The Tetris Randomizer algorithm implemented in Groovy. Specifically the TGM2 variant.

TetrisRandomizer.groovy

def rng = new Random()

def blocks = ['T', 'I', 'L', 'J', 'S', 'Z', 'O']
def history = ['Z', 'S', 'Z', 'S'] as ArrayDeque

def maxTilePosition = 4

def nextPiece = {

    def block
	
    for (i in 1..6) {

        block = blocks[rng.nextInt(maxTilePosition)]

        if (!(block in history)) break
    }

    maxTilePosition = 7

    history.remove()
    history.add(block)

    return block
}