WebdavRepo: store attachments

Tested with a webdav server to confirm that attachment and its parent
directories can be created.

Caveat:
- The attachment: link cannot be resolved. Because this link currently
only resolves to local files, it cannot deal with remote files (like
webdav). To handle remote files, need additional changes to download
and cache the remote files.

app/src/main/java/com/orgzly/android/repos/WebdavRepo.kt

@@ -8,6 +8,7 @@ import com.thegrizzlylabs.sardineandroid.impl.OkHttpSardine
 import okhttp3.OkHttpClient
 import okio.Buffer
 import java.io.File
+import java.io.FileNotFoundException
 import java.io.FileOutputStream
 import java.io.InputStream
 import java.security.KeyStore
@@ -165,7 +166,36 @@ class WebdavRepo(
     }
 
     override fun storeFile(file: File?, pathInRepo: String?, fileName: String?): VersionedRook {
-        TODO("Not yet implemented")
+        if (file == null || !file.exists()) {
+            throw FileNotFoundException("File $file does not exist")
+        }
+
+        val folderUri = Uri.withAppendedPath(uri, pathInRepo)
+        val fileUrl = Uri.withAppendedPath(folderUri, fileName).toUrl()
+
+        createRecursive(uri.toUrl(), pathInRepo!!)
+
+        sardine.put(fileUrl, file, null)
+
+        return sardine.list(fileUrl).first().toVersionedRook()
+    }
+
+    private fun createRecursive(parent: String, path: String): String {
+        if ("." == path || "" == path) {
+            return parent
+        }
+        val l = path.lastIndexOf('/')
+        val p = if (l >= 0) {
+            createRecursive(parent, path.substring(0, l))
+        } else {
+            parent
+        }
+        val subdir = path.substring(l + 1)
+        val folder = p + "/" + subdir
+        if (!sardine.exists(folder)) {
+            sardine.createDirectory(folder)
+        }
+        return folder
     }
 
     override fun renameBook(from: Uri, name: String?): VersionedRook {