from pathlib import PurePath
from typing import Set


class MarkDuplicateError(Exception):
    """
    Tried to mark a file that was already marked.
    """

    def __init__(self, path: PurePath):
        super().__init__(f"A previous file already used path {path}")
        self.path = path


class MarkConflictError(Exception):
    """
    Marking the path would have caused a conflict.

    A conflict can have two reasons: Either the new file has the same path as
    the parent directory of a known file, or a parent directory of the new file
    has the same path as a known file. In either case, adding the new file
    would require a file and a directory to share the same path, which is
    usually not possible.
    """

    def __init__(self, path: PurePath, collides_with: PurePath):
        super().__init__(f"File at {path} collides with previous file at {collides_with}")
        self.path = path
        self.collides_with = collides_with


# TODO Use PurePath.is_relative_to when updating to 3.9
def is_relative_to(a: PurePath, b: PurePath) -> bool:
    try:
        a.relative_to(b)
        return True
    except ValueError:
        return False


class Report:
    """
    A report of a synchronization. Includes all files found by the crawler, as
    well as the set of changes made to local files.
    """

    def __init__(self) -> None:
        self.reserved_files: Set[PurePath] = set()
        self.known_files: Set[PurePath] = set()

        self.new_files: Set[PurePath] = set()
        self.changed_files: Set[PurePath] = set()
        self.deleted_files: Set[PurePath] = set()

    def mark_reserved(self, path: PurePath) -> None:
        self.reserved_files.add(path)

    def mark(self, path: PurePath) -> None:
        """
        Mark a previously unknown file as known.

        May throw a MarkDuplicateError or a MarkConflictError. For more detail,
        see the respective exception's docstring.
        """

        for other in self.marked:
            if path == other:
                raise MarkDuplicateError(path)

            if is_relative_to(path, other) or is_relative_to(other, path):
                raise MarkConflictError(path, other)

        self.known_files.add(path)

    @property
    def marked(self) -> Set[PurePath]:
        return self.known_files | self.reserved_files

    def is_marked(self, path: PurePath) -> bool:
        return path in self.marked

    def add_file(self, path: PurePath) -> None:
        """
        Unlike mark(), this function accepts any paths.
        """

        self.new_files.add(path)

    def change_file(self, path: PurePath) -> None:
        """
        Unlike mark(), this function accepts any paths.
        """

        self.changed_files.add(path)

    def delete_file(self, path: PurePath) -> None:
        """
        Unlike mark(), this function accepts any paths.
        """

        self.deleted_files.add(path)