<?php

declare(strict_types=1);

namespace App\Service;

use App\Form\Model\BookingDto;

/**
 * Handles automatic room assignment for booking participants.
 *
 * This service automatically assigns participants to selected rooms based on room capacity
 * and quantity, eliminating the need for manual room selection in the booking flow.
 */
class RoomAssigner
{
    /**
     * Determines if automatic room assignment should be performed.
     *
     * Auto-assignment is only performed when exactly one room type is selected to avoid
     * UX issues with individual participant forms. With multiple room types, users should
     * manually select rooms to avoid having to unselect preassigned rooms.
     *
     * @param BookingDto $dto The booking DTO containing room selections
     *
     * @return bool True if auto-assignment should proceed, false otherwise
     */
    public function shouldAutoAssignRooms(BookingDto $dto): bool
    {
        $selectedRoomTypeCount = 0;

        foreach ($dto->roomSelections as $roomSelection) {
            if (null !== $roomSelection->quantity && $roomSelection->quantity > 0) {
                ++$selectedRoomTypeCount;
            }
        }

        return 1 === $selectedRoomTypeCount;
    }

    /**
     * Automatically assigns participants to rooms based on selected room quantities and capacities.
     *
     * Assignment algorithm:
     * - Iterates through selected rooms in order
     * - For each room quantity, assigns minPax participants to that room ID
     * - Ensures sequential assignment (participant 0, 1, 2, etc.)
     *
     * Example:
     * - 2x "Doppelzimmer" (capacity 2) = participants 0-1 → room A, participants 2-3 → room A
     * - 1x "3-Bett-Zimmer" (capacity 3) = participants 4-6 → room B
     *
     * Note: Only performs assignment if shouldAutoAssignRooms() returns true.
     *
     * @param BookingDto $dto The booking DTO containing room selections and participants
     */
    public function assignParticipantsToRooms(BookingDto $dto): void
    {
        // Skip auto-assignment if multiple room types selected
        if (false === $this->shouldAutoAssignRooms($dto)) {
            return;
        }

        $participantIndex = 0;
        $selectedRooms = $dto->getSelectedRooms();
        $availableRooms = $dto->travel->getAvailableRooms();

        foreach ($selectedRooms as $roomSelection) {
            $room = $availableRooms[$roomSelection->id] ?? null;

            if (null === $room) {
                continue; // Skip if room not found
            }

            $capacityPerRoom = $room->minPax ?? 1;

            // Assign participants for each room quantity
            for ($i = 0; $i < $roomSelection->quantity; ++$i) {
                // Assign participants according to room capacity
                for ($j = 0; $j < $capacityPerRoom; ++$j) {
                    if (isset($dto->participants[$participantIndex])) {
                        $dto->participants[$participantIndex]->assignedRoomId = $room->id;
                        ++$participantIndex;
                    }
                }
            }
        }
    }

    /**
     * Assigns rooms to participants if any participants need room assignment.
     *
     * Checks if any participants have null room assignments, and if so,
     * triggers the auto-assignment process. This is a convenience method
     * that combines the check and assignment into a single call.
     *
     * @param BookingDto $dto The booking DTO to update
     *
     * @return bool True if assignment was performed, false if not needed
     */
    public function assignRoomsIfNeeded(BookingDto $dto): bool
    {
        foreach ($dto->participants as $participant) {
            if (null === $participant->assignedRoomId) {
                $this->assignParticipantsToRooms($dto);

                return true;
            }
        }

        return false;
    }

    /**
     * Validates and resets room assignments that reference rooms no longer selected.
     *
     * This method ensures room assignments remain valid after room selection changes in Step 1.
     * When a user goes back to Step 1 and changes room selections, existing assignments may
     * reference room IDs that are no longer in the selected rooms list. This method detects
     * such invalid assignments and resets them to null.
     *
     * @param BookingDto $dto The booking DTO to validate
     *
     * @return bool True if any assignments were reset, false if all were valid
     */
    public function validateAndResetInvalidAssignments(BookingDto $dto): bool
    {
        $selectedRoomIds = $this->getSelectedRoomIds($dto);
        $resetOccurred = false;

        foreach ($dto->participants as $participant) {
            if (null !== $participant->assignedRoomId && false === in_array($participant->assignedRoomId, $selectedRoomIds, true)) {
                $participant->assignedRoomId = null;
                $resetOccurred = true;
            }
        }

        return $resetOccurred;
    }

    /**
     * Gets the list of room IDs from currently selected rooms.
     *
     * @param BookingDto $dto The booking DTO containing room selections
     *
     * @return array<int> Array of selected room IDs
     */
    private function getSelectedRoomIds(BookingDto $dto): array
    {
        $ids = [];
        foreach ($dto->getSelectedRooms() as $roomSelection) {
            $ids[] = $roomSelection->id;
        }

        return $ids;
    }
}