<?php

declare(strict_types=1);

namespace GraphQL\Type\Definition;

use GraphQL\Language\AST\FieldNode;
use GraphQL\Language\AST\FragmentDefinitionNode;
use GraphQL\Language\AST\FragmentSpreadNode;
use GraphQL\Language\AST\InlineFragmentNode;
use GraphQL\Language\AST\OperationDefinitionNode;
use GraphQL\Language\AST\SelectionSetNode;
use GraphQL\Type\Schema;
use function array_merge_recursive;

/**
 * Structure containing information useful for field resolution process.
 *
 * Passed as 4th argument to every field resolver. See [docs on field resolving (data fetching)](data-fetching.md).
 */
class ResolveInfo
{
    /**
     * The name of the field being resolved.
     *
     * @api
     * @var string
     */
    public $fieldName;

    /**
     * AST of all nodes referencing this field in the query.
     *
     * @api
     * @var FieldNode[]
     */
    public $fieldNodes = [];

    /**
     * Expected return type of the field being resolved.
     *
     * @api
     * @var ScalarType|ObjectType|InterfaceType|UnionType|EnumType|ListOfType|NonNull
     */
    public $returnType;

    /**
     * Parent type of the field being resolved.
     *
     * @api
     * @var ObjectType
     */
    public $parentType;

    /**
     * Path to this field from the very root value.
     *
     * @api
     * @var string[][]
     */
    public $path;

    /**
     * Instance of a schema used for execution.
     *
     * @api
     * @var Schema
     */
    public $schema;

    /**
     * AST of all fragments defined in query.
     *
     * @api
     * @var FragmentDefinitionNode[]
     */
    public $fragments = [];

    /**
     * Root value passed to query execution.
     *
     * @api
     * @var mixed
     */
    public $rootValue;

    /**
     * AST of operation definition node (query, mutation).
     *
     * @api
     * @var OperationDefinitionNode|null
     */
    public $operation;

    /**
     * Array of variables passed to query execution.
     *
     * @api
     * @var mixed[]
     */
    public $variableValues = [];

    /** @var QueryPlan */
    private $queryPlan;

    /**
     * @param FieldNode[]                                                               $fieldNodes
     * @param ScalarType|ObjectType|InterfaceType|UnionType|EnumType|ListOfType|NonNull $returnType
     * @param string[][]                                                                $path
     * @param FragmentDefinitionNode[]                                                  $fragments
     * @param mixed|null                                                                $rootValue
     * @param mixed[]                                                                   $variableValues
     */
    public function __construct(
        string $fieldName,
        iterable $fieldNodes,
        $returnType,
        ObjectType $parentType,
        array $path,
        Schema $schema,
        array $fragments,
        $rootValue,
        ?OperationDefinitionNode $operation,
        array $variableValues
    ) {
        $this->fieldName      = $fieldName;
        $this->fieldNodes     = $fieldNodes;
        $this->returnType     = $returnType;
        $this->parentType     = $parentType;
        $this->path           = $path;
        $this->schema         = $schema;
        $this->fragments      = $fragments;
        $this->rootValue      = $rootValue;
        $this->operation      = $operation;
        $this->variableValues = $variableValues;
    }

    /**
     * Helper method that returns names of all fields selected in query for
     * $this->fieldName up to $depth levels.
     *
     * Example:
     * query MyQuery{
     * {
     *   root {
     *     id,
     *     nested {
     *      nested1
     *      nested2 {
     *        nested3
     *      }
     *     }
     *   }
     * }
     *
     * Given this ResolveInfo instance is a part of "root" field resolution, and $depth === 1,
     * method will return:
     * [
     *     'id' => true,
     *     'nested' => [
     *         nested1 => true,
     *         nested2 => true
     *     ]
     * ]
     *
     * Warning: this method it is a naive implementation which does not take into account
     * conditional typed fragments. So use it with care for fields of interface and union types.
     *
     * @param int $depth How many levels to include in output
     *
     * @return bool[]
     *
     * @api
     */
    public function getFieldSelection($depth = 0)
    {
        $fields = [];

        /** @var FieldNode $fieldNode */
        foreach ($this->fieldNodes as $fieldNode) {
            if ($fieldNode->selectionSet === null) {
                continue;
            }

            $fields = array_merge_recursive(
                $fields,
                $this->foldSelectionSet($fieldNode->selectionSet, $depth)
            );
        }

        return $fields;
    }

    public function lookAhead() : QueryPlan
    {
        if ($this->queryPlan === null) {
            $this->queryPlan = new QueryPlan(
                $this->parentType,
                $this->schema,
                $this->fieldNodes,
                $this->variableValues,
                $this->fragments
            );
        }

        return $this->queryPlan;
    }

    /**
     * @return bool[]
     */
    private function foldSelectionSet(SelectionSetNode $selectionSet, int $descend) : array
    {
        $fields = [];
        foreach ($selectionSet->selections as $selectionNode) {
            if ($selectionNode instanceof FieldNode) {
                $fields[$selectionNode->name->value] = $descend > 0 && ! empty($selectionNode->selectionSet)
                    ? $this->foldSelectionSet($selectionNode->selectionSet, $descend - 1)
                    : true;
            } elseif ($selectionNode instanceof FragmentSpreadNode) {
                $spreadName = $selectionNode->name->value;
                if (isset($this->fragments[$spreadName])) {
                    /** @var FragmentDefinitionNode $fragment */
                    $fragment = $this->fragments[$spreadName];
                    $fields   = array_merge_recursive(
                        $this->foldSelectionSet($fragment->selectionSet, $descend),
                        $fields
                    );
                }
            } elseif ($selectionNode instanceof InlineFragmentNode) {
                $fields = array_merge_recursive(
                    $this->foldSelectionSet($selectionNode->selectionSet, $descend),
                    $fields
                );
            }
        }

        return $fields;
    }
}