// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package android.net.http;

import android.annotation.IntDef;
import android.annotation.SuppressLint;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.time.Duration;

/**
 * A class configuring the HTTP connection migration functionality.
 *
 * <p>Connection migration stops open connections to servers from being destroyed when the
 * client device switches its L4 connectivity (typically the IP address as a result of using
 * a different network). This is particularly common with mobile devices losing
 * wifi connectivity and switching to cellular data, or vice versa (a.k.a. the parking lot
 * problem). QUIC uses connection identifiers which are independent of the underlying
 * transport layer to make this possible. If the client connects to a new network and wants
 * to preserve the existing connection, they can do so by using a connection identifier the server
 * knows to be a continuation of the existing connection.
 *
 * <p>The features are only available for QUIC connections and the server needs to support
 * connection migration.
 *
 * @see <a href="https://www.rfc-editor.org/rfc/rfc9000.html#section-9">Connection
 *     Migration specification</a>
 */
// SuppressLint to be consistent with other cronet code
@SuppressLint("UserHandleName")
public class ConnectionMigrationOptions {
    private final @MigrationOptionState int mEnableDefaultNetworkMigration;
    private final @MigrationOptionState int mEnablePathDegradationMigration;
    @Nullable
    private final Boolean mAllowServerMigration;
    @Nullable
    private final Boolean mMigrateIdleConnections;
    @Nullable
    private final Duration mIdleMigrationPeriod;
    private final @MigrationOptionState int mAllowNonDefaultNetworkUsage;
    @Nullable
    private final Duration mMaxTimeOnNonDefaultNetwork;
    @Nullable
    private final Integer mMaxWriteErrorNonDefaultNetworkMigrationsCount;
    @Nullable
    private final Integer mMaxPathDegradingNonDefaultMigrationsCount;

    /**
     * Option is unspecified, platform default value will be used.
     */
    public static final int MIGRATION_OPTION_UNSPECIFIED = 0;

    /**
     * Option is enabled.
     */
    public static final int MIGRATION_OPTION_ENABLED = 1;

    /**
     * Option is disabled.
     */
    public static final int MIGRATION_OPTION_DISABLED = 2;

    /** @hide */
    @Retention(RetentionPolicy.SOURCE)
    @IntDef(flag = false, prefix = "MIGRATION_OPTION_", value = {
            MIGRATION_OPTION_UNSPECIFIED,
            MIGRATION_OPTION_ENABLED,
            MIGRATION_OPTION_DISABLED,
    })
    public @interface MigrationOptionState {}

    /**
     * See {@link Builder#setDefaultNetworkMigration(int)}
     */
    public @MigrationOptionState int getDefaultNetworkMigration() {
        return mEnableDefaultNetworkMigration;
    }

    /**
     * See {@link Builder#setPathDegradationMigration(int)}
     */
    public @MigrationOptionState int getPathDegradationMigration() {
        return mEnablePathDegradationMigration;
    }

    /**
     * See {@link Builder#setAllowNonDefaultNetworkUsage(int)}
     */
    public @MigrationOptionState int getAllowNonDefaultNetworkUsage() {
        return mAllowNonDefaultNetworkUsage;
    }

    ConnectionMigrationOptions(@NonNull Builder builder) {
        this.mEnableDefaultNetworkMigration = builder.mEnableDefaultNetworkMigration;
        this.mEnablePathDegradationMigration = builder.mEnablePathDegradationMigration;
        this.mAllowServerMigration = builder.mAllowServerMigration;
        this.mMigrateIdleConnections = builder.mMigrateIdleConnections;
        this.mIdleMigrationPeriod = builder.mIdleConnectionMigrationPeriod;
        this.mAllowNonDefaultNetworkUsage = builder.mAllowNonDefaultNetworkUsage;
        this.mMaxTimeOnNonDefaultNetwork = builder.mMaxTimeOnNonDefaultNetwork;
        this.mMaxWriteErrorNonDefaultNetworkMigrationsCount = builder.mMaxWriteErrorNonDefaultNetworkMigrationsCount;
        this.mMaxPathDegradingNonDefaultMigrationsCount = builder.mMaxPathDegradingNonDefaultMigrationsCount;
    }

    /**
     * Builder for {@link ConnectionMigrationOptions}.
     */
    public static final class Builder {
        private @MigrationOptionState int mEnableDefaultNetworkMigration;
        private @MigrationOptionState int mEnablePathDegradationMigration;
        @Nullable
        private Boolean mAllowServerMigration;
        @Nullable
        private Boolean mMigrateIdleConnections;
        @Nullable
        private Duration mIdleConnectionMigrationPeriod;
        private @MigrationOptionState int mAllowNonDefaultNetworkUsage;
        @Nullable
        private Duration mMaxTimeOnNonDefaultNetwork;
        @Nullable
        private Integer mMaxWriteErrorNonDefaultNetworkMigrationsCount;
        @Nullable
        private Integer mMaxPathDegradingNonDefaultMigrationsCount;

        public Builder() {}

        /**
         * Sets whether to enable the possibility of migrating connections on default network
         * change. If enabled, active QUIC connections will be migrated onto the new network when
         * the platform indicates that the default network is changing.
         *
         * @see <a href="https://developer.android.com/training/basics/network-ops/reading-network-state#listening-events">Android
         *     Network State</a>
         *
         * @param state one of the MIGRATION_OPTION_* values
         * @return this builder for chaining
         */
        @NonNull
        public Builder setDefaultNetworkMigration(@MigrationOptionState int state) {
            this.mEnableDefaultNetworkMigration = state;
            return this;
        }

        /**
         * Sets whether to enable the possibility of migrating connections if the current path is
         * performing poorly.
         *
         * <p>Depending on other configuration, this can result to migrating the connections within
         * the same default network, or to a non-default network.
         *
         * @param state one of the MIGRATION_OPTION_* values
         * @return this builder for chaining
         */
        @NonNull
        public Builder setPathDegradationMigration(@MigrationOptionState int state) {
            this.mEnablePathDegradationMigration = state;
            return this;
        }

        /**
         * Sets whether connections can be migrated to an alternate network when Cronet detects
         * a degradation of the path currently in use. Requires setting
         * {@link #setPathDegradationMigration(int)} to {@link #MIGRATION_OPTION_ENABLED} to
         * have any effect.
         *
         * <p>Note: This setting can result in requests being sent on non-default metered networks,
         * eating into the users' data budgets and incurring extra costs. Make sure you're using
         * metered networks sparingly.
         *
         * @param state one of the MIGRATION_OPTION_* values
         * @return this builder for chaining
         */
        @Experimental
        @NonNull
        public Builder setAllowNonDefaultNetworkUsage(@MigrationOptionState int state) {
            this.mAllowNonDefaultNetworkUsage = state;
            return this;
        }

        /**
         * Creates and returns the final {@link ConnectionMigrationOptions} instance, based on the
         * values in this builder.
         */
        @NonNull
        public ConnectionMigrationOptions build() {
            return new ConnectionMigrationOptions(this);
        }
    }

    /**
     * Creates a new builder for {@link ConnectionMigrationOptions}.
     *
     * {@hide}
     */
    @NonNull
    public static Builder builder() {
        return new Builder();
    }

    /**
     * An annotation for APIs which are not considered stable yet.
     *
     * <p>Applications using experimental APIs must acknowledge that they're aware of using APIs
     * that are not considered stable. The APIs might change functionality, break or cease to exist
     * without notice.
     *
     * <p>It's highly recommended to reach out to Cronet maintainers ({@code net-dev@chromium.org})
     * before using one of the APIs annotated as experimental outside of debugging
     * and proof-of-concept code. Be ready to help to help polishing the API, or for a "sorry,
     * really not production ready yet".
     *
     * <p>If you still want to use an experimental API in production, you're doing so at your
     * own risk. You have been warned.
     *
     * {@hide}
     */
    public @interface Experimental {}
}