import os


class DependencyResolutionError(Exception):
    pass


class DependencyItem:
    def __init__(self):
        self.__target = None
        self.__dep_list = None


    def name(self):
        return None


    def target(self):
        return self.__target


    def dependencies(self):
        return None


    def dependency_list(self):
        return self.__dep_list


    def publish(self):
        return None


    def reset_resolution(self):
        self.__dep_list = None


    def resolve(self, **kwargs):
        if self.__dep_list is not None:
            return self.__dep_list

        ctx = None
        dep_list = None
        if 'ctx' in kwargs:
            ctx = kwargs['ctx']
        else:
            ctx = {}

        if 'dep_list' in kwargs:
            dep_list = kwargs['dep_list']
        else:
            dep_list = []

        if self.name() in ctx:
            return

        ctx[self.name()] = self

        deps = self.dependencies()
        if deps is None:
            return

        for d in deps.values():
            d_value = d.resolve_self()
            if d_value is not None:
                d_value.resolve(ctx=ctx, dep_list=dep_list)

        dep_list.append(self)
        return dep_list


class Dependency:
    def __init__(self, parent):
        self.__parent = parent


    def name(self, parent):
        return None


    def parent_name(self):
        return self.__parent


    def resolve_self(self):
        return None


    def is_resolved(self):
        return False


class SeedDependency(Dependency):
    def __init__(self, **kwargs):
        self.__target_seed = None
        if 'name' in kwargs:
            self.__name = kwargs['name']
        if 'parent' in kwargs:
            super().__init__(kwargs['parent'])


    def name(self):
        return self.__name


    def target(self):
        return self.__target_seed


    def resolve_self(self):
        from seed import Seed
        if self.__target_seed is not None:
            return self.__target_seed

        target = Seed.get(self.__name)
        if target is None:
            raise DependencyResolutionError(
                    '{} depends on seed "{}", but the required seed cannot be found'.format(self.parent_name(), self.__name))

        self.__target_seed = target
        return self.__target_seed


    def is_resolved(self):
        return self.__target_seed is not None


class ProgramDependency(Dependency):
    def __init__(self, **kwargs):
        if 'name' in kwargs:
            self.__name = kwargs['name']
        if 'parent' in kwargs:
            super().__init__(kwargs['parent'])


    def __is_exe(self, fpath):
        return os.path.isfile(fpath) and os.access(fpath, os.X_OK)


    def name(self):
        return self.__name


    def resolve_self(self):
        if self.__is_exe(self.__name):
            return None

        path_string = os.environ['PATH']
        path_list = path_string.split(':')
        for d in path_list:
            exe_path = os.path.join(d, self.__name)
            if self.__is_exe(exe_path):
                return None

        raise DependencyResolutionError(f'{self.parent_name()} depends on command `{self.__name}`, but the command cannot be found. Make sure that the named command exists, the containing directory is in $PATH if necessary, and the executable file has the correct permissions.')