Extract MxcTools and add test.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/mxc/MxcTools.kt

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.libraries.matrix.api.mxc
+
+import javax.inject.Inject
+
+class MxcTools @Inject constructor() {
+    /**
+     * Regex to match a Matrix Content (mxc://) URI.
+     *
+     * See: https://spec.matrix.org/v1.8/client-server-api/#matrix-content-mxc-uris
+     */
+    private val mxcRegex = Regex("""^mxc://([^/]+)/([^/]+)$""")
+
+    /**
+     * Sanitizes an mxcUri to be used as a relative file path.
+     *
+     * @param mxcUri the Matrix Content (mxc://) URI of the file.
+     * @return the relative file path as "<server-name>/<media-id>" or null if the mxcUri is invalid.
+     */
+    fun mxcUri2FilePath(mxcUri: String): String? = mxcRegex.matchEntire(mxcUri)?.let { match ->
+        buildString {
+            append(match.groupValues[1])
+            append("/")
+            append(match.groupValues[2])
+        }
+    }
+}