/*
 * 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 <stdbool.h>
#include <lauxlib.h>
#include "melisma.h"
#include "mutil.h"

#define PAN_TYPENAME "pan"

struct pan
{
	ml_channel *l_out;
	ml_channel *r_out;
	float       val;
	bool        map;
};

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

	float val,*in,*l_out,*r_out,*map;
	in = args->in[0];
	l_out = args->out[0];
	r_out = args->out[1];
	map = pan->map ? args->in[1] : NULL;

	for (size_t i = 0; i < args->nframes; i++)
	{
		val = map ? map[i] : pan->val;
		l_out[i] = val*in[i];
		r_out[i] = (1 - val)*in[i];
	}
}

static int l_init(lua_State *s)
{
	ml_channel *dst,*src,*map_dst,*map_src = NULL;
	float val = 0;

	if (lua_isuserdata(s,1))
	{
		map_src = mutil_get_channel(s,1);
	}
	else
	{
		val = luaL_checknumber(s,1);
	}

	src = mutil_get_channel(s,2);

	struct pan *pan = calloc(1,sizeof(*pan));
	pan->val = val;
	pan->map = map_src != NULL;

	ml_node *node = ml_create_node(proc,pan);
	ml_label_node(node,"pan");

	dst = ml_add_input(node);
	pan->l_out = ml_add_output(node);
	pan->r_out = ml_add_output(node);

	ml_connect(src,dst);

	if (pan->map)
	{
		map_dst = ml_add_input(node);
		ml_connect(map_src,map_dst);
	}

	*(void**) lua_newuserdata(s,sizeof(void*)) = pan;
	luaL_setmetatable(s,PAN_TYPENAME);

	return 1;
}

static int l_left(lua_State *s)
{
	struct pan *pan = *(void**) luaL_checkudata(s,1,PAN_TYPENAME);
	*(void**) lua_newuserdata(s,sizeof(void*)) = pan->l_out;
	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
	return 1;
}

static int l_right(lua_State *s)
{
	struct pan *pan = *(void**) luaL_checkudata(s,1,PAN_TYPENAME);
	*(void**) lua_newuserdata(s,sizeof(void*)) = pan->r_out;
	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
	return 1;
}

static int l_set(lua_State *s)
{
	struct pan *pan = *(void**) luaL_checkudata(s,1,PAN_TYPENAME);
	pan->val = luaL_checknumber(s,2);
	return 0;
}

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

/*** Panning

	local mpan = require 'melisma.pan'
	local mexpression = require 'melisma.expression'
	local moscil = require 'melisma.oscil'

	local wt = moscil.wavetable.sin()
	local lfo_oscil = moscil.init(wt,1,1)
	local lfo = (1 + mexpression.input(lfo_oscil,0) / 2):build()

	local oscil = moscil.init(wt,440,0.5)
	local pan = mpan.init(lfo,oscil)

	local left = pan:left()
	local right = pan:right()

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

/*** Initialize a panning unit.

A panning value ranges from 0 to 1, where a value of 0
will pan everything to the left.

@static
@function init
@tparam number|channel x Constant pan or a controlling signal.
@tparam channel sig Input signal.
@treturn pan The newly created panning unit.
*/
	lua_pushcfunction(s,l_init);
	lua_setfield(s,tbl,"init");

/*** Get the left output signal.
@function left
@treturn channel
*/
	lua_pushcfunction(s,l_left);
	lua_setfield(s,tbl,"left");


/*** Get the right output signal.
@function right
@treturn channel
*/
	lua_pushcfunction(s,l_right);
	lua_setfield(s,tbl,"right");

/*** Set the panning value.
@function set
@tparam number x
*/
	lua_pushcfunction(s,l_set);
	lua_setfield(s,tbl,"set");

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

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

	lua_settop(s,tbl);
	return 1;
}