feat: implement a basic backend (#1)

Reviewed-on: https://git.reya.su/reya/signed/pulls/1

crates/signed_core/src/model.rs

@@ -0,0 +1,86 @@
+use nostr::prelude::*;
+
+/// Parsed NIP-34 repository announcement (plain data, ready for the UI).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Announcement {
+    /// Author of the announcement event.
+    pub owner: PublicKey,
+    /// When the announcement was published (for latest-wins resolution).
+    pub created_at: Timestamp,
+    /// Repository ID (`d` tag).
+    pub id: String,
+    pub name: Option<String>,
+    pub description: Option<String>,
+    /// Webpage URLs for browsing.
+    pub web: Vec<String>,
+    /// URLs for `git clone`.
+    pub clone: Vec<String>,
+    /// Relays the repository monitors for patches and issues.
+    pub relays: Vec<String>,
+    /// Earliest unique commit ID (`r` tag with `euc` marker).
+    pub euc: Option<String>,
+    /// Other recognized maintainers.
+    pub maintainers: Vec<PublicKey>,
+}
+
+impl Announcement {
+    /// Parse a kind `30617` event. Returns `None` if the kind is wrong or the `d` tag is missing.
+    pub fn from_event(event: &Event) -> Option<Self> {
+        if event.kind != Kind::GitRepoAnnouncement {
+            return None;
+        }
+
+        let mut id: Option<String> = None;
+        let mut name: Option<String> = None;
+        let mut description: Option<String> = None;
+        let mut web: Vec<String> = Vec::new();
+        let mut clone: Vec<String> = Vec::new();
+        let mut relays: Vec<String> = Vec::new();
+        let mut euc: Option<String> = None;
+        let mut maintainers: Vec<PublicKey> = Vec::new();
+
+        for tag in event.tags.iter() {
+            let values: &[String] = tag.as_slice();
+            match tag.kind() {
+                "d" => id = tag.content().map(str::to_owned),
+                "name" => name = tag.content().map(str::to_owned),
+                "description" => description = tag.content().map(str::to_owned),
+                "web" => web.extend(values.iter().skip(1).cloned()),
+                "clone" => clone.extend(values.iter().skip(1).cloned()),
+                "relays" => relays.extend(values.iter().skip(1).cloned()),
+                "r" => {
+                    if values.get(2).map(String::as_str) == Some("euc") {
+                        euc = tag.content().map(str::to_owned);
+                    }
+                }
+                "maintainers" => {
+                    maintainers.extend(
+                        values
+                            .iter()
+                            .skip(1)
+                            .filter_map(|v| PublicKey::from_hex(v).ok()),
+                    );
+                }
+                _ => {}
+            }
+        }
+
+        Some(Self {
+            owner: event.pubkey,
+            created_at: event.created_at,
+            id: id?,
+            name,
+            description,
+            web,
+            clone,
+            relays,
+            euc,
+            maintainers,
+        })
+    }
+
+    /// The repository address of this announcement.
+    pub fn addr(&self) -> crate::RepoAddr {
+        crate::RepoAddr::new(self.owner, self.id.clone())
+    }
+}