Add support for button entities (#2824)

esphome/components/button/button.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/entity_base.h"
+#include "esphome/core/helpers.h"
+
+namespace esphome {
+namespace button {
+
+#define LOG_BUTTON(prefix, type, obj) \
+  if ((obj) != nullptr) { \
+    ESP_LOGCONFIG(TAG, "%s%s '%s'", prefix, LOG_STR_LITERAL(type), (obj)->get_name().c_str()); \
+    if (!(obj)->get_icon().empty()) { \
+      ESP_LOGCONFIG(TAG, "%s  Icon: '%s'", prefix, (obj)->get_icon().c_str()); \
+    } \
+  }
+
+/** Base class for all buttons.
+ *
+ * A button is just a momentary switch that does not have a state, only a trigger.
+ */
+class Button : public EntityBase {
+ public:
+  explicit Button();
+  explicit Button(const std::string &name);
+
+  /** Press this button. This is called by the front-end.
+   *
+   * For implementing buttons, please override press_action.
+   */
+  void press();
+
+  /** Set callback for state changes.
+   *
+   * @param callback The void() callback.
+   */
+  void add_on_press_callback(std::function<void()> &&callback);
+
+ protected:
+  /** You should implement this virtual method if you want to create your own button.
+   */
+  virtual void press_action(){};
+
+  uint32_t hash_base() override;
+
+  CallbackManager<void()> press_callback_{};
+};
+
+}  // namespace button
+}  // namespace esphome