package dev.lexian.remotepacksync;

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.time.Duration;
import java.util.HexFormat;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/** Downloads and validates a SHA-1 checksum without downloading the resource pack itself. */
public final class RemoteSha1Fetcher {
    private static final Pattern SHA1_PATTERN = Pattern.compile("(?i)(?<![0-9a-f])[0-9a-f]{40}(?![0-9a-f])");
    private static final Duration REQUEST_TIMEOUT = Duration.ofSeconds(15);
    private static final int MAX_RESPONSE_BYTES = 64 * 1024;

    private final HttpClient client = HttpClient.newBuilder()
            .connectTimeout(Duration.ofSeconds(10))
            .followRedirects(HttpClient.Redirect.NORMAL)
            .build();

    public byte[] fetch(URI sha1Url) throws IOException, InterruptedException {
        HttpRequest request = HttpRequest.newBuilder(sha1Url)
                .GET()
                .timeout(REQUEST_TIMEOUT)
                .header("Accept", "text/plain, text/*;q=0.9, */*;q=0.1")
                .header("User-Agent", "RemotePackSync/v1.0.0")
                .build();

        HttpResponse<byte[]> response = client.send(request, HttpResponse.BodyHandlers.ofByteArray());
        if (response.statusCode() < 200 || response.statusCode() >= 300) {
            throw new IOException("SHA-1 endpoint returned HTTP " + response.statusCode());
        }
        if (response.body().length > MAX_RESPONSE_BYTES) {
            throw new IOException("SHA-1 response exceeds " + MAX_RESPONSE_BYTES + " bytes");
        }

        String responseText = new String(response.body(), java.nio.charset.StandardCharsets.UTF_8);
        Matcher matcher = SHA1_PATTERN.matcher(responseText);
        if (!matcher.find()) {
            throw new IOException("SHA-1 response does not contain a 40-character hexadecimal SHA-1");
        }
        return HexFormat.of().parseHex(matcher.group());
    }
}