-- Localize functions to avoid table lookups (better performance).
local string_sub, string_find = string.sub, string.find

function string.split_iter(str, delim, include_empty, max_splits, sep_is_pattern)
	delim = delim or ","
	max_splits = max_splits or -1
	local pos, endp, seplen = 1, #str+1, #delim
	local plain = not sep_is_pattern
	local function iter()
		if (not pos) or pos > endp then
			return
		elseif max_splits == 0 then
			local s = string_sub(str, pos)
			pos = nil
			return s
		end
		local np, npe = string_find(str, delim, pos, plain)
		local s = string_sub(str, pos, np and np - 1)
		pos = npe and npe + 1
		if include_empty or (s ~= "") then
			max_splits = max_splits - 1
			return s
		else
			-- Tail call
			return iter()
		end
	end
	return iter
end

--------------------------------------------------------------------------------
function string.split(str, delim, include_empty, max_splits, sep_is_pattern)
	local items, n = { }, 0
	for part in string.split_iter(str, delim, include_empty, max_splits, sep_is_pattern) do
		n = n + 1
		items[n] = part
	end
	return items
end

local function repr(x)
	return (type(x) == "string" and ("%q"):format(x)
			or tostring(x))
end

local function expect(x, y)
	return (rawequal(x, y) or error("assertion failed:"
			.." expected "..repr(y)..", got "..repr(x), 2))
end

local function test_string_split()
	local items, iter

	-- Defaults
	items = ("a,b,c"):split()
	expect(items[1], "a")
	expect(items[2], "b")
	expect(items[3], "c")
	expect(items[4], nil)

	-- Simple split
	items = ("a,b,c"):split(",")
	expect(items[1], "a")
	expect(items[2], "b")
	expect(items[3], "c")
	expect(items[4], nil)

	-- With max_splits
	items = ("a,b,c"):split(",", nil, 1)
	expect(items[1], "a")
	expect(items[2], "b,c")
	expect(items[3], nil)

	-- With include_empty = true
	items = ("a,,b"):split(",", true)
	expect(items[1], "a")
	expect(items[2], "")
	expect(items[3], "b")
	expect(items[4], nil)

	-- Trailing sep with include_empty = false
	items = ("a,b,"):split(",")
	expect(items[1], "a")
	expect(items[2], "b")
	expect(items[3], nil)

	-- Trailing sep with include_empty = true
	items = ("a,b,"):split(",", true)
	expect(items[1], "a")
	expect(items[2], "b")
	expect(items[3], "")
	expect(items[4], nil)

	-- With sep_is_pattern = true
	items = ("a:  \t\n ;b,,,,c"):split("[,;:%s]+", nil, nil, true)
	expect(items[1], "a")
	expect(items[2], "b")
	expect(items[3], "c")
	expect(items[4], nil)

	-- Iterator
	iter = ("a,b,;c"):split_iter("[,;]", true, nil, true)
	expect(iter(), "a")
	expect(iter(), "b")
	expect(iter(), "")
	expect(iter(), "c")
	expect(iter(), nil)
end

test_string_split()