use base64::Engine;
use sha1::{Digest, Sha1};

use super::{
    RpcServerConfig,
    http_surface::{
        HttpRequest, contains_ascii_case_insensitive, header_value, http_response,
        http_response_with_headers, normalized_rpc_path,
    },
};

/// Computes the `Sec-WebSocket-Accept` value for a client-provided handshake key.
fn websocket_accept_value(key: &str) -> String {
    let mut sha1 = Sha1::new();
    sha1.update(key.as_bytes());
    sha1.update(b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11");
    let digest = sha1.finalize();
    base64::engine::general_purpose::STANDARD.encode(digest)
}

/// Builds the HTTP upgrade response for a successful RPC WebSocket handshake.
pub(super) fn websocket_upgrade_response(
    config: &RpcServerConfig,
    request: &HttpRequest,
) -> Vec<u8> {
    if !config.enable_websocket_rpc {
        return http_response("404 Not Found", "text/plain", b"websocket-rpc disabled");
    }
    if normalized_rpc_path(&request.path) != "/jsonrpc" {
        return http_response("404 Not Found", "text/plain", b"unknown websocket path");
    }
    if !request.method.eq_ignore_ascii_case("GET") {
        return http_response(
            "405 Method Not Allowed",
            "text/plain",
            b"websocket upgrade requires GET",
        );
    }
    let Some(key) = header_value(&request.headers, "sec-websocket-key") else {
        return http_response(
            "400 Bad Request",
            "text/plain",
            b"missing sec-websocket-key",
        );
    };
    if !header_value(&request.headers, "upgrade")
        .is_some_and(|value| value.eq_ignore_ascii_case("websocket"))
    {
        return http_response(
            "400 Bad Request",
            "text/plain",
            b"missing websocket upgrade header",
        );
    }
    if !header_value(&request.headers, "connection")
        .is_some_and(|value| contains_ascii_case_insensitive(value, "upgrade"))
    {
        return http_response(
            "400 Bad Request",
            "text/plain",
            b"missing connection upgrade header",
        );
    }
    if header_value(&request.headers, "sec-websocket-version")
        .is_none_or(|value| value.trim() != "13")
    {
        return http_response_with_headers(
            "426 Upgrade Required",
            Some("text/plain"),
            &[("Sec-WebSocket-Version", "13".to_owned())],
            b"unsupported websocket version",
        );
    }

    let mut headers = vec![
        ("Upgrade", "websocket".to_owned()),
        ("Connection", "Upgrade".to_owned()),
        ("Sec-WebSocket-Accept", websocket_accept_value(key)),
    ];
    if let Some(origin) = &config.allow_origin {
        headers.push(("Access-Control-Allow-Origin", origin.clone()));
    }
    http_response_with_headers("101 Switching Protocols", None, &headers, b"")
}