<?php

namespace App\Services\Link;

use App\Models\LinkClick;
use App\Models\ShortLink;
use App\Support\Link\LinkGeoResolver;
use App\Support\Link\LinkUserAgentParser;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Log;
use Throwable;

class LinkClickRecorder
{
    public function __construct(private readonly LinkClickCounterBuffer $counters) {}

    /**
     * Record one click.
     *
     * link_clicks is the source of truth and is insert-only, so it carries no lock
     * contention no matter how popular a link becomes. The denormalised totals on
     * short_links / link_wallets are buffered in Redis and flushed on a schedule —
     * see LinkClickCounterBuffer for why they can no longer be written inline.
     *
     * Nothing here may break the redirect: a visitor who clicked a link must be sent
     * on their way even if analytics fails entirely.
     */
    public function record(ShortLink $link, Request $request): void
    {
        try {
            $ipHash = hash('sha256', $request->ip().'|'.config('app.key'));
            $isUnique = $this->isUnique($link, $ipHash);
            $parsed = LinkUserAgentParser::parse((string) $request->userAgent());

            LinkClick::create([
                'short_link_id' => $link->id,
                'ip_hash' => $ipHash,
                'user_agent' => $this->truncate($request->userAgent(), 512),
                'referer' => $this->truncate($request->header('referer'), 512),
                'device_type' => $parsed['device_type'],
                'browser' => $parsed['browser'],
                'os' => $parsed['os'],
                'country' => LinkGeoResolver::countryCode($request),
                'is_unique' => $isUnique,
                'clicked_at' => now(),
            ]);

            $this->counters->add($link, $isUnique);
        } catch (Throwable $e) {
            Log::warning('link click recording failed', [
                'short_link_id' => $link->id,
                'error' => $e->getMessage(),
            ]);
        }
    }

    /**
     * First click from this IP within the window?
     *
     * Relies on the (short_link_id, ip_hash, clicked_at) index. Without it this is a
     * scan over every click the link has ever received, which degrades as the link
     * gets popular — the opposite of what a viral link needs.
     */
    private function isUnique(ShortLink $link, string $ipHash): bool
    {
        $windowHours = (int) config('link.click_unique_window_hours', 24);

        return ! LinkClick::query()
            ->where('short_link_id', $link->id)
            ->where('ip_hash', $ipHash)
            ->where('clicked_at', '>=', now()->subHours($windowHours))
            ->exists();
    }

    private function truncate(?string $value, int $max): ?string
    {
        if ($value === null) {
            return null;
        }

        return mb_strlen($value) > $max ? mb_substr($value, 0, $max) : $value;
    }
}