Module:fun

local export = {}

local debug_track_module = "Module:debug/track"
local table_get_unprotected_metatable = "Module:table/getUnprotectedMetatable"

local chain -- defined below
local chain_iter -- defined below
local format = string.format
local gmatch = string.gmatch
local ipairs = ipairs
local is_callable -- defined below
local pairs = pairs
local pcall = pcall
local rawget = rawget
local require = require
local select = select
local tostring = tostring
local type = type
local unpack = unpack or table.unpack -- Lua 5.2 compatibility
local unroll -- defined below
local xpcall = xpcall

local function debug_track(...)
	debug_track = require(debug_track_module)
	return debug_track(...)
end

local function get_unprotected_metatable(...)
	get_unprotected_metatable = require(table_get_unprotected_metatable)
	return get_unprotected_metatable(...)
end

local function _iterString(iter, i)
	i = i + 1
	local char = iter()
	if char ~= nil then
		return i, char
	end
end

-- Iterate over UTF-8-encoded codepoints in string.
local function iterString(str)
	return _iterString, gmatch(str, ".*"), 0
end

--[==[
Return {true} if the input is a function or functor (an object which can be called like a function, because it has a {__call} metamethod).

Note: if the input is an object with a {__call} metamethod, but this function is not able to find it because the object's metatable is protected with {__metatable}, then it will return {false} by default, or {nil} if the {allow_maybe} flag is set.]==]
function export.is_callable(f, allow_maybe)
	if type(f) == "function" then
		return true
	end
	-- An object is a functor if it has a `__call` metamethod. The only way to truly confirm this is by trying to call it, but that could be expensive or have side effects, so look for a `__call` metamethod instead. If the metatable is protected with `__metatable`, this may not be possible.
	local mt = get_unprotected_metatable(f)
	if mt == nil then
		return false
	-- `get_unprotected_metatable` returns false if the metatable is protected.
	elseif mt == false then
		debug_track("fun/is_callable/protected metatable")
		if allow_maybe then
			return nil
		end
		return false
	end
	-- `__call` metamethods have to be functions, so don't recurse to check it.
	local __call = rawget(mt, "__call")
	return __call and type(__call) == "function" or false
end
is_callable = export.is_callable

	--[==[
	A version of {xpcall} which takes any arguments to be given to {f} as additional arguments after the error handler.
	
	This fixes a deficiency in the standard version of {xpcall}, which is not able to handle arguments to be given to {f}, and brings it in line with {pcall}.]==]
function export.xpcall(f, err_handler, ...)
	-- If there are no arguments, just call xpcall() with `f`.
	if select("#", ...) == 0 then
		return xpcall(f, err_handler)
	end
	-- Any arguments have to be smuggled in via a table, as ... can't be an
	-- upvalue, and it's not possible to use pcall() to get aroud this, because
	-- xpcall() calls the error handler before the stack unwinds.
	local args = {...}
	return xpcall(function()
		return f(unpack(args))
	end, err_handler)
end

do
	local function catch_values(f, success, ...)
		if success then
			return success, ...
		-- Error message will only take this exact form if `f` is not callable,
		-- because it will contain a traceback if it was thrown further up the
		-- stack.
		elseif (...) == format("attempt to call a %s value", type(f)) then
			return false
		end
		return error(...)
	end

	--[==[
	A special form of {pcall()}, which returns {true} plus the result value(s) if {f} is callable, or {false} if it isn't. Errors that occur within the called function are not protected.]==]
	function export.try_call(f, ...)
		local callable = is_callable(f, true)
		if callable then
			return true, f(...)
		elseif callable == false then
			return false
		end
		-- If `callable` is nil, there's a protected metatable, so there's no way to check without doing a protected call.
		return catch_values(f, pcall(f, ...))
	end
end

--[==[
Takes two or more functions as arguments, and returns a new function which calls each of the input functions in turn. Any arguments given to the returned function are given to the first function, and all other functions receive the output value(s) from the previous function.]==]
function export.chain(func1, func2, ...)
	local function chained_func(...)
		return func2(func1(...))
	end
	if select("#", ...) == 0 then
		return chained_func
	end
	return chain(chained_func, ...)
end
chain = export.chain

--[==[
Takes the usual for-loop parameters (an iterator, plus an optional state and initial index), and unrolls the iterator by returning every (first) value returned by the iterator.

For instance, {unroll(pairs(t))} will return every key in {t}, and {unroll(string.gmatch(s, "%w+"))} will return every word in {s}.]==]
function export.unroll(iter, state, k)
	k = iter(state, k)
	if k ~= nil then
		return k, unroll(iter, state, k)
	end
end
unroll = export.unroll

--[==[
Takes a generator function (i.e. a function that returns an iterator, such as {ipairs}) and one or more additional functions, and returns a new generator function. Any arguments given to the new generator (e.g. an input table) are given to the original generator, and the additional functions are called on each iteration. The first additional function takes the output from the original iterator (i.e. the function returned by the original generator), and any further functions receive the output value(s) from the previous function. This can be used to modify the values returned from an iterator.]==]
function export.chainIter(gen, new_iter, ...)
	if select("#", ...) > 0 then
		new_iter = chain(new_iter, ...)
	end
	return function(...)
		local orig_iter, state, k = gen(...)
		
		-- k has to be the first value returned by orig_iter on the last iteration, not whatever new_iter returned.
		local function catch_values(...)
			k = ...
			if k ~= nil then
				return new_iter(...)
			end
		end
		
		return function()
			return catch_values(orig_iter(state, k))
		end, state, k
	end
end
chain_iter = export.chainIter

do
	local function catch_values(start, iter, state, k, ...)
		if start == k or k == nil then
			return k, ...
		end
		return catch_values(start, iter, state, iter(state, k))
	end
	
	function export.iterateFrom(start, iter, state, k)
		local first = true
		return function(state, k)
			if first then
				first = false
				return catch_values(start, iter, state, iter(state, k))
			end
			return iter(state, k)
		end, state, k
	end
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 array = {}
	for k, v in (type(iterable) == "string" and iterString or (isArray or iterable ~= nil) and ipairs or pairs)(iterable) do
		array = func(v, k, iterable)
	end
	return array
end

function export.mapIter(func, iter, state, init)
	-- init could be anything
	local array, i = {}, 0
	for x, y in iter, state, init do
		i = i + 1
		array = func(y, x, state)
	end
	return array
end

do
	local function iter_tuples(tuples)
		local i = tuples.i
		if i > 1 then
			i = i - 1
			tuples.i = i
			return unpack(tuples)
		end
	end
	
	-- Takes an iterator function, and returns a new iterator that iterates in reverse, given the same arguments.
	-- Note: changes to the state during iteration are not taken into account, since all the return values are calculated in advance.
	function export.reverseIter(func)
		return function(...)
			-- Store all returned values as a list of tuples, then iterate in reverse over that list.
			local tuples, i, iter, state, val1 = {}, 0, func(...)
			while true do
				i = i + 1
				local vals = {iter(state, val1)}
				-- Terminates if the first return value is nil, even if other values are non-nil.
				val1 = vals
				if val1 == nil then
					tuples.i = i
					return iter_tuples, tuples
				end
				tuples = vals
			end
		end
	end
end

function export.forEach(func, iterable, isArray)
	for k, v in (type(iterable) == "string" and iterString or (isArray or iterable ~= nil) and ipairs or pairs)(iterable) do
		func(v, k, iterable)
	end
	return nil
end

-------------------------------------------------
-- From http://lua-users.orghttps://dictious.com/en/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)
	for k, v in ((isArray or t ~= nil) and ipairs or pairs)(t) do
		if func(v, k, t) then
			return true
		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)
	for k, v in ((isArray or t ~= nil) and ipairs or pairs)(t) do
		if not func(v, k, t) then
			return false
		end
	end
	return true
end

function export.filter(func, t, isArray)
	local new_t = {}
	if isArray or t ~= 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 = v
			end
		end
	else
		for k, v in pairs(t) do
			if func(v, k, t) then
				new_t = 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 is_callable(v) then
			t = export.logReturnValues(v, tostring(k))
		end
	end
	return t
end

return export