#!/usr/bin/env lua
--- For example:
---
---     $ ./headers.lua db/c.lua C23
---     assert.h
---     ctype.h
---     ...
local public = {}
local private = {}
private.tags = {}
private.tags_lookup = {}
private.headers = {}


local tag do
	local methods = {}
	function methods:add (header)
		table.insert(self.headers_, header)
	end
	local function headers (self)
		local result = {}
		for _, value in pairs(self.headers_) do
			if type(value) == "function" then
				value(result)
			else
				table.insert(result, value)
			end
		end
		return result
	end
	local mt = {
		__tostring=function (self) return self.name end,
		__index=function (self, key)
			if key == "headers" then
				return headers(self)
			end
			return methods[key]
		end,
	}
	function tag (name)
		return setmetatable({name=name, headers_={}}, mt)
	end
end


local alias do
	local mt = {
		__tostring = function (self) return string.format("%s (%s)", self.name, tostring(self.tag)) end,
		__index = function (self, key) return self.tag[key] end,
	}
	function alias (name, tag)
		return setmetatable({name=name, tag=tag}, mt)
	end
end


local function include (source)
	return function (target)
		for _, header in pairs(source.headers) do
			table.insert(target, header)
		end
	end
end


local function remove (header)
	return function (target)
		for key, value in pairs(target) do
			if value == header then
				table.remove(target, key)
			end
		end
	end
end


local function get_or_create_tag (name)
	local found = private.tags_lookup[name]
	if not found then
		found = tag(name)
		table.insert(private.tags, found)
		private.tags_lookup[name] = found
	end
	return found
end


function public.aliases (name)
	local tag = get_or_create_tag(name)
	return function (aliases)
		for _, name in pairs(aliases) do
			private.tags_lookup[name] = alias(name, tag)
		end
	end
end


function public.headers (name)
	local tag = get_or_create_tag(name)
	return function (filenames)
		for _, header in pairs(filenames) do
			tag:add(header)
		end
	end
end


function public.include (tag)
	tag = private.tags_lookup[tag] or error("invalid tag: " .. tag, 2)
	return include(tag)
end


function public.remove (header)
	return remove(header)
end


local db = loadfile(arg[1], nil, public)
db()
if arg[2] then
	local tag = private.tags_lookup[arg[2]]
	for _, header in pairs(tag.headers) do
		print(header)
	end
else
	for _, tag in pairs(private.tags_lookup) do
		print(tag)
	end
end