'' examples/manual/libraries/cryptlib.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'cryptlib'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=ExtLibcryptlib
'' --------

#include Once "cryptlib.bi"

Function calc_hash( ByVal filename As String, ByVal algo As CRYPT_ALGO_TYPE ) As String
	Const BUFFER_SIZE = 8192
	Dim As Byte buffer( 0 To BUFFER_SIZE-1 )
	Dim As String result

	'' A context owns the algorithm state until cryptDestroyContext().  Every
	'' path after creation releases it before returning to the caller.
	Dim As CRYPT_CONTEXT ctx
	Dim As Long status = cryptCreateContext( @ctx, CRYPT_UNUSED, algo )
	If cryptStatusError( status ) Then
		Return ""
	End If

	'' open input file in binary mode
	Dim As Integer f = FreeFile()
	If( Open( filename For Binary Access Read As #f ) <> 0 ) Then
		cryptDestroyContext( ctx )
		Return ""
	End If

	'' Seek() uses a pointer-width file position.  The byte count is bounded by
	'' BUFFER_SIZE before it is passed to cryptlib's 32-bit length parameter.
	Do Until( EOF( f ) )
		Dim As LongInt oldpos = Seek( f )
		Get #f, , buffer()
		Dim As LongInt readlength = Seek( f ) - oldpos
		'' GET reports a stream read failure through Err even without a legacy
		'' ON ERROR handler.  The check prevents hashing an incomplete block.
		'' FB-LINTER: DISABLE-NEXT-LINE FBL613
		If Err <> 0 OrElse readlength < 0 OrElse readlength > BUFFER_SIZE Then
			status = CRYPT_ERROR_READ
			Exit Do
		End If

		If readlength > 0 Then
			status = cryptEncrypt( ctx, @buffer(0), CLng( readlength ) )
			If cryptStatusError( status ) Then
				Exit Do
			End If
		End If
	Loop

	'' close input file
	Close #f

	If cryptStatusOK( status ) Then
		'' A zero-length final update completes the hash calculation.
		status = cryptEncrypt( ctx, 0, 0 )
	End If

	If cryptStatusOK( status ) Then
		Dim As Long buffersize = BUFFER_SIZE
		status = cryptGetAttributeString( ctx, CRYPT_CTXINFO_HASHVALUE, @buffer(0), @buffersize )

		If cryptStatusOK( status ) AndAlso buffersize >= 0 AndAlso buffersize <= BUFFER_SIZE Then
			'' Each digest byte needs exactly two digits.  Preallocating also avoids
			'' repeated string reallocation while a file is being displayed.
			result = String( buffersize * 2, " " )
			For i As Long = 0 To buffersize - 1
				'' result has two writable characters for every iteration.
				'' FB-LINTER: DISABLE-NEXT-LINE FBL514
				Mid( result, i * 2 + 1, 2 ) = Right( "0" & Hex( CUByte( buffer(i) ) ), 2 )
			Next
		End If
	End If

	'' free the context
	cryptDestroyContext( ctx )

	Return result
End Function

	Dim As String filename = Trim( Command(1) )
	If( Len( filename ) = 0 ) Then
		Print "Usage: hash.exe filename"
		End -1
	End If

	'' init cryptlib
	cryptInit( )

	'' calculate hashes
	Print "md5:  "; calc_hash( filename, CRYPT_ALGO_MD5 )
	Print "sha1: "; calc_hash( filename, CRYPT_ALGO_SHA1 )

	'' shutdown cryptlib
	cryptEnd( )

	Sleep

' end of cryptlib.bas