Module:parser

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The following documentation is located at Module:parser/documentation.
Useful links: subpage list • links • transclusions • testcases • sandbox
This module needs documentation.
Please document this module by describing its purpose and usage on the documentation page. 

local export = {}

local scribunto_metamethods_module = "Module:Scribunto/metamethods"
local table_deep_copy_module = "Module:table/deepCopy"
local table_get_nested_module = "Module:table/getNested"
local table_set_nested_module = "Module:table/setNested"

local concat = table.concat
local find = string.find
local getmetatable = getmetatable
local insert = table.insert
local next = next
local rawget = rawget
local rawset = rawset
local remove = table.remove
local require = require
local select = select
local setmetatable = setmetatable
local sub = string.sub
local type = type
local unpack = unpack or table.unpack -- Lua 5.2 compatibility

local node_classes = {}

local function deep_copy(...)
	deep_copy = require(table_deep_copy_module)
	return deep_copy(...)
end

local function get_nested(...)
	get_nested = require(table_get_nested_module)
	return get_nested(...)
end

local function set_nested(...)
	set_nested = require(table_set_nested_module)
	return set_nested(...)
end

--[==[
Loaders for objects, which load data (or some other object) into some variable, which can then be accessed as "foo or get_foo()", where the function get_foo sets the object to "foo" and then returns it. This ensures they are only loaded when needed, and avoids the need to check for the existence of the object each time, since once "foo" has been set, "get_foo" will not be called again.]==]
	local metamethods
	local function get_metamethods()
		-- Use require, since lookup times are much slower with mw.loadData.
		metamethods, get_metamethods = require(scribunto_metamethods_module), nil
		return metamethods
	end

------------------------------------------------------------------------------------
--
-- Helper functions
--
------------------------------------------------------------------------------------

local function inherit_metamethods(child, parent)
	if parent then
		for method, value in next, parent do
			if child == nil and (metamethods or get_metamethods()) ~= nil then
				child = value
			end
		end
	end
	return child
end

local function signed_index(t, n)
	return n and n <= 0 and #t + 1 + n or n
end

local function is_node(value)
	if value == nil then
		return false
	end
	local mt = getmetatable(value)
	return not (mt == nil or node_classes == nil)
end

local function node_class(value)
	if value == nil then
		return nil
	end
	local mt = getmetatable(value)
	if mt == nil then
		return nil
	end
	return mt ~= nil and node_classes or nil
end

local function class_else_type(value)
	if value == nil then
		return type(value)
	end
	local mt = getmetatable(value)
	if mt == nil then
		return type(value)
	end
	local class = node_classes
	return class == nil and type(value) or class
end

-- Recursively calling tostring() adds to the C stack (limit: 200), whereas
-- calling __tostring metamethods directly does not. Occasionally relevant when
-- dealing with very deep nesting.
local tostring
do
	local _tostring = _G.tostring
	
	function tostring(value)
		if is_node(value) then
			return value:__tostring(value)
		end
		return _tostring(value)
	end
end

------------------------------------------------------------------------------------
--
-- Nodes
--
------------------------------------------------------------------------------------

local Node = {}
Node.__index = Node

function Node:next(i)
	i = i + 1
	return self, self, i
end

--[==[
Implements recursive iteration over a node tree.

By default, when a node is encountered (which may contain other nodes), it is returned on the first iteration, and then any child nodes are returned on each subsequent iteration; the same process is then followed if any of those children contain nodes themselves. Once a particular node has been fully traversed, the iterator then continues with any sibling nodes. The iterator will use the `next` method of each node to traverse it, which may differ depending on the node class.

Each iteration returns three values: `value`, `node` and `key`. Together, these can be used to manipulate the node tree at any given point without needing to know the full structure. Note that when the input node is returned on the first iteration, `node` and `key` will be nil.

The optional argument `test` can be used to limit the return values. This should be a function that returns a boolean value, where a return value of true means that the child will be returned by the iterator. If a node is not returned by the iterator, it will still be traversed, as it may contain children that should be returned.

The method `iterate_nodes` is provided as a special instance of iterate which uses `is_node` as the test.]==]
function Node:iterate(test)
	local node, k, n, nodes, keys, returned_self = self, 0, 0
	-- Special case if `test` is `is_node`.
	local is_node_is_test = test == is_node
	
	return function()
		if not returned_self then
			returned_self = true
			if test == nil or test(self) then
				return self
			end
		end
		-- Get `v`, which is the value at the last-returned key of the current node; if `v` is a node, it will be iterated over (i.e. recursive iteration). By default, `v` will be the last-returned value, but looking it up here means that any modifications made to the node during the loop will be taken into account. This makes it possible to swap one node out for something else (e.g. another node), or to remove it entirely, without being locked into recursively iterating over the old node; instead, the new node (if any) will be iterated over. This means node trees can be modified on-the-fly during the course of a single loop.
		local v, node_check = node, true
		while true do
			-- If `v` is a node, memoize the current node and key, then iterate over it.
			if node_check and is_node(v) then
				-- `n` is the current memo level.
				n = n + 1
				if nodes then
					nodes, keys = node, k
				else
					nodes, keys = {node}, {k}
				end
				node, k = v, 0
			end
			v, node, k = node:next(k)
			-- If `v` is nil, move down one level, then continue iterating the node on that level (if any), or otherwise terminate the loop.
			if v == nil then
				if n == 0 then
					return nil
				end
				node, k, n = nodes, keys, n - 1
			elseif test == nil or test(v) then
				return v, node, k
			-- If `test` is `is_node`, there's no point checking it again on the next loop.
			elseif node_check and is_node_is_test then
				node_check = false
			end
		end
	end
end

function Node:iterate_nodes(...)
	local args_n = select("#", ...)
	if args_n == 0 then
		return self:iterate(is_node)
	elseif args_n == 1 then
		local class = ...
		return self:iterate(function(value)
			return node_class(value) == class
		end)
	end
	local classes = {}
	for i = 1, args_n do
		classes = true
	end
	return self:iterate(function(value)
		return classes
	end)
end

function Node:__tostring()
	local output = {}
	for i = 1, #self do
		insert(output, tostring(self))
	end
	return concat(output)
end

function Node:clone()
	return deep_copy(self, "keep", true)
end

function Node:new_class(class)
	local t = {type = class}
	t.__index = t
	t = inherit_metamethods(t, self)
	node_classes = class
	return setmetatable(t, self)
end

function Node:new(t)
	rawset(t, "_parse_data", nil)
	return setmetatable(t, self)
end

do
	local Proxy = {}

	function Proxy:__index(k)
		local v = Proxy
		if v ~= nil then
			return v
		end
		return self.__chars
	end

	function Proxy:__newindex(k, v)
		local key = self.__keys
		if key then
			self.__chars = v
			self.__parents = v
		elseif key == false then
			error("Character is immutable.")
		else
			error("Invalid key.")
		end
	end

	function Proxy:build(a, b, c)
		local len = self.__len + 1
		self.__chars = a
		self.__parents = b
		self.__keys = c
		self.__len = len
	end

	function Proxy:iter(i)
		i = i + 1
		local char = self.__chars
		if char ~= nil then
			return i, self, self, self.__parents, self.__keys
		end
	end
	
	function Node:new_proxy()
		return setmetatable({
			__node = self,
			__chars = {},
			__parents = {},
			__keys = {},
			__len = 0
		}, Proxy)
	end
end

function export.node()
	return Node:new_class("node")
end

------------------------------------------------------------------------------------
--
-- Parser
--
------------------------------------------------------------------------------------

local Parser = {}
Parser.__index = Parser

function Parser:get_layer(n)
	if n ~= nil then
		return rawget(self, #self + n)
	end
	return self.current_layer
end

function Parser:emit(a, b)
	local layer = self.current_layer
	if b ~= nil then
		insert(layer, signed_index(layer, a), b)
	else
		rawset(layer, #layer + 1, a)
	end
end

function Parser:emit_tokens(a, b)
	local layer = self.current_layer
	if b ~= nil then
		a = signed_index(layer, a)
		for i = 1, #b do
			insert(layer, a + i - 1, b)
		end
	else
		local len = #layer
		for i = 1, #a do
			len = len + 1
			rawset(layer, len, a)
		end
	end
end

function Parser:remove(n)
	local layer = self.current_layer
	if n ~= nil then
		return remove(layer, signed_index(layer, n))
	end
	local len = #layer
	local token = layer
	layer = nil
	return token
end

function Parser:replace(a, b)
	local layer = self.current_layer
	layer = b
end

-- Unlike default table.concat, this respects __tostring metamethods.
function Parser:concat(a, b, c)
	if a == nil or a > 0 then
		return self:concat(0, a, b)
	end
	local layer, ret, n = self:get_layer(a), {}, 0
	for i = b and signed_index(layer, b) or 1, c and signed_index(layer, c) or #layer do
		n = n + 1
		ret = tostring(layer)
	end
	return concat(ret)
end

function Parser:emitted(delta)
	if delta == nil then
		delta = -1
	end
	local get_layer, i = self.get_layer, 0
	while true do
		local layer = get_layer(self, i)
		if layer == nil then
			return nil
		end
		local layer_len = #layer
		if -delta <= layer_len then
			return rawget(layer, layer_len + delta + 1)
		end
		delta = delta + layer_len
		i = i - 1
	end
end

function Parser:push(route)
	local layer = {_parse_data = {
		head = self.head,
		route = route,
	}}
	self = layer
	self.current_layer = layer
end

function Parser:push_sublayer(handler, inherit)
	local pdata = {
		handler = handler,
		sublayer = true,
	}
	local sublayer = {
		_parse_data = pdata,
	}
	if inherit then
		local layer_parse_data = self.current_layer._parse_data
		setmetatable(pdata, inherit_metamethods({
			__index = layer_parse_data,
			__newindex = layer_parse_data
		}, getmetatable(layer_parse_data)))
	end
	self = sublayer
	self.current_layer = sublayer
end

function Parser:pop()
	local len, layer = #self
	while true do
		layer = self
		self = nil
		len = len - 1
		if len == 0 then
			self.current_layer = self
			break
		elseif layer._parse_data.sublayer == nil then
			self.current_layer = self
			break
		end
		self:emit_tokens(layer)
	end
	return setmetatable(layer, nil)
end

function Parser:pop_sublayer()
	local len, layer = #self, self.current_layer
	self = nil
	self.current_layer = len == 1 and self or self
	return setmetatable(layer, nil)
end

function Parser:get(route, ...)
	self:push(route)
	local layer = route(self, ...)
	if layer == nil then
		layer = self:traverse()
	end
	return layer
end

function Parser:try(route, ...)
	local failed_routes = self.failed_routes
	if failed_routes ~= nil then
		local failed_layer = get_nested(failed_routes, route, self.head)
		if failed_layer ~= nil then
			return false, failed_layer
		end
	end
	local layer = self:get(route, ...)
	return not layer._parse_data.fail, layer
end

function Parser:fail_route()
	local layer = self:pop()
	local pdata = layer._parse_data
	pdata.fail = true
	local layer_head = pdata.head
	set_nested(self, layer, "failed_routes", pdata.route, layer_head)
	self.head = layer_head
	return layer
end

function Parser:traverse()
	local consume, advance = self.consume, self.advance
	while true do
		local layer = consume(self)
		if layer ~= nil then
			return layer
		end
		advance(self)
	end
end

-- Converts a handler into a switch table the first time it's called, which avoids creating unnecessary objects, and prevents any scoping issues caused by parser methods being assigned to table keys before they've been declared.
-- false is used as the default key.
do
	local Switch = {}
	
	function Switch:__call(parser, this)
		return (self or self)(parser, this)
	end
	
	function Parser:switch(func, t)
		local pdata = self.current_layer._parse_data
		-- Point handler to the new switch table if the calling function is the current handler.
		if pdata.handler == func then
			pdata.handler = t
		end
		return setmetatable(t, Switch)
	end
end

-- Generate a new parser class object, which is used as the template for any parser objects. These should be customized with additional/modified methods as needed.
function Parser:new_class()
	local t = {}
	t.__index = t
	return setmetatable(inherit_metamethods(t, self), self)
end

-- Generate a new parser object, which is used for a specific parse.
function Parser:new(text)
	return setmetatable({
		text = text,
		head = 1
	}, self)
end

function Parser:parse(data)
	local parser = self:new(data.text)
	local success, tokens = parser:try(unpack(data.route))
	if #parser > 0 then
		-- This shouldn't happen.
		error("Parser exited with non-empty stack.")
	elseif success then
		local node = data.node
		return true, node:new(tokens, unpack(node, 2)), parser
	elseif data.allow_fail then
		return false, nil, parser
	end
	error("Parser exited with failed route.")
end

export.class_else_type = class_else_type
export.is_node = is_node
export.tostring = tostring

local ArrayParser = Parser:new_class()

function ArrayParser:read(delta)
	local v = self.text
	return v == nil and "" or v
end

function ArrayParser:advance(n)
	self.head = self.head + (n == nil and 1 or n)
end

function ArrayParser:jump(head)
	self.head = head
end

function ArrayParser:consume(this, ...)
	if this == nil then
		this = self:read()
	end
	local pdata = self.current_layer._parse_data
	return pdata.handler(self, this, ...)
end

function export.array_parser()
	return ArrayParser:new_class()
end

local StringParser = Parser:new_class()

function StringParser:read(i, j)
	local head, i = self.head, i or 0
	return sub(self.text, head + i, head + (j or i))
end

function StringParser:advance(n)
	self.head = self.head + (n or self.current_layer._parse_data.step or 1)
end

function StringParser:jump(head)
	local pdata = self.current_layer._parse_data
	self.head, pdata.next, pdata.next_len = head, nil, nil
end

-- If `ignore_nonmatch` is set, any non-match segment before the match will be ignored.
function StringParser:set_pattern(pattern, ignore_nonmatch)
	local pdata = self.current_layer._parse_data
	pdata.pattern, pdata.next, pdata.next_len = "(" .. pattern .. ")", nil, nil
	if ignore_nonmatch then
		pdata.ignore_nonmatch = true
	end
end

function StringParser:consume()
	local pdata = self.current_layer._parse_data
	local this = pdata.next
	-- Use `next` and `next_len` from the previous iteration, if available.
	if this then
		pdata.step, pdata.next, pdata.next_len = pdata.next_len, nil, nil
		return pdata.handler(self, this)
	end
	local text, head, loc1, loc2 = self.text, self.head
	loc1, loc2, this = find(text, pdata.pattern, head)
	-- If there was no match, default to find(text, "$", head), with `this` as
	-- the empty string.
	if not loc1 then
		this, loc1 = "", #text + 1
		loc2 = loc1 - 1 -- zero-length matches cause loc2 to be less than loc1
	end
	-- If `this` is at `head`, consume it.
	if loc1 == head then
		pdata.step = loc2 - loc1 + 1
	-- If `ignore_nonmatch` is set, ignore everything before `this`, then
	-- consume it.
	elseif pdata.ignore_nonmatch then
		self.head, pdata.step = loc1, loc2 - loc1 + 1
	-- Otherwise, consume everything before `this`, and memoize the match and
	-- match length; the length is dealt with separately, as it could be 0 if
	-- `next` is an index (e.g. if the pattern is the empty string).
	else
		this, pdata.step, pdata.next, pdata.next_len = sub(text, head, loc1 - 1), loc1 - head, this, loc2 - loc1 + 1
	end
	return pdata.handler(self, this)
end

function export.string_parser()
	return StringParser:new_class()
end

return export
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