Adding simple config guide

docs/config/gson_config.md

@@ -0,0 +1,136 @@
+# Config files
+
+Sooner or later you'll get to the point where you'd like to make certain things toggleable.
+For such things, we can utilize included `Gson` library to read and write json configs.
+
+## Why gson?
+
+As mentioned above, `Gson` is already available in vanilla minecraft, meaning that you won't need
+any extra dependencies. If you don't need anything special and you're fine with `json` format, `Gson` will
+probably cover your needs. Not to mention that it will auto add the missing fields when updating
+the config without need to overwrite old values.
+
+## Config structure
+
+We'll use a custom config class that has fields that user / admin will be able to change.
+See below example.
+
+```java
+public class MyModConfig {
+
+    public float activationRange = 8.0F;
+
+    public boolean show = true;
+
+	public String message = "This is a config guide.";
+
+}
+```
+We can access our config values like this:
+```java
+MyModConfig config = new MyModConfig();
+
+if(config.show)
+	System.out.println(config.message);
+
+config.show = false;
+
+// Do other stuff with values ...
+```
+
+We can present the config object in the following json structure.
+
+```json
+{
+	"activationRange": 8.0,
+	"show": true,
+	"message": "This is a config guide."
+}
+```
+
+## Saving, reading and parsing
+
+If `config` only exists in our memory, it's not that usefull, as changes will be reset
+after server restart. If we want to make them permanent, we should write the config to a file.
+
+```java
+public class MyModConfig {
+    private static final Gson gson = new GsonBuilder()
+            .setPrettyPrinting() // Makes the json use new lines instead of being a "one-liner"
+            .serializeNulls() // Makes fields with `null` value to be written as well.
+            .disableHtmlEscaping() // We'll be able to use custom chars without them being saved differently
+            .create();
+
+	// Config values
+    public float activationRange = 8.0F;
+
+    public boolean show = true;
+
+	public String message = "This is a config guide.";
+
+
+	// Reading and saving
+
+    /**
+     * Loads config file.
+     *
+     * @param file file to load the config file from.
+     * @return MyModConfig object
+     */
+    public static MyModConfig loadConfigFile(File file) {
+        MyModConfig config = null;
+
+        if (file.exists()) {
+			// An existing config is present, we should use its values
+            try (BufferedReader fileReader = new BufferedReader(
+                    new InputStreamReader(new FileInputStream(file), StandardCharsets.UTF_8)
+            )) {
+				// Parses the config file and puts the values into config object
+                config = gson.fromJson(fileReader, MyModConfig.class);
+            } catch (IOException e) {
+                throw new RuntimeException("[MyMod] Problem occurred when trying to load config: ", e);
+            }
+        }
+		// gson.fromJson() can return null if file is empty
+		if (config == null) {
+			config = new MyModConfig();
+		}
+
+		// Saves the file in order to write new fields if they were added
+		config.saveConfigFile(file);
+        return config;
+    }
+
+    /**
+     * Saves the config to the given file.
+     *
+     * @param file file to save config to
+     */
+    public void saveConfigFile(File file) {
+        try (Writer writer = new OutputStreamWriter(new FileOutputStream(file), StandardCharsets.UTF_8)) {
+            gson.toJson(this, writer);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+}
+```
+
+Now that we have those new methods, we should use the following code to load the config.
+```java
+File configFile = new File("./config/my_mod_config.json");
+MyModConfig config = MyModConfig.loadConfigFile(configFile);
+
+if(config.show)
+	System.out.println(config.message);
+
+config.show = false;
+
+// We can save it now
+// If you'd like, you can also save the file parameter when loading
+config.save(configFile);
+
+// Do other stuff with values ...
+```
+
+This will automatically create new config file or read the existing one.

mkdocs.yml

@@ -9,6 +9,8 @@ nav:
   - permissions.md
   - mixin-injects.md
   - nbt.md
+  - "Configs":
+    - "Using gson": config/gson_config.md
 
 theme:
   name: material