local utils = require('libs/utils')

local function noTitleFn()
  return ""
end

local savedTextColor = nil
local savedBackgroundColor = nil

local function saveTermConfig()
  savedTextColor = term.getTextColor()
  savedBackgroundColor = term.getBackgroundColor()
end

local function restoreTermConfig()
  term.setTextColor(savedTextColor)
  term.setBackgroundColor(savedBackgroundColor)
end

local function getTotalCount(countersMap)
  local total = 0
  for _, counter in pairs(countersMap) do
    total = total + (counter or 0)
  end
  return total
end

local function omitN(t, n)
  local result = {}

  for k,v in pairs(t) do
    if n == 0 then
      result[k] = v
    end
    n = n - 1
  end

  return result
end

local function pickN(t, n)
  local result = {}

  for k,v in pairs(t) do
    if n == 0 then
      break
    end
    result[k] = v
    n = n - 1
  end

  return result
end

local TITLE_MARGIN = 1

local function renderCountersMap(countersMap, selectedCounter, titleFn)
  term.setCursorPos(1, 1)
  local _, height = term.getSize()
  -- local nbCounters = utils.sizeof(countersMap)
  local selectedCounterKey = countersMap[selectedCounter]
  -- local totalCount = getTotalCount(countersMap)

  local topMargin = 0
  local bottomMargin = 0

  if titleFn ~= noTitleFn then
    term.clearLine()
    term.write('custom title: ' .. titleFn(countersMap, selectedCounter))
    topMargin = TITLE_MARGIN
  end

  local availableHeight = height - topMargin - bottomMargin

  local selectedPage = math.floor(selectedCounter / availableHeight) + 1
  -- local totalPages = (nbCounters % availableHeight) + 1

  local nbElementsToOmit = (selectedPage - 1) * availableHeight
  local displayedCounters = pickN(omitN(countersMap, nbElementsToOmit), availableHeight)

  local cursorYIndex = 1 + topMargin
  for k,v in pairs(displayedCounters) do
    term.clearLine()
    term.setCursorPos(1, cursorYIndex)

    if k == selectedCounterKey then
      term.setBackgroundColor(colors.white)
      term.setTextColor(colors.black)
    else
      term.setBackgroundColor(colors.black)
      term.setTextColor(colors.white)
    end

    term.write(tostring(k) .. ' ' .. tostring(v))
    cursorYIndex = cursorYIndex + 1
  end
end

local function CountersSelector(initialCountersMap, config)
  local countersMap = utils.shallowClone(initialCountersMap)
  local counterMax = config.counterMax
  local titleFn = config.titleFn or noTitleFn

  if not counterMax then
    error('no counterMax found in CountersSelector config')
  end

  if utils.sizeof(countersMap) == 0 then
    error('empty countersMap provided')
  end

  saveTermConfig()
  term.clear()

  local selectedCounter = 1
  local nbCounters = utils.sizeof(countersMap)
  local globalCounter = getTotalCount(countersMap)

  if globalCounter > counterMax then
    error('counter cannot be greater than the counterMax')
  end

  local shouldContinue = true
  while shouldContinue do
    renderCountersMap(countersMap, selectedCounter, titleFn)

    local _, keyPressed, isHeld = os.pullEvent('key')

    if keyPressed == keys.up then
      selectedCounter = math.max(1, selectedCounter - 1)
    elseif keyPressed == keys.down then
      selectedCounter = math.min(nbCounters, selectedCounter + 1)
    elseif keyPressed == keys.left and globalCounter > 0 then
      local currentCount = countersMap[selectedCounter]
      if currentCount and currentCount > 0 then
        countersMap[selectedCounter] = currentCount - 1
        globalCounter = globalCounter - 1
      end
    elseif keyPressed == keys.right and globalCounter < counterMax then
      local currentCount = countersMap[selectedCounter]
      if currentCount then
        countersMap[selectedCounter] = currentCount + 1
        globalCounter = globalCounter + 1
      end
    elseif keyPressed == keys.enter then
      shouldContinue = false
    end
  end

  restoreTermConfig()

  return countersMap, selectedCounter
end

return CountersSelector