-- 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, 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, and any other byte is
-- whitespace, which maps to no css class.
local function lex_words(self, text)
	local tokens = {}
	local pos = 1
	while pos <= #text do
		local start, stop = text:find("^%a+", pos)
		if not start then
			start, stop = text:find("^%d+", pos)
			if start then
				tokens[#tokens + 1] = "number"
			else
				start, stop = text:find("^'[^']*'", pos)
				if start then
					tokens[#tokens + 1] = "string.double"
				else
					stop = pos
					tokens[#tokens + 1] = "whitespace"
				end
			end
		else
			tokens[#tokens + 1] = "keyword"
		end
		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)
	if filename:match("%.viadetect$") then
		return "fake"
	end
	return nil
end

return M