feat: persistent settings in LittleFS JSON

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

WeatherPredictor/WeatherPredictor.ino

@@ -6,6 +6,7 @@
 #include "rtc_time.h"
 #include "forecast.h"
 #include "history.h"
+#include "app_settings.h"
 
 static void i2cScan() {
   Serial.println(F("I2C scan:"));
@@ -59,6 +60,14 @@ void setup() {
                   historyCount(), d, classifyTrend(d));
   else
     Serial.println(F("history: not enough data for trend"));
+
+  // --- settings self-test (remove after Task 8) ---
+  settingsBegin();
+  Serial.printf("settings: alt=%.0f tz=%d lat=%.4f lon=%.4f\n",
+                settings.altitudeM, settings.tzOffsetMin, settings.lat, settings.lon);
+  settings.altitudeM += 1.0f;   // change and persist to test round-trip
+  settingsSave();
+  Serial.println(F("settings: incremented altitude and saved"));
 }
 
 void loop() {

WeatherPredictor/app_settings.cpp

@@ -0,0 +1,52 @@
+#include <LittleFS.h>
+#include <ArduinoJson.h>
+#include "config.h"
+#include "app_settings.h"
+
+AppSettings settings;
+static const char* PATH = "/settings.json";
+
+void settingsDefaults() {
+  settings.altitudeM   = DEFAULT_ALTITUDE_M;
+  settings.tzOffsetMin = DEFAULT_TZ_OFFSET_MIN;
+  settings.lat         = DEFAULT_LAT;
+  settings.lon         = DEFAULT_LON;
+}
+
+static bool settingsLoad() {
+  File f = LittleFS.open(PATH, "r");
+  if (!f) return false;
+  JsonDocument doc;
+  DeserializationError err = deserializeJson(doc, f);
+  f.close();
+  if (err) return false;
+  settings.altitudeM   = doc["altitude"] | DEFAULT_ALTITUDE_M;
+  settings.tzOffsetMin = doc["tz"]       | DEFAULT_TZ_OFFSET_MIN;
+  settings.lat         = doc["lat"]      | DEFAULT_LAT;
+  settings.lon         = doc["lon"]      | DEFAULT_LON;
+  return true;
+}
+
+bool settingsSave() {
+  JsonDocument doc;
+  doc["altitude"] = settings.altitudeM;
+  doc["tz"]       = settings.tzOffsetMin;
+  doc["lat"]      = settings.lat;
+  doc["lon"]      = settings.lon;
+  File f = LittleFS.open(PATH, "w");
+  if (!f) return false;
+  serializeJson(doc, f);
+  f.close();
+  return true;
+}
+
+void settingsBegin() {
+  if (!LittleFS.begin()) {
+    LittleFS.format();
+    LittleFS.begin();
+  }
+  settingsDefaults();
+  if (!settingsLoad()) {   // first boot: persist defaults
+    settingsSave();
+  }
+}

WeatherPredictor/app_settings.h

@@ -0,0 +1,15 @@
+#pragma once
+#include <Arduino.h>
+
+struct AppSettings {
+  float altitudeM;
+  int   tzOffsetMin;
+  float lat;
+  float lon;
+};
+
+extern AppSettings settings;
+
+void settingsBegin();
+bool settingsSave();
+void settingsDefaults();