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

#define SPRING_TYPENAME "spring"

struct spring
{
	ml_node  *node;
	float     target;
	float     value;
	float     freq;
	float     damping;
	float     velocity;
	bool      mapped;
};

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

	float *out = args->out[0];
	float *mapped = spring->mapped ? args->in[0] : NULL;
	float dt = 1.f/ml_sample_rate();

	for (size_t i = 0; i < args->nframes; i++)
	{
		float target = mapped ? mapped[i] : spring->target;
		float w = 2*M_PI*spring->freq;
		float f = (target - spring->value)*w*w;
		float d = 2*w*spring->velocity*spring->damping;
		float a = f - d;

		spring->velocity += a*dt;
		spring->value += spring->velocity*dt;

		out[i] = spring->value;
	}
}

static int l_damping(lua_State *s)
{
	struct spring *spring = *(void**) luaL_checkudata(s,1,SPRING_TYPENAME);
	float x = luaL_checknumber(s,2);
	spring->damping = x;
	return 0;
}

static int l_freq(lua_State *s)
{
	struct spring *spring = *(void**) luaL_checkudata(s,1,SPRING_TYPENAME);
	float x = luaL_checknumber(s,2);
	spring->freq = x;
	return 0;
}

static int l_target(lua_State *s)
{
	struct spring *spring = *(void**) luaL_checkudata(s,1,SPRING_TYPENAME);
	float x = luaL_checknumber(s,2);
	spring->target = x;
	return 0;
}

static int l_map(lua_State *s)
{
	struct spring *spring = *(void**) luaL_checkudata(s,1,SPRING_TYPENAME);

	if (spring->mapped)
	{
		luaL_error(s,"already mapped");
	}

	ml_channel *src = *(void**) luaL_checkudata(s,2,MELISMA_OUTPUT_CHANNEL_TYPENAME);
	ml_channel *dst = ml_add_input(spring->node);
	ml_connect(src,dst);

	spring->mapped = true;

	return 0;
}

static int l_sample(lua_State *s)
{
	struct spring *spring = *(void**) luaL_checkudata(s,1,SPRING_TYPENAME);
	lua_pushnumber(s,spring->value);
	return 1;
}

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

static int l_init(lua_State *s)
{
	float value = luaL_checknumber(s,1);
	float freq = luaL_checknumber(s,2);
	float damping = luaL_checknumber(s,3);

	struct spring *spring = calloc(1,sizeof(*spring));
	spring->value = value;
	spring->freq = freq;
	spring->damping = damping;
	spring->mapped = false;

	spring->node = ml_create_node(proc,spring);
	ml_add_output(spring->node);

	*(void**) lua_newuserdata(s,sizeof(void*)) = spring;
	luaL_setmetatable(s,SPRING_TYPENAME);

	return 1;
}

int luaopen_melisma_spring(lua_State *s)
{
	lua_newtable(s);
	int tbl = lua_gettop(s);

	lua_pushcfunction(s,l_init);
	lua_setfield(s,tbl,"init");

	lua_pushcfunction(s,l_freq);
	lua_setfield(s,tbl,"freq");

	lua_pushcfunction(s,l_damping);
	lua_setfield(s,tbl,"damping");

	lua_pushcfunction(s,l_target);
	lua_setfield(s,tbl,"target");

	lua_pushcfunction(s,l_sample);
	lua_setfield(s,tbl,"sample");

	lua_pushcfunction(s,l_map);
	lua_setfield(s,tbl,"map");

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

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

	lua_pushcfunction(s,l_call);
	lua_setfield(s,mt,"__call");

	lua_settop(s,tbl);
	return 1;
}