-- Energy Tracking with Create Addition Display Link (Final, Commented)
--
-- This script measures the energy (FE) stored in a modular accumulator,
-- calculates the rate of change over a specified interval, estimates
-- time to full or empty, and outputs four lines to a Create Crafts &
-- Additions Display Link attached to the "top" of the ComputerCraft computer.

-- Wraps a peripheral on a given side and ensures it implements required methods.
local function wrapPeripheral(side, methods)
  -- Attempt to wrap the peripheral; error if not found.
  local obj = peripheral.wrap(side)
  if not obj then
    error("No peripheral found on '" .. side .. "'")
  end
  -- Verify each required method exists on the wrapped object.
  for _, m in ipairs(methods) do
    if type(obj[m]) ~= "function" then
      error("Peripheral on '" .. side .. "' missing method: " .. m)
    end
  end
  return obj
end

-- Wrap the FE accumulator (right side) and the Display Link (top side).
local acc  = wrapPeripheral("right", {"getEnergy", "getCapacity", "getPercent"})
local disp = wrapPeripheral("top",   {"clear", "setLine", "print"})

-- Helper functions to read data from the accumulator.
local function readEnergy()
  -- Returns current FE in the accumulator.
  return acc.getEnergy(acc)
end
local function readCapacity()
  -- Returns maximum FE capacity of the accumulator.
  return acc.getCapacity(acc)
end
local function readPercent()
  -- Returns current FE as a fraction or percentage.
  return acc.getPercent(acc)
end

-- Determine measurement interval from command-line arg or default to 60 seconds.
local interval = tonumber(arg and arg[1]) or 60

-- Take the first energy reading and timestamp.
local e1 = readEnergy()
local t1 = os.clock()

-- Sleep for the specified interval to measure change over time.
os.sleep(interval)

-- Take the second energy reading and timestamp.
local e2 = readEnergy()
local t2 = os.clock()

-- Compute rate of energy change (FE per second).
local dt    = t2 - t1
if dt == 0 then error("Zero time difference; cannot compute rate.") end
local dE    = e2 - e1
local rate  = dE / dt

-- Read capacity and compute estimated time to full/empty (in seconds).
local capacity = readCapacity()
local eta
if rate > 0 then
  -- Filling: time until full
  eta = (capacity - e2) / rate
else
  -- Draining: time until empty
  eta = e2 / -rate
end
eta = math.max(0, eta)  -- Prevent negative ETA

-- Prepare the four display lines:
-- 1) "FE: current/maximum"
-- 2) "Rate: X.X FE/s"
-- 3) "ETA: Y s"
-- 4) "%: Z.Z%"
local percent = readPercent()
-- Normalize percent: if <=1, treat as fraction
if percent <= 1 then percent = percent * 100 end

local line1 = string.format("FE: %d/%d", e2, capacity)
local line2 = string.format("Rate: %.1f FE/s", rate)
local line3 = string.format("ETA: %ds", math.floor(eta))
local line4 = string.format("%%: %.1f%%", percent)

-- Output the lines to the Display Link.
-- The Create Addition Display Link API requires setLine() then print().
disp.clear()
disp.setLine(1)
disp.print(line1)
disp.setLine(2)
disp.print(line2)
disp.setLine(3)
disp.print(line3)
disp.setLine(4)
disp.print(line4)