<?php

namespace ChargeForms\Includes\Logic;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/** PHP mirror of assets/src/builder/logic/engine/graph.js — same Kahn's-algorithm approach, same edge-detection rule (only source:'field' reads/writes participate). See that file's header comment for the full reasoning. */
class Dependency_Graph {

	/** Walks a trigger tree and collects every field id it reads via source:'field' conditions — mirrors engine/readRefs.js. */
	public static function collect_read_field_refs( $node, array &$out = [] ) {
		if ( empty( $node ) ) {
			return $out;
		}
		if ( 'condition' === ( $node['type'] ?? null ) ) {
			if ( 'field' === ( $node['source'] ?? null ) && ! empty( $node['ref'] ) ) {
				$out[ $node['ref'] ] = true;
			}
			return $out;
		}
		if ( 'group' === ( $node['type'] ?? null ) ) {
			foreach ( $node['children'] ?? [] as $child ) {
				self::collect_read_field_refs( $child, $out );
			}
		}
		return $out;
	}

	private static function collect_write_field_refs( array $rule ) {
		$refs = [];
		foreach ( $rule['actions'] ?? [] as $action ) {
			if ( ! empty( $action['target'] ) ) {
				$refs[ $action['target'] ] = true;
			}
		}
		return $refs;
	}

	/** Returns [ 'order' => string[], 'cycle' => string[] ] — see graph.js's identically-named function for the full algorithm explanation. */
	public static function build_evaluation_order( array $rules ) {
		$ids       = array_map( fn( $r ) => $r['id'], $rules );
		$writes_by = []; // fieldId -> [ ruleId => true ]
		$reads_by  = []; // ruleId -> [ fieldId => true ]

		foreach ( $rules as $rule ) {
			$reads_by[ $rule['id'] ] = self::collect_read_field_refs( $rule['trigger'] ?? null );
			foreach ( array_keys( self::collect_write_field_refs( $rule ) ) as $field_id ) {
				$writes_by[ $field_id ][ $rule['id'] ] = true;
			}
		}

		$adjacency  = array_fill_keys( $ids, [] ); // ruleId -> [ ruleId => true ] it must run before
		$in_degree  = array_fill_keys( $ids, 0 );

		foreach ( $rules as $rule ) {
			foreach ( array_keys( $reads_by[ $rule['id'] ] ) as $field_id ) {
				foreach ( array_keys( $writes_by[ $field_id ] ?? [] ) as $writer_id ) {
					if ( $writer_id === $rule['id'] ) {
						continue;
					}
					if ( empty( $adjacency[ $writer_id ][ $rule['id'] ] ) ) {
						$adjacency[ $writer_id ][ $rule['id'] ] = true;
						$in_degree[ $rule['id'] ]++;
					}
				}
			}
		}

		// Kahn's algorithm.
		$queue = array_values( array_filter( $ids, fn( $id ) => 0 === $in_degree[ $id ] ) );
		$order = [];
		while ( ! empty( $queue ) ) {
			$id      = array_shift( $queue );
			$order[] = $id;
			foreach ( array_keys( $adjacency[ $id ] ) as $next ) {
				$in_degree[ $next ]--;
				if ( 0 === $in_degree[ $next ] ) {
					$queue[] = $next;
				}
			}
		}

		$cycle = array_values( array_filter( $ids, fn( $id ) => $in_degree[ $id ] > 0 ) );
		return [ 'order' => $order, 'cycle' => $cycle ];
	}
}