<?php

namespace WP_CLI\Traverser;

use UnexpectedValueException;
use WP_CLI\Exception\NonExistentKeyException;

class RecursiveDataStructureTraverser {

    /**
     * @var mixed The data to traverse set by reference.
     */
    protected $data;

    /**
     * @var null|string The key the data belongs to in the parent's data.
     */
    protected $key;

    /**
     * @var null|static The parent instance of the traverser.
     */
    protected $parent;

    /**
     * RecursiveDataStructureTraverser constructor.
     *
     * @param mixed       $data            The data to read/manipulate by reference.
     * @param string|int  $key             The key/property the data belongs to.
     * @param static|null $parent_instance The parent instance of the traverser.
     */
    public function __construct( &$data, $key = null, $parent_instance = null ) {
        $this->data   =& $data;
        $this->key    = $key;
        $this->parent = $parent_instance;
    }

    /**
     * Get the nested value at the given key path.
     *
     * @param string|int|array $key_path
     *
     * @return static
     */
    public function get( $key_path ) {
        return $this->traverse_to( (array) $key_path )->value();
    }

    /**
     * Get the current data.
     *
     * @return mixed
     */
    public function value() {
        return $this->data;
    }

    /**
     * Update a nested value at the given key path.
     *
     * @param string|int|array $key_path
     * @param mixed $value
     */
    public function update( $key_path, $value ) {
        $this->traverse_to( (array) $key_path )->set_value( $value );
    }

    /**
     * Update the current data with the given value.
     *
     * This will mutate the variable which was passed into the constructor
     * as the data is set and traversed by reference.
     *
     * @param mixed $value
     */
    public function set_value( $value ) {
        $this->data = $value;
    }

    /**
     * Unset the value at the given key path.
     *
     * @param $key_path
     */
    public function delete( $key_path ) {
        $this->traverse_to( (array) $key_path )->unset_on_parent();
    }

    /**
     * Define a nested value while creating keys if they do not exist.
     *
     * @param array $key_path
     * @param mixed $value
     */
    public function insert( $key_path, $value ) {
        try {
            $this->update( $key_path, $value );
        } catch ( NonExistentKeyException $exception ) {
            $exception->get_traverser()->create_key();
            $this->insert( $key_path, $value );
        }
    }

    /**
     * Delete the key on the parent's data that references this data.
     */
    public function unset_on_parent() {
        $this->parent->delete_by_key( $this->key );
    }

    /**
     * Delete the given key from the data.
     *
     * @param $key
     */
    public function delete_by_key( $key ) {
        if ( is_array( $this->data ) ) {
            unset( $this->data[ $key ] );
        } else {
            unset( $this->data->$key );
        }
    }

    /**
     * Get an instance of the traverser for the given hierarchical key.
     *
     * @param array $key_path Hierarchical key path within the current data to traverse to.
     *
     * @throws NonExistentKeyException
     *
     * @return self
     */
    public function traverse_to( array $key_path ) {
        $current = array_shift( $key_path );

        if ( null === $current ) {
            return $this;
        }

        if ( ! $this->exists( $current ) ) {
            $exception = new NonExistentKeyException( "No data exists for key \"{$current}\"" );
            $exception->set_traverser( new self( $this->data, $current, $this->parent ) );
            throw $exception;
        }

        foreach ( $this->data as $key => &$key_data ) {
            if ( $key === $current ) {
                $traverser = new self( $key_data, $key, $this );
                return $traverser->traverse_to( $key_path );
            }
        }
    }

    /**
     * Create the key on the current data.
     *
     * @throws UnexpectedValueException
     */
    protected function create_key() {
        if ( is_array( $this->data ) ) {
            $this->data[ $this->key ] = null;
        } elseif ( is_object( $this->data ) ) {
            $this->data->{$this->key} = null;
        } else {
            $type = gettype( $this->data );
            throw new UnexpectedValueException(
                "Cannot create key \"{$this->key}\" on data type {$type}"
            );
        }
    }

    /**
     * Check if the given key exists on the current data.
     *
     * @param string $key
     *
     * @return bool
     */
    public function exists( $key ) {
        return ( is_array( $this->data ) && array_key_exists( $key, $this->data ) ) ||
            ( is_object( $this->data ) && property_exists( $this->data, $key ) );
    }
}