CMakeExternalProject.pdf

diff --git a/CMake/BuildExternalDeps.cmake b/CMake/BuildExternalDeps.cmake
new file mode 100644
index 0000000..a247a7d
--- /dev/null
+++ b/CMake/BuildExternalDeps.cmake
@@ -0,0 +1,75 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+include(ExternalProject)
+
+if (NOT ABSL_BUILD_DEPS_FROM_SOURCE)
+  message(FATAL_ERROR "This file should only be included when building external deps")
+endif()
+
+set(INSTALL_PREFIX ${CMAKE_BINARY_DIR}/install-deps)
+
+set(CCTZ_FOUND ON)
+set(CCTZ_PREFIX ${CMAKE_CURRENT_BINARY_DIR}/google-cctz)
+set(CCTZ_LIBRARIES ${INSTALL_PREFIX}/lib/libcctz.a)
+set(CCTZ_INCLUDE_DIRS ${INSTALL_PREFIX}/include)
+string(REPLACE "-std=" "" STD_VER "${ABSL_STD_CXX_FLAG}")
+ExternalProject_Add(google-cctz
+        PREFIX google-cctz
+        SOURCE_DIR ${CCTZ_PREFIX}/src
+        BINARY_DIR ${CCTZ_PREFIX}/build
+        STAMP_DIR ${CCTZ_PREFIX}/stamp
+        INSTALL_DIR ${INSTALL_PREFIX}
+        GIT_REPOSITORY https://github.com/google/cctz.git
+        CONFIGURE_COMMAND ""
+        BUILD_ALWAYS ON
+        BUILD_COMMAND
+          make -C <BINARY_DIR>
+          -f <SOURCE_DIR>/Makefile
+          SRC=<SOURCE_DIR>/
+          CXX=${CMAKE_CXX_COMPILER}
+          STD=${STD_VER}
+        INSTALL_COMMAND
+          make -C <BINARY_DIR>
+          -f <SOURCE_DIR>/Makefile
+          install
+          SRC=<SOURCE_DIR>/
+          CXX=${CMAKE_CXX_COMPILER}
+          STD=${STD_VER}
+          PREFIX=<INSTALL_DIR>
+        )
+
+set(GTEST_FOUND ON)
+set(GMOCK_FOUND ON)
+set(GTEST_PREFIX ${CMAKE_CURRENT_BINARY_DIR}/google-test)
+set(GTEST_LIBRARIES ${INSTALL_PREFIX}/lib/libgtest.a)
+set(GMOCK_LIBRARIES ${INSTALL_PREFIX}/lib/libgmock.a)
+set(GTEST_MAIN_LIBRARIES ${INSTALL_PREFIX}/lib/libgtest_main.a)
+set(GTEST_INCLUDE_DIRS ${INSTALL_PREFIX}/include)
+set(GMOCK_INCLUDE_DIRS ${INSTALL_PREFIX}/include)
+
+ExternalProject_Add(google-test
+          PREFIX google-test
+          SOURCE_DIR ${GTEST_PREFIX}/src
+          BINARY_DIR ${GTEST_PREFIX}/build
+          INSTALL_DIR ${INSTALL_PREFIX}
+          STAMP_DIR ${GTEST_PREFIX}/stamp
+          GIT_REPOSITORY https://github.com/google/googletest.git
+          CMAKE_CACHE_ARGS
+            -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>
+          )
+
+mark_as_advanced(GTEST_FOUND GTEST_INCLUDE_DIRS GTEST_LIBRARIES GTEST_MAIN_LIBRARIES)
+mark_as_advanced(GMOCK_FOUND GMOCK_INCLUDE_DIRS GMOCK_LIBRARIES)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 743e999..5a4f812 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -30,21 +30,26 @@ include(AbseilHelpers)
 option(ABSL_ENABLE_PIC "Enable / disable position-independent code generation" OFF)
 set(ABSL_STD_CXX_FLAG "${CMAKE_CXX_STD_CXX11}" CACHE STRING "c++ std flag (default: c++11)")
 
+option(ABSL_BUILD_DEPS_FROM_SOURCE "Enable building Abseils dependancies from source" OFF)
+
 
 # pthread
 find_package(Threads REQUIRED)
 
 # check for GTest
-find_package(GTest REQUIRED)
-find_package(GMock REQUIRED)
-include_directories(${GTEST_INCLUDE_DIRS} ${GMOCK_INCLUDE_DIRS})
-
-# check for other google dependencies
-find_package(CCTZ REQUIRED)
-include_directories(${CCTZ_INCLUDE_DIRS})
+if (ABSL_BUILD_DEPS_FROM_SOURCE)
+  include(BuildExternalDeps)
+else()
+  find_package(GTest REQUIRED)
+  find_package(GMock REQUIRED)
+  find_package(CCTZ REQUIRED)
+endif()
 
-# include current path
-include_directories(${CMAKE_CURRENT_SOURCE_DIR})
+include_directories(
+    ${GTEST_INCLUDE_DIRS}
+    ${GMOCK_INCLUDE_DIRS}
+    ${CCTZ_INCLUDE_DIRS}
+    ${CMAKE_CURRENT_SOURCE_DIR})
 
 # -std=X
 set(CMAKE_CXX_FLAGS "${ABSL_STD_CXX_FLAG} ${CMAKE_CXX_FLAGS}")