#!/bin/sh
# returns 0 on successful build or nothing to build
# non-zero exit status only on error during building
set -e  # stop immediately on error

# [0-9]*.cc -> mu.cc -> .build/*.cc -> .build/*.o -> .build/mu_bin
# (layers)   |        |              |             |
#          tangle  cleave          $CXX          $CXX

# can also be called with a layer to only build until
#   $ ./build --until 050
UNTIL_LAYER=${2:-zzz}

# there's two mechanisms for fast builds here:
# - if a command is quick to run, always run it but update the result only on any change
# - otherwise run it only if the output is 'older_than' the inputs
#
# avoid combining both mechanisms for a single file
# otherwise you'll see spurious messages about files being updated
# risk: a file may unnecessarily update without changes, causing unnecessary work downstream

test "$CXX" || export CXX=c++
test "$CC" || export CC=cc
test "$CFLAGS" || export CFLAGS="-g -O3"
export CFLAGS="$CFLAGS -Wall -Wextra -ftrapv -fno-strict-aliasing"

# return 1 if $1 is older than _any_ of the remaining args
older_than() {
  local target=$1
  shift
  if [ ! -e $target ]
  then
#?     echo "$target doesn't exist"
    echo "updating $target" >&2
    return 0  # success
  fi
  local f
  for f in $*
  do
    if [ $f -nt $target ]
    then
      echo "updating $target" >&2
      return 0  # success
    fi
  done
  return 1  # failure
}

# redirect to $1, unless it's already identical
update() {
  if [ ! -e $1 ]
  then
    cat > $1
  else
    cat > $1.tmp
    diff -q $1 $1.tmp >/dev/null  &&  rm $1.tmp  ||  mv $1.tmp $1
  fi
}

update_cp() {
  if [ ! -e $2/$1 ]
  then
    cp $1 $2
  elif [ $1 -nt $2/$1 ]
  then
    cp $1 $2
  fi
}

noisy_cd() {
  cd $1
  echo "-- `pwd`" >&2
}

older_than enumerate/enumerate enumerate/enumerate.cc && {
  $CXX $CFLAGS enumerate/enumerate.cc -o enumerate/enumerate
}

older_than tangle/tangle tangle/*.cc && {
  noisy_cd tangle
    {
      grep -h "^struct .* {" [0-9]*.cc  |sed 's/\(struct *[^ ]*\).*/\1;/'
      grep -h "^typedef " [0-9]*.cc
    }  |update type_list
    grep -h "^[^ #].*) {" [0-9]*.cc  |sed 's/ {.*/;/'  |update function_list
    ls [0-9]*.cc  |grep -v "\.test\.cc$"  |sed 's/.*/#include "&"/'  |update file_list
    ls [0-9]*.test.cc  |sed 's/.*/#include "&"/'  |update test_file_list
    grep -h "^[[:space:]]*void test_" [0-9]*.cc  |sed 's/^\s*void \(.*\)() {$/\1,/'  |update test_list
    $CXX $CFLAGS boot.cc -o tangle
  noisy_cd ..  # no effect; just to show us returning to the parent directory
}

LAYERS=$(./enumerate/enumerate --until $UNTIL_LAYER  |grep '.cc$')
older_than mu.cc $LAYERS enumerate/enumerate tangle/tangle && {
  # no update here; rely on 'update' calls downstream
  ./tangle/tangle $LAYERS  > mu.cc
}

older_than cleave/cleave cleave/cleave.cc && {
  $CXX -O3 -Wall -Wextra -fno-strict-aliasing cleave/cleave.cc -o cleave/cleave
  rm -rf .build
}

mkdir -p .build
grep -h "^[^[:space:]#].*) {$" mu.cc  |grep -v ":.*("  |sed 's/ {.*/;/'  |update .build/function_list
grep -h "^\s*void test_" mu.cc  |sed 's/^\s*void \(.*\)() {.*/\1,/'  |update .build/test_list
mkdir -p .build/termbox
update_cp termbox/termbox.h .build/termbox

older_than mu_bin mu.cc *_list cleave/cleave termbox/* && {
  ./cleave/cleave mu.cc .build
  noisy_cd .build
    grep ';' global_definitions_list  |sed 's/[=(].*/;/'  |sed 's/^[^\/# ]/extern &/'  |sed 's/^extern extern /extern /'  |update global_declarations_list
    for f in mu_*.cc
    do
      older_than `echo $f  |sed 's/\.cc$/.o/'` $f header global_declarations_list function_list test_list && {
        $CXX $CFLAGS -c $f
      }
    done
  noisy_cd ../termbox
    older_than utf8.o utf8.c && {
      $CC $CFLAGS -c utf8.c
    }
    older_than termbox.o termbox.c termbox.h input.inl output.inl bytebuffer.inl && {
      $CC $CFLAGS -c termbox.c
    }
    older_than libtermbox.a *.o && {
      ar rcs libtermbox.a *.o
    }
  noisy_cd ..
  $CXX $CFLAGS .build/*.o termbox/libtermbox.a -o .build/mu_bin
  cp .build/mu_bin .
}

## [0-9]*.mu -> core.mu

MU_LAYERS=$(./enumerate/enumerate --until $UNTIL_LAYER  |grep '.mu$') || exit 0  # ok if no .mu files
cat $MU_LAYERS  |update core.mu

exit 0

# scenarios considered:
#   no output when nothing needs updating
#     no output for mu.cc when .mu files modified
#     touch mu.cc but don't modify it; no output on second build
#     touch a .cc layer but don't modify it; no output on second build
#   only a single layer is recompiled when changing a C++ function
#   stop immediately after failure in tangle