fix(model-server): allow to delete branches

The old API allowed to delete branches by setting them to null.
Restored this behavior to avoid breaking changes.

Author: slisson

model-server/src/main/kotlin/org/modelix/model/server/handlers/KeyValueLikeModelServer.kt

@@ -285,7 +285,7 @@ class KeyValueLikeModelServer(val repositoriesManager: RepositoriesManager) {
         // Now we use the RepositoriesManager to merge changes instead of just overwriting a branch.
 
         val hashedObjects = LinkedHashMap<String, String>()
-        val branchChanges = LinkedHashMap<BranchReference, String>()
+        val branchChanges = LinkedHashMap<BranchReference, String?>()
         val userDefinedEntries = LinkedHashMap<String, String?>()
 
         for ((key, value) in newEntries) {
@@ -294,7 +294,7 @@ class KeyValueLikeModelServer(val repositoriesManager: RepositoriesManager) {
                     hashedObjects[key] = value ?: throw IllegalArgumentException("No value provided for $key")
                 }
                 BranchReference.tryParseBranch(key) != null -> {
-                    branchChanges[BranchReference.tryParseBranch(key)!!] = value ?: throw IllegalArgumentException("Deleting branch $key not allowed")
+                    branchChanges[BranchReference.tryParseBranch(key)!!] = value
                 }
                 key.startsWith(PROTECTED_PREFIX) -> {
                     throw NoPermissionException("Access to keys starting with '$PROTECTED_PREFIX' is only permitted to the model server itself.")
@@ -317,7 +317,11 @@ class KeyValueLikeModelServer(val repositoriesManager: RepositoriesManager) {
             storeClient.putAll(hashedObjects)
             storeClient.putAll(userDefinedEntries)
             for ((branch, value) in branchChanges) {
-                repositoriesManager.mergeChanges(branch, value)
+                if (value == null) {
+                    repositoriesManager.removeBranches(branch.repositoryId, setOf(branch.branchName))
+                } else {
+                    repositoriesManager.mergeChanges(branch, value)
+                }
             }
         }
     }

model-server/src/main/kotlin/org/modelix/model/server/handlers/RepositoriesManager.kt

@@ -121,6 +121,31 @@ class RepositoriesManager(val client: LocalModelClient) {
         }
     }
 
+    fun removeRepository(repository: RepositoryId) {
+        store.runTransaction {
+            for (branchName in getBranchNames(repository)) {
+                putVersionHash(repository.getBranchReference(branchName), null)
+            }
+            store.put(branchListKey(repository), null)
+            val existingRepositories = getRepositories()
+            val remainingRepositories = existingRepositories - repository
+            store.put(REPOSITORIES_LIST_KEY, remainingRepositories.joinToString("\n") { it.id })
+        }
+    }
+
+    fun removeBranches(repository: RepositoryId, branchNames: Set<String>) {
+        if (branchNames.isEmpty()) return
+        store.runTransaction {
+            val key = branchListKey(repository)
+            val existingBranches = store[key]?.lines()?.toSet() ?: emptySet()
+            val remainingBranches = existingBranches - branchNames
+            store.put(key, remainingBranches.joinToString("\n"))
+            for (branchName in branchNames) {
+                putVersionHash(repository.getBranchReference(branchName), null)
+            }
+        }
+    }
+
     fun mergeChanges(branch: BranchReference, newVersionHash: String): String {
         var result: String? = null
         store.runTransaction {
@@ -155,7 +180,7 @@ class RepositoriesManager(val client: LocalModelClient) {
             ?: store[legacyBranchKey(branch)]?.also { store.put(branchKey(branch), it, true) }
     }
 
-    private fun putVersionHash(branch: BranchReference, hash: String) {
+    private fun putVersionHash(branch: BranchReference, hash: String?) {
         store.put(branchKey(branch), hash, false)
         store.put(legacyBranchKey(branch), hash, false)
     }