feat: implement NFT metadata freezing (#368)

contracts/nft-reward/src/errors.rs

@@ -17,8 +17,5 @@ pub enum NftErrorCode {
     NftNotTransferable = 11,
     NftLocked = 12,
     InvalidMetadata = 13,
-    InvalidTitle = 14,
-    InvalidDescription = 15,
-    InvalidImageUri = 16,
-    InvalidHuntTitle = 17,
+    MetadataFrozen = 14,
 }

contracts/nft-reward/src/lib.rs

@@ -102,6 +102,7 @@
     pub transferable: bool,
     pub minted_at: u64,
     pub locked: bool,
+    pub metadata_frozen: bool,
 }
 
 /// Event emitted when an NFT is minted.
@@ -143,6 +144,14 @@
     pub updater: Address,
 }
 
+/// Event emitted when an NFT's metadata is permanently frozen.
+#[contracttype]
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct NftMetadataFrozenEvent {
+    pub nft_id: u64,
+    pub owner: Address,
+}
+
 /// Event emitted when admin batch-updates image URIs across NFTs.
 #[contracttype]
 #[derive(Clone, Debug, PartialEq, Eq)]
@@ -180,7 +189,7 @@
 /// Contract version constant.
 pub const CONTRACT_VERSION: u32 = 2;
 
 #[contractimpl]
 impl NftReward {
     /// Initializes the NFT reward contract with an admin, minter, and optional max supply cap.
     pub fn initialize(
@@ -600,6 +609,7 @@
             transferable,
             minted_at,
             locked: false,
+            metadata_frozen: false,
         };
 
         Storage::save_nft(&env, &nft_data);
@@ -676,12 +686,12 @@
     }
 
     /// Returns the configured admin address, if set.
     pub fn get_admin(env: Env) -> Option<Address> {
         Storage::get_admin(&env)
     }
 
     /// Sets the RewardManager contract address. Only the admin can call this.
     pub fn set_reward_manager(
         env: Env,
         admin: Address,
         reward_manager: Address,
@@ -731,7 +741,11 @@
             return Err(crate::errors::NftErrorCode::NotOwner);
         }
 
-        let new_description = Self::validate_metadata_field(
+        if nft.metadata_frozen {
+            return Err(crate::errors::NftErrorCode::MetadataFrozen);
+        }
+
+        let new_description = Self::sanitize_metadata_field(
             &env,
             &new_description,
             MAX_NFT_DESCRIPTION_BYTES,
@@ -752,6 +766,36 @@
         Ok(())
     }
 
+    /// Permanently freezes the NFT's metadata, preventing future updates. Owner only.
+    pub fn freeze_nft_metadata(
+        env: Env,
+        nft_id: u64,
+        owner: Address,
+    ) -> Result<(), crate::errors::NftErrorCode> {
+        owner.require_auth();
+
+        let mut nft =
+            Storage::get_nft(&env, nft_id).ok_or(crate::errors::NftErrorCode::NftNotFound)?;
+
+        if nft.owner != owner {
+            return Err(crate::errors::NftErrorCode::NotOwner);
+        }
+
+        if nft.metadata_frozen {
+            return Err(crate::errors::NftErrorCode::MetadataFrozen);
+        }
+
+        nft.metadata_frozen = true;
+        Storage::save_nft(&env, &nft);
+
+        env.events().publish(
+            (Symbol::new(&env, "NftMetadataFrozen"), nft_id),
+            NftMetadataFrozenEvent { nft_id, owner },
+        );
+
+        Ok(())
+    }
+
     /// Returns the total number of NFTs minted so far.
     pub fn total_supply(env: Env) -> u64 {
         Storage::get_nft_counter(&env)
@@ -784,7 +828,7 @@
         }
 
         // Apply bounded scan limit to prevent excessive gas consumption
         let bounded_limit = limit.min(MAX_SCAN_LIMIT);
         let end = offset.saturating_add(bounded_limit).min(total_count);
 
         let mut result = Vec::new(&env);
@@ -866,7 +910,7 @@
     }
 
     /// Searches NFTs by title (case-insensitive partial match).
     /// Returns a vector of NFT IDs whose titles contain the search query.
 
     pub fn search_by_title(env: Env, _query: String) -> Vec<u64> {
         Vec::new(&env)