local lfs = require(jit and 'lfs_ffi' or 'lfs')
local inspect
function inspect(t,s)
	s = s or ""
	r = ""
	for k,v in pairs(t) do
		r = r..(s..k..": "..(type(v) == "table" and "\n"..inspect(v,s.."  ") or tostring(v).."\n"))
	end
	return r
end

local path = lfs.currentdir() .. "/build.lua"

local buildf = loadfile(path)
if not buildf then
	error "no build file"
end

local function initvar(name, default)
	_G[name] = os.getenv(name) or default or ""
end

initvar("CC", "gcc")
initvar("CFLAGS")
initvar("LINK")
initvar("SRC", "*.c")

opt = {}

for _,arg in ipairs(arg) do
	opt[arg] = true
end

function buildobj(o)
	local cmd = ("%s %s %s -c -o %s %s"):format(CC, CFLAGS, LINK, o.out, o.src)
	print("BUILDING OBJECT:\n"..cmd)
	os.execute(cmd)
end

function buildprog()
	local objs = ""
	for _,o in ipairs(OBJ) do
		objs = objs..o.path.." "
	end
	local cmd = ("%s %s %s -o %s %s"):format(CC, CFLAGS, LINK, PROG, objs)
	print("BUILDING PROGRAM:\n"..cmd)
	os.execute(cmd)
end

buildf()

if not PROG then
	error "must provide 'PROG'"
end

function issourcefile(f)
	return f:sub(#f-1,#f) == ".c" or f:sub(#f-3,#f) == ".cpp"
end

local function concat(dir,file) --concats directory name + filename
	if not dir or dir == lfs.currentdir() then
		return file
	else
	
		return ({(dir .. "/" .. file)
			:gsub("[^/]*/../", "") --remove redundant expressions as in "foo/../bar" -> "bar"
		})[1]
	end
end

if SRC =="*.c" then
	SRC = {}
	local find
	function find(dir)
		--print("searching in "..dir)
		for f,_ in lfs.dir(dir) do
			local attr = lfs.attributes(concat(dir,f))
			if attr and (attr.mode == "file" or attr.mode == "link") and issourcefile(f) then
				table.insert(SRC, concat(dir,f))
			elseif attr and attr.mode == "directory" and f ~= "." and f ~= ".." and f ~= ".git" then
				find(concat(dir,f)) --recursive
			end
		end
	end
	find(lfs.currentdir())
end

if _SHOWSRC then
	print(inspect(SRC))
end

function getdeps(p, exclude)
	--print(p)
	local f = io.open(p)
	if not f then
		return nil
	end

	exclude = exclude or {}
	for k,v in ipairs(exclude) do exclude[v] = true end
	local deps = {}

	local _,_,dir = p:find("(.*)/.*$")

	for l in f:lines() do
		local _,_,s = l:find('%s*#include%s*\"(.*)\"')
		if s then
			s = concat(dir,s)
			print(s)
			local dep2 = getdeps(s, deps)
			if not exclude[s] then
				for k,v in ipairs(dep2) do
					table.insert(deps, v)
				end
				table.insert(deps,s)
			end
		end
	end

	for k,v in pairs(deps) do
		if type(k) == "string" then
			deps[k] = nil
		end
	end
	return deps
end

OBJ = {}

for k,v in ipairs(SRC) do
	OBJ[k] = {
		path = v:gsub("%.cp?p?$", ".o"),
		deps = getdeps(v),
		src = v
	}
	table.insert(OBJ[k].deps, v)
end

if _SHOWOBJ then
	print(inspect(OBJ))
end

if opt.clean then
	local objs = ""
	for _,o in ipairs(OBJ) do
		objs = objs..o.path.." "
	end

	local cmd = ("rm %s %s"):format(objs, PROG)
	print("CLEANING: "..cmd)
	return os.execute(cmd)
end

local tobuild = {}

for _,o in ipairs(OBJ) do
	local attr = lfs.attributes(o.path)
	if not attr then
			table.insert(tobuild, {src = o.src, out = o.path})
	else
		local o_mod = attr.modification
		for _,dep in ipairs(o.deps) do
			local d_mod = lfs.attributes(dep).modification
			--print(o_mod-d_mod)
			if d_mod > o_mod then
				--dependency is newer: rebuild
				table.insert(tobuild, {src = o.src, out = o.path})
				break
			end
		end
	end
end

if #tobuild < 1 then
	print "nothing to do"
	return 0
end

if _SHOWBUILD then
	print(inspect(tobuild))
end

for _,o in ipairs(tobuild) do
	buildobj(o)
end

buildprog()