Turn filename separators into dashes rather than dropping them

Splits the forbidden set: / \ | : were separating words, so they become
"-"; ? * < > " ' just go. Runs of dashes and spaces collapse to " - "
when the run held whitespace and to a bare "-" when it did not, so
"Show | Series" reads "Show - Series" while "AC/DC" stays "AC-DC".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RPyeapneuXrCdojsaiXGbe

src/download.rs

@@ -7,33 +7,56 @@ use tokio::io::AsyncWriteExt;
 
 use crate::config::{Config, Feed as FeedCfg, Organize};
 
-/// Characters the original's stringCleaning() stripped, plus the control range and the
-/// trailing dots/spaces it left in. A real length cap is new -- the Python had none.
-const FORBIDDEN: &[char] = &['/', '\\', '?', '*', ':', '<', '>', '|', '"', '\''];
+/// Forbidden characters that were separating words: they become "-" so the words stay
+/// apart. The original's stringCleaning() deleted them, turning "Show | Series" into
+/// "Show  Series".
+const SEPARATORS: &[char] = &['/', '\\', '|', ':'];
+/// Forbidden characters that were never separators: they just go.
+const STRIPPED: &[char] = &['?', '*', '<', '>', '"', '\''];
+/// A real length cap is new -- the Python had none.
 const MAX_NAME_BYTES: usize = 255;
 
 /// Keeps UTF-8: the original transliterated to ASCII via latin1_to_ascii because 2004
 /// filesystems demanded it. Ours do not.
 pub fn sanitize(name: &str) -> String {
-    let stripped: String = name
+    let mapped: String = name
         .chars()
         .map(|c| if c.is_control() { ' ' } else { c })
-        .filter(|c| !FORBIDDEN.contains(c))
+        .filter(|c| !STRIPPED.contains(c))
+        .map(|c| if SEPARATORS.contains(&c) { '-' } else { c })
         .collect();
 
-    // Stripping a separator leaves a gap: "Show | Series | Delta" would otherwise become
-    // "Show  Series  Delta". Collapse runs of whitespace rather than leaving the seams.
-    let mut out = String::with_capacity(stripped.len());
-    for c in stripped.chars() {
-        if c.is_whitespace() {
-            if !out.ends_with(' ') {
-                out.push(' ');
-            }
-        } else {
+    // Collapse each run of dashes and spaces into one thing. A run containing a dash
+    // becomes " - " when it also had whitespace ("Show | Series" -> "Show - Series",
+    // "Ep 12: One" -> "Ep 12 - One") and a bare "-" when it did not ("AC/DC" -> "AC-DC").
+    // A run of plain whitespace collapses to a single space.
+    let mut out = String::with_capacity(mapped.len());
+    let mut chars = mapped.chars().peekable();
+    while let Some(c) = chars.next() {
+        if !(c == '-' || c.is_whitespace()) {
             out.push(c);
+            continue;
+        }
+        let mut has_dash = c == '-';
+        let mut has_space = c.is_whitespace();
+        while let Some(&next) = chars.peek() {
+            if next == '-' {
+                has_dash = true;
+            } else if next.is_whitespace() {
+                has_space = true;
+            } else {
+                break;
+            }
+            chars.next();
+        }
+        match (has_dash, has_space) {
+            (true, true) => out.push_str(" - "),
+            (true, false) => out.push('-'),
+            _ => out.push(' '),
         }
     }
-    out = out.trim().trim_matches('.').trim().to_owned();
+    // Leading/trailing separators and dots are noise, and a leading "-" trips up CLI tools.
+    out = out.trim().trim_matches(|c| c == '.' || c == '-').trim().to_owned();
 
     if out.len() > MAX_NAME_BYTES {
         // Truncate on a char boundary, keeping the extension if there is a plausible one.
@@ -278,21 +301,24 @@ mod tests {
 
     #[test]
     fn sanitize_strips_path_and_control_characters() {
-        assert_eq!(sanitize("../../etc/passwd"), "etcpasswd");
-        assert_eq!(sanitize("Ep 12: The \"Best\" One?"), "Ep 12 The Best One");
+        assert_eq!(sanitize("../../etc/passwd"), "etc-passwd");
+        assert_eq!(sanitize("Ep 12: The \"Best\" One?"), "Ep 12 - The Best One");
         assert_eq!(sanitize("bad\u{0}name\u{7}.mp3"), "bad name .mp3");
         assert_eq!(sanitize("  spaced.mp3  "), "spaced.mp3");
     }
 
     #[test]
-    fn sanitize_collapses_the_gaps_left_by_stripped_separators() {
+    fn sanitize_turns_separators_into_dashes() {
         // A real Patreon feed title; the pipes are forbidden characters.
         assert_eq!(
             sanitize("Get in the Trunk | Anthology Series | Delta Green"),
-            "Get in the Trunk Anthology Series Delta Green"
+            "Get in the Trunk - Anthology Series - Delta Green"
         );
-        assert_eq!(sanitize("Ep 12: The One"), "Ep 12 The One");
-        assert_eq!(sanitize("a   b"), "a b");
+        assert_eq!(sanitize("Ep 12: The One"), "Ep 12 - The One");
+        assert_eq!(sanitize("a   b"), "a b", "plain whitespace stays whitespace");
+        assert_eq!(sanitize("AC/DC"), "AC-DC", "no spaces around it, so no spaces added");
+        assert_eq!(sanitize("well-known.mp3"), "well-known.mp3", "existing dashes survive");
+        assert_eq!(sanitize("Show -- Thing"), "Show - Thing");
     }
 
     #[test]