#[[
    This module enables CCache support by inserting a ccache executable as
    the compiler launcher for C and C++ if there is a ccache executable availbale
    on the system.

    CCache support will be automatically enabled if it is found on the system.
    CCache can be forced on or off by setting the MONGO_USE_CCACHE CMake option to
    ON or OFF.
]]

find_program (CCACHE_EXECUTABLE ccache)

# Enable ccache for compiling if not already configured.
if (CCACHE_EXECUTABLE AND NOT DEFINED MONGO_USE_CCACHE)
    message (STATUS "Found ccache: ${CCACHE_EXECUTABLE}")

    execute_process (
        COMMAND ${CCACHE_EXECUTABLE} --version | perl -ne "print $1 if /^ccache version (.+)$/"
        OUTPUT_VARIABLE CCACHE_VERSION
        OUTPUT_STRIP_TRAILING_WHITESPACE
    )

    # Assume `ccache --version` mentions a simple version string, e.g. "1.2.3".
    # Permit patch number to be omitted, e.g. "1.2".
    set (SIMPLE_SEMVER_REGEX "([0-9]+)\.([0-9]+)(\.([0-9]+))?")
    string (REGEX MATCH "${SIMPLE_SEMVER_REGEX}" CCACHE_VERSION ${CCACHE_VERSION})

    if (CCACHE_VERSION)
        message (STATUS "Detected ccache version: ${CCACHE_VERSION}")
    else ()
        message (WARNING "Could not obtain ccache version from `ccache --version`. Defaulting to 0.1.0.")
        set (CCACHE_VERSION 0.1.0)
    endif ()

    # Avoid spurious "ccache.conf: No such file or directory" errors due to ccache being invoked in parallel, which was patched in ccache version 3.4.3.
    if (CCACHE_VERSION VERSION_LESS "3.4.3")
        message (STATUS "Detected ccache version ${CCACHE_VERSION} is less than 3.4.3, which may lead to spurious failures when run in parallel. See https://github.com/ccache/ccache/issues/260 for more information.")
        message (STATUS "Compiling with CCache disabled. Enable by setting MONGO_USE_CCACHE to ON")
        option (MONGO_USE_CCACHE "Use CCache when compiling" OFF)
    else ()
        message (STATUS "Compiling with CCache enabled. Disable by setting MONGO_USE_CCACHE to OFF")
        option (MONGO_USE_CCACHE "Use CCache when compiling" ON)
    endif ()
endif (CCACHE_EXECUTABLE AND NOT DEFINED MONGO_USE_CCACHE)

if (MONGO_USE_CCACHE)
    set (CMAKE_CXX_COMPILER_LAUNCHER "${CCACHE_EXECUTABLE}")
    set (CMAKE_C_COMPILER_LAUNCHER "${CCACHE_EXECUTABLE}")
endif ()