Re-implement scheduler system (check #1321)

src/main/java/emu/grasscutter/server/scheduler/ServerTask.java

@@ -0,0 +1,67 @@
+package emu.grasscutter.server.scheduler;
+
+import emu.grasscutter.Grasscutter;
+import lombok.*;
+
+/**
+ * This class works the same as a runnable, except with more information.
+ */
+public final class ServerTask implements Runnable {
+    /* The runnable to run. */
+    private final Runnable runnable;
+    /* This ID is assigned by the scheduler. */
+    @Getter private final int taskId;
+    /* The period at which the task should be run. */
+    /* The delay between the first execute. */
+    private final int period, delay;
+
+    public ServerTask(Runnable runnable, int taskId, int period, int delay) {
+        this.runnable = runnable;
+        this.taskId = taskId;
+        this.period = period;
+        this.delay = delay;
+    }
+
+    /* The amount of times the task has been run. */
+    @Getter private int ticks = 0;
+    /* Should the check consider delay? */
+    private boolean considerDelay = true;
+
+    /**
+     * Cancels the task from running the next time.
+     */
+    public void cancel() {
+        Grasscutter.getGameServer().getScheduler().cancelTask(this.taskId);
+    }
+
+    /**
+     * Checks if the task should run at the current tick.
+     * @return True if the task should run, false otherwise.
+     */
+    public boolean shouldRun() {
+        if(this.delay != -1 && this.considerDelay) {
+            this.considerDelay = false;
+            return this.ticks == this.delay;
+        } else if(this.period != -1)
+            return this.ticks % this.period == 0;
+        else return true;
+    }
+
+    /**
+     * Checks if the task should be canceled.
+     * @return True if the task should be canceled, false otherwise.
+     */
+    public boolean shouldCancel() {
+        return this.period == -1;
+    }
+
+    /**
+     * Runs the task.
+     */
+    @Override public void run() {
+        // Run the runnable.
+        this.runnable.run();
+        // Increase tick count.
+        this.ticks++;
+    }
+}