pfUI:RegisterModule("rangecheck", function ()

  if C.unitframes.rangecheck == "0" then return end

  -- table of 40y spells per class
  local spells = {
    ["PALADIN"] = {
      "Interface\\Icons\\Spell_Holy_FlashHeal",
      "Interface\\Icons\\Spell_Holy_HolyBolt",
    },
    ["PRIEST"] = {
      "Interface\\Icons\\Spell_Holy_FlashHeal",
      "Interface\\Icons\\Spell_Holy_LesserHeal",
      "Interface\\Icons\\Spell_Holy_Heal",
      "Interface\\Icons\\Spell_Holy_GreaterHeal",
      "Interface\\Icons\\Spell_Holy_Renew",
    },
    ["DRUID"] = {
      "Interface\\Icons\\Spell_Nature_HealingTouch",
      "Interface\\Icons\\Spell_Nature_ResistNature",
      "Interface\\Icons\\Spell_Nature_Rejuvenation",
    },
    ["SHAMAN"] = {
      "Interface\\Icons\\Spell_Nature_MagicImmunity",
      "Interface\\Icons\\Spell_Nature_HealingWaveLesser",
      "Interface\\Icons\\Spell_Nature_HealingWaveGreater",
    },
  }

  local _, class = UnitClass("player")
  if not spells[class] then return end

  -- units that should be scanned
  local units = {}
  table.insert(units, "pet")
  for i=1,4 do table.insert(units, "party" .. i) end
  for i=1,4 do table.insert(units, "partypet" .. i) end
  for i=1,40 do table.insert(units, "raid" .. i) end
  for i=1,40 do table.insert(units, "raidpet" .. i) end
  local numunits = table.getn(units)

  -- cache for unit relations
  local unitcache = {}

  -- actual unit-range table
  local unitdata = { }

  -- the interval between each range check
  local interval = tonumber(C.unitframes.rangechecki)/numunits

  pfUI.rangecheck = CreateFrame("Frame", "pfRangecheck", UIParent)
  pfUI.rangecheck.id = 1
  pfUI.rangecheck:RegisterEvent("ACTIONBAR_SLOT_CHANGED")
  pfUI.rangecheck:RegisterEvent("PLAYER_ENTERING_WORLD")
  pfUI.rangecheck:RegisterEvent("PLAYER_ENTER_COMBAT")
  pfUI.rangecheck:RegisterEvent("PLAYER_LEAVE_COMBAT")
  pfUI.rangecheck:SetScript("OnEvent", function()
    if event == "ACTIONBAR_SLOT_CHANGED" or event == "PLAYER_ENTERING_WORLD" then
      pfUI.rangecheck.slot = this:GetRangeSlot()
    elseif event == "PLAYER_ENTER_COMBAT" then
      this.lastattack = GetTime()
      this:Hide()
    elseif event == "PLAYER_LEAVE_COMBAT" then
      if not this:ReAttack() then
        this:Show()
      end
    end
  end)

  pfUI.rangecheck:SetScript("OnUpdate", function()
    if ( this.tick or 1) > GetTime() then
      return
    else
      this.tick = GetTime() + interval
    end

    -- skip invalid units
    while not this:NeedRangeScan(units[this.id]) and this.id <= numunits do
      this.id = this.id + 1
    end

    if this.id <= numunits and pfUI.rangecheck.slot then
      local unit = units[this.id]
      if not UnitIsUnit("target", unit) then
        -- suspend for various conditions
        if pfUI.loot and pfUI.loot:IsShown() then return nil end
        if LootFrame and LootFrame:IsShown() then return nil end
        if InspectFrame and InspectFrame:IsShown() then return nil end
        if TradeFrame and TradeFrame:IsShown() then return nil end

        pfScanActive = true
        TargetUnit(unit)
        unitdata[unit] = IsActionInRange(pfUI.rangecheck.slot)
        TargetLastTarget()
        pfScanActive = false
        this:ReAttack()
      end

      this.id = this.id + 1
    else
      this.id = 1
    end
  end)

  function pfUI.rangecheck:ReAttack()
    -- we accidentally broke the autoattack... restoring the old state
    if this.lastattack and this.lastattack + interval > GetTime() and UnitCanAttack("player", "target") then
      AttackTarget()
      return true
    else
      return nil
    end
  end

  function pfUI.rangecheck:NeedRangeScan(unit)
    if not UnitExists(unit) then return nil end
    if not UnitIsVisible(unit) then return nil end
    if CheckInteractDistance(unit, 4) then return nil end
    return true
  end

  function pfUI.rangecheck:GetRealUnit(unit)
    if unitdata[unit] then return unit end

    if unitcache[unit] then
      if UnitIsUnit(unitcache[unit], unit) then
        return unitcache[unit]
      end
    end

    for id, realunit in pairs(units) do
      if UnitIsUnit(realunit, unit) then
        unitcache[unit] = realunit
        return realunit
      end
    end

    return unit
  end

  function pfUI.rangecheck:GetRangeSlot()
    for i=1,120 do
      local texture = GetActionTexture(i)
      for _, check in pairs(spells[class]) do
        if check == texture then
          return i
        end
      end
    end

    return nil
  end

  function pfUI.rangecheck:UnitInSpellRange(unit)
    if not pfUI.rangecheck.slot then return nil end

    if UnitIsUnit("target", unit) then
      return IsActionInRange(pfUI.rangecheck.slot) == 1 and 1 or nil
    end

    local unit = pfUI.rangecheck:GetRealUnit(unit)

    if unitdata[unit] and unitdata[unit] == 1 then
      return 1
    elseif not unitdata[unit] then
      return 1
    else
      return nil
    end
  end
end)