feat: add storage rent sweep and estimated_storage_footprint (#40)

contracts/badge-nft/src/lib.rs

@@ -28,6 +28,7 @@ pub trait BadgeNFTInterface {
     fn get_badges(env: Env, learner: Address) -> Vec<Badge>;
     fn get_badge_count(env: Env, learner: Address) -> u32;
     fn has_badge(env: Env, learner: Address, course_id: u32) -> bool;
+    fn estimated_storage_footprint(env: Env) -> u32;
 }
 
 #[contractevent]
@@ -121,6 +122,9 @@ mod contract_impl {
                 }
             }
 
+            // If this is a brand-new badge vec, increment the holder counter.
+            let is_new_holder = badges.is_empty();
+
             let minted_at = env.ledger().timestamp();
             let new_badge = Badge {
                 course_id,
@@ -129,6 +133,17 @@ mod contract_impl {
             badges.push_back(new_badge);
             env.storage().persistent().set(&badges_key, &badges);
 
+            if is_new_holder {
+                let prev: u32 = env
+                    .storage()
+                    .instance()
+                    .get(&DataKey::BadgeHolderCount)
+                    .unwrap_or(0);
+                env.storage()
+                    .instance()
+                    .set(&DataKey::BadgeHolderCount, &(prev + 1));
+            }
+
             BadgeMinted {
                 learner,
                 course_id,
@@ -250,6 +265,20 @@ mod contract_impl {
             false
         }
 
+        /// Returns the estimated number of persistent storage entries held by
+        /// this contract.
+        ///
+        /// Each unique learner that has ever received at least one badge
+        /// contributes one `DataKey::UserBadges(Address)` entry.  The count is
+        /// maintained via the `BadgeHolderCount` instance-storage counter which
+        /// is incremented the first time a learner's badge vec is created.
+        pub fn estimated_storage_footprint(env: Env) -> u32 {
+            env.storage()
+                .instance()
+                .get(&DataKey::BadgeHolderCount)
+                .unwrap_or(0)
+        }
+
         /// Upgrades the contract WASM. Only callable by the Protocol Admin.
         /// Replaces the BadgeNFT WASM with the supplied hash on the
         /// Soroban host. Admin-only. Emits `ContractUpgraded` on

contracts/badge-nft/src/test.rs

@@ -448,3 +448,51 @@ fn test_has_badge_multiple_badges() {
     assert!(!client.has_badge(&learner, &4));
     assert!(client.has_badge(&learner, &5));
 }
+
+// ── estimated_storage_footprint ───────────────────────────────────────────────
+
+#[test]
+fn test_badge_estimated_footprint_initial_zero() {
+    let (env, client) = setup();
+    let admin = Address::generate(&env);
+    client.initialize(&admin);
+    assert_eq!(client.estimated_storage_footprint(), 0);
+}
+
+#[test]
+fn test_badge_estimated_footprint_one_per_holder() {
+    let (env, client) = setup();
+    let admin = Address::generate(&env);
+    client.initialize(&admin);
+
+    let learner_a = Address::generate(&env);
+    let learner_b = Address::generate(&env);
+
+    // Mint first badge for learner_a — creates a new holder slot
+    client.mint_badge(&admin, &learner_a, &1);
+    assert_eq!(client.estimated_storage_footprint(), 1);
+
+    // Mint second badge for learner_a — same slot, count stays at 1
+    client.mint_badge(&admin, &learner_a, &2);
+    assert_eq!(client.estimated_storage_footprint(), 1);
+
+    // Mint a badge for learner_b — new holder slot
+    client.mint_badge(&admin, &learner_b, &1);
+    assert_eq!(client.estimated_storage_footprint(), 2);
+}
+
+#[test]
+fn test_badge_estimated_footprint_unaffected_by_revoke() {
+    let (env, client) = setup();
+    let admin = Address::generate(&env);
+    client.initialize(&admin);
+
+    let learner = Address::generate(&env);
+    client.mint_badge(&admin, &learner, &10);
+    assert_eq!(client.estimated_storage_footprint(), 1);
+
+    // Revoking a badge removes from the vec but the key still exists
+    client.revoke_badge(&admin, &learner, &10);
+    // Footprint counter stays at 1 — the Vec key is still present (empty)
+    assert_eq!(client.estimated_storage_footprint(), 1);
+}

contracts/badge-nft/src/types.rs

@@ -12,4 +12,9 @@ pub struct Badge {
 pub enum DataKey {
     Admin,
     UserBadges(Address),
+    /// Running count of unique learner addresses that have at least one badge.
+    /// Incremented the first time a learner's badge vec is created; never
+    /// decremented (revocation reduces vec length, but the key stays).
+    /// Used by `estimated_storage_footprint`.
+    BadgeHolderCount,
 }

contracts/badge-nft/test_snapshots/test/test_badge_estimated_footprint_initial_zero.1.json

@@ -0,0 +1,91 @@
+{
+  "generators": {
+    "address": 2,
+    "nonce": 0,
+    "mux_id": 0
+  },
+  "auth": [
+    [],
+    [],
+    []
+  ],
+  "ledger": {
+    "protocol_version": 23,
+    "sequence_number": 0,
+    "timestamp": 0,
+    "network_id": "0000000000000000000000000000000000000000000000000000000000000000",
+    "base_reserve": 0,
+    "min_persistent_entry_ttl": 4096,
+    "min_temp_entry_ttl": 16,
+    "max_entry_ttl": 6312000,
+    "ledger_entries": [
+      [
+        {
+          "contract_data": {
+            "contract": "CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD2KM",
+            "key": "ledger_key_contract_instance",
+            "durability": "persistent"
+          }
+        },
+        [
+          {
+            "last_modified_ledger_seq": 0,
+            "data": {
+              "contract_data": {
+                "ext": "v0",
+                "contract": "CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD2KM",
+                "key": "ledger_key_contract_instance",
+                "durability": "persistent",
+                "val": {
+                  "contract_instance": {
+                    "executable": {
+                      "wasm": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+                    },
+                    "storage": [
+                      {
+                        "key": {
+                          "vec": [
+                            {
+                              "symbol": "Admin"
+                            }
+                          ]
+                        },
+                        "val": {
+                          "address": "CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFCT4"
+                        }
+                      }
+                    ]
+                  }
+                }
+              }
+            },
+            "ext": "v0"
+          },
+          4095
+        ]
+      ],
+      [
+        {
+          "contract_code": {
+            "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+          }
+        },
+        [
+          {
+            "last_modified_ledger_seq": 0,
+            "data": {
+              "contract_code": {
+                "ext": "v0",
+                "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+                "code": ""
+              }
+            },
+            "ext": "v0"
+          },
+          4095
+        ]
+      ]
+    ]
+  },
+  "events": []
+}