package GraphQL::Execution;

use 5.014;
use strict;
use warnings;
use Types::Standard -all;
use Types::TypeTiny -all;
use GraphQL::Type::Library -all;
use GraphQL::MaybeTypeCheck;
use GraphQL::Language::Parser qw(parse);
use GraphQL::Error;
use JSON::MaybeXS;
use GraphQL::Debug qw(_debug);
use GraphQL::Introspection qw(
  $SCHEMA_META_FIELD_DEF $TYPE_META_FIELD_DEF $TYPE_NAME_META_FIELD_DEF
);
use GraphQL::Directive;
use GraphQL::Schema qw(lookup_type);
use Exporter 'import';
use Scalar::Util qw(blessed);

=head1 NAME

GraphQL::Execution - Execute GraphQL queries

=cut

our @EXPORT_OK = qw(
  execute
);
our $VERSION = '0.02';

my $JSON = JSON::MaybeXS->new->allow_nonref;
use constant DEBUG => $ENV{GRAPHQL_DEBUG}; # "DEBUG and" gets optimised out if false

=head1 SYNOPSIS

  use GraphQL::Execution qw(execute);
  my $result = execute($schema, $doc, $root_value);

=head1 DESCRIPTION

Executes a GraphQL query, returns results.

=head1 METHODS

=head2 execute

  my $result = execute(
    $schema,
    $doc, # can also be AST
    $root_value,
    $context_value,
    $variable_values,
    $operation_name,
    $field_resolver,
    $promise_code,
  );

=over

=item $schema

A L<GraphQL::Schema>.

=item $doc

Either a GraphQL query document to be fed in to
L<GraphQL::Language::Parser/parse>, or a return value from that.

=item $root_value

A root value that can be used by field-resolvers. The default one needs
a code-ref, a hash-ref or an object.

For instance:

  my $schema = GraphQL::Schema->from_doc(<<'EOF');
  type Query { dateTimeNow: String, hi: String }
  EOF
  my $root_value = {
    dateTimeNow => sub { DateTime->now->ymd },
    hi => "Bob",
  };
  my $data = execute($schema, "{ dateTimeNow hi }", $root_value);

will return:

    {
      data => {
        dateTimeNow => { ymd => '20190501' },
        hi => 'Bob',
      }
    }

Be aware that with the default field-resolver, when it calls a method,
that method will get called with L<GraphQL::Type::Library/$args>
L<GraphQL::Type::Library/$context>, L<GraphQL::Type::Library/$info>. To
override that to pass no parameters, this is suitable as a
C<$field_resolver> parameters:

    sub {
      my ($root_value, $args, $context, $info) = @_;
      my $field_name = $info->{field_name};
      my $property = ref($root_value) eq 'HASH'
        ? $root_value->{$field_name}
        : $root_value;
      return $property->($args, $context, $info) if ref $property eq 'CODE';
      return $root_value->$field_name if ref $property; # no args
      $property;
    }

=item $context_value

A per-request scalar, that will be passed to field-resolvers.

=item $variable_values

A hash-ref, typically the decoded JSON object supplied by a
client. E.g. for this query:

  query q($input: TestInputObject) {
    fieldWithObjectInput(input: $input)
  }

The C<$variable_values> will need to be a JSON object with a
key C<input>, whose value will need to conform to the L<input
type|GraphQL::Type::InputObject> C<TestInputObject>.

The purpose of this is to avoid needing to hard-code input values in
your query. This aids in, among other things, being able to whitelist
individual queries as acceptable, non-abusive queries to your system;
and being able to generate client-side code for client-side validation
rather than including the full GraphQL system in client code.

=item $operation_name

A string (or C<undef>) that if given will be the name of one of the
operations in the query.

=item $field_resolver

A code-ref to be used instead of the default field-resolver.

=item $promise_code

If you need to return a promise, supply a hash-ref matching
L<GraphQL::Type::Library/PromiseCode>.

=back

=cut

fun execute(
  (InstanceOf['GraphQL::Schema']) $schema,
  Str | ArrayRef[HashRef] $doc,
  Any $root_value = undef,
  Any $context_value = undef,
  Maybe[HashRef] $variable_values = undef,
  Maybe[Str] $operation_name = undef,
  Maybe[CodeLike] $field_resolver = undef,
  Maybe[PromiseCode] $promise_code = undef,
) :ReturnType(ExecutionResult | Promise) {
  my $context = eval {
    my $ast = ref($doc) ? $doc : parse($doc);
    _build_context(
      $schema,
      $ast,
      $root_value,
      $context_value,
      $variable_values,
      $operation_name,
      $field_resolver,
      $promise_code,
    );
  };
  DEBUG and _debug('execute', $context, $@);
  return _build_response(_wrap_error($@)) if $@;
  my $result = _execute_operation(
    $context,
    $context->{operation},
    $root_value,
  );
  DEBUG and _debug('execute(result)', $result, $@);
  _build_response($result, 1);
}

fun _build_response(
  ExecutionPartialResult | Promise $result,
  Bool $force_data = 0,
) :ReturnType(ExecutionResult | Promise) {
  return $result->then(sub { _build_response(@_) }) if is_Promise($result);
  my @errors = @{$result->{errors} || []};
  +{
    $force_data ? (data => undef) : (), # default if none given
    %$result,
    @errors ? (errors => [ map $_->to_json, @{$result->{errors}} ]) : (),
  };
}

fun _wrap_error(
  Any $error,
) :ReturnType(ExecutionPartialResult) {
  return $error if is_ExecutionPartialResult($error);
  +{ errors => [ GraphQL::Error->coerce($error) ] };
}

fun _build_context(
  (InstanceOf['GraphQL::Schema']) $schema,
  ArrayRef[HashRef] $ast,
  Any $root_value,
  Any $context_value,
  Maybe[HashRef] $variable_values,
  Maybe[Str] $operation_name,
  Maybe[CodeLike] $field_resolver,
  Maybe[PromiseCode] $promise_code,
) :ReturnType(HashRef) {
  my %fragments = map {
    ($_->{name} => $_)
  } grep $_->{kind} eq 'fragment', @$ast;
  my @operations = grep $_->{kind} eq 'operation', @$ast;
  die "No operations supplied.\n" if !@operations;
  die "Can only execute document containing fragments or operations\n"
    if @$ast != keys(%fragments) + @operations;
  my $operation = _get_operation($operation_name, \@operations);
  {
    schema => $schema,
    fragments => \%fragments,
    root_value => $root_value,
    context_value => $context_value,
    operation => $operation,
    variable_values => _variables_apply_defaults(
      $schema,
      $operation->{variables} || {},
      $variable_values || {},
    ),
    field_resolver => $field_resolver || \&_default_field_resolver,
    promise_code => $promise_code,
  };
}

# takes each operation var: query q(a: String)
#  applies to it supplied variable from web request
#  if none, applies any defaults in the operation var: query q(a: String = "h")
#  converts with graphql_to_perl (which also validates) to Perl values
# return { varname => { value => ..., type => $type } }
fun _variables_apply_defaults(
  (InstanceOf['GraphQL::Schema']) $schema,
  HashRef $operation_variables,
  HashRef $variable_values,
) :ReturnType(HashRef) {
  my @bad = grep {
    ! lookup_type($operation_variables->{$_}, $schema->name2type)->DOES('GraphQL::Role::Input');
  } keys %$operation_variables;
  die "Variable '\$$bad[0]' is type '@{[
    lookup_type($operation_variables->{$bad[0]}, $schema->name2type)->to_string
  ]}' which cannot be used as an input type.\n" if @bad;
  +{ map {
    my $opvar = $operation_variables->{$_};
    my $opvar_type = lookup_type($opvar, $schema->name2type);
    my $parsed_value;
    my $maybe_value = $variable_values->{$_} // $opvar->{default_value};
    eval { $parsed_value = $opvar_type->graphql_to_perl($maybe_value) };
    if ($@) {
      my $error = $@;
      $error =~ s#\s+at.*line\s+\d+\.#.#;
      # JSON cannot encode scalar references
      my $jsonable = _coerce_for_error($maybe_value);
      die "Variable '\$$_' got invalid value @{[$JSON->canonical->encode($jsonable)]}.\n$error";
    }
    ($_ => { value => $parsed_value, type => $opvar_type })
  } keys %$operation_variables };
}

fun _get_operation(
  Maybe[Str] $operation_name,
  ArrayRef[HashRef] $operations,
) {
  DEBUG and _debug('_get_operation', @_);
  if (!$operation_name) {
    die "Must provide operation name if query contains multiple operations.\n"
      if @$operations > 1;
    return $operations->[0];
  }
  my @matching = grep $_->{name} eq $operation_name, @$operations;
  return $matching[0] if @matching == 1;
  die "No operations matching '$operation_name' found.\n";
}

fun _execute_operation(
  HashRef $context,
  HashRef $operation,
  Any $root_value,
) :ReturnType(ExecutionPartialResult | Promise) {
  my $op_type = $operation->{operationType} || 'query';
  my $type = $context->{schema}->$op_type;
  return _wrap_error("No $op_type in schema") if !$type;
  my ($fields) = $type->_collect_fields(
    $context,
    $operation->{selections},
    [[], {}],
    {},
  );
  DEBUG and _debug('_execute_operation(fields)', $fields, $root_value);
  my $path = [];
  my $execute = $op_type eq 'mutation'
    ? \&_execute_fields_serially : \&_execute_fields;
  my $result = eval {
    my $result = $execute->($context, $type, $root_value, $path, $fields);
    return $result if !is_Promise($result);
    $result->then(undef, sub {
      $context->{promise_code}{resolve}->(
        +{ data => undef, %{_wrap_error($_[0])} }
      );
    });
  };
  return _wrap_error($@) if $@;
  $result;
}

fun _execute_fields(
  HashRef $context,
  (InstanceOf['GraphQL::Type']) $parent_type,
  Any $root_value,
  ArrayRef $path,
  FieldsGot $fields,
) :ReturnType(ExecutionPartialResult | Promise) {
  my (%name2executionresult, @errors);
  my $promise_present;
  DEBUG and _debug('_execute_fields', $parent_type->to_string, $fields, $root_value);
  my ($field_names, $nodes_defs) = @$fields;
  for my $result_name (@$field_names) {
    my $nodes = $nodes_defs->{$result_name};
    my $field_node = $nodes->[0];
    my $field_name = $field_node->{name};
    my $field_def = _get_field_def($context->{schema}, $parent_type, $field_name);
    DEBUG and _debug('_execute_fields(resolve)', $parent_type->to_string, $nodes, $root_value, $field_def);
    next if !$field_def;
    my $resolve = $field_def->{resolve} || $context->{field_resolver};
    my $info = _build_resolve_info(
      $context,
      $parent_type,
      $field_def,
      [ @$path, $result_name ],
      $nodes,
    );
    my $result = _resolve_field_value_or_error(
      $context,
      $field_def,
      $nodes,
      $resolve,
      $root_value,
      $info,
    );
    DEBUG and _debug('_execute_fields(resolved)', $parent_type->to_string, $result);
    $result = _complete_value_catching_error(
      $context,
      $field_def->{type},
      $nodes,
      $info,
      [ @$path, $result_name ],
      $result,
    );
    $promise_present ||= is_Promise($result);
    DEBUG and _debug("_execute_fields(complete)($result_name)", $result);
    $name2executionresult{$result_name} = $result;
  }
  DEBUG and _debug('_execute_fields(done)', \%name2executionresult, \@errors, $promise_present);
  return _promise_for_hash($context, \%name2executionresult, \@errors)
    if $promise_present;
  _merge_hash(
    [ keys %name2executionresult ],
    [ values %name2executionresult ],
    \@errors,
  );
}

fun _merge_hash(
  ArrayRef[Str] $keys,
  ArrayRef[ExecutionPartialResult] $values,
  (ArrayRef[InstanceOf['GraphQL::Error']]) $errors,
) :ReturnType(ExecutionPartialResult) {
  DEBUG and _debug('_merge_hash', $keys, $values, $errors);
  my @errors = (@$errors, map @{$_->{errors} || []}, @$values);
  my %name2data;
  for (my $i = @$values - 1; $i >= 0; $i--) {
    $name2data{$keys->[$i]} = $values->[$i]{data};
  }
  DEBUG and _debug('_merge_hash(after)', \%name2data, \@errors);
  +{
    %name2data ? (data => \%name2data) : (),
    @errors ? (errors => \@errors) : ()
  };
}

fun _promise_for_hash(
  HashRef $context,
  HashRef $hash,
  (ArrayRef[InstanceOf['GraphQL::Error']]) $errors,
) :ReturnType(Promise) {
  my ($keys, $values) = ([ keys %$hash ], [ values %$hash ]);
  DEBUG and _debug('_promise_for_hash', $keys);
  die "Given a promise in object but no PromiseCode given\n"
    if !$context->{promise_code};
  $context->{promise_code}{all}->(@$values)->then(sub {
    DEBUG and _debug('_promise_for_hash(all)', \@_);
    _merge_hash($keys, [ map $_->[0], @_ ], $errors);
  });
}

fun _execute_fields_serially(
  HashRef $context,
  (InstanceOf['GraphQL::Type']) $parent_type,
  Any $root_value,
  ArrayRef $path,
  FieldsGot $fields,
) {
  DEBUG and _debug('_execute_fields_serially', $parent_type->to_string, $fields, $root_value);
  # TODO implement
  goto &_execute_fields;
}

use constant FIELDNAME2SPECIAL => {
  map { ($_->{name} => $_) } $SCHEMA_META_FIELD_DEF, $TYPE_META_FIELD_DEF
};
fun _get_field_def(
  (InstanceOf['GraphQL::Schema']) $schema,
  (InstanceOf['GraphQL::Type']) $parent_type,
  StrNameValid $field_name,
) :ReturnType(Maybe[HashRef]) {
  return $TYPE_NAME_META_FIELD_DEF
    if $field_name eq $TYPE_NAME_META_FIELD_DEF->{name};
  return FIELDNAME2SPECIAL->{$field_name}
    if FIELDNAME2SPECIAL->{$field_name} and $parent_type == $schema->query;
  $parent_type->fields->{$field_name};
}

# NB similar ordering as _execute_fields - graphql-js switches
fun _build_resolve_info(
  HashRef $context,
  (InstanceOf['GraphQL::Type']) $parent_type,
  HashRef $field_def,
  ArrayRef $path,
  ArrayRef[HashRef] $nodes,
) {
  {
    field_name => $nodes->[0]{name},
    field_nodes => $nodes,
    return_type => $field_def->{type},
    parent_type => $parent_type,
    path => $path,
    schema => $context->{schema},
    fragments => $context->{fragments},
    root_value => $context->{root_value},
    operation => $context->{operation},
    variable_values => $context->{variable_values},
    promise_code => $context->{promise_code},
  };
}

fun _resolve_field_value_or_error(
  HashRef $context,
  HashRef $field_def,
  ArrayRef[HashRef] $nodes,
  Maybe[CodeLike] $resolve,
  Maybe[Any] $root_value,
  HashRef $info,
) {
  DEBUG and _debug('_resolve_field_value_or_error', $nodes, $field_def, eval { $JSON->encode($nodes->[0]) });
  my $result = eval {
    my $args = _get_argument_values(
      $field_def, $nodes->[0], $context->{variable_values},
    );
    DEBUG and _debug("_resolve_field_value_or_error(args)", $args, eval { $JSON->encode($args) });
    $resolve->($root_value, $args, $context->{context_value}, $info)
  };
  return GraphQL::Error->coerce($@) if $@;
  $result;
}

fun _complete_value_catching_error(
  HashRef $context,
  (InstanceOf['GraphQL::Type']) $return_type,
  ArrayRef[HashRef] $nodes,
  HashRef $info,
  ArrayRef $path,
  Any $result,
) :ReturnType(ExecutionPartialResult | Promise) {
  DEBUG and _debug('_complete_value_catching_error(before)', $return_type->to_string, $result);
  if ($return_type->isa('GraphQL::Type::NonNull')) {
    return _complete_value_with_located_error(@_);
  }
  my $result = eval {
    my $c = _complete_value_with_located_error(@_);
    return $c if !is_Promise($c);
    $c->then(undef, sub {
      $context->{promise_code}{resolve}->(_wrap_error(@_))
    });
  };
  DEBUG and _debug("_complete_value_catching_error(after)(@{[$return_type->to_string]})", $return_type->to_string, $result, $@);
  return _wrap_error($@) if $@;
  $result;
}

fun _complete_value_with_located_error(
  HashRef $context,
  (InstanceOf['GraphQL::Type']) $return_type,
  ArrayRef[HashRef] $nodes,
  HashRef $info,
  ArrayRef $path,
  Any $result,
) :ReturnType(ExecutionPartialResult | Promise) {
  my $result = eval {
    my $c = _complete_value(@_);
    return $c if !is_Promise($c);
    $c->then(undef, sub {
      $context->{promise_code}{reject}->(
        _located_error($_[0], $nodes, $path)
      )
    });
  };
  DEBUG and _debug('_complete_value_with_located_error(after)', $return_type->to_string, $result, $@);
  die _located_error($@, $nodes, $path) if $@;
  $result;
}

fun _complete_value(
  HashRef $context,
  (InstanceOf['GraphQL::Type']) $return_type,
  ArrayRef[HashRef] $nodes,
  HashRef $info,
  ArrayRef $path,
  Any $result,
) :ReturnType(ExecutionPartialResult | Promise) {
  DEBUG and _debug('_complete_value', $return_type->to_string, $path, $result);
  if (is_Promise($result)) {
    my @outerargs = @_[0..4];
    return $result->then(sub { _complete_value(@outerargs, $_[0]) });
  }
  die $result if GraphQL::Error->is($result);
  if ($return_type->isa('GraphQL::Type::NonNull')) {
    my $completed = _complete_value(
      $context,
      $return_type->of,
      $nodes,
      $info,
      $path,
      $result,
    );
    DEBUG and _debug('_complete_value(NonNull)', $return_type->to_string, $completed);
    # The !is_Promise is necessary unlike in the JS because there the
    # null-check will work fine on either a promise or a real value.
    die GraphQL::Error->coerce(
      "Cannot return null for non-nullable field @{[$info->{parent_type}->name]}.@{[$info->{field_name}]}."
    ) if !is_Promise($completed) and !defined $completed->{data};
    return $completed;
  }
  return { data => undef } if !defined $result;
  $return_type->_complete_value(
    $context,
    $nodes,
    $info,
    $path,
    $result,
  );
}

fun _located_error(
  Any $error,
  ArrayRef[HashRef] $nodes,
  ArrayRef $path,
) {
  DEBUG and _debug('_located_error', $error);
  $error = GraphQL::Error->coerce($error);
  return $error if $error->locations;
  GraphQL::Error->coerce($error)->but(
    locations => [ map $_->{location}, @$nodes ],
    path => $path,
  );
}

fun _get_argument_values(
  (HashRef | InstanceOf['GraphQL::Directive']) $def,
  HashRef $node,
  Maybe[HashRef] $variable_values = {},
) {
  my $arg_defs = $def->{args};
  my $arg_nodes = $node->{arguments};
  DEBUG and _debug("_get_argument_values", $arg_defs, $arg_nodes, $variable_values, eval { $JSON->encode($node) });
  return {} if !$arg_defs;
  my @bad = grep { !exists $arg_nodes->{$_} and !defined $arg_defs->{$_}{default_value} and $arg_defs->{$_}{type}->isa('GraphQL::Type::NonNull') } keys %$arg_defs;
  die GraphQL::Error->new(
    message => "Argument '$bad[0]' of type ".
      "'@{[$arg_defs->{$bad[0]}{type}->to_string]}' not given.",
    nodes => [ $node ],
  ) if @bad;
  @bad = grep {
    ref($arg_nodes->{$_}) eq 'SCALAR' and
    $variable_values->{${$arg_nodes->{$_}}} and
    !_type_will_accept($arg_defs->{$_}{type}, $variable_values->{${$arg_nodes->{$_}}}{type})
  } keys %$arg_defs;
  die GraphQL::Error->new(
    message => "Variable '\$${$arg_nodes->{$bad[0]}}' of type '@{[$variable_values->{${$arg_nodes->{$bad[0]}}}{type}->to_string]}'".
      " where expected '@{[$arg_defs->{$bad[0]}{type}->to_string]}'.",
    nodes => [ $node ],
  ) if @bad;
  my @novar = grep {
    ref($arg_nodes->{$_}) eq 'SCALAR' and
    (!$variable_values or !exists $variable_values->{${$arg_nodes->{$_}}}) and
    !defined $arg_defs->{$_}{default_value} and
    $arg_defs->{$_}{type}->isa('GraphQL::Type::NonNull')
  } keys %$arg_defs;
  die GraphQL::Error->new(
    message => "Argument '$novar[0]' of type ".
      "'@{[$arg_defs->{$novar[0]}{type}->to_string]}'".
      " was given variable '\$${$arg_nodes->{$novar[0]}}' but no runtime value.",
    nodes => [ $node ],
  ) if @novar;
  my @enumfail = grep {
    ref($arg_nodes->{$_}) eq 'REF' and
    ref(${$arg_nodes->{$_}}) eq 'SCALAR' and
    !$arg_defs->{$_}{type}->isa('GraphQL::Type::Enum') and
    !($arg_defs->{$_}{type}->isa('GraphQL::Type::NonNull') and $arg_defs->{$_}{type}->of->isa('GraphQL::Type::Enum'))
  } keys %$arg_defs;
  die GraphQL::Error->new(
    message => "Argument '$enumfail[0]' of type ".
      "'@{[$arg_defs->{$enumfail[0]}{type}->to_string]}'".
      " was given ${${$arg_nodes->{$enumfail[0]}}} which is enum value.",
    nodes => [ $node ],
  ) if @enumfail;
  my @enumstring = grep {
    defined($arg_nodes->{$_}) and
    !ref($arg_nodes->{$_})
  } grep $arg_defs->{$_}{type}->isa('GraphQL::Type::Enum'), keys %$arg_defs;
  die GraphQL::Error->new(
    message => "Argument '$enumstring[0]' of type ".
      "'@{[$arg_defs->{$enumstring[0]}{type}->to_string]}'".
      " was given '$arg_nodes->{$enumstring[0]}' which is not enum value.",
    nodes => [ $node ],
  ) if @enumstring;
  return {} if !$arg_nodes;
  my %coerced_values;
  for my $name (keys %$arg_defs) {
    my $arg_def = $arg_defs->{$name};
    my $arg_type = $arg_def->{type};
    my $argument_node = $arg_nodes->{$name};
    my $default_value = $arg_def->{default_value};
    DEBUG and _debug("_get_argument_values($name)", $arg_def, $arg_type, $argument_node, $default_value);
    if (!exists $arg_nodes->{$name}) {
      # none given - apply type arg's default if any. already validated perl
      $coerced_values{$name} = $default_value if exists $arg_def->{default_value};
      next;
    } elsif (ref($argument_node) eq 'SCALAR') {
      # scalar ref means it's a variable. already validated perl
      $coerced_values{$name} =
        ($variable_values && $variable_values->{$$argument_node} && $variable_values->{$$argument_node}{value})
        // $default_value;
      next;
    } else {
      # query literal or variable. JSON land, needs convert/validate
      $coerced_values{$name} = _coerce_value(
        $argument_node, $variable_values, $default_value
      );
    }
    next if !exists $coerced_values{$name};
    DEBUG and _debug("_get_argument_values($name after initial)", $arg_def, $arg_type, $argument_node, $default_value, eval { $JSON->encode(\%coerced_values) });
    eval { $coerced_values{$name} = $arg_type->graphql_to_perl($coerced_values{$name}) };
    DEBUG and do { local $@; _debug("_get_argument_values($name after coerce)", eval { $JSON->encode(\%coerced_values) }) };
    if ($@) {
      my $error = $@;
      $error =~ s#\s+at.*line\s+\d+\.#.#;
      # JSON can't encode scalar references
      my $jsonable = _coerce_for_error($coerced_values{$name});
      die GraphQL::Error->new(
        message => "Argument '$name' got invalid value"
          . " @{[$JSON->encode($jsonable)]}.\nExpected '"
          . $arg_type->to_string . "'.\n$error",
        nodes => [ $node ],
      );
    }
  }
  \%coerced_values;
}

fun _coerce_for_error(Any $value) {
  my $ref = ref $value;
  my $ret = 'SCALAR' eq $ref ? $$value
          : 'ARRAY'  eq $ref ? [ map { _coerce_for_error($_) } @$value ]
          : 'HASH'   eq $ref ? { map { $_ => _coerce_for_error($value->{$_}) } keys %$value }
          :                    $value
          ;
  return $ret;
}

fun _coerce_value(
  Any $argument_node,
  Maybe[HashRef] $variable_values,
  Any $default_value,
) {
  if (ref($argument_node) eq 'SCALAR') {
    # scalar ref means it's a variable. already validated perl but
    # revalidate again as may be in middle of array which would need
    # validate
    return
      ($variable_values && $variable_values->{$$argument_node} && $variable_values->{$$argument_node}{value})
      // $default_value;
  } elsif (ref($argument_node) eq 'REF') {
    # double ref means it's an enum value. JSON land, needs convert/validate
    return $$$argument_node;
  } elsif (ref($argument_node) eq 'ARRAY') {
    # list. recurse
    return [ map _coerce_value(
      $_, $variable_values, $default_value
    ), @$argument_node ];
  } elsif (ref($argument_node) eq 'HASH') {
    # hash. recurse
    return +{ map { $_ => _coerce_value(
      $argument_node->{$_}, $variable_values, $default_value
    ) } keys %$argument_node };
  } else {
    # query literal. JSON land, needs convert/validate
    return $argument_node;
  }
}

fun _type_will_accept(
  (ConsumerOf['GraphQL::Role::Input']) $arg_type,
  (ConsumerOf['GraphQL::Role::Input']) $var_type,
) {
  return 1 if $arg_type == $var_type;
  $arg_type = $arg_type->of if $arg_type->isa('GraphQL::Type::NonNull');
  $var_type = $var_type->of if $var_type->isa('GraphQL::Type::NonNull');
  return 1 if $arg_type == $var_type;
  return 1 if $arg_type->to_string eq $var_type->to_string;
  '';
}

# $root_value is either a hash with fieldnames as keys and either data
#   or coderefs as values
# OR it's just a coderef itself
# OR it's an object which gets tried for fieldname as method
# any code gets called with obvious args
fun _default_field_resolver(
  CodeLike | HashRef | InstanceOf $root_value,
  HashRef $args,
  Any $context,
  HashRef $info,
) {
  my $field_name = $info->{field_name};
  my $property = is_HashRef($root_value)
    ? $root_value->{$field_name}
    : $root_value;
  DEBUG and _debug('_default_field_resolver', $root_value, $field_name, $args, $property);
  if (length(ref $property) and (
    ref($property) eq 'CODE' or
    (blessed $property and overload::Method($property, '&{}'))
  )) {
    DEBUG and _debug('_default_field_resolver', 'codelike');
    return $property->($args, $context, $info);
  }
  if (length(ref $root_value) and blessed($root_value) and $root_value->can($field_name)) {
    DEBUG and _debug('_default_field_resolver', 'method');
    return $root_value->$field_name($args, $context, $info);
  }
  $property;
}

1;