DarkRoom/apps/darkroom-android/android/java/paris/tourolle/darkroom/Saf.java

package paris.tourolle.darkroom;

import android.content.ContentResolver;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.provider.DocumentsContract;
import android.util.Log;

import java.io.IOException;
import java.io.OutputStream;

/**
 * Writing an export into a folder the user granted through
 * {@link FolderPicker} — the Storage Access Framework, which is the only way
 * this app reaches a folder on the device (FR-PLAT-AND-1).
 *
 * <p>A tree URI is not a path: a child is found by listing the folder and
 * matching its display name, and created through the provider, which may
 * rename it on a collision. So the name that was actually written is handed
 * back, and the album records that one.
 *
 * <p>Two static calls, strings and a byte array in, a string out, for the
 * reason {@link Intents} gives: every call here would be a signature typed as
 * a string on the Rust side, and the fewer of those the better.
 */
public final class Saf {
    private static final String TAG = "DarkRoom";

    private Saf() {
    }

    /** Whether {@code name} already exists in the folder. False on any error. */
    public static boolean exists(Context context, String tree, String name) {
        try {
            return find(context.getContentResolver(), Uri.parse(tree), name) != null;
        } catch (RuntimeException e) {
            Log.w(TAG, "checking " + name + " in " + tree, e);
            return false;
        }
    }

    /**
     * Write {@code bytes} as {@code name} in the folder, replacing a file of
     * that name when {@code replace} is set.
     *
     * @return the name the file has in the folder — the provider may have
     *         added " (1)" — or null on failure, with the reason in the log.
     */
    public static String write(Context context, String tree, String name, String mime,
            byte[] bytes, boolean replace) {
        ContentResolver resolver = context.getContentResolver();
        Uri treeUri = Uri.parse(tree);
        try {
            Uri target = replace ? find(resolver, treeUri, name) : null;
            if (target == null) {
                Uri folder = DocumentsContract.buildDocumentUriUsingTree(treeUri,
                        DocumentsContract.getTreeDocumentId(treeUri));
                target = DocumentsContract.createDocument(resolver, folder, mime, name);
            }
            if (target == null) {
                Log.w(TAG, "the folder refused to create " + name + " in " + tree);
                return null;
            }
            // "wt": truncate. A replacement shorter than what it replaces
            // must not keep the old file's tail.
            try (OutputStream out = resolver.openOutputStream(target, "wt")) {
                if (out == null) {
                    Log.w(TAG, "no stream for " + target);
                    return null;
                }
                out.write(bytes);
            }
            String written = displayName(resolver, target);
            return written != null ? written : name;
        } catch (IOException | RuntimeException e) {
            Log.w(TAG, "writing " + name + " to " + tree, e);
            return null;
        }
    }

    /** The document for {@code name} directly in the tree's folder, or null. */
    private static Uri find(ContentResolver resolver, Uri tree, String name) {
        String folderId = DocumentsContract.getTreeDocumentId(tree);
        Uri children = DocumentsContract.buildChildDocumentsUriUsingTree(tree, folderId);
        String[] columns = {
                DocumentsContract.Document.COLUMN_DOCUMENT_ID,
                DocumentsContract.Document.COLUMN_DISPLAY_NAME,
        };
        try (Cursor c = resolver.query(children, columns, null, null, null)) {
            if (c == null) {
                return null;
            }
            while (c.moveToNext()) {
                if (name.equals(c.getString(1))) {
                    return DocumentsContract.buildDocumentUriUsingTree(tree, c.getString(0));
                }
            }
        }
        return null;
    }

    private static String displayName(ContentResolver resolver, Uri document) {
        String[] columns = {DocumentsContract.Document.COLUMN_DISPLAY_NAME};
        try (Cursor c = resolver.query(document, columns, null, null, null)) {
            if (c != null && c.moveToFirst()) {
                return c.getString(0);
            }
        } catch (RuntimeException e) {
            Log.w(TAG, "reading the name of " + document, e);
        }
        return null;
    }
}