--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libmlk-adventure/adventure/actions/spawner.c	Sun Dec 06 22:50:48 2020 +0100
@@ -0,0 +1,95 @@
+/*
+ * spawner.c -- spawn battle while moving
+ *
+ * Copyright (c) 2020 David Demelier <markand@malikania.fr>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <assert.h>
+#include <math.h>
+#include <stdlib.h>
+
+#include <core/alloc.h>
+#include <core/game.h>
+#include <core/util.h>
+
+#include <rpg/map.h>
+
+#include "spawner.h"
+
+struct self {
+	struct action action;
+	struct map *map;
+	int last_x;
+	int last_y;
+	unsigned int steps;
+};
+
+static inline unsigned int
+distance(const struct self *self)
+{
+	unsigned int gap_x = fmax(self->last_x, self->map->player_x) -
+	                     fmin(self->last_x, self->map->player_x);
+	unsigned int gap_y = fmax(self->last_y, self->map->player_y) -
+			     fmin(self->last_y, self->map->player_y);
+
+	return fmin(self->steps, gap_x + gap_y);
+}
+
+static bool
+update(struct action *act, unsigned int ticks)
+{
+	(void)ticks;
+
+	struct self *self = act->data;
+
+	if (self->map->player_movement) {
+		self->steps -= distance(self);
+		self->last_x = self->map->player_x;
+		self->last_y = self->map->player_y;
+
+		if (self->steps == 0) {
+			/* TODO: start battle here. */
+			return false;
+		}
+	}
+
+	return false;
+}
+
+static void
+finish(struct action *act)
+{
+	free(act->data);
+}
+
+struct action *
+spawner_new(struct map *map, unsigned int low, unsigned int high)
+{
+	assert(map);
+
+	struct self *self;
+
+	self = alloc_new0(sizeof (*self));
+	self->map = map;
+	self->last_x = map->player_x;
+	self->last_y = map->player_y;
+	self->steps = nrand(low, high);
+
+	self->action.data = self;
+	self->action.update = update;
+	self->action.finish = finish;
+
+	return &self->action;
+}