#! /bin/sh
set -euf

## SYNOPSIS
# build compile SRCFILE DSTFILE
# build deps SRCFILE
build() {
  case "$1" in
    compile) build_compile "$2" "$3";;
    deps) build_deps "$2";;
    *) echo "build: $1: bad command" >&2; return 23;;
  esac
}

## build directives
build_include_directive='#@include \([0-9A-Za-z]\+\)'

## usage: build_compile SRCFILE DSTFILE
build_compile() {
  cp "$1" "$2"

  while needs_compilation "$2"; do
    script="$(make_sedscript_maker_shellscript "$2" | sh)"
    sed -n "$script" "$2" >"$2.tmp"
    mv "$2.tmp" "$2"
  done

  chmod +x "$2"
}

## usage: needs_compilation SRCFILE
# Returns true if SRCFILE contains compilation directives.
needs_compilation() {
  grep -q "^$build_include_directive$" "$1"
}

## usage: make_sedscript_maker_shellscript SRCFILE
# Print a shellscript that creates a sedscript that resolves all the build
# directives in SRCFILE.
make_sedscript_maker_shellscript() {
  echo 'set -euf'
  deps="$(build_deps "$1")"
  for lib in $deps; do
    echo "_build_include_$(basename $lib)=$lib"
  done
  nl -b a -s ' ' "$1" |
  sed '
    s:^ *::
    s:^\([0-9]\+\) '"$build_include_directive"'$:\1a\\\\\
# BEGIN \2\
      \1r\$_build_include_\2\
      \1a\\\\\
# END \2:
    s:^\([0-9]\+\) .*:\1p:
  
    1s:^:echo ":
    $s:$:":
  '
}

## usage: build_deps SRCFILE
build_deps() {
  for libname in $(sed -n 's:^'"$build_include_directive"'$:\1:p' "$1"); do
    build_resolve "$libname"
  done
}

## usage: build_resolve LIBNAME
build_resolve() {
  echo "$BUILD_PATH" | tr : \\n |
    xargs -I: printf '%s/%s\n' : "$1" |
    xargs -I: ls -d : 2>/dev/null |
    head -n 1 |
    grep . ||
  {
    echo "build resolve: $1: library not found" >&2
    return 23
  }
}

build "$@"