#  Copyright 2020 The Monogon Project Authors.
#
#  SPDX-License-Identifier: Apache-2.0
#
#  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.

# Bazel rules for generating Kubernetes-style API types using
# github.com/kubernetes/code-generator.
#
# k8s.io/code-gen generators target a peculiar filesystem/package structure for
# generated code:
#
#    example.com/project/apis/goodbye/v1/doc.go          - hand written
#                                       /types.go        - hand written
#                                       /zz_generated.go - generated
#    example.com/project/apis/hello/v1/doc.go            - hand written
#                                     /types.go          - hand written
#                                     /zz_generated.go   - generated
#    example.com/project/generated/clientset/...         - generated
#    example.com/project/generated/informers/...         - generated
#    example.com/project/generated/listers/...           - generated
#
# This means, that usually the generated files are both colocated directly
# with the package (for zz_generated.deepcopy.go, generated by deepcopy)
# and have their own package (for files generated by clientset, informers,
# listers).
#
# Most importantly, however, multiple Go packages (in the above example,
# goodbye/v1 and hello/v1) are used to in turn generate multiple output Go
# packages. This proves problematic when generating code for Bazel, as we have
# to consume the result of code generation from multiple Bazel targets (each
# representing a different generated Go package).
#
# To handle this, we split up the code generation into four main steps. These
# need to be manually instantiated by any use who wants to consume these rules.
#
#  1. Create a rules_go go_path that contains all hand-written API packages.
#  2. Parse hand written API packages using go_kubernetes_resource_bundle, via
#     the generated go_path. This prepares outputs (ie., 'runs' generators),
#     and creates an internal provider (KubeResourceBundle) that contains
#     informations about generated Go packages.
#  3. For every output package, create a go_kubernetes_library target,
#     specifying the bundle from which it's supposed to be created, and which
#     particular library from that bundle should be used.
#  4. Next to every go_kubernetes_library, create a go_library with the same
#     importpath which embeds the go_kubernetes_library. The split between
#     go_kubernetes_library and go_library is required to let Gazelle know
#     about the availability of given importpaths at given Bazel targets
#     (unfortunately, it seems like Gazelle is unable to parse rules that emit
#     the same providers as go_library does, instead requiring us to use a full
#     go_library rule instead).
#
# Point 3. is somwhat different for the generated deepcopy code, which has to
# live alongside (in the same importpath) as the hand-written API go_library,
# and needs to be embedded into that. Special care has to be taken to not cause
# a cycle (handwritten API -> go_path -> bundle -> kubernetes_library ->
# go_library) in this case. This is done via a select() which selectively
# enables the inclusion of the generated deepcopy code within the hand-written
# API library, only enabling it for the target build, not the preprocessing
# done by go_kubernetes_resource_bundle.
#
# Or, in graphical form:
#
#   .------------.   .------------.
#   | go_library |   | go_library |
#   |------------|   |------------|
#   | goodbye/v1 |   | hello/v2   |
#   '------------'   '------------'
#        '------. .--------'
#           .---------.
#           | go_path |
#           '---------'
#                | (preprocessing transition)
#  .-------------------------------.
#  | go_kubernetes_resource_bundle |
#  '-------------------------------'
#              |   '--------------------------.
#  .---------------------------.  .--------------------------.
#  |   go_kubernetes_library   |  |   go_kubernetes_library  |
#  |---------------------------|  |--------------------------| ... others ...
#  | clientset/verioned/typed  |  | clientset/verioned/fake  |
#  '---------------------------'  '--------------------------'
#              |                               |
#  .---------------------------.  .--------------------------.
#  |       go_library          |  |       go_library         |
#  |---------------------------|  |--------------------------| ... others ...
#  | clientset/versioned/typed |  | clientset/versioned/fake |
#  '---------------------------'  '--------------------------'
#

load("@io_bazel_rules_go//go:def.bzl", "GoLibrary", "GoPath", "go_context")

def _preprocessing_transition_impl(settings, attr):
    return {"//metropolis/build/kube-code-generator:preprocessing": "yes"}

# preprocessing_transition is attached to the incoming go_path in
# go_kubernetes_resource_bundle, unsets the
# //metropolis/build/kube-code-generator:embed_deepcopy config setting.
# This allows go_libraries that make up the handwritten API libraries to only
# embed the generated deepcopy when they are pulled in for build reasons, not
# when the graph is being traversed in order to generate the deepcopy itself.
# This breaks up the cycle that would happen otherwise.
preprocessing_transition = transition(
    implementation = _preprocessing_transition_impl,
    inputs = [],
    outputs = ["//metropolis/build/kube-code-generator:preprocessing"],
)

# KubeResourceBundle is emitted by go_kubernetes_resource_bundle and contains
# informations about libraries generated by the kubernetes code-generators.
KubeResourceBundle = provider(
    "Information about the generated Go sources of a k8s.io/code-generator-built library.",
    fields = {
        "libraries": "Map from Go importpath to list of Files that make up this importpath.",
    },
)

def _go_kubernetes_library_impl(ctx):
    go = go_context(ctx)
    bundle = ctx.attr.bundle[KubeResourceBundle]
    libraries = bundle.libraries

    found_importpaths = [l.importpath for l in libraries]

    libraries = [l for l in libraries if l.importpath == ctx.attr.importpath]
    if len(libraries) < 1:
        fail("importpath {} not found in bundle (have {})".format(ctx.attr.importpath, ", ".join(found_importpaths)))
    if len(libraries) > 1:
        fail("internal error: multiple libraries with importpath {} found in bundle".format(ctx.attr.importpath))
    library = libraries[0]

    source = go.library_to_source(go, ctx.attr, library, ctx.coverage_instrumented())
    return [library, source, OutputGroupInfo(go_generated_srcs = depset(library.srcs))]

# go_kubernetes_library picks a single Go library from a kube_resource_bundle
# and prepares it for being embedded into a go_library.
go_kubernetes_library = rule(
    implementation = _go_kubernetes_library_impl,
    attrs = {
        "bundle": attr.label(
            mandatory = True,
            providers = [KubeResourceBundle],
            doc = "A go_kubernetes_resource_bundle that contains the result of a kubernetes code-generation run.",
        ),
        "importpath": attr.string(
            mandatory = True,
            doc = "The importpath of the library picked from the bundle, same as the importpath of the go_library that embeds it.",
        ),
        "deps": attr.label_list(
            providers = [GoLibrary],
            doc = "All build dependencies of this library.",
        ),
        "_go_context_data": attr.label(
            default = "@io_bazel_rules_go//:go_context_data",
        ),
    },
    toolchains = ["@io_bazel_rules_go//go:toolchain"],
)

# _gotool_run is a helper function which runs an executable under
# //metropolis/build/gotoolwrap, effectively setting up everything required to
# use standard Go tooling on the monogon workspace (ie. GOPATH/GOROOT). This is
# required by generators to run 'go fmt'.
#
# The optional `copyout` argument configures which files to copy out from the
# GOPATH into declared files. The contents of the list should be strings that
# refer to a file within GOPATH/src, eg. source.monogon.dev/foo/bar/baz.go. The
# files is then going to be copied into the path corresponding to a declared
# file of the same basename.
def _gotool_run(cg, executable, arguments, copyout=[], **kwargs):
    ctx = cg.ctx
    go = go_context(ctx)
    gopath = ctx.attr.gopath[0][GoPath]

    inputs = [
        gopath.gopath_file,
    ] + kwargs.get("inputs", [])

    tools = [
        executable,
        go.sdk.go,
    ] + go.sdk.srcs + go.sdk.tools + kwargs.get("tools", [])

    copyout_env = []
    for path in copyout:
        to = cg.output_root + "/" + path
        copyout_env.append("{}:{}".format(path, to))

    env = {
        "GOTOOLWRAP_GOPATH": gopath.gopath_file.path,
        "GOTOOLWRAP_GOROOT": go.sdk.root_file.dirname,
        "GOTOOLWRAP_COPYOUT": ';'.join(copyout_env),
    }
    env.update(kwargs.get("env", {}))

    kwargs_ = dict([(k, v) for (k, v) in kwargs.items() if k not in [
        "executable",
        "arguments",
        "inputs",
        "env",
        "tools",
    ]])

    ctx.actions.run(
        executable = ctx.executable._gotoolwrap,
        arguments = [executable.path] + arguments,
        env = env,
        inputs = inputs,
        tools = tools,
        **kwargs_
    )

# _output_directory returns the relative path into which
# ctx.action.declare_file writes are rooted. This is used as code-generators
# require a root path for all outputted files, instead of a list of files to
# emit.
def _output_directory(ctx):
    # We combine bin_dir, the BUILDfile path and the target name. This seems
    # wrong. Is there no simpler way to do this?
    buildfile_path = ctx.build_file_path
    parts = buildfile_path.split("/")
    if not parts[-1].startswith("BUILD"):
        fail("internal error: unexpected BUILD file path: {}", parts[-1])
    package_path = "/".join(parts[:-1])
    return "/".join([ctx.bin_dir.path, package_path, ctx.attr.name])

# _cg returns a 'codegen context', a struct that's used to accumulate the
# results of code generation. It assumes all output will be rooted in a
# generated importpath (with more 'shortened' importpaths underneath the root),
# and collects outputs to pass to the codegen execution action. It also
# collects a map of importpaths to outputs that make it up.
def _cg(ctx, importpath):
    output_root = _output_directory(ctx)

    return struct(
        # The 'root' importpath, under which 'shortened' importpaths reside.
        importpath = importpath,
        # The prefix into which all files will be emitted. We use the target
        # name for convenience.
        output_prefix = ctx.attr.name,
        # The full relative path visible to the codegen, pointing to the same
        # directory as output_prefix (just from the point of view of the
        # runtime filesystem, not the ctx.actions filepath declaration API).
        output_root = output_root,
        # The list of outputs that have to be generated by the codegen.
        outputs = [],
        # List of files compatible with the `copyout` argument of _gotool_run.
        # Populated by calls to _declare_library. Should be used when the tool
        # generates files within the GOPATH instead of directly at declared
        # output file locations.
        copyout = [],
        # A map of importpath to list of outputs (from the above list) that
        # make up a generated Go package/library.
        libraries = {},
        ctx = ctx,
    )

# _declare_library adds a single Go package/library at importpath to the
# codegen context with the given file paths (rooted in the importpath).
def _declare_library(cg, importpath, files):
    importpath = cg.importpath + "/" + importpath
    cg.libraries[importpath] = []
    for f in files:
        output = cg.ctx.actions.declare_file("{}/{}/{}".format(
            cg.output_prefix,
            importpath,
            f,
        ))
        cg.outputs.append(output)
        cg.libraries[importpath].append(output)
        cg.copyout.append("{}/{}".format(importpath, f))

# _declare_libraries declares multiple Go package/libraries to the codegen
# context. The key of the dictionary is the importpath of the library, and the
# value are the file names of generated outputs.
def _declare_libraries(cg, libraries):
    for k, v in libraries.items():
        _declare_library(cg, k, v)

# _codegen_clientset runs the clientset codegenerator.
def _codegen_clientset(ctx):
    cg = _cg(ctx, ctx.attr.importpath)

    _declare_libraries(cg, {
        "clientset/versioned": ["clientset.go"],
        "clientset/versioned/fake": ["register.go", "clientset_generated.go"],
        "clientset/versioned/scheme": ["register.go", "doc.go"],
    })

    for api, types in ctx.attr.apis.items():
        client_name = api.split("/")[-2]
        _declare_libraries(cg, {
            "clientset/versioned/typed/{}".format(api): [
                "doc.go",
                "generated_expansion.go",
                "{}_client.go".format(client_name),
            ] + [
                "{}.go".format(t)
                for t in types
            ],
            "clientset/versioned/typed/{}/fake".format(api): [
                "doc.go",
                "fake_{}_client.go".format(client_name),
            ],
        })

    _gotool_run(
        cg,
        mnemonic = "ClientsetGen",
        executable = ctx.executable._client_gen,
        arguments = [
            "--clientset-name",
            "versioned",
            "--input-base",
            ctx.attr.apipath,
            "--input",
            ",".join(ctx.attr.apis),
            "--output-pkg",
            cg.importpath + "/clientset",
            "--output-dir",
            cg.output_root + "/" + cg.importpath + "/clientset",
            "--go-header-file",
            ctx.file.boilerplate.path,
        ],
        inputs = [
            ctx.file.boilerplate,
        ],
        outputs = cg.outputs,
    )

    return cg.libraries

# _codegen_deepcopy runs the deepcopy codegenerator (outputting to the apipath,
# not the importpath).
def _codegen_deepcopy(ctx):
    cg = _cg(ctx, ctx.attr.apipath)

    for api, types in ctx.attr.apis.items():
        _declare_libraries(cg, {
            api: ["zz_generated.deepcopy.go"],
        })

    _gotool_run(
        cg,
        copyout = cg.copyout,
        mnemonic = "DeepcopyGen",
        executable = ctx.executable._deepcopy_gen,
        arguments = [
            "--go-header-file",
            ctx.file.boilerplate.path,
            "--stderrthreshold",
            "0",
            "--output-file",
            "zz_generated.deepcopy.go",
        ] + ["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis],
        inputs = [
            ctx.file.boilerplate,
        ],
        outputs = cg.outputs,
    )
    return cg.libraries

# _codegen_informer runs the informer codegenerator.
def _codegen_informer(ctx):
    cg = _cg(ctx, ctx.attr.importpath)

    _declare_libraries(cg, {
        "informers/externalversions": ["factory.go", "generic.go"],
        "informers/externalversions/internalinterfaces": ["factory_interfaces.go"],
    })

    for api, types in ctx.attr.apis.items():
        client_name = api.split("/")[-2]
        _declare_libraries(cg, {
            "informers/externalversions/{}".format(client_name): ["interface.go"],
            "informers/externalversions/{}".format(api): [
                "interface.go",
            ] + [
                "{}.go".format(t)
                for t in types
            ],
        })

    _gotool_run(
        cg,
        mnemonic = "InformerGen",
        executable = ctx.executable._informer_gen,
        arguments = [
            "--versioned-clientset-package",
            "{}/clientset/versioned".format(ctx.attr.importpath),
            "--listers-package",
            "{}/listers".format(ctx.attr.importpath),
            "--output-pkg",
            "{}/informers".format(ctx.attr.importpath),
            "--output-dir",
            cg.output_root + "/" + cg.importpath + "/informers",
            "--go-header-file",
            ctx.file.boilerplate.path,
        ] + ["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis],
        inputs = [
            ctx.file.boilerplate,
        ],
        outputs = cg.outputs,
    )

    return cg.libraries

# _codegen_lister runs the lister codegenerator.
def _codegen_lister(ctx):
    cg = _cg(ctx, ctx.attr.importpath)

    for api, types in ctx.attr.apis.items():
        client_name = api.split("/")[-2]
        _declare_libraries(cg, {
            "listers/{}".format(api): [
                "expansion_generated.go",
            ] + [
                "{}.go".format(t)
                for t in types
            ],
        })

    _gotool_run(
        cg,
        mnemonic = "ListerGen",
        executable = ctx.executable._lister_gen,
        arguments = [
            "--output-pkg",
            "{}/listers".format(ctx.attr.importpath),
            "--output-dir",
            cg.output_root + "/" + cg.importpath + "/listers",
            "--go-header-file",
            ctx.file.boilerplate.path,
            "-v",
            "10",
        ] + ["{}/{}".format(ctx.attr.apipath, api) for api in ctx.attr.apis],
        inputs = [
            ctx.file.boilerplate,
        ],
        outputs = cg.outputs,
    )

    return cg.libraries

# _update_dict_check is a helper function that updates dict a with dict b,
# ensuring there's no overwritten keys.
def _update_dict_check(a, b):
    for k in b.keys():
        if k in a:
            fail("internal error: repeat importpath {}", k)
    a.update(b)

def _go_kubernetes_resource_bundle_impl(ctx):
    go = go_context(ctx)

    all_gens = {}
    _update_dict_check(all_gens, _codegen_clientset(ctx))
    _update_dict_check(all_gens, _codegen_deepcopy(ctx))
    _update_dict_check(all_gens, _codegen_informer(ctx))
    _update_dict_check(all_gens, _codegen_lister(ctx))

    libraries = []
    for importpath, srcs in all_gens.items():
        library = go.new_library(
            go,
            srcs = srcs,
            importpath = importpath,
        )
        libraries.append(library)

    return [KubeResourceBundle(libraries = libraries)]

# go_kubernetes_resource_bundle runs kubernetes code-generators on a codepath
# for some requested APIs, and whose output can be made into Go library targets
# via go_kubernetes_library. This bundle corresponds to a single Kubernetes API
# resource group.
go_kubernetes_resource_bundle = rule(
    implementation = _go_kubernetes_resource_bundle_impl,
    attrs = {
        "gopath": attr.label(
            mandatory = True,
            providers = [GoPath],
            cfg = preprocessing_transition,
            doc = "A rules_go go_path that contains all the API libraries for which codegen should be run.",
        ),
        "importpath": attr.string(
            mandatory = True,
            doc = """
                The root importpath of the generated code (apart from deepcopy
                codegen). The Bazel target path corresponding to this
                importpath needs to contain the go_kubernetes_library and
                go_library targets that allow to actually build against the
                generated code.
            """,
        ),
        "apipath": attr.string(
            mandatory = True,
            doc = "The root importpath of the APIs for which to generate code.",
        ),
        "apis": attr.string_list_dict(
            mandatory = True,
            doc = """
                The APIs underneath importpath for which to generated code,
                eg. foo/v1, mapping into a list of lowercased types generated
                from each (eg. widget for `type Widget struct`).
            """,
        ),
        "boilerplate": attr.label(
            default = "//metropolis/build/kube-code-generator:boilerplate.go.txt",
            allow_single_file = True,
            doc = "Header that will be used in the generated code.",
        ),
        "_go_context_data": attr.label(
            default = "@io_bazel_rules_go//:go_context_data",
        ),
        "_gotoolwrap": attr.label(
            default = Label("//metropolis/build/gotoolwrap"),
            allow_single_file = True,
            executable = True,
            cfg = "exec",
        ),
        "_deepcopy_gen": attr.label(
            default = Label("@io_k8s_code_generator//cmd/deepcopy-gen"),
            allow_single_file = True,
            executable = True,
            cfg = "exec",
        ),
        "_client_gen": attr.label(
            default = Label("@io_k8s_code_generator//cmd/client-gen"),
            allow_single_file = True,
            executable = True,
            cfg = "exec",
        ),
        "_informer_gen": attr.label(
            default = Label("@io_k8s_code_generator//cmd/informer-gen"),
            allow_single_file = True,
            executable = True,
            cfg = "exec",
        ),
        "_lister_gen": attr.label(
            default = Label("@io_k8s_code_generator//cmd/lister-gen"),
            allow_single_file = True,
            executable = True,
            cfg = "exec",
        ),
        "_allowlist_function_transition": attr.label(
            default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
        ),
    },
    toolchains = ["@io_bazel_rules_go//go:toolchain"],
)