local language = {}
setmetatable(language, {__index=_G})
setfenv(1, language)


-- local utility functions

-- convert string to array of characters
local function string_to_array(str)
	local arr = {}
	for i=1,#str do
		table.insert(arr, string.sub(str, i, i))
	end
	return arr
end


-- iterate over lines in string
local function lines(str)
	local clean = function(s) return string.gsub(s, "\n", "") end
	return coroutine.wrap(function()
		for line in string.gmatch(str, "[^\n]*\n") do
			coroutine.yield(clean(line))
		end
		local lastline = string.match(str, "\n?[^\n]+$")
		if lastline then
			coroutine.yield(clean(lastline))
		end
	end)
end


-- parse phonemes from string
local function parse_phonemes(str)
	local phonemes = {}
	for line in lines(str) do
		if string.match(line, "^%s*#") then
			-- this is a comment, ignore
		elseif string.match(line, "^%s*$") then
			-- ignore blank lines
		else
			class, phones = string.match(line, "(.)=(.*)")
			-- remove whitespace from phones
			phones = string.gsub(phones, "%s", "")
			phonemes[class] = string_to_array(phones)
		end
	end
	return phonemes
end


-- parse syllables from string
local function parse_syllables(str)
	local syllables = {}
	for line in lines(str) do
		if string.match(line, "^%s*$") then
			-- ignore blank lines
		else
			line = string.gsub(line, "%s", "")
			table.insert(syllables, string_to_array(line))
		end
	end
	return syllables
end


-- parse orthography patterns from string
local function parse_orthography(str, phonemes)
	local rules = {}
	for line in lines(str) do
		if string.match(str, '^%s*$') then
			-- ignore blank lines
		else
			-- trim whitespace
			line = string.gsub(line, "%s*$", "")
			local pattern, replace = string.match(line, "(.*)=(.*)")
			if not pattern then
				-- ???
			else
				pattern = string.gsub(pattern, "%%(.)", function(class)
					if phonemes[class] == nil then
						return '%' .. class
					end
					return '[' .. table.concat(phonemes[class], '') .. ']'
				end)
				table.insert(rules, { pattern=pattern, replace=replace })
			end
		end
	end
	return rules
end


-- randomly choose an element from an array with a given distribution
local function random_choice(tbl, distribution)
	local x = distribution(math.random())
	local bin = math.floor(x * #tbl) + 1
	return tbl[bin]
end


-- probability distributions

-- uniform (flat) distribution
function uniform(x)
	return x
end


function quadratic(x)
	return x*x
end






Language = {}

function Language.new(_, phonemes, syllables, orthography, len_min, len_max, p_dist, s_dist, l_dist)
	local self = {}
	setmetatable(self, {__index=Language})
	self.phonemes = parse_phonemes(phonemes)
	self.p_dist = p_dist or uniform
	self.syllables = parse_syllables(syllables)
	self.s_dist = s_dist or uniform
	self.orthography = parse_orthography(orthography, self.phonemes)
	self.length = {}
	for len=len_min,len_max do
		table.insert(self.length, len)
	end
	self.l_dist = l_dist or uniform
	return self
end
setmetatable(Language, {__call=Language.new})


function Language.random_phone(self, class)
	return random_choice(self.phonemes[class], self.p_dist)
end


function Language.syllable(self)
	-- pick a random syllable type
	local syl = random_choice(self.syllables, self.s_dist)
	local result = ''
	for _, ch in ipairs(syl) do
		if self.phonemes[ch] then
			result = result .. self:random_phone(ch)
		else
			result = result .. ch
		end
	end
	return result
end


function Language.word(self)
	local len = random_choice(self.length, self.l_dist)
	local word = ''
	for i=1,len do
		word = word .. self:syllable()
	end
	return word
end


function Language.romanize(self, text)
	local result = text
	for _, rule in ipairs(self.orthography) do
		result = string.gsub(result, rule.pattern, rule.replace)
	end
	return result 
end


return language