# Copyright 2015 MongoDB Inc.
#
# 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.

import json
import SCons
import itertools

# Implements the ability for SCons to emit a compilation database for the MongoDB project. See
# http://clang.llvm.org/docs/JSONCompilationDatabase.html for details on what a compilation
# database is, and why you might want one. The only user visible entry point here is
# 'env.CompilationDatabase'. This method takes an optional 'target' to name the file that
# should hold the compilation database, otherwise, the file defaults to compile_commands.json,
# which is the name that most clang tools search for by default.

# TODO: Is there a better way to do this than this global? Right now this exists so that the
# emitter we add can record all of the things it emits, so that the scanner for the top level
# compilation database can access the complete list, and also so that the writer has easy
# access to write all of the files. But it seems clunky. How can the emitter and the scanner
# communicate more gracefully?
__COMPILATION_DB_ENTRIES=[]

# Cribbed from Tool/cc.py and Tool/c++.py. It would be better if
# we could obtain this from SCons.
_CSuffixes = ['.c']
if not SCons.Util.case_sensitive_suffixes('.c', '.C'):
    _CSuffixes.append('.C')

_CXXSuffixes = ['.cpp', '.cc', '.cxx', '.c++', '.C++']
if SCons.Util.case_sensitive_suffixes('.c', '.C'):
    _CXXSuffixes.append('.C')

# We make no effort to avoid rebuilding the entries. Someday, perhaps we could and even
# integrate with the cache, but there doesn't seem to be much call for it.
class __CompilationDbNode(SCons.Node.Python.Value):
    def __init__(self, value):
        SCons.Node.Python.Value.__init__(self, value)
        self.Decider(changed_since_last_build_node)


def changed_since_last_build_node(node, target, prev_ni, repo_node=None):
    """ Dummy decider to force always building"""
    return True


def makeEmitCompilationDbEntry(comstr):
    """
    Effectively this creates a lambda function to capture:
    * command line
    * source
    * target
    :param comstr: unevaluated command line
    :return: an emitter which has captured the above
    """
    user_action = SCons.Action.Action(comstr)

    def EmitCompilationDbEntry(target, source, env):
        """
        This emitter will be added to each c/c++ object build to capture the info needed
        for clang tools
        :param target: target node(s)
        :param source: source node(s)
        :param env: Environment for use building this node
        :return: target(s), source(s)
        """

        dbtarget = __CompilationDbNode(source)

        entry = env.__COMPILATIONDB_Entry(
            target=dbtarget,
            source=[],
            __COMPILATIONDB_UTARGET=target,
            __COMPILATIONDB_USOURCE=source,
            __COMPILATIONDB_UACTION=user_action,
            __COMPILATIONDB_ENV=env)

        # TODO: Technically, these next two lines should not be required: it should be fine to
        # cache the entries. However, they don't seem to update properly. Since they are quick
        # to re-generate disable caching and sidestep this problem.
        env.AlwaysBuild(entry)
        env.NoCache(entry)

        __COMPILATION_DB_ENTRIES.append(dbtarget)

        return target, source

    return EmitCompilationDbEntry


def CompilationDbEntryAction(target, source, env, **kw):
    """
    Create a dictionary with evaluated command line, target, source
    and store that info as an attribute on the target
    (Which has been stored in __COMPILATION_DB_ENTRIES array
    :param target: target node(s)
    :param source: source node(s)
    :param env: Environment for use building this node
    :param kw:
    :return: None
    """

    command = env['__COMPILATIONDB_UACTION'].strfunction(
        target=env['__COMPILATIONDB_UTARGET'],
        source=env['__COMPILATIONDB_USOURCE'],
        env=env['__COMPILATIONDB_ENV'],)

    entry = {
        "directory": env.Dir('#').abspath,
        "command": command,
        "file": str(env['__COMPILATIONDB_USOURCE'][0])
    }

    target[0].write(entry)


def WriteCompilationDb(target, source, env):
    entries = []

    for s in __COMPILATION_DB_ENTRIES:
        entries.append(s.read())

    with open(str(target[0]), 'w') as target_file:
        json.dump(entries, target_file,
                  sort_keys=True,
                  indent=4,
                  separators=(',', ': '))


def ScanCompilationDb(node, env, path):
    return __COMPILATION_DB_ENTRIES

def generate(env, **kwargs):

    static_obj, shared_obj = SCons.Tool.createObjBuilders(env)

    env['COMPILATIONDB_COMSTR'] = kwargs.get(
        'COMPILATIONDB_COMSTR', 'Building compilation database $TARGET')

    components_by_suffix = itertools.chain(
        itertools.product(_CSuffixes, [
            (static_obj, SCons.Defaults.StaticObjectEmitter, '$CCCOM'),
            (shared_obj, SCons.Defaults.SharedObjectEmitter, '$SHCCCOM'),
        ]),
        itertools.product(_CXXSuffixes, [
            (static_obj, SCons.Defaults.StaticObjectEmitter, '$CXXCOM'),
            (shared_obj, SCons.Defaults.SharedObjectEmitter, '$SHCXXCOM'),
        ]),
    )

    for entry in components_by_suffix:
        suffix = entry[0]
        builder, base_emitter, command = entry[1]

        # Assumes a dictionary emitter
        emitter = builder.emitter[suffix]
        builder.emitter[suffix] = SCons.Builder.ListEmitter(
            [
                emitter,
                makeEmitCompilationDbEntry(command),
            ]
        )

    env['BUILDERS']['__COMPILATIONDB_Entry'] = SCons.Builder.Builder(
        action=SCons.Action.Action(CompilationDbEntryAction, None),
    )

    env['BUILDERS']['__COMPILATIONDB_Database'] = SCons.Builder.Builder(
        action=SCons.Action.Action(WriteCompilationDb, "$COMPILATIONDB_COMSTR"),
        target_scanner=SCons.Scanner.Scanner(
            function=ScanCompilationDb,
            node_class=None)
    )

    def CompilationDatabase(env, target):
        result = env.__COMPILATIONDB_Database(
            target=target,
            source=[])

        env.AlwaysBuild(result)
        env.NoCache(result)

        return result

    env.AddMethod(CompilationDatabase, 'CompilationDatabase')

def exists(env):
    return True