# Copyright 2020 MongoDB Inc.
#
# 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 AUTHORS OR COPYRIGHT HOLDERS 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.
#

import math
import os
import re
import subprocess

import SCons
from pkg_resources import parse_version

# This is the oldest version of ccache that offers support for -gsplit-dwarf
_ccache_version_min = parse_version("3.2.3")


def exists(env):
    """Look for a viable ccache implementation that meets our version requirements."""
    if not env.subst("$CCACHE"):
        return False

    ccache = env.WhereIs("$CCACHE")
    if not ccache:
        print(f"Error: ccache not found at {env['CCACHE']}")
        return False

    if 'CCACHE_VERSION' in env and env['CCACHE_VERSION'] >= _ccache_version_min:
        return True

    pipe = SCons.Action._subproc(
        env,
        SCons.Util.CLVar(ccache) + ["--version"],
        stdin="devnull",
        stderr="devnull",
        stdout=subprocess.PIPE,
    )

    if pipe.wait() != 0:
        print(f"Error: failed to execute '{env['CCACHE']}'")
        return False

    validated = False
    for line in pipe.stdout:
        line = line.decode("utf-8")
        if validated:
            continue  # consume all data
        version_banner = re.search(r"^ccache version", line)
        if not version_banner:
            continue
        ccache_version = re.split("ccache version (.+)", line)
        if len(ccache_version) < 2:
            continue
        ccache_version = parse_version(ccache_version[1])
        if ccache_version >= _ccache_version_min:
            validated = True

    if validated:
        env['CCACHE_VERSION'] = ccache_version
    else:
        print(f"Error: failed to verify ccache version >= {_ccache_version_min}, found {ccache_version}")

    return validated


def generate(env):
    """Add ccache support."""

    # Absoluteify
    env["CCACHE"] = env.WhereIs("$CCACHE")

    # Propagate CCACHE related variables into the command environment
    for var, host_value in os.environ.items():
        if var.startswith("CCACHE_"):
            env["ENV"][var] = host_value

    # SERVER-48289: Adding roll-your-own CFLAGS and CXXFLAGS can cause some very "weird" issues
    # with using icecc and ccache if they turn out not to be supported by the compiler. Rather
    # than try to filter each and every flag someone might try for the ones we know don't
    # work, we'll just let the compiler ignore them. A better approach might be to pre-filter
    # flags coming in from the environment by passing them through the appropriate *IfSupported
    # method, but that's a much larger effort.
    if env.ToolchainIs("clang"):
        env.AppendUnique(CCFLAGS=["-Qunused-arguments"])

    # Check whether icecream is requested and is a valid tool.
    if "ICECC" in env:
        icecream = SCons.Tool.Tool('icecream')
        icecream_enabled = bool(icecream) and icecream.exists(env)
    else:
        icecream_enabled = False

    # Set up a performant ccache configuration. Here, we don't use a second preprocessor and
    # pass preprocessor arguments that deterministically expand source files so a stable
    # hash can be calculated on them. This both reduces the amount of work ccache needs to
    # do and increases the likelihood of a cache hit.
    if env.ToolchainIs("clang"):
        if not env.get('CCACHE_EXTRAFILES_USE_SOURCE_PATHS', False):
            env["ENV"].pop("CCACHE_CPP2", None)
            env["ENV"]["CCACHE_NOCPP2"] = "1"
            env.AppendUnique(CCFLAGS=["-frewrite-includes"])
        else:
            env["ENV"].pop("CCACHE_NOCPP2", None)
            env["ENV"]["CCACHE_CPP2"] = "1"
    elif env.ToolchainIs("gcc"):
        if icecream_enabled and not env.get('CCACHE_EXTRAFILES_USE_SOURCE_PATHS', False):
            # Newer versions of Icecream will drop -fdirectives-only from
            # preprocessor and compiler flags if it does not find a remote
            # build host to build on. ccache, on the other hand, will not
            # pass the flag to the compiler if CCACHE_NOCPP2=1, but it will
            # pass it to the preprocessor. The combination of setting
            # CCACHE_NOCPP2=1 and passing the flag can lead to build
            # failures.

            # See: https://jira.mongodb.org/browse/SERVER-48443
            # We have an open issue with Icecream and ccache to resolve the
            # cause of these build failures. Once the bug is resolved and
            # the fix is deployed, we can remove this entire conditional
            # branch and make it like the one for clang.
            # TODO: https://github.com/icecc/icecream/issues/550
            env["ENV"].pop("CCACHE_CPP2", None)
            env["ENV"]["CCACHE_NOCPP2"] = "1"
        else:
            env["ENV"].pop("CCACHE_NOCPP2", None)
            env["ENV"]["CCACHE_CPP2"] = "1"
            env.AppendUnique(CCFLAGS=["-fdirectives-only"])

    # Ensure ccache accounts for any extra files in use that affects the generated object
    # file. This can be used for situations where a file is passed as an argument to a
    # compiler parameter and differences in the file need to be accounted for in the
    # hash result to prevent erroneous cache hits.
    if "CCACHE_EXTRAFILES" in env and env["CCACHE_EXTRAFILES"]:
        env["ENV"]["CCACHE_EXTRAFILES"] = ":".join([
            denyfile.path
            for denyfile in env["CCACHE_EXTRAFILES"]
        ])

    # Make a generator to expand to CCACHE in the case where we are
    # not a conftest. We don't want to use ccache for configure tests
    # because we don't want to use icecream for configure tests, but
    # when icecream and ccache are combined we can't easily filter out
    # configure tests for icecream since in that combination we use
    # CCACHE_PREFIX to express the icecc tool, and at that point it is
    # too late for us to meaningfully filter out conftests. So we just
    # disable ccache for conftests entirely.  Which feels safer
    # somehow anyway.
    def ccache_generator(target, source, env, for_signature):
        if "conftest" not in str(target[0]):
            return '$CCACHE'
        return ''
    env['CCACHE_GENERATOR'] = ccache_generator

    # Add ccache to the relevant command lines. Wrap the reference to
    # ccache in the $( $) pattern so that turning ccache on or off
    # doesn't invalidate your build.
    env["CCCOM"] = "$( $CCACHE_GENERATOR $)" + env["CCCOM"]
    env["CXXCOM"] = "$( $CCACHE_GENERATOR $)" + env["CXXCOM"]
    env["SHCCCOM"] = "$( $CCACHE_GENERATOR $)" + env["SHCCCOM"]
    env["SHCXXCOM"] = "$( $CCACHE_GENERATOR $)" + env["SHCXXCOM"]