<?php declare(strict_types=1);

namespace GraphQL\Utils;

use GraphQL\Error\InvariantViolation;
use GraphQL\Type\Definition\Argument;
use GraphQL\Type\Definition\Directive;
use GraphQL\Type\Definition\EnumType;
use GraphQL\Type\Definition\ImplementingType;
use GraphQL\Type\Definition\InputObjectType;
use GraphQL\Type\Definition\InterfaceType;
use GraphQL\Type\Definition\ListOfType;
use GraphQL\Type\Definition\NamedType;
use GraphQL\Type\Definition\NonNull;
use GraphQL\Type\Definition\ObjectType;
use GraphQL\Type\Definition\ScalarType;
use GraphQL\Type\Definition\Type;
use GraphQL\Type\Definition\UnionType;
use GraphQL\Type\Schema;

/**
 * Utility for finding breaking/dangerous changes between two schemas.
 *
 * @phpstan-type Change array{type: string, description: string}
 * @phpstan-type Changes array{
 *     breakingChanges: array<int, Change>,
 *     dangerousChanges: array<int, Change>
 * }
 *
 * @see \GraphQL\Tests\Utils\BreakingChangesFinderTest
 */
class BreakingChangesFinder
{
    public const BREAKING_CHANGE_FIELD_CHANGED_KIND = 'FIELD_CHANGED_KIND';
    public const BREAKING_CHANGE_FIELD_REMOVED = 'FIELD_REMOVED';
    public const BREAKING_CHANGE_TYPE_CHANGED_KIND = 'TYPE_CHANGED_KIND';
    public const BREAKING_CHANGE_TYPE_REMOVED = 'TYPE_REMOVED';
    public const BREAKING_CHANGE_TYPE_REMOVED_FROM_UNION = 'TYPE_REMOVED_FROM_UNION';
    public const BREAKING_CHANGE_VALUE_REMOVED_FROM_ENUM = 'VALUE_REMOVED_FROM_ENUM';
    public const BREAKING_CHANGE_ARG_REMOVED = 'ARG_REMOVED';
    public const BREAKING_CHANGE_ARG_CHANGED_KIND = 'ARG_CHANGED_KIND';
    public const BREAKING_CHANGE_REQUIRED_ARG_ADDED = 'REQUIRED_ARG_ADDED';
    public const BREAKING_CHANGE_REQUIRED_INPUT_FIELD_ADDED = 'REQUIRED_INPUT_FIELD_ADDED';
    public const BREAKING_CHANGE_IMPLEMENTED_INTERFACE_REMOVED = 'IMPLEMENTED_INTERFACE_REMOVED';
    public const BREAKING_CHANGE_DIRECTIVE_REMOVED = 'DIRECTIVE_REMOVED';
    public const BREAKING_CHANGE_DIRECTIVE_ARG_REMOVED = 'DIRECTIVE_ARG_REMOVED';
    public const BREAKING_CHANGE_DIRECTIVE_LOCATION_REMOVED = 'DIRECTIVE_LOCATION_REMOVED';
    public const BREAKING_CHANGE_REQUIRED_DIRECTIVE_ARG_ADDED = 'REQUIRED_DIRECTIVE_ARG_ADDED';
    public const DANGEROUS_CHANGE_ARG_DEFAULT_VALUE_CHANGED = 'ARG_DEFAULT_VALUE_CHANGE';
    public const DANGEROUS_CHANGE_VALUE_ADDED_TO_ENUM = 'VALUE_ADDED_TO_ENUM';
    public const DANGEROUS_CHANGE_IMPLEMENTED_INTERFACE_ADDED = 'IMPLEMENTED_INTERFACE_ADDED';
    public const DANGEROUS_CHANGE_TYPE_ADDED_TO_UNION = 'TYPE_ADDED_TO_UNION';
    public const DANGEROUS_CHANGE_OPTIONAL_INPUT_FIELD_ADDED = 'OPTIONAL_INPUT_FIELD_ADDED';
    public const DANGEROUS_CHANGE_OPTIONAL_ARG_ADDED = 'OPTIONAL_ARG_ADDED';

    /**
     * Given two schemas, returns an Array containing descriptions of all the types
     * of breaking changes covered by the other functions down below.
     *
     * @throws \TypeError
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findBreakingChanges(Schema $oldSchema, Schema $newSchema): array
    {
        return array_merge(
            self::findRemovedTypes($oldSchema, $newSchema),
            self::findTypesThatChangedKind($oldSchema, $newSchema),
            self::findFieldsThatChangedTypeOnObjectOrInterfaceTypes($oldSchema, $newSchema),
            self::findFieldsThatChangedTypeOnInputObjectTypes($oldSchema, $newSchema)['breakingChanges'],
            self::findTypesRemovedFromUnions($oldSchema, $newSchema),
            self::findValuesRemovedFromEnums($oldSchema, $newSchema),
            self::findArgChanges($oldSchema, $newSchema)['breakingChanges'],
            self::findInterfacesRemovedFromObjectTypes($oldSchema, $newSchema),
            self::findRemovedDirectives($oldSchema, $newSchema),
            self::findRemovedDirectiveArgs($oldSchema, $newSchema),
            self::findAddedNonNullDirectiveArgs($oldSchema, $newSchema),
            self::findRemovedDirectiveLocations($oldSchema, $newSchema)
        );
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any breaking
     * changes in the newSchema related to removing an entire type.
     *
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findRemovedTypes(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $breakingChanges = [];
        foreach (array_keys($oldTypeMap) as $typeName) {
            if (! isset($newTypeMap[$typeName])) {
                $breakingChanges[] = [
                    'type' => self::BREAKING_CHANGE_TYPE_REMOVED,
                    'description' => "{$typeName} was removed.",
                ];
            }
        }

        return $breakingChanges;
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any breaking
     * changes in the newSchema related to changing the type of a type.
     *
     * @throws \TypeError
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findTypesThatChangedKind(
        Schema $schemaA,
        Schema $schemaB
    ): array {
        $schemaATypeMap = $schemaA->getTypeMap();
        $schemaBTypeMap = $schemaB->getTypeMap();

        $breakingChanges = [];
        foreach ($schemaATypeMap as $typeName => $schemaAType) {
            if (! isset($schemaBTypeMap[$typeName])) {
                continue;
            }

            $schemaBType = $schemaBTypeMap[$typeName];
            if ($schemaAType instanceof $schemaBType) {
                continue;
            }

            if ($schemaBType instanceof $schemaAType) {
                continue;
            }

            $schemaATypeKindName = self::typeKindName($schemaAType);
            $schemaBTypeKindName = self::typeKindName($schemaBType);
            $breakingChanges[] = [
                'type' => self::BREAKING_CHANGE_TYPE_CHANGED_KIND,
                'description' => "{$typeName} changed from {$schemaATypeKindName} to {$schemaBTypeKindName}.",
            ];
        }

        return $breakingChanges;
    }

    /**
     * @param Type&NamedType $type
     *
     * @throws \TypeError
     */
    private static function typeKindName(NamedType $type): string
    {
        if ($type instanceof ScalarType) {
            return 'a Scalar type';
        }

        if ($type instanceof ObjectType) {
            return 'an Object type';
        }

        if ($type instanceof InterfaceType) {
            return 'an Interface type';
        }

        if ($type instanceof UnionType) {
            return 'a Union type';
        }

        if ($type instanceof EnumType) {
            return 'an Enum type';
        }

        if ($type instanceof InputObjectType) {
            return 'an Input type';
        }

        throw new \TypeError('Unknown type: ' . $type->name);
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findFieldsThatChangedTypeOnObjectOrInterfaceTypes(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $breakingChanges = [];
        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (
                ! $oldType instanceof ObjectType && ! $oldType instanceof InterfaceType
                || ! $newType instanceof ObjectType && ! $newType instanceof InterfaceType
                || ! ($newType instanceof $oldType)
            ) {
                continue;
            }

            $oldTypeFieldsDef = $oldType->getFields();
            $newTypeFieldsDef = $newType->getFields();
            foreach ($oldTypeFieldsDef as $fieldName => $fieldDefinition) {
                // Check if the field is missing on the type in the new schema.
                if (! isset($newTypeFieldsDef[$fieldName])) {
                    $breakingChanges[] = [
                        'type' => self::BREAKING_CHANGE_FIELD_REMOVED,
                        'description' => "{$typeName}.{$fieldName} was removed.",
                    ];
                } else {
                    $oldFieldType = $oldTypeFieldsDef[$fieldName]->getType();
                    $newFieldType = $newTypeFieldsDef[$fieldName]->getType();
                    $isSafe = self::isChangeSafeForObjectOrInterfaceField(
                        $oldFieldType,
                        $newFieldType
                    );
                    if (! $isSafe) {
                        $breakingChanges[] = [
                            'type' => self::BREAKING_CHANGE_FIELD_CHANGED_KIND,
                            'description' => "{$typeName}.{$fieldName} changed type from {$oldFieldType} to {$newFieldType}.",
                        ];
                    }
                }
            }
        }

        return $breakingChanges;
    }

    private static function isChangeSafeForObjectOrInterfaceField(
        Type $oldType,
        Type $newType
    ): bool {
        if ($oldType instanceof NamedType) {
            return // if they're both named types, see if their names are equivalent
                ($newType instanceof NamedType && $oldType->name === $newType->name)
                // moving from nullable to non-null of the same underlying type is safe
                || ($newType instanceof NonNull
                    && self::isChangeSafeForObjectOrInterfaceField($oldType, $newType->getWrappedType()));
        }

        if ($oldType instanceof ListOfType) {
            return // if they're both lists, make sure the underlying types are compatible
                ($newType instanceof ListOfType && self::isChangeSafeForObjectOrInterfaceField(
                    $oldType->getWrappedType(),
                    $newType->getWrappedType()
                ))
                // moving from nullable to non-null of the same underlying type is safe
                || ($newType instanceof NonNull
                    && self::isChangeSafeForObjectOrInterfaceField($oldType, $newType->getWrappedType()));
        }

        if ($oldType instanceof NonNull) {
            // if they're both non-null, make sure the underlying types are compatible
            return $newType instanceof NonNull
                && self::isChangeSafeForObjectOrInterfaceField($oldType->getWrappedType(), $newType->getWrappedType());
        }

        return false;
    }

    /**
     * @throws InvariantViolation
     *
     * @return Changes
     */
    public static function findFieldsThatChangedTypeOnInputObjectTypes(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $breakingChanges = [];
        $dangerousChanges = [];
        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (! ($oldType instanceof InputObjectType) || ! ($newType instanceof InputObjectType)) {
                continue;
            }

            $oldTypeFieldsDef = $oldType->getFields();
            $newTypeFieldsDef = $newType->getFields();
            foreach (array_keys($oldTypeFieldsDef) as $fieldName) {
                if (! isset($newTypeFieldsDef[$fieldName])) {
                    $breakingChanges[] = [
                        'type' => self::BREAKING_CHANGE_FIELD_REMOVED,
                        'description' => "{$typeName}.{$fieldName} was removed.",
                    ];
                } else {
                    $oldFieldType = $oldTypeFieldsDef[$fieldName]->getType();
                    $newFieldType = $newTypeFieldsDef[$fieldName]->getType();

                    $isSafe = self::isChangeSafeForInputObjectFieldOrFieldArg(
                        $oldFieldType,
                        $newFieldType
                    );
                    if (! $isSafe) {
                        $oldFieldTypeString = $oldFieldType instanceof NamedType
                            ? $oldFieldType->name
                            : $oldFieldType;
                        $newFieldTypeString = $newFieldType instanceof NamedType
                            ? $newFieldType->name
                            : $newFieldType;

                        $breakingChanges[] = [
                            'type' => self::BREAKING_CHANGE_FIELD_CHANGED_KIND,
                            'description' => "{$typeName}.{$fieldName} changed type from {$oldFieldTypeString} to {$newFieldTypeString}.",
                        ];
                    }
                }
            }

            // Check if a field was added to the input object type
            foreach ($newTypeFieldsDef as $fieldName => $fieldDef) {
                if (isset($oldTypeFieldsDef[$fieldName])) {
                    continue;
                }

                $newTypeName = $newType->name;
                if ($fieldDef->isRequired()) {
                    $breakingChanges[] = [
                        'type' => self::BREAKING_CHANGE_REQUIRED_INPUT_FIELD_ADDED,
                        'description' => "A required field {$fieldName} on input type {$newTypeName} was added.",
                    ];
                } else {
                    $dangerousChanges[] = [
                        'type' => self::DANGEROUS_CHANGE_OPTIONAL_INPUT_FIELD_ADDED,
                        'description' => "An optional field {$fieldName} on input type {$newTypeName} was added.",
                    ];
                }
            }
        }

        return [
            'breakingChanges' => $breakingChanges,
            'dangerousChanges' => $dangerousChanges,
        ];
    }

    /** @throws InvariantViolation */
    private static function isChangeSafeForInputObjectFieldOrFieldArg(
        Type $oldType,
        Type $newType
    ): bool {
        if ($oldType instanceof NamedType) {
            if (! $newType instanceof NamedType) {
                return false;
            }

            // if they're both named types, see if their names are equivalent
            return $oldType->name === $newType->name;
        }

        if ($oldType instanceof ListOfType) {
            // if they're both lists, make sure the underlying types are compatible
            return $newType instanceof ListOfType
                && self::isChangeSafeForInputObjectFieldOrFieldArg(
                    $oldType->getWrappedType(),
                    $newType->getWrappedType()
                );
        }

        if ($oldType instanceof NonNull) {
            return // if they're both non-null, make sure the underlying types are compatible
                ($newType instanceof NonNull && self::isChangeSafeForInputObjectFieldOrFieldArg(
                    $oldType->getWrappedType(),
                    $newType->getWrappedType()
                ))
                // moving from non-null to nullable of the same underlying type is safe
                || ! ($newType instanceof NonNull)
                && self::isChangeSafeForInputObjectFieldOrFieldArg($oldType->getWrappedType(), $newType);
        }

        return false;
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any breaking
     * changes in the newSchema related to removing types from a union type.
     *
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findTypesRemovedFromUnions(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $typesRemovedFromUnion = [];
        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (! ($oldType instanceof UnionType) || ! ($newType instanceof UnionType)) {
                continue;
            }

            $typeNamesInNewUnion = [];
            foreach ($newType->getTypes() as $type) {
                $typeNamesInNewUnion[$type->name] = true;
            }

            foreach ($oldType->getTypes() as $type) {
                if (! isset($typeNamesInNewUnion[$type->name])) {
                    $typesRemovedFromUnion[] = [
                        'type' => self::BREAKING_CHANGE_TYPE_REMOVED_FROM_UNION,
                        'description' => "{$type->name} was removed from union type {$typeName}.",
                    ];
                }
            }
        }

        return $typesRemovedFromUnion;
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any breaking
     * changes in the newSchema related to removing values from an enum type.
     *
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findValuesRemovedFromEnums(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $valuesRemovedFromEnums = [];
        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (! ($oldType instanceof EnumType) || ! ($newType instanceof EnumType)) {
                continue;
            }

            $valuesInNewEnum = [];
            foreach ($newType->getValues() as $value) {
                $valuesInNewEnum[$value->name] = true;
            }

            foreach ($oldType->getValues() as $value) {
                if (! isset($valuesInNewEnum[$value->name])) {
                    $valuesRemovedFromEnums[] = [
                        'type' => self::BREAKING_CHANGE_VALUE_REMOVED_FROM_ENUM,
                        'description' => "{$value->name} was removed from enum type {$typeName}.",
                    ];
                }
            }
        }

        return $valuesRemovedFromEnums;
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any
     * breaking or dangerous changes in the newSchema related to arguments
     * (such as removal or change of type of an argument, or a change in an
     * argument's default value).
     *
     * @throws InvariantViolation
     *
     * @return Changes
     */
    public static function findArgChanges(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $breakingChanges = [];
        $dangerousChanges = [];

        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (
                ! $oldType instanceof ObjectType && ! $oldType instanceof InterfaceType
                || ! $newType instanceof ObjectType && ! $newType instanceof InterfaceType
                || ! ($newType instanceof $oldType)
            ) {
                continue;
            }

            $oldTypeFields = $oldType->getFields();
            $newTypeFields = $newType->getFields();

            foreach ($oldTypeFields as $fieldName => $oldField) {
                if (! isset($newTypeFields[$fieldName])) {
                    continue;
                }

                foreach ($oldField->args as $oldArgDef) {
                    $newArgDef = null;
                    foreach ($newTypeFields[$fieldName]->args as $newArg) {
                        if ($newArg->name === $oldArgDef->name) {
                            $newArgDef = $newArg;
                        }
                    }

                    if ($newArgDef !== null) {
                        $isSafe = self::isChangeSafeForInputObjectFieldOrFieldArg(
                            $oldArgDef->getType(),
                            $newArgDef->getType()
                        );
                        $oldArgType = $oldArgDef->getType();
                        $oldArgName = $oldArgDef->name;
                        if (! $isSafe) {
                            $newArgType = $newArgDef->getType();
                            $breakingChanges[] = [
                                'type' => self::BREAKING_CHANGE_ARG_CHANGED_KIND,
                                'description' => "{$typeName}.{$fieldName} arg {$oldArgName} has changed type from {$oldArgType} to {$newArgType}",
                            ];
                        } elseif ($oldArgDef->defaultValueExists() && $oldArgDef->defaultValue !== $newArgDef->defaultValue) {
                            $dangerousChanges[] = [
                                'type' => self::DANGEROUS_CHANGE_ARG_DEFAULT_VALUE_CHANGED,
                                'description' => "{$typeName}.{$fieldName} arg {$oldArgName} has changed defaultValue",
                            ];
                        }
                    } else {
                        $breakingChanges[] = [
                            'type' => self::BREAKING_CHANGE_ARG_REMOVED,
                            'description' => "{$typeName}.{$fieldName} arg {$oldArgDef->name} was removed",
                        ];
                    }

                    // Check if arg was added to the field
                    foreach ($newTypeFields[$fieldName]->args as $newTypeFieldArgDef) {
                        $oldArgDef = null;
                        foreach ($oldTypeFields[$fieldName]->args as $oldArg) {
                            if ($oldArg->name === $newTypeFieldArgDef->name) {
                                $oldArgDef = $oldArg;
                            }
                        }

                        if ($oldArgDef !== null) {
                            continue;
                        }

                        $newTypeName = $newType->name;
                        $newArgName = $newTypeFieldArgDef->name;
                        if ($newTypeFieldArgDef->isRequired()) {
                            $breakingChanges[] = [
                                'type' => self::BREAKING_CHANGE_REQUIRED_ARG_ADDED,
                                'description' => "A required arg {$newArgName} on {$newTypeName}.{$fieldName} was added",
                            ];
                        } else {
                            $dangerousChanges[] = [
                                'type' => self::DANGEROUS_CHANGE_OPTIONAL_ARG_ADDED,
                                'description' => "An optional arg {$newArgName} on {$newTypeName}.{$fieldName} was added",
                            ];
                        }
                    }
                }
            }
        }

        return [
            'breakingChanges' => $breakingChanges,
            'dangerousChanges' => $dangerousChanges,
        ];
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findInterfacesRemovedFromObjectTypes(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();
        $breakingChanges = [];

        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (! ($oldType instanceof ImplementingType) || ! ($newType instanceof ImplementingType)) {
                continue;
            }

            $oldInterfaces = $oldType->getInterfaces();
            $newInterfaces = $newType->getInterfaces();
            foreach ($oldInterfaces as $oldInterface) {
                $interfaceWasRemoved = true;
                foreach ($newInterfaces as $newInterface) {
                    if ($oldInterface->name === $newInterface->name) {
                        $interfaceWasRemoved = false;
                    }
                }

                if ($interfaceWasRemoved) {
                    $breakingChanges[] = [
                        'type' => self::BREAKING_CHANGE_IMPLEMENTED_INTERFACE_REMOVED,
                        'description' => "{$typeName} no longer implements interface {$oldInterface->name}.",
                    ];
                }
            }
        }

        return $breakingChanges;
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findRemovedDirectives(Schema $oldSchema, Schema $newSchema): array
    {
        $removedDirectives = [];

        $newSchemaDirectiveMap = self::getDirectiveMapForSchema($newSchema);
        foreach ($oldSchema->getDirectives() as $directive) {
            if (! isset($newSchemaDirectiveMap[$directive->name])) {
                $removedDirectives[] = [
                    'type' => self::BREAKING_CHANGE_DIRECTIVE_REMOVED,
                    'description' => "{$directive->name} was removed",
                ];
            }
        }

        return $removedDirectives;
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<string, Directive>
     */
    private static function getDirectiveMapForSchema(Schema $schema): array
    {
        $directives = [];
        foreach ($schema->getDirectives() as $directive) {
            $directives[$directive->name] = $directive;
        }

        return $directives;
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findRemovedDirectiveArgs(Schema $oldSchema, Schema $newSchema): array
    {
        $removedDirectiveArgs = [];
        $oldSchemaDirectiveMap = self::getDirectiveMapForSchema($oldSchema);

        foreach ($newSchema->getDirectives() as $newDirective) {
            if (! isset($oldSchemaDirectiveMap[$newDirective->name])) {
                continue;
            }

            foreach (
                self::findRemovedArgsForDirectives(
                    $oldSchemaDirectiveMap[$newDirective->name],
                    $newDirective
                ) as $arg
            ) {
                $removedDirectiveArgs[] = [
                    'type' => self::BREAKING_CHANGE_DIRECTIVE_ARG_REMOVED,
                    'description' => "{$arg->name} was removed from {$newDirective->name}",
                ];
            }
        }

        return $removedDirectiveArgs;
    }

    /** @return array<int, Argument> */
    public static function findRemovedArgsForDirectives(Directive $oldDirective, Directive $newDirective): array
    {
        $removedArgs = [];
        $newArgMap = self::getArgumentMapForDirective($newDirective);
        foreach ($oldDirective->args as $arg) {
            if (! isset($newArgMap[$arg->name])) {
                $removedArgs[] = $arg;
            }
        }

        return $removedArgs;
    }

    /** @return array<string, Argument> */
    private static function getArgumentMapForDirective(Directive $directive): array
    {
        $args = [];
        foreach ($directive->args as $arg) {
            $args[$arg->name] = $arg;
        }

        return $args;
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findAddedNonNullDirectiveArgs(Schema $oldSchema, Schema $newSchema): array
    {
        $addedNonNullableArgs = [];
        $oldSchemaDirectiveMap = self::getDirectiveMapForSchema($oldSchema);

        foreach ($newSchema->getDirectives() as $newDirective) {
            if (! isset($oldSchemaDirectiveMap[$newDirective->name])) {
                continue;
            }

            foreach (
                self::findAddedArgsForDirective(
                    $oldSchemaDirectiveMap[$newDirective->name],
                    $newDirective
                ) as $arg
            ) {
                if ($arg->isRequired()) {
                    $addedNonNullableArgs[] = [
                        'type' => self::BREAKING_CHANGE_REQUIRED_DIRECTIVE_ARG_ADDED,
                        'description' => "A required arg {$arg->name} on directive {$newDirective->name} was added",
                    ];
                }
            }
        }

        return $addedNonNullableArgs;
    }

    /** @return array<int, Argument> */
    public static function findAddedArgsForDirective(Directive $oldDirective, Directive $newDirective): array
    {
        $addedArgs = [];
        $oldArgMap = self::getArgumentMapForDirective($oldDirective);
        foreach ($newDirective->args as $arg) {
            if (! isset($oldArgMap[$arg->name])) {
                $addedArgs[] = $arg;
            }
        }

        return $addedArgs;
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findRemovedDirectiveLocations(Schema $oldSchema, Schema $newSchema): array
    {
        $removedLocations = [];
        $oldSchemaDirectiveMap = self::getDirectiveMapForSchema($oldSchema);

        foreach ($newSchema->getDirectives() as $newDirective) {
            if (! isset($oldSchemaDirectiveMap[$newDirective->name])) {
                continue;
            }

            foreach (
                self::findRemovedLocationsForDirective(
                    $oldSchemaDirectiveMap[$newDirective->name],
                    $newDirective
                ) as $location
            ) {
                $removedLocations[] = [
                    'type' => self::BREAKING_CHANGE_DIRECTIVE_LOCATION_REMOVED,
                    'description' => "{$location} was removed from {$newDirective->name}",
                ];
            }
        }

        return $removedLocations;
    }

    /** @return array<int, string> */
    public static function findRemovedLocationsForDirective(Directive $oldDirective, Directive $newDirective): array
    {
        $removedLocations = [];
        $newLocationSet = array_flip($newDirective->locations);
        foreach ($oldDirective->locations as $oldLocation) {
            if (! array_key_exists($oldLocation, $newLocationSet)) {
                $removedLocations[] = $oldLocation;
            }
        }

        return $removedLocations;
    }

    /**
     * Given two schemas, returns an Array containing descriptions of all the types
     * of potentially dangerous changes covered by the other functions down below.
     *
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findDangerousChanges(Schema $oldSchema, Schema $newSchema): array
    {
        return array_merge(
            self::findArgChanges($oldSchema, $newSchema)['dangerousChanges'],
            self::findValuesAddedToEnums($oldSchema, $newSchema),
            self::findInterfacesAddedToObjectTypes($oldSchema, $newSchema),
            self::findTypesAddedToUnions($oldSchema, $newSchema),
            self::findFieldsThatChangedTypeOnInputObjectTypes($oldSchema, $newSchema)['dangerousChanges']
        );
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any dangerous
     * changes in the newSchema related to adding values to an enum type.
     *
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findValuesAddedToEnums(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $valuesAddedToEnums = [];
        foreach ($oldTypeMap as $typeName => $oldType) {
            $newType = $newTypeMap[$typeName] ?? null;
            if (! ($oldType instanceof EnumType) || ! ($newType instanceof EnumType)) {
                continue;
            }

            $valuesInOldEnum = [];
            foreach ($oldType->getValues() as $value) {
                $valuesInOldEnum[$value->name] = true;
            }

            foreach ($newType->getValues() as $value) {
                if (! isset($valuesInOldEnum[$value->name])) {
                    $valuesAddedToEnums[] = [
                        'type' => self::DANGEROUS_CHANGE_VALUE_ADDED_TO_ENUM,
                        'description' => "{$value->name} was added to enum type {$typeName}.",
                    ];
                }
            }
        }

        return $valuesAddedToEnums;
    }

    /**
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findInterfacesAddedToObjectTypes(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();
        $interfacesAddedToObjectTypes = [];

        foreach ($newTypeMap as $typeName => $newType) {
            $oldType = $oldTypeMap[$typeName] ?? null;
            if (
                ! $oldType instanceof ObjectType && ! $oldType instanceof InterfaceType
                || ! $newType instanceof ObjectType && ! $newType instanceof InterfaceType
            ) {
                continue;
            }

            $oldInterfaces = $oldType->getInterfaces();
            $newInterfaces = $newType->getInterfaces();
            foreach ($newInterfaces as $newInterface) {
                $interfaceWasAdded = true;
                foreach ($oldInterfaces as $oldInterface) {
                    if ($oldInterface->name === $newInterface->name) {
                        $interfaceWasAdded = false;
                    }
                }

                if ($interfaceWasAdded) {
                    $interfacesAddedToObjectTypes[] = [
                        'type' => self::DANGEROUS_CHANGE_IMPLEMENTED_INTERFACE_ADDED,
                        'description' => "{$newInterface->name} added to interfaces implemented by {$typeName}.",
                    ];
                }
            }
        }

        return $interfacesAddedToObjectTypes;
    }

    /**
     * Given two schemas, returns an Array containing descriptions of any dangerous
     * changes in the newSchema related to adding types to a union type.
     *
     * @throws InvariantViolation
     *
     * @return array<int, Change>
     */
    public static function findTypesAddedToUnions(
        Schema $oldSchema,
        Schema $newSchema
    ): array {
        $oldTypeMap = $oldSchema->getTypeMap();
        $newTypeMap = $newSchema->getTypeMap();

        $typesAddedToUnion = [];
        foreach ($newTypeMap as $typeName => $newType) {
            $oldType = $oldTypeMap[$typeName] ?? null;
            if (! ($oldType instanceof UnionType) || ! ($newType instanceof UnionType)) {
                continue;
            }

            $typeNamesInOldUnion = [];
            foreach ($oldType->getTypes() as $type) {
                $typeNamesInOldUnion[$type->name] = true;
            }

            foreach ($newType->getTypes() as $type) {
                if (! isset($typeNamesInOldUnion[$type->name])) {
                    $typesAddedToUnion[] = [
                        'type' => self::DANGEROUS_CHANGE_TYPE_ADDED_TO_UNION,
                        'description' => "{$type->name} was added to union type {$typeName}.",
                    ];
                }
            }
        }

        return $typesAddedToUnion;
    }
}
