(s,2);
	dl->delay = v;
	clamp(dl);
	*(void**) lua_newuserdata(s,sizeof(void*)) = dl;
	luaL_setmetatable(s,DELAY_TYPENAME);
	return 1;
}

static int l_gain(lua_State *s)
{
	struct delay *dl = *(void**) luaL_checkudata(s,1,DELAY_TYPENAME);
	float v = luaL_checknumber(s,2);
	dl->gain = v;
	clamp(dl);
	*(void**) lua_newuserdata(s,sizeof(void*)) = dl;
	luaL_setmetatable(s,DELAY_TYPENAME);
	return 1;
}

static int l_feedback(lua_State *s)
{
	struct delay *dl = *(void**) luaL_checkudata(s,1,DELAY_TYPENAME);
	float v = luaL_checknumber(s,2);
	dl->feedback = v;
	clamp(dl);
	*(void**) lua_newuserdata(s,sizeof(void*)) = dl;
	luaL_setmetatable(s,DELAY_TYPENAME);
	return 1;
}

static int l_wetdrymix(lua_State *s)
{
	struct delay *dl = *(void**) luaL_checkudata(s,1,DELAY_TYPENAME);
	float v = luaL_checknumber(s,2);
	dl->wetdrymix = v;
	clamp(dl);
	*(void**) lua_newuserdata(s,sizeof(void*)) = dl;
	luaL_setmetatable(s,DELAY_TYPENAME);
	return 1;
}

int luaopen_melisma_delay(lua_State *s)
{
	ml_check_version();

/*** Digital delay line.
@classmod delay
*/
	lua_newtable(s);
	int tbl = lua_gettop(s);

/*** Create a delay line.
@static
@function init
@tparam channel input Input signal.
@treturn delay Newly created delay line.
*/
	lua_pushcfunction(s,l_init);
	lua_setfield(s,tbl,"init");

/*** Set delay.
@function delay
@tparam number d delay in seconds.
@treturn delay
*/
	lua_pushcfunction(s,l_delay);
	lua_setfield(s,tbl,"delay");

/*** Set gain.
@function gain
@tparam number g Gain (**TODO**: Use decibels).
@treturn delay
*/
	lua_pushcfunction(s,l_gain);
	lua_setfield(s,tbl,"gain");

/*** Set feedback.
@function feedback
@tparam number f Feedback.
@treturn delay
*/
	lua_pushcfunction(s,l_feedback);
	lua_setfield(s,tbl,"feedback");

/*** Set wet/dry mix.
@function wetdrymix
@tparam number wd Wet/dry mix.
@treturn delay
*/
	lua_pushcfunction(s,l_wetdrymix);
	lua_setfield(s,tbl,"wetdrymix");

	lua_pushcfunction(s,l_out);
	lua_setfield(s,tbl,MUTIL_OUTPUT_CHANNEL_FUNCTION);

	luaL_newmetatable(s,DELAY_TYPENAME);
	int mt = lua_gettop(s);

	lua_pushvalue(s,tbl);
	lua_setfield(s,mt,"__index");

	lua_settop(s,tbl);
	return 1;
}