feat(ui): add discussions and semantic theming

Generate web discussion snapshots in CI; native builds use the public
feed and an offline cache.

src/discussions.rs

@@ -0,0 +1,240 @@
+//! GitHub Discussions shown on the Start page.
+//!
+//! Native builds read GitHub's public Atom feed and the public Discussions
+//! page, which exposes the repository's pinned-discussion section without an
+//! access token. The last successful result is cached for offline launches.
+//! Web builds read `discussions.json`, generated by the Pages workflow through
+//! GitHub's authenticated GraphQL API.
+
+pub const DISCUSSIONS_URL: &str =
+    "https://github.com/HakanSeven12/OpenCADStudio/discussions";
+
+#[cfg(not(target_arch = "wasm32"))]
+const FEED_URL: &str =
+    "https://github.com/HakanSeven12/OpenCADStudio/discussions.atom";
+
+#[derive(Clone, Debug, serde::Serialize, serde::Deserialize)]
+pub struct DiscussionEntry {
+    pub number: u64,
+    pub title: String,
+    pub url: String,
+    pub author: String,
+    pub updated_at: String,
+    #[serde(default)]
+    pub pinned: bool,
+}
+
+fn sort_entries(entries: &mut [DiscussionEntry]) {
+    entries.sort_by(|a, b| {
+        b.pinned
+            .cmp(&a.pinned)
+            .then_with(|| b.updated_at.cmp(&a.updated_at))
+            .then_with(|| b.number.cmp(&a.number))
+    });
+}
+
+fn parse_json(body: &str) -> Result<Vec<DiscussionEntry>, String> {
+    let mut entries: Vec<DiscussionEntry> =
+        serde_json::from_str(body).map_err(|e| e.to_string())?;
+    entries.retain(|entry| {
+        entry.number > 0
+            && !entry.title.trim().is_empty()
+            && entry.url.starts_with("https://github.com/")
+    });
+    sort_entries(&mut entries);
+    Ok(entries)
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+fn cache_path() -> Option<std::path::PathBuf> {
+    crate::config::config_dir().map(|dir| dir.join("discussions.json"))
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn load_cached() -> Vec<DiscussionEntry> {
+    cache_path()
+        .and_then(|path| std::fs::read_to_string(path).ok())
+        .and_then(|body| parse_json(&body).ok())
+        .or_else(|| parse_json(include_str!("../web/discussions.json")).ok())
+        .unwrap_or_default()
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn fetch_discussions() -> Result<Vec<DiscussionEntry>, String> {
+    let agent: ureq::Agent = ureq::Agent::config_builder()
+        .timeout_global(Some(std::time::Duration::from_secs(15)))
+        .build()
+        .into();
+    let feed = get_text(&agent, FEED_URL)?;
+    let page = get_text(&agent, DISCUSSIONS_URL)?;
+    let pinned = pinned_numbers(&page);
+    let mut entries = parse_atom(&feed);
+    if entries.is_empty() {
+        return Err("GitHub Discussions feed returned no entries".into());
+    }
+    for entry in &mut entries {
+        entry.pinned = pinned.contains(&entry.number);
+    }
+    sort_entries(&mut entries);
+
+    if let Some(path) = cache_path() {
+        if let Some(parent) = path.parent() {
+            let _ = std::fs::create_dir_all(parent);
+        }
+        if let Ok(body) = serde_json::to_string(&entries) {
+            let _ = std::fs::write(path, body);
+        }
+    }
+    Ok(entries)
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+fn get_text(agent: &ureq::Agent, url: &str) -> Result<String, String> {
+    agent
+        .get(url)
+        .header(
+            "User-Agent",
+            concat!("OpenCADStudio/", env!("CARGO_PKG_VERSION")),
+        )
+        .call()
+        .map_err(|e| e.to_string())?
+        .body_mut()
+        .with_config()
+        .limit(4 * 1024 * 1024)
+        .read_to_string()
+        .map_err(|e| e.to_string())
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+fn parse_atom(feed: &str) -> Vec<DiscussionEntry> {
+    feed.split("<entry>")
+        .skip(1)
+        .filter_map(|tail| {
+            let entry = tail.split_once("</entry>")?.0;
+            let url_start = entry.find(
+                "href=\"https://github.com/HakanSeven12/OpenCADStudio/discussions/",
+            )? + "href=\"".len();
+            let url_tail = &entry[url_start..];
+            let url = url_tail.split_once('"')?.0.to_string();
+            let number = url.rsplit('/').next()?.parse().ok()?;
+            let title = xml_text(entry, "title")?;
+            let author_block = entry.split_once("<author>")?.1.split_once("</author>")?.0;
+            let author = xml_text(author_block, "name").unwrap_or_default();
+            let updated_at = xml_text(entry, "updated").unwrap_or_default();
+            Some(DiscussionEntry {
+                number,
+                title,
+                url,
+                author,
+                updated_at,
+                pinned: false,
+            })
+        })
+        .collect()
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+fn xml_text(block: &str, tag: &str) -> Option<String> {
+    let open = format!("<{tag}>");
+    let close = format!("</{tag}>");
+    let value = block.split_once(&open)?.1.split_once(&close)?.0;
+    let compact = value.split_whitespace().collect::<Vec<_>>().join(" ");
+    if compact.is_empty() {
+        None
+    } else {
+        Some(
+            compact
+                .replace("&quot;", "\"")
+                .replace("&#39;", "'")
+                .replace("&apos;", "'")
+                .replace("&lt;", "<")
+                .replace("&gt;", ">")
+                .replace("&amp;", "&"),
+        )
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+fn pinned_numbers(page: &str) -> std::collections::HashSet<u64> {
+    let mut numbers = std::collections::HashSet::new();
+    let Some(after_heading) = page.split_once("id=\"pinned-discussions\"").map(|(_, rest)| rest)
+    else {
+        return numbers;
+    };
+    let section = after_heading
+        .split_once("</ul>")
+        .map(|(section, _)| section)
+        .unwrap_or(after_heading);
+    let marker = "/HakanSeven12/OpenCADStudio/discussions/";
+    let mut rest = section;
+    while let Some(pos) = rest.find(marker) {
+        let tail = &rest[pos + marker.len()..];
+        let digits = tail
+            .chars()
+            .take_while(|ch| ch.is_ascii_digit())
+            .collect::<String>();
+        if let Ok(number) = digits.parse() {
+            numbers.insert(number);
+        }
+        rest = tail;
+    }
+    numbers
+}
+
+#[cfg(target_arch = "wasm32")]
+pub async fn fetch_discussions_web() -> Result<Vec<DiscussionEntry>, String> {
+    use wasm_bindgen::JsCast;
+    use wasm_bindgen_futures::JsFuture;
+
+    let window = web_sys::window().ok_or("no window")?;
+    let response = JsFuture::from(window.fetch_with_str("discussions.json"))
+        .await
+        .map_err(|_| "fetch failed")?;
+    let response: web_sys::Response =
+        response.dyn_into().map_err(|_| "not a Response")?;
+    if !response.ok() {
+        return Err(format!("HTTP {}", response.status()));
+    }
+    let text = JsFuture::from(response.text().map_err(|_| "text() unavailable")?)
+        .await
+        .map_err(|_| "body read failed")?;
+    let body = text.as_string().ok_or("body is not a string")?;
+    parse_json(&body)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[cfg(not(target_arch = "wasm32"))]
+    #[test]
+    fn pinned_discussions_are_sorted_first() {
+        let feed = r#"
+            <entry>
+              <link type="text/html" rel="alternate" href="https://github.com/HakanSeven12/OpenCADStudio/discussions/2"/>
+              <title>New &amp; recent</title>
+              <updated>2026-07-28T10:00:00+00:00</updated>
+              <author><name>alice</name></author>
+            </entry>
+            <entry>
+              <link type="text/html" rel="alternate" href="https://github.com/HakanSeven12/OpenCADStudio/discussions/1"/>
+              <title>Pinned</title>
+              <updated>2026-07-20T10:00:00+00:00</updated>
+              <author><name>bob</name></author>
+            </entry>
+        "#;
+        let page = r#"
+          <h2 id="pinned-discussions">Pinned Discussions</h2>
+          <ul><a href="/HakanSeven12/OpenCADStudio/discussions/1">Pinned</a></ul>
+        "#;
+        let pinned = pinned_numbers(page);
+        let mut entries = parse_atom(feed);
+        for entry in &mut entries {
+            entry.pinned = pinned.contains(&entry.number);
+        }
+        sort_entries(&mut entries);
+
+        assert_eq!(entries[0].number, 1);
+        assert_eq!(entries[1].title, "New & recent");
+    }
+}