/*
 * Copyright 2022 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 androidx.appsearch.app;

import android.os.Parcel;
import android.os.Parcelable;

import androidx.annotation.IntDef;
import androidx.annotation.NonNull;
import androidx.annotation.RestrictTo;
import androidx.appsearch.annotation.CanIgnoreReturnValue;
import androidx.appsearch.flags.FlaggedApi;
import androidx.appsearch.flags.Flags;
import androidx.appsearch.safeparcel.AbstractSafeParcelable;
import androidx.appsearch.safeparcel.SafeParcelable;
import androidx.appsearch.safeparcel.stub.StubCreators.JoinSpecCreator;
import androidx.core.util.Preconditions;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.Objects;

/**
 * This class represents the specifications for the joining operation in search.
 *
 * <p> Joins are only possible for matching on the qualified id of an outer document and a
 * property value within a subquery document. In the subquery documents, these values may be
 * referred to with a property path such as "email.recipient.id" or "entityId" or a property
 * expression. One such property expression is "this.qualifiedId()", which refers to the
 * document's combined package, database, namespace, and id.
 *
 * <p>Note that in order for perform the join, the property referred to by
 * {@link #getChildPropertyExpression} has to be a property with
 * {@link AppSearchSchema.StringPropertyConfig#getJoinableValueType} set to
 * {@link AppSearchSchema.StringPropertyConfig#JOINABLE_VALUE_TYPE_QUALIFIED_ID}. Otherwise no
 * documents will be joined to any {@link SearchResult}.
 *
 * <p> Take these outer query and subquery results for example:
 *
 * <pre>{@code
 * Outer result {
 *   id: id1
 *   score: 5
 * }
 * Subquery result 1 {
 *   id: id2
 *   score: 2
 *   entityId: pkg$db/ns#id1
 *   notes: This is some doc
 * }
 * Subquery result 2 {
 *   id: id3
 *   score: 3
 *   entityId: pkg$db/ns#id2
 *   notes: This is another doc
 * }
 * }</pre>
 *
 * <p> In this example, subquery result 1 contains a property "entityId" whose value is
 * "pkg$db/ns#id1", referring to the outer result. If you call {@link Builder} with "entityId", we
 * will retrieve the value of the property "entityId" from the child document, which is
 * "pkg$db#ns/id1". Let's say the qualified id of the outer result is "pkg$db#ns/id1". This would
 * mean the subquery result 1 document will be matched to that parent document. This is done by
 * adding a {@link SearchResult} containing the child document to the top-level parent
 * {@link SearchResult#getJoinedResults}.
 *
 * <p> If {@link #getChildPropertyExpression} is "notes", we will check the values of the notes
 * property in the subquery results. In subquery result 1, this values is "This is some doc", which
 * does not equal the qualified id of the outer query result. As such, subquery result 1 will not be
 * joined to the outer query result.
 *
 * <p> It's possible to define an advanced ranking strategy in the nested {@link SearchSpec} and
 * also use {@link SearchSpec#RANKING_STRATEGY_JOIN_AGGREGATE_SCORE} in the outer
 * {@link SearchSpec}. In this case, the parents will be ranked based on an aggregation, such as
 * the sum, of the signals calculated by scoring the joined documents with the advanced ranking
 * strategy.
 *
 * <p> In terms of scoring, if {@link SearchSpec#RANKING_STRATEGY_JOIN_AGGREGATE_SCORE} is set in
 * {@link SearchSpec#getRankingStrategy}, the scores of the outer SearchResults can be influenced
 * by the ranking signals of the subquery results. For example, if the
 * {@link JoinSpec#getAggregationScoringStrategy} is set to:
 * <ul><li>
 * {@link JoinSpec#AGGREGATION_SCORING_MIN_RANKING_SIGNAL}, the ranking signal of the outer
 * {@link SearchResult} will be set to the minimum of the ranking signals of the subquery results.
 * In this case, it will be the minimum of 2 and 3, which is 2.
 * </li>
 * <li>
 * {@link JoinSpec#AGGREGATION_SCORING_MAX_RANKING_SIGNAL}, the ranking signal of the outer
 * {@link SearchResult} will be 3.
 * </li>
 * <li>
 * {@link JoinSpec#AGGREGATION_SCORING_AVG_RANKING_SIGNAL}, the ranking signal of the outer
 * {@link SearchResult} will be 2.5.
 * </li>
 * <li>
 * {@link JoinSpec#AGGREGATION_SCORING_RESULT_COUNT}, the ranking signal of the outer
 * {@link SearchResult} will be 2 as there are two joined results.
 * </li>
 * <li>
 * {@link JoinSpec#AGGREGATION_SCORING_SUM_RANKING_SIGNAL}, the ranking signal of the outer
 * {@link SearchResult} will be 5, the sum of 2 and 3.
 * </li>
 * <li>
 * {@link JoinSpec#AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL}, the ranking signal of the outer
 * {@link SearchResult} will stay as it is.
 * </li>
 * </ul>
 *
 * <p> Referring to "this.childrenRankingSignals()" in the ranking signal of the outer query will
 * return the signals calculated by scoring the joined documents using the scoring strategy in the
 * nested {@link SearchSpec}, as in {@link SearchResult#getRankingSignal}.
 */
@SafeParcelable.Class(creator = "JoinSpecCreator")
@SuppressWarnings("HiddenSuperclass")
public final class JoinSpec extends AbstractSafeParcelable {
    /** Creator class for {@link JoinSpec}. */
    @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
    @FlaggedApi(Flags.FLAG_ENABLE_SAFE_PARCELABLE_2)
    @NonNull
    public static final Parcelable.Creator<JoinSpec> CREATOR = new JoinSpecCreator();

    @Field(id = 1, getter = "getNestedQuery")
    private final String mNestedQuery;

    @Field(id = 2, getter = "getNestedSearchSpec")
    private final SearchSpec mNestedSearchSpec;

    @Field(id = 3, getter = "getChildPropertyExpression")
    private final String mChildPropertyExpression;

    @Field(id = 4, getter = "getMaxJoinedResultCount")
    private final int mMaxJoinedResultCount;

    @Field(id = 5, getter = "getAggregationScoringStrategy")
    private final int mAggregationScoringStrategy;

    private static final int DEFAULT_MAX_JOINED_RESULT_COUNT = 10;

    /**
     * A property expression referring to the combined package name, database name, namespace, and
     * id of the document.
     *
     * <p> For instance, if a document with an id of "id1" exists in the namespace "ns" within
     * the database "db" created by package "pkg", this would evaluate to "pkg$db/ns#id1".
     *
     * <!--@exportToFramework:hide-->
     */
    @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
    public static final String QUALIFIED_ID = "this.qualifiedId()";

    /**
     * Aggregation scoring strategy for join spec.
     *
     * @exportToFramework:hide
     */
    // NOTE: The integer values of these constants must match the proto enum constants in
    // {@link JoinSpecProto.AggregationScoreStrategy.Code}
    @IntDef(value = {
            AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL,
            AGGREGATION_SCORING_RESULT_COUNT,
            AGGREGATION_SCORING_MIN_RANKING_SIGNAL,
            AGGREGATION_SCORING_AVG_RANKING_SIGNAL,
            AGGREGATION_SCORING_MAX_RANKING_SIGNAL,
            AGGREGATION_SCORING_SUM_RANKING_SIGNAL
    })
    @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
    @Retention(RetentionPolicy.SOURCE)
    public @interface AggregationScoringStrategy {
    }

    /**
     * Do not score the aggregation of joined documents. This is for the case where we want to
     * perform a join, but keep the parent ranking signal.
     */
    public static final int AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL = 0;
    /** Score the aggregation of joined documents by counting the number of results. */
    public static final int AGGREGATION_SCORING_RESULT_COUNT = 1;
    /** Score the aggregation of joined documents using the smallest ranking signal. */
    public static final int AGGREGATION_SCORING_MIN_RANKING_SIGNAL = 2;
    /** Score the aggregation of joined documents using the average ranking signal. */
    public static final int AGGREGATION_SCORING_AVG_RANKING_SIGNAL = 3;
    /** Score the aggregation of joined documents using the largest ranking signal. */
    public static final int AGGREGATION_SCORING_MAX_RANKING_SIGNAL = 4;
    /** Score the aggregation of joined documents using the sum of ranking signal. */
    public static final int AGGREGATION_SCORING_SUM_RANKING_SIGNAL = 5;

    @Constructor
    JoinSpec(
            @Param(id = 1) @NonNull String nestedQuery,
            @Param(id = 2) @NonNull SearchSpec nestedSearchSpec,
            @Param(id = 3) @NonNull String childPropertyExpression,
            @Param(id = 4) int maxJoinedResultCount,
            @Param(id = 5) @AggregationScoringStrategy int aggregationScoringStrategy) {
        mNestedQuery = Objects.requireNonNull(nestedQuery);
        mNestedSearchSpec = Objects.requireNonNull(nestedSearchSpec);
        mChildPropertyExpression = Objects.requireNonNull(childPropertyExpression);
        mMaxJoinedResultCount = maxJoinedResultCount;
        mAggregationScoringStrategy = aggregationScoringStrategy;
    }


    /**
     * Returns the query to run on the joined documents.
     */
    @NonNull
    public String getNestedQuery() {
        return mNestedQuery;
    }

    /**
     * The property expression that is used to get values from child documents, returned from the
     * nested search. These values are then used to match them to parent documents. These are
     * analogous to foreign keys.
     *
     * @return the property expression to match in the child documents.
     * @see Builder
     */
    @NonNull
    public String getChildPropertyExpression() {
        return mChildPropertyExpression;
    }

    /**
     * Returns the max amount of {@link SearchResult} objects to return with the parent document,
     * with a default of 10 SearchResults.
     */
    public int getMaxJoinedResultCount() {
        return mMaxJoinedResultCount;
    }

    /**
     * Returns the search spec used to retrieve the joined documents.
     *
     * <p> If {@link Builder#setNestedSearch} is never called, this will return a {@link SearchSpec}
     * with all default values. This will match every document, as the nested search query will
     * be "" and no schema will be filtered out.
     */
    @NonNull
    public SearchSpec getNestedSearchSpec() {
        return mNestedSearchSpec;
    }

    /**
     * Gets the joined document list scoring strategy.
     *
     * <p> The default scoring strategy is {@link #AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL},
     * which specifies that the score of the outer parent document will be used.
     *
     * @see SearchSpec#RANKING_STRATEGY_JOIN_AGGREGATE_SCORE
     */
    @AggregationScoringStrategy
    public int getAggregationScoringStrategy() {
        return mAggregationScoringStrategy;
    }

    @Override
    @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
    @FlaggedApi(Flags.FLAG_ENABLE_SAFE_PARCELABLE_2)
    public void writeToParcel(@NonNull Parcel dest, int flags) {
        JoinSpecCreator.writeToParcel(this, dest, flags);
    }

    /** Builder for {@link JoinSpec objects}. */
    public static final class Builder {

        // The default nested SearchSpec.
        private static final SearchSpec EMPTY_SEARCH_SPEC = new SearchSpec.Builder().build();

        private String mNestedQuery = "";
        private SearchSpec mNestedSearchSpec = EMPTY_SEARCH_SPEC;
        private final String mChildPropertyExpression;
        private int mMaxJoinedResultCount = DEFAULT_MAX_JOINED_RESULT_COUNT;
        @AggregationScoringStrategy
        private int mAggregationScoringStrategy =
                AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL;

        /**
         * Create a specification for the joining operation in search.
         *
         * <p> The child property expressions Specifies how to join documents. Documents with
         * a child property expression equal to the qualified id of the parent will be retrieved.
         *
         * <p> Property expressions differ from {@link PropertyPath} as property expressions may
         * refer to document properties or nested document properties such as "person.business.id"
         * as well as a property expression. Currently the only property expression is
         * "this.qualifiedId()". {@link PropertyPath} objects may only reference document properties
         * and nested document properties.
         *
         * <p> In order to join a child document to a parent document, the child document must
         * contain the parent's qualified id at the property expression specified by this
         * method.
         *
         * @param childPropertyExpression the property to match in the child documents.
         */
        // TODO(b/256022027): Reword comments to reference either "expression" or "PropertyPath"
        //  once wording is finalized.
        // TODO(b/256022027): Add another method to allow providing PropertyPath objects as
        //  equality constraints.
        // TODO(b/256022027): Change to allow for multiple child property expressions if multiple
        //  parent property expressions get supported.
        public Builder(@NonNull String childPropertyExpression) {
            Preconditions.checkNotNull(childPropertyExpression);
            mChildPropertyExpression = childPropertyExpression;
        }

        /** @exportToFramework:hide */
        @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
        public Builder(@NonNull JoinSpec joinSpec) {
            Preconditions.checkNotNull(joinSpec);
            mNestedQuery = joinSpec.getNestedQuery();
            mNestedSearchSpec = joinSpec.getNestedSearchSpec();
            mChildPropertyExpression = joinSpec.getChildPropertyExpression();
            mMaxJoinedResultCount = joinSpec.getMaxJoinedResultCount();
            mAggregationScoringStrategy = joinSpec.getAggregationScoringStrategy();
        }

        /**
         * Sets the query and the SearchSpec for the documents being joined. This will score and
         * rank the joined documents as well as filter the joined documents.
         *
         * <p>If {@link SearchSpec#RANKING_STRATEGY_JOIN_AGGREGATE_SCORE} is set in
         * the outer {@link SearchSpec}, the resulting signals will be used to rank the parent
         * documents. Note that the aggregation strategy also needs to be set with
         * {@link JoinSpec.Builder#setAggregationScoringStrategy}, otherwise the default will be
         * {@link JoinSpec#AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL}, which will just use
         * the parent documents ranking signal.
         *
         * <p> If this method is never called, {@link JoinSpec#getNestedQuery} will return an empty
         * string, meaning we will join with every possible document that matches the equality
         * constraints and hasn't been filtered out by the type or namespace filters.
         *
         * @see JoinSpec#getNestedQuery
         * @see JoinSpec#getNestedSearchSpec
         */
        @SuppressWarnings("MissingGetterMatchingBuilder")
        // See getNestedQuery & getNestedSearchSpec
        @CanIgnoreReturnValue
        @NonNull
        public Builder setNestedSearch(@NonNull String nestedQuery,
                @NonNull SearchSpec nestedSearchSpec) {
            Preconditions.checkNotNull(nestedQuery);
            Preconditions.checkNotNull(nestedSearchSpec);
            mNestedQuery = nestedQuery;
            mNestedSearchSpec = nestedSearchSpec;

            return this;
        }

        /**
         * Sets the max amount of {@link SearchResults} to return with the parent document, with a
         * default of 10 SearchResults.
         *
         * <p>This does NOT limit the number of results that are joined with the parent
         * document for scoring. This means that, when set, only a maximum of
         * {@code maxJoinedResultCount} results will be returned with each parent document, but
         * all results that are joined with a parent will factor into the score.
         */
        @CanIgnoreReturnValue
        @NonNull
        public Builder setMaxJoinedResultCount(int maxJoinedResultCount) {
            mMaxJoinedResultCount = maxJoinedResultCount;
            return this;
        }

        /**
         * Sets how we derive a single score from a list of joined documents.
         *
         * <p> The default scoring strategy is
         * {@link #AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL}, which specifies that the
         * ranking signal of the outer parent document will be used.
         *
         * @see SearchSpec#RANKING_STRATEGY_JOIN_AGGREGATE_SCORE
         */
        @CanIgnoreReturnValue
        @NonNull
        public Builder setAggregationScoringStrategy(
                @AggregationScoringStrategy int aggregationScoringStrategy) {
            Preconditions.checkArgumentInRange(aggregationScoringStrategy,
                    AGGREGATION_SCORING_OUTER_RESULT_RANKING_SIGNAL,
                    AGGREGATION_SCORING_SUM_RANKING_SIGNAL, "aggregationScoringStrategy");
            mAggregationScoringStrategy = aggregationScoringStrategy;
            return this;
        }

        /**
         * Constructs a new {@link JoinSpec} from the contents of this builder.
         */
        @NonNull
        public JoinSpec build() {
            return new JoinSpec(
                    mNestedQuery,
                    mNestedSearchSpec,
                    mChildPropertyExpression,
                    mMaxJoinedResultCount,
                    mAggregationScoringStrategy
            );
        }
    }
}