local fs = require("filesystem")
local shell = require("shell")
local gpu = require("component").gpu
local event = require("event")
local computer = require("computer")

local resX, resY = gpu.getResolution()
local textBuffer = gpu.allocateBuffer(resX, resY - 1)

local args = {...}
local file = args[1]
if not file then
    print("\x1b[91mEnter a file name.")
    return
end
if fs.isDirectory(file) then
    print("\x1b[91mThe specified file is a directory.")
    return
end

if file:sub(1, 1) ~= "/" then
    file = fs.concat(shell.getWorkingDirectory(), file)
end

local data = ""
if fs.exists(file) then
    local handle = fs.open(file)
    local tmpdata
    repeat
        tmpdata = handle:read(math.huge or math.maxinteger)
        data = data .. (tmpdata or "")
    until not tmpdata
end

local lines = {}
for line in data:gmatch("[^\r\n]+") do
  table.insert(lines, line)
end

local function renderText(xOffset, yOffset)
  gpu.setActiveBuffer(textBuffer)
  gpu.setBackground(0x000000)
  gpu.setForeground(0xFFFFFF)
  gpu.fill(1, 1, resX, resY - 1, " ")
  for i = yOffset + 1, #lines do
    gpu.set(1, i - yOffset, lines[i]:sub(xOffset + 1))
  end
  gpu.setActiveBuffer(0)
  gpu.bitblt(0, 1, 1, resX, resY - 1, textBuffer, 1, 1)
end

-- Initialize screen
renderText(0, 0)
gpu.setForeground(0x000000)
gpu.setBackground(0xFFFFFF)
gpu.set(1, resY, "^X")
gpu.set(10, resY, "^S")
gpu.setForeground(0xFFFFFF)
gpu.setBackground(0x000000)
gpu.set(4, resY, "Exit")
gpu.set(13, resY, "Save")

local textOffsetX = 0
local textOffsetY = 0

while true do
  local renderBufferFlag = false -- Flag to render the whole text buffer
  -- Handle events
  repeat
    local eventArgs = {event.pull("key_down", 0.05)}

    if eventArgs[1] == "key_down" then
      -- Mouse events might be added later, that's why this if statement is here
      if keyboard.getCtrlDown() then
        -- Special commands
        print(eventArgs[4], keyboard.keys[eventArgs[4]])
        if keyboard.keys[eventArgs[4]] == "x" then
          goto exit
        end
      end

      if keyboard.keys[eventArgs[4]] == "up" and textOffsetY > 0 then
        textOffsetY = textOffsetY - 1
        renderBufferFlag = true
      end
      if keyboard.keys[eventArgs[4]] == "down" then
        textOffsetY = textOffsetY + 1
        renderBufferFlag = true
      end
      if keyboard.keys[eventArgs[4]] == "left" and textOffsetX > 0 then
        textOffsetX = textOffsetX - 1
        renderBufferFlag = true
      end
      if keyboard.keys[eventArgs[4]] == "right" then
        textOffsetX = textOffsetX + 1
        renderBufferFlag = true
      end
    end
  until not next(eventArgs)
  if renderBufferFlag then
    renderText(textOffsetX, textOffsetY)
  end
end

-- Cleanup
::exit::
gpu.freeBuffer(textBuffer)
gpu.setActiveBuffer(0)
terminal.clear()