import vga

const
  vgaWidth = 80
  vgaHeight = 25
  terminalBufferBaseAddress = 0xB8000
  bufferWidthSkip = vgaWidth * 2

var
  terminalRow, terminalColumn = 0
  terminalColour: int

proc terminalWriteAtPoint(writeChar: char, colour: int, xPos: int, yPos: int) =
  let index = terminalBufferBaseAddress + (yPos * bufferWidthSkip + (xPos * 2))
  cast[ptr int16](index)[] = vga.vgaEntry(writeChar, terminalColour)

proc terminalClear*() =
  for x in 0..<vgaWidth:
    for y in 0..<vgaHeight:
      terminalWriteAtPoint(' ', terminalColour, x, y)
  terminalRow = 0
  terminalColumn = 0

proc terminalInitialize*() =
  terminalColour = vgaEntryColour(VGA_Colour.lightGreen, VGA_Colour.red)
  terminalClear()

proc terminalScroll() =
  for y in 0..< (vgaHeight - 1):
    for x in 0..<vgaWidth:
      let xval = x * 2
      let index1 = terminalBufferBaseAddress + (y * bufferWidthSkip + xval)
      let index2 = terminalBufferBaseAddress +
        ((y + 1) * bufferWidthSkip + xval)
      cast[ptr int16](index1)[] = cast[ptr int16](index2)[]

proc setTerminalColour(newColour: int) =
  terminalColour = newColour

proc terminalWriteChar(writeChar: char) =
  if(writeChar == '\L'):
    if(terminalRow < vgaHeight): inc(terminalRow)
    #else: # If we are at the bottom of the screen then scroll the screen.
      #terminalScroll()
    terminalColumn = 0
    return
  terminalWriteAtPoint(writeChar, terminalColour, terminalColumn, terminalRow)
  inc(terminalColumn)
  if(terminalColumn == vgaWidth):
    terminalColumn = 0
    if(terminalRow < vgaHeight): inc(terminalRow)
    #else: # If we are at the bottom of the screen then scroll the screen.
      #terminalScroll()

proc terminalWrite*(data: string) =
  for character in data:
    terminalWriteChar(character)

proc terminalWrite*(data: char) =
  terminalWriteChar(data)

var parsedData = ['0','0','0','0','0','0','0','0','0','0']

proc terminalWrite*(data: int) =
  var input = data
  var i = 0
  if(input == 0):
    terminalWrite('0')
    return
  if(input < 0):
    terminalWrite('-')
    input = input * -1
  while(input != 0):
    let parsedChar: char = char(48 + (input mod 10))
    parsedData[i] = parsedChar
    i = i + 1
    input = input div 10
  while i > 0:
    i = i - 1
    terminalWrite(parsedData[i])