Module:fun

local export = {}

local libraryUtil = require("libraryUtil")

local checkType = libraryUtil.checkType
local checkTypeMulti = libraryUtil.checkTypeMulti
local format = string.format
local ipairs = ipairs
local is_callable = require("Module:utilities").is_callable
local pairs = pairs
local select = select
local setmetatable = setmetatable
local tostring = tostring
local type = type
local unpack = unpack

local iterableTypes = { "table", "string" }

local function _check(funcName, expectType)
	if type(expectType) == "string" then
		return function(argIndex, arg, nilOk)
			return checkType(funcName, argIndex, arg, expectType, nilOk)
		end
	else
		return function(argIndex, arg, expectType, nilOk)
			if type(expectType) == "table" then
				if not (nilOk and arg == nil) then
					return checkTypeMulti(funcName, argIndex, arg, expectType)
				end
			else
				return checkType(funcName, argIndex, arg, expectType, nilOk)
			end
		end
	end
end

-- Iterate over UTF-8-encoded codepoints in string.
local function iterString(str)
	local iter = string.gmatch(str, ".[\128-\191]*")
	local i = 0
	local function iterator()
		i = i + 1
		local char = iter()
		if char then
			return i, char
		end
	end
	
	return iterator
end

function export.chain(func1, func2, ...)
	return func1(func2(...))
end

--	map(function(number) return number ^ 2 end,
--		{ 1, 2, 3 })									--> { 1, 4, 9 }
--	map(function (char) return string.char(string.byte(char) - 0x20) end,
--		"abc")											--> { "A", "B", "C" }
function export.map(func, iterable, isArray)
	local check = _check 'map'
	check(1, func, "function")
	check(2, iterable, iterableTypes)
	
	local array = {}
	local iterator = type(iterable) == "string" and iterString
		or (isArray or iterable[1] ~= nil) and ipairs or pairs
	for i_or_k, val in iterator(iterable) do
		array[i_or_k] = func(val, i_or_k, iterable)
	end
	return array
end

function export.mapIter(func, iter, iterable, initVal)
	local check = _check 'mapIter'
	check(1, func, "function")
	check(2, iter, "function")
	check(3, iterable, iterableTypes, true)
	
	-- initVal could be anything
	
	local array = {}
	local i = 0
	for x, y in iter, iterable, initVal do
		i = i + 1
		array[i] = func(y, x, iterable)
	end
	return array
end

function export.forEach(func, iterable, isArray)
	local check = _check 'forEach'
	check(1, func, "function")
	check(2, iterable, iterableTypes)
	
	local iterator = type(iterable) == "string" and iterString
		or (isArray or iterable[1] ~= nil) and ipairs or pairs
	for i_or_k, val in iterator(iterable) do
		func(val, i_or_k, iterable)
	end
	return nil
end

-------------------------------------------------
-- From http://lua-users.org/wiki/CurriedLua
-- reverse(...) : take some tuple and return a tuple of elements in reverse order
--
-- e.g. "reverse(1,2,3)" returns 3,2,1
local function reverse(...)
	-- reverse args by building a function to do it, similar to the unpack() example
	local function reverseHelper(acc, v, ...)
		if select('#', ...) == 0 then
			return v, acc()
		else
			return reverseHelper(function() return v, acc() end, ...)
		end
	end
	
	-- initial acc is the end of the list
	return reverseHelper(function() return end, ...)
end

function export.curry(func, numArgs)
	-- currying 2-argument functions seems to be the most popular application
	numArgs = numArgs or 2
	
	-- no sense currying for 1 arg or less
	if numArgs <= 1 then return func end
	
	-- helper takes an argTrace function, and number of arguments remaining to be applied
	local function curryHelper(argTrace, n)
		if n == 0 then
			-- kick off argTrace, reverse argument list, and call the original function
			return func(reverse(argTrace()))
		else
			-- "push" argument (by building a wrapper function) and decrement n
			return function(onearg)
				return curryHelper(function() return onearg, argTrace() end, n - 1)
			end
		end
	end
	
	-- push the terminal case of argTrace into the function first
	return curryHelper(function() return end, numArgs)
end

-------------------------------------------------

--	some(function(val) return val % 2 == 0 end,
--		{ 2, 3, 5, 7, 11 })						--> true
function export.some(func, t, isArray)
	if isArray or t[1] ~= nil then -- array
		for i, v in ipairs(t) do
			if func(v, i, t) then
				return true
			end
		end
	else
		for k, v in pairs(t) do
			if func(v, k, t) then
				return true
			end
		end
	end
	return false
end

--	all(function(val) return val % 2 == 0 end,
--		{ 2, 4, 8, 10, 12 })					--> true
function export.all(func, t, isArray)
	if isArray or t[1] ~= nil then -- array
		for i, v in ipairs(t) do
			if not func(v, i, t) then
				return false
			end
		end
	else
		for k, v in pairs(t) do
			if not func(v, k, t) then
				return false
			end
		end
	end
	return true
end

function export.filter(func, t, isArray)
	local new_t = {}
	if isArray or t[1] ~= nil then -- array
		local new_i = 0
		for i, v in ipairs(t) do
			if func(v, i, t) then
				new_i = new_i + 1
				new_t[new_i] = v
			end
		end
	else
		for k, v in pairs(t) do
			if func(v, k, t) then
				new_t[k] = v -- or create array?
			end
		end
	end
	return new_t
end

function export.fold(func, t, accum)
	for i, v in ipairs(t) do
		accum = func(accum, v, i, t)
	end
	return accum
end


-------------------------------
-- Fancy stuff
local function capture(...)
	local vals = { n = select('#', ...), ... }
	return function()
		return unpack(vals, 1, vals.n)
	end
end

-- Log input and output of function.
-- Receives a function and returns a modified form of that function.
function export.logReturnValues(func, prefix)
	return function(...)
		local inputValues = capture(...)
		local returnValues = capture(func(...))
		if prefix then
			mw.log(prefix, inputValues())
			mw.log(returnValues())
		else
			mw.log(inputValues())
			mw.log(returnValues())
		end
		return returnValues()
	end
end

export.log = export.logReturnValues

-- Convenience function to make all functions in a table log their input and output.
function export.logAll(t)
	for k, v in pairs(t) do
		if type(v) == "function" then
			t[k] = export.logReturnValues(v, tostring(k))
		end
	end
	return t
end

----- M E M O I Z A T I O N-----
-- Memoizes a function or callable table.
-- Supports any number of arguments and return values.
do
	local args_key, func_key
	-- Placeholders for values which can't be table keys: nil, NaN and -NaN are disallowed as keys, while -0 is treated as 0.
	local _nil, _pos_nan, _neg_nan, _neg_0
	
	local Memo = {}
	
	-- Return values are memoized as tables of return values, which are looked up using each input argument as a key, followed by args_key. e.g. if the input arguments were (1, 2, 3), the memo would be located at t[1][2][3][args_key]. args_key is always used as the final lookup key so that (for example) the memo for f(1, 2, 3), f[1][2][3][args_key], doesn't interfere with the memo for f(1, 2), f[1][2][args_key]. Certain possible argument values can't be used as table keys, so we use placeholders for them instead: e.g. f("foo", nil, "bar") would be memoized at f["foo"][_nil]["bar"][args_key]. These values are:
		-- nil.
		-- NaN and -NaN, which are the only values for which v ~= v is true; they only seem to differ on conversion to string ("nan" and "-nan").
		-- -0, which is equivalent to 0 in most situations, but becomes "-0" on conversion to string; it also behaves differently in some operations (e.g. 1/a evaluates to inf if a is 0, but -inf if a is -0).
	local function get_memo(memo, n, nargs, this, ...)
		-- nil
		if this == nil then
			_nil = _nil or {}
			this = _nil
		-- NaN and -NaN
		elseif this ~= this then
			if tostring(this) == "nan" then
				_pos_nan = _pos_nan or {}
				this = _pos_nan
			else
				_neg_nan = _neg_nan or {}
				this = _neg_nan
			end
		-- -0
		elseif this == 0 and 1 / this < 0 then
			_neg_0 = _neg_0 or {}
			this = _neg_0
		end
		local next_memo = memo[this]
		if next_memo == nil then
			next_memo = {}
			memo[this] = next_memo
		end
		memo = next_memo
		return n == nargs and memo or get_memo(memo, n + 1, nargs, ...)
	end
	
	-- Catch the function output values, and return the hidden variable arg (which is {...}, and available when a function has ...). We do this instead of catching the output in a table directly, because arg also contains the key "n", which is equal to select("#", ...). i.e. it's the number of arguments in ..., including any nils returned after the last non-nil value (e.g. select("#", nil) == 1, select("#") == 0, select("#", nil, "foo", nil, nil) == 4 etc.). The distinction between nil and nothing affects some native functions (e.g. tostring() throws an error, but tostring(nil) returns "nil"), so it needs to be reconstructable from the memo.
	local function catch_output(...)
		return arg
	end
	
	function Memo:__call(...)
		local nargs = select("#", ...)
		local memo = nargs == 0 and self or get_memo(self, 1, nargs, ...)
		args_key = args_key or {}
		local output = memo[args_key]
		if output == nil then
			output = catch_output(self[func_key](...))
			memo[args_key] = output
		end
		-- Unpack from 1 to the original number of return values (memoized as output.n); unpack returns nil for any values not in output.
		return unpack(output, 1, output.n)
	end
	
	function export.memoize(func)
		if not is_callable(func) then
			error(format(
	            "Only functions and callable tables are memoizable. Received %s (a %s)",
	             tostring(func), type(func)))
		end
		func_key = func_key or {}
		return setmetatable({[func_key] = func}, Memo)
	end
end

return export