require 'fun' ()
local utf8 = require 'utf8'

local ASCII_CHAR_PATTERN   = '[\32-\126\009\010\013]'
local UNICODE_CHAR_PATTERN = '[\01-\127\192-\255][\128-\191]*'

local function ledgible_subsequences_in (str)
	return totable(str:gmatch(ASCII_CHAR_PATTERN..'+'))
end

local function probability_of_ascii_string (str)
	local sub_seqs = ledgible_subsequences_in(str)
	local nr_characters           =  #str
	local nr_ledgible_characters  =  foldl(operator.add, map(operator.len, sub_seqs))
	local len_of_longest_subseq   =  foldl(math.max, map(operator.len, sub_seqs))
	return ((len_of_longest_subseq/nr_ledgible_characters) + (nr_ledgible_characters / nr_characters)) / 2
end

local function probability_of_utf8_string (str)
	local valid_bytes  =  0
	for char, valid in utf8.iterate(str) do
		if valid then  valid_bytes = valid_bytes + #char  end
	end
	return valid_bytes / #str
end

local function probability_of_utf16_string (str)
	return 0
end

local function probability_of_binary_data (str)
	return 2/3
end

local str_representations = {
	ascii  = probability_of_ascii_string,
	utf8   = probability_of_utf8_string ,
	utf16  = probability_of_utf16_string,
	binary = probability_of_binary_data,
}

return function (str)
	local str_info, most_likely, most_likely_prob = {}, 'ascii', 0
	for repr_name, prob_func in pairs(str_representations) do
		local prob = prob_func(str)
		str_info[repr_name..'_prob'] = prob
		if prob >= most_likely_prob then
			most_likely, most_likely_prob  =  repr_name, prob
		end
	end
	       str_info.most_likely = most_likely
	return str_info
end