Module:parser

Documentation for this module may be created at Module:parser/doc

local export = {}

local concat = table.concat
local deepcopy -- Assigned when needed.
local getmetatable = getmetatable
local insert = table.insert
local next = next
local rawget = rawget
local rawset = rawset
local remove = table.remove
local setmetatable = setmetatable
local type = type
local unpack = unpack

local classes = {}
local metamethods = mw.loadData("Module:data/metamethods")

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

local function get_nested(t, k, ...)
	if t == nil then
		return nil
	elseif ... == nil then
		return t[k]
	end
	return get_nested(t[k], ...)
end

local function set_nested(t, k, v, ...)
	if ... ~= nil then
		local t_next = t[k]
		if t_next == nil then
			t_next = {}
			t[k] = t_next
		end
		return set_nested(t_next, v, ...)
	end
	t[k] = v
end

local function inherit_metamethods(child, parent)
	if parent then
		for method, value in next, parent do
			if child[method] == nil and metamethods[method] ~= nil then
				child[method] = 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)
	return classes[getmetatable(value)] ~= nil
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

local function class_else_type(value)
	local class = classes[getmetatable(value)]
	if class ~= nil then
		return class
	end
	return type(value)
end

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

local Node = {}
Node.__index = Node

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

function Node:next_node(i)
	local v
	repeat
		v, self, i = self:next(i)
	until v == nil or is_node(v)
	return v, self, i
end

-- Implements recursive iteration over a node tree, using functors to maintain state (which uses a lot less memory than closures). Iterator1 exists only to return the calling node on the first iteration, while Iterator2 uses a stack to store the state of each layer in the tree.

-- 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 followed if any of those children contain nodes themselves. Once a particular node has been fully traversed, the iterator moves back up one layer and continues with any sibling nodes.

-- 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.

-- By default, the iterator will use the `next` method of each node, but this can be changed with the `next_func` parameter, which accepts a string argument with the name of a next method. This is because trees might consist of several different classes of node, and each might have different next methods that are tailored to their particular structures. In addition, each class of node might have multiple different next methods, which can be named according to their purposes. `next_func` ensures that the iterator uses equivalent next methods between different types of node.

-- Currently, two next methods are available: `next`, which simply iterates over the node conventionally, and `next_node`, which only returns children that are themselves nodes. Custom next methods can be declared by any calling module.
do
	local Iterator1, Iterator2 = {}, {}
	Iterator1.__index = Iterator2 -- Not a typo.
	Iterator2.__index = Iterator2
	
	function Iterator1:__call()
		setmetatable(self, Iterator2)
		return self[1].node
	end
	
	function Iterator2:push(node)
		local layer = {
			k = 0,
			node = node
		}
		self[#self + 1] = layer
		self[-1] = layer
		return self
	end
	
	function Iterator2:pop()
		local len = #self
		self[len] = nil
		self[-1] = self[len - 1]
	end
	
	function Iterator2:iterate(layer, ...)
		local v, node, k = ...
		if v ~= nil then
			layer.k = k
			return ...
		end
		self:pop()
		layer = self[-1]
		if layer ~= nil then
			node = layer.node
			return self:iterate(layer, node[self.next_func](node, layer.k))
		end
	end
	
	function Iterator2:__call()
		local layer = self[-1]
		local node, k = layer.node, layer.k
		local curr_val = node[k]
		if is_node(curr_val) then
			self:push(curr_val)
			layer = self[-1]
			node, k = layer.node, layer.k
		end
		return self:iterate(layer, node[self.next_func](node, k))
	end
	
	function Node:__pairs(next_func)
		return setmetatable({
			next_func = next_func == nil and "next" or next_func
		}, Iterator1):push(self)
	end
end

function Node:rawpairs()
	return next, self
end

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

function Node:clone()
	if not deepcopy then
		deepcopy = require("Module:table").deepcopy
	end
	return deepcopy(self, "keep", true)
end

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

Node.keys_to_remove = {"fail", "handler", "head", "override", "route"}

function Node:new(t)
	setmetatable(t, nil)
	local keys_to_remove = self.keys_to_remove
	for i = 1, #keys_to_remove do
		t[keys_to_remove[i]] = nil
	end
	return setmetatable(t, self)
end

do
	local Proxy = {}

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

	function Proxy:__newindex(k, v)
		local key = self.__keys[k]
		if key then
			self.__chars[k] = v
			self.__parents[key] = 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[len] = a
		self.__parents[len] = b
		self.__keys[len] = c
		self.__len = len
	end

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

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

local Parser = {}
Parser.__index = Parser

function Parser:read(delta)
	local v = self.text[self.head + (delta or 0)]
	return v == nil and "" or v
end

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

function Parser:layer(n)
	if n ~= nil then
		return rawget(self, #self + n)
	end
	return self[-1]
end

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

function Parser:remove(n)
	local layer = self[-1]
	if n ~= nil then
		return remove(layer, signed_index(layer, n))
	end
	local len = #layer
	local token = layer[len]
	layer[len] = nil
	return token
end

function Parser:replace(a, b)
	local layer = self[-1]
	layer[signed_index(layer, a)] = 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: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[n] = tostring(layer[i])
	end
	return concat(ret)
end

function Parser:emitted(delta)
	if delta == nil then
		delta = -1
	end
	local i = 0
	while true do
		local layer = self:layer(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 = {
		head = self.head,
		route = route
	}
	self[#self + 1] = layer
	self[-1] = layer
end

function Parser:push_sublayer(handler, inherit)
	local sublayer = {
		handler = handler,
		sublayer = true
	}
	if inherit then
		local layer = self[-1]
		setmetatable(sublayer, inherit_metamethods({
			__index = layer,
			__newindex = layer
		}, getmetatable(layer)))
	end
	self[#self + 1] = sublayer
	self[-1] = sublayer
end

function Parser:pop()
	local len, layer = #self
	while true do
		layer = self[len]
		self[len] = nil
		len = len - 1
		local new = self[len]
		self[-1] = new == nil and self or new
		if layer.sublayer == nil then
			break
		end
		self:emit_tokens(layer)
	end
	return layer
end

function Parser:pop_sublayer()
	local len, layer = #self, self[-1]
	self[len] = nil
	local new = self[len - 1]
	self[-1] = new == nil and self or new
	setmetatable(layer, nil)
	layer.sublayer = nil
	return layer
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_layer = get_nested(self.failed_routes, route, self.head)
	if failed_layer ~= nil then
		return false, failed_layer
	end
	local layer = self:get(route, ...)
	return not layer.fail, layer
end

function Parser:consume(this, ...)
	local layer = self[-1]
	if this == nil then
		this = self:read()
	end
	return (layer.override or layer.handler)(self, this, ...)
end

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

function Parser:traverse()
	while true do
		local layer = self:consume()
		if layer ~= nil then
			return layer
		end
		self:advance()
	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[this] or self[false])(parser, this)
	end
	
	function Parser:switch(func, t)
		local layer = self[-1]
		-- Point handler to the new switch table if the calling function is the current handler.
		if layer.handler == func then
			layer.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[1]: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

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

return export