Subversion Repositories currency_converter

unit VtsCurConv;

interface

uses

  SysUtils, Classes, Controls;

type

  EVtsCurConvException = class(Exception);

  TVtsCurApiKey = string;

  TVtsCur = string;

  TVtsRate = double;

  TVtsCurConv = class(TObject)

  private

    FSecure: boolean;

    FMaxAgeSeconds: integer;

    FConfirmWebAccess: boolean;

    FFallBackToCache: boolean;

    FInteractiveAPIKeyInput: boolean;

  protected

    function GetJsonRaw(HistoricDate: TDate=0): string;

    procedure QueryAPIKey(msg: string=''); virtual;

  public

    property Secure: boolean read FSecure write FSecure;

    property MaxAgeSeconds: integer read FMaxAgeSeconds write FMaxAgeSeconds;

    property ConfirmWebAccess: boolean read FConfirmWebAccess write FConfirmWebAccess;

    property FallBackToCache: boolean read FFallBackToCache write FFallBackToCache;

    property InteractiveAPIKeyInput: boolean read FInteractiveAPIKeyInput write FInteractiveAPIKeyInput;

    class procedure WriteAPIKey(key: TVtsCurApiKey; UserMode: boolean=true);

    class function ReadAPIKey: TVtsCurApiKey;

    class function DeleteAPIKey(UserMode: boolean=true): boolean;

    function Convert(value: Currency; fromCur, toCur: TVtsCur; HistoricDate: TDate=0): Currency;

    function GetAcceptedCurrencies(sl: TStringList=nil; HistoricDate: TDate=0): integer;

  end;

implementation

uses

  Windows, Registry, uLkJSON, Dialogs, IdHTTP, DateUtils;

function FileGetContents(filename: string): string;

var

  sl: TStringList;

begin

  sl := TStringList.Create;

  try

    sl.LoadFromFile(filename);

    result := sl.Text;

  finally

    sl.Free;

  end;

end;

procedure FilePutContents(filename, content: string);

var

  sl: TStringList;

begin

  sl := TStringList.Create;

  try

    sl.Text := content;

    sl.SaveToFile(filename);

  finally

    sl.Free;

  end;

end;

function GetPage(aURL: string): string;

var

  Response: TStringStream;

  HTTP: TIdHTTP;

const

  HTTP_RESPONSE_OK = 200;

begin

  // https://stackoverflow.com/questions/9239267/how-to-download-a-web-page-into-a-variable

  Result := '';

  Response := TStringStream.Create('');

  try

    HTTP := TIdHTTP.Create(nil);

    try

      HTTP.Get(aURL, Response);

      if HTTP.ResponseCode = HTTP_RESPONSE_OK then

        Result := Response.DataString

      else

        raise EVtsCurConvException.CreateFmt('Cannot download from %s', [aURL]);

    finally

      HTTP.Free;

    end;

  finally

    Response.Free;

  end;

end;

function GetTempDir: string;

var

  Dir: string;

  Len: DWord;

begin

  SetLength(Dir, MAX_PATH);

  Len := GetTempPath(MAX_PATH, PChar(Dir));

  if Len > 0 then

  begin

    SetLength(Dir, Len);

    Result := Dir;

  end

  else

    RaiseLastOSError;

end;

{ TVtsCurConv }

class procedure TVtsCurConv.WriteAPIKey(key: TVtsCurApiKey; UserMode: boolean=true);

  procedure _WriteAPIKey(root: HKEY);

  var

    reg: TRegistry;

  begin

    reg := TRegistry.Create;

    try

      reg.RootKey := root;

      if reg.OpenKey('Software\ViaThinkSoft\CurrencyConverter', true) then

      begin

        reg.WriteString('APIKey', key);

        reg.CloseKey;

      end

      else raise EVtsCurConvException.Create('Cannot open registry key');

    finally

      reg.Free;

    end;

  end;

begin

  if UserMode then

    _WriteAPIKey(HKEY_CURRENT_USER)

  else

    _WriteAPIKey(HKEY_LOCAL_MACHINE);

end;

class function TVtsCurConv.DeleteAPIKey(UserMode: boolean=true): boolean;

  procedure _DeleteAPIKey(root: HKEY);

  var

    reg: TRegistry;

  begin

    reg := TRegistry.Create;

    try

      reg.RootKey := root;

      if reg.OpenKey('Software\ViaThinkSoft\CurrencyConverter', true) then

      begin

        result := reg.DeleteValue('APIKey');

        reg.CloseKey;

      end;

    finally

      reg.Free;

    end;

  end;

begin

  result := false;

  if UserMode then

    _DeleteAPIKey(HKEY_CURRENT_USER)

  else

    _DeleteAPIKey(HKEY_LOCAL_MACHINE);

end;

class function TVtsCurConv.ReadAPIKey: TVtsCurApiKey;

  function _ReadAPIKey(root: HKEY): string;

  var

    reg: TRegistry;

  begin

    result := '';

    reg := TRegistry.Create;

    try

      reg.RootKey := root;

      if reg.OpenKeyReadOnly('Software\ViaThinkSoft\CurrencyConverter') then

      begin

        if reg.ValueExists('APIKey') then result := reg.ReadString('APIKey');

        reg.CloseKey;

      end;

    finally

      reg.Free;

    end;

  end;

begin

  result := _ReadAPIKey(HKEY_CURRENT_USER);

  if result = '' then result := _ReadAPIKey(HKEY_LOCAL_MACHINE);

end;

function TVtsCurConv.Convert(value: Currency; fromCur, toCur: TVtsCur; HistoricDate: TDate=0): Currency;

var

  rateTo, rateFrom: TVtsRate;

  i: Integer;

  rateToFound: Boolean;

  rateFromFound: Boolean;

  sJSON: String;

  xSource: TlkJSONstring;

  xRoot: TlkJSONobject;

  xQuotes: TlkJSONobject;

  xRate: TlkJSONnumber;

begin

  result := 0; // to avoid that the compiler shows a warning

  fromCur := Trim(UpperCase(fromCur));

  toCur := Trim(UpperCase(toCur));

  sJSON := GetJsonRaw(HistoricDate);

  xRoot := TlkJSON.ParseText(sJSON) as TlkJSONobject;

  try

    xSource := xRoot.Field['source'] as TlkJSONstring;

    if not assigned(xSource) then raise EVtsCurConvException.Create('JSON entry "source" is missing!');

    xQuotes := xRoot.Field['quotes'] as TlkJSONobject;

    if not assigned(xQuotes) then raise EVtsCurConvException.Create('JSON entry "quotes" is missing!');

    rateToFound := false;

    rateFromFound := false;

    rateTo := 0.00; // to avoid that the compiler shows a warning

    rateFrom := 0.00; // to avoid that the compiler shows a warning

    for i := 0 to xQuotes.Count - 1 do

    begin

      if Length(xQuotes.NameOf[i]) <> 6 then raise EVtsCurConvException.Create('Length of quotes-entry is unexpected!');

      xRate := xQuotes.Field[xQuotes.NameOf[i]] as TlkJSONnumber;

      if not Assigned(xRate) then raise EVtsCurConvException.Create('JSON entry quotes->rate is missing!');

      if Copy(xQuotes.NameOf[i], 1, 3) = xSource.Value then

      begin

        if Copy(xQuotes.NameOf[i], 4, 3) = toCur then

        begin

          rateTo := xRate.Value;

          rateToFound := true;

        end;

        if Copy(xQuotes.NameOf[i], 4, 3) = fromCur then

        begin

          rateFrom := xRate.Value;

          rateFromFound := true;

        end;

      end;

    end;

    if not rateToFound then raise EVtsCurConvException.CreateFmt('Currency "%s" not supported', [toCur]);

    if not rateFromFound then raise EVtsCurConvException.CreateFmt('Currency "%s" not supported', [fromCur]);

    result := value * rateTo / rateFrom;

  finally

    xRoot.Free;

  end;

end;

procedure TVtsCurConv.QueryAPIKey(msg: string='');

var

  s: string;

begin

  s := Trim(InputBox('currencylayer.com', Trim(msg + ' Please enter your API key:'), ''));

  if s = '' then raise EVtsCurConvException.Create('No API key provided.');

  WriteAPIKey(s);

end;

function TVtsCurConv.GetAcceptedCurrencies(sl: TStringList=nil; HistoricDate: TDate=0): integer;

var

  i: Integer;

  sJSON: String;

  xSource: TlkJSONstring;

  xRoot: TlkJSONobject;

  xQuotes: TlkJSONobject;

begin

  result := 0;

  sJSON := GetJsonRaw(HistoricDate);

  xRoot := TlkJSON.ParseText(sJSON) as TlkJSONobject;

  try

    xSource := xRoot.Field['source'] as TlkJSONstring;

    if not assigned(xSource) then raise EVtsCurConvException.Create('JSON entry "source" is missing!');

    xQuotes := xRoot.Field['quotes'] as TlkJSONobject;

    if not assigned(xQuotes) then raise EVtsCurConvException.Create('JSON entry "quotes" is missing!');

    for i := 0 to xQuotes.Count - 1 do

    begin

      if Length(xQuotes.NameOf[i]) <> 6 then raise EVtsCurConvException.Create('Length of quotes-entry is unexpected!');

      if Copy(xQuotes.NameOf[i], 1, 3) = xSource.Value then

      begin

        Inc(result);

        if Assigned(sl) then sl.Add(Copy(xQuotes.NameOf[i], 4, 3));

      end;

    end;

  finally

    xRoot.Free;

  end;

end;

function TVtsCurConv.GetJsonRaw(HistoricDate: TDate=0): string;

  procedure _HandleKeyInvalidOrMissing(cacheFileName: string; msg: string; out doRetry: boolean; out json: string);

  begin

    if FallBackToCache then

    begin

      if not InteractiveAPIKeyInput then

      begin

        json := FileGetContents(cacheFileName);

        doRetry := false;

      end

      else

      begin

        if MessageDlg(Trim(msg + ' Do you want to enter a new one?'), mtError, mbYesNoCancel, 0) = ID_YES then

        begin

          QueryAPIKey;

          doRetry := true;

        end

        else

        begin

          json := FileGetContents(cacheFileName);

          doRetry := false;

        end;

      end;

    end

    else // if not FallBackToCache then

    begin

      if not InteractiveAPIKeyInput then

      begin

        raise EVtsCurConvException.Create(msg);

      end

      else

      begin

        QueryAPIKey(msg);

        doRetry := true;

      end;

    end;

  end;

var

  sJSON, msg, protocol: string;

  xRoot: TlkJSONobject;

  xSuccess: TlkJSONboolean;

  keyInvalid, doRetry: boolean;

  sDate: string;

  url: string;

  cacheDirName, cacheFileName: string;

  needDownload: boolean;

  mTime: TDateTime;

begin

  try

    {$REGION 'Determinate file location and URL'}

    // cacheDirName := IncludeTrailingPathDelimiter(GetSpecialPath(CSIDL_PROGRAM_FILES_COMMON)) + 'ViaThinkSoft\CurrencyConverter\';

    cacheDirName := IncludeTrailingPathDelimiter(GetTempDir) + 'ViaThinkSoft\CurrencyConverter\';

    if not ForceDirectories(cacheDirName) then

    begin

      raise EVtsCurConvException.CreateFmt('Cannot create directory %s', [cacheDirName]);

    end;

    if Secure then protocol := 'https' else protocol := 'http';

    if HistoricDate = 0 then

    begin

      sDate := '';

      url := protocol + '://www.apilayer.net/api/live?access_key=' + ReadAPIKey;

      cacheFileName := IncludeTrailingPathDelimiter(cacheDirName) + 'live.json';

    end

    else

    begin

      DateTimeToString(sDate, 'YYYY-MM-DD', HistoricDate);

      url := protocol + '://www.apilayer.net/api/historical?date=' + sDate + '&access_key=' + ReadAPIKey;

      cacheFileName := IncludeTrailingPathDelimiter(cacheDirName) + 'historical-' + sDate + '.json';

    end;

    {$ENDREGION}

    {$REGION 'Determinate if we need to download or not'}

    if HistoricDate = 0 then

    begin

      needDownload := true;

      if MaxAgeSeconds < -1 then

      begin

        raise EVtsCurConvException.Create('Invalid maxage');

      end

      else if MaxAgeSeconds = -1 then

      begin

        // Only download once

        needDownload := not FileExists(cacheFileName);

      end

      else if MaxAgeSeconds = 0 then

      begin

        // Always download

        needDownload := true;

      end

      else if MaxAgeSeconds > 0 then

      begin

        // Download if older than <MaxAge> seconds

        FileAge(cacheFileName, mTime);

        needDownload := not FileExists(cacheFileName) or (SecondsBetween(Now, mTime) > MaxAgeSeconds);

      end;

    end

    else

    begin

      needDownload := not FileExists(cacheFileName)

    end;

    {$ENDREGION}

    if not needDownload then

    begin

      sJSON := FileGetContents(cacheFileName);

    end

    else

    begin

      doRetry := false;

      {$REGION 'Is an API key available?'}

      if ReadAPIKey = '' then

      begin

        _HandleKeyInvalidOrMissing(cacheFileName, 'No API key provided.', doRetry, sJSON);

        if not doRetry then

        begin

          result := sJSON;

          Exit;

        end;

      end;

      {$ENDREGION}

      {$REGION 'Download and check if everything is OK'}

      repeat

        {$REGION 'Confirm web access?'}

        if ConfirmWebAccess and (MessageDlg('Download ' + url + ' to ' + cacheFileName + ' ?', mtConfirmation, mbYesNoCancel, 0) <> ID_YES) then

        begin

          if FallBackToCache then

          begin

            result := FileGetContents(cacheFileName);

            Exit;

          end

          else Abort;

        end;

        {$ENDREGION}

        doRetry := false;

        sJSON := GetPage(url);

        xRoot := TlkJSON.ParseText(sJSON) as TlkJSONobject;

        if not assigned(xRoot) then raise EVtsCurConvException.Create('JSON file invalid');

        xSuccess := xRoot.Field['success'] as TlkJSONboolean;

        if not assigned(xSuccess) then raise EVtsCurConvException.Create('Cannot determinate status of the query.');

        if xSuccess.Value then

        begin

          try

            FilePutContents(cacheFileName, sJSON);

          except

            // Since this is only a cache, we should not break the whole process if only the saving fails

          end;

        end

        else

        begin

          {$REGION 'Get information of the error'}

          try

            keyInvalid := xRoot.Field['error'].Field['code'].Value = 101;

            msg := Format('%s (%s, %s)', [

              xRoot.Field['error'].Field['info'].Value,

              xRoot.Field['error'].Field['code'].Value,

              xRoot.Field['error'].Field['type'].Value]);

          except

            keyInvalid := false;

            msg := 'Unknown error while loading JSON.';

          end;

          {$ENDREGION}

          if keyInvalid then

          begin

            _HandleKeyInvalidOrMissing(cacheFileName, 'API key invalid.', doRetry, sJSON);

          end

          else // if not keyInvalid then

          begin

            if FallBackToCache then

            begin

              result := FileGetContents(cacheFileName);

              Exit;

            end

            else

            begin

              raise EVtsCurConvException.Create(msg);

            end;

          end;

        end;

      until not doRetry;

      {$ENDREGION}

    end;

    result := sJSON;

  finally

    FreeAndNil(xRoot);

  end;

end;

end.