slightly more graceful config reading: reads entry by entry

reads from default only if an entry is not present, and then writes those defaults to the file if anything was changed

src/config/mod.rs

@@ -7,6 +7,7 @@ mod load;
 
 use rltk::prelude::*;
 use toml::de::Error as TomlError;
+use toml::Value;
 use serde::{ Serialize, Deserialize };
 
 lazy_static! {
@@ -69,10 +70,25 @@ impl From<TomlError> for ReadError {
 }
 
 impl Config {
-    pub fn load_from_file(filename: &str) -> Result<Self, ReadError> {
-        let contents = std::fs::read_to_string(filename).map_err(|e| ReadError::Io(e))?;
-        let config: Config = toml::from_str(&contents).map_err(|e| ReadError::Toml(e))?;
-        return Ok(config);
+    pub fn load_from_file(filename: &str) -> Config {
+        if let Ok(contents) = std::fs::read_to_string(filename) {
+            let parsed_config: Result<Value, _> = toml::from_str(&contents);
+            if let Ok(parsed_config) = parsed_config {
+                let mut config = Config::default();
+                let mut requires_write = false;
+                requires_write |= config.logging.apply_values(&parsed_config);
+                requires_write |= config.visuals.apply_values(&parsed_config);
+
+                if requires_write {
+                    if let Err(write_err) = config.save_to_file(filename) {
+                        eprintln!("Error writing config: {:?}", write_err);
+                    }
+                }
+
+                return config;
+            }
+        }
+        Config::default()
     }
     pub fn save_to_file(&self, filename: &str) -> Result<(), Box<dyn std::error::Error>> {
         let toml_string = toml::to_string(self)?;
@@ -81,23 +97,51 @@ impl Config {
     }
 }
 
-#[cfg(not(target_arch = "wasm32"))]
-pub fn try_load_configuration() -> Config {
-    let config: Config = match Config::load_from_file("config.toml") {
-        Ok(config) => {
-            console::log(format!("Successfully loaded config: {:?}", config));
-            config
+macro_rules! apply_bool_value {
+    ($config:expr, $parsed_config:expr, $changed:expr, $field:ident) => {
+        if let Some(value) = $parsed_config.get(stringify!($field)).and_then(|v| v.as_bool()) {
+            if $config.$field != value {
+                $config.$field = value;
+                $changed = true;
             }
-        Err(e) => {
-            console::log(format!("Error loading config: {:?}", e));
-            let config = Config::default();
-            if let Err(write_err) = config.save_to_file("config.toml") {
-                eprintln!("Error writing default config: {:?}", write_err);
-            }
-            config
         }
     };
+}
 
+trait Section {
+    fn apply_values(&mut self, parsed_config: &Value) -> bool;
+}
+
+impl Section for LogConfig {
+    fn apply_values(&mut self, parsed_config: &Value) -> bool {
+        if let Some(section) = parsed_config.get("logging") {
+            let mut missing = false;
+            apply_bool_value!(self, section, missing, log_spawning);
+            apply_bool_value!(self, section, missing, log_ticks);
+            missing
+        } else {
+            true
+        }
+    }
+}
+
+impl Section for VisualConfig {
+    fn apply_values(&mut self, parsed_config: &Value) -> bool {
+        if let Some(section) = parsed_config.get("visuals") {
+            let mut missing = false;
+            apply_bool_value!(self, section, missing, with_scanlines);
+            apply_bool_value!(self, section, missing, with_screen_burn);
+            apply_bool_value!(self, section, missing, with_darken_by_distance);
+            missing
+        } else {
+            true
+        }
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn try_load_configuration() -> Config {
+    let config: Config = Config::load_from_file("config.toml");
     return config;
 }