<?php

declare(strict_types=1);

namespace App\Models;

use Illuminate\Database\Eloquent\Builder;
use Illuminate\Database\Eloquent\Concerns\HasUlids;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;
use Illuminate\Database\Eloquent\Relations\HasMany;
use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Support\Collection;

final class Event extends Model
{
    use HasFactory;
    use HasUlids;
    use SoftDeletes;

    /** @var array<string, list<string>> Allowed status transitions */
    public const STATUS_TRANSITIONS = [
        'draft' => ['published'],
        'published' => ['registration_open', 'draft'],
        'registration_open' => ['buildup', 'published'],
        'buildup' => ['showday'],
        'showday' => ['teardown'],
        'teardown' => ['closed'],
        'closed' => [],
    ];

    /**
     * Statuses that cascade from a festival parent to its children.
     * When the parent reaches one of these, children in an earlier status follow.
     */
    private const CASCADE_STATUSES = ['showday', 'teardown', 'closed'];

    /** Ordered list used to determine "earlier" status. */
    private const STATUS_ORDER = [
        'draft' => 0,
        'published' => 1,
        'registration_open' => 2,
        'buildup' => 3,
        'showday' => 4,
        'teardown' => 5,
        'closed' => 6,
    ];

    protected $fillable = [
        'organisation_id',
        'parent_event_id',
        'name',
        'slug',
        'start_date',
        'end_date',
        'timezone',
        'status',
        'event_type',
        'event_type_label',
        'sub_event_label',
        'is_recurring',
        'recurrence_rule',
        'recurrence_exceptions',
    ];

    protected function casts(): array
    {
        return [
            'start_date' => 'date',
            'end_date' => 'date',
            'is_recurring' => 'boolean',
            'recurrence_exceptions' => 'array',
            'event_type' => 'string',
        ];
    }

    public function organisation(): BelongsTo
    {
        return $this->belongsTo(Organisation::class);
    }

    public function users(): BelongsToMany
    {
        return $this->belongsToMany(User::class, 'event_user_roles')
            ->withPivot('role')
            ->withTimestamps();
    }

    public function invitations(): HasMany
    {
        return $this->hasMany(UserInvitation::class);
    }

    public function locations(): HasMany
    {
        return $this->hasMany(Location::class);
    }

    public function festivalSections(): HasMany
    {
        return $this->hasMany(FestivalSection::class);
    }

    public function timeSlots(): HasMany
    {
        return $this->hasMany(TimeSlot::class);
    }

    public function persons(): HasMany
    {
        return $this->hasMany(Person::class);
    }

    public function crowdLists(): HasMany
    {
        return $this->hasMany(CrowdList::class);
    }

    public function parent(): BelongsTo
    {
        return $this->belongsTo(Event::class, 'parent_event_id');
    }

    public function children(): HasMany
    {
        return $this->hasMany(Event::class, 'parent_event_id')
            ->orderBy('start_date')
            ->orderBy('name');
    }

    // ----- Status State Machine -----

    public function canTransitionTo(string $newStatus): bool
    {
        $allowed = self::STATUS_TRANSITIONS[$this->status] ?? [];

        return in_array($newStatus, $allowed, true);
    }

    /** @return list<string> Missing prerequisites (empty = OK) */
    public function getTransitionPrerequisites(string $newStatus): array
    {
        $missing = [];

        switch ($newStatus) {
            case 'published':
                if (! $this->name || ! $this->start_date || ! $this->end_date) {
                    $missing[] = 'Event must have a name, start date, and end date.';
                }
                break;
            case 'registration_open':
                if ($this->timeSlots()->count() === 0) {
                    $missing[] = 'At least one time slot must exist before opening registration.';
                }
                if ($this->festivalSections()->count() === 0) {
                    $missing[] = 'At least one section must exist before opening registration.';
                }
                break;
        }

        return $missing;
    }

    /** @return array{errors: list<string>} */
    public function canTransitionToWithPrerequisites(string $newStatus): array
    {
        if (! $this->canTransitionTo($newStatus)) {
            return ['errors' => ["Status transition from '{$this->status}' to '{$newStatus}' is not allowed."]];
        }

        return ['errors' => $this->getTransitionPrerequisites($newStatus)];
    }

    public function transitionTo(string $newStatus): void
    {
        if (! $this->canTransitionTo($newStatus)) {
            throw new \InvalidArgumentException(
                "Cannot transition from '{$this->status}' to '{$newStatus}'."
            );
        }

        $this->update(['status' => $newStatus]);

        if ($this->isFestival() && in_array($newStatus, self::CASCADE_STATUSES, true)) {
            $this->cascadeStatusToChildren($newStatus);
        }
    }

    /**
     * Cascade a status to all children that are in an earlier lifecycle stage.
     */
    private function cascadeStatusToChildren(string $newStatus): void
    {
        $targetOrder = self::STATUS_ORDER[$newStatus];

        $earlierStatuses = array_keys(
            array_filter(self::STATUS_ORDER, fn (int $order) => $order < $targetOrder)
        );

        $this->children()
            ->whereIn('status', $earlierStatuses)
            ->update(['status' => $newStatus]);
    }

    // ----- Scopes -----

    public function scopeTopLevel(Builder $query): Builder
    {
        return $query->whereNull('parent_event_id');
    }

    public function scopeChildren(Builder $query): Builder
    {
        return $query->whereNotNull('parent_event_id');
    }

    public function scopeFestivals(Builder $query): Builder
    {
        return $query->whereIn('event_type', ['festival', 'series']);
    }

    public function scopeWithChildren(Builder $query): Builder
    {
        return $query->where(function (Builder $q) {
            $q->whereIn('id', function ($sub) {
                $sub->select('id')->from('events')->whereNull('parent_event_id');
            })->orWhereIn('parent_event_id', function ($sub) {
                $sub->select('id')->from('events')->whereNull('parent_event_id');
            });
        });
    }

    // ----- Helpers -----

    public function isFestival(): bool
    {
        return $this->event_type !== 'event' && $this->parent_event_id === null;
    }

    public function isSubEvent(): bool
    {
        return $this->parent_event_id !== null;
    }

    public function isFlatEvent(): bool
    {
        return $this->parent_event_id === null && $this->children()->count() === 0;
    }

    public function hasChildren(): bool
    {
        return $this->children()->exists();
    }

    public function scopeDraft(Builder $query): Builder
    {
        return $query->where('status', 'draft');
    }

    public function scopePublished(Builder $query): Builder
    {
        return $query->where('status', 'published');
    }

    public function scopeActive(Builder $query): Builder
    {
        return $query->whereIn('status', ['showday', 'buildup', 'teardown']);
    }

    /**
     * Eager-load the event's own time slots plus, for sub-events,
     * time slots from parent cross_event sections.
     */
    public function scopeWithOperationalContext(Builder $query): Builder
    {
        return $query->with(['timeSlots', 'festivalSections', 'parent.timeSlots', 'parent.festivalSections']);
    }

    /**
     * Get all time slots relevant for shift planning:
     * - Flat event: own time slots
     * - Festival parent: own time slots + all children's time slots
     * - Sub-event: own time slots + parent's time slots
     */
    public function getAllRelevantTimeSlots(): Collection
    {
        $ownSlots = $this->timeSlots()->orderBy('date')->orderBy('start_time')->get();

        if ($this->isFestival()) {
            $childIds = $this->children()->pluck('id');
            $childSlots = TimeSlot::whereIn('event_id', $childIds)
                ->orderBy('date')
                ->orderBy('start_time')
                ->get();

            return $ownSlots->merge($childSlots)->sortBy(['date', 'start_time'])->values();
        }

        if ($this->isSubEvent() && $this->parent_event_id) {
            $parentSlots = TimeSlot::where('event_id', $this->parent_event_id)
                ->orderBy('date')
                ->orderBy('start_time')
                ->get();

            return $ownSlots->merge($parentSlots)->sortBy(['date', 'start_time'])->values();
        }

        return $ownSlots;
    }
}