using System.Security.Cryptography;
using System.Text;
using System.Web;
using System.Collections.Specialized;
using Uwaa.HTTP.Websockets;

namespace Uwaa.HTTP;

/// <summary>
/// Contains the method, path, query, headers, and content of a HTTP request.
/// </summary>
public record HttpRequest
{
    /// <summary>
    /// The HTTP method of the request.
    /// </summary>
    public HttpMethod Method { get; set; } = HttpMethod.Any;

    /// <summary>
    /// The HTTP path being requested.
    /// </summary>
    public string Path { get; set; } = string.Empty;

    /// <summary>
    /// Additional paramters in the path of the request.
    /// </summary>
    public NameValueCollection Query { get; set; }

    /// <summary>
    /// HTTP header fields included in the request.
    /// </summary>
    public HttpFields Fields { get; set; }

    /// <summary>
    /// The body of the HTTP request, if any.
    /// </summary>
    public HttpContent? Content { get; set; }

    /// <summary>
    /// If true, the connection is requesting to be upgrading to a websocket.
    /// </summary>
    public bool IsWebsocket => Fields.Upgrade == "websocket";

    /// <summary>
    /// Whether or not the request is valid.
    /// </summary>
    public bool Valid => Method != HttpMethod.Any && Path.StartsWith('/');

    public HttpRequest(HttpMethod method, string path, HttpContent? content = null) : this(method, path, new HttpFields(), content)
    {
    }

    public HttpRequest(HttpMethod method, string path, HttpFields fields, HttpContent? content = null)
    {
        Method = method;
        Fields = fields;
        Content = content;

        string[] pathParts = path.Split('?', 2, StringSplitOptions.RemoveEmptyEntries);
        Path = pathParts[0];
        Query = HttpUtility.ParseQueryString(pathParts.Length > 1 ? pathParts[1] : string.Empty);
    }

    /// <summary>
    /// Returns true if the client is accepting the provided type, otherwise false.
    /// </summary>
    public bool CanAccept(MIMEType type)
    {
        if (Fields.Accept == null)
            return true;

        for (int i = 0; i < Fields.Accept.Length; i++)
            if (Fields.Accept[i].Match(type))
                return true;

        return false;
    }

    internal async Task WriteTo(HttpStream stream)
    {
        StringBuilder sb = new StringBuilder();

        sb.Append(Method.ToString());
        sb.Append(' ');
        sb.Append(Path);
        if (Query != null && Query.Count > 0)
        {
            sb.Append('?');
            for (int i = 0; i < Query.Count; i++)
            {
                if (i > 0)
                    sb.Append('&');
                sb.Append(HttpUtility.UrlEncode(Query.GetKey(i)));
                sb.Append('=');
                sb.Append(HttpUtility.UrlEncode(Query[i]));
            }
            
        }
        sb.Append(" HTTP/1.1\r\n");

        void writeField(string key, string value)
        {
            sb.Append(key);
            sb.Append(": ");
            sb.Append(value);
            sb.Append("\r\n");
        }

        if (Content.HasValue)
        {
            Fields.ContentLength = Content.Value.Content.Length;
            Fields.ContentType = Content.Value.Type.ToString();
        }
        else
        {
            Fields.ContentLength = null;
            Fields.ContentType = null;
        }

        Fields.EmitAll(writeField);
        sb.Append("\r\n");

        await stream.Write(Encoding.ASCII.GetBytes(sb.ToString()));

        if (Content.HasValue)
            await stream.Write(Content.Value.Content);

        await stream.Flush();
    }

    /// <summary>
    /// Generates a response which upgrades the connection to a websocket.
    /// </summary>
    /// <param name="callback">The websocket execution function to call.</param>
    /// <param name="protocols">Subprotocols which can be accepted. If null or empty, any protocol will be accepted.</param>
    /// <returns>Returns a <seealso cref="SwitchingProtocols"/> response.</returns>
    /// <remarks>
    /// If an upgrade has not been requested or no subprotocol can be negotiated, this will return null.
    /// </remarks>
    public SwitchingProtocols? UpgradeToWebsocket(WebsocketHandler callback, params string[]? protocols)
    {
        if (Fields.WebSocketKey == null)
            return null;

        //Subprotocol negotiation
        string? chosenProtocol = null;
        string? requestedProtocols = Fields.WebSocketProtocol;
        if (requestedProtocols != null && protocols != null && protocols.Length > 0)
        {
            foreach (string requested in requestedProtocols.ToLower().Split(',', StringSplitOptions.TrimEntries))
            {
                foreach (string supported in protocols)
                {
                    if (requested.Equals(supported, StringComparison.InvariantCultureIgnoreCase))
                    {
                        chosenProtocol = supported;
                        goto a;
                    }
                }
            }
            return null;
        }

    a:
        string acceptKey = Convert.ToBase64String(SHA1.HashData(Encoding.ASCII.GetBytes(Fields.WebSocketKey + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11")));
        return new SwitchingProtocols(acceptKey, chosenProtocol, callback);
    }
}