love2d - Flawed game logic in Lua code -

the code simple snake clone , don't want let snake me able go left if it's going right already.

it works if press left when going right if example presses left within time frame starts move left.

function self.update(dt)     if love.keyboard.isdown(self.left) , self.prevvelocity.x ~= 1          self.velocity.x = -1         self.velocity.y = 0     end      if love.keyboard.isdown(self.right) , self.prevvelocity.x ~= -1          self.velocity.x = 1              self.velocity.y = 0     end          if love.keyboard.isdown(self.up) , self.prevvelocity.y ~= 1           self.velocity.x = 0         self.velocity.y = -1     end      if love.keyboard.isdown(self.down) , self.prevvelocity.y ~= -1            self.velocity.x = 0         self.velocity.y = 1     end       if self.timesincelastmove < self.speedinverted         self.timesincelastmove = self.timesincelastmove + dt     else          table.remove(self.tail, 1)          tail = { x = self.position.x, y = self.position.y }          table.insert(self.tail, tail)          self.position.x = self.position.x + self.velocity.x * tilesize         self.position.y = self.position.y + self.velocity.y * tilesize          self.prevvelocity = self.velocity          self.timesincelastmove = 0;     end end 

function self.update(dt)     if love.keyboard.isdown(self.left) , self.prevvelocity.x ~= 1          self.velocity.x = -1         self.velocity.y = 0     end      if love.keyboard.isdown(self.right) , self.prevvelocity.x ~= -1          self.velocity.x = 1              self.velocity.y = 0     end          if love.keyboard.isdown(self.up) , self.prevvelocity.y ~= 1           self.velocity.x = 0         self.velocity.y = -1     end      if love.keyboard.isdown(self.down) , self.prevvelocity.y ~= -1            self.velocity.x = 0         self.velocity.y = 1     end       self.timesincelastmove = self.timesincelastmove + dt      if self.timesincelastmove >= self.speedinverted         self.timesincelastmove = self.timesincelastmove - self.speedinverted          self.position.x = self.position.x + self.velocity.x * tilesize         self.position.y = self.position.y + self.velocity.y * tilesize          table.remove(self.tail, 1)         local head = { x = self.position.x, y = self.position.y }         table.insert(self.tail, head)          self.prevvelocity = { x = self.velocity.x, y = self.velocity.y }     end end