import binascii
import copy

import pygit2
from pygit2.enums import ObjectType

import gitubuntu.importer
from gitubuntu.source_builder import Source, SourceSpec
import gitubuntu.spec


"""Build test git repositories as data structures

Represent a git repository as a data structure, nesting using Tree objects as
required. Name objects in a flat namespace using the name keyword object to
these constructors.

Use a SourceTree object to get something that behaves like a Tree but is
actually the exact source of a full, unpacked source package described using
source_builder.Source. As source_builder.Source is slow, however, using a Tree
directly is preferred when the behaviour under test does not need a complete
source tree.

Reference the same object with a Placeholder giving the name of the target to
its constructor. This allows a build in a single data structure instead of
having to use multiple statements to grab references to other parts of the same
structure.

Use a Commit object to represent a git commit (constructed with a Tree object
to represent the git tree contained within it), and a Repo object to
contain and create multiple commits as needed, including ones that reference
each other using Placeholder objects.

Write any object (including any children as necessary) using the write method,
which takes a single pygit2.Repository parameter. This returns the pygit2.Oid
of the top level written object.

Objects must be treated as immutable. The result of mutating an object after it has been constructed is undefined.
"""


__all__ = [
    'Blob',
    'Commit',
    'Repo',
    'ExecutableBlob',
    'SourceTree',
    'Symlink',
    'Placeholder',
    'Tree',
]

# General notes

# Sometimes tests need to check an object hash matches something in a supplied
# builder repo tree. In this case, it seems redundant and messy to have to
# write that object again to get its hash. Perhaps objects should cache their
# hashes or something?


DEFAULT_AUTHOR_SIGNATURE = pygit2.Signature(
    # Match the default from source_builder.CHANGELOG_TEMPLATE
    name='git ubuntu',
    email='ubuntu-distributed-devel@lists.ubuntu.com',
    time=0,  # don't default to current time for hash reproducibility
    offset=0,
)

DEFAULT_COMMITTER_SIGNATURE = pygit2.Signature(
    name=gitubuntu.spec.SYNTHESIZED_COMMITTER_NAME,
    email=gitubuntu.spec.SYNTHESIZED_COMMITTER_EMAIL,
    time=0,
    offset=0,
)


class NamedMixin:
    def __init__(self, name=None):
        self.name = name


class WriteMixin:
    def write(self, repo, record=None):
        record = record or dict()
        try:
            return record[self]
        except KeyError:
            record[self] = self._obj_to_oid(repo, record)
            return record[self]


class Placeholder:
    def __init__(self, target_name):
        self.target_name = target_name

    def walk(self, parent=None):
        yield parent, self


class Blob(NamedMixin, WriteMixin):
    GIT_TREE_ATTR = pygit2.GIT_FILEMODE_BLOB

    def __init__(self, content, **kwargs):
        """Construct a Blob

        @param content: a bytes object of the desired blob contents
        """
        super().__init__(**kwargs)
        self.content = content

    def walk(self, parent=None):
        yield parent, self

    def _obj_to_oid(self, repo, record):
        return repo.create_blob(self.content)


class ExecutableBlob(Blob):
    GIT_TREE_ATTR = pygit2.GIT_FILEMODE_BLOB_EXECUTABLE


class Symlink(NamedMixin, WriteMixin):
    GIT_TREE_ATTR = pygit2.GIT_FILEMODE_LINK

    def __init__(self, target, **kwargs):
        """Construct a symlink

        @param target: a bytes object containing the target

        target is not interpreted; it is exactly equivalent to the first
        parameter to ln(1).
        """
        super().__init__(**kwargs)
        self.target = target

    def walk(self, parent=None):
        yield parent, self

    def _obj_to_oid(self, repo, record):
        return repo.create_blob(self.target)


class Tree(NamedMixin, WriteMixin):
    GIT_TREE_ATTR = pygit2.GIT_FILEMODE_TREE

    def __init__(self, entries, **kwargs):
        """Construct a tree

        A tree is equivalent to a directory and contains zero or more entries

        @param entries: a dictionary whose values are other objects from this
                        module
        """
        super().__init__(**kwargs)
        self.entries = entries

    def replace(self, old, new):
        # XXX inefficient
        for name, entry in self.entries.items():
            if entry is old:
                self.entries[name] = new
                return
        raise KeyError("Cannot find %r in entries" % old)

    def walk(self, parent=None):
        for entry in self.entries.values():
            yield from entry.walk(parent=self)
        yield parent, self

    def _obj_to_oid(self, repo, record):
        tree_builder = repo.TreeBuilder()
        for name, entry in self.entries.items():
            tree_builder.insert(
                name,  # name
                entry.write(repo, record=record),  # oid
                entry.GIT_TREE_ATTR,  # attr
            )
        return tree_builder.write()


class SourceTree(NamedMixin, WriteMixin):
    def __init__(self, source, patches_applied=False, **kwargs):
        """Construct a git tree representation of a source_builder.Source

        :param source_tree.SourceBuilder source: the source whose git tree this
            object will represent
        :param patches_applied bool: whether patches should be applied
            in this source tree
        """
        super().__init__(**kwargs)
        self.source = source
        self.patches_applied = patches_applied

    def walk(self, parent=None):
        yield parent, self

    def _obj_to_oid(self, repo, record):
        with self.source as dsc_path:
            oid_str = gitubuntu.importer.dsc_to_tree_hash(
                repo,
                dsc_path,
                self.patches_applied,
            )
        return pygit2.Oid(binascii.unhexlify(oid_str))


class _Signature:
    """Wrapper around pygit2.Signature

    pygit2.Signature doesn't support copy.deepcopy(), which we expect to work
    for Repo and Commit objects. So provide a wrapper that Repo and Commit
    objects can use to store pygit2.Signature objects that can be deep-copied.
    """
    def __init__(self, signature):
        self.signature = signature

    @classmethod
    def from_pygit2_signature(cls, other):
        return cls(other)

    def __deepcopy__(self, memo):
        return type(self)(pygit2.Signature(
            name=self.signature.name,
            email=self.signature.email,
            time=self.signature.time,
            offset=self.signature.offset,
        ))


class Commit(NamedMixin, WriteMixin):
    def __init__(
        self,
        tree=None,
        parents=None,
        message=None,
        author=DEFAULT_AUTHOR_SIGNATURE,
        committer=DEFAULT_COMMITTER_SIGNATURE,
        **kwargs,
    ):
        """Construct a Commit object

        :param Tree tree: the tree contained by the commit. If None, an empty
            tree is used.
        :param list(Commit) parents: the commit objects that are the parents of
            this commit. The list may be empty if the commit is to have no
            parent.
        :param str message: the commit message.
        :param pygit2.Signature author: use this author for the commit
        :param pygit2.Signature committer: use this committer for the commit
        :param **kwargs: other parameters supplied to superclasses.
        """
        super().__init__(**kwargs)
        self.tree = tree or Tree({})
        self.parents = parents or []
        self.message = 'Test commit' if message is None else message
        self.author = _Signature.from_pygit2_signature(author)
        self.committer = _Signature.from_pygit2_signature(committer)

    @classmethod
    def from_spec(
        cls,
        parents=None,
        message=None,
        name=None,
        patches_applied=False,
        **kwargs,
    ):
        """Construct a Commit object containing a test source package

        :param list(Commit) parents: the commit objects that are the parents of
            this commit. The list may be empty if the commit is to have no
            parent.
        :param str message: the commit message.
        :param str name: the value for the name attribute of the constructed
            object, used for matching with Placeholder objects after
            construction.
        :param bool patches_applied: whether the tree inside the commit should
            have patches applied. Passed to the SourceTree constructor. If
            True, then the test source package is generated with patches using
            the has_patches argument to the SourceSpec constructor, unless
            overridden by kwargs.
        :param **kwargs: additional parameters are passed to the SourceSpec
            constructor to customise the test source package used for the tree
            of the commit.
        """
        spec_args = {'has_patches': patches_applied}
        spec_args.update(kwargs)

        return cls(
            tree=SourceTree(
                Source(SourceSpec(**spec_args)),
                patches_applied=patches_applied,
            ),
            parents=parents,
            message=message,
            name=name,
        )

    def replace(self, old, new):
        for i, parent in enumerate(self.parents):
            if parent is old:
                self.parents[i] = new
                return
        raise KeyError("Cannot find %r in parents" % old)

    def walk(self, parent=None):
        for commit_parent in self.parents:
            yield from commit_parent.walk(parent=self)
        yield from self.tree.walk(parent=self)
        yield parent, self

    def _obj_to_oid(self, repo, record=None):
        return repo.create_commit(
            None,
            self.author.signature,
            self.committer.signature,
            self.message,
            self.tree.write(repo),
            [parent.write(repo, record=record) for parent in self.parents],
        )


class Repo:
    """Represent a graph of commits

    We keep the commits as a list, but understand that they may relate to each
    other using parenting relationships.

    We keep the branches and tags as dictionaries of str names to either
    Commit objects or placeholder strings.

    This is affectively a commit container that exists for the
    convenience of writing them to a git repository at once.
    """
    def __init__(
        self,
        commits=None,
        branches=None,
        tags=None,
        tagger=DEFAULT_COMMITTER_SIGNATURE,
    ):
        """Construct a Repo instance

        :param list(Commit) commits: the commits this Repo should
            contain. These may be related to each other with parenting
            relationships, but do not have to be.
        :param dict(str: Commit or Placeholder) branches: the branches
            this Repo should contain. A branch has a name and a target
            to point to. The target can be a Commit object or
            Placeholder object.
        :param dict(str: Commit or Placeholder) tags: the tags this Repo
            should contain. A tag has a name and a target to point to.
            The target can be a Commit object or Placeholder object.
        :param pygit2.Signature tagger: if specified, use this instead of
            DEFAULT_COMMITTER_SIGNATURE as the tagger of any tags.
        """
        self.commit_list = commits or list()
        self.branches = branches or dict()
        self.tags = tags or dict()
        self.tagger = _Signature.from_pygit2_signature(tagger)

    def replace(self, old, new):
        for name, target in self.branches.items():
            if target is old:
                self.branches[name] = new
                return
        for name, target in self.tags.items():
            if target is old:
                self.tags[name] = new
                return
        raise KeyError("Cannot find %r in tags or branches" % old)

    def write(self, repo, record=None):
        replace_placeholders(self)
        record = record or dict()
        written_commits = [
            commit.write(repo=repo, record=record)
            for commit
            in self.commit_list
        ]
        for name, target in self.branches.items():
            repo.create_branch(
                name,
                repo.get(target.write(repo)).peel(pygit2.Commit),
            )
        for name, target in self.tags.items():
            repo.create_tag(
                name,
                target.write(repo),
                ObjectType.COMMIT,
                self.tagger.signature,
                'Tag message',
            )
        return written_commits[0] if written_commits else None

    def walk(self):
        for commit in self.commit_list:
            yield from commit.walk(parent=self)
        for _, branch in self.branches.items():
            yield self, branch
        for _, tag in self.tags.items():
            yield self, tag

    def copy(self, add_commits=None, update_branches=None, update_tags=None):
        """Clone the Repo, optionally with some changes

        :param list(Commit) add_commits: commits to add to the cloned Repo
        :param dict(str: Commit or Placeholder) branches: branches to update in
            the cloned Repo.
        :param dict(str: Commit or Placeholder) tags: tags to update in the
            cloned Repo.

        "update" is in the sense of a dict object's update method: this allows
        for both the definition of new branches and tags, and updates to
        existing branches and tags.

        There is currently no facility to delete branches or tags.
        """
        new_repo = copy.deepcopy(self)
        if add_commits:
            new_repo.commit_list.extend(add_commits)
        if update_branches:
            new_repo.branches.update(update_branches)
        if update_tags:
            new_repo.tags.update(update_tags)
        return new_repo


def find_node(top, name):
    for parent, obj in top.walk():
        if isinstance(obj, NamedMixin):
            if obj.name == name:
                return obj
    raise KeyError("Object named %r not found" % name)


def replace_placeholders(top):
    """
    Walk @top replacing Placeholder objects with the object specified by
    the Placeholder's target_name.

    Raises KeyError if a Placeholder's target_name cannot be found under
    @top
    """

    for parent, obj in top.walk():
        if isinstance(obj, Placeholder):
            parent.replace(obj, find_node(top, obj.target_name))