######################################################################
# Makefile
#
# This makefile is the one called by user, but it's only a trampoline
# to create the build directory and call the real Makefile.build
#
# make can be invoqued with 'make build=<your_build_directory> ...'
# all other options and target are passed to the real makefile.
#
# As an exception to the rule of not modifying source directory, a
# .build.mak file is created to cache the configured build directory.
# Subsequent invocations of make could be done without passing
# 'build=...' parameter.
#
# distclean target is catched to destroy both the .build.mak and
# the whole build directory.
#
######################################################################

# build directory is cached in BUILD_MAK file between make invocations
BUILD_MAK = .build.mak
ifneq ($(wildcard $(BUILD_MAK)),)
include $(BUILD_MAK)
endif

# default build directory 'build'
build ?= build

# ($call quiet-command,CMD,MSG)
# execute CMD and display MSG
# if verbose mode is enabled (with 'make V=1`) print full CMD instead of MSG
quiet-command = $(if $(V),$1,$(if $(2),@echo $2 && $1, @$1))

# if the target is distclean, skip allmost rules
# to doing anything which will be immediately
# deleted after
ifeq ($(filter distclean,$(MAKECMDGOALS)),)

# default target (when one invokes 'make' without target)
# so we have a non-empty target which could be catched by
# the catch-all target below.
default-all:

# The catch-all target, which pass build to the main
# makefile in the build directory.
# strip-out 'default-all' for targets' list
%: | $(build)
	$(call quiet-command, \
		$(MAKE) -C $(build) $(filter-out default-all,$@) \
		, "MAKE $(filter-out default-all,$@)")

# Creates the buld directory
# and populates it with a link to the build makefile
$(build): | $(BUILD_MAK)
	$(call quiet-command,\
		mkdir -p $@; \
		ln -sf $(CURDIR)/Makefile.build $@/Makefile \
		, "MKBUILD $@")

# always create BUILD_MAK to cache build configuration
# but don't update it if not changed
$(BUILD_MAK): FORCE
	@echo build=$(build) > $@.tmp
	@cmp -s $@.tmp $@ || (mv $@.tmp $@ && echo "GEN  $@")
	@rm -f $@.tmp

else # if distclean

distclean:
	$(call quiet-command, rm -rf $(build) $(BUILD_MAK), "DISTCLEAN $(build)")

endif # distclean


.PHONY: distclean FORCE

#ifndef V
#.SILENT:
#endif