local p = {}

-- Find "{{{x|" where "x" is an arg name
local function findDefStart (code, i, argstosub)
    while true do
        local s, e, a = code:find("{{{([^{}|]+)|", i)
        if not s then return nil end
        if argstosub[a] then return s, e, a end
        i = e + 1
    end
end

-- Skip stuff after "{{{x|", find "}}}"
local function findDefEnd (code, i)
    while true do
        local s, e = code:find("^[^{}]*", i)  -- skip non-braces
        i = e + 1
        s, e = code:find("^%b{}", i)  -- skip balanced braces
        if not s then break end
        i = e + 1
    end
    return code:find("^}}}", i) 
end

-- Replace "{{{x|...}}}" by "{{{x}}}" where "x" is an arg name.
-- Without this, we'd have to handle both "{{{x}}}" and "{{{x|...}}}"
-- in the main loop, which would be cumbersome and inefficient.
-- All but the last batch are guaranteed to have the full size,
-- so we know that the parameters don't need defaults.
local function dropDefs (code, size)
	local argstosub = {}
	argstosub["i"] = "{{{i}}}"
	for i = 1, size do
		argstosub[tostring(i)] = "{{{" .. i .. "}}}"
	end

    local result = {}
    local i = 1
    while true do
        local s, e, a = findDefStart(code, i, argstosub)
        if not s then break end  -- no more "{{{x|", done
        _, e = findDefEnd(code, e + 1)
        if not e then break end  -- no "}}}", bad syntax, let wiki deal with it
        table.insert(result, code:sub(i, s - 1))  -- append up to "{{{x|"
        table.insert(result, argstosub[a])  -- append "{{{x}}}"
        i = e + 1
    end
    table.insert(result, code:sub(i))
	return table.concat(result)
end

function p.main(frame) 
	local size = tonumber(frame.args[1])
	local sep = frame.args[2]
	local code = frame.args[3] or frame.args.code
	local result = {}
	local batch = {}
	code = mw.text.unstripNoWiki(code)
	code = code:gsub('&lt;', '<'):gsub('&gt;', '>')
	local cleanCode = dropDefs(code, size)
	local idx = 0
	for i, value in ipairs(frame:getParent().args) do
		table.insert(batch, value)
		if #batch == size then
			idx = idx + 1
			local argstosub = {}
			for j, value2 in pairs(batch) do
				argstosub[tostring(j)] = value2
			end
			argstosub["i"] = idx
			local actualCode = cleanCode:gsub("{{{([^{}]+)}}}", argstosub)
			table.insert(result, frame:preprocess(actualCode))
			batch = {}
		end
	end
	if #batch > 0 then
		idx = idx + 1
		local argstosub = {}
		for j, value2 in pairs(batch) do
			argstosub[tostring(j)] = value2
		end
		argstosub["i"] = idx
		-- Do the last sub in a child frame and use the original code to handle defaults
		local childFrame = frame:newChild{title=frame:getParent().title, args = argstosub}
		table.insert(result, childFrame:preprocess(code))
	end
	if frame.args.conjunction then
		return mw.text.listToText(result, sep, frame.args.conjunction)
	else
		return table.concat(result, sep)
	end
end

return p