local NAME = 'I2CETLua.TemplateEngine'
local CLASS_NAME = 'TemplateEngine'
local VERSION = '1.0.1'
local DESCRIPTION = 'I2 Cheat Engine Lua Modules'
local AUTHOR = 'TheyCallMeTim13@Gmail.com'
if BEBUG then print(NAME, ...) end


--
---- TemplateEngine
	TemplateEngine = {
		Name = NAME, 
		ClassName = CLASS_NAME, 
		Description = DESCRIPTION, 
		Version = VERSION, 
		Author = AUTHOR, 
		License = LICENSE,
		----
	}


---- https://nachtimwald.com/2014/08/06/using-lua-as-a-templating-engine/
local function appender(builder, text, code)
	if code then
		builder[#builder+1] = code
	else
		---- [[ has a \n immediately after it. Lua will strip the first \n 
		---- 	so we add one knowing it will be removed to ensure that 
		---- 	if text starts with a \n it won't be lost.
		local fmt = '_ret[#_ret+1] = [%s[\n%s]%s]'
		local mlsFix = string.rep('=', 100)
		builder[#builder+1] = string.format(fmt, mlsFix, text, mlsFix)
	end
end

local function runBlock(builder, text)
	local func
	local tag
	tag = text:sub(1, 2)
	if tag == '<<' then
		func = function(code)
			return ('_ret[#_ret+1] = %s'):format(code)
		end
	elseif tag == '<%' then
		func = function(code)
			return code
		end
	end
	if func then
		appender(builder, nil, func(text:sub(3, #text-3)))
	else
		appender(builder, text)
	end
end

local function compile(template, environmentOrLoadLocalEnv, loadLocalEnv)
	---- Turn the template into a string that can be run though Lua. 
	---- 	Builder will be used to efficiently build the string we'll run. 
	---- 	The string will use it's own builder (_ret). Each part that comprises 
	---- 	_ret will be the various pieces of the template. Strings, variables 
	---- 	that should be printed and functions that should be run.
	if not template or template == '' then return '' end
	local env = { }
	if type(environmentOrLoadLocalEnv) == 'table' then
		env = environmentOrLoadLocalEnv
	elseif type(environmentOrLoadLocalEnv) == 'boolean' then
		loadLocalEnv = environmentOrLoadLocalEnv
	end
	env.__index = env
	setmetatable(env, { __index = _G })
	if loadLocalEnv then
		local i = 1
		while true do
			local name, value = debug.getlocal(2, i)
			if not name then break end
			env[name] = value
			i = i + 1
		end
	end
	local builder = { '_ret = {}\n' }
	local pos = 1
	local b
	local func
	local err
	while pos < #template do
		---- Look for start of a Lua block.
		b = template:find('<[<%%]', pos)
		if not b then
			break
		end
		---- Check if this is a block or escaped <.
		if template:sub(b-1, b-1) == '\\' then
			appender(builder, template:sub(pos, b-2))
			appender(builder, '<')
			pos = b+1
		else
			---- Add all text up until this block.
			appender(builder, template:sub(pos, b-1))
			---- Find the end of the block.
			pos = template:find('[>%%]>', b)
			if not pos then
				appender(builder, 'End tag missing')
				break
			end
			runBlock(builder, template:sub(b, pos+2))
			---- Skip back the >> (pos points to the start of >>).
			pos = pos+2
		end
	end
	---- Add any text after the last block. Or all of it if there
	---- are no blocks.
	if pos then
		appender(builder, template:sub(pos, #template))
	end

	builder[#builder+1] = 'return table.concat(_ret)'
	---- Run the Lua code we built though Lua and get the result.
	func, err = load(table.concat(builder, '\n'), 'template', 't', env)
	if not func then
		return nil, err
	end
	return func()
end


function TemplateEngine.compile(template, environmentOrLoadLocalEnv, loadLocalEnv)
	return compile(template, environmentOrLoadLocalEnv, loadLocalEnv)
end

function TemplateEngine.compileFile(filePath, environmentOrLoadLocalEnv, loadLocalEnv)
	local f, err = io.open(filePath, 'r')
	if f and not err then
		local template = f:read('*all')
		f:close()
		return compile(template, environmentOrLoadLocalEnv, loadLocalEnv)
	else
		return nil, err
	end
end


return TemplateEngine