<?php

declare (strict_types=1);
namespace GDAVSCOPE\Amp\Dns;

final class DnsConfig
{
    private array $nameservers;
    private array $knownHosts;
    private float $timeout = 3;
    // seconds.
    private int $attempts = 2;
    private array $searchList = [];
    private int $ndots = 1;
    private bool $rotation = \false;
    /**
     * @throws DnsConfigException
     */
    public function __construct(array $nameservers, array $knownHosts = [])
    {
        if (\count($nameservers) < 1) {
            throw new DnsConfigException("At least one nameserver is required for a valid config");
        }
        foreach ($nameservers as $nameserver) {
            $this->validateNameserver($nameserver);
        }
        // Windows does not include localhost in its host file. Fetch it from the system instead
        if (!isset($knownHosts[DnsRecord::A]["localhost"]) && !isset($knownHosts[DnsRecord::AAAA]["localhost"])) {
            // PHP currently provides no way to **resolve** IPv6 hostnames (not even with fallback)
            $local = \gethostbyname("localhost");
            if ($local !== "localhost") {
                $knownHosts[DnsRecord::A]["localhost"] = $local;
            } else {
                $knownHosts[DnsRecord::AAAA]["localhost"] = '::1';
            }
        }
        $this->nameservers = $nameservers;
        $this->knownHosts = $knownHosts;
    }
    public function withSearchList(array $searchList): self
    {
        $self = clone $this;
        // Replace null with '.' for backward compatibility
        $self->searchList = \array_map(fn($search) => $search ?? '.', $searchList);
        return $self;
    }
    /**
     * @throws DnsConfigException
     */
    public function withNdots(int $ndots): self
    {
        if ($ndots < 0) {
            throw new DnsConfigException("Invalid ndots ({$ndots}), must be greater or equal to 0");
        }
        $self = clone $this;
        $self->ndots = \min($ndots, 15);
        return $self;
    }
    public function withRotationEnabled(bool $enabled = \true): self
    {
        $self = clone $this;
        $self->rotation = $enabled;
        return $self;
    }
    public function withTimeout(float $timeout): self
    {
        if ($timeout < 0) {
            throw new DnsConfigException("Invalid timeout ({$timeout}), must be 0 or greater");
        }
        $self = clone $this;
        $self->timeout = $timeout;
        return $self;
    }
    public function withAttempts(int $attempts): self
    {
        if ($attempts < 1) {
            throw new DnsConfigException("Invalid attempt count ({$attempts}), must be 1 or greater");
        }
        $self = clone $this;
        $self->attempts = $attempts;
        return $self;
    }
    public function getNameservers(): array
    {
        return $this->nameservers;
    }
    public function getKnownHosts(): array
    {
        return $this->knownHosts;
    }
    public function getTimeout(): float
    {
        return $this->timeout;
    }
    public function getAttempts(): int
    {
        return $this->attempts;
    }
    public function getSearchList(): array
    {
        return $this->searchList;
    }
    public function getNdots(): int
    {
        return $this->ndots;
    }
    public function isRotationEnabled(): bool
    {
        return $this->rotation;
    }
    /**
     * @throws DnsConfigException
     */
    private function validateNameserver(string $nameserver): void
    {
        if ($nameserver[0] === "[") {
            // IPv6
            $addr = \strstr(\substr($nameserver, 1), "]", \true);
            $addrEnd = \strrpos($nameserver, "]");
            if ($addrEnd === \false) {
                throw new DnsConfigException("Invalid nameserver: {$nameserver}");
            }
            $port = \substr($nameserver, $addrEnd + 1);
            if ($port !== "" && !\preg_match("(^:(\\d+)\$)", $port)) {
                throw new DnsConfigException("Invalid nameserver: {$nameserver}");
            }
            $port = $port === "" ? 53 : \substr($port, 1);
        } else {
            // IPv4
            $arr = \explode(":", $nameserver, 2);
            if (\count($arr) === 2) {
                [$addr, $port] = $arr;
            } else {
                $addr = $arr[0];
                $port = 53;
            }
        }
        $addr = \trim($addr, "[]");
        $port = (int) $port;
        if (!\inet_pton($addr)) {
            throw new DnsConfigException("Invalid server IP: {$addr}");
        }
        if ($port < 1 || $port > 65535) {
            throw new DnsConfigException("Invalid server port: {$port}");
        }
    }
}
