-- Copyright 2007-2023 Mitchell. See LICENSE.

--- @module lexer
local M = dofile(_HOME .. '/lexers/lexer.lua')

--- A ';'-separated list of directory paths that contain lexers for syntax highlighting.
_G._LEXERPATH = string.format('%s/lexers;%s/lexers', _USERHOME, _HOME)

M.property = setmetatable({}, {__index = function() return '' end}) -- avoid auto-initialization
local names = M.names
M.names = function(path) return names(path or _LEXERPATH) end

--- Emitted after loading a language lexer.
-- This is useful for automatically loading language modules as source files are opened, or
-- setting up language-specific editing features for source files.
-- Arguments:
--
-- - *name*: The language lexer's name.
_G.events.LEXER_LOADED = 'lexer_loaded'

-- LuaDoc is in core/.buffer.luadoc.
local function get_lexer(buffer, current)
	if not current then return buffer.lexer_language end
	local style_at, name_of_style = buffer.style_at, buffer.name_of_style
	local pos = buffer.current_pos
	while pos > 0 do
		local style = style_at[pos]
		local lang = name_of_style(buffer, style):match('^whitespace%.(.+)$')
		if lang then return lang end
		repeat pos = pos - 1 until pos < 1 or style_at[pos] ~= style
	end
	return buffer.lexer_language
end

-- LuaDoc is in core/.buffer.luadoc.
-- Note: cannot use `M.` references here since these buffer functions persist through reset
-- (thus referencing the original, unreset `M` upvalue).
local function set_lexer(buffer, name)
	if not assert_type(name, 'string/nil', 2) then
		name = lexer.detect(buffer.filename or '', buffer:get_line(1):sub(1, 128)) or 'text'
	end

	-- Setup the lexer.
	for k in pairs(lexer.property) do lexer.property[k] = nil end -- clear existing properties
	lexer.property['scintillua.lexers'] = _LEXERPATH
	rawset(buffer, 'lexer', lexer.load(name))
	rawset(buffer, 'lexer_language', name)
	if rawget(buffer, 'lexer') then
		rawset(buffer, 'named_styles', #buffer.lexer._TAGS)
		if buffer.lexer._CHILDREN then
			local ws = {} -- style numbers considered to be whitespace styles in multi-language lexers
			for i = 1, view.STYLE_MAX do ws[i] = buffer:name_of_style(i):find('whitespace') ~= nil end
			if #ws > 0 then buffer._ws = ws end
		end
	end

	-- Update styles, forward folding properties to the lexer, copy lexer-specific properties to
	-- the buffer, and refresh syntax highlighting.
	if view.set_styles then view.set_styles(buffer ~= ui.command_entry and view or ui.command_entry) end
	for k, v in pairs(view) do
		if not k:find('^fold') then goto continue end
		lexer.property[(k ~= 'folding' and k:gsub('_', '.') or 'fold'):gsub('^fold%.',
			'fold.scintillua.')] = v and '1' or '0'
		::continue::
	end
	for k in pairs(buffer.property) do buffer.property[k] = nil end
	for k, v in pairs(lexer.property) do buffer.property[k] = v end
	local last_line = view.first_visible_line + view.lines_on_screen
	buffer:colorize(1, buffer:position_from_line(last_line + 1))

	if buffer ~= ui.command_entry then events.emit(events.LEXER_LOADED, name) end
	events.emit(events.UPDATE_UI, buffer.UPDATE_CONTENT) -- for updating statusbar
end

-- Documentation is in core/.buffer.luadoc.
local function name_of_style(buffer, style_num)
	local lexer = rawget(buffer, 'lexer')
	return lexer and lexer._TAGS[assert_type(style_num, 'number', 2)] or 'Unknown'
end

-- Documentation is in core/.buffer.luadoc.
local function style_of_name(buffer, name)
	local lexer = rawget(buffer, 'lexer')
	return lexer and lexer._TAGS[assert_type(name, 'string', 2):gsub('_', '.')] or view.STYLE_DEFAULT
end

--- Performs syntax highlighting in buffer *buffer* from *start_pos* to *end_pos*.
-- Start from the beginning of the current style so the lexer can match the tag.
-- For multilang lexers, start at whitespace since embedded languages have whitespace.[lang]
-- styles. This is so the lexer can start matching child languages instead of parent ones
-- if necessary.
-- @param buffer A buffer.
-- @param start_pos Position to start syntax highlighting at.
-- @param end_pos Position to stop syntax highlighting at.
local function highlight(buffer, start_pos, end_pos)
	local style_at, ws = buffer.style_at, buffer._ws
	local init_style = start_pos > 1 and style_at[start_pos - 1] or view.STYLE_DEFAULT
	while start_pos > 1 and style_at[start_pos - 1] == init_style do start_pos = start_pos - 1 end
	if ws then while start_pos > 1 and not ws[style_at[start_pos]] do start_pos = start_pos - 1 end end

	-- Setup buffer-specific lexer fields.
	local name_of_style, line_from_position = buffer.name_of_style, buffer.line_from_position
	lexer.style_at = setmetatable({}, {
		__index = function(_, pos) return name_of_style(buffer, style_at[start_pos + pos - 1]) end
	})
	lexer.fold_level = buffer.fold_level
	lexer.line_from_position =
		function(pos) return line_from_position(buffer, start_pos + pos - 1) end
	lexer.line_state, lexer.indent_amount = buffer.line_state, buffer.line_indentation

	-- Invoke the lexer and style text from the returned table of tags.
	buffer:start_styling(start_pos, 0)
	local styles = buffer.lexer:lex(buffer:text_range(start_pos, end_pos), init_style)
	local set_styling, tags, pos = buffer.set_styling, buffer.lexer._TAGS, 1
	for i = 1, #styles, 2 do
		local e = styles[i + 1]
		set_styling(buffer, e - pos, tags[styles[i]] or view.STYLE_DEFAULT) -- support legacy lexers
		pos = e
	end
	buffer:set_styling(end_pos - (start_pos + pos - 1), view.STYLE_DEFAULT)

	-- Invoke the folder and fold the text from the returned table of fold levels.
	local line = buffer:line_from_position(start_pos)
	start_pos = buffer:position_from_line(line)
	local level = buffer.fold_level[line] & buffer.FOLDLEVELNUMBERMASK
	local folds = buffer.lexer:fold(buffer:text_range(start_pos, end_pos), line, level)
	for line, level in pairs(folds) do buffer.fold_level[line] = level end
end

local mutex
-- Performs syntax highlighting as needed.
events.connect(events.STYLE_NEEDED, function(end_pos, buffer)
	if mutex then return end -- avoid recursion and stack overflow
	if not buffer then return end -- printed initialization errors during startup can trigger this
	local start_pos = buffer:position_from_line(buffer:line_from_position(buffer.end_styled))
	local ok, errmsg
	mutex = true
	if rawget(buffer, 'lexer') then ok, errmsg = pcall(highlight, buffer, start_pos, end_pos) end
	mutex = nil
	if not ok then
		buffer:start_styling(start_pos, 0)
		buffer:set_styling(end_pos - start_pos, view.STYLE_DEFAULT)
		if errmsg then error(errmsg, 2) end
	end
end)

-- Gives new buffers lexer-specific functions and sets a default lexer (or resets the current
-- one on reset).
events.connect(events.BUFFER_NEW, function()
	rawset(buffer, 'property', setmetatable({}, {__index = function() return '' end}))
	buffer.get_lexer, buffer.set_lexer = get_lexer, set_lexer
	buffer.name_of_style, buffer.style_of_name = name_of_style, style_of_name
	set_lexer(buffer, not rawget(buffer, 'lexer') and 'text' or buffer.lexer._name)
end)

--- Refreshes styles for the buffer's lexer.
local function refresh_styles() if view.set_styles then view:set_styles() end end
events.connect(events.BUFFER_AFTER_SWITCH, refresh_styles)
events.connect(events.VIEW_AFTER_SWITCH, refresh_styles)
events.connect(events.VIEW_NEW, refresh_styles)

return M
