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GraphqL Java
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package graphql.schema.idl;

import graphql.GraphQLError;
import graphql.InvalidSyntaxError;
import graphql.PublicApi;
import graphql.language.Definition;
import graphql.language.Document;
import graphql.language.SDLDefinition;
import graphql.parser.InvalidSyntaxException;
import graphql.parser.Parser;
import graphql.parser.ParserEnvironment;
import graphql.parser.ParserOptions;
import graphql.schema.idl.errors.NonSDLDefinitionError;
import graphql.schema.idl.errors.SchemaProblem;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.nio.file.Files;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import static graphql.parser.ParserEnvironment.newParserEnvironment;
import static java.nio.charset.Charset.defaultCharset;

/**
 * This can take a graphql schema definition and parse it into a {@link TypeDefinitionRegistry} of
 * definitions ready to be placed into {@link SchemaGenerator} say
 */
@PublicApi
public class SchemaParser {

    /**
     * Parse a file of schema definitions and create a {@link TypeDefinitionRegistry}
     *
     * @param file the file to parse
     *
     * @return registry of type definitions
     *
     * @throws SchemaProblem if there are problems compiling the schema definitions
     */
    public TypeDefinitionRegistry parse(File file) throws SchemaProblem {
        try {
            return parse(Files.newBufferedReader(file.toPath(), defaultCharset()));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Parse a inputStream of schema definitions and create a {@link TypeDefinitionRegistry}
     *
     * @param inputStream the inputStream to parse
     *
     * @return registry of type definitions
     *
     * @throws SchemaProblem if there are problems compiling the schema definitions
     */
    public TypeDefinitionRegistry parse(InputStream inputStream) throws SchemaProblem {
        return parse(new InputStreamReader(inputStream));
    }

    /**
     * Parse a reader of schema definitions and create a {@link TypeDefinitionRegistry}
     *
     * @param reader the reader to parse
     *
     * @return registry of type definitions
     *
     * @throws SchemaProblem if there are problems compiling the schema definitions
     */
    public TypeDefinitionRegistry parse(Reader reader) throws SchemaProblem {
        return parse(reader, null);
    }

    /**
     * Parse a reader of schema definitions and create a {@link TypeDefinitionRegistry}
     *
     * @param reader        the reader to parse
     * @param parserOptions the parse options to use while parsing
     *
     * @return registry of type definitions
     *
     * @throws SchemaProblem if there are problems compiling the schema definitions
     */
    public TypeDefinitionRegistry parse(Reader reader, ParserOptions parserOptions) throws SchemaProblem {
        try (Reader input = reader) {
            return parseImpl(input, parserOptions);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Parse a string of schema definitions and create a {@link TypeDefinitionRegistry}
     *
     * @param schemaInput the schema string to parse
     *
     * @return registry of type definitions
     *
     * @throws SchemaProblem if there are problems compiling the schema definitions
     */
    public TypeDefinitionRegistry parse(String schemaInput) throws SchemaProblem {
        return parseImpl(new StringReader(schemaInput));
    }

    public TypeDefinitionRegistry parseImpl(Reader schemaInput) {
        // why it this public - (head shake)
        return parseImpl(schemaInput, null);
    }

    private TypeDefinitionRegistry parseImpl(Reader schemaInput, ParserOptions parseOptions) {
        try {
            if (parseOptions == null) {
                parseOptions = ParserOptions.getDefaultSdlParserOptions();
            }
            ParserEnvironment parserEnvironment = newParserEnvironment().document(schemaInput).parserOptions(parseOptions).build();
            Document document = Parser.parse(parserEnvironment);

            return buildRegistry(document);
        } catch (InvalidSyntaxException e) {
            throw handleParseException(e.toInvalidSyntaxError());
        }
    }

    private SchemaProblem handleParseException(InvalidSyntaxError invalidSyntaxError) throws RuntimeException {
        return new SchemaProblem(Collections.singletonList(invalidSyntaxError));
    }

    /**
     * special method to build directly a TypeDefinitionRegistry from a Document
     * useful for Introspection => IDL (Document) => TypeDefinitionRegistry
     *
     * @param document containing type definitions
     *
     * @return the TypeDefinitionRegistry containing all type definitions from the document
     *
     * @throws SchemaProblem if an error occurs
     */
    public TypeDefinitionRegistry buildRegistry(Document document) {
        List errors = new ArrayList<>();
        TypeDefinitionRegistry typeRegistry = new TypeDefinitionRegistry();
        List definitions = document.getDefinitions();
        for (Definition definition : definitions) {
            if (definition instanceof SDLDefinition) {
                typeRegistry.add((SDLDefinition) definition).ifPresent(errors::add);
            } else {
                errors.add(new NonSDLDefinitionError(definition));
            }
        }
        if (errors.size() > 0) {
            throw new SchemaProblem(errors);
        } else {
            return typeRegistry;
        }
    }
}