<?php defined('BASEPATH') or exit('No direct script access allowed');

/* ----------------------------------------------------------------------------
 * Easy!Appointments - Open Source Web Scheduler
 *
 * @package     EasyAppointments
 * @author      A.Tselegidis <alextselegidis@gmail.com>
 * @copyright   Copyright (c) 2013 - 2020, Alex Tselegidis
 * @license     http://opensource.org/licenses/GPL-3.0 - GPLv3
 * @link        http://easyappointments.org
 * @since       v1.2.0
 * ---------------------------------------------------------------------------- */

require_once __DIR__ . '/API_V1_Controller.php';
require_once __DIR__ . '/../../Appointments.php';

use EA\Engine\Types\UnsignedInteger;

/**
 * Availabilities Controller
 *
 * @property CI_Session session
 * @property CI_Loader load
 * @property CI_Input input
 * @property CI_Output output
 * @property CI_Config config
 * @property CI_Lang lang
 * @property CI_Cache cache
 * @property CI_DB_query_builder db
 * @property CI_Security security
 * @property Google_Sync google_sync
 * @property Ics_file ics_file
 * @property Appointments_Model appointments_model
 * @property Providers_Model providers_model
 * @property Services_Model services_model
 * @property Customers_Model customers_model
 * @property Settings_Model settings_model
 * @property Timezones_Model timezones_model
 * @property Roles_Model roles_model
 * @property Secretaries_Model secretaries_model
 * @property Admins_Model admins_model
 * @property User_Model user_model
 *
 * @package Controllers
 * @subpackage API
 */
class Availabilities extends API_V1_Controller {
    /**
     * Class Constructor
     */
    public function __construct()
    {
        parent::__construct();
        $this->load->model('appointments_model');
        $this->load->model('providers_model');
        $this->load->model('services_model');
        $this->load->model('settings_model');
    }

    /**
     * GET API Method
     *
     * Provide the "providerId", "serviceId" and "date" GET parameters to get the availabilities for a specific date.
     * If no "date" was provided then the current date will be used.
     */
    public function get()
    {
        try
        {
            $providerId = new UnsignedInteger($this->input->get('providerId'));
            $serviceId = new UnsignedInteger($this->input->get('serviceId'));

            if ($this->input->get('date'))
            {
                $date = new DateTime($this->input->get('date'));
            }
            else
            {
                $date = new DateTime();
            }

            $provider = $this->providers_model->get_row($providerId->get());
            $service = $this->services_model->get_row($serviceId->get());

            $emptyPeriods = $this->_getProviderAvailableTimePeriods($providerId->get(),
                $date->format('Y-m-d'), []);

            $availableHours = $this->_calculateAvailableHours($emptyPeriods,
                $date->format('Y-m-d'), $service['duration'], FALSE, $service['availabilities_type']);

            if ($service['attendants_number'] > 1)
            {
                $availableHours = $this->_getMultipleAttendantsHours($date->format('Y-m-d'), $service, $provider);
            }

            // If the selected date is today, remove past hours. It is important  include the timeout before
            // booking that is set in the back-office the system. Normally we might want the customer to book
            // an appointment that is at least half or one hour from now. The setting is stored in minutes.
            if ($date->format('Y-m-d') === date('Y-m-d'))
            {
                $bookAdvanceTimeout = $this->settings_model->get_setting('book_advance_timeout');

                foreach ($availableHours as $index => $value)
                {
                    $availableHour = strtotime($value);
                    $currentHour = strtotime('+' . $bookAdvanceTimeout . ' minutes', strtotime('now'));
                    if ($availableHour <= $currentHour)
                    {
                        unset($availableHours[$index]);
                    }
                }
            }

            $availableHours = array_values($availableHours);
            sort($availableHours, SORT_STRING);
            $availableHours = array_values($availableHours);

            $this->output
                ->set_content_type('application/json')
                ->set_output(json_encode($availableHours));
        }
        catch (Exception $exception)
        {
            exit($this->_handleException($exception));
        }
    }

    /**
     * Get an array containing the free time periods (start - end) of a selected date.
     *
     * This method is very important because there are many cases where the system needs to
     * know when a provider is available for an appointment. This method will return an array
     * that belongs to the selected date and contains values that have the start and the end
     * time of an available time period.
     *
     * @param int $provider_id The provider's record id.
     * @param string $selected_date The date to be checked (MySQL formatted string).
     * @param array $exclude_appointments This array contains the ids of the appointments that
     * will not be taken into consideration when the available time periods are calculated.
     *
     * @return array Returns an array with the available time periods of the provider.
     */
    protected function _getProviderAvailableTimePeriods(
        $provider_id,
        $selected_date,
        $exclude_appointments = []
    )
    {
        $this->load->model('appointments_model');
        $this->load->model('providers_model');

        // Get the provider's working plan and reserved appointments.
        $working_plan = json_decode($this->providers_model->get_setting('working_plan', $provider_id), TRUE);

        $where_clause = [
            'id_users_provider' => $provider_id
        ];

        $reserved_appointments = $this->appointments_model->get_batch($where_clause);

        // Sometimes it might be necessary to not take into account some appointment records
        // in order to display what the providers' available time periods would be without them.
        foreach ($exclude_appointments as $excluded_id)
        {
            foreach ($reserved_appointments as $index => $reserved)
            {
                if ($reserved['id'] == $excluded_id)
                {
                    unset($reserved_appointments[$index]);
                }
            }
        }

        // Find the empty spaces on the plan. The first split between the plan is due to
        // a break (if exist). After that every reserved appointment is considered to be
        // a taken space in the plan.
        $selected_date_working_plan = $working_plan[strtolower(date('l', strtotime($selected_date)))];
        $available_periods_with_breaks = [];

        if (isset($selected_date_working_plan['breaks']))
        {
            $start = new DateTime($selected_date_working_plan['start']);
            $end = new DateTime($selected_date_working_plan['end']);
            $available_periods_with_breaks[] = [
                'start' => $selected_date_working_plan['start'],
                'end' => $selected_date_working_plan['end']
            ];

            // Split the working plan to available time periods that do not contain the breaks in them.
            foreach ($selected_date_working_plan['breaks'] as $index => $break)
            {
                $break_start = new DateTime($break['start']);
                $break_end = new DateTime($break['end']);

                if ($break_start < $start)
                {
                    $break_start = $start;
                }

                if ($break_end > $end)
                {
                    $break_end = $end;
                }

                if ($break_start >= $break_end)
                {
                    continue;
                }

                foreach ($available_periods_with_breaks as $key => $open_period)
                {
                    $s = new DateTime($open_period['start']);
                    $e = new DateTime($open_period['end']);

                    if ($s < $break_end && $break_start < $e)
                    { // check for overlap
                        $changed = FALSE;
                        if ($s < $break_start)
                        {
                            $open_start = $s;
                            $open_end = $break_start;
                            $available_periods_with_breaks[] = [
                                'start' => $open_start->format("H:i"),
                                'end' => $open_end->format("H:i")
                            ];
                            $changed = TRUE;
                        }

                        if ($break_end < $e)
                        {
                            $open_start = $break_end;
                            $open_end = $e;
                            $available_periods_with_breaks[] = [
                                'start' => $open_start->format("H:i"),
                                'end' => $open_end->format("H:i")
                            ];
                            $changed = TRUE;
                        }

                        if ($changed)
                        {
                            unset($available_periods_with_breaks[$key]);
                        }
                    }
                }
            }
        }

        // Break the empty periods with the reserved appointments.
        $available_periods_with_appointments = $available_periods_with_breaks;

        foreach ($reserved_appointments as $appointment)
        {
            foreach ($available_periods_with_appointments as $index => &$period)
            {
                $a_start = strtotime($appointment['start_datetime']);
                $a_end = strtotime($appointment['end_datetime']);
                $p_start = strtotime($selected_date . ' ' . $period['start']);
                $p_end = strtotime($selected_date . ' ' . $period['end']);

                if ($a_start <= $p_start && $a_end <= $p_end && $a_end <= $p_start)
                {
                    // The appointment does not belong in this time period, so we
                    // will not change anything.
                }
                else
                {
                    if ($a_start <= $p_start && $a_end <= $p_end && $a_end >= $p_start)
                    {
                        // The appointment starts before the period and finishes somewhere inside.
                        // We will need to break this period and leave the available part.
                        $period['start'] = date('H:i', $a_end);
                    }
                    else
                    {
                        if ($a_start >= $p_start && $a_end <= $p_end)
                        {
                            // The appointment is inside the time period, so we will split the period
                            // into two new others.
                            unset($available_periods_with_appointments[$index]);
                            $available_periods_with_appointments[] = [
                                'start' => date('H:i', $p_start),
                                'end' => date('H:i', $a_start)
                            ];
                            $available_periods_with_appointments[] = [
                                'start' => date('H:i', $a_end),
                                'end' => date('H:i', $p_end)
                            ];
                        }
                        else
                        {
                            if ($a_start >= $p_start && $a_end >= $p_start && $a_start <= $p_end)
                            {
                                // The appointment starts in the period and finishes out of it. We will
                                // need to remove the time that is taken from the appointment.
                                $period['end'] = date('H:i', $a_start);
                            }
                            else
                            {
                                if ($a_start >= $p_start && $a_end >= $p_end && $a_start >= $p_end)
                                {
                                    // The appointment does not belong in the period so do not change anything.
                                }
                                else
                                {
                                    if ($a_start <= $p_start && $a_end >= $p_end && $a_start <= $p_end)
                                    {
                                        // The appointment is bigger than the period, so this period needs to be removed.
                                        unset($available_periods_with_appointments[$index]);
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }

        return array_values($available_periods_with_appointments);
    }

    /**
     * Calculate the available appointment hours.
     *
     * Calculate the available appointment hours for the given date. The empty spaces
     * are broken down to 15 min and if the service fit in each quarter then a new
     * available hour is added to the "$available_hours" array.
     *
     * @param array $empty_periods Contains the empty periods as generated by the
     * "_getProviderAvailableTimePeriods" method.
     * @param string $selected_date The selected date to be search (format )
     * @param int $service_duration The service duration is required for the hour calculation.
     * @param bool $manage_mode (optional) Whether we are currently on manage mode (editing an existing appointment).
     * @param string $availabilities_type Optional ('flexible'), the service availabilities type.
     *
     * @return array Returns an array with the available hours for the appointment.
     */
    protected function _calculateAvailableHours(
        array $empty_periods,
        $selected_date,
        $service_duration,
        $manage_mode = FALSE,
        $availabilities_type = 'flexible'
    )
    {
        $this->load->model('settings_model');

        $available_hours = [];

        foreach ($empty_periods as $period)
        {
            $start_hour = new DateTime($selected_date . ' ' . $period['start']);
            $end_hour = new DateTime($selected_date . ' ' . $period['end']);
            $interval = $availabilities_type === AVAILABILITIES_TYPE_FIXED ? (int)$service_duration : 15;

            $current_hour = $start_hour;
            $diff = $current_hour->diff($end_hour);

            while (($diff->h * 60 + $diff->i) >= intval($service_duration))
            {
                $available_hours[] = $current_hour->format('H:i');
                $current_hour->add(new DateInterval('PT' . $interval . 'M'));
                $diff = $current_hour->diff($end_hour);
            }
        }

        return $available_hours;
    }

    /**
     * Get multiple attendants hours.
     *
     * This method will add the extra appointment hours whenever a service accepts multiple attendants.
     *
     * @param string $selected_date The selected appointment date.
     * @param array $service Selected service data.
     * @param array $provider Selected provider data.
     *
     * @return array Retunrs the available hours array.
     */
    protected function _getMultipleAttendantsHours(
        $selected_date,
        $service,
        $provider
    )
    {
        $this->load->model('appointments_model');
        $this->load->model('services_model');
        $this->load->model('providers_model');

        $unavailabilities = $this->appointments_model->get_batch([
            'is_unavailable' => TRUE,
            'DATE(start_datetime)' => $selected_date,
            'id_users_provider' => $provider['id']
        ]);

        $working_plan = json_decode($provider['settings']['working_plan'], TRUE);
        $working_day = strtolower(date('l', strtotime($selected_date)));
        $working_hours = $working_plan[$working_day];

        $periods = [
            [
                'start' => new DateTime($selected_date . ' ' . $working_hours['start']),
                'end' => new DateTime($selected_date . ' ' . $working_hours['end'])
            ]
        ];

        $periods = $this->_removeBreaks($selected_date, $periods, $working_hours['breaks']);
        $periods = $this->_removeUnavailabilities($periods, $unavailabilities);

        $hours = [];

        $interval_value = $service['availabilities_type'] == AVAILABILITIES_TYPE_FIXED ? $service['duration'] : '15';
        $interval = new DateInterval('PT' . (int)$interval_value . 'M');
        $duration = new DateInterval('PT' . (int)$service['duration'] . 'M');

        foreach ($periods as $period)
        {
            $slot_start = clone $period['start'];
            $slot_end = clone $slot_start;
            $slot_end->add($duration);

            while ($slot_end <= $period['end'])
            {
                // Check reserved attendants for this time slot and see if current attendants fit.
                $appointment_attendants_number = $this->appointments_model->get_attendants_number_for_period($slot_start,
                    $slot_end, $service['id']);

                if ($appointment_attendants_number < $service['attendants_number'])
                {
                    $hours[] = $slot_start->format('H:i');
                }

                $slot_start->add($interval);
                $slot_end->add($interval);
            }
        }

        return $hours;
    }

    /**
     * Remove breaks from available time periods.
     *
     * @param string $selected_date Selected data (Y-m-d format).
     * @param array $periods Time periods of the current date.
     * @param array $breaks Breaks array for the current date.
     *
     * @return array Returns the available time periods without the breaks.
     */
    public function _removeBreaks($selected_date, $periods, $breaks)
    {
        if ( ! $breaks)
        {
            return $periods;
        }

        foreach ($breaks as $break)
        {
            $break_start = new DateTime($selected_date . ' ' . $break['start']);
            $break_end = new DateTime($selected_date . ' ' . $break['end']);

            foreach ($periods as &$period)
            {
                $period_start = $period['start'];
                $period_end = $period['end'];

                if ($break_start <= $period_start && $break_end >= $period_start && $break_end <= $period_end)
                {
                    // left
                    $period['start'] = $break_end;
                    continue;
                }

                if ($break_start >= $period_start && $break_start <= $period_end && $break_end >= $period_start && $break_end <= $period_end)
                {
                    // middle
                    $period['end'] = $break_start;
                    $periods[] = [
                        'start' => $break_end,
                        'end' => $period_end
                    ];
                    continue;
                }

                if ($break_start >= $period_start && $break_start <= $period_end && $break_end >= $period_end)
                {
                    // right
                    $period['end'] = $break_start;
                    continue;
                }

                if ($break_start <= $period_start && $break_end >= $period_end)
                {
                    // break contains period
                    $period['start'] = $break_end;
                    continue;
                }
            }
        }

        return $periods;
    }

    /**
     * Remove the unavailabilities from the available time periods of the selected date.
     *
     * @param array $periods Available time periods.
     * @param array $unavailabilities Unavailabilities of the current date.
     *
     * @return array Returns the available time periods without the unavailabilities.
     */
    public function _removeUnavailabilities($periods, $unavailabilities)
    {
        foreach ($unavailabilities as $unavailability)
        {
            $unavailability_start = new DateTime($unavailability['start_datetime']);
            $unavailability_end = new DateTime($unavailability['end_datetime']);

            foreach ($periods as &$period)
            {
                $period_start = $period['start'];
                $period_end = $period['end'];

                if ($unavailability_start <= $period_start && $unavailability_end >= $period_start && $unavailability_end <= $period_end)
                {
                    // left
                    $period['start'] = $unavailability_end;
                    continue;
                }

                if ($unavailability_start >= $period_start && $unavailability_start <= $period_end && $unavailability_end >= $period_start && $unavailability_end <= $period_end)
                {
                    // middle
                    $period['end'] = $unavailability_start;
                    $periods[] = [
                        'start' => $unavailability_end,
                        'end' => $period_end
                    ];
                    continue;
                }

                if ($unavailability_start >= $period_start && $unavailability_start <= $period_end && $unavailability_end >= $period_end)
                {
                    // right
                    $period['end'] = $unavailability_start;
                    continue;
                }

                if ($unavailability_start <= $period_start && $unavailability_end >= $period_end)
                {
                    // Unavaibility contains period
                    $period['start'] = $unavailability_end;
                    continue;
                }
            }
        }

        return $periods;
    }
}