/*
 * 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 LOOKBACK_TYPENAME "lookback"

struct lookback
{
	ml_node *node;
	size_t   cursor;
	size_t   len;
	float    buf[];
};

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

	for (size_t i = 0; i < args->nframes; i++)
	{
		args->out[0][i] = lb->buf[lb->cursor];
		lb->buf[lb->cursor] = args->in[0][i];

		lb->cursor++;

		if (lb->cursor == lb->len)
		{
			lb->cursor = 0;
		}
	}
}

static int l_init(lua_State *s)
{
	float t = luaL_checknumber(s,1);
	ml_channel *src = mutil_get_channel(s,2);

	unsigned long sr = ml_sample_rate();
	unsigned long len = sr*t;

	struct lookback *lb = calloc(1,sizeof(*lb) + len*sizeof(lb->buf[0]));
	lb->len = len;

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

	ml_channel *dst = ml_add_input(node);
	ml_connect(src,dst);
	ml_add_output(node);

	*(void**) lua_newuserdata(s,sizeof(void*)) = lb;
	luaL_setmetatable(s,LOOKBACK_TYPENAME);

	return 1;
}

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

int luaopen_melisma_lookback(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_out);
	lua_setfield(s,tbl,MUTIL_OUTPUT_CHANNEL_FUNCTION);

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

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

	lua_settop(s,tbl);
	return 1;
}