from datetime import datetime
from .elements import SRef
from .reader import ProgressGetter

class Library(object):
    def __init__(self):
        self.version = 0
        self.name = "NONAME"

        self.last_access = datetime.now()
        self.last_mod    = datetime.now()

        # unit setup
        self.units_per_dbunit = 1
        self.meters_per_unit  = 1

        self.structures = {}

    class LinkError(Exception):
        element = None
        pass

    def link_refs(self, progress_callback=None):
        class Progress(ProgressGetter):
            total   = 0
            current = 0

            def __init__(self, lib):
                for key, value in lib.structures.items():
                    self.total += len(value.references)

            def progress(self):
                return float(self.current) / self.total

            def inc(self):
                self.current += 1

        count = Progress(self)

        for key, value in self.structures.items():
            for element in value.references:             
                if isinstance(element.structure, str):
                    # try to resolve link
                    try:
                        ref = self.structures[element.structure]
                        element.structure = ref
                    except KeyError:
                        err = LinkError("dangeling sref (structure {} is not defined in library)".format(element.structure))
                        err.element = element

                        raise err

                count.inc()

                if progress_callback:
                    progress_callback(count)