func Tesses.CrossLang.PackageManager()
{
    func ParseFileName(name)
    {
        
        var index = name.LastIndexOf('.');
        if(index == -1) throw "We expect an extension";
        if(name.Substring(index) != ".crvm") throw "We expect the extension .crvm";
        name = name.Substring(0,index);
        //Name-VERSION-[dev|alpha|beta|prod]

        var lastIndex = name.LastIndexOf('-');
        var verStage = name.Substring(lastIndex+1);
        var versionStr = verStage;
        if(verStage == "dev" || verStage == "alpha" || verStage == "beta" || verStage == "prod")
        {
            var lastIndex2 = name.LastIndexOf('-', lastIndex-1);
            return {
                Name = name.Substring(0,lastIndex2),
                Version = name.Substring(lastIndex2+1)
            };
        }
        else
        {
            return {
                Name = name.Substring(0,lastIndex),
                Version = name.Substring(lastIndex+1)
            };
        }
    }
    var configRoot = Path.FromString(Env.Config) / "Tesses" / "CrossLang";
    var packageCache = configRoot / "PackageCache";
    FS.Local.CreateDirectory(packageCache);
    func FileReadByteArray(fs,path)
    {
        var f = fs.OpenFile(path,"rb");
            var ms = FS.MemoryStream(true);
            f.CopyTo(ms);
            var buff = ms.GetBytes();
            f.Close();
        return buff;
    }
   func FileReadString  (fs,path) {
            var buff = FileReadByteArray(fs,path).ToString();
            ms.Close();
            return text;
        }
    return {
        Offline = false,
        ParseFileName,
        GetPackageServers = ()=>{
            var packageConfigFile = configRoot / "package_servers.json";
            if(FS.Local.RegularFileExists(packageConfigFile))
            {
                return Json.Decode(FileReadString(FS.Local, packageConfigFile));
            }
            return ["https://cpkg.tesseslanguage.com/"];
        },
        GetPackage = (this,name, version) =>
        {
            var v = Tesses.CrossLang.Version.Parse(version);
            var useCache = v.Stage != Tesses.CrossLang.Version.Dev;
            var pkgFile = packageCache / name / v.ToString();
            if(useCache && FS.Local.RegularFileExists(pkgFile))   
            {
                return FileReadByteArray(FS.Local,pkgFile);
            }
            if(this.Offline) return null;

            each(var item : this.GetPackageServers())
            {
                //https://cpkg.tesseslanguage.com/api/v1/download?name=MyPackage&version=1.0.0.0-prod
                var uri = $"{item.TrimEnd('/')}/api/v1/download?name={Net.Http.UrlEncode(name)}&version={Net.Http.UrlEncode(version)}";
                var req = Net.Http.MakeRequest(uri);
                if(req.StatusCode == 200)
                {
                    var strm = FS.MemoryStream(true);
                    req.CopyToStream(strm);
                    
                    if(useCache) {
                        FS.Local.CreateDirectory(packageCache / name);
                        var f = FS.Local.OpenFile(pkgFile,"wb");
                        strm.Seek(0,0);
                        strm.CopyTo(f);
                        f.Close();
                    }
                    var data = strm.GetBytes();
                    strm.Close();
                    req.Close();
                    return data;
                }
            }
            return null;
        },
        GetLatest = (this,name) => {
            var pkgServers = this.GetPackageServers();
            if(this.Offline || pkgServers.Count == 0)
            {
                //user has declared they are offline or don't have packageServers look through packages locally
                var version = Tesses.CrossLang.Version.Create(0,0,0,0,0);
                var configRoot = Path.FromString(Env.Config) / "Tesses" / "CrossLang";
                var dir = configRoot / "PackageCache" / name;
                if(FS.Local.DirectoryExists(dir))
                each(var f : FS.Local.EnumeratePaths(dir))
                {
                    var v = Tesses.CrossLang.Version.Parse(f.GetFileName());
                    if(v >= version)
                    {
                        version = v;
                    }
                }

                if(version.VersionInt == 0) return null;
                return version.ToString();
            }
            else
            {
                each(var item : pkgServers)
                {
                    var uri = $"{item.TrimEnd('/')}/api/v1/latest?name={Net.Http.UrlEncode(name)}";
                    var req = Net.Http.MakeRequest(uri);
                    if(req.StatusCode == 200)
                    {
                        var res0 = req.ReadAsString();
                      
                        var res = Json.Decode(res0);
                        req.Close();
                        return res.version;
                    }
                }

            }
            return null;
        }
    };
}