<?php
/**
 * The code generator.
 *
 * @package Antwork\FieldCode
 */

namespace Antwork\FieldCode;

defined( 'ABSPATH' ) || exit;

/**
 * Generates, on the server and from the saved field group, the code of each field. No state: the same fields give the same code.
 */
final class Generator {

	/**
	 * Location rules.
	 *
	 * @var Locations
	 */
	private $locations;

	/**
	 * Renderers while a snippet is being generated (the filter runs once per snippet, not once per sub-field).
	 *
	 * @var array<string,callable>|null
	 */
	private $current_renderers = null;

	/**
	 * Constructor.
	 *
	 * @param Locations|null $locations Location rules.
	 */
	public function __construct( ?Locations $locations = null ) {
		$this->locations = $locations ? $locations : new Locations();
	}

	/**
	 * Renderers by field type: built-in ones, and the ones other plugins add or replace.
	 *
	 * @return array<string,callable>
	 */
	public function renderers(): array {
		$defaults = Renderers::defaults();

		/**
		 * Renderers of field types: field type => callable( array $field, array $args ): string.
		 * Add one to cover a field type of another plugin, or replace one. See docs/hooks.md for $args.
		 *
		 * @param array<string,callable> $renderers Renderers.
		 */
		$filtered = apply_filters( 'awfc_field_renderers', $defaults );
		if ( ! is_array( $filtered ) ) {
			return $defaults;
		}
		return array_filter(
			$filtered,
			static function ( $renderer, $type ) {
				return is_string( $type ) && is_callable( $renderer );
			},
			ARRAY_FILTER_USE_BOTH
		);
	}

	/**
	 * Code of one field.
	 *
	 * @param array $field Field.
	 * @param array $args  Access to the value: var, value, post_id, container, generator (see Renderers). Other keys
	 *                     (from the renderer of another plugin) reach the renderer unchanged.
	 * @return string|null The code; '' for a field type that holds no value (Message, Tab...); null for a field type not covered.
	 */
	public function field_code( array $field, array $args ): ?string {
		$type      = isset( $field['type'] ) && is_string( $field['type'] ) ? $field['type'] : '';
		$renderers = null !== $this->current_renderers ? $this->current_renderers : $this->renderers();
		if ( '' === $type || ! isset( $renderers[ $type ] ) ) {
			return null;
		}
		$args['generator'] = $this;
		$code              = call_user_func( $renderers[ $type ], $field, $args );
		return is_string( $code ) ? $code : null;
	}

	/**
	 * Code of a field of a field group, with its header and footer.
	 *
	 * @param array  $field   Field.
	 * @param string $post_id PHP expression of the post ID passed to get_field(), or '' for the current post.
	 * @param array  $group   Field group.
	 * @return string|null See field_code().
	 */
	public function snippet( array $field, string $post_id = '', array $group = array() ): ?string {
		$name                    = isset( $field['name'] ) && is_scalar( $field['name'] ) ? (string) $field['name'] : '';
		$args                    = array(
			'var'       => '$' . Code::name( $name ),
			'value'     => Code::get_field( $name, $post_id ),
			'post_id'   => $post_id,
			// The array the value is read from: none at the top of a group, where the value comes from get_field().
			'container' => '',
		);
		$this->current_renderers = $this->renderers();
		try {
			$code = $this->field_code( $field, $args );
		} finally {
			$this->current_renderers = null;
		}
		if ( null === $code || '' === $code ) {
			return $code;
		}
		$context = array(
			'post_id' => $post_id,
			'group'   => $group,
		);

		/**
		 * Code placed before the code of each field (a comment, a type annotation...).
		 *
		 * @param string $header  Header ('' by default).
		 * @param array  $field   Field.
		 * @param array  $context post_id (PHP expression) and group (field group).
		 */
		$header = apply_filters( 'awfc_snippet_header', '', $field, $context );

		/**
		 * Code placed after the code of each field.
		 *
		 * @param string $footer  Footer ('' by default).
		 * @param array  $field   Field.
		 * @param array  $context post_id (PHP expression) and group (field group).
		 */
		$footer = apply_filters( 'awfc_snippet_footer', '', $field, $context );

		$parts = array( is_string( $header ) ? $header : '', $code, is_string( $footer ) ? $footer : '' );
		return implode( "\n", array_filter( $parts, 'strlen' ) );
	}

	/**
	 * Code of every field of a field group.
	 *
	 * @param array $group  Field group.
	 * @param array $fields Its fields, in order.
	 * @return array{post_id:string,uncovered_locations:string[],uncovered_rules:string[],fields:array<int,array{key:string,name:string,label:string,type:string,code:string|null}>}
	 */
	public function group_code( array $group, array $fields ): array {
		$location = $this->locations->read( $group );
		$result   = array();
		foreach ( $fields as $field ) {
			if ( ! is_array( $field ) ) {
				continue;
			}
			$code = $this->snippet( $field, $location['post_id'], $group );
			if ( '' === $code ) {
				continue;
			}
			$result[] = array(
				'key'   => isset( $field['key'] ) && is_scalar( $field['key'] ) ? (string) $field['key'] : '',
				'name'  => isset( $field['name'] ) && is_scalar( $field['name'] ) ? (string) $field['name'] : '',
				'label' => isset( $field['label'] ) && is_scalar( $field['label'] ) ? (string) $field['label'] : '',
				'type'  => isset( $field['type'] ) && is_scalar( $field['type'] ) ? (string) $field['type'] : '',
				'code'  => $code,
			);
		}
		return array(
			'post_id'             => $location['post_id'],
			'uncovered_locations' => $location['uncovered'],
			'uncovered_rules'     => $location['uncovered_rules'],
			'fields'              => $result,
		);
	}
}