package graphql.schema;

import graphql.DeprecatedAt;
import graphql.GraphQLContext;
import graphql.PublicApi;
import graphql.execution.ExecutionId;
import graphql.execution.ExecutionStepInfo;
import graphql.execution.MergedField;
import graphql.execution.directives.QueryDirectives;
import graphql.introspection.IntrospectionDataFetchingEnvironment;
import graphql.language.Document;
import graphql.language.Field;
import graphql.language.FragmentDefinition;
import graphql.language.OperationDefinition;
import org.dataloader.DataLoader;
import org.dataloader.DataLoaderRegistry;

import java.util.List;
import java.util.Locale;
import java.util.Map;


/**
 * A DataFetchingEnvironment instance of passed to a {@link DataFetcher} as a execution context and its
 * the place where you can find out information to help you resolve a data value given a graphql field input
 */
@SuppressWarnings("TypeParameterUnusedInFormals")
@PublicApi
public interface DataFetchingEnvironment extends IntrospectionDataFetchingEnvironment {

    /**
     * This is the value of the current object to be queried.
     * Or to put it differently: it is the value of the parent field.
     * <p>
     * For the root query, it is equal to {{@link DataFetchingEnvironment#getRoot}
     *
     * @param <T> you decide what type it is
     *
     * @return can be null for the root query, otherwise it is never null
     */
    <T> T getSource();

    /**
     * @return the arguments that have been passed in via the graphql query
     */
    Map<String, Object> getArguments();

    /**
     * Returns true of the named argument is present
     *
     * @param name the name of the argument
     *
     * @return true of the named argument is present
     */
    boolean containsArgument(String name);

    /**
     * Returns the named argument
     *
     * @param name the name of the argument
     * @param <T>  you decide what type it is
     *
     * @return the named argument or null if it's not present
     */
    <T> T getArgument(String name);

    /**
     * Returns the named argument or the default value
     *
     * @param name         the name of the argument
     * @param defaultValue the default value if the argument is not present
     * @param <T>          you decide what type it is
     *
     * @return the named argument or the default if it's not present
     */
    <T> T getArgumentOrDefault(String name, T defaultValue);

    /**
     * Returns a legacy context argument that is set up when the {@link graphql.GraphQL#execute(graphql.ExecutionInput)} method
     * is invoked.
     * <p>
     * This is an info object which is provided to all DataFetchers, but never used by graphql-java itself.
     *
     * @param <T> you decide what type it is
     *
     * @return can be null
     *
     * @deprecated - use {@link #getGraphQlContext()} instead
     */
    @Deprecated
    @DeprecatedAt("2021-07-05")
    <T> T getContext();

    /**
     * Returns a shared context argument that is set up when the {@link graphql.GraphQL#execute(graphql.ExecutionInput)} )} method
     * is invoked.
     * <p>
     * This is an info object which is provided to all DataFetchers.
     *
     * @return can NOT be null
     */
    GraphQLContext getGraphQlContext();

    /**
     * This returns a context object that parent fields may have returned
     * via {@link graphql.execution.DataFetcherResult#getLocalContext()} which can be used to pass down extra information to
     * fields beyond the normal {@link #getSource()}
     * <p>
     * This differs from {@link #getGraphQlContext()} in that it's field specific and passed from parent field to child field,
     * whilst {@link #getGraphQlContext()} is global for the whole query.
     * <p>
     * If the field is a top level field then 'localContext' equals null since it's never be set until those
     * fields execute.
     *
     * @param <T> you decide what type it is
     *
     * @return can be null if no field context objects are passed back by previous parent fields
     */
    <T> T getLocalContext();

    /**
     * This is the source object for the root query.
     *
     * @param <T> you decide what type it is
     *
     * @return can be null
     */
    <T> T getRoot();

    /**
     * @return the definition of the current field
     */
    GraphQLFieldDefinition getFieldDefinition();


    /**
     * @return the list of fields
     *
     * @deprecated Use {@link #getMergedField()}.
     */
    @Deprecated
    @DeprecatedAt("2018-12-20")
    List<Field> getFields();

    /**
     * It can happen that a query has overlapping fields which
     * are querying the same data. If this is the case they get merged
     * together and fetched only once, but this method returns all of the Fields
     * from the query.
     * <p>
     * Most of the time you probably want to use {@link #getField()}.
     * <p>
     * Example query with more than one Field returned:
     *
     * <pre>
     * {@code
     *
     *      query Foo {
     *          bar
     *          ...BarFragment
     *      }
     *
     *      fragment BarFragment on Query {
     *          bar
     *      }
     * }
     * </pre>
     *
     * @return the list of fields currently queried
     */
    MergedField getMergedField();

    /**
     * @return returns the field which is currently queried. See also {@link #getMergedField()}.
     */
    Field getField();

    /**
     * @return graphql type of the current field
     */
    GraphQLOutputType getFieldType();


    /**
     * @return the field {@link ExecutionStepInfo} for the current data fetch operation
     */
    ExecutionStepInfo getExecutionStepInfo();

    /**
     * @return the type of the parent of the current field
     */
    GraphQLType getParentType();

    /**
     * @return the underlying graphql schema
     */
    GraphQLSchema getGraphQLSchema();

    /**
     * @return the {@link FragmentDefinition} map for the current data fetch operation
     */
    Map<String, FragmentDefinition> getFragmentsByName();

    /**
     * @return the {@link ExecutionId} for the current data fetch operation
     */
    ExecutionId getExecutionId();

    /**
     * @return the {@link DataFetchingFieldSelectionSet} for the current data fetch operation
     */
    DataFetchingFieldSelectionSet getSelectionSet();

    /**
     * This gives you access to the directives related to this field
     *
     * @return the {@link graphql.execution.directives.QueryDirectives} for the currently executing field
     *
     * @see graphql.execution.directives.QueryDirectives for more information
     */
    QueryDirectives getQueryDirectives();

    /**
     * This allows you to retrieve a named dataloader from the underlying {@link org.dataloader.DataLoaderRegistry}
     *
     * @param dataLoaderName the name of the data loader to fetch
     * @param <K>            the key type
     * @param <V>            the value type
     *
     * @return the named data loader or null
     *
     * @see org.dataloader.DataLoaderRegistry#getDataLoader(String)
     */
    <K, V> DataLoader<K, V> getDataLoader(String dataLoaderName);

    /**
     * @return the {@link org.dataloader.DataLoaderRegistry} in play
     */
    DataLoaderRegistry getDataLoaderRegistry();

    /**
     * @return the current {@link java.util.Locale} instance used for this request
     */
    Locale getLocale();

    /**
     * @return the current operation that is being executed
     */
    OperationDefinition getOperationDefinition();

    /**
     * @return the current query Document that is being executed
     */
    Document getDocument();

    /**
     * This returns the variables that have been passed into the query.  Note that this is the query variables themselves and not the
     * arguments to the field, which is accessed via {@link #getArguments()}
     * <p>
     * The field arguments are created by interpolating any referenced variables and AST literals and resolving them into the arguments.
     * <p>
     * Also note that the raw query variables are "coerced" into a map where the leaf scalar and enum types are called to create
     * input coerced values.  So the values you get here are not exactly as passed via {@link graphql.ExecutionInput#getVariables()}
     * but have been processed.
     *
     * @return the coerced variables that have been passed to the query that is being executed
     */
    Map<String, Object> getVariables();
}
