import os

from hashlib import sha1
from uuid import uuid4

from lakesuperior.store_layouts.non_rdf.base_non_rdf_layout import \
        BaseNonRdfLayout

class DefaultLayout(BaseNonRdfLayout):
    '''
    This is momentarily a stub until more non-RDF layouts use cases are
    gathered.
    '''

    ## INTERFACE METHODS ##

    def persist(self, stream, bufsize=8192):
        '''
        Store the stream in the file system.

        This method handles the file in chunks. for each chunk it writes to a
        temp file and adds to a checksum. Once the whole file is written out
        to disk and hashed, the temp file is moved to its final location which
        is determined by the hash value.

        @param stream (IOstream): file-like object to persist.
        @param bufsize (int) Chunk size. 2**12 to 2**15 is a good range.
        '''
        tmp_file = '{}/tmp/{}'.format(self.root, uuid4())
        try:
            with open(tmp_file, 'wb') as f:
                self._logger.debug('Writing temp file to {}.'.format(tmp_file))

                hash = sha1()
                while True:
                    buf = stream.read(bufsize)
                    if not buf:
                        break
                    hash.update(buf)
                    f.write(buf)
        except:
            self._logger.exception('File write failed on {}.'.format(tmp_file))
            os.unlink(tmp_file)
            raise

        # Move temp file to final destination.
        uuid = hash.hexdigest()
        dst = self.local_path(uuid)
        self._logger.debug('Saving file to disk: {}'.format(dst))
        if not os.access(os.path.dirname(dst), os.X_OK):
            os.makedirs(os.path.dirname(dst))

        # If the file exists already, don't bother rewriting it.
        if os.path.exists(dst):
            self._logger.info(
                    'File exists on {}. Not overwriting.'.format(dst))
            os.unlink(tmp_file)
        else:
            os.rename(tmp_file, dst)

        return uuid


    def delete(self, uuid):
        '''
        See BaseNonRdfLayout.delete.
        '''
        os.unlink(self.local_path(uuid))


    ## PROTECTED METHODS ##

    def local_path(self, uuid):
        '''
        Generate the resource path splitting the resource checksum according to
        configuration parameters.

        @param uuid (string) The resource UUID. This corresponds to the content
        checksum.
        '''
        self._logger.debug('Generating path from uuid: {}'.format(uuid))
        bl = self._conf['pairtree_branch_length']
        bc = self._conf['pairtree_branches']
        term = len(uuid) if bc==0 else min(bc*bl, len(uuid))

        path = [ uuid[i:i+bl] for i in range(0, term, bl) ]

        if bc > 0:
            path.append(uuid[term:])
        path.insert(0, self.root)

        return '/'.join(path)