create Settings library

modules/Settings.js

@@ -0,0 +1,145 @@
+/*
+
+Usage:
+
+```
+// open settings for an app
+var appSettings = require('Settings').app(appname);
+// read a single setting
+value = appSettings.get(path, default);
+// omit path to read all app settings
+value = appSettings.get();
+// write a single app setting
+appSettings.set(path, value)
+// omit path and pass an object as values to overwrite all settings for an app
+appSettings.set(values)
+
+// open Bangle settings
+var globalSettings = require('Settings').Bangle();
+value = globalSettings.get(path, default);
+// read all global settings
+values = globalSettings.get();
+// write a global setting
+globalSettings.set(path, value)
+// overwrite all global settings
+globalSettings.set(values)
+```
+
+For example:
+```
+var settings = require('Settings').app('test');
+settings.set('foo.bar.baz', 123);  // writes to 'test.settings.json'
+settings.set('foo.bar.bam', 456);  // updates 'test.settings.json'
+// 'test.settings.json' now contains  {foo:{bar:{baz:123,bam:456}}}
+baz = settings.get('foo.bar.baz');   // baz = 123
+bar = settings.get('foo.bar');       // bar = {baz: 123, bam:456}
+def = settings.get('asdf.jkl', 123); // def = 123
+all = settings.get();                // all = {foo: { bar: {baz: 123, bam:456} } }
+
+settings.set({fuz: 789});  // overwrites 'test.settings.json'
+// 'test.settings.json' now contains  {fuz:789}
+fuz = settings.get('fuz');          // fuz = 789
+baz = settings.get('foo.bar.baz');  // baz = undefined
+
+wakeOnTouch = require('Settings').Bangle().get('options.wakeOnTouch', false);
+```
+
+*/
+
+/**
+ *
+ * @param{string} file Settings file
+ * @param path Path to setting, omit to get complete settings object
+ * @param def Default value
+ * @return {*} Setting
+ */
+function get(file, path, def) {
+  let setting = require("Storage").readJSON(file);
+  if (def===undefined && ["object", "undefined"].includes(typeof path)) {
+    // get(app) or get(app, def): get all settings
+    def = path;
+    path = [];
+  } else {
+    path = path.split(".");
+  }
+  if (path.includes("")) {
+    throw "Settings: path cannot contain empty elements";
+  }
+  while(path.length) {
+    const key = path.shift();
+    if (typeof setting!=="object" || !(key in setting)) {
+      return def;
+    }
+    setting = setting[key];
+  }
+  return setting;
+}
+
+/**
+ * @param {string} file Settings file
+ * @param path Path to setting, omit to replace all settings
+ * @param value Value to store
+ */
+function set(file, path, value) {
+  if (value===undefined && typeof path==="object") {
+    // set(file, value): overwrite settings completely
+    require("Storage").writeJSON(file, path);
+    return;
+  }
+  path = path.split("."); // empty string is not OK (becomes [""])
+  if (path.includes("")) {
+    throw "Settings: path cannot contain empty elements";
+  }
+  let setting;
+  try {setting = get(file);} catch(e) {} // if reading old settings failed we write a fresh object
+  if (typeof setting!=="object") {
+    setting = {};
+  }
+  let root = setting; // keep a reference to root object
+  const leaf = path.pop();
+  while(path.length) {
+    const key = path.shift();
+    if (!(key in setting) || typeof (setting[key])!=="object") {
+      setting[key] = {};
+    }
+    setting = setting[key];
+  }
+  setting[leaf] = value;
+  require("Storage").write(file, root);
+}
+
+/**
+ * Open settings file
+ *
+ * @param {string} file Settings file
+ * @return {object} Settings setter and getter
+ */
+function open(file) {
+  return {
+    set: (path, val) => set(file, path, val),
+    get: (path, def) => get(file, path, def),
+  };
+}
+
+/**
+ * Open settings file directly
+ * Please use require('Settings').app() or require('Settings').Bangle() instead
+ *
+ * @param {string} file Settings file to open
+ * @return Settings object
+ */
+exports.open = open;
+
+/**
+ * Open app settings file
+ *
+ * @param {string} app App name for which to open settings
+ * @return Settings object
+ */
+exports.app = (app) => open(app+".settings.json");
+/**
+ * Open global settings file
+ *
+ * @return Settings object
+ */
+exports.Bangle = () => open("setting.json");