# Mgear Build Tool by Matt McCutchen
# http://www.kepreon.com/~matt/mgear/


# Remember the original default goal so we can restore it at the end of mgear.mk.
mg-orig-default-goal:=$(.DEFAULT_GOAL)

# We use second-expansion heavily to dynamically compute prerequisites when they
# are needed.  Second-expansion lets us follow make's implicit rule search
# instead of trying to anticipate which prerequisites it will need in advance.
.SECONDEXPANSION:

# Deletion of intermediate files messes everything up.
# TODO: See if we can relax this requirement.
.SECONDARY:


# TEXT UTILITIES
empty:=
bs:=\$(empty)
hash:=\#
comma:=,
pct:=%
define nl


endef
# Shell-quote: a'b => 'a'\''b'
sq='$(subst ','\'',$1)'
# Make-quote: a$\nb => a$$$(nl)b
# This is enough to assign the value, *but not to use it as an argument!*
mqas=$(subst $(hash),$$(hash),$(subst $(nl),$$(nl),$(subst $$,$$$$,$1)))
# Make the value safe to use as an argument without doubling $.
# *The implementation is incomplete*; I will improve it as needed.
msarg=$(subst $(comma),$$(comma),$1)
# Return nonempty if the strings are equal, empty otherwise.
# If the strings have only nice characters, you can do $(filter x$1,x$2).
streq=$(findstring x$1,$(findstring x$2,x$1))

# $(call fmt-make-assignment,foo,bar)
# Output a make assignment that stores bar in variable foo.
# The result is like `foo:=bar' but handles leading spaces, $, and
# newlines appearing in bar safely.
fmt-make-assignment=$1:=$$(empty)$(call mqas,$2)


# TARGET OBFUSCATION

# Mgear uses two kinds of "obfuscated targets" (those that are not the simple
# names of real files):
# - An always-exists target like /.//. is used as a prerequisite of an implicit
#   rule.  Since it exists, make doesn't second-expand its own prerequisites
#   until it is actually run.  This way, a target's prerequisites can depend on
#   the results of previous command scripts.
# - An alternative-name target like /.//./proc/self/cwd/bar is used to check the
#   mtime of a file without actually building it or introducing a circular
#   dependency.

# $(newoid) allocates and returns a new obfuscation ID (oid).  Example:
#    x:=$(newoid)
# You can then refer to target $x or $x$(aname)bar (for any file bar).
# Prerequisites and commands come from $($x@opr) and $($x@ocmd).
# Target-specific variables $(oid) and $(otgt) (if alternate-name) are
# available.

opfx:=/./
# TODO If the system doesn't support /proc/self/cwd, use something else.
aname:=/proc/self/cwd/
nextoid:=/./.
newoid=$(nextoid)$(eval nextoid:=$(subst /.//////,//./,$(patsubst /.//////%,/././%,$(nextoid:.=/.))))

# Target-specific variables for obfuscated targets.
$(opfx)%: oid=$(word 1,$(subst $(aname), ,$@))
$(opfx)%: otgt=$(word 2,$(subst $(aname), ,$@))

# High-priority implicit rule for obfuscated targets.  Works for both always-
# exists and alternate-name targets.
$(opfx)%: $$($$(oid)@opr)
	$($(oid)@ocmd)

# Make won't use the same implicit rule more than once on its stack, so provide
# a second copy of the rule to allow two obfuscated targets on the stack.
# Needed for $(mg-genfile-oid)$(aname)bar.g <- $(mg-scout-oid)$(aname)bar .
# The prerequisites must look different before second-expansion so the second
# rule isn't discarded as a duplicate.
$(opfx)%: $$(empty) $$($$(oid)@opr)
	$($(oid)@ocmd)

# MAIN BUILD LOGIC

# DESIGN:
#
# - To each generated file bar corresponds a "genfile" bar.g that contains some
# information about how bar was generated, including the command (for rebuild on
# command change) and the warnings (for replay).
#
# - bar.g's mtime is the last time mgear verified that bar was up to date.  bar
# needs to be regenerated iff a prerequisite is newer than *bar.g* (not bar).
# If a prerequisite changes but the command gives the same contents for bar,
# bar.g is touched but bar itself is not touched because files that depend on it
# need not be regenerated.
#
# - If bar is newer than bar.g, the user has overridden it, and we should leave
# the override in place but warn the user about it.
#
# - The user's Makefile defines mgear rules by calling mg-define-rule.  Each
# mgear rule becomes one underlying make rule with the same target and a little
# extra magic.  This is important so that all implicit rule competition takes
# place at the same target.  Additionally, the prerequisites are passed to an
# obfuscated target for bar.g to see if any are newer than bar.g.  This is done
# by the single obfuscated implicit rule, keeping the number of implicit rules
# low. Then the command script for bar checks for overrides, command change,
# prerequisite change, etc. and acts accordingly.
#
# Target metadata variables for bar: (* means stored in bar.g)
# Now some variables are reused instead of remembered for every target.
#
# @name:=bar
#     Name of the target to which @cmd, @warnings, @deps refer.
#
# @cmd:=cat foo >bar.tmp
#     Generation command as given to the shell.*
#
# @warnings:=$(empty)yikes!
#     Data that the command printed to stdout or stderr, presumably warnings.*
#
# @deps:=included@x oops@
#     If dependency-logging, list of filename@revision used.  Revision is x for
#     exists and empty for doesn't exist.  Later perhaps x will be the mtime.*
#
# bar@gdeps:=foo
#     Static dependencies of bar, for checking by bar.g.
#
# bar@gq:=foo $(mg-scout-oid)$(aname)bar
#     $? from the rule for bar.g; used by the rule for bar.
#
# bar@checked:=1
#     Set when mgear determines that a file is up to date or depends on it being
#     so determined.  Used to decide which prerequisite to check next for a
#     dependency-logging command.
#
# bar@dlc-ran:=1
#     Indicates that mgear is in the middle of building bar using a dependency-
#     logging command.  Means that bar.g.tmp, not bar.g, is the most current
#     genfile.
#
## If the rule for bar is overridden, we clear the information from bar.g so
## that it is as if bar.g didn't exist. -- Not currently needed
#
# Some make features with which mgear's compatibility has not been investigated:
# - Command-line options (especially --dry-run, --question, --touch,
#   --always-make, --keep-going, --jobs, --assume-old, and --assume-new)
# - Static pattern rules
# - Vpath

# $(call gload,foo.o)
# Load foo.o's genfile, if any, into $(@cmd), etc.
define gload
$(if $(filter $(@name),$1),,$(eval 
# TODO: Store and check the version of mgear that wrote the genfile. 
#@mgear-version:=
@cmd:=
@warnings:=
@deps:=
-include $1.g
@name:=$1
))
endef
@name:=

# bar.g: scout bar and its dependencies and store $?.  When implicit rules
# compete for bar, we depend on the rule make uses being the last one it
# second-expands so that $(bar@gdeps) is still correct.
mg-genfile-oid:=$(newoid)
mg-scout-oid:=$(newoid)
$(mg-genfile-oid)@opr=$($(otgt:.g=)@gdeps) $(if $(wildcard $(otgt:.g=)),$(mg-scout-oid)$(aname)$(otgt:.g=),) MG-FORCE
$(mg-genfile-oid)@ocmd=$(eval $(otgt:.g=)@gq:=$(filter-out MG-%,$?))
$(mg-scout-oid)@opr:=
$(mg-scout-oid)@ocmd:=

# Mgear-ized automatic variables.
# For now, if you really want the eventual target, write $$(@).
mg@ = $@.tmp
# $%: haven't thought about it much, but probably needs no translation
mg< = $(firstword $(mg^))
mg? = $(filter-out $(opfx)%,$($@@gq))
mg^ = $(filter-out MG-% $(opfx)%,$^)
mg+ = $(filter-out MG-% $(opfx)%,$+)
# $|: needs no translation
# $*: needs no translation

# $(call mg-translate-cmd,cat $$< >$$@)
# Replaces references to automatic variables with references to their mgear-ized
# counterparts.  There might be false matches, e.g., $$@ => $$(mg@) ;
# to prevent that, write $$$(empty)@ instead.  (c.f. autoconf empty quadrigraph)
mg-translate-cmd=$(subst $$@,$$(mg@),$(subst $$?,$$(mg?),$(subst $$<,$$(mg<),$(subst $$^,$$(mg^),$(subst $$+,$$(mg+),$1)))))

# $(call mg-prereq-predict,target,prerequisites)
# Expands to code that does the following at second-expansion time:
# 1. Computes the actual prerequisites from the given prerequisite patterns by
#    translating % to $* and prepending a directory if appropriate.
# 2. Saves both existing ($+) and newly computed prerequisites to $(bar@gdeps)
#    where the rule for bar.g can get them.
# Factor out set-gdeps because make gets confused if the macro for the
# prerequisites has a colon.  Make replaces the first % with the stem *before
# expansion*, so use $(pct) to protect some %s.
mg-set-gdeps=$(eval $@@gdeps:=$1)
mg-prereq-predict=$$$$(call mg-set-gdeps,$$$$+ $(if $(findstring /,$1),$$$$(subst $$$$(pct),$$$*,$2),$$$$(addprefix $$$$(dir $$$$@),$$$$(subst $$$$(pct),$$$$*,$2))))

# Used to make the rule for bar always run so we can act based on $(bar@gdeps)
# and check for command change.
MG-FORCE:
.PHONY: MG-FORCE

# $(call mg-define-rule,target,prerequisites,cmdvar)
# Defines a rule.  cmdvar is *the name of a variable* containing the command.  
# The variable is read immediately with $(value) and then expanded in the scope
# of mgear-ized automatic variables each time the rule is run.
#
# I eradicated the target-specific variables because they fail when there are
# multiple implicit rules with the same target pattern.
#
# Rule for the target.  Set $(bar@gdeps) to all prerequisites.  Apply the new
# prerequisites.  The command script always runs.  Depend on bar.g to get
# $(bar@gq).
define mg-define-rule
$(eval $1: $(call mg-prereq-predict,$1,$2) $2 MG-FORCE $(mg-genfile-oid)$(aname)$$$$@.g
	$$(call mg-rule-cmd,$(call msarg,$(call mg-translate-cmd,$(value $3)))))
endef

# TODO Provide a way to define static pattern rules.

# Procedure to generate bar.  Now $@ is bar, so we say $@.g for bar.g.
# If an override:
#     1. Complain.  (Should we stop "`bar' is up to date" using @:; ?)
#     2. This would be the place to clear bar's metadata if we wanted to.
# Otherwise, check prereqs, command, and nonexistence to decide whether bar
# needs to be regenerated.  If so:
#     1. Note that the genfile is about to change.
#     2. Echo the command being run.
#     On error, skip to 8:
#        3. Open the new genfile bar.g.tmp for writing.
#        4. Run the command to bar.tmp, storing warnings in bar.g.tmp.
#        5. Store the command in bar.g.tmp.  Do it here to ensure that bar.g.tmp
#           is at least as new as bar.tmp.
#        6. If bar.tmp differs from bar:
#           a. Clear and touch bar.g (so bar doesn't become an override if we're
#              killed between steps 6b and 7).
#           b. Move in the new bar.
#        7. Now that bar is known to be up to date, move in the new bar.g.
#     8. Defensively remove both temporary files and exit with the exit code
#        from before the removal. (trap EXIT)
# If not:
#     1. If there were warnings, replay them.  (HMMM To stderr?)
# HMMM .tmp in displayed command looks ugly
define mg-rule-cmd
	$(if $(filter $(mg-scout-oid)$(aname)$@,$($@@gq)),\
		$(info mgear: warning: Manually created/modified file at $@ overrides rule.)\
	,$(call gload,$@)$(if $($@@gq)$(if $(wildcard $@),,TARGET-DNE)$(mg-check-cmd),\
		$(eval $@@gloaded:=)$(info $1)\
		@trap 'rm -f $@.tmp $@.g.tmp' EXIT &&\
		exec 3>$@.g.tmp &&\
		set -o pipefail && { $(mg-run-cmd) | tee /dev/fd/4 | $(mg-wrap-warnings) >&3; } 4>&1 &&\
		$(mg-assign-cmd) >&3 &&\
		$(mg-maybe-move-target) &&\
		mv -f $@.g.tmp $@.g\
	,$(if $(@warnings),\
		$(info $1 # mgear warning replay$(nl)$(@warnings))\
	)))
endef

# If the command changed, we must regenerate.
# HMMM What if the working directory changes?  Most likely, the command will
# also change and mgear will do the right thing. 
mg-check-cmd=$(if $(call streq,$1,$(@cmd)),,COMMAND-CHANGED)

# Pieces of mg-generate that I factored out to make mg-generate more readable.
mg-assign-cmd=echo $(call sq,$(call fmt-make-assignment,@cmd,$1))
mg-run-cmd={ ($1) 2>&1 && { [ -r $@.tmp ] || { echo 'mgear: error: Command for $@ succeeded without creating it!'; false; }; }; }
mg-wrap-warnings=sed -re '1s/^/@warnings:=$$(empty)/; 1!s/^/@warnings+=$$(nl)/'
# Drat bash's lack of precedence between || and &&.  Extra braces necessary.
mg-maybe-move-target={ cmp -s $@ $@.tmp || { echo >$@.g && mv -f $@.tmp $@; }; }

# Just add additional prerequisites.  This cannot add prerequisite patterns to
# an implicit rule, but it can add specific prerequisites to an individual use
# of an implicit rule.  Currently, mgear picks up the target's prerequisites
# from make, so this just attaches the given prerequisites to the target, but
# the implementation might change in the future.
mg-define-prereq=$(eval $1: $2)


# CLEAN

# A command that finds all genfiles in a given directory and deletes them and
# the corresponding generated files.  If a file is overridden, only the genfile
# is deleted.
#
# Example:
#
# clean:
#         $(call mg-clean-cmd,.)
# .PHONY: clean

define mg-clean-cmd
	@exec 3>&1 &&\
	find $1 -name '*.g' | while read gf; do\
	f="$${gf%.g}" &&\
	if ! [ "$$f" -nt "$$gf" ]; then\
		echo "rm -f '$$f'" >&3 && echo "$$f";\
	fi &&\
	echo "$$gf";\
	done | xargs rm -f
endef


# DEPENDENCY-LOGGING COMMANDS

mg-dlc-static-run-oid:=$(mg-genfile-oid)

# $(call mg-define-rule-dlc,target,static-prerequisites,cmd,dep-converter)
# Analogue of mg-define-rule for a dependency-logging command.
# I haven't decided on the format for the dep-converter yet.
define mg-define-rule-dlc
$(eval 

# FINISH

# Rule for the target.  Set $(bar@gdeps) to all prerequisites.  Apply the new
# prerequisites.  The command script always runs.  Finally, do the static run
# and then the first dynamic check.
$1: $(call mg-prereq-predict,$1,$2) $2 MG-FORCE $(mg-dlc-static-run-oid)$(aname)$$$$@.g  $$$$(call dlc-next-dchk,$$$$(target))
# TODO: Move the finished file into place or something
#	$$(call mg-rule-cmd,$3)
)
endef

#mg-dlc-next-dchk=$(call mg-dlc-next-dchk-1,$1,$(newoid))
#mg-dlc-next-dchk-1=$(eval $2@opr=$$(call mg-dlc-dchk-pr,$1,$2))$2
#
## $(call mg-dlc-dchk-pr,target,oid)
#mg-dlc-dchk-pr=$(call mg-dlc-dchk-pr-1,$1,$2,$(call next-unchecked-prereq,$($1@deps)))
## $(call mg-next-unchecked-prereq,foo.c bar.h baz.h)
#mg-next-unchecked-prereq=$(firstword $(foreach p,$1,$(if $($p@checked),,$p)))
#define mg-dlc-dchk-pr-1
#$(if $3,$(call mg-dlc-drun,$1,$2,$3) $(call mg-dlc-next-dchk,$1),)
#endef
#
## $(call mg-dlc-drun,target,oid,prereq). FINISH
#define mg-dlc-drun
#$(eval 
#$2$(aname)$3@opr:=$3
#$2$(aname)$3@ocmd:=
#)$2$(aname)$3
#endef
#
#
## END

# We don't want anything we defined to become the default goal.
.DEFAULT_GOAL := $(mg-orig-default-goal)