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

#include <lauxlib.h>

#include "melisma.h"
#include "mutil.h"

#define GAIN_TYPENAME "gain"

struct gain
{
	ml_node *node;
	float    value;
	int      mapped;
	int      db;
};

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

	float *in = args->in[0];
	float *out = args->out[0];
	float *mapped = gain->mapped ? args->in[1] :  NULL;
	float v;

	for (size_t i = 0; i < args->nframes; i++)
	{
		v = mapped ? mapped[i] : gain->value;

		if (gain->db)
		{
			v = powf(10,v/20.f);
		}

		out[i] = v*in[i];
	}
}

static int l_init(lua_State *s)
{
	int db_i = lua_upvalueindex(1);
	int db = lua_tointeger(s,db_i);
	ml_channel *audio_src, *mapped_src = NULL;
	ml_channel *audio_dst, *mapped_dst;
	float value = 0;


	if (lua_isuserdata(s,1))
	{
		mapped_src = mutil_get_channel(s,1);
	}
	else
	{
		value = luaL_checknumber(s,1);
	}

	audio_src = mutil_get_channel(s,2);

	struct gain *gain = calloc(1,sizeof(*gain));
	gain->value = value;
	gain->mapped = mapped_src != NULL;
	gain->db = db;

	ml_node *node = ml_create_node(proc,gain);
	ml_label_node(node,"gain");
	gain->node = node;

	ml_add_output(node);

	audio_dst = ml_add_input(node);
	ml_connect(audio_src,audio_dst);

	if (mapped_src)
	{
		mapped_dst = ml_add_input(node);
		ml_connect(mapped_src,mapped_dst);
	}

	*(void**) lua_newuserdata(s,sizeof(void*)) = gain;
	luaL_setmetatable(s,GAIN_TYPENAME);

	return 1;
}

static int l_out(lua_State *s)
{
	struct gain *gain = *(void**) luaL_checkudata(s,1,GAIN_TYPENAME);
	*(void**) lua_newuserdata(s,sizeof(void*)) = ml_get_output(gain->node,0);
	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
	return 1;
}

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

/*** Apply gain to signals.
	local mgain = require 'melisma.gain'

	-- Interprets `cntl` as decibels and applies it to `input`
	local input = ...
	local cntl = ...
	local gain = mgain.db(input,cntl)

@classmod gain
*/
	lua_newtable(s);
	int tbl = lua_gettop(s);

/*** Creates a linear gain unit.
@static
@function linear
@tparam channel input Input signal.
@tparam number|channel gain Constant gain or a controlling signal.
@treturn gain The newly created gain unit.
*/
	lua_pushinteger(s,0);
	lua_pushcclosure(s,l_init,1);
	lua_setfield(s,tbl,"linear");

/*** Creates a decibel gain unit.
@static
@function db
@tparam channel input Input signal.
@tparam number|channel gain Constant gain in decibels or a controlling signal.
@treturn gain The newly created gain unit.
*/
	lua_pushinteger(s,1);
	lua_pushcclosure(s,l_init,1);
	lua_setfield(s,tbl,"db");

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

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

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

	lua_settop(s,tbl);
	return 1;
}