feat: add TOML configuration file support with JSON backward compatibility

- Add toml dependency for dual format support
- Implement automatic format detection based on file extension
- Add smart config file discovery (TOML preferred, JSON fallback)
- Maintain full backward compatibility with existing JSON configs
- Default new installations to TOML format for better readability
- Update config path handling to support both extensions
- Add comprehensive tests for both TOML and JSON formats
- Update documentation with dual format examples and migration info
- Mark issue #17 as complete in ROADMAP

All acceptance criteria fulfilled:
✅ Creates default config file if not exists (TOML format)
✅ Loads printer settings from config (both formats)
✅ CLI arguments override config values (preserved functionality)
✅ Validates configuration format (format-specific error messages)
✅ Clear error messages for invalid config (JSON/TOML specific)

Resolves #17

Author: krjordan

Cargo.lock

@@ -9,6 +9,7 @@ rumqttc = "0.24"
 tokio = { version = "1.0", features = ["full"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+toml = "0.8"
 tokio-native-tls = "0.3"
 rustls = "0.22"
 thiserror = "1.0"

Cargo.toml

@@ -281,18 +281,50 @@ This project is licensed under the MIT License - see the [LICENSE](LICENSE) file
 
 ## Configuration System
 
-PulsePrint-CLI now includes a comprehensive configuration system for managing multiple printers.
+PulsePrint-CLI includes a comprehensive configuration system for managing multiple printers with support for both TOML and JSON formats.
+
+### Configuration File Formats
+
+PulsePrint-CLI supports both **TOML** (preferred) and **JSON** configuration formats:
+
+- **New installations**: Default to TOML format (`config.toml`)
+- **Existing installations**: Continue to support JSON format (`config.json`) 
+- **Format detection**: Automatic based on file extension
+- **Backward compatibility**: Existing JSON configs work seamlessly
 
 ### Configuration File Location
 
-The configuration file is automatically stored in the appropriate location for your operating system:
+Configuration files are automatically stored in the appropriate location for your operating system:
 
-- **Linux**: `~/.config/pulseprint-cli/config.json`
-- **macOS**: `~/Library/Application Support/pulseprint-cli/config.json`
-- **Windows**: `%APPDATA%\pulseprint-cli\config.json`
+- **Linux**: `~/.config/pulseprint-cli/config.toml` (or `config.json`)
+- **macOS**: `~/Library/Application Support/pulseprint-cli/config.toml` (or `config.json`)
+- **Windows**: `%APPDATA%\pulseprint-cli\config.toml` (or `config.json`)
 
 ### Configuration Structure
 
+#### TOML Format (Preferred)
+
+```toml
+default_printer = "my_printer"
+
+[printers.my_printer]
+name = "my_printer"
+ip = "192.168.1.100"
+device_id = "01S00A000000000"
+access_code = "12345678"
+port = 8883
+use_tls = true
+
+[mqtt_settings]
+keep_alive_secs = 30
+connection_timeout_secs = 10
+retry_attempts = 5
+retry_delay_secs = 5
+queue_size = 10
+```
+
+#### JSON Format (Legacy Support)
+
 ```json
 {
   "printers": {
@@ -326,7 +358,7 @@ The configuration file is automatically stored in the appropriate location for y
 - ✅ Basic printer monitoring
 - ✅ CLI interface with help system
 - ✅ Error handling and retry logic
-- ✅ Configuration management system
+- ✅ Configuration management system with TOML and JSON support (issue #17)
 - ✅ Multiple printer support with named configurations
 - ✅ Printer management CLI commands (add, remove, list, set-default)
 - ✅ Message parsing for MQTT JSON messages (issue #15)

README.md

@@ -13,7 +13,7 @@ PulsePrint-CLI aims to be the premier command-line tool for monitoring and manag
 - [x] MQTT client implementation (issue #14)
 - [x] Basic printer connection via local network
 - [x] Simple status polling (`monitor` command)
-- [x] Configuration file support (JSON)
+- [x] Configuration file support with TOML and JSON formats (issue #17)
 - [x] Single printer monitoring
 
 #### v0.2.0 - Core Monitoring (Target: September 2025)

ROADMAP.md

@@ -1,11 +1,17 @@
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::fs;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 #[cfg(test)]
 mod tests;
 
+#[derive(Debug, Clone)]
+pub enum ConfigFormat {
+    Json,
+    Toml,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct PrinterConfig {
     pub name: String,
@@ -77,16 +83,57 @@ impl Default for MqttSettings {
 }
 
 impl AppConfig {
+    pub fn detect_format(path: &Path) -> ConfigFormat {
+        match path.extension().and_then(|ext| ext.to_str()) {
+            Some("toml") => ConfigFormat::Toml,
+            Some("json") => ConfigFormat::Json,
+            _ => ConfigFormat::Toml, // Default to TOML for new configs
+        }
+    }
+
     pub fn load_from_file(path: &PathBuf) -> Result<Self, ConfigError> {
+        // Try both formats if the specified file doesn't exist
         if !path.exists() {
+            // Try to find existing config in either format
+            if let Some(existing_path) = Self::find_existing_config_file(path) {
+                return Self::load_from_existing_file(&existing_path);
+            }
             return Ok(Self::default());
         }
 
+        Self::load_from_existing_file(path)
+    }
+
+    fn find_existing_config_file(preferred_path: &Path) -> Option<PathBuf> {
+        let base_dir = preferred_path.parent()?;
+
+        // Try TOML first, then JSON
+        let toml_path = base_dir.join("config.toml");
+        let json_path = base_dir.join("config.json");
+
+        if toml_path.exists() {
+            Some(toml_path)
+        } else if json_path.exists() {
+            Some(json_path)
+        } else {
+            None
+        }
+    }
+
+    fn load_from_existing_file(path: &PathBuf) -> Result<Self, ConfigError> {
         let contents = fs::read_to_string(path)
             .map_err(|e| ConfigError::IoError(format!("Failed to read config file: {e}")))?;
 
-        let config: AppConfig = serde_json::from_str(&contents)
-            .map_err(|e| ConfigError::ParseError(format!("Failed to parse config: {e}")))?;
+        let format = Self::detect_format(path);
+
+        let config: AppConfig = match format {
+            ConfigFormat::Json => serde_json::from_str(&contents).map_err(|e| {
+                ConfigError::ParseError(format!("Failed to parse JSON config: {e}"))
+            })?,
+            ConfigFormat::Toml => toml::from_str(&contents).map_err(|e| {
+                ConfigError::ParseError(format!("Failed to parse TOML config: {e}"))
+            })?,
+        };
 
         Ok(config)
     }
@@ -98,8 +145,16 @@ impl AppConfig {
             })?;
         }
 
-        let contents = serde_json::to_string_pretty(self)
-            .map_err(|e| ConfigError::SerializeError(format!("Failed to serialize config: {e}")))?;
+        let format = Self::detect_format(path);
+
+        let contents = match format {
+            ConfigFormat::Json => serde_json::to_string_pretty(self).map_err(|e| {
+                ConfigError::SerializeError(format!("Failed to serialize JSON config: {e}"))
+            })?,
+            ConfigFormat::Toml => toml::to_string_pretty(self).map_err(|e| {
+                ConfigError::SerializeError(format!("Failed to serialize TOML config: {e}"))
+            })?,
+        };
 
         fs::write(path, contents)
             .map_err(|e| ConfigError::IoError(format!("Failed to write config file: {e}")))?;
@@ -166,15 +221,26 @@ impl AppConfig {
     }
 
     pub fn get_config_path() -> PathBuf {
+        Self::get_config_path_with_format(ConfigFormat::Toml)
+    }
+
+    pub fn get_config_path_with_format(format: ConfigFormat) -> PathBuf {
+        let extension = match format {
+            ConfigFormat::Json => "json",
+            ConfigFormat::Toml => "toml",
+        };
+
         // Check for test environment override
         if let Ok(test_config_dir) = std::env::var("PULSEPRINT_TEST_CONFIG_DIR") {
-            return PathBuf::from(test_config_dir).join("config.json");
+            return PathBuf::from(test_config_dir).join(format!("config.{extension}"));
         }
 
         if let Some(config_dir) = dirs::config_dir() {
-            config_dir.join("pulseprint-cli").join("config.json")
+            config_dir
+                .join("pulseprint-cli")
+                .join(format!("config.{extension}"))
         } else {
-            PathBuf::from(".pulseprint-config.json")
+            PathBuf::from(format!(".pulseprint-config.{extension}"))
         }
     }
 }