-- This module de-links most wikitext.

require("strict")

local p = {}

local getArgs

local function delinkReversePipeTrick(s)
	if s:match("^%[%[|.*[|\n]") then -- Check for newlines or multiple pipes.
		return s
	end
	return s:match("%[%[|(.*)%]%]")

end

local function delinkPipeTrick(s)
	-- We need to deal with colons, brackets, and commas, per [[Help:Pipe trick]].
	-- First, remove the text before the first colon, if any.
	if s:match(":") then
		s = s:match("%[%[.-:(.*)|%]%]")
	-- If there are no colons, grab all of the text apart from the square brackets and the pipe.
	else
		s = s:match("%[%[(.*)|%]%]")
	end
	
	-- Next up, brackets and commas.
	if s:match("%(.-%)$") then -- Brackets trump commas.
		s = s:match("(.-) ?%(.-%)$")
	elseif s:match(",") then -- If there are no brackets, display only the text before the first comma.
		s = s:match("(.-),.*$")
	end
	return s
end

-- Return wikilink target |wikilinks=target
local function getDelinkedTarget(s)
	local result = s
	-- Deal with the reverse pipe trick.
	if result:match("%[%[|") then
		return delinkReversePipeTrick(result)
	end
	
	result = mw.uri.decode(result, "PATH") -- decode percent-encoded entities. Leave underscores and plus signs.
	result = mw.text.decode(result, true) -- decode HTML entities.
	
	-- Check for bad titles. To do this we need to find the
	-- title area of the link, i.e. the part before any pipes.
	local target_area
	if result:match("|") then -- Find if we're dealing with a piped link.
		target_area = result:match("^%[%[(.-)|.*%]%]")
	else
		target_area = result:match("^%[%[(.-)%]%]")
	end

	-- Check for bad characters.
	if mw.ustring.match(target_area, "[%[%]<>{}%%%c\n]") and mw.ustring.match(target_area, "[%[%]<>{}%%%c\n]") ~= "?" then
		return s
	end
	
	return target_area
end

local function getDelinkedLabel(s)
	local result = s
	-- Deal with the reverse pipe trick.
	if result:match("%[%[|") then
		return delinkReversePipeTrick(result)
	end

	result = mw.uri.decode(result, "PATH") -- decode percent-encoded entities. Leave underscores and plus signs.
	result = mw.text.decode(result, true) -- decode HTML entities.

	-- Check for bad titles. To do this we need to find the
	-- title area of the link, i.e. the part before any pipes.
	local target_area
	if result:match("|") then -- Find if we're dealing with a piped link.
		target_area = result:match("^%[%[(.-)|.*%]%]")
	else
		target_area = result:match("^%[%[(.-)%]%]")
	end

	-- Check for bad characters.
	if mw.ustring.match(target_area, "[%[%]<>{}%%%c\n]") and mw.ustring.match(target_area, "[%[%]<>{}%%%c\n]") ~= "?" then
		return s
	end

	-- Check for categories, interwikis, and files.
	local colon_prefix = result:match("%[%[(.-):.*%]%]") or "" -- Get the text before the first colon.
	local ns = mw.site.namespaces[colon_prefix] -- see if this is a known namespace
	if mw.language.isKnownLanguageTag(colon_prefix) or (ns and (ns.canonicalName == "File" or ns.canonicalName == "Category")) then
		return ""
	end

	-- Remove the colon if the link is using the [[Help:Colon trick]].
	if result:match("%[%[:") then
		result = "[[" .. result:match("%[%[:(.*%]%])")
	end

	-- Deal with links using the [[Help:Pipe trick]].
	if mw.ustring.match(result, "^%[%[[^|]*|%]%]") then
		return delinkPipeTrick(result)
	end
	
	-- Find the display area of the wikilink
	if result:match("|") then -- Find if we're dealing with a piped link.
		result = result:match("^%[%[.-|(.+)%]%]")
		-- Remove new lines from the display of multiline piped links,
		-- where the pipe is before the first new line.
		result = result:gsub("\n", "")
	else
		result = result:match("^%[%[(.-)%]%]")
	end

	return result
end

local function delinkURL(s)
	-- Assume we have already delinked internal wikilinks, and that
	-- we have been passed some text between two square brackets [foo].
	
	-- If the text contains a line break it is not formatted as a URL, regardless of other content.
	if s:match("\n") then
		return s
	end
	
	-- Check if the text has a valid URL prefix and at least one valid URL character.
	local valid_url_prefixes = {"//", "http://", "https://", "ftp://", "gopher://", "mailto:", "news:", "irc://"} 
	local url_prefix
	for _ ,v in ipairs(valid_url_prefixes) do
		if mw.ustring.match(s, '^%[' .. v ..'[^"%s].*%]' ) then
			url_prefix = v
			break
		end
	end
	
	-- Get display text
	if not url_prefix then
		return s
	end
	s = s:match("^%[" .. url_prefix .. "(.*)%]") -- Grab all of the text after the URL prefix and before the final square bracket.
	s = s:match('^.-(["<> ].*)') or "" -- Grab all of the text after the first URL separator character ("<> ).
	s = mw.ustring.match(s, "^%s*(%S.*)$") or "" -- If the separating character was a space, trim it off.
	
	local s_decoded = mw.text.decode(s, true)
	if mw.ustring.match(s_decoded, "%c") then
		return s
	end

	return s_decoded

end

local function delinkLinkClass(text, pattern, delinkFunction)
	if type(text) ~= "string" then
		error("Attempt to de-link non-string input.", 2)
	end
	if type(pattern) ~= "string" or mw.ustring.sub(pattern, 1, 1) ~= "^" then
		error('Invalid pattern detected. Patterns must begin with "^".', 2)
	end
	-- Iterate over the text string, and replace any matched text. using the 
	-- delink function. We need to iterate character by character rather 
	-- than just use gsub, otherwise nested links aren't detected properly.
	local result = ""
	while text ~= "" do
		-- Replace text using one iteration of gsub.
		text = mw.ustring.gsub(text, pattern, delinkFunction, 1)
		-- Append the left-most character to the result string.
		result = result .. mw.ustring.sub(text, 1, 1)
		text = mw.ustring.sub(text, 2, -1)
	end
	return result
end

function p._delink(args)
	local text = args[1] or ""
	if args.refs == "yes" then
		-- Remove any [[Help:Strip markers]] representing ref tags. In most situations 
		-- this is not a good idea - only use it if you know what you are doing!
		text = mw.ustring.gsub(text, "UNIQ%w*%-ref%-%d*%-QINU", "")
	end
	if args.comments ~= "no" then
		text = text:gsub("<!%-%-.-%-%->", "") -- Remove html comments.
	end

	if args.wikilinks ~= "no" and args.wikilinks ~= "target" then
		-- De-link wikilinks and return the label portion of the wikilink.
		text = delinkLinkClass(text, "^%[%[.-%]%]", getDelinkedLabel)
	elseif args.wikilinks == "target" then
		-- De-link wikilinks and return the target portions of the wikilink.
		text = delinkLinkClass(text, "^%[%[.-%]%]", getDelinkedTarget)
	end
	if args.urls ~= "no" then
		text = delinkLinkClass(text, "^%[.-%]", delinkURL) -- De-link URLs.
	end
	if args.whitespace ~= "no" then
		-- Replace single new lines with a single space, but leave double new lines
		-- and new lines only containing spaces or tabs before a second new line.
		text = mw.ustring.gsub(text, "([^\n \t][ \t]*)\n([ \t]*[^\n \t])", "%1 %2")
		text = text:gsub("[ \t]+", " ") -- Remove extra tabs and spaces.
	end
	return text
end

function p.delink(frame)
	if not getArgs then
		getArgs = require('Module:Arguments').getArgs
	end
	return p._delink(getArgs(frame, {wrappers = 'Template:Delink'}))
end

return p