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

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

local function addLine(pos)
  if pos <= #lines then
    for i = #lines, pos, -1 do
      lines[i + 1] = lines[i]
    end
    lines[pos] = ""
  else
    table.insert(lines, "")
  end
end

local function removeLine(pos)
  length = #lines
  for i = pos + 1, length do
    lines[i - 1] = lines[i]
  end
  lines[length] = nil
end

local function save()
  gpu.setForeground(0xFFFFFF)
  gpu.setBackground(0x000000)
  gpu.set(1, resY, "Enter a location to save:")

  local savepath = file or ""
  local saveCursorX = 27 + #savepath
  local ready = false
  local eventArgs = {}

  gpu.fill(27, resY, resX - 27, 1, " ")
  gpu.set(27, resY, savepath)
  gpu.setForeground(0x000000)
  gpu.setBackground(0xFFFFFF)
  gpu.set(saveCursorX, resY, " ")
  gpu.setForeground(0xFFFFFF)
  gpu.setBackground(0x000000)

  repeat
    local shouldRender = false
    coroutine.yield()

    eventArgs = {event.pull("key_down", 0)}
    if keyboard.keys[eventArgs[4]] == "enter" then
      ready = true
    end
    if keyboard.keys[eventArgs[4]] == "back" then
      savepath = string.sub(savepath, 1, #savepath - 1)
      if saveCursorX > 27 then
        saveCursorX = saveCursorX - 1
      end
      shouldRender = true
    end
    if not keyboard.keys.special[eventArgs[4]] and keyboard.keys[eventArgs[4]] then
      savepath = savepath .. (string.char(eventArgs[3]) or "")
      saveCursorX = saveCursorX + 1
      shouldRender = true
    end

    if shouldRender then
      gpu.fill(27, resY, resX - 27, 1, " ")
      gpu.set(27, resY, savepath)
      gpu.setForeground(0x000000)
      gpu.setBackground(0xFFFFFF)
      gpu.set(saveCursorX, resY, " ")
      gpu.setForeground(0xFFFFFF)
      gpu.setBackground(0x000000)
    end
  until ready

  gpu.fill(1, resY, resX, 1, " ")
  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 text = table.concat(lines, "\n")
  local handle = fs.open(savepath, "w")
  handle:write(text)
  handle:close()
  file = savepath
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 scrollX = 0
local scrollY = 0
local cursorX = 1 -- Absolute position, not accounting for scrolling
local cursorY = 1
local cursorWhite = true
local oldTime = computer.uptime()

while true do
  local renderBufferFlag = false -- Flag to render the whole text buffer
  -- Handle events
  local previousCursorX -- Used for blackening the previous cursor location when the cursor is moved
  local previousCursorY
  coroutine.yield()
  local eventArgs = {}
  repeat
    eventArgs = {event.pull("key_down", 0)}

    -- The logical solution here for flashing the cursor would be to set the timeout to 0.5, and, if the timeout is reached, change the color.
    -- However, that makes scrolling freeze the screen up completely.
    -- Thus, for flashing the cursor, a timer is needed.

    if computer.uptime() >= oldTime + 0.5 then
      oldTime = computer.uptime()
      cursorWhite = not cursorWhite
    end

    if next(eventArgs) ~= nil then
      cursorWhite = true
      oldTime = computer.uptime()
    end

    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
        if keyboard.keys[eventArgs[4]] == "x" then
          goto exit
        end
        if keyboard.keys[eventArgs[4]] == "s" then
          save()
        end
      end

      if keyboard.keys[eventArgs[4]] == "up" and cursorY > 1 then
        if cursorY - scrollY <= 1 then
          renderBufferFlag = true
          scrollY = scrollY - 1
        else
          if not previousCursorX and not previousCursorY then
            previousCursorX = cursorX
            previousCursorY = cursorY
          end
        end
        cursorY = cursorY - 1
        -- The cursor absolute position still has to be moved, even if on-screen it won't move
        if cursorX > string.len(lines[cursorY]) + 1 then -- cursor snapping, +1 to be 1 char in front of end of line
            cursorX = string.len(lines[cursorY]) + 1
        end
      end
      if keyboard.keys[eventArgs[4]] == "down" then
        if cursorY - scrollY >= resY - 1 then
          renderBufferFlag = true
          scrollY = scrollY + 1
        else
          if not previousCursorX and not previousCursorY then
            previousCursorX = cursorX
            previousCursorY = cursorY
          end
        end
        cursorY = cursorY + 1
        if cursorX > string.len(lines[cursorY]) + 1 then
            cursorX = string.len(lines[cursorY]) + 1
        end
      end
      if keyboard.keys[eventArgs[4]] == "left" and cursorX > 1 then
        if cursorX - scrollX <= 1 then
          renderBufferFlag = true
          scrollX = scrollX - 1
        else
          if not previousCursorX and not previousCursorY then
            previousCursorX = cursorX
            previousCursorY = cursorY
          end
        end
        cursorX = cursorX - 1
      end
      if keyboard.keys[eventArgs[4]] == "right" and cursorX < string.len(lines[cursorY]) + 1 then
        if cursorX - scrollX >= resX then
          renderBufferFlag = true
          scrollX = scrollX + 1
        else
          if not previousCursorX and not previousCursorY then
            previousCursorX = cursorX
            previousCursorY = cursorY
          end
        end
        cursorX = cursorX + 1
      end
      if not keyboard.keys.special[eventArgs[4]] then
        local line = lines[cursorY] or ""
        line = string.sub(line, 1, cursorX - 1) .. string.char(eventArgs[3]) .. string.sub(line, cursorX, -1)
        lines[cursorY] = line
        cursorX = cursorX + 1
        renderBufferFlag = true
      end
      if keyboard.keys[eventArgs[4]] == "back" then
        local line = lines[cursorY]
        local prevline = lines[cursorY - 1]
        if cursorX > 1 then
          line = string.sub(line, 1, cursorX - 2) .. string.sub(line, cursorX, -1) -- remove 1 char
        elseif prevline then
          prevline = prevline .. line -- copy line up to the next before removing it
          ocelot.log(prevline)
          line = nil
        end
        if line then
          lines[cursorY] = line
        else
          removeLine(cursorY)
        end
        lines[cursorY - 1] = prevline
        if not line then
          cursorY = cursorY - 1 -- this can only trigger if the line is not the first
        end
        if cursorX > 1 then
          cursorX = cursorX - 1
        end
        renderBufferFlag = true
      end
      if keyboard.keys[eventArgs[4]] == "enter" then
        addLine(cursorY + 1)
        cursorY = cursorY + 1
        cursorX = 1
        renderBufferFlag = true
      end
    end
  until next(eventArgs) == nil
  local displayedCursorX = cursorX - scrollX
  local displayedCursorY = cursorY - scrollY
  local previousDisplayedCursorX -- What a mouthful
  local previousDisplayedCursorY
  if previousCursorX and previousCursorY then
    previousDisplayedCursorX = previousCursorX - scrollX
    previousDisplayedCursorY = previousCursorY - scrollY
  end

  if renderBufferFlag then
    renderText(scrollX, scrollY)
    if cursorWhite then
      -- If the cursor is black, then there's no need to do anything because there is no cursor after calling renderText().
      gpu.setForeground(0x000000)
      gpu.setBackground(0xFFFFFF)
      local letter = gpu.get(displayedCursorX, displayedCursorY)
      gpu.set(displayedCursorX, displayedCursorY, letter)
      -- TODO: Account for scrolling
    end
  else
    if cursorWhite then
      if previousCursorX or previousCursorY then
        -- Remove old cursor
        gpu.setForeground(0xFFFFFF)
        gpu.setBackground(0x000000)
        local letter = gpu.get(previousDisplayedCursorX, previousDisplayedCursorY)
        gpu.set(previousDisplayedCursorX, previousDisplayedCursorY, letter)
      end

      gpu.setForeground(0x000000)
      gpu.setBackground(0xFFFFFF)
      local letter = gpu.get(displayedCursorX, displayedCursorY)
      gpu.set(displayedCursorX, displayedCursorY, letter)
    else
      -- If renderText() hasn't been called, the cursor may still be white and need to be turned black.
      gpu.setForeground(0xFFFFFF)
      gpu.setBackground(0x000000)
      local letter = gpu.get(displayedCursorX, displayedCursorY)
      gpu.set(displayedCursorX, displayedCursorY, letter)
    end
  end
end

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