# - Returns a version string from Git
#
# These functions force a re-configure on each git commit so that you can
# trust the values of the variables in your build system.
#
#  get_git_head_revision(<refspecvar> <hashvar> [<additional arguments to git describe> ...])
#
# Returns the refspec and sha hash of the current head revision
#
#  git_describe(<var> [<additional arguments to git describe> ...])
#
# Returns the results of git describe on the source tree, and adjusting
# the output so that it tests false if an error occurs.
#
#  git_get_exact_tag(<var> [<additional arguments to git describe> ...])
#
# Returns the results of git describe --exact-match on the source tree,
# and adjusting the output so that it tests false if there was no exact
# matching tag.
#
# Requires CMake 2.6 or newer (uses the 'function' command)
#
# Original Author:
# 2009-2010 Ryan Pavlik <rpavlik@iastate.edu> <abiryan@ryand.net>
# http://academic.cleardefinition.com
# Iowa State University HCI Graduate Program/VRAC
#
# Copyright Iowa State University 2009-2010.
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE_1_0.txt or copy at
# http://www.boost.org/LICENSE_1_0.txt)

if(__get_git_revision_description)
	return()
endif()
set(__get_git_revision_description YES)

# We must run the following at "include" time, not at function call time,
# to find the path to this module rather than the path to a calling list file
get_filename_component(_gitdescmoddir ${CMAKE_CURRENT_LIST_FILE} PATH)

function(get_git_head_revision _refspecvar _hashvar)
	set(GIT_PARENT_DIR "${CMAKE_SOURCE_DIR}")
	set(GIT_DIR "${GIT_PARENT_DIR}/.git")
	while(NOT EXISTS "${GIT_DIR}")	# .git dir not found, search parent directories
		set(GIT_PREVIOUS_PARENT "${GIT_PARENT_DIR}")
		get_filename_component(GIT_PARENT_DIR ${GIT_PARENT_DIR} PATH)
		if(GIT_PARENT_DIR STREQUAL GIT_PREVIOUS_PARENT)
			# We have reached the root directory, we are not in git
			set(${_refspecvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
			set(${_hashvar} "GITDIR-NOTFOUND" PARENT_SCOPE)
			return()
		endif()
		set(GIT_DIR "${GIT_PARENT_DIR}/.git")
	endwhile()
	set(GIT_DATA "${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/git-data")
	if(NOT EXISTS "${GIT_DATA}")
		file(MAKE_DIRECTORY "${GIT_DATA}")
	endif()

	if(NOT EXISTS "${GIT_DIR}/HEAD")
		return()
	endif()
	set(HEAD_FILE "${GIT_DATA}/HEAD")
	configure_file("${GIT_DIR}/HEAD" "${HEAD_FILE}" COPYONLY)

	configure_file("${_gitdescmoddir}/GetGitRevisionDescription.cmake.in"
		"${GIT_DATA}/grabRef.cmake"
		@ONLY)
	include("${GIT_DATA}/grabRef.cmake")

	set(${_refspecvar} "${HEAD_REF}" PARENT_SCOPE)
	set(${_hashvar} "${HEAD_HASH}" PARENT_SCOPE)
endfunction()

function(git_describe _var)
	if(NOT GIT_FOUND)
		find_package(Git QUIET)
	endif()
	if(NOT GIT_FOUND)
		set(${_var} "n/a" PARENT_SCOPE)
		return()
	endif()
	get_git_head_revision(refspec hash)
	if(NOT hash)
		set(${_var} "n/a" PARENT_SCOPE)
		return()
	endif()

	execute_process(COMMAND "${GIT_EXECUTABLE}" describe ${hash} ${ARGN}
		WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
		RESULT_VARIABLE res
		OUTPUT_VARIABLE out
		ERROR_QUIET
		OUTPUT_STRIP_TRAILING_WHITESPACE)
	if(NOT res EQUAL 0)
		set(out "n/a")
	endif()

	set(${_var} "${out}" PARENT_SCOPE)
endfunction()

function(git_get_exact_tag _var)
	git_describe(out --exact-match ${ARGN})
	set(${_var} "${out}" PARENT_SCOPE)
endfunction()