<?php
namespace Relay\Files;

use Relay\Support\RelayError;

/** A list of file-list entry numbers (the files a destination still needs), 8 bytes each. */
final class IndexList
{
    private string $path;

    public function __construct(string $path)
    {
        $this->path = $path;
    }

    public function count(): int
    {
        clearstatcache(true, $this->path);
        return is_file($this->path) ? intdiv((int) filesize($this->path), 8) : 0;
    }

    /** @param int[] $indexes */
    public function add(array $indexes): void
    {
        if ($indexes === []) {
            return;
        }
        $this->truncate($this->count());
        $data = '';
        foreach ($indexes as $i) {
            $data .= pack('J', (int) $i);
        }
        Fs::ensure_dir(dirname($this->path));
        if (file_put_contents($this->path, $data, FILE_APPEND) !== strlen($data)) {
            throw new RelayError('files.write_failed', esc_html__('Could not write the file list. The disk may be full.', 'siterelay'));
        }
    }

    /** @return int[] up to $max numbers from position $from on */
    public function slice(int $from, int $max): array
    {
        $count = $this->count();
        if ($from < 0 || $from >= $count || $max <= 0) {
            return [];
        }
        $h = Fs::open($this->path, 'rb');
        fseek($h, $from * 8);
        $data = (string) Fs::read($h, min($max, $count - $from) * 8);
        Fs::close($h);
        return array_values(unpack('J*', $data) ?: []);
    }

    public function truncate(int $count): void
    {
        clearstatcache(true, $this->path);
        if (is_file($this->path) && filesize($this->path) !== max(0, $count) * 8) {
            $h = Fs::open($this->path, 'r+b');
            ftruncate($h, max(0, $count) * 8);
            Fs::close($h);
            clearstatcache(true, $this->path);
        }
    }

    public function delete(): void
    {
        wp_delete_file($this->path);
    }
}