add auto-indent on enter and content-based lang detection for untitled docs

viewport/src/editor.rs

@@ -144,8 +144,66 @@ impl EditorState {
         match message {
             Message::EditorAction(action) => {
                 let is_edit = action.is_edit();
+
+                let auto_indent = if let text_editor::Action::Edit(text_editor::Edit::Enter) = &action {
+                    let cursor = self.content.cursor();
+                    let line_text = self.content.line(cursor.position.line)
+                        .map(|l| l.text.to_string())
+                        .unwrap_or_default();
+                    let base = leading_whitespace(&line_text).to_string();
+                    let trimmed = line_text.trim_end();
+                    let extra = matches!(trimmed.as_bytes().last(), Some(b'{' | b'[' | b'('));
+                    if extra {
+                        Some(format!("{base}    "))
+                    } else {
+                        Some(base)
+                    }
+                } else {
+                    None
+                };
+
+                let dedent = if let text_editor::Action::Edit(text_editor::Edit::Insert(ch)) = &action {
+                    matches!(ch, '}' | ']' | ')').then(|| {
+                        let cursor = self.content.cursor();
+                        let line_text = self.content.line(cursor.position.line)
+                            .map(|l| l.text.to_string())
+                            .unwrap_or_default();
+                        let prefix = &line_text[..cursor.position.column];
+                        if prefix.chars().all(|c| c == ' ' || c == '\t') && prefix.len() >= 4 {
+                            Some(prefix.len())
+                        } else {
+                            None
+                        }
+                    }).flatten()
+                } else {
+                    None
+                };
+
                 self.content.perform(action);
+
+                if let Some(indent) = auto_indent {
+                    if !indent.is_empty() {
+                        self.content.perform(text_editor::Action::Edit(
+                            text_editor::Edit::Paste(Arc::new(indent)),
+                        ));
+                    }
+                }
+
+                if let Some(col) = dedent {
+                    let remove = col.min(4);
+                    self.content.perform(text_editor::Action::Move(Motion::Left));
+                    for _ in 0..remove {
+                        self.content.perform(text_editor::Action::Edit(
+                            text_editor::Edit::Backspace,
+                        ));
+                    }
+                    self.content.perform(text_editor::Action::Move(Motion::Right));
+                }
+
                 if is_edit {
+                    if self.lang.is_none() {
+                        self.lang = detect_lang_from_content(&self.content.text());
+                    }
                     self.reparse();
                     self.run_eval();
                 }
@@ -426,7 +484,30 @@ fn lang_from_extension(ext: &str) -> Option<String> {
         "zig" => "zig",
         "sql" => "sql",
         "mk" => "make",
+        "cord" | "cordial" => "rust",
         _ => return None,
     };
     Some(lang.to_string())
 }
+
+fn detect_lang_from_content(text: &str) -> Option<String> {
+    let keywords = ["fn ", "let ", "if ", "else ", "while ", "for ", "/="];
+    let mut hits = 0;
+    for line in text.lines().take(50) {
+        let trimmed = line.trim();
+        for kw in &keywords {
+            if trimmed.starts_with(kw) || trimmed.contains(&format!(" {kw}")) {
+                hits += 1;
+            }
+        }
+        if hits >= 2 {
+            return Some("rust".into());
+        }
+    }
+    None
+}
+
+fn leading_whitespace(line: &str) -> &str {
+    let end = line.len() - line.trim_start().len();
+    &line[..end]
+}