gather_mats

-- Moves items from SRC to DEST as specified by INPUT_FILE, which is a JSON
-- file in the format obtained by using the copy button of St'ructure Tools'
-- Copy Paste Gadget

local SRC = "left"
local DEST = "right"
local INPUT_FILE = "input.json"

local src = peripheral.wrap(SRC)
local dest = peripheral.wrap(DEST)

local function clear_dest()
  for slot, item in pairs(dest.list()) do
    local pushCount = dest.pushItems(SRC, slot)
    if pushCount < item.count then
      print("Not enough room in SRC to clear DEST into")
      error()
    end
  end
end

local needed = {}
do
  local success, input = pcall(function()
    io.input(INPUT_FILE)
    return textutils.unserializeJSON(io.read("*a")).header.material_list.root_entry
  end)
  if not success then
    print("Error deserializing JSON")
    error()
  end
  for _, v in pairs(input) do
    needed[v.item.item] = v.count
  end
end

clear_dest()

local srcMats = {}
do
  for slot, item in pairs(src.list()) do
    srcMats[item.name] = srcMats[item.name] or {slots = {}, total = 0}
    local t = srcMats[item.name]
    t.slots[#t.slots + 1] = slot
    t.total = t.total + item.count
  end
end

local errored = false

-- Move mats to dest
for item, neededCount in pairs(needed) do
  local stillNeeded = neededCount
  local t = srcMats[item] or {slots = {}, total = 0}
  for _, slot in ipairs(t.slots) do
    stillNeeded = stillNeeded - dest.pullItems(SRC, slot, neededCount)
    if stillNeeded <= 0 then
      break
    end
  end

  if stillNeeded > 0 then
    print("Missing " .. stillNeeded .. "/" .. neededCount .. " " .. item)
    errored = true
  end
end

if errored then
  -- Detect the possibility that dest is not big enough
  local filled_dest_slots = 0
  for _ in pairs(dest.list()) do
    filled_dest_slots = filled_dest_slots + 1
  end
  if filled_dest_slots >= dest.size() then
    print("Warning: previous errors may be due to destination storage not being big enough")
  end

  clear_dest()
  error()
end

print("Success")