/*
 * Copyright (C) 2012 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 com.android.imap2;

import android.content.Context;
import android.os.Build;
import android.telephony.TelephonyManager;
import android.util.Base64;
import android.util.Log;

import com.android.emailcommon.Device;
import com.android.emailcommon.Logging;
import com.android.emailcommon.VendorPolicyLoader;
import com.google.common.annotations.VisibleForTesting;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.regex.Pattern;

public class ImapId {
    private static String sImapId;

    /**
     * Return, or create and return, an string suitable for use in an IMAP ID message.
     * This is constructed similarly to the way the browser sets up its user-agent strings.
     * See RFC 2971 for more details.  The output of this command will be a series of key-value
     * pairs delimited by spaces (there is no point in returning a structured result because
     * this will be sent as-is to the IMAP server).  No tokens, parenthesis or "ID" are included,
     * because some connections may append additional values.
     *
     * The following IMAP ID keys may be included:
     *   name                   Android package name of the program
     *   os                     "android"
     *   os-version             "version; model; build-id"
     *   vendor                 Vendor of the client/server
     *   x-android-device-model Model (only revealed if release build)
     *   x-android-net-operator Mobile network operator (if known)
     *   AGUID                  A device+account UID
     *
     * In addition, a vendor policy .apk can append key/value pairs.
     *
     * @param userName the username of the account
     * @param host the host (server) of the account
     * @param capabilities a list of the capabilities from the server
     * @return a String for use in an IMAP ID message.
     */
    public static String getImapId(Context context, String userName, String host,
            String capabilities) {
        // The first section is global to all IMAP connections, and generates the fixed
        // values in any IMAP ID message
        synchronized (ImapId.class) {
            if (sImapId == null) {
                TelephonyManager tm =
                        (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
                String networkOperator = tm.getNetworkOperatorName();
                if (networkOperator == null) networkOperator = "";

                sImapId = makeCommonImapId(context.getPackageName(), Build.VERSION.RELEASE,
                        Build.VERSION.CODENAME, Build.MODEL, Build.ID, Build.MANUFACTURER,
                        networkOperator);
            }
        }

        // This section is per Store, and adds in a dynamic elements like UID's.
        // We don't cache the result of this work, because the caller does anyway.
        StringBuilder id = new StringBuilder(sImapId);

        // Optionally add any vendor-supplied id keys
        String vendorId = VendorPolicyLoader.getInstance(context).getImapIdValues(userName, host,
                capabilities);
        if (vendorId != null) {
            id.append(' ');
            id.append(vendorId);
        }

        // Generate a UID that mixes a "stable" device UID with the email address
        try {
            String devUID = Device.getConsistentDeviceId(context);
            MessageDigest messageDigest;
            messageDigest = MessageDigest.getInstance("SHA-1");
            messageDigest.update(userName.getBytes());
            messageDigest.update(devUID.getBytes());
            byte[] uid = messageDigest.digest();
            String hexUid = Base64.encodeToString(uid, Base64.NO_WRAP);
            id.append(" \"AGUID\" \"");
            id.append(hexUid);
            id.append('\"');
        } catch (NoSuchAlgorithmException e) {
            Log.d(Logging.LOG_TAG, "couldn't obtain SHA-1 hash for device UID");
        }
        return id.toString();
    }

    /**
     * Helper function that actually builds the static part of the IMAP ID string.  This is
     * separated from getImapId for testability.  There is no escaping or encoding in IMAP ID so
     * any rogue chars must be filtered here.
     *
     * @param packageName context.getPackageName()
     * @param version Build.VERSION.RELEASE
     * @param codeName Build.VERSION.CODENAME
     * @param model Build.MODEL
     * @param id Build.ID
     * @param vendor Build.MANUFACTURER
     * @param networkOperator TelephonyManager.getNetworkOperatorName()
     * @return the static (never changes) portion of the IMAP ID
     */
    @VisibleForTesting
    static String makeCommonImapId(String packageName, String version,
            String codeName, String model, String id, String vendor, String networkOperator) {

        // Before building up IMAP ID string, pre-filter the input strings for "legal" chars
        // This is using a fairly arbitrary char set intended to pass through most reasonable
        // version, model, and vendor strings: a-z A-Z 0-9 - _ + = ; : . , / <space>
        // The most important thing is *not* to pass parens, quotes, or CRLF, which would break
        // the format of the IMAP ID list.
        Pattern p = Pattern.compile("[^a-zA-Z0-9-_\\+=;:\\.,/ ]");
        packageName = p.matcher(packageName).replaceAll("");
        version = p.matcher(version).replaceAll("");
        codeName = p.matcher(codeName).replaceAll("");
        model = p.matcher(model).replaceAll("");
        id = p.matcher(id).replaceAll("");
        vendor = p.matcher(vendor).replaceAll("");
        networkOperator = p.matcher(networkOperator).replaceAll("");

        // "name" "com.android.email"
        StringBuffer sb = new StringBuffer("\"name\" \"");
        sb.append(packageName);
        sb.append("\"");

        // "os" "android"
        sb.append(" \"os\" \"android\"");

        // "os-version" "version; build-id"
        sb.append(" \"os-version\" \"");
        if (version.length() > 0) {
            sb.append(version);
        } else {
            // default to "1.0"
            sb.append("1.0");
        }
        // add the build ID or build #
        if (id.length() > 0) {
            sb.append("; ");
            sb.append(id);
        }
        sb.append("\"");

        // "vendor" "the vendor"
        if (vendor.length() > 0) {
            sb.append(" \"vendor\" \"");
            sb.append(vendor);
            sb.append("\"");
        }

        // "x-android-device-model" the device model (on release builds only)
        if ("REL".equals(codeName)) {
            if (model.length() > 0) {
                sb.append(" \"x-android-device-model\" \"");
                sb.append(model);
                sb.append("\"");
            }
        }

        // "x-android-mobile-net-operator" "name of network operator"
        if (networkOperator.length() > 0) {
            sb.append(" \"x-android-mobile-net-operator\" \"");
            sb.append(networkOperator);
            sb.append("\"");
        }

        return sb.toString();
    }

}