/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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 android.view.textclassifier;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.graphics.drawable.Drawable;
import android.net.Uri;
import android.os.LocaleList;
import android.os.ParcelFileDescriptor;
import android.provider.Browser;
import android.provider.Settings;
import android.text.Spannable;
import android.text.TextUtils;
import android.text.method.WordIterator;
import android.text.style.ClickableSpan;
import android.text.util.Linkify;
import android.util.Log;
import android.util.Patterns;
import android.view.View;
import android.widget.TextViewMetrics;

import com.android.internal.annotations.GuardedBy;
import com.android.internal.logging.MetricsLogger;
import com.android.internal.util.Preconditions;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.text.BreakIterator;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Default implementation of the {@link TextClassifier} interface.
 *
 * <p>This class uses machine learning to recognize entities in text.
 * Unless otherwise stated, methods of this class are blocking operations and should most
 * likely not be called on the UI thread.
 *
 * @hide
 */
final class TextClassifierImpl implements TextClassifier {

    private static final String LOG_TAG = DEFAULT_LOG_TAG;
    private static final String MODEL_DIR = "/etc/textclassifier/";
    private static final String MODEL_FILE_REGEX = "textclassifier\\.smartselection\\.(.*)\\.model";
    private static final String UPDATED_MODEL_FILE_PATH =
            "/data/misc/textclassifier/textclassifier.smartselection.model";

    private final Context mContext;

    private final MetricsLogger mMetricsLogger = new MetricsLogger();

    private final Object mSmartSelectionLock = new Object();
    @GuardedBy("mSmartSelectionLock") // Do not access outside this lock.
    private Map<Locale, String> mModelFilePaths;
    @GuardedBy("mSmartSelectionLock") // Do not access outside this lock.
    private Locale mLocale;
    @GuardedBy("mSmartSelectionLock") // Do not access outside this lock.
    private int mVersion;
    @GuardedBy("mSmartSelectionLock") // Do not access outside this lock.
    private SmartSelection mSmartSelection;

    private TextClassifierConstants mSettings;

    TextClassifierImpl(Context context) {
        mContext = Preconditions.checkNotNull(context);
    }

    @Override
    public TextSelection suggestSelection(
            @NonNull CharSequence text, int selectionStartIndex, int selectionEndIndex,
            @Nullable LocaleList defaultLocales) {
        validateInput(text, selectionStartIndex, selectionEndIndex);
        try {
            if (text.length() > 0) {
                final SmartSelection smartSelection = getSmartSelection(defaultLocales);
                final String string = text.toString();
                final int[] startEnd = smartSelection.suggest(
                        string, selectionStartIndex, selectionEndIndex);
                final int start = startEnd[0];
                final int end = startEnd[1];
                if (start <= end
                        && start >= 0 && end <= string.length()
                        && start <= selectionStartIndex && end >= selectionEndIndex) {
                    final TextSelection.Builder tsBuilder = new TextSelection.Builder(start, end);
                    final SmartSelection.ClassificationResult[] results =
                            smartSelection.classifyText(
                                    string, start, end,
                                    getHintFlags(string, start, end));
                    final int size = results.length;
                    for (int i = 0; i < size; i++) {
                        tsBuilder.setEntityType(results[i].mCollection, results[i].mScore);
                    }
                    return tsBuilder
                            .setLogSource(LOG_TAG)
                            .setVersionInfo(getVersionInfo())
                            .build();
                } else {
                    // We can not trust the result. Log the issue and ignore the result.
                    Log.d(LOG_TAG, "Got bad indices for input text. Ignoring result.");
                }
            }
        } catch (Throwable t) {
            // Avoid throwing from this method. Log the error.
            Log.e(LOG_TAG,
                    "Error suggesting selection for text. No changes to selection suggested.",
                    t);
        }
        // Getting here means something went wrong, return a NO_OP result.
        return TextClassifier.NO_OP.suggestSelection(
                text, selectionStartIndex, selectionEndIndex, defaultLocales);
    }

    @Override
    public TextClassification classifyText(
            @NonNull CharSequence text, int startIndex, int endIndex,
            @Nullable LocaleList defaultLocales) {
        validateInput(text, startIndex, endIndex);
        try {
            if (text.length() > 0) {
                final String string = text.toString();
                SmartSelection.ClassificationResult[] results = getSmartSelection(defaultLocales)
                        .classifyText(string, startIndex, endIndex,
                                getHintFlags(string, startIndex, endIndex));
                if (results.length > 0) {
                    final TextClassification classificationResult =
                            createClassificationResult(
                                    results, string.subSequence(startIndex, endIndex));
                    return classificationResult;
                }
            }
        } catch (Throwable t) {
            // Avoid throwing from this method. Log the error.
            Log.e(LOG_TAG, "Error getting assist info.", t);
        }
        // Getting here means something went wrong, return a NO_OP result.
        return TextClassifier.NO_OP.classifyText(
                text, startIndex, endIndex, defaultLocales);
    }

    @Override
    public LinksInfo getLinks(
            @NonNull CharSequence text, int linkMask, @Nullable LocaleList defaultLocales) {
        Preconditions.checkArgument(text != null);
        try {
            return LinksInfoFactory.create(
                    mContext, getSmartSelection(defaultLocales), text.toString(), linkMask);
        } catch (Throwable t) {
            // Avoid throwing from this method. Log the error.
            Log.e(LOG_TAG, "Error getting links info.", t);
        }
        // Getting here means something went wrong, return a NO_OP result.
        return TextClassifier.NO_OP.getLinks(text, linkMask, defaultLocales);
    }

    @Override
    public void logEvent(String source, String event) {
        if (LOG_TAG.equals(source)) {
            mMetricsLogger.count(event, 1);
        }
    }

    @Override
    public TextClassifierConstants getSettings() {
        if (mSettings == null) {
            mSettings = TextClassifierConstants.loadFromString(Settings.Global.getString(
                    mContext.getContentResolver(), Settings.Global.TEXT_CLASSIFIER_CONSTANTS));
        }
        return mSettings;
    }

    private SmartSelection getSmartSelection(LocaleList localeList) throws FileNotFoundException {
        synchronized (mSmartSelectionLock) {
            localeList = localeList == null ? LocaleList.getEmptyLocaleList() : localeList;
            final Locale locale = findBestSupportedLocaleLocked(localeList);
            if (locale == null) {
                throw new FileNotFoundException("No file for null locale");
            }
            if (mSmartSelection == null || !Objects.equals(mLocale, locale)) {
                destroySmartSelectionIfExistsLocked();
                final ParcelFileDescriptor fd = getFdLocked(locale);
                mSmartSelection = new SmartSelection(fd.getFd());
                closeAndLogError(fd);
                mLocale = locale;
            }
            return mSmartSelection;
        }
    }

    @NonNull
    private String getVersionInfo() {
        synchronized (mSmartSelectionLock) {
            if (mLocale != null) {
                return String.format("%s_v%d", mLocale.toLanguageTag(), mVersion);
            }
            return "";
        }
    }

    @GuardedBy("mSmartSelectionLock") // Do not call outside this lock.
    private ParcelFileDescriptor getFdLocked(Locale locale) throws FileNotFoundException {
        ParcelFileDescriptor updateFd;
        try {
            updateFd = ParcelFileDescriptor.open(
                    new File(UPDATED_MODEL_FILE_PATH), ParcelFileDescriptor.MODE_READ_ONLY);
        } catch (FileNotFoundException e) {
            updateFd = null;
        }
        ParcelFileDescriptor factoryFd;
        try {
            final String factoryModelFilePath = getFactoryModelFilePathsLocked().get(locale);
            if (factoryModelFilePath != null) {
                factoryFd = ParcelFileDescriptor.open(
                        new File(factoryModelFilePath), ParcelFileDescriptor.MODE_READ_ONLY);
            } else {
                factoryFd = null;
            }
        } catch (FileNotFoundException e) {
            factoryFd = null;
        }

        if (updateFd == null) {
            if (factoryFd != null) {
                return factoryFd;
            } else {
                throw new FileNotFoundException(
                        String.format("No model file found for %s", locale));
            }
        }

        final int updateFdInt = updateFd.getFd();
        final boolean localeMatches = Objects.equals(
                locale.getLanguage().trim().toLowerCase(),
                SmartSelection.getLanguage(updateFdInt).trim().toLowerCase());
        if (factoryFd == null) {
            if (localeMatches) {
                return updateFd;
            } else {
                closeAndLogError(updateFd);
                throw new FileNotFoundException(
                        String.format("No model file found for %s", locale));
            }
        }

        if (!localeMatches) {
            closeAndLogError(updateFd);
            return factoryFd;
        }

        final int updateVersion = SmartSelection.getVersion(updateFdInt);
        final int factoryVersion = SmartSelection.getVersion(factoryFd.getFd());
        if (updateVersion > factoryVersion) {
            closeAndLogError(factoryFd);
            mVersion = updateVersion;
            return updateFd;
        } else {
            closeAndLogError(updateFd);
            mVersion = factoryVersion;
            return factoryFd;
        }
    }

    @GuardedBy("mSmartSelectionLock") // Do not call outside this lock.
    private void destroySmartSelectionIfExistsLocked() {
        if (mSmartSelection != null) {
            mSmartSelection.close();
            mSmartSelection = null;
        }
    }

    @GuardedBy("mSmartSelectionLock") // Do not call outside this lock.
    @Nullable
    private Locale findBestSupportedLocaleLocked(LocaleList localeList) {
        // Specified localeList takes priority over the system default, so it is listed first.
        final String languages = localeList.isEmpty()
                ? LocaleList.getDefault().toLanguageTags()
                : localeList.toLanguageTags() + "," + LocaleList.getDefault().toLanguageTags();
        final List<Locale.LanguageRange> languageRangeList = Locale.LanguageRange.parse(languages);

        final List<Locale> supportedLocales =
                new ArrayList<>(getFactoryModelFilePathsLocked().keySet());
        final Locale updatedModelLocale = getUpdatedModelLocale();
        if (updatedModelLocale != null) {
            supportedLocales.add(updatedModelLocale);
        }
        return Locale.lookup(languageRangeList, supportedLocales);
    }

    @GuardedBy("mSmartSelectionLock") // Do not call outside this lock.
    private Map<Locale, String> getFactoryModelFilePathsLocked() {
        if (mModelFilePaths == null) {
            final Map<Locale, String> modelFilePaths = new HashMap<>();
            final File modelsDir = new File(MODEL_DIR);
            if (modelsDir.exists() && modelsDir.isDirectory()) {
                final File[] models = modelsDir.listFiles();
                final Pattern modelFilenamePattern = Pattern.compile(MODEL_FILE_REGEX);
                final int size = models.length;
                for (int i = 0; i < size; i++) {
                    final File modelFile = models[i];
                    final Matcher matcher = modelFilenamePattern.matcher(modelFile.getName());
                    if (matcher.matches() && modelFile.isFile()) {
                        final String language = matcher.group(1);
                        final Locale locale = Locale.forLanguageTag(language);
                        modelFilePaths.put(locale, modelFile.getAbsolutePath());
                    }
                }
            }
            mModelFilePaths = modelFilePaths;
        }
        return mModelFilePaths;
    }

    @Nullable
    private Locale getUpdatedModelLocale() {
        try {
            final ParcelFileDescriptor updateFd = ParcelFileDescriptor.open(
                    new File(UPDATED_MODEL_FILE_PATH), ParcelFileDescriptor.MODE_READ_ONLY);
            final Locale locale = Locale.forLanguageTag(
                    SmartSelection.getLanguage(updateFd.getFd()));
            closeAndLogError(updateFd);
            return locale;
        } catch (FileNotFoundException e) {
            return null;
        }
    }

    private TextClassification createClassificationResult(
            SmartSelection.ClassificationResult[] classifications, CharSequence text) {
        final TextClassification.Builder builder = new TextClassification.Builder()
                .setText(text.toString());

        final int size = classifications.length;
        for (int i = 0; i < size; i++) {
            builder.setEntityType(classifications[i].mCollection, classifications[i].mScore);
        }

        final String type = getHighestScoringType(classifications);
        builder.setLogType(IntentFactory.getLogType(type));

        final Intent intent = IntentFactory.create(mContext, type, text.toString());
        final PackageManager pm;
        final ResolveInfo resolveInfo;
        if (intent != null) {
            pm = mContext.getPackageManager();
            resolveInfo = pm.resolveActivity(intent, 0);
        } else {
            pm = null;
            resolveInfo = null;
        }
        if (resolveInfo != null && resolveInfo.activityInfo != null) {
            builder.setIntent(intent)
                    .setOnClickListener(TextClassification.createStartActivityOnClickListener(
                            mContext, intent));

            final String packageName = resolveInfo.activityInfo.packageName;
            if ("android".equals(packageName)) {
                // Requires the chooser to find an activity to handle the intent.
                builder.setLabel(IntentFactory.getLabel(mContext, type));
            } else {
                // A default activity will handle the intent.
                intent.setComponent(new ComponentName(packageName, resolveInfo.activityInfo.name));
                Drawable icon = resolveInfo.activityInfo.loadIcon(pm);
                if (icon == null) {
                    icon = resolveInfo.loadIcon(pm);
                }
                builder.setIcon(icon);
                CharSequence label = resolveInfo.activityInfo.loadLabel(pm);
                if (label == null) {
                    label = resolveInfo.loadLabel(pm);
                }
                builder.setLabel(label != null ? label.toString() : null);
            }
        }
        return builder.setVersionInfo(getVersionInfo()).build();
    }

    private static int getHintFlags(CharSequence text, int start, int end) {
        int flag = 0;
        final CharSequence subText = text.subSequence(start, end);
        if (Patterns.AUTOLINK_EMAIL_ADDRESS.matcher(subText).matches()) {
            flag |= SmartSelection.HINT_FLAG_EMAIL;
        }
        if (Patterns.AUTOLINK_WEB_URL.matcher(subText).matches()
                && Linkify.sUrlMatchFilter.acceptMatch(text, start, end)) {
            flag |= SmartSelection.HINT_FLAG_URL;
        }
        return flag;
    }

    private static String getHighestScoringType(SmartSelection.ClassificationResult[] types) {
        if (types.length < 1) {
            return "";
        }

        String type = types[0].mCollection;
        float highestScore = types[0].mScore;
        final int size = types.length;
        for (int i = 1; i < size; i++) {
            if (types[i].mScore > highestScore) {
                type = types[i].mCollection;
                highestScore = types[i].mScore;
            }
        }
        return type;
    }

    /**
     * Closes the ParcelFileDescriptor and logs any errors that occur.
     */
    private static void closeAndLogError(ParcelFileDescriptor fd) {
        try {
            fd.close();
        } catch (IOException e) {
            Log.e(LOG_TAG, "Error closing file.", e);
        }
    }

    /**
     * @throws IllegalArgumentException if text is null; startIndex is negative;
     *      endIndex is greater than text.length() or is not greater than startIndex
     */
    private static void validateInput(@NonNull CharSequence text, int startIndex, int endIndex) {
        Preconditions.checkArgument(text != null);
        Preconditions.checkArgument(startIndex >= 0);
        Preconditions.checkArgument(endIndex <= text.length());
        Preconditions.checkArgument(endIndex > startIndex);
    }

    /**
     * Detects and creates links for specified text.
     */
    private static final class LinksInfoFactory {

        private LinksInfoFactory() {}

        public static LinksInfo create(
                Context context, SmartSelection smartSelection, String text, int linkMask) {
            final WordIterator wordIterator = new WordIterator();
            wordIterator.setCharSequence(text, 0, text.length());
            final List<SpanSpec> spans = new ArrayList<>();
            int start = 0;
            int end;
            while ((end = wordIterator.nextBoundary(start)) != BreakIterator.DONE) {
                final String token = text.substring(start, end);
                if (TextUtils.isEmpty(token)) {
                    continue;
                }

                final int[] selection = smartSelection.suggest(text, start, end);
                final int selectionStart = selection[0];
                final int selectionEnd = selection[1];
                if (selectionStart >= 0 && selectionEnd <= text.length()
                        && selectionStart <= selectionEnd) {
                    final SmartSelection.ClassificationResult[] results =
                            smartSelection.classifyText(
                                    text, selectionStart, selectionEnd,
                                    getHintFlags(text, selectionStart, selectionEnd));
                    if (results.length > 0) {
                        final String type = getHighestScoringType(results);
                        if (matches(type, linkMask)) {
                            final Intent intent = IntentFactory.create(
                                    context, type, text.substring(selectionStart, selectionEnd));
                            if (hasActivityHandler(context, intent)) {
                                final ClickableSpan span = createSpan(context, intent);
                                spans.add(new SpanSpec(selectionStart, selectionEnd, span));
                            }
                        }
                    }
                }
                start = end;
            }
            return new LinksInfoImpl(text, avoidOverlaps(spans, text));
        }

        /**
         * Returns true if the classification type matches the specified linkMask.
         */
        private static boolean matches(String type, int linkMask) {
            type = type.trim().toLowerCase(Locale.ENGLISH);
            if ((linkMask & Linkify.PHONE_NUMBERS) != 0
                    && TextClassifier.TYPE_PHONE.equals(type)) {
                return true;
            }
            if ((linkMask & Linkify.EMAIL_ADDRESSES) != 0
                    && TextClassifier.TYPE_EMAIL.equals(type)) {
                return true;
            }
            if ((linkMask & Linkify.MAP_ADDRESSES) != 0
                    && TextClassifier.TYPE_ADDRESS.equals(type)) {
                return true;
            }
            if ((linkMask & Linkify.WEB_URLS) != 0
                    && TextClassifier.TYPE_URL.equals(type)) {
                return true;
            }
            return false;
        }

        /**
         * Trim the number of spans so that no two spans overlap.
         *
         * This algorithm first ensures that there is only one span per start index, then it
         * makes sure that no two spans overlap.
         */
        private static List<SpanSpec> avoidOverlaps(List<SpanSpec> spans, String text) {
            Collections.sort(spans, Comparator.comparingInt(span -> span.mStart));
            // Group spans by start index. Take the longest span.
            final Map<Integer, SpanSpec> reps = new LinkedHashMap<>();  // order matters.
            final int size = spans.size();
            for (int i = 0; i < size; i++) {
                final SpanSpec span = spans.get(i);
                final LinksInfoFactory.SpanSpec rep = reps.get(span.mStart);
                if (rep == null || rep.mEnd < span.mEnd) {
                    reps.put(span.mStart, span);
                }
            }
            // Avoid span intersections. Take the longer span.
            final LinkedList<SpanSpec> result = new LinkedList<>();
            for (SpanSpec rep : reps.values()) {
                if (result.isEmpty()) {
                    result.add(rep);
                    continue;
                }

                final SpanSpec last = result.getLast();
                if (rep.mStart < last.mEnd) {
                    // Spans intersect. Use the one with characters.
                    if ((rep.mEnd - rep.mStart) > (last.mEnd - last.mStart)) {
                        result.set(result.size() - 1, rep);
                    }
                } else {
                    result.add(rep);
                }
            }
            return result;
        }

        private static ClickableSpan createSpan(final Context context, final Intent intent) {
            return new ClickableSpan() {
                // TODO: Style this span.
                @Override
                public void onClick(View widget) {
                    context.startActivity(intent);
                }
            };
        }

        private static boolean hasActivityHandler(Context context, @Nullable Intent intent) {
            if (intent == null) {
                return false;
            }
            final ResolveInfo resolveInfo = context.getPackageManager().resolveActivity(intent, 0);
            return resolveInfo != null && resolveInfo.activityInfo != null;
        }

        /**
         * Implementation of LinksInfo that adds ClickableSpans to the specified text.
         */
        private static final class LinksInfoImpl implements LinksInfo {

            private final CharSequence mOriginalText;
            private final List<SpanSpec> mSpans;

            LinksInfoImpl(CharSequence originalText, List<SpanSpec> spans) {
                mOriginalText = originalText;
                mSpans = spans;
            }

            @Override
            public boolean apply(@NonNull CharSequence text) {
                Preconditions.checkArgument(text != null);
                if (text instanceof Spannable && mOriginalText.toString().equals(text.toString())) {
                    Spannable spannable = (Spannable) text;
                    final int size = mSpans.size();
                    for (int i = 0; i < size; i++) {
                        final SpanSpec span = mSpans.get(i);
                        spannable.setSpan(span.mSpan, span.mStart, span.mEnd, 0);
                    }
                    return true;
                }
                return false;
            }
        }

        /**
         * Span plus its start and end index.
         */
        private static final class SpanSpec {

            private final int mStart;
            private final int mEnd;
            private final ClickableSpan mSpan;

            SpanSpec(int start, int end, ClickableSpan span) {
                mStart = start;
                mEnd = end;
                mSpan = span;
            }
        }
    }

    /**
     * Creates intents based on the classification type.
     */
    private static final class IntentFactory {

        private IntentFactory() {}

        @Nullable
        public static Intent create(Context context, String type, String text) {
            type = type.trim().toLowerCase(Locale.ENGLISH);
            text = text.trim();
            switch (type) {
                case TextClassifier.TYPE_EMAIL:
                    return new Intent(Intent.ACTION_SENDTO)
                            .setData(Uri.parse(String.format("mailto:%s", text)));
                case TextClassifier.TYPE_PHONE:
                    return new Intent(Intent.ACTION_DIAL)
                            .setData(Uri.parse(String.format("tel:%s", text)));
                case TextClassifier.TYPE_ADDRESS:
                    return new Intent(Intent.ACTION_VIEW)
                            .setData(Uri.parse(String.format("geo:0,0?q=%s", text)));
                case TextClassifier.TYPE_URL:
                    final String httpPrefix = "http://";
                    final String httpsPrefix = "https://";
                    if (text.toLowerCase().startsWith(httpPrefix)) {
                        text = httpPrefix + text.substring(httpPrefix.length());
                    } else if (text.toLowerCase().startsWith(httpsPrefix)) {
                        text = httpsPrefix + text.substring(httpsPrefix.length());
                    } else {
                        text = httpPrefix + text;
                    }
                    return new Intent(Intent.ACTION_VIEW, Uri.parse(text))
                            .putExtra(Browser.EXTRA_APPLICATION_ID, context.getPackageName());
                default:
                    return null;
            }
        }

        @Nullable
        public static String getLabel(Context context, String type) {
            type = type.trim().toLowerCase(Locale.ENGLISH);
            switch (type) {
                case TextClassifier.TYPE_EMAIL:
                    return context.getString(com.android.internal.R.string.email);
                case TextClassifier.TYPE_PHONE:
                    return context.getString(com.android.internal.R.string.dial);
                case TextClassifier.TYPE_ADDRESS:
                    return context.getString(com.android.internal.R.string.map);
                case TextClassifier.TYPE_URL:
                    return context.getString(com.android.internal.R.string.browse);
                default:
                    return null;
            }
        }

        @Nullable
        public static int getLogType(String type) {
            type = type.trim().toLowerCase(Locale.ENGLISH);
            switch (type) {
                case TextClassifier.TYPE_EMAIL:
                    return TextViewMetrics.SUBTYPE_ASSIST_MENU_ITEM_EMAIL;
                case TextClassifier.TYPE_PHONE:
                    return TextViewMetrics.SUBTYPE_ASSIST_MENU_ITEM_PHONE;
                case TextClassifier.TYPE_ADDRESS:
                    return TextViewMetrics.SUBTYPE_ASSIST_MENU_ITEM_ADDRESS;
                case TextClassifier.TYPE_URL:
                    return TextViewMetrics.SUBTYPE_ASSIST_MENU_ITEM_URL;
                default:
                    return TextViewMetrics.SUBTYPE_ASSIST_MENU_ITEM_OTHER;
            }
        }
    }
}