implement TextBuffer -> PostBuffer downcasting

Signed-off-by: kernelkind <kernelkind@gmail.com>

crates/notedeck_columns/src/post.rs

@@ -2,7 +2,9 @@ use egui::TextBuffer;
 use enostr::{FullKeypair, Pubkey};
 use nostrdb::{Note, NoteBuilder, NoteReply};
 use std::{
+    any::TypeId,
     collections::{BTreeMap, HashMap, HashSet},
+    hash::{DefaultHasher, Hash, Hasher},
     ops::Range,
 };
 use tracing::error;
@@ -351,6 +353,18 @@ impl PostBuffer {
     }
 }
 
+pub fn downcast_post_buffer(buffer: &dyn TextBuffer) -> Option<&PostBuffer> {
+    let mut hasher = DefaultHasher::new();
+    TypeId::of::<PostBuffer>().hash(&mut hasher);
+    let post_id = hasher.finish() as usize;
+
+    if buffer.type_id() == post_id {
+        unsafe { Some(&*(buffer as *const dyn TextBuffer as *const PostBuffer)) }
+    } else {
+        None
+    }
+}
+
 pub struct PostOutput {
     pub text: String,
     pub mentions: Vec<Pubkey>,
@@ -555,6 +569,12 @@ impl TextBuffer for PostBuffer {
             }
         }
     }
+
+    fn type_id(&self) -> usize {
+        let mut hasher = DefaultHasher::new();
+        TypeId::of::<PostBuffer>().hash(&mut hasher);
+        hasher.finish() as usize
+    }
 }
 
 fn first_is_desired_char(text: &str, desired: char) -> bool {