<?php

namespace App\Services;

use App\Models\Event;
use App\Models\Funnel;
use App\Models\PageView;
use Illuminate\Support\Carbon;
use Illuminate\Support\Collection;
use Illuminate\Support\Facades\DB;

class FunnelAnalysisService
{
    public function __construct(
        private readonly Funnel $funnel,
        private readonly Carbon $from,
        private readonly Carbon $to,
    ) {}

    /**
     * Analyze funnel: for each step, count how many unique visitors completed it
     * (in order, within the same session or across sessions in the date range).
     *
     * Returns: [{label, type, value, visitors, drop_off, drop_off_pct, conversion_pct}]
     */
    public function analyze(): array
    {
        $steps = $this->funnel->steps;
        if (empty($steps)) {
            return [];
        }

        $websiteId = $this->funnel->website_id;

        // Step 1: get all visitor IDs who completed the first step
        $currentVisitorIds = $this->visitorIdsForStep($steps[0], $websiteId);
        $firstStepCount = $currentVisitorIds->count();

        $results = [];
        foreach ($steps as $i => $step) {
            if ($i === 0) {
                $stepVisitors = $firstStepCount;
            } else {
                $stepVisitorIds = $this->visitorIdsForStep($step, $websiteId);
                $currentVisitorIds = $currentVisitorIds->intersect($stepVisitorIds);
                $stepVisitors = $currentVisitorIds->count();
            }

            $prevCount = $i > 0 ? $results[$i - 1]['visitors'] : $stepVisitors;
            $dropOff = $prevCount - $stepVisitors;
            $dropOffPct = $prevCount > 0 ? round(($dropOff / $prevCount) * 100, 1) : 0;
            $conversionPct = $firstStepCount > 0 ? round(($stepVisitors / $firstStepCount) * 100, 1) : 0;

            $results[] = [
                'label' => $step['label'] ?? $step['value'],
                'type' => $step['type'],
                'value' => $step['value'],
                'visitors' => $stepVisitors,
                'drop_off' => $dropOff,
                'drop_off_pct' => $dropOffPct,
                'conversion_pct' => $conversionPct,
            ];
        }

        return $results;
    }

    private function visitorIdsForStep(array $step, int $websiteId): Collection
    {
        if ($step['type'] === 'pageview') {
            return PageView::where('website_id', $websiteId)
                ->whereBetween('viewed_at', [$this->from, $this->to])
                ->where('path', $step['value'])
                ->distinct()
                ->pluck('visitor_id');
        }

        return Event::where('website_id', $websiteId)
            ->whereBetween('occurred_at', [$this->from, $this->to])
            ->where('name', $step['value'])
            ->distinct()
            ->pluck('visitor_id');
    }
}