local component = require'component'
local gpu = component.gpu


-- # create table containing all screens
local screens = component.list('screen')

-- # instead of invoking 'component.list' every time we make a gpu call
-- # we just update the list whenever a screen is added or removed
local function updatescreens(event, addr, ctype)
  if ctype ~= 'screen' then return nil end
  if event == 'component_added' then
    screens[addr] = 'screen'
  else
    screens[addr] = nil
  end
end

-- # listening to component adding or removing events, invoking 'updatescreen' on event
require'event'.listen('component_added', updatescreens)
require'event'.listen('component_removed', updatescreens)

-- # creating proxy table for gpu calls
local vgpu = {}
-- # making vgpu its own metatable
setmetatable(vgpu, vgpu)

-- # would not make sense to call 'bind' for every screen
vgpu.bind = gpu.bind

-- # '__index' function
function vgpu.__index(self, key)
  -- # since some gpu methods return some data, we differentiate between 'setter' and 'getter' methods
  -- # most setter function have 'set' in their name, 'fill' and 'copy' are the exception
  local setter = { copy = true; fill = true}
  if key:find('set') or setter[key] then
    -- # function that will only call the methods, does not return anything (for setters)
    return function(...)
      for addr in pairs(screens) do
        self.bind(addr)
        gpu[key](...)
      end
    end
  else
    -- # function that will return data (for getters)
    -- # returns table with screen address as key and table or single object as value
    -- # {'addr 1' = value1, 'addr 2' = value2, ...}
    return function(...)
      local res = {}
      for addr in pairs(screens) do
        self.bind(addr)
        local r = {gpu[key](...)}
        res[addr] = #r == 1 and r[1] or r
      end
      return res
    end
  end
end

-- returns gpu proxy, so it can be used as a module
return vgpu