Refactor power saving logic into display drivers and add ST7789 support

display/low_level_display_st7789.cpp

@@ -69,11 +69,51 @@ void LowLevelDisplayST7789::refresh() {
 }
 
 void LowLevelDisplayST7789::set_backlight(bool on) {
-    // TODO: Implement
-    (void)on;
+    set_brightness(on ? 100 : 0);
+}
+
+void LowLevelDisplayST7789::set_brightness(uint8_t brightness) {
+    st7789_set_brightness(brightness);
+}
+
+uint8_t LowLevelDisplayST7789::get_brightness() const {
+    return st7789_get_brightness();
 }
 
 void LowLevelDisplayST7789::set_rotation(uint8_t rotation) {
     // TODO: Implement
     (void)rotation;
 }
+
+void LowLevelDisplayST7789::on_idle_2min() {
+    if (!is_dimmed && !is_sleeping) {
+        saved_brightness = get_brightness();
+        set_brightness(5); // Dim to 5%
+        is_dimmed = true;
+        printf("ST7789: Dimmed to 5%%\n");
+    }
+}
+
+void LowLevelDisplayST7789::on_idle_10min() {
+    if (!is_sleeping) {
+        st7789_sleep();
+        is_sleeping = true;
+        is_dimmed = true; // Sleep implies dimmed
+        printf("ST7789: Entered sleep mode\n");
+    }
+}
+
+void LowLevelDisplayST7789::on_user_interaction() {
+    if (is_sleeping) {
+        st7789_wake();
+        // Restore brightness if we have a saved value, or default to 100
+        set_brightness(saved_brightness > 0 ? saved_brightness : 100);
+        is_sleeping = false;
+        is_dimmed = false;
+        printf("ST7789: Woke from sleep\n");
+    } else if (is_dimmed) {
+        set_brightness(saved_brightness > 0 ? saved_brightness : 100);
+        is_dimmed = false;
+        printf("ST7789: Restored brightness\n");
+    }
+}