fix: improve decode validation and warn on unknown Morse token

main.cpp

@@ -1,6 +1,8 @@
 #include <cctype>
 #include <iostream>
 #include <map>
+#include <optional>
+#include <sstream>
 #include <string>
 
 using namespace std;
@@ -55,10 +57,12 @@ private:
   }
 
 public:
-  char decode(const string &morse) {
+  optional<char> decode(const string &morse) const {
     const auto &morse_to_char = get_morse_to_char();
     auto it = morse_to_char.find(morse);
-    return it != morse_to_char.end() ? it->second : '?';
+    if (it == morse_to_char.end())
+      return nullopt;
+    return it->second;
   }
 };
 
@@ -123,56 +127,41 @@ void decode_mode() {
     if (tolower(input[0]) == 'e')
       return;
 
-    size_t start = input.find_first_not_of(" \t");
-    if (start == string::npos)
-      continue;
-    size_t end = input.find_last_not_of(" \t");
-
     string decoded_message;
-    string current_morse;
-    bool needs_word_separator = false;
-    bool has_invalid_chars = false;
-    bool in_separator = false;
+    bool has_invalid_tokens = false;
+    bool has_unknown_codes = false;
 
-    auto decode_and_add = [&]() {
-      char decoded = decoder.decode(current_morse);
-      cout << current_morse << " -> " << decoded << "\n";
-      decoded_message += decoded;
-      current_morse.clear();
-    };
-
-    for (size_t i = start; i <= end; ++i) {
-      char c = input[i];
-
-      if (c == ' ' || c == '/') {
-        if (!in_separator && !current_morse.empty()) {
-          decode_and_add();
-          in_separator = true;
-        }
-        if (c == '/')
-          needs_word_separator = true;
-      } else if (c == '.' || c == '-') {
-        if (in_separator) {
-          if (needs_word_separator && !decoded_message.empty()) {
+    istringstream stream(input);
+    string token;
+    while (stream >> token) {
+      if (token == "/") {
+        if (!decoded_message.empty() && decoded_message.back() != ' ')
           decoded_message += ' ';
-            needs_word_separator = false;
-          }
-          in_separator = false;
-        }
-        current_morse += c;
-      } else {
-        in_separator = false;
-        has_invalid_chars = true;
-      }
+        continue;
       }
 
-    if (!current_morse.empty())
-      decode_and_add();
-
-    if (has_invalid_chars) {
-      cout << "\nWarning: Invalid characters were ignored.\n";
+      if (token.find_first_not_of(".-") != string::npos) {
+        has_invalid_tokens = true;
+        cout << token << " -> [ignored: invalid characters]\n";
+        continue;
       }
 
+      optional<char> decoded = decoder.decode(token);
+      if (!decoded) {
+        has_unknown_codes = true;
+        cout << token << " -> [unknown]\n";
+        continue;
+      }
+
+      cout << token << " -> " << *decoded << "\n";
+      decoded_message += *decoded;
+    }
+
+    if (has_invalid_tokens)
+      cout << "\nWarning: Tokens with invalid characters were ignored.\n";
+    if (has_unknown_codes)
+      cout << "Warning: Unknown Morse codes were skipped.\n";
+
     cout << "\nFinal message: " << decoded_message << "\n\n";
   }
 }