Add file selection screen

src/CrossPointState.cpp

@@ -0,0 +1,46 @@
+#include "CrossPointState.h"
+
+#include <HardwareSerial.h>
+#include <SD.h>
+#include <Serialization.h>
+
+#include <fstream>
+
+constexpr uint8_t STATE_VERSION = 1;
+constexpr char STATE_FILE[] = "/sd/.crosspoint/state.bin";
+
+void CrossPointState::serialize(std::ostream& os) const {
+  serialization::writePod(os, STATE_VERSION);
+  serialization::writeString(os, openEpubPath);
+}
+
+CrossPointState* CrossPointState::deserialize(std::istream& is) {
+  const auto state = new CrossPointState();
+
+  uint8_t version;
+  serialization::readPod(is, version);
+  if (version != STATE_VERSION) {
+    Serial.printf("CrossPointState: Unknown version %u\n", version);
+    return state;
+  }
+
+  serialization::readString(is, state->openEpubPath);
+  return state;
+}
+
+void CrossPointState::saveToFile() const {
+  std::ofstream outputFile(STATE_FILE);
+  serialize(outputFile);
+  outputFile.close();
+}
+
+CrossPointState* CrossPointState::loadFromFile() {
+  if (!SD.exists(&STATE_FILE[3])) {
+    return new CrossPointState();
+  }
+
+  std::ifstream inputFile(STATE_FILE);
+  CrossPointState* state = deserialize(inputFile);
+  inputFile.close();
+  return state;
+}