<?php

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

class AdGhost_Proximity {

    const MIN_CHARS_HEADING = 150;

    const MIN_CHARS_IMAGE = 100;

    private $elements = [];

    private $content;

    public function __construct($content) {
        $this->content  = $content;
        $this->elements = $this->find_elements($content);
    }

    public static function min_chars($kind) {
        $default = ($kind === 'image') ? self::MIN_CHARS_IMAGE : self::MIN_CHARS_HEADING;
        return (int) apply_filters('adghost_proximity_min_chars', $default, $kind);
    }

    public function reason_for($offset) {
        foreach ($this->elements as $el) {
            $min = self::min_chars($el['kind']);
            if ($min <= 0) {
                continue;
            }

            if ($el['end'] <= $offset) {

                $gap = $this->text_length($el['end'], $offset);
                if ($gap < $min) {
                    return sprintf(
                        'Only %d characters below %s (needs %d)',
                        $gap,
                        $el['label'],
                        $min
                    );
                }
            }
        }

        return null;
    }

    public function filter(array $points, ?array &$rejected = null) {
        $collect = is_array($rejected);
        $out = [];
        foreach ($points as $p) {
            $reason = $this->reason_for($p['offset'] ?? 0);
            if ($reason !== null) {
                if ($collect) {
                    $rejected[$p['id']] = $reason;
                }
                continue;
            }
            $out[] = $p;
        }
        return $out;
    }

    private function text_length($from, $to) {
        if ($to <= $from) {
            return 0;
        }
        $slice = substr($this->content, $from, $to - $from);

        $slice = preg_replace('/<!--.*?-->/s', '', $slice);
        return strlen(trim(preg_replace('/\s+/', ' ', wp_strip_all_tags($slice))));
    }

    private function find_elements($content) {
        $out = [];

        if (preg_match_all('/<(h[1-6])(\s[^>]*)?>.*?<\/\1>/is', $content, $m, PREG_OFFSET_CAPTURE)) {
            foreach ($m[0] as $i => $match) {
                $out[] = [
                    'start' => $match[1],
                    'end'   => $match[1] + strlen($match[0]),
                    'kind'  => 'heading',
                    'label' => 'a <' . strtolower($m[1][$i][0]) . '> heading',
                ];
            }
        }

        if (preg_match_all('/<figure\b[^>]*>.*?<\/figure>|<img\b[^>]*>/is', $content, $m, PREG_OFFSET_CAPTURE)) {
            foreach ($m[0] as $match) {
                $out[] = [
                    'start' => $match[1],
                    'end'   => $match[1] + strlen($match[0]),
                    'kind'  => 'image',
                    'label' => 'an image',
                ];
            }
        }

        return $out;
    }
}