Ensure new custom sleep image every time

When picking a random sleep image from a set of custom images, compare
the randomly chosen index against a cached value in settings. If the
value matches, use the next image (rolling over if it's the last image).
Cache the chosen image index to settings in either case.

src/CrossPointSettings.cpp

@@ -14,7 +14,7 @@ CrossPointSettings CrossPointSettings::instance;
 namespace {
 constexpr uint8_t SETTINGS_FILE_VERSION = 1;
 // Increment this when adding new persisted settings fields
-constexpr uint8_t SETTINGS_COUNT = 17;
+constexpr uint8_t SETTINGS_COUNT = 18;
 constexpr char SETTINGS_FILE[] = "/.crosspoint/settings.bin";
 }  // namespace
 
@@ -46,6 +46,7 @@ bool CrossPointSettings::saveToFile() const {
   serialization::writePod(outputFile, sleepScreenCoverMode);
   serialization::writeString(outputFile, std::string(opdsServerUrl));
   serialization::writePod(outputFile, textAntiAliasing);
+  serialization::writePod(outputFile, lastUsedSleep);
   outputFile.close();
 
   Serial.printf("[%lu] [CPS] Settings saved to file\n", millis());
@@ -110,6 +111,8 @@ bool CrossPointSettings::loadFromFile() {
     }
     serialization::readPod(inputFile, textAntiAliasing);
     if (++settingsRead >= fileSettingsCount) break;
+    serialization::readPod(inputFile, lastUsedSleep);
+    if (++settingsRead >= fileSettingsCount) break;
   } while (false);
 
   inputFile.close();

src/CrossPointSettings.h

@@ -82,6 +82,8 @@ class CrossPointSettings {
   uint8_t screenMargin = 5;
   // OPDS browser settings
   char opdsServerUrl[128] = "";
+  // Last used sleep screen index (for custom screens)
+  uint8_t lastUsedSleep = 0;
 
   ~CrossPointSettings() = default;
 

src/activities/boot_sleep/SleepActivity.cpp

@@ -81,7 +81,11 @@ void SleepActivity::renderCustomSleepScreen() const {
     if (numFiles > 0) {
       // Generate a random number between 1 and numFiles
       const auto randomFileIndex = random(numFiles);
-      const auto filename = "/sleep/" + files[randomFileIndex];
+      // If we re-generated the same index as the last sleep screen, use the next one (modulo the number of files we have)
+      const auto realFileIndex = randomFileIndex == SETTINGS.lastUsedSleep? randomFileIndex+1 % numFiles : randomFileIndex;
+      SETTINGS.lastUsedSleep = realFileIndex;
+      SETTINGS.saveToFile();
+      const auto filename = "/sleep/" + files[realFileIndex];
       FsFile file;
       if (SdMan.openFileForRead("SLP", filename, file)) {
         Serial.printf("[%lu] [SLP] Randomly loading: /sleep/%s\n", millis(), files[randomFileIndex].c_str());