local doc   = require "wslua.doc"
local fndef = require "wslua.fndef"
local ty    = require "wslua.ty"

local list = require "wslua.list"



local string = setmetatable({}, {__index = string})

doc.module{
	name  = "wslua.string",
	what  = "Additional string functionality",
	descr = [[
This module also contains all functions from the default `string` library, and can be used as a drop-in replacement. Use
the main `wslua` module to inject this module into the string metatable.
]],
}


string.split = fndef({
	name  = "string.split",
	what  = "Split a string into segments using a separator.",
	args  = {
		{name = "subj", type = ty.stringish, what = "String to be split."},
		{name = "sep", type = ty.string & ~ ty.eq(""), what = "Separator pattern to split on."},
		{name = "plain", type = #ty.boolean, what = "Match `sep` literally, not as a pattern."},
	},
	ret   = {
		{type = ty.class(list) & ty.list(ty.string, 1)},
	},
	tests = {
		function() return "{}", string.split("", "/"):__tostring() end,
		function() return "{1, 2, 3}", string.split("1/2/3", "/", true):__tostring() end,
		function() return "{1, 2, 3}", string.split("1 2 3", "%s"):__tostring() end,
		function() return "{1, 2, }", string.split("1 2 ", "%s"):__tostring() end,
		function() return "{, 2, 3}", string.split(" 2 3", "%s"):__tostring() end,
		function() return "{1, 2, , 3}", string.split("1 2  3", "%s"):__tostring() end,
	},
},
function(subj, sep)
	subj = tostring(subj)

	local ret = list()
	local i   = 1

	while true do
		local a, b = subj:find(sep, i, plain)
		if not a then break end
		ret:insert(subj:sub(i, a-1))
		i = b + 1
	end

	ret:insert(subj:sub(i, -1))

	return ret
end)


string.print = fndef({
	name  = "string.print",
	what  = "Print a string to a stream.",
	descr = [[
Mainly useful if injected into the string metatable using the main `wslua` module, that allows `:print()` at the end of
a long call chain.
]],
	args  = {
		{name = "s", type = ty.string},
		{name = "file", type = #ty.file, what = "File to print to, defaults to `stdout`."},
		{name = "nonl", type = #ty.boolean, what = "Don't add a newline after the string, defaults to `false` (= add a newline)."},
	},
	ret   = {
		{type = ty.string, what = "s"},
	}
},
function(s, file, nonl)
	file = file or io.stdout
	file:write(s)
	if not nonl then file:write("\n") end
	return s
end)


string.template = fndef({
	name  = "string.template",
	what  = "Process a string with embedded Lua snippets.",
	descr = [=[
There are two kinds of snippets: expression snippets and statement snippets. Expression snippets start with `%[[` and
end with the first `]]` afterwards, statement snippets are delimited by `%{{` and `}}`. An arbitrary amount of `=`s can
be placed between the brackets, with semantics analogous to Lua strings/comments.

The function "inverts" the string:

- Everything except the snippets is put inside string literals, which are fed to a concatenation function.
- Expression snippets are wrapped in `tostring` calls, and then also fed to the concatenation function.
- Statement snippets are left as-is between the other code.

The resulting code is executed inside the specified `env`.
]=],
	args  = {
		{name = "input", type = ty.stringish, what = "String to process."},
		{name = "loc", type = ty.stringish, what = "Location information used to generate error messages."},
		{name = "env", type = ty.table, what = "Environment to execute snippets in."},
	},
	ret   = {
		{type = ty.string},
	},
	tests = {
		function() return "", string.template("", "test", {}) end,
		function() return "asdfg", string.template("as%[=[d]=]fg", "test", {d = "d"}) end,
		function() return "Hello, World!", string.template("Hello, %[[name()]]!", "test", {name = function() return "World" end}) end,
		function() return "Hello, World!", string.template("%{{ name = 'World' }}Hello, %[[ name ]]!", "test", {}) end,
	},
	ex    = [=[
require "wslua" ();
local t = "%{{ name = 'World' }}%[[greeting]], %[[name]]!"
s:template("test string", {name = "Lua"}):print()
]=]
},
function(input, loc, env)
	input   = tostring(input  )
	loc     = tostring(loc    )

	local s = table.concat({
		"local ___out___ = ...; ___out___[=========[",
		input
			:gsub("%%%[(=*)%[(.-)%]%1%]", "]=========] ___out___(%2) ___out___[=========[")
			:gsub("%%{(=*){(.-)}%1}", "]=========] %2 ___out___[=========[")
			:gsub("___out___%[=========%[\n", "___out___'\\n' %1"),
		"]=========]"
	})

	local ret = list{}
	assert(load(s, tostring(loc), "t", env))(function(s) ret:insert(tostring(s)) end)
	return ret:concat()
end)

return string