add guestbook and moderation

crates/concord/src/chat.rs

@@ -6,7 +6,9 @@ use anyhow::Result;
 use nostr_sdk::prelude::*;
 
 use crate::derive::channel_group_key;
-use crate::edition::canonical_decimal;
+use crate::edition::{
+    AuthorityCitation, TAG_CITATION, canonical_decimal, citation_from, citation_tag,
+};
 use crate::stream::{
     KIND_WRAP, KIND_WRAP_EPHEMERAL, OpenedStream, SealForm, StreamError, build_rumor_ms,
     build_seal, channel_binding_tags, check_channel_binding, open_wrap, resolve_ms_strict,
@@ -96,6 +98,7 @@ pub enum ChatAction {
     Delete {
         target: EventId,
         target_kind: Option<u16>,
+        citation: Option<AuthorityCitation>,
     },
     Typing,
     Opaque,
@@ -217,6 +220,7 @@ pub fn build_delete(
     epoch: Epoch,
     target: EventId,
     target_kind: Option<u16>,
+    citation: Option<&AuthorityCitation>,
     at_ms: u64,
 ) -> UnsignedEvent {
     let mut tags = channel_binding_tags(channel, epoch);
@@ -226,6 +230,10 @@ pub fn build_delete(
         tags.push(Tag::custom(TAG_TARGET_KIND, [target_kind.to_string()]));
     }
 
+    if let Some(citation) = citation {
+        tags.push(citation_tag(citation));
+    }
+
     build_rumor_ms(KIND_DELETE, author, "", tags, at_ms)
 }
 
@@ -317,10 +325,10 @@ pub fn plane_keys(
         .collect()
 }
 
-/// Folds the chat plane into timeline rows, newest first. A delete is honored
-/// only from the message's own author, and a deletion is terminal: an edit or a
-/// reaction arriving later never revives it.
-pub fn fold(rumors: &[ChatRumor]) -> Vec<ChatMessage> {
+pub fn fold(
+    rumors: &[ChatRumor],
+    can_delete: impl Fn(&PublicKey, Option<&AuthorityCitation>, &PublicKey) -> bool,
+) -> Vec<ChatMessage> {
     let mut order: Vec<usize> = (0..rumors.len()).collect();
     order.sort_by_key(|&index| (rumors[index].at_ms, rumors[index].id));
 
@@ -356,8 +364,6 @@ pub fn fold(rumors: &[ChatRumor]) -> Vec<ChatMessage> {
         });
     }
 
-    // Mutations replay so the last one applied is the winner: the highest
-    // `at_ms` and, between equal ones, the lower inner rumor id.
     let mut mutations: Vec<usize> = (0..rumors.len()).collect();
     mutations.sort_by_key(|&index| (rumors[index].at_ms, Reverse(rumors[index].id)));
 
@@ -378,12 +384,16 @@ pub fn fold(rumors: &[ChatRumor]) -> Vec<ChatMessage> {
                 message.content = content.clone();
                 message.edited_at = Some(rumor.at_ms);
             }
-            ChatAction::Delete { target, .. } => {
+            ChatAction::Delete {
+                target, citation, ..
+            } => {
                 let Some(&slot) = slot.get(target) else {
                     continue;
                 };
 
-                if messages[slot].author == rumor.author {
+                let author = messages[slot].author;
+
+                if author == rumor.author || can_delete(&rumor.author, citation.as_ref(), &author) {
                     messages[slot].deleted = true;
                 }
             }
@@ -454,6 +464,7 @@ fn action_of(rumor: &UnsignedEvent) -> Result<ChatAction, ChatError> {
         KIND_DELETE => Ok(ChatAction::Delete {
             target: required_id(rumor, TAG_TARGET)?,
             target_kind: optional_kind(rumor, TAG_TARGET_KIND)?,
+            citation: optional_citation(rumor)?,
         }),
         KIND_TYPING => Ok(ChatAction::Typing),
         KIND_WEBXDC => Ok(ChatAction::Opaque),
@@ -469,8 +480,7 @@ fn optional_reply(
         return Ok(None);
     };
 
-    // NIP-C7 `q` and NIP-22 `E`/`e` put a relay hint at index 2 and the
-    // referenced author at index 3, which is a SHOULD, so absent reads as unknown.
+    // NIP-C7 `q` and NIP-22 `E`/`e` put a relay hint at index 2 and the referenced author at index 3.
     let author = match fields.get(3).map(String::as_str) {
         Some(hex) if !hex.is_empty() => Some(pubkey(hex, name)?),
         _ => None,
@@ -500,6 +510,16 @@ fn optional_kind(rumor: &UnsignedEvent, name: &'static str) -> Result<Option<u16
         .map_err(|_| ChatError::BadTag(name))
 }
 
+fn optional_citation(rumor: &UnsignedEvent) -> Result<Option<AuthorityCitation>, ChatError> {
+    let Some(fields) = tag(rumor, TAG_CITATION)? else {
+        return Ok(None);
+    };
+
+    citation_from(fields)
+        .map(Some)
+        .ok_or(ChatError::BadTag(TAG_CITATION))
+}
+
 fn expiration_of(rumor: &UnsignedEvent) -> Result<Option<Timestamp>, ChatError> {
     let Some(fields) = tag(rumor, TAG_EXPIRATION)? else {
         return Ok(None);
@@ -646,6 +666,7 @@ mod tests {
                     Epoch(0),
                     id,
                     Some(KIND_MESSAGE),
+                    None,
                     AT + 3_000,
                 ),
                 &group,
@@ -654,7 +675,7 @@ mod tests {
             ),
         ];
 
-        let folded = fold(&rumors);
+        let folded = fold(&rumors, |_, _, _| false);
 
         assert_eq!(folded.len(), 1);
         assert_eq!(folded[0].id, id);
@@ -698,6 +719,7 @@ mod tests {
                     Epoch(0),
                     id,
                     Some(KIND_MESSAGE),
+                    None,
                     AT + 2_000,
                 ),
                 &group,
@@ -706,7 +728,7 @@ mod tests {
             ),
         ];
 
-        let folded = fold(&rumors);
+        let folded = fold(&rumors, |_, _, _| false);
 
         assert_eq!(folded.len(), 1);
         assert_eq!(folded[0].content, "hello");
@@ -851,4 +873,75 @@ mod tests {
             Err(ChatError::DuplicateTag(TAG_TARGET))
         ));
     }
+
+    #[test]
+    fn a_moderator_delete_needs_the_roster_and_a_citation() {
+        let alice = Keys::generate();
+        let moderator = Keys::generate();
+        let peer = Keys::generate();
+        let group = group();
+
+        let message = read(
+            &build_message(alice.public_key(), &channel(), Epoch(0), "hello", None, AT),
+            &group,
+            &alice,
+            Epoch(0),
+        );
+        let id = message.id;
+        let citation = AuthorityCitation {
+            entity: [0x33; 32],
+            version: 1,
+            hash: [0x44; 32],
+        };
+
+        let delete = |author: &Keys, citation: Option<&AuthorityCitation>| {
+            read(
+                &build_delete(
+                    author.public_key(),
+                    &channel(),
+                    Epoch(0),
+                    id,
+                    Some(KIND_MESSAGE),
+                    citation,
+                    AT + 1_000,
+                ),
+                &group,
+                author,
+                Epoch(0),
+            )
+        };
+
+        let can_delete =
+            |actor: &PublicKey, citation: Option<&AuthorityCitation>, author: &PublicKey| {
+                actor != author && citation.is_some() && actor == &moderator.public_key()
+            };
+
+        let cited = vec![message.clone(), delete(&moderator, Some(&citation))];
+        assert!(matches!(
+            &cited[1].action,
+            ChatAction::Delete { citation: Some(parsed), .. } if *parsed == citation
+        ));
+        assert!(
+            fold(&cited, can_delete)[0].deleted,
+            "a cited moderator delete lands"
+        );
+
+        let uncited = vec![message.clone(), delete(&moderator, None)];
+        assert!(
+            !fold(&uncited, can_delete)[0].deleted,
+            "an uncited delete names no rank"
+        );
+
+        let peer_delete = vec![message.clone(), delete(&peer, Some(&citation))];
+        assert!(
+            !fold(&peer_delete, can_delete)[0].deleted,
+            "a peer's delete is not authority"
+        );
+
+        let own = vec![message.clone(), delete(&alice, None)];
+        assert!(
+            fold(&own, |_, _, _| false)[0].deleted,
+            "a self-delete never consults the predicate"
+        );
+    }
 }