using System.Buffers.Text;
using System.Net;
using System.Text;
using Proxd_man.Config.Outbound;
using Proxd_man.Config.Stream;

namespace Proxd_man.ShareLink;

/// <summary>
/// Shadowsocks 分享链接解析器.
///
/// 遵循了 Shadowsocks 的 <a href="https://github.com/shadowsocks/shadowsocks-org/wiki/SIP002-URI-Scheme"> SIP002 URI Scheme 规范</a>.
/// </summary>
public class ShadowSocksLinkParser : IShareLinkParser
{
    public bool CanParse(string shareLink)
    {
        return shareLink.StartsWith("ss://", StringComparison.CurrentCultureIgnoreCase);
    }

    public BaseOutboundSetting Parse(string shareLink)
    {
        var content = shareLink[5..];
        if (content.Length == 0)
        {
            throw new InvalidShareLinkException("Shadowsocks 分享链接内容为空.");
        }

        // 按照顺序, 先解析 userInfo.
        var userInfoEndAt = content.IndexOf('@');
        if (userInfoEndAt == -1)
        {
            throw new InvalidShareLinkException("Shadowsocks 分享链接中未包含用户信息.");
        }
        
        var userInfo = content[..userInfoEndAt];
        string userInfoContent;
        
        if (userInfo.Contains(':'))
        {
            userInfoContent = userInfo.Trim();
        }
        else
        {
            if (!Base64.IsValid(userInfo))
            {
                throw new InvalidShareLinkException("Shadowsocks 分享链接中的用户信息不是有效的 Base64 字符串.");
            }
            
            var userInfoBytes = Convert.FromBase64String(userInfo);
            userInfoContent = Encoding.UTF8.GetString(userInfoBytes);
        }

        var userInfoParts = userInfoContent.Split(':', 2);
        var method = userInfoParts[0];
        var password = userInfoParts[1];
        
        // 开始解析 userInfo 后面的内容.
        content = content[(userInfoEndAt + 1)..];
        
        var pathSeparatorAt = content.IndexOf('/');
        var fragmentSeparatorAt = content.IndexOf('#');
        int hostEndAt;

        // 首先检查一下合法性, 遵循这些规则:
        // 如果有 pathSeparator, 则检查是否有 "?", 且是否位于 pathSeparator 之后, 否则抛出异常.
        // 其次, fragmentSeparator 只能出现在 pathSeparator 之后.
        
        if (pathSeparatorAt != -1)
        {
            if (content.Contains('?') && content.IndexOf('?') < pathSeparatorAt)
            {
                throw new InvalidShareLinkException("Shadowsocks 分享链接中的 path 部分不合法.");
            }
            
            if (fragmentSeparatorAt != -1 && fragmentSeparatorAt < pathSeparatorAt)
            {
                throw new InvalidShareLinkException("Shadowsocks 分享链接中的 tag 部分不合法.");
            }
            
            hostEndAt = pathSeparatorAt;
        } else if (fragmentSeparatorAt != -1)
        {
            hostEndAt = fragmentSeparatorAt;
        }
        else
        {
            hostEndAt = content.Length;
        }

        if (content[pathSeparatorAt..].Contains("?plugin="))
        {
            throw new InvalidShareLinkException("Shadowsocks 分享链接暂时不支持 plugin 参数.");
        }

        var name = fragmentSeparatorAt != -1 ? null :
            // 需要 Url 解码
            WebUtility.UrlDecode(content[(fragmentSeparatorAt + 1)..].Trim());
        
        var hostContent = content[..hostEndAt];
        var hostPortParts = hostContent.Split(':');
        switch (hostPortParts.Length)
        {
            case > 2:
                throw new InvalidShareLinkException("Shadowsocks 分享链接中的 host 部分不合法.");
            case < 2:
                throw new InvalidShareLinkException("Shadowsocks 分享链接中的 host 部分不包含端口.");
        }
        
        var host = hostPortParts[0];
        if (!int.TryParse(hostPortParts[1], out var port))
        {
            throw new InvalidShareLinkException("Shadowsocks 分享链接中的端口不是一个数字.");
        }

        if (port is < 0 or > 65535)
        {
            throw new InvalidShareLinkException("Shadowsocks 分享链接中的端口超出了端口范围.");
        }
        
        return new ShadowSocksOutboundSetting
        {
            Name = name ?? $"{host}:{port}",
            StreamSetting = new RawStreamSetting(),

            Address = host,
            Port = port,
            Method = method,
            Password = password
        };
    }
}

/// <summary>
/// Shadowsocks 分享链接解析器.
/// 
/// 这个版本使用 Uri 进行解析, 而不是手搓解析过程.
///
/// 遵循了 Shadowsocks 的 <a href="https://github.com/shadowsocks/shadowsocks-org/wiki/SIP002-URI-Scheme"> SIP002 URI Scheme 规范</a>.
/// </summary>
public class ShadowSocksLinkParserV2 : IShareLinkParser
{
    public bool CanParse(string shareLink)
    {
        return shareLink.StartsWith("ss://", StringComparison.CurrentCultureIgnoreCase);
    }

    public BaseOutboundSetting Parse(string shareLink)
    {
        var shareLinkUri = new Uri(shareLink);

        var userInfoContent = shareLinkUri.UserInfo;

        if (!userInfoContent.Contains(':'))
        {
            if (!Base64.IsValid(userInfoContent))
            {
                throw new InvalidShareLinkException("Shadowsocks 分享链接中的用户信息不是有效的 Base64 字符串.");
            }
            
            var userInfoBytes = Convert.FromBase64String(userInfoContent);
            userInfoContent = Encoding.UTF8.GetString(userInfoBytes);
        }
        
        var userInfoParts = userInfoContent.Split(':');
        if (userInfoParts.Length != 2)
        {
            throw new InvalidShareLinkException("Shadowsocks 分享链接中的 userInfo 不合法.");
        } 
        
        var method = WebUtility.UrlDecode(userInfoParts[0]);
        var password = WebUtility.UrlDecode(userInfoParts[1]);
        
        var host = shareLinkUri.Host;
        var port = (ushort) shareLinkUri.Port;
        
        return new ShadowSocksOutboundSetting
        {
            Name = string.IsNullOrEmpty(shareLinkUri.Fragment) ? $"{host}:{port}" : WebUtility.UrlDecode(shareLinkUri.Fragment.Trim()),
            StreamSetting = new RawStreamSetting(),

            Address = host,
            Port = port,
            Method = method,
            Password = password
        };
    }
}

public class VMessLinkParser : IShareLinkParser
{
    public bool CanParse(string shareLink)
    {
        return shareLink.StartsWith("vmess://", StringComparison.CurrentCultureIgnoreCase);
    }

    public BaseOutboundSetting Parse(string shareLink)
    {
        throw new NotImplementedException();
    }
}