Editor WIP

local running = true

local width, height = term.getSize()

local scroll = 0

local lines = {""}
local cmdHist = {}
local highlights = {}

local currentLine = 1
local currentChar = 1

local insertMode = false
local edited = false

local status = "[New File]"

local tArgs = {...}

local function trim(text)
  return (text:gsub("^%s*(.-)%s*$", "%1"))
end

local function splitWords(text)
  local words = {}
  for word in text:gmatch("%S+") do
    table.insert(words, word)
  end
  return words
end

local function sortByIndex(tab, index)
  table.sort(table, function (a, b)
    return (a[index] > b[index])
  end)
end

local function doSetColor(color, bgColor, invertOnNormal)
  if term.isColor() then
    term.setTextColor(color)
    if bgColor ~= nil then
      term.setBackgroundColor(bgColor)
    end
  else
    if invertOnNormal then
      term.setTextColor(colors.black)
      term.setBackgroundColor(colors.white)
    else
      term.setTextColor(colors.white)
      term.setBackgroundColor(colors.black)
    end
  end
end

local function addHighlight(line, start, stop, color)
  local cand = {line, start, stop, color}
  for h = 1, #highlights do
    local exhi = highlights[h]
    if cand[1] == exhi[1] then
      if cand[4] == exhi[4] then
        local centered = cand[2] >= exhi[2] and cand[3] <= exhi[3]
        if centered then
          return
        end
        if cand[2] <= exhi[3]+1 and cand[3] >= exhi[2]-1 then
          highlights[h][2] = math.min(cand[2], exhi[2])
          highlights[h][3] = math.max(cand[3], exhi[3])
          return
        end
      end
    end
  end
  table.insert(highlights, cand)
end

local function drawTextDisplay()
  for i = 1, height-1 do
    doSetColor(colors.white, colors.black)
    term.setCursorPos(1, i)
    term.clearLine()
    if i+scroll > #lines then
      doSetColor(colors.blue, colors.black, true)
      term.write("~")
    else
      local lineh = {}
      for h = 1, #highlights do
        if highlights[h][1] == i then
          table.insert(lineh, highlights[h])
        end
      end
      local line = lines[i+scroll]
      if #lineh > 0 then
        term.write(line:sub(1, lineh[1][2]-1))
        for h = 1, #lineh do
          local high = lineh[h]
          doSetColor(colors.white, high[4], true)
          term.setCursorPos(high[2], i)
          term.write(line:sub(high[2], high[3]))
          doSetColor(colors.white, colors.black)
          term.setCursorPos(high[3]+1, i)
          if h < #lineh then
            term.write(line:sub(high[3]+1, lineh[h+1][2]-1))
          else
            term.write(line:sub(high[3]+1, #line))
          end
        end
      else
        term.write(line)
      end
    end
  end
  doSetColor(colors.white, colors.black)
end

local function drawBottomLineDisplay()
  term.setCursorPos(1, height)
  local lnstr = "L"..currentLine..", C"..currentChar
  term.clearLine()
  local dispstatus = status
  if dispstatus:sub(1, 4) == "err:" then
    dispstatus = status:sub(5, #dispstatus)
    doSetColor(colors.white, colors.red, true)
  end
  term.write(dispstatus)
  doSetColor(colors.white, colors.black)
  term.setCursorPos(width-#lnstr, height)
  term.write(lnstr)
end

local function positionCursor()
  currentChar = math.min(currentChar, #lines[currentLine]+1)
  local y = currentLine-scroll
  local x = currentChar
  term.setCursorPos(x, y)
end

local function calculateScroll()
  if height+scroll < currentLine then
    scroll = currentLine-height+1
  elseif currentLine <= scroll then
    scroll = currentLine-1
  end
end

local function updateHighlights()
  for i = 1,#highlights do
    table.remove(highlights)
  end
  -- will do more soon
end

local function moveRight()
  if currentChar <= #lines[currentLine] then
    currentChar = currentChar + 1
  end
  updateHighlights()
end

local function moveLeft()
  if currentChar > 1 then
    currentChar = currentChar - 1
  end
  updateHighlights()
end

local function moveUp()
  if currentLine > 1 then
    currentLine = currentLine - 1
  end
  updateHighlights()
end

local function moveDown()
  if currentLine < #lines then
    currentLine = currentLine + 1
  end
  updateHighlights()
end

local function insertChar(char)
  local line = lines[currentLine]
  if currentChar >= #line then
    line = line..char
  elseif currentChar == 1 then
    line = char..line
  else
    local first = line:sub(1,currentChar-1)
    local last = line:sub(currentChar, #line)
    line = first..char..last
  end
  lines[currentLine] = line
  currentChar = currentChar + 1
  edited = true
  updateHighlights()
end

local function insertLine()
  local line = lines[currentLine]
  local indent = line:gsub("^(%s*).*", "%1")
  if currentChar >= #line then
    table.insert(lines, currentLine+1, indent)
  elseif currentChar == 1 then
    table.insert(lines, currentLine, indent)
  else
    local first = line:sub(1, currentChar-1)
    local last = line:sub(currentChar, #line)
    lines[currentLine] = first
    table.insert(lines, currentLine+1, indent..last)
  end
  currentLine = currentLine + 1
  currentChar = 1+#indent
  edited = true
  updateHighlights()
end

local function deleteBefore()
  if currentChar > 1 then
    local line = lines[currentLine]
    local first = line:sub(1, currentChar-2)
    local last = line:sub(currentChar, #line)
    line = first..last
    lines[currentLine] = line
    currentChar = currentChar - 1
  elseif currentLine > 1 then
    local firstLine = lines[currentLine-1]
    local secondLine = lines[currentLine]
    lines[currentLine-1] = firstLine..secondLine
    table.remove(lines, currentLine)
    currentLine = currentLine - 1
    currentChar = #firstLine + 1
  end
  edited = true
end

local function deleteAfter()
  local line = lines[currentLine]
  if currentChar <= #line then
    local first = line:sub(1, currentChar-1)
    local last = line:sub(currentChar+1, #line)
    line = first..last
    lines[currentLine] = line
  elseif currentLine < #lines then
    local firstLine = line
    local secondLine = lines[currentLine+1]
    lines[currentLine] = firstLine..secondLine
    table.remove(lines, currentLine+1)
  end
  edited = true
end

local function indent()
  local line = lines[currentLine]
  lines[currentLine] = "  "..line
  currentChar = currentChar + 2
end

local function runCmd(data)
  if data[1] == "quit" then
    if edited then
      status = "err:There are unsaved changes (type quit! to force)"
      return
    end
    running = false
    return
  elseif data[1] == "quit!" then
    running = false
    return
  elseif data[1] == "nil" or data[1] == "none" then
    status = ""
    return
  elseif data[1] == "goto" then
    local line = tonumber(data[2])
    if line == nil then
      status = "err:Usage: goto <line_number>"
      return
    end
    if line < 1 or line > #lines then
      status = "err:Invalid line number"
      return
    end
    currentLine = line
    addHighlight(line, 1, #lines[currentLine], colors.green)
    return
  elseif data[1] == "save" then
    if data[2] == nil then
      status = "err:Usage: save <filename>"
      return
    end
    local path = shell.resolve(data[2])
    if fs.exists(path) then
      status = "err:File exists (force with save!)"
      return
    end
    runCmd({"save!", data[2]})
    return
  elseif data[1] == "save!" then
    local path = shell.resolve(data[2])
    local dir = fs.getDir(path)
    if not fs.exists(dir) then
      status = "err:Directory does not exist"
      return
    end
    if fs.isReadOnly(path) then
      status = "err:Location is read-only"
      return
    end
    local handle = fs.open(path, "w")
    for l = 1, #lines do
      handle.writeLine(lines[l])
    end
    handle.flush()
    handle.close()
    status = "Saved as "..path:sub(#dir+1, #path)
    edited = false
    return
  elseif data[1] == "open" then
    if edited then
      status = "err:Unsaved changes (force with open!)"
      return
    end
    runCmd({"open!", data[2]})
    return
  elseif data[1] == "open!" then
    local path = shell.resolve(data[2])
    if not fs.exists(path) then
      status = "err:File does not exist"
      return
    end
    if fs.isDir(path) then
      status = "err:Cannot open directory"
      return
    end
    local handle = fs.open(path, "r")
    lines = {}
    while true do
      local line = handle.readLine()
      if line == nil then break end
      table.insert(lines, line)
    end
    handle.close()
    currentLine = 1
    currentChar = 1
    status = "Opened "..data[2]
    edited = false
    return
  end
  status = "err:Unknown command \""..data[1].."\""
end

local function loop()
  while running do
    term.setCursorBlink(true)
    calculateScroll()
    drawTextDisplay()
    drawBottomLineDisplay()
    positionCursor()
    ev, a, b, c = os.pullEventRaw()
    if ev == "terminate" then
      running = false
    elseif ev == "key" then
      if insertMode then
        if a == keys.f1 then
          insertMode = false
          status = ""
        elseif a == keys.enter then
          insertLine()
        elseif a == keys.backspace then
          deleteBefore()
        elseif a == keys.delete then
          deleteAfter()
        elseif a == keys.tab then
          indent()
        end
      end
      if a == keys.left then
        moveLeft()
      elseif a == keys.right then
        moveRight()
      elseif a == keys.up then
        moveUp()
      elseif a == keys.down then
        moveDown()
      end
    elseif ev == "char" then
      if insertMode then
        insertChar(a)
      elseif a == "i" then
        insertMode = true
        status = "--INSERT--"
      elseif a == ":" then
        term.setCursorPos(1, height)
        term.write(string.rep(' ', #status))
        term.setCursorPos(1, height)
        term.write(":")
        local cmd = read(nil, cmdHist)
        if #cmdHist == 0 or cmdHist[#cmdHist] ~= trim(cmd) then
          table.insert(cmdHist, trim(cmd))
        end
        runCmd(splitWords(cmd))
      end
    end
  end
end

if #tArgs > 0 then
  local path = shell.resolve(tArgs[1])
  if fs.exists(path) then
    runCmd({"open", tArgs[1]})
  else
    status = path.." [New File]"
  end
end

loop()
term.clear()
term.setTextColor(colors.white)
term.setTextColor(colors.black)
term.setCursorPos(1,1)