feat: rewrite the nip-4e implementation (#1)

Make NIP-4e a core feature, not an optional feature.

Note:
- The UI is broken and needs to be updated in a separate PR.

Reviewed-on: #1

crates/state/src/gossip.rs

@@ -0,0 +1,107 @@
+use std::collections::{HashMap, HashSet};
+
+use nostr_sdk::prelude::*;
+
+/// Gossip
+#[derive(Debug, Clone, Default)]
+pub struct Gossip {
+    /// Gossip relays for each public key
+    relays: HashMap<PublicKey, HashSet<(RelayUrl, Option<RelayMetadata>)>>,
+    /// Messaging relays for each public key
+    messaging_relays: HashMap<PublicKey, HashSet<RelayUrl>>,
+}
+
+impl Gossip {
+    /// Get read relays for a given public key
+    pub fn read_relays(&self, public_key: &PublicKey) -> Vec<RelayUrl> {
+        self.relays
+            .get(public_key)
+            .map(|relays| {
+                relays
+                    .iter()
+                    .filter_map(|(url, metadata)| {
+                        if metadata.is_none() || metadata == &Some(RelayMetadata::Read) {
+                            Some(url.to_owned())
+                        } else {
+                            None
+                        }
+                    })
+                    .collect()
+            })
+            .unwrap_or_default()
+    }
+
+    /// Get write relays for a given public key
+    pub fn write_relays(&self, public_key: &PublicKey) -> Vec<RelayUrl> {
+        self.relays
+            .get(public_key)
+            .map(|relays| {
+                relays
+                    .iter()
+                    .filter_map(|(url, metadata)| {
+                        if metadata.is_none() || metadata == &Some(RelayMetadata::Write) {
+                            Some(url.to_owned())
+                        } else {
+                            None
+                        }
+                    })
+                    .collect()
+            })
+            .unwrap_or_default()
+    }
+
+    /// Insert gossip relays for a public key
+    pub fn insert_relays(&mut self, event: &Event) {
+        self.relays.entry(event.pubkey).or_default().extend(
+            event
+                .tags
+                .iter()
+                .filter_map(|tag| {
+                    if let Some(TagStandard::RelayMetadata {
+                        relay_url,
+                        metadata,
+                    }) = tag.clone().to_standardized()
+                    {
+                        Some((relay_url, metadata))
+                    } else {
+                        None
+                    }
+                })
+                .take(3),
+        );
+
+        log::info!("Updating gossip relays for: {}", event.pubkey);
+    }
+
+    /// Get messaging relays for a given public key
+    pub fn messaging_relays(&self, public_key: &PublicKey) -> Vec<RelayUrl> {
+        self.messaging_relays
+            .get(public_key)
+            .cloned()
+            .unwrap_or_default()
+            .into_iter()
+            .collect()
+    }
+
+    /// Insert messaging relays for a public key
+    pub fn insert_messaging_relays(&mut self, event: &Event) {
+        self.messaging_relays
+            .entry(event.pubkey)
+            .or_default()
+            .extend(
+                event
+                    .tags
+                    .iter()
+                    .filter_map(|tag| {
+                        if let Some(TagStandard::Relay(url)) = tag.as_standardized() {
+                            Some(url.to_owned())
+                        } else {
+                            None
+                        }
+                    })
+                    .take(3),
+            );
+
+        log::info!("Updating messaging relays for: {}", event.pubkey);
+    }
+}