# Adding parallelism by default
MAKEFLAGS += -j4

# For tests purposes, appending to this file to log the execution sequence across parallel calls
COMMAND_LOG := commands.txt
# We can define a canned recipe to add the log to the text file
# Important: Ensure to use `=` instead `:=`. The single equal sign makes the
# variable expand in the caller, and colon-equal sign expands once at definition,
# and at definition the `$1` variable doesn't exists yet (injected by `call` function).
# This is called the two variable "flavors". Read more at '(make) Flavors'
log-cmd = echo "$$(date -Is): $1" >>$(COMMAND_LOG)
# It can be multi-line as well:
# define log-cmd
# echo "$$(date -Is): $1" >>$(COMMAND_LOG)
# endef

# When calling `make` with no goal, run `dist`. See '(make) Special Variables'
.DEFAULT_GOAL = dist

# `&:` means a "grouped target". It means this recipe outputs the all files at once. See Info '(make) Multiple Targets'
# It's executed if any of its files needs to be generated, and no matter how much is missing, it runs only once
data/a.json data/b.json data/c.json&:
        # The leading @ suppress the print of called command in stdout
        @sleep 1 # Adding sleep to test parallelism
        # The `call` lets you provide parameters for canned recipes. See '(make) Call Function'
        $(call log-cmd,generate data to fulfill $@)
        mkdir -p data/
        touch data/{a,b,c}.json

# Some command that processes data and outputs a intermediary file. Dummy actions for exemplification
# The percentage defines a pattern target, we can see it as this regex: "^data/(.+)-processed\.json$",
# But it's only available if the dependency "^data/(.+)\.json$" exists. See '(make) Pattern Rules'
data/%-processed.json: data/%.json
        @sleep 1
        touch '$@'
        $(call log-cmd,processed $< data to fulfill $@)

# The .dirstamp is a trick to let Make know when it's time to update the dependencies.
# It generates a blank file inside the dependencies dir so it can compare the modification time against the lock file.
node_modules/.dirstamp: package-lock.json
        @sleep 2
        $(call log-cmd,npm install)
        mkdir -p node_modules/ # Manually creating because we're not really running `npm install`
        touch '$@' # Important to satisfy the target
# We can even define an alias for deps installation command
.PHONY: deps
deps: node_modules/.dirstamp

# We can easily depend on any target file of its recipe
# Directories are not good as targets as they're mostly called all the time, therefore I'm using .PHONY which make it run all the time.
# For $(foreach VAR,LIST,TEXT), see '(make) Foreach Function'
.PHONY: dist
dist: deps $(foreach x,a b c,data/$x-processed.json)
        @sleep 1
        $(call log-cmd,built the app)

# The leading dash instructs Make to ignore the error. See '(make) Errors'
.PHONY: clean
clean:
        -rm -r node_modules/ data/ dist/
        -rm $(COMMAND_LOG)

make clean >/dev/null # Calling clean separately to prevent running it in parallel with the rest
\time -f 'not parallel took %E' make -j1 dist 2>&1 >/dev/null
make clean >/dev/null
\time -f 'parallel took %E' make dist 2>&1 >/dev/null

make the_future