-- A miniature stand-in for the Scintillua lexer module, just enough for the
-- syntax-highlight checks to drive every path through the filter without the
-- real collection installed. load() hands out one of the toy lexers below by
-- name and detect() recognises a single filename suffix or a shebang naming
-- fake, so a check can tell the detection path apart from the extension path
-- by which lexer ends up running. Anything the filter treats as optional, a lexer that will not
-- load or one that raises while lexing, has a name here too.

local M = {}

-- Tokens come back the way Scintillua returns them, one flat list of a tag
-- name and the position just past the token it names. Letter runs are
-- keywords, digit runs are numbers, a single quoted run carries a dotted tag
-- so the dotted first component lookup gets exercised, a run after a colon or
-- a dollar sign takes one of the tags only the css lexer uses, and any other
-- byte is whitespace, which maps to no css class.
local patterns = {
	{ "^:%a+", "pseudoclass" },
	{ "^%$%a+", "property" },
	{ "^%a+", "keyword" },
	{ "^%d+", "number" },
	{ "^'[^']*'", "string.double" },
}

local function lex_words(self, text)
	local tokens = {}
	local pos = 1
	while pos <= #text do
		local tag, stop = "whitespace", pos
		for _, pattern in ipairs(patterns) do
			local start, finish = text:find(pattern[1], pos)
			if start then
				tag, stop = pattern[2], finish
				break
			end
		end
		tokens[#tokens + 1] = tag
		tokens[#tokens + 1] = stop + 1
		pos = stop + 1
	end
	return tokens
end

-- Tags only the first four bytes and stops, so the filter has to append the
-- untagged tail itself or the check for it fails.
local function lex_short(self, text)
	if #text < 5 then
		return {}
	end
	return { "keyword", 5 }
end

local function lex_raise(self, text)
	error("this lexer always raises")
end

local lexers = {
	fake = { lex = lex_words },
	short = { lex = lex_short },
	badlex = { lex = lex_raise },
}

function M.load(name)
	local lexer = lexers[name]
	if lexer == nil then
		error("no fake lexer named " .. tostring(name))
	end
	return lexer
end

function M.detect(filename, line)
	if filename:match("%.viadetect$") then
		return "fake"
	end
	if line ~= nil and line:match("^#!.*fake") then
		return "fake"
	end
	return nil
end

return M