unit VtsCurConv;
interface
uses
SysUtils, Classes;
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;
resourcestring
S_CANNOT_DOWNLOAD = 'Cannot download from %s';
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(S_CANNOT_DOWNLOAD, [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;
resourcestring
S_CANNOT_OPEN_REGISTRY = 'Cannot open registry key';
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(S_CANNOT_OPEN_REGISTRY);
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;
resourcestring
S_JSON_ENTRY_MISSING = 'JSON entry "%s" is missing!';
S_WRONG_QUOTE_LEN = 'Length of quotes-entry is unexpected!';
S_JSON_RATE_MISSING = 'JSON entry quotes->rate is missing!';
S_CURRENCY_NOT_SUPPORTED = 'Currency "%s" not supported';
begin
result := 0; // to avoid that the compiler shows a warning
fromCur := Trim(UpperCase(fromCur));
toCur := Trim(UpperCase(toCur));
if fromCur = toCur then
begin
result := value;
exit;
end;
sJSON := GetJsonRaw(HistoricDate);
xRoot := TlkJSON.ParseText(sJSON) as TlkJSONobject;
try
xSource := xRoot.Field['source'] as TlkJSONstring;
if not assigned(xSource) then raise EVtsCurConvException.CreateFmt(S_JSON_ENTRY_MISSING, ['source']);
xQuotes := xRoot.Field['quotes'] as TlkJSONobject;
if not assigned(xQuotes) then raise EVtsCurConvException.CreateFmt(S_JSON_ENTRY_MISSING, ['quotes']);
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(S_WRONG_QUOTE_LEN);
xRate := xQuotes.Field[xQuotes.NameOf[i]] as TlkJSONnumber;
if not Assigned(xRate) then raise EVtsCurConvException.Create(S_JSON_RATE_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(S_CURRENCY_NOT_SUPPORTED, [toCur]);
if not rateFromFound then raise EVtsCurConvException.CreateFmt(S_CURRENCY_NOT_SUPPORTED, [fromCur]);
result := value * rateTo / rateFrom;
finally
xRoot.Free;
end;
end;
procedure TVtsCurConv.QueryAPIKey(msg: string='');
var
s: string;
resourcestring
S_CURRENCYLAYER = 'currencylayer.com';
S_ENTER_KEY = 'Please enter your API key:';
S_NO_API_KEY = 'No API key provided.';
begin
s := Trim(InputBox(S_CURRENCYLAYER, Trim(msg + ' ' + S_ENTER_KEY), ''));
if s = '' then raise EVtsCurConvException.Create(S_NO_API_KEY);
WriteAPIKey(s);
end;
function TVtsCurConv.GetAcceptedCurrencies(sl: TStringList=nil; HistoricDate: TDate=0): integer;
var
i: Integer;
sJSON: String;
xSource: TlkJSONstring;
xRoot: TlkJSONobject;
xQuotes: TlkJSONobject;
resourcestring
S_JSON_ENTRY_MISSING = 'JSON entry "%s" is missing!';
S_WRONG_QUOTE_LEN = 'Length of quotes-entry is unexpected!';
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.CreateFmt(S_JSON_ENTRY_MISSING, ['source']);
xQuotes := xRoot.Field['quotes'] as TlkJSONobject;
if not assigned(xQuotes) then raise EVtsCurConvException.CreateFmt(S_JSON_ENTRY_MISSING, ['quotes']);
for i := 0 to xQuotes.Count - 1 do
begin
if Length(xQuotes.NameOf[i]) <> 6 then raise EVtsCurConvException.Create(S_WRONG_QUOTE_LEN);
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);
resourcestring
S_ENTER_NEW_KEY = 'Do you want to enter a new one?';
S_NO_CACHE_EXISTING = 'Cannot get the data online, and no cache exists. Please check your internet connection and API key.';
begin
if FallBackToCache then
begin
if not InteractiveAPIKeyInput then
begin
if not FileExists(cacheFileName) then
begin
raise Exception.Create(S_NO_CACHE_EXISTING);
end;
json := FileGetContents(cacheFileName);
doRetry := false;
end
else
begin
if MessageDlg(Trim(msg + ' ' + S_ENTER_NEW_KEY), mtError, mbYesNoCancel, 0) = ID_YES then
begin
QueryAPIKey;
doRetry := true;
end
else
begin
if not FileExists(cacheFileName) then
begin
raise Exception.Create(S_NO_CACHE_EXISTING);
end;
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;
function protocol: string;
begin
if Secure then result := 'https' else result := 'http';
end;
function url: string;
var
sDate: string;
begin
if HistoricDate = 0 then
begin
sDate := '';
result := protocol + '://www.apilayer.net/api/live?access_key=' + ReadAPIKey;
end
else
begin
DateTimeToString(sDate, 'YYYY-MM-DD', HistoricDate);
result := protocol + '://www.apilayer.net/api/historical?date=' + sDate + '&access_key=' + ReadAPIKey;
end;
end;
function cacheFileName: string;
resourcestring
S_CANNOT_CREATE_DIR = 'Cannot create directory %s';
var
sDate: string;
cacheDirName: string;
begin
// cacheDirName := IncludeTrailingPathDelimiter(GetSpecialPath(CSIDL_PROGRAM_FILES_COMMON)) + 'ViaThinkSoft\CurrencyConverter\';
cacheDirName := IncludeTrailingPathDelimiter(GetTempDir) + 'ViaThinkSoft\CurrencyConverter\';
if not ForceDirectories(cacheDirName) then
begin
raise EVtsCurConvException.CreateFmt(S_CANNOT_CREATE_DIR, [cacheDirName]);
end;
if HistoricDate = 0 then
begin
sDate := '';
result := IncludeTrailingPathDelimiter(cacheDirName) + 'live.json';
end
else
begin
DateTimeToString(sDate, 'YYYY-MM-DD', HistoricDate);
result := IncludeTrailingPathDelimiter(cacheDirName) + 'historical-' + sDate + '.json';
end;
end;
var
sJSON, msg: string;
xRoot: TlkJSONobject;
xSuccess: TlkJSONboolean;
keyInvalid, doRetry: boolean;
needDownload: boolean;
mTime: TDateTime;
resourcestring
S_INVALID_MAXAGE = 'Invalid maxage';
S_NO_API_KEY_PROVIDED = 'No API key provided.';
S_DOWNLOAD_QUERY = 'Download %s to %s ?';
S_JSON_FILE_INVALID = 'JSON file invalid';
S_UNKNOWN_SUCCESS = 'Cannot determinate status of the query.';
S_JSON_UNKNOWN_ERROR = 'Unknown error while loading JSON.';
S_API_KEY_INVALID = 'API key invalid.';
begin
{$REGION 'Determinate if we need to download or not'}
if HistoricDate = 0 then
begin
needDownload := true;
if MaxAgeSeconds < -1 then
begin
raise EVtsCurConvException.Create(S_INVALID_MAXAGE);
end
else if MaxAgeSeconds = -1 then
begin
// Only download once
needDownload := not FileExists(cacheFileName);
end
else if MaxAgeSeconds = 0 then
begin
// Always download
needDownload := true;
end
else if MaxAgeSeconds > 0 then
begin
// Download if older than <MaxAge> seconds
FileAge(cacheFileName, mTime);
needDownload := not FileExists(cacheFileName) or (SecondsBetween(Now, mTime) > MaxAgeSeconds);
end;
end
else
begin
needDownload := not FileExists(cacheFileName)
end;
{$ENDREGION}
if not needDownload and FileExists(cacheFileName) then
begin
sJSON := FileGetContents(cacheFileName);
end
else
begin
doRetry := false;
{$REGION 'Is an API key available?'}
if ReadAPIKey = '' then
begin
_HandleKeyInvalidOrMissing(cacheFileName, S_NO_API_KEY_PROVIDED, doRetry, sJSON);
if not doRetry then
begin
result := sJSON;
Exit;
end;
end;
{$ENDREGION}
{$REGION 'Download and check if everything is OK'}
repeat
{$REGION 'Confirm web access?'}
if ConfirmWebAccess and (MessageDlg(Format(S_DOWNLOAD_QUERY, [url, cacheFileName]), mtConfirmation, mbYesNoCancel, 0) <> ID_YES) then
begin
if FallBackToCache and FileExists(cacheFileName) then
begin
result := FileGetContents(cacheFileName);
Exit;
end
else Abort;
end;
{$ENDREGION}
doRetry := false;
sJSON := GetPage(url);
xRoot := TlkJSON.ParseText(sJSON) as TlkJSONobject;
if not assigned(xRoot) then raise EVtsCurConvException.Create(S_JSON_FILE_INVALID);
try
xSuccess := xRoot.Field['success'] as TlkJSONboolean;
if not assigned(xSuccess) then raise EVtsCurConvException.Create(S_UNKNOWN_SUCCESS);
if xSuccess.Value then
begin
try
FilePutContents(cacheFileName, sJSON);
except
// Since this is only a cache, we should not break the whole process if only the saving fails
end;
end
else
begin
{$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 := S_JSON_UNKNOWN_ERROR;
end;
{$ENDREGION}
if keyInvalid then
begin
_HandleKeyInvalidOrMissing(cacheFileName, S_API_KEY_INVALID, doRetry, sJSON);
end
else // if not keyInvalid then
begin
if FallBackToCache and FileExists(cacheFileName) then
begin
result := FileGetContents(cacheFileName);
Exit;
end
else
begin
raise EVtsCurConvException.Create(msg);
end;
end;
end;
finally
FreeAndNil(xRoot);
end;
until not doRetry;
{$ENDREGION}
end;
result := sJSON;
// "USDUSD" missing 06 Aug 2022. A bug?? Reported https://github.com/apilayer/currencylayer-API/issues/16
if Pos('"USDUSD"', result) = 0 then
result := StringReplace(result, '"quotes":{', '"quotes":{"USDUSD":1,', []);
end;
end.