<?php

declare(strict_types=1);

namespace App\Services\Metrics;

use Carbon\CarbonInterface;
use Illuminate\Database\Query\Builder;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Schema;

/**
 * Windowed deltas from cumulative hourly artwork metric snapshots.
 *
 * Each snapshot stores running totals. Period growth is:
 *   latest in window
 *   - baseline at or immediately before the window start
 *
 * If the artwork was created/published during the window, baseline is 0.
 * If an older artwork has no pre-window snapshot (warm-up / missing hours),
 * fall back to MIN in the window — never SUM cumulatives, never lifetime totals.
 */
final class ArtworkHourlySnapshotWindow
{
    /**
     * How far before the window start to look for a baseline snapshot.
     * Keeps the baseline scan bounded at 30-day table scale.
     */
    public const BASELINE_LOOKBACK_HOURS = 36;

    /**
     * @return array{
     *     views: int,
     *     downloads: int,
     *     favourites: int,
     *     comments: int,
     *     shares: int,
     *     requested_days: int,
     *     table_coverage_days: float,
     *     user_coverage_days: float,
     *     window_complete: bool,
     *     oldest_bucket: ?string,
     *     newest_bucket: ?string,
     *     user_oldest_bucket: ?string,
     *     user_newest_bucket: ?string,
     * }
     */
    public function userWindow(int $userId, int $days = 30): array
    {
        $days = max(1, $days);
        $coverage = $this->tableCoverage($days);
        $empty = $this->emptyResult($days, $coverage);

        if ($userId <= 0 || ! Schema::hasTable('artwork_metric_snapshots_hourly')) {
            return $empty;
        }

        $since = now()->subDays($days);

        $row = DB::query()
            ->fromSub($this->artworkPeriodDeltas($since, $userId), 'deltas')
            ->selectRaw('COALESCE(SUM(views_delta), 0) as views')
            ->selectRaw('COALESCE(SUM(downloads_delta), 0) as downloads')
            ->selectRaw('COALESCE(SUM(favourites_delta), 0) as favourites')
            ->selectRaw('COALESCE(SUM(comments_delta), 0) as comments')
            ->selectRaw('COALESCE(SUM(shares_delta), 0) as shares')
            ->first();

        $userBounds = DB::table('artwork_metric_snapshots_hourly as snapshots')
            ->join('artworks', 'artworks.id', '=', 'snapshots.artwork_id')
            ->where('artworks.user_id', $userId)
            ->whereNull('artworks.deleted_at')
            ->where('snapshots.bucket_hour', '>=', $since)
            ->selectRaw('MIN(snapshots.bucket_hour) as oldest_bucket')
            ->selectRaw('MAX(snapshots.bucket_hour) as newest_bucket')
            ->first();

        $userCoverageDays = $this->coverageDays(
            $userBounds->oldest_bucket ?? null,
            $userBounds->newest_bucket ?? null,
        );

        return [
            'views' => (int) ($row->views ?? 0),
            'downloads' => (int) ($row->downloads ?? 0),
            'favourites' => (int) ($row->favourites ?? 0),
            'comments' => (int) ($row->comments ?? 0),
            'shares' => (int) ($row->shares ?? 0),
            'requested_days' => $days,
            'table_coverage_days' => $coverage['coverage_days'],
            'user_coverage_days' => $userCoverageDays,
            'window_complete' => $coverage['window_complete'],
            'oldest_bucket' => $coverage['oldest_bucket'],
            'newest_bucket' => $coverage['newest_bucket'],
            'user_oldest_bucket' => $userBounds->oldest_bucket ?? null,
            'user_newest_bucket' => $userBounds->newest_bucket ?? null,
        ];
    }

    /**
     * Per-artwork non-negative period deltas for cumulative snapshot columns.
     */
    public function artworkPeriodDeltas(CarbonInterface|\DateTimeInterface $start, ?int $userId = null): Builder
    {
        $inWindow = DB::table('artwork_metric_snapshots_hourly as snapshots');
        $this->constrainOwner($inWindow, $userId);
        $inWindow
            ->where('snapshots.bucket_hour', '>=', $start)
            ->groupBy('snapshots.artwork_id')
            ->select('snapshots.artwork_id')
            ->selectRaw('MAX(snapshots.views_count) as views_latest')
            ->selectRaw('MIN(snapshots.views_count) as views_min')
            ->selectRaw('MAX(snapshots.downloads_count) as downloads_latest')
            ->selectRaw('MIN(snapshots.downloads_count) as downloads_min')
            ->selectRaw('MAX(snapshots.favourites_count) as favourites_latest')
            ->selectRaw('MIN(snapshots.favourites_count) as favourites_min')
            ->selectRaw('MAX(snapshots.comments_count) as comments_latest')
            ->selectRaw('MIN(snapshots.comments_count) as comments_min')
            ->selectRaw('MAX(snapshots.shares_count) as shares_latest')
            ->selectRaw('MIN(snapshots.shares_count) as shares_min');

        $baselineFrom = \Carbon\Carbon::parse($start)->subHours(self::BASELINE_LOOKBACK_HOURS);
        $baseline = DB::table('artwork_metric_snapshots_hourly as snapshots');
        $this->constrainOwner($baseline, $userId);
        $baseline
            ->where('snapshots.bucket_hour', '<', $start)
            ->where('snapshots.bucket_hour', '>=', $baselineFrom)
            ->groupBy('snapshots.artwork_id')
            ->select('snapshots.artwork_id')
            ->selectRaw('MAX(snapshots.views_count) as views_baseline')
            ->selectRaw('MAX(snapshots.downloads_count) as downloads_baseline')
            ->selectRaw('MAX(snapshots.favourites_count) as favourites_baseline')
            ->selectRaw('MAX(snapshots.comments_count) as comments_baseline')
            ->selectRaw('MAX(snapshots.shares_count) as shares_baseline');

        $bornSql = $this->quotedTimestamp($start);

        return DB::query()
            ->fromSub($inWindow, 'win')
            ->leftJoinSub($baseline, 'base', 'base.artwork_id', '=', 'win.artwork_id')
            ->join('artworks', 'artworks.id', '=', 'win.artwork_id')
            ->select('win.artwork_id')
            ->selectRaw($this->deltaExpression('views', $bornSql) . ' as views_delta')
            ->selectRaw($this->deltaExpression('downloads', $bornSql) . ' as downloads_delta')
            ->selectRaw($this->deltaExpression('favourites', $bornSql) . ' as favourites_delta')
            ->selectRaw($this->deltaExpression('comments', $bornSql) . ' as comments_delta')
            ->selectRaw($this->deltaExpression('shares', $bornSql) . ' as shares_delta');
    }

    /**
     * @return array{oldest_bucket: ?string, newest_bucket: ?string, coverage_days: float, window_complete: bool, requested_days: int}
     */
    public function tableCoverage(int $days = 30): array
    {
        $days = max(1, $days);

        if (! Schema::hasTable('artwork_metric_snapshots_hourly')) {
            return [
                'oldest_bucket' => null,
                'newest_bucket' => null,
                'coverage_days' => 0.0,
                'window_complete' => false,
                'requested_days' => $days,
            ];
        }

        $bounds = DB::table('artwork_metric_snapshots_hourly')
            ->selectRaw('MIN(bucket_hour) as oldest_bucket')
            ->selectRaw('MAX(bucket_hour) as newest_bucket')
            ->first();

        $coverageDays = $this->coverageDays(
            $bounds->oldest_bucket ?? null,
            $bounds->newest_bucket ?? null,
        );

        return [
            'oldest_bucket' => $bounds->oldest_bucket ?? null,
            'newest_bucket' => $bounds->newest_bucket ?? null,
            'coverage_days' => $coverageDays,
            'window_complete' => $coverageDays + (1 / 24) >= $days,
            'requested_days' => $days,
        ];
    }

    private function constrainOwner(Builder $query, ?int $userId): void
    {
        if ($userId === null) {
            return;
        }

        $query->join('artworks as owner_artworks', 'owner_artworks.id', '=', 'snapshots.artwork_id')
            ->where('owner_artworks.user_id', $userId)
            ->whereNull('owner_artworks.deleted_at');
    }

    private function quotedTimestamp(CarbonInterface|\DateTimeInterface $start): string
    {
        return DB::getPdo()->quote(\Carbon\Carbon::parse($start)->toDateTimeString());
    }

    private function deltaExpression(string $metric, string $bornSql): string
    {
        $latest = "COALESCE(win.{$metric}_latest, 0)";
        $min = "COALESCE(win.{$metric}_min, 0)";
        $base = "base.{$metric}_baseline";
        $bornInWindow = "COALESCE(artworks.published_at, artworks.created_at) >= {$bornSql}";
        $observed = $this->clampNonNegative("{$latest} - {$min}");
        $fromBaseline = $this->clampNonNegative("{$latest} - {$base}");

        return "CASE WHEN {$bornInWindow} THEN {$latest} WHEN {$base} IS NOT NULL THEN {$fromBaseline} ELSE {$observed} END";
    }

    private function clampNonNegative(string $expression): string
    {
        if (DB::connection()->getDriverName() === 'sqlite') {
            return "CASE WHEN ({$expression}) > 0 THEN ({$expression}) ELSE 0 END";
        }

        return "GREATEST({$expression}, 0)";
    }

    /**
     * @return array<string, mixed>
     */
    private function emptyResult(int $days, array $coverage): array
    {
        return [
            'views' => 0,
            'downloads' => 0,
            'favourites' => 0,
            'comments' => 0,
            'shares' => 0,
            'requested_days' => $days,
            'table_coverage_days' => $coverage['coverage_days'],
            'user_coverage_days' => 0.0,
            'window_complete' => $coverage['window_complete'],
            'oldest_bucket' => $coverage['oldest_bucket'],
            'newest_bucket' => $coverage['newest_bucket'],
            'user_oldest_bucket' => null,
            'user_newest_bucket' => null,
        ];
    }

    private function coverageDays(?string $oldest, ?string $newest): float
    {
        if ($oldest === null || $newest === null) {
            return 0.0;
        }

        $rangeStart = \Carbon\Carbon::parse($oldest);
        $rangeEnd = \Carbon\Carbon::parse($newest);

        if ($rangeEnd->lessThan($rangeStart)) {
            return 0.0;
        }

        return round(abs($rangeStart->diffInMinutes($rangeEnd)) / 1440, 2);
    }
}