def _genrule_repository(ctx):
    ctx.download_and_extract(
        ctx.attr.urls,
        "",  # output
        ctx.attr.sha256,
        "",  # type
        ctx.attr.strip_prefix,
    )
    for ii, patch in enumerate(ctx.attr.patches):
        patch_input = "patch-input-%d.patch" % (ii,)
        ctx.symlink(patch, patch_input)
        patch_result = ctx.execute(["patch", "-p0", "--input", patch_input])
        if patch_result.return_code != 0:
            fail("Failed to apply patch %r: %s" % (patch, patch_result.stderr))

    # https://github.com/bazelbuild/bazel/issues/3766
    genrule_cmd_file = Label("@envoy//bazel").relative(str(ctx.attr.genrule_cmd_file))
    ctx.symlink(genrule_cmd_file, "_envoy_genrule_cmd.genrule_cmd")
    cat_genrule_cmd = ctx.execute(["cat", "_envoy_genrule_cmd.genrule_cmd"])
    if cat_genrule_cmd.return_code != 0:
        fail("Failed to read genrule command %r: %s" % (
            genrule_cmd_file,
            cat_genrule_cmd.stderr,
        ))

    ctx.file("WORKSPACE", "workspace(name=%r)" % (ctx.name,))
    ctx.symlink(ctx.attr.build_file, "BUILD.bazel")

    # Inject the genrule_cmd content into a .bzl file that can be loaded
    # from the repository BUILD file. We force the user to look up the
    # command content "by label" so the inclusion source is obvious.
    ctx.file("genrule_cmd.bzl", """
_GENRULE_CMD = {%r: %r}
def genrule_cmd(label):
    return _GENRULE_CMD[label]
""" % (str(genrule_cmd_file), cat_genrule_cmd.stdout))

genrule_repository = repository_rule(
    attrs = {
        "urls": attr.string_list(
            mandatory = True,
            allow_empty = False,
        ),
        "sha256": attr.string(),
        "strip_prefix": attr.string(),
        "patches": attr.label_list(
            allow_files = [".patch"],
            allow_empty = True,
        ),
        "genrule_cmd_file": attr.label(
            mandatory = True,
            allow_single_file = [".genrule_cmd"],
        ),
        "build_file": attr.label(
            mandatory = True,
            allow_single_file = [".BUILD"],
        ),
    },
    implementation = _genrule_repository,
)

def _genrule_cc_deps(ctx):
    outs = depset()
    for dep in ctx.attr.deps:
        outs = dep.cc.transitive_headers + dep.cc.libs + outs
    return DefaultInfo(files = outs)

genrule_cc_deps = rule(
    attrs = {
        "deps": attr.label_list(
            providers = [],  # CcStarlarkApiProvider
            mandatory = True,
            allow_empty = False,
        ),
    },
    implementation = _genrule_cc_deps,
)

def _absolute_bin(path):
    # If the binary path looks like it's relative to the current directory,
    # transform it to be absolute by appending "${PWD}".
    if "/" in path and not path.startswith("/"):
        return '"${PWD}"/%r' % (path,)
    return "%r" % (path,)

def _genrule_environment(ctx):
    lines = []

    # Bazel uses the same command for C and C++ compilation.
    c_compiler = ctx.var["CC"]

    # Bare minimum cflags to get included test binaries to link.
    #
    # See .bazelrc for the full set.
    asan_flags = ["-fsanitize=address,undefined"]
    tsan_flags = ["-fsanitize=thread"]

    # Older versions of GCC in Ubuntu, including GCC 5 used in CI images,
    # incorrectly invoke the older `/usr/bin/ld` with gold-specific options when
    # building with sanitizers enabled. Work around this by forcing use of gold
    # in sanitize mode.
    #
    # This is not a great solution because it doesn't detect GCC when Bazel has
    # wrapped it in an intermediate script, but it works well enough to keep CI
    # running.
    #
    # https://stackoverflow.com/questions/37603238/fsanitize-not-using-gold-linker-in-gcc-6-1
    force_ld = []
    if "clang" in c_compiler:
        force_ld = ["-fuse-ld=lld"]
    elif "gcc" in c_compiler or "g++" in c_compiler:
        force_ld = ["-fuse-ld=gold"]

    cc_flags = []
    ld_flags = []
    ld_libs = []
    if ctx.var.get("ENVOY_CONFIG_COVERAGE"):
        ld_libs.append("-lgcov")
    if ctx.var.get("ENVOY_CONFIG_ASAN"):
        cc_flags += asan_flags
        ld_flags += asan_flags
        ld_flags += force_ld
    if ctx.var.get("ENVOY_CONFIG_TSAN"):
        cc_flags += tsan_flags
        ld_flags += tsan_flags
        ld_flags += force_ld

    lines.append("export CFLAGS=%r" % (" ".join(cc_flags),))
    lines.append("export LDFLAGS=%r" % (" ".join(ld_flags),))
    lines.append("export LIBS=%r" % (" ".join(ld_libs),))
    lines.append("export CC=%s" % (_absolute_bin(c_compiler),))
    lines.append("export CXX=%s" % (_absolute_bin(c_compiler),))

    # Some Autoconf helper binaries leak, which makes ./configure think the
    # system is unable to do anything. Turn off leak checking during part of
    # the build.
    lines.append("export ASAN_OPTIONS=detect_leaks=0")

    lines.append("")
    out = ctx.actions.declare_file(ctx.attr.name + ".sh")
    ctx.actions.write(out, "\n".join(lines))
    return DefaultInfo(files = depset([out]))

genrule_environment = rule(
    implementation = _genrule_environment,
)