Module:Item

local p = {}

local function escape(str)
 return str:gsub("[|\\]", function (c) return string.format("\\%03d", c:byte()) end)
end

local function unescape(str)
 return str:gsub("\\(%d%d%d)", function (d) return string.char(d) end)
end

-- Implements [[Template:Item]]
function p.pack(frame)
 local parent = frame:getParent()
 local result = ''
 for key, value in pairs(parent.args) do
  result = result .. "|" .. escape(tostring(key)) .. "|" .. escape(value)
 end
 return result .. "|";
end

local function unpack(str)
 local result = { }
 for key, value in str:gfind("|([^|]*)|([^|]*)") do
  result[unescape(key)] = unescape(value)
 end
 return result
end

-- Implements [[Template:Component]]
function p.component(frame)
 return unpack(frame.args[1])[frame.args[2]]
end

local function getItems(frame)
 return frame:getParent().args
end

local function invert(tbl)
 local result = { }
 for key, value in pairs(tbl) do
  result[value] = key
 end
 return result
end

-- Add args into item as appropriate (see [[Template:Format item]])
local function addArgs(
 item,   -- unpacked item to modify
 args,   -- arguments for adding into item
 ignore, -- pass in invert{keys to ignore}
 shift   -- for numbered arguments, args[key+shift] is assigned to item[key]
 -- returns: item
)
 for key, value in pairs(args) do
  if not ignore[key] then
   local _, _, paramKey = string.find(key, "^param (.*)")
   local _, _, importantKey = string.find(key, "^important (.*)")
   paramKey = paramKey or importantKey or key
   if shift and type(paramKey) == "number" then
    paramKey = paramKey - shift
    if paramKey < 1 then paramKey = nil end
   end
   if paramKey and (importantKey or item[paramKey] == nil) then
    item[paramKey] = value
   end
  end
 end
 
 return item
end

-- Implements [[Template:Format item]]
function p.format(frame)
 local args = frame:getParent().args
 local ignore = invert{ "template", "item" }
 local templateArgs = addArgs(unpack(args.item), args, ignore)
 
 return frame:expandTemplate{ title = args.template, args = templateArgs }
end

-- See [[Template:Item#Format each item using a template]]
function p.each(frame)
 local args = frame.args
 local items = getItems(frame)
 local separator = args[1] or ""
 local prepend = args[2] or ""
 local append = args[3] or ""
 local ignore = invert{ "template" }
 local shift = 3

 local result = ""
 for i, item in ipairs(items) do
  local templateArgs = addArgs(unpack(item), args, ignore, shift)
  result = result .. prepend .. frame:expandTemplate{ title = args.template, args = templateArgs } .. append
  if items[i + 1] then
   result = result .. separator
  end
 end
 return result
end

-- See [[Template:Item#Gather given parameter from all items]]
function p.gather(frame)
 local args = frame.args
 local items = getItems(frame)
 local parameter = args.parameter or "1"
 
 local templateArgs = { }
 for i, item in ipairs(items) do
  templateArgs[i] = unpack(item)[parameter]
 end
 
 return frame:expandTemplate{ title = args.template, args = templateArgs }
end

return p