/*
 * Copyright (C) 2012-2024 Robin Haberkorn
 *
 * 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 <http://www.gnu.org/licenses/>.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>

#include <glib.h>
#include <glib/gstdio.h>

#include "sciteco.h"
#include "cmdline.h"
#include "undo.h"

//#define DEBUG

TECO_DEFINE_UNDO_SCALAR(gchar);
TECO_DEFINE_UNDO_SCALAR(gint);
TECO_DEFINE_UNDO_SCALAR(guint);
TECO_DEFINE_UNDO_SCALAR(gsize);
TECO_DEFINE_UNDO_SCALAR(teco_int_t);
TECO_DEFINE_UNDO_SCALAR(gboolean);
TECO_DEFINE_UNDO_SCALAR(gconstpointer);

/**
 * An undo token.
 *
 * Undo tokens are generated to revert any
 * changes to the editor state, ie. they
 * define an action to take upon rubout.
 *
 * Undo tokens are organized into an undo stack.
 */
typedef struct teco_undo_token_t {
	struct teco_undo_token_t *next;
	teco_undo_action_t action_cb;
	guint8 user_data[];
} teco_undo_token_t;

/**
 * Stack of teco_undo_token_t lists.
 *
 * Each stack element represents
 * a command line character (the undo tokens
 * generated by that character), so it's OK
 * to use a data structure that may need
 * reallocation but is space efficient.
 * This data structure allows us to omit the
 * command line program counter from teco_undo_token_t
 * but wastes a few bytes for input characters
 * that produce no undo tokens (e.g. NOPs like space).
 */
static GPtrArray *teco_undo_heads;

gboolean teco_undo_enabled = FALSE;

static void __attribute__((constructor))
teco_undo_init(void)
{
	teco_undo_heads = g_ptr_array_new();
}

/**
 * Allocate and push undo token.
 *
 * This does nothing if undo is disabled and should
 * not be used when ownership of some data is to be
 * passed to the undo token.
 */
gpointer
teco_undo_push_size(teco_undo_action_t action_cb, gsize size)
{
	if (!teco_undo_enabled)
		return NULL;

	teco_undo_token_t *token = g_malloc(sizeof(teco_undo_token_t) + size);
	token->action_cb = action_cb;

#ifdef DEBUG
	g_printf("UNDO PUSH %p\n", token);
#endif

	/*
	 * There can very well be 0 undo tokens
	 * per input character (e.g. NOPs like space).
	 */
	while (teco_undo_heads->len <= teco_cmdline.pc)
		g_ptr_array_add(teco_undo_heads, NULL);
	g_assert(teco_undo_heads->len == teco_cmdline.pc+1);

	token->next = g_ptr_array_index(teco_undo_heads,
	                                teco_undo_heads->len-1);
	g_ptr_array_index(teco_undo_heads, teco_undo_heads->len-1) = token;

	return token->user_data;
}

void
teco_undo_pop(gint pc)
{
	while ((gint)teco_undo_heads->len > pc) {
		teco_undo_token_t *top =
			g_ptr_array_remove_index(teco_undo_heads,
			                         teco_undo_heads->len-1);

		while (top) {
			teco_undo_token_t *next = top->next;

#ifdef DEBUG
			g_printf("UNDO POP %p\n", top);
			fflush(stdout);
#endif
			top->action_cb(top->user_data, TRUE);

			g_free(top);
			top = next;
		}
	}
}

void
teco_undo_clear(void)
{
	while (teco_undo_heads->len) {
		teco_undo_token_t *top =
			g_ptr_array_remove_index(teco_undo_heads,
			                         teco_undo_heads->len-1);

		while (top) {
			teco_undo_token_t *next = top->next;
			top->action_cb(top->user_data, FALSE);
			g_free(top);
			top = next;
		}
	}
}

/*
 * NOTE: This destructor should always be run, even with NDEBUG,
 * as there are undo tokens that release more than memory (e.g. files).
 */
static void __attribute__((destructor))
teco_undo_cleanup(void)
{
	teco_undo_clear();
	g_ptr_array_free(teco_undo_heads, TRUE);
}