Avoid failing when the user chooses a filename that already exists in Downloads

app/src/main/java/org/mydomain/myscan/FileUtils.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2025 Pierre-Yves Nicolas
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option)
+ * any later version.
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.mydomain.myscan
+
+import java.io.File
+
+fun getAvailableFilename(desiredFile: File): File {
+    var file = desiredFile
+    val dir = desiredFile.parentFile
+    val desiredName = desiredFile.name
+    val nameWithoutExtension = desiredName.removeSuffix(".pdf")
+    var counter = 1
+    while (file.exists()) {
+        file = File(dir, "${nameWithoutExtension}_$counter.pdf")
+        counter++
+    }
+    return file
+}

app/src/main/java/org/mydomain/myscan/MainActivity.kt

@@ -126,8 +126,8 @@ class MainActivity : ComponentActivity() {
                     downloadsDir.mkdirs()
                 }
                 val generatedFile = generatedPdf.uri.toFile()
-                val targetFile = File(downloadsDir, generatedFile.name)
-                // TODO Handle case where the target file already exists (choose a unique name)
+                val desiredFile = File(downloadsDir, generatedFile.name)
+                val targetFile = getAvailableFilename(desiredFile)
                 generatedFile.copyTo(targetFile)
                 viewModel.markFileSaved(targetFile.toUri())
 

app/src/test/java/org/mydomain/myscan/FileUtilsTest.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2025 Pierre-Yves Nicolas
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option)
+ * any later version.
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.mydomain.myscan
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+import java.io.File
+import kotlin.io.path.createTempDirectory
+
+class FileUtilsTest {
+
+    @Test
+    fun getAvailableName() {
+        val dir = createTempDirectory().toFile()
+        val f = File(dir, "f.pdf")
+        val f1 = File(dir, "f_1.pdf")
+        val f2 = File(dir, "f_2.pdf")
+
+        assertThat(f.exists()).isFalse
+        assertThat(f1.exists()).isFalse
+        assertThat(getAvailableFilename(f)).isEqualTo(f)
+
+        f.apply { writeText("dummy") }
+        assertThat(f.exists()).isTrue
+        assertThat(getAvailableFilename(f)).isEqualTo(f1)
+
+        f1.apply { writeText("dummy") }
+        assertThat(f1.exists()).isTrue
+        assertThat(getAvailableFilename(f)).isEqualTo(f2)
+    }
+
+}