xref: /appsearch/appsearch/src/main/java/androidx/appsearch/app/AppSearchSession.java

/*
 * Copyright 2020 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.
 */
// @exportToFramework:skipFile()
package androidx.appsearch.app;

import android.annotation.SuppressLint;

import androidx.annotation.RequiresFeature;
import androidx.appsearch.flags.FlaggedApi;
import androidx.appsearch.flags.Flags;

import com.google.common.util.concurrent.ListenableFuture;

import org.jspecify.annotations.NonNull;

import java.io.Closeable;
import java.util.List;
import java.util.Set;

/**
 * Provides a connection to a single AppSearch database.
 *
 * <p>An {@link AppSearchSession} instance provides access to database operations such as setting
 * a schema, adding documents, and searching.
 *
 * <p>Instances of this interface are usually obtained from a storage implementation, e.g.
 * {@code LocalStorage.createSearchSessionAsync()} or
 * {@code PlatformStorage.createSearchSessionAsync()}.
 *
 * <p>All implementations of this interface must be thread safe.
 *
 * @see GlobalSearchSession
 */
public interface AppSearchSession extends Closeable {

    /**
     * Sets the schema that represents the organizational structure of data within the AppSearch
     * database.
     *
     * <p>Upon creating an {@link AppSearchSession}, {@link #setSchemaAsync} should be called. If
     * the schema needs to be updated, or it has not been previously set, then the provided schema
     * will be saved and persisted to disk. Otherwise, {@link #setSchemaAsync} is handled
     * efficiently as a no-op call.
     *
     * @param  request the schema to set or update the AppSearch database to.
     * @return a {@link ListenableFuture} which resolves to a {@link SetSchemaResponse} object.
     */
    @NonNull ListenableFuture<SetSchemaResponse> setSchemaAsync(@NonNull SetSchemaRequest request);

    /**
     * Retrieves the schema most recently successfully provided to {@link #setSchemaAsync}.
     *
     * @return The pending {@link GetSchemaResponse} of performing this operation.
     */
    // This call hits disk; async API prevents us from treating these calls as properties.
    @SuppressLint("KotlinPropertyAccess")
    @NonNull ListenableFuture<GetSchemaResponse> getSchemaAsync();

    /**
     * Retrieves the set of all namespaces in the current database with at least one document.
     *
     * @return The pending result of performing this operation. */
    @NonNull ListenableFuture<Set<String>> getNamespacesAsync();

    /**
     * Indexes documents into the {@link AppSearchSession} database.
     *
     * <p>Each {@link GenericDocument} object must have a {@code schemaType} field set to an
     * {@link AppSearchSchema} type that has been previously registered by calling the
     * {@link #setSchemaAsync} method.
     *
     * @param request containing documents to be indexed.
     * @return a {@link ListenableFuture} which resolves to an {@link AppSearchBatchResult}.
     * The keys of the returned {@link AppSearchBatchResult} are the IDs of the input documents.
     * The values are either {@code null} if the corresponding document was successfully indexed,
     * or a failed {@link AppSearchResult} otherwise.
     */
    @NonNull ListenableFuture<AppSearchBatchResult<String, Void>> putAsync(
            @NonNull PutDocumentsRequest request);

    /**
     * Gets {@link GenericDocument} objects by document IDs in a namespace from the
     * {@link AppSearchSession} database.
     *
     * @param request a request containing a namespace and IDs to get documents for.
     * @return A {@link ListenableFuture} which resolves to an {@link AppSearchBatchResult}.
     * The keys of the {@link AppSearchBatchResult} represent the input document IDs from the
     * {@link GetByDocumentIdRequest} object. The values are either the corresponding
     * {@link GenericDocument} object for the ID on success, or an {@link AppSearchResult}
     * object on failure. For example, if an ID is not found, the value for that ID will be set
     * to an {@link AppSearchResult} object with result code:
     * {@link AppSearchResult#RESULT_NOT_FOUND}.
     */
    @NonNull ListenableFuture<AppSearchBatchResult<String, GenericDocument>> getByDocumentIdAsync(
            @NonNull GetByDocumentIdRequest request);

    /**
     * Opens a batch of AppSearch Blobs for writing.
     *
     * <p>A "blob" is a large binary object. It is used to store a significant amount of data that
     * is not searchable, such as images, videos, audio files, or other binary data. Unlike other
     * fields in AppSearch, blobs are stored as blob files on disk rather than in memory, and use
     * {@link android.os.ParcelFileDescriptor} to read and write. This allows for efficient handling
     * of large, non-searchable content.
     *
     * <p> Once done writing, call {@link #commitBlobAsync} to commit blob files.
     *
     * <p> This call will create a empty blob file for each given {@link AppSearchBlobHandle}, and
     * a {@link android.os.ParcelFileDescriptor} of that blob file will be returned in the
     * {@link OpenBlobForWriteResponse}.
     *
     * <p> If the blob file is already stored in AppSearch and committed. A failed
     * {@link AppSearchResult} with error code {@link AppSearchResult#RESULT_ALREADY_EXISTS} will be
     * associated with the {@link AppSearchBlobHandle}.
     *
     * <p> If the blob file is already stored in AppSearch but not committed. A
     * {@link android.os.ParcelFileDescriptor} of that blob file will be returned for continue
     * writing.
     *
     * <p> For given duplicate {@link AppSearchBlobHandle}, the same
     * {@link android.os.ParcelFileDescriptor} pointing to the same blob file will be returned.
     *
     * <p> Pending blob files won't be lost or auto-commit if {@link AppSearchSession} closed.
     * Pending blob files will be stored in disk rather than memory. You can re-open
     * {@link AppSearchSession} and re-write the pending blob files.
     *
     * <p> A committed blob file will be considered as an orphan if no {@link GenericDocument}
     * references it. Uncommitted pending blob files and orphan blobs files will be cleaned up if
     * they has been created for an extended period (default is 1 week).
     *
     * <p> Both pending blob files and committed blob files can be manually removed via
     * {@link #removeBlobAsync}.
     *
     * <p class="caution">
     * The returned {@link OpenBlobForWriteResponse} must be closed after use to avoid
     * resource leaks. Failing to close it will result in system file descriptor exhaustion.
     * </p>
     *
     * @param handles The {@link AppSearchBlobHandle}s that identifies the blobs.
     * @return a response containing the writeable file descriptors.
     *
     * @see GenericDocument.Builder#setPropertyBlobHandle
     */
    @RequiresFeature(
            enforcement = "androidx.appsearch.app.Features#isFeatureSupported",
            name = Features.BLOB_STORAGE)
    @FlaggedApi(Flags.FLAG_ENABLE_BLOB_STORE)
    @ExperimentalAppSearchApi
    default @NonNull ListenableFuture<OpenBlobForWriteResponse> openBlobForWriteAsync(
            @NonNull Set<AppSearchBlobHandle> handles) {
        throw new UnsupportedOperationException(Features.BLOB_STORAGE
                + " is not available on this AppSearch implementation.");
    }

    /**
     * Removes the blob data from AppSearch.
     *
     * <p> After this call, the blob data is removed immediately and cannot be recovered. It will
     * not accessible via {@link #openBlobForReadAsync}. {@link #openBlobForWriteAsync} could reopen
     * and rewrite it.
     *
     * <p> This API can be used to remove pending blob data and committed blob data.
     *
     * <p class="caution">
     * Removing a committed blob data that is still referenced by documents will leave those
     * documents with no readable blob content. It is highly recommended to let AppSearch control
     * the blob data's life cycle. AppSearch automatically recycles orphaned and pending blob data.
     * The default time to recycle pending and orphan blob file is 1 week. A blob file will be
     * considered as an orphan if no {@link GenericDocument} references it. If you want to remove a
     * committed blob data, you should remove the reference documents first.
     * </p>
     *
     * @param handles The {@link AppSearchBlobHandle}s that identifies the blob data.
     * @return a response containing the remove results.
     */
    @RequiresFeature(
            enforcement = "androidx.appsearch.app.Features#isFeatureSupported",
            name = Features.BLOB_STORAGE)
    @FlaggedApi(Flags.FLAG_ENABLE_BLOB_STORE)
    @ExperimentalAppSearchApi
    default @NonNull ListenableFuture<RemoveBlobResponse> removeBlobAsync(
            @NonNull Set<AppSearchBlobHandle> handles) {
        throw new UnsupportedOperationException(Features.BLOB_STORAGE
                + " is not available on this AppSearch implementation.");
    }

    /**
     * Commits the blobs to make it retrievable and immutable.
     *
     * <p>After this call, the blob is readable via {@link #openBlobForReadAsync}. Any change to
     * the content or rewrite via {@link #openBlobForWriteAsync} of this blob won't be allowed.
     *
     * <p> If the blob is already stored in AppSearch and committed. A failed
     * {@link AppSearchResult} with error code {@link AppSearchResult#RESULT_ALREADY_EXISTS} will be
     * associated with the {@link AppSearchBlobHandle}.
     *
     * <p>If the blob content doesn't match the digest in {@link AppSearchBlobHandle}, a failed
     * {@link AppSearchResult} with error code {@link AppSearchResult#RESULT_INVALID_ARGUMENT} will
     * be associated with the {@link AppSearchBlobHandle}. The pending Blob file will be removed
     * from AppSearch.
     *
     * <p> Pending blobs won't be lost or auto-commit if {@link AppSearchSession} closed.
     * Pending blobs will store in disk rather than memory. You can re-open {@link AppSearchSession}
     * and re-write the pending blobs.
     *
     * <p> The default time to recycle pending and orphan blobs is 1 week. A blob will be considered
     * as an orphan if no {@link GenericDocument} references it.
     *
     * <p> Both pending blob files and committed blob files can be manually removed via
     * {@link #removeBlobAsync}.
     *
     * @param handles The {@link AppSearchBlobHandle}s that identifies the blobs.
     * @return a response containing the commit results.
     *
     * @see GenericDocument.Builder#setPropertyBlobHandle
     */
    @RequiresFeature(
            enforcement = "androidx.appsearch.app.Features#isFeatureSupported",
            name = Features.BLOB_STORAGE)
    @FlaggedApi(Flags.FLAG_ENABLE_BLOB_STORE)
    @ExperimentalAppSearchApi
    default @NonNull ListenableFuture<CommitBlobResponse> commitBlobAsync(
            @NonNull Set<AppSearchBlobHandle> handles) {
        throw new UnsupportedOperationException(Features.BLOB_STORAGE
                + " is not available on this AppSearch implementation.");
    }

    /**
     * Opens a batch of AppSearch Blobs for reading.
     *
     * <p> Only blobs committed via {@link #commitBlobAsync} are available for reading.
     *
     * <p class="caution">
     * The returned {@link OpenBlobForReadResponse} must be closed after use to avoid
     * resource leaks. Failing to close it will result in system file descriptor exhaustion.
     * </p>
     *
     * @param handles The {@link AppSearchBlobHandle}s that identifies the blobs.
     * @return a response containing the readable file descriptors.
     *
     * @see GenericDocument.Builder#setPropertyBlobHandle
     */
    @RequiresFeature(
            enforcement = "androidx.appsearch.app.Features#isFeatureSupported",
            name = Features.BLOB_STORAGE)
    @FlaggedApi(Flags.FLAG_ENABLE_BLOB_STORE)
    @ExperimentalAppSearchApi
    default @NonNull ListenableFuture<OpenBlobForReadResponse> openBlobForReadAsync(
            @NonNull Set<AppSearchBlobHandle> handles) {
        throw new UnsupportedOperationException(Features.BLOB_STORAGE
                + " is not available on this AppSearch implementation.");
    }

    /**
     * Sets the visibility configuration for all blob namespaces within an appsearch database.
     *
     * <p> Blobs under the same namespace will share same visibility settings.
     *
     * <p> The default setting is blobs will be only visible to the owner package and System. To
     * configure other kinds of sharing, set {@link SchemaVisibilityConfig} via
     * {@link SetBlobVisibilityRequest}.
     *
     * @param request The request holds visibility settings for all blob namespaces
     * @return The pending result of performing this operation which resolves to {@code null} on
     *     success.
     */
    @RequiresFeature(
            enforcement = "androidx.appsearch.app.Features#isFeatureSupported",
            name = Features.BLOB_STORAGE)
    @FlaggedApi(Flags.FLAG_ENABLE_BLOB_STORE)
    @ExperimentalAppSearchApi
    default @NonNull ListenableFuture<Void> setBlobVisibilityAsync(
            @NonNull SetBlobVisibilityRequest request) {
        throw new UnsupportedOperationException(Features.BLOB_STORAGE
                + " is not available on this AppSearch implementation.");
    }

    /**
     * Retrieves documents from the open {@link AppSearchSession} that match a given query string
     * and type of search provided.
     *
     * <p>Query strings can be empty, contain one term with no operators, or contain multiple
     * terms and operators.
     *
     * <p>For query strings that are empty, all documents that match the {@link SearchSpec} will be
     * returned.
     *
     * <p>For query strings with a single term and no operators, documents that match the
     * provided query string and {@link SearchSpec} will be returned.
     *
     * <p>The following operators are supported:
     *
     * <ul>
     *     <li>AND (implicit)
     *     <p>AND is an operator that matches documents that contain <i>all</i>
     *     provided terms.
     *     <p><b>NOTE:</b> A space between terms is treated as an "AND" operator. Explicitly
     *     including "AND" in a query string will treat "AND" as a term, returning documents that
     *     also contain "AND".
     *     <p>Example: "apple AND banana" matches documents that contain the
     *     terms "apple", "and", "banana".
     *     <p>Example: "apple banana" matches documents that contain both "apple" and
     *     "banana".
     *     <p>Example: "apple banana cherry" matches documents that contain "apple", "banana", and
     *     "cherry".
     *
     *     <li>OR
     *     <p>OR is an operator that matches documents that contain <i>any</i> provided term.
     *     <p>Example: "apple OR banana" matches documents that contain either "apple" or "banana".
     *     <p>Example: "apple OR banana OR cherry" matches documents that contain any of
     *     "apple", "banana", or "cherry".
     *
     *     <li>Exclusion (-)
     *     <p>Exclusion (-) is an operator that matches documents that <i>do not</i> contain the
     *     provided term.
     *     <p>Example: "-apple" matches documents that do not contain "apple".
     *
     *     <li>Grouped Terms
     *     <p>For queries that require multiple operators and terms, terms can be grouped into
     *     subqueries. Subqueries are contained within an open "(" and close ")" parenthesis.
     *     <p>Example: "(donut OR bagel) (coffee OR tea)" matches documents that contain
     *     either "donut" or "bagel" and either "coffee" or "tea".
     *
     *     <li>Property Restricts
     *     <p>For queries that require a term to match a specific {@link AppSearchSchema}
     *     property of a document, a ":" must be included between the property name and the term.
     *     <p>Example: "subject:important" matches documents that contain the term "important" in
     *     the "subject" property.
     * </ul>
     *
     * <p>The above description covers the query operators that are supported on all versions of
     * AppSearch. Additional operators and their required features are described below.
     *
     * <p>{@link Features#LIST_FILTER_QUERY_LANGUAGE}: This feature covers the expansion of the
     * query language to conform to the definition of the list filters language (https://aip
     * .dev/160). This includes:
     * <ul>
     *     <li>addition of explicit 'AND' and 'NOT' operators</li>
     *     <li>property restricts are allowed with groupings (ex. "prop:(a OR b)")</li>
     *     <li>addition of custom functions to control matching</li>
     * </ul>
     *
     * <p>The newly added custom functions covered by this feature are:
     * <ul>
     *     <li>createList(String...)</li>
     *     <li>search(String, {@code List<String>})</li>
     *     <li>propertyDefined(String)</li>
     * </ul>
     *
     * <p>createList takes a variable number of strings and returns a list of strings.
     * It is for use with search.
     *
     * <p>search takes a query string that will be parsed according to the supported
     * query language and an optional list of strings that specify the properties to be
     * restricted to. This exists as a convenience for multiple property restricts. So,
     * for example, the query `(subject:foo OR body:foo) (subject:bar OR body:bar)`
     * could be rewritten as `search("foo bar", createList("subject", "body"))`.
     *
     * <p>propertyDefined takes a string specifying the property of interest and matches all
     * documents of any type that defines the specified property
     * (ex. `propertyDefined("sender.name")`). Note that propertyDefined will match so long as
     * the document's type defines the specified property. Unlike the "hasProperty" function
     * below, this function does NOT require that the document actually hold any values for this
     * property.
     *
     * <p>{@link Features#NUMERIC_SEARCH}: This feature covers numeric search expressions. In the
     * query language, the values of properties that have
     * {@link AppSearchSchema.LongPropertyConfig#INDEXING_TYPE_RANGE} set can be matched with a
     * numeric search expression (the property, a supported comparator and an integer value).
     * Supported comparators are <, <=, ==, >= and >.
     *
     * <p>Ex. `price < 10` will match all documents that has a numeric value in its price
     * property that is less than 10.
     *
     * <p>{@link Features#VERBATIM_SEARCH}: This feature covers the verbatim string operator
     * (quotation marks).
     *
     * <p>Ex. `"foo/bar" OR baz` will ensure that 'foo/bar' is treated as a single 'verbatim' token.
     *
     * <p>{@link Features#LIST_FILTER_HAS_PROPERTY_FUNCTION}: This feature covers the
     * "hasProperty" function in query expressions, which takes a string specifying the property
     * of interest and matches all documents that hold values for this property. Not to be
     * confused with the "propertyDefined" function, which checks whether a document's schema
     * has defined the property, instead of whether a document itself has this property.
     *
     * <p>Ex. `foo hasProperty("sender.name")` will return all documents that have the term "foo"
     * AND have values in the property "sender.name". Consider two documents, documentA and
     * documentB, of the same schema with an optional property "sender.name". If documentA sets
     * "foo" in this property but documentB does not, then `hasProperty("sender.name")` will only
     * match documentA. However, `propertyDefined("sender.name")` will match both documentA and
     * documentB, regardless of whether a value is actually set.
     *
     * <p>{@link Features#LIST_FILTER_MATCH_SCORE_EXPRESSION_FUNCTION}: This feature covers the
     * "matchScoreExpression" function in query expressions.
     *
     * <p>Usage: matchScoreExpression({score_expression}, {low}, {high})
     * <ul>
     *     <li>matchScoreExpression matches all documents with scores falling within the
     *     specified range. These scores are calculated using the provided score expression,
     *     which adheres to the syntax defined in
     *     {@link SearchSpec.Builder#setRankingStrategy(String)}.</li>
     *     <li>"score_expression" is a string value that specifies the score expression.</li>
     *     <li>"low" and "high" are floating point numbers that specify the score range. The
     *     "high" parameter is optional; if not provided, it defaults to positive infinity.</li>
     * </ul>
     *
     * <p>Ex. `matchScoreExpression("this.documentScore()", 3, 4)` will return all documents that
     * have document scores from 3 to 4.
     *
     * <p>{@link Features#SCHEMA_EMBEDDING_PROPERTY_CONFIG}: This feature covers the
     * "semanticSearch" and "getEmbeddingParameter" functions in query expressions, which are
     * used for semantic search.
     *
     * <p>Usage: semanticSearch(getEmbeddingParameter({embedding_index}), {low}, {high}, {metric})
     * <ul>
     *     <li>semanticSearch matches all documents that have at least one embedding vector with
     *     a matching model signature (see {@link EmbeddingVector#getModelSignature()}) and a
     *     similarity score within the range specified based on the provided metric.</li>
     *     <li>getEmbeddingParameter({embedding_index}) retrieves the embedding search passed in
     *     {@link SearchSpec.Builder#addEmbeddingParameters} based on the index specified, which
     *     starts from 0.</li>
     *     <li>"low" and "high" are floating point numbers that specify the similarity score
     *     range. If omitted, they default to negative and positive infinity, respectively.</li>
     *     <li>"metric" is a string value that specifies how embedding similarities should be
     *     calculated. If omitted, it defaults to the metric specified in
     *     {@link SearchSpec.Builder#setDefaultEmbeddingSearchMetricType(int)}. Possible
     *     values:</li>
     *     <ul>
     *         <li>"COSINE"</li>
     *         <li>"DOT_PRODUCT"</li>
     *         <li>"EUCLIDEAN"</li>
     *     </ul>
     * </ul>
     *
     * <p>Examples:
     * <ul>
     *     <li>Basic: semanticSearch(getEmbeddingParameter(0), 0.5, 1, "COSINE")</li>
     *     <li>With a property restriction:
     *     property1:semanticSearch(getEmbeddingParameter(0), 0.5, 1)</li>
     *     <li>Hybrid: foo OR semanticSearch(getEmbeddingParameter(0), 0.5, 1)</li>
     *     <li>Complex: (foo OR semanticSearch(getEmbeddingParameter(0), 0.5, 1)) AND bar</li>
     * </ul>
     *
     * <p>{@link Features#SEARCH_SPEC_SEARCH_STRING_PARAMETERS}: This feature covers the
     * "getSearchStringParameter" function in query expressions, which substitutes the string
     * provided at the same index in {@link SearchSpec.Builder#addSearchStringParameters} into the
     * query as plain text. This string is then segmented, normalized and stripped of
     * punctuation-only segments. The remaining tokens are then AND'd together. This function is
     * useful for callers who wish to provide user input, but want to ensure that that user input
     * does not invoke any query operators.
     *
     * <p>Usage: getSearchStringParameter({search_parameter_strings_index})
     *
     * <p>Ex. `foo OR getSearchStringParameter(0)` with {@link SearchSpec#getSearchStringParameters}
     * returning {"bar OR baz."}. The string "bar OR baz." will be segmented into "bar", "OR",
     * "baz", ".". Punctuation is removed and the segments are normalized to "bar", "or", "baz".
     * This query will be equivalent to `foo OR (bar AND or AND baz)`.
     *
     * <p>The availability of each of these features can be checked by calling
     * {@link Features#isFeatureSupported} with the desired feature.
     *
     * <p>Additional search specifications, such as filtering by {@link AppSearchSchema} type or
     * adding projection, can be set by calling the corresponding {@link SearchSpec.Builder} setter.
     *
     * <p>This method is lightweight. The heavy work will be done in
     * {@link SearchResults#getNextPageAsync}.
     *
     * @param queryExpression query string to search.
     * @param searchSpec      spec for setting document filters, adding projection, setting term
     *                        match type, etc.
     * @return a {@link SearchResults} object for retrieved matched documents.
     */
    // TODO(b/326656531): Refine the javadoc to provide guidance on the best practice of
    //  embedding searches and how to select an appropriate metric.
    @NonNull SearchResults search(@NonNull String queryExpression, @NonNull SearchSpec searchSpec);

    /**
     * Retrieves suggested Strings that could be used as {@code queryExpression} in
     * {@link #search(String, SearchSpec)} API.
     *
     * <p>The {@code suggestionQueryExpression} can contain one term with no operators, or contain
     * multiple terms and operators. Operators will be considered as a normal term. Please see the
     * operator examples below. The {@code suggestionQueryExpression} must end with a valid term,
     * the suggestions are generated based on the last term. If the input
     * {@code suggestionQueryExpression} doesn't have a valid token, AppSearch will return an
     * empty result list. Please see the invalid examples below.
     *
     * <p>Example: if there are following documents with content stored in AppSearch.
     * <ul>
     *     <li>document1: "term1"
     *     <li>document2: "term1 term2"
     *     <li>document3: "term1 term2 term3"
     *     <li>document4: "org"
     * </ul>
     *
     * <p>Search suggestions with the single term {@code suggestionQueryExpression} "t", the
     * suggested results are:
     * <ul>
     *     <li>"term1" - Use it to be queryExpression in {@link #search} could get 3
     *     {@link SearchResult}s, which contains document 1, 2 and 3.
     *     <li>"term2" - Use it to be queryExpression in {@link #search} could get 2
     *     {@link SearchResult}s, which contains document 2 and 3.
     *     <li>"term3" - Use it to be queryExpression in {@link #search} could get 1
     *     {@link SearchResult}, which contains document 3.
     * </ul>
     *
     * <p>Search suggestions with the multiple term {@code suggestionQueryExpression} "org t", the
     * suggested result will be "org term1" - The last token is completed by the suggested
     * String.
     *
     * <p>Operators in {@link #search} are supported.
     * <p><b>NOTE:</b> Exclusion and Grouped Terms in the last term is not supported.
     * <p>example: "apple -f": This Api will throw an
     * {@link androidx.appsearch.exceptions.AppSearchException} with
     * {@link AppSearchResult#RESULT_INVALID_ARGUMENT}.
     * <p>example: "apple (f)": This Api will return an empty results.
     *
     * <p>Invalid example: All these input {@code suggestionQueryExpression} don't have a valid
     * last token, AppSearch will return an empty result list.
     * <ul>
     *     <li>""      - Empty {@code suggestionQueryExpression}.
     *     <li>"(f)"   - Ending in a closed brackets.
     *     <li>"f:"    - Ending in an operator.
     *     <li>"f    " - Ending in trailing space.
     * </ul>
     *
     * @param suggestionQueryExpression the non empty query string to search suggestions
     * @param searchSuggestionSpec      spec for setting document filters
     * @return The pending result of performing this operation which resolves to a List of
     *         {@link SearchSuggestionResult} on success. The returned suggestion Strings are
     *         ordered by the number of {@link SearchResult} you could get by using that suggestion
     *         in {@link #search}.
     *
     * @see #search(String, SearchSpec)
     */
    @NonNull ListenableFuture<List<SearchSuggestionResult>> searchSuggestionAsync(
            @NonNull String suggestionQueryExpression,
            @NonNull SearchSuggestionSpec searchSuggestionSpec);

    /**
     * Reports usage of a particular document by namespace and ID.
     *
     * <p>A usage report represents an event in which a user interacted with or viewed a document.
     *
     * <p>For each call to {@link #reportUsageAsync}, AppSearch updates usage count and usage
     * recency * metrics for that particular document. These metrics are used for ordering
     * {@link #search} results by the {@link SearchSpec#RANKING_STRATEGY_USAGE_COUNT} and
     * {@link SearchSpec#RANKING_STRATEGY_USAGE_LAST_USED_TIMESTAMP} ranking strategies.
     *
     * <p>Reporting usage of a document is optional.
     *
     * @param request The usage reporting request.
     * @return The pending result of performing this operation which resolves to {@code null} on
     *     success.
     */
    @NonNull ListenableFuture<Void> reportUsageAsync(@NonNull ReportUsageRequest request);

    /**
     * Removes {@link GenericDocument} objects by document IDs in a namespace from the
     * {@link AppSearchSession} database.
     *
     * <p>Removed documents will no longer be surfaced by {@link #search} or
     * {@link #getByDocumentIdAsync}
     * calls.
     *
     * <p>Once the database crosses the document count or byte usage threshold, removed documents
     * will be deleted from disk.
     *
     * @param request {@link RemoveByDocumentIdRequest} with IDs in a namespace to remove from the
     *                index.
     * @return a {@link ListenableFuture} which resolves to an {@link AppSearchBatchResult}.
     * The keys of the {@link AppSearchBatchResult} represent the input IDs from the
     * {@link RemoveByDocumentIdRequest} object. The values are either {@code null} on success,
     * or a failed {@link AppSearchResult} otherwise. IDs that are not found will return a failed
     * {@link AppSearchResult} with a result code of {@link AppSearchResult#RESULT_NOT_FOUND}.
     */
    @NonNull ListenableFuture<AppSearchBatchResult<String, Void>> removeAsync(
            @NonNull RemoveByDocumentIdRequest request);

    /**
     * Removes {@link GenericDocument}s from the index by Query. Documents will be removed if they
     * match the {@code queryExpression} in given namespaces and schemaTypes which is set via
     * {@link SearchSpec.Builder#addFilterNamespaces} and
     * {@link SearchSpec.Builder#addFilterSchemas}.
     *
     * <p> An empty {@code queryExpression} matches all documents.
     *
     * <p> An empty set of namespaces or schemaTypes matches all namespaces or schemaTypes in
     * the current database.
     *
     * @param queryExpression Query String to search.
     * @param searchSpec      Spec containing schemaTypes, namespaces and query expression
     *                        indicates how document will be removed. All specific about how to
     *                        scoring, ordering, snippeting and resulting will be ignored.
     * @return The pending result of performing this operation.
     * @throws IllegalArgumentException if the {@link SearchSpec} contains a {@link JoinSpec}.
     * {@link JoinSpec} lets you join docs that are not owned by the caller, so the semantics of
     * failures from this method would be complex.
     */
    @NonNull ListenableFuture<Void> removeAsync(@NonNull String queryExpression,
            @NonNull SearchSpec searchSpec);

    /**
     * Gets the storage info for this {@link AppSearchSession} database.
     *
     * <p>This may take time proportional to the number of documents and may be inefficient to
     * call repeatedly.
     *
     * @return a {@link ListenableFuture} which resolves to a {@link StorageInfo} object.
     */
    @NonNull ListenableFuture<StorageInfo> getStorageInfoAsync();

    /**
     * Flush all schema and document updates, additions, and deletes to disk if possible.
     *
     * <p>The request is not guaranteed to be handled and may be ignored by some implementations of
     * AppSearchSession.
     *
     * @return The pending result of performing this operation.
     * {@link androidx.appsearch.exceptions.AppSearchException} with
     * {@link AppSearchResult#RESULT_INTERNAL_ERROR} will be set to the future if we hit error when
     * save to disk.
     */
    @NonNull ListenableFuture<Void> requestFlushAsync();

    /**
     * Returns the {@link Features} to check for the availability of certain features
     * for this session.
     */
    @NonNull Features getFeatures();

    /**
     * Closes the {@link AppSearchSession} to persist all schema and document updates, additions,
     * and deletes to disk.
     */
    @Override
    void close();
}