package paris.tourolle.darkroom;

import android.app.Activity;
import android.content.ActivityNotFoundException;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.webkit.WebResourceRequest;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;

/**
 * The manual that ships in the APK, shown in a WebView.
 *
 * <h2>Why an activity of our own rather than the browser</h2>
 *
 * <p>The desktop hands the manual to the system browser. Android leaves no
 * way to do the same: the page is an asset inside the APK, which is not a
 * file; an unpacked copy in app-private storage is a file no browser may
 * read; a {@code file:} URI handed to another app is refused since API 24;
 * and a {@code content:} URI serves the page but leaves the browser to fetch
 * every picture by a relative URL against the provider, which browsers do not
 * reliably do. A WebView reads {@code file:///android_asset/} straight from
 * the APK, pictures and section anchor included, and nothing is unpacked.
 *
 * <h2>What it is not</h2>
 *
 * <p>A browser. JavaScript stays off (the page has none), and a link that
 * leaves the manual — the design documents are on the forge — goes to the
 * user's browser rather than opening inside this view, so the only thing ever
 * shown here is the page the APK carries.
 *
 * <p>Started by {@code dr_ui::manual} with {@code Intent.setClassName}, so the
 * name here and there must agree; a test in lib.rs checks the manifest
 * declares it.
 */
public final class ManualActivity extends Activity {
    /** The section to open at, a heading's anchor. Absent opens the top. */
    public static final String EXTRA_ANCHOR = "anchor";

    private static final String PAGE = "file:///android_asset/manual/index.html";

    private WebView web;

    @Override
    protected void onCreate(Bundle saved) {
        super.onCreate(saved);
        setTitle("DarkRoom manual");

        web = new WebView(this);
        WebSettings settings = web.getSettings();
        settings.setJavaScriptEnabled(false);
        // Pinch to zoom into a screenshot, which is 1600 pixels wide and drawn
        // at the width of a phone.
        settings.setBuiltInZoomControls(true);
        settings.setDisplayZoomControls(false);
        web.setWebViewClient(new WebViewClient() {
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
                Uri uri = request.getUrl();
                if ("file".equals(uri.getScheme())) {
                    return false;
                }
                try {
                    startActivity(new Intent(Intent.ACTION_VIEW, uri));
                } catch (ActivityNotFoundException e) {
                    // No browser on the device: the link does nothing, which
                    // is all it could do.
                }
                return true;
            }
        });
        setContentView(web);

        if (saved != null) {
            web.restoreState(saved);
        } else {
            String anchor = getIntent().getStringExtra(EXTRA_ANCHOR);
            web.loadUrl(anchor == null || anchor.isEmpty() ? PAGE : PAGE + "#" + anchor);
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle out) {
        super.onSaveInstanceState(out);
        web.saveState(out);
    }

    /** Back walks back through the sections visited, then leaves. */
    @Override
    public void onBackPressed() {
        if (web.canGoBack()) {
            web.goBack();
        } else {
            super.onBackPressed();
        }
    }

    @Override
    protected void onDestroy() {
        web.destroy();
        super.onDestroy();
    }
}