<?php

namespace DayTidy\Booking;

use DayTidy\Db;

class CapacityLocks
{
    private Db $db;

    /**
     * @var string[]
     */
    private array $locks = [];

    public function __construct(?Db $db = null)
    {
        $this->db = $db ?: new Db();
    }

    public function acquire(Draft $draft, int $timeout = 5, bool $preserve_existing_assignments = false): bool
    {
        return $this->acquireMany([$draft], $timeout, $preserve_existing_assignments);
    }

    /**
     * @param Draft[] $drafts
     */
    public function acquireMany(array $drafts, int $timeout = 5, bool $preserve_existing_assignments = false): bool
    {
        foreach ($drafts as $draft)
        {
            if (!$draft instanceof Draft) continue;

            $draft->lockResourceAssignments(!$preserve_existing_assignments);
        }

        foreach ($this->lockKeys($drafts) as $key)
        {
            $locked = (int) $this->db->getVar(
                $this->db->prepare('SELECT GET_LOCK(%s, %d)', $key, $timeout)
            );

            if ($locked !== 1)
            {
                $this->release();

                return false;
            }

            $this->locks[] = $key;
        }

        return true;
    }

    public function release(): void
    {
        foreach (array_reverse($this->locks) as $key)
        {
            $this->db->getVar(
                $this->db->prepare('SELECT RELEASE_LOCK(%s)', $key)
            );
        }

        $this->locks = [];
    }

    /**
     * @param Draft[] $drafts
     * @return string[]
     */
    private function lockKeys(array $drafts): array
    {
        $keys = [];

        foreach ($drafts as $draft)
        {
            if (!$draft instanceof Draft) continue;

            foreach ($this->optionSessionKeys($draft) as $key) $keys[] = $key;
            foreach ($this->resourceKeys($draft) as $key) $keys[] = $key;
        }

        $keys = array_values(array_unique($keys));
        sort($keys);

        return $keys;
    }

    /**
     * @return string[]
     */
    private function optionSessionKeys(Draft $draft): array
    {
        $keys = [];
        $offering_id = $draft->getOffering()->id();

        foreach ($draft->getOptions() as $option_id => $quantity)
        {
            if (absint($quantity) <= 0) continue;

            foreach ($draft->sessionsForOption(absint($option_id)) as $session)
            {
                $keys[] = $this->lockKey('option:' . $offering_id . ':' . absint($option_id) . ':' . $session);
            }
        }

        return $keys;
    }

    /**
     * @return string[]
     */
    private function resourceKeys(Draft $draft): array
    {
        $keys = [];

        foreach ($draft->getResources() as $resource_id)
        {
            $resource_id = absint($resource_id);
            if ($resource_id <= 0) continue;

            $keys[] = $this->lockKey('resource:' . $resource_id);
        }

        return $keys;
    }

    private function lockKey(string $identity): string
    {
        return 'bu_' . substr(md5($this->db->wpdb()->prefix), 0, 8) . '_' . md5($identity);
    }
}