# Ugh, this is needed by some rules below.
.SECONDEXPANSION:

# All source files.
SOURCES = $(foreach dir,$(SOURCE_DIRS),$(call rwildcard, $(dir), *.c)$(call rwildcard, $(dir), *.cpp))

# All object files.
OBJECTS = $(patsubst %,$(OBJECT_DIR)/%,$(patsubst %.c,%.c.o,$(patsubst %.cpp,%.cpp.o,$(SOURCES))))

# Dependency lists
DEP_FILES = $(patsubst %.o,%.d,$(OBJECTS))

.PHONY: foo
foo:
    @echo $(DEP_FILES)

# Fancy alias for the primary target.
.PHONY: build
build: $(OUTPUT_FILE)

# The target that actually builds the executable.
# I'm not sure why we need `.SECONDEXPANSION:` and `$$` before `(OBJECTS)`, but it's definitely necessary.
# Note that object files come before linker flags.
$(OUTPUT_FILE): $$(OBJECTS)
    @echo [Linking] $(OUTPUT_FILE)
    @$(CXX) $(OBJECTS) $(LDFLAGS) -o $@
    @echo [Done]

# Targets that compile source files.
# Note that flags come before the source file.
$(OBJECT_DIR)/%.c.o: %.c $(dir $@)
    @echo [C] $<
    $(call mkdir,$(dir $@))
    @$(CC) -MMD -MP $(CFLAGS) $< -c -o $@
$(OBJECT_DIR)/%.cpp.o: %.cpp $(dir $@)
    @echo [C++] $<
    $(call mkdir,$(dir $@))
    @$(CXX) -MMD -MP $(CXXFLAGS) $< -c -o $@

# Target that cleans the build.
.PHONY: clean
clean:
    $(call rmdir,$(OBJECT_DIR))
    $(call rmfile,$(OUTPUT_FILE))

# FUNCTIONS

# Recursive wildcard function.
# Source: https://stackoverflow.com/a/18258352/2752075
# Recursively searches a directory for all files matching a pattern.
# The first parameter is a directory, the second is a pattern.
# Don't use `.` as a directory, or else it'll search your entire drive! (Huh.) Instead use an empty parameter.
# Example usage: SOURCES = $(call rwildcard, src, *.cpp)
rwildcard=$(foreach d,$(wildcard $1*),$(call rwildcard,$d/,$2)$(filter $(subst *,%,$2),$d))

# OS-specific functions
# `-` at the beginning makes `make` ignore errors when executing shell commands.
# `|| cd .` forces error code to be 0, silencing errors. Unlike `-` it prints no warnings.
# Example usage: $(call rmfile, bin/out.exe)
HOST_OS = linux
ifneq ($(OS), Windows_NT)
HOST_OS = linux
else ifndef MSYSTEM
HOST_OS = windows
else
HOST_OS = linux
endif

ifeq ($(HOST_OS), windows)
SILENT = >NUL 2>NUL || cd .
rmfile = @del /F /Q $(subst /,\,$1) $(SILENT)
rmdir = @rd /S /Q $(subst /,\,$1) $(SILENT)
mkdir = @mkdir >NUL 2>NUL $(subst /,\,$1) $(SILENT)
else
SILENT = >/dev/null 2>/dev/null || cd .
rmfile = @del /F /Q $1 $(SILENT)
rmdir = @rm -rf $1 $(SILENT)
mkdir = @mkdir -p $1 $(SILENT)
endif

-include $(DEP_FILES)