♻️ (ls_client.rs): refactor subscription logic for clarity and maintainability

♻️ (ls_client.rs): remove hardcoded base_params and use dynamic params for session creation
♻️ (ls_client.rs): remove commented-out subscription code for cleanup
✨ (ls_client.rs): handle new server messages for connection errors and subscription confirmations
🚚 (ls_client.rs): remove unnecessary println at the end of connect function
✨ (main.rs): change adapter set from "QUOTE_ADAPTER" to "DEMO" for client initialization
✨ (subscription.rs): add Default trait implementation for Snapshot enum
✨ (subscription.rs): implement ToString trait for Snapshot and SubscriptionMode enums
🐛 (subscription.rs): fix error message in set_item_group method to be more descriptive

1 files changed, 31 insertions, 2 deletions

diff --git a/src/subscription.rs b/src/subscription.rs
index be10380..e008804 100644
--- a/src/subscription.rs
+++ b/src/subscription.rs
@@ -3,14 +3,32 @@ use std::collections::HashMap;
 use std::fmt::{self, Debug, Formatter};
 
 /// Enum representing the snapshot delivery preferences to be requested to Lightstreamer Server for the items in the Subscription.
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub enum Snapshot {
     Yes,
     No,
     Number(usize),
+    #[default]
     None,
 }
 
+impl Default for &Snapshot {
+    fn default() -> Self {
+        &Snapshot::None
+    }
+}
+
+impl ToString for Snapshot {
+    fn to_string(&self) -> String {
+        match self {
+            Snapshot::Yes => "true".to_string(),
+            Snapshot::No => "false".to_string(),
+            Snapshot::Number(n) => n.to_string(),
+            Snapshot::None => "none".to_string(),
+        }
+    }
+}
+
 /// Enum representing the subscription mode.
 #[derive(Debug, PartialEq, Eq)]
 pub enum SubscriptionMode {
@@ -32,6 +50,17 @@ impl SubscriptionMode {
     }
 }
 
+impl ToString for SubscriptionMode {
+    fn to_string(&self) -> String {
+        match self {
+            SubscriptionMode::Merge => "MERGE".to_string(),
+            SubscriptionMode::Distinct => "DISTINCT".to_string(),
+            SubscriptionMode::Raw => "RAW".to_string(),
+            SubscriptionMode::Command => "COMMAND".to_string(),
+        }
+    }
+}
+
 /// Struct representing a Subscription to be submitted to a Lightstreamer Server.
 /// It contains subscription details and the listeners needed to process the real-time data.
 pub struct Subscription {
@@ -187,7 +216,7 @@ impl Subscription {
     /// - `group`: A String to be expanded into an item list by the Metadata Adapter.
     pub fn set_item_group(&mut self, group: String) -> Result<(), String> {
         if self.is_active {
-            return Err("Subscription is active".to_string());
+            return Err("Subscription is active. This method can only be called while the Subscription instance is in its 'inactive' state.".to_string());
         }
         self.item_group = Some(group);
         Ok(())