#!/bin/sh
# Generate some basic info on source code version to be included in program.
#
# Copyright (c) 2006-2007 Luc Verhaegen <libv@skynet.be>
# Copyright (C) 2007 Hans Ulrich Niedermann <hun@n-dimensional.de>
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation
# the rights to use, copy, modify, merge, publish, distribute, sublicense,
# and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
# THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
# OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
# ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.
#
# The author thanks the nice people on #git for the assistance!
#
# Simple testing of this script:
#   env SED="/sbin/busybox sed" \
#   /sbin/busybox sh git-buildmsg --example > moo.c \
#     && gcc -Wall -Wextra -Wno-unused -o moo moo.c \
#     && ./moo
#   (bash and other seds should also do)
#
# Note:
#   A man page for this script does NOT make sense. It is supposed to be
#   copied into and shipped with other peoples' source trees.
#
# Ideas:
#  * Output for languages other than C (Erlang, Python, Perl, sh, ...)
#  * Recognize difference between being built from "non-git" sources and
#    a dist tarball generated from git rev XYZ.

# The caller may have found these programs for us
SED="${SED-sed}"

# Initialize
GIT_DIR=".git"
working_dir="$(pwd)"

# Who am I?
self="$(basename "$0")"

# Default settings
ifndef_symbol="GIT_BUILDMSG_H"
outfile="-"
print_example=false
srcdir="$(pwd)"
error_if_no_git=false

# Help messages
USAGE="[<option>...]"
LONG_USAGE="\
  -h --help             Print this help message.
  -V --version          Print version number.

  -x --example          Print complete example program.
  -o --output FILENAME  Set output file name.
  -s --srcdir DIRNAME   Set source tree dir name.

  -e --error-if-no-git  Abort with exitcode!=0 if git worktree not found."

# Parse command line parameter, affecting defaults
while [ "x$1" != "x" ]
do
    case "$1" in
        -x|--example)
            print_example=:
            ;;
        -o|--output)
            if shift; then
                outfile="$1"
                [ "x$outfile" = "x-" ] || \
                    ifndef_symbol=`basename "$outfile" | $SED 's|\.|_|g; s|[^A-Za-z0-9_]||g' | tr a-z A-Z`
            else
                echo "$self: Fatal: \"$1\" option requires parameter." >&2
                exit 1
            fi
            ;;
        -V|--version)
	    echo "$self (@PACKAGE_NAME@) @PACKAGE_VERSION@"
	    exit
	    ;;
        -h|--help)
            echo "Usage: ${self} $USAGE"
	    [ -n "$LONG_USAGE" ] && echo "$LONG_USAGE"
            exit
            ;;
	-s|--srcdir)
	    if shift; then
		srcdir="$1"
		[ -d "$srcdir" ] || {
		    echo "$self: Fatal: \"$1\" not a directory." >&2
		    exit 1
		}
	    else
		echo "$self: Fatal: \"$1\" option requires directory parameter."
		exit 1
	    fi
	    ;;
	-e|--error-if-no-git)
	    error_if_no_git=:
	    ;;
        *)
            echo "$self: Fatal: Invalid command line paramenter: \"$1\"" >&2
            exit 1
            ;;
    esac
    shift
done

# If not printing to stdout, redirect stdout to output file
outfile_exists=false
rename_new_output=false
if [ "x$outfile" = "x-" ]
then
    : # keep using stdout
else
    if [ -e "$outfile" ]; then
	outfile_exists=:
    fi
    exec 1> "${outfile}.new"
fi

# Done with creating output files, so we can change to source dir
cd "$srcdir"

# Detect git tools (should work with old and new git versions)
git_found=yes
for git_tool in git-symbolic-ref git-rev-parse git-diff-files git-diff-index
do
    [ x`which $git_tool 2>/dev/null` = "x" ] && { git_found=no; break; }
done

# Determine data about git tree
is_git_worktree=no
if [ "x$git_found" = "xyes" ]; then
    if [ -e "$GIT_DIR/index" ]; then
	is_git_worktree="yes"

        # Commit ID
        git_commitid=`git-rev-parse HEAD | $SED -n 's/^\(.\{8\}\).*/\1/p'` || \
	    { echo "Error running git-rev-parse HEAD" >&2; exit 1; }

        # Branch
        git_branch=`git-symbolic-ref HEAD | $SED -n 's|^refs/heads/||p'` || \
	    { echo "Error running git-symbolic-ref HEAD" >&2; exit 1; }

        # Any uncommitted changes we should know about?
        # Or technically: Are the working tree or index dirty?
	git_dirty_tree=yes
        if git-diff-files --quiet && git-diff-index --cached --quiet HEAD; then
	    git_dirty_tree=no
        fi
    fi
fi

# Write program header
cat<<EOF
/*
 * Basic versioning gathered from the git repository.
 * Automatically generated by ${self}.
 */

#ifndef ${ifndef_symbol}
#define ${ifndef_symbol} 1

/* whether this header file is from a dist tarball */
#undef GIT_IS_DIST

EOF

# Write git specific defines
if [ "x$git_found" = "xno" ]; then
    echo "/* git is not installed */"
    echo "#undef GIT_IS_GIT_WORKTREE"
elif [ "x$is_git_worktree" = "xno" ]; then
    echo "/* This is not a git repository */"
    echo "#undef GIT_IS_GIT_WORKTREE"
else
    echo "/* This is a git repository */"
    echo "#define GIT_IS_GIT_WORKTREE 1"
    echo ""
    if [ "x$is_git_worktree" = "xyes" ]; then
	echo "/* Git ID of last commit */"
	echo "#define GIT_COMMIT_ID \"${git_commitid}..\""
	echo ""

	echo "/* Branch this tree is on */"
	echo "#define GIT_BRANCH \"$git_branch\""
	echo ""

	if [ "x$git_dirty_tree" = "xyes" ]; then
	    echo "/* Commit ID uniquely defines the state of this code */"
	    echo "#undef GIT_DIRTY_WORKTREE"
	else
	    echo "/* Local changes might be breaking things */"
	    echo "#define GIT_DIRTY_WORKTREE 1"
	fi
    else
	echo "/* Git ID of last commit */"
	echo "#undef GIT_COMMIT_ID"
	echo ""
	echo "/* Branch this tree is on */"
	echo "#undef GIT_BRANCH"
    fi
fi

# Define a few immediately useful message strings
cat<<EOF

/* Define GIT_MESSAGE such that
 *    printf("%s: built from %s", argv[0], GIT_MESSAGE);
 * forms a proper sentence.
 */

#ifdef GIT_IS_DIST
# define GIT_DIST_MSG "dist of "
# define GIT_DIST_MSG_2 " (possibly modified)"
#else
# define GIT_DIST_MSG ""
# define GIT_DIST_MSG_2 ""
#endif

#ifdef GIT_IS_GIT_WORKTREE

# ifdef GIT_DIRTY_WORKTREE
#  define GIT_CHANGE_MSG " + changes"
# else
#  define GIT_CHANGE_MSG ""
# endif /* GIT_DIRTY_WORKTREE */

# define GIT_MESSAGE \\
        GIT_DIST_MSG \\
        "git branch " GIT_BRANCH ", " \\
        "commit " GIT_COMMIT_ID GIT_CHANGE_MSG GIT_DIST_MSG_2

#else
# define GIT_MESSAGE GIT_DIST_MSG "non-git sources" GIT_DIST_MSG_2
#endif /* GIT_IS_GIT_WORKTREE */

#endif /* ${ifndef_symbol} */
EOF

# Example program
if "$print_example"
then
    cat<<EOF

/* example program demonstrating the use of ${self} output */
#include <stdio.h>
#include <string.h>

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

int main(int argc, char *argv[])
{
    const char *const idx = strrchr(argv[0], '/');
    const char *const prog = (idx)?(idx+1):(argv[0]);
#ifdef PACKAGE_VERSION
    printf("%s: version %s, built from %s\n", prog, PACKAGE_VERSION, GIT_MESSAGE);
#elif defined(GIT_USED)
    printf("%s: built from %s\n", prog, GIT_MESSAGE);
#endif
    return 0;
}
EOF
fi

# Change back to working dir for the remaining output file manipulations.
cd "$working_dir"

# If necessary, overwrite outdated output file with new one
if [ "x$outfile" != "x-" ]
then
    if [ -f "$outfile" ]; then
        if cmp "$outfile" "$outfile.new" > /dev/null; then
            echo "$self: Output is unchanged, keeping $outfile" >&2
            rm -f "$outfile.new"
        else
            echo "$self: Output has changed, updating $outfile" >&2
            mv -f "$outfile.new" "$outfile"
        fi
    else
        echo "$self: Output is new file, creating $outfile" >&2
        mv -f "$outfile.new" "$outfile"
    fi
fi

if "$error_if_no_git" && [ "x$is_git_worktree" = "xno" ]; then
    echo "$self: No git worktree found. Aborting with error, as requested." >&2
    exit 2
fi

# THE END.