Roughly,

Initial

• create origin for that svn url
• svn checkout url@1 (anonymous checkout)
• iterate logs over revisions from start to HEAD
  • checkout svn revision
  • compute sha1 contents and directories and upper directory sha1
  • create swh revision for that svn revision
• create occurrence targetting the last revision (with reference to svn one in metadata)
• send all data for storage in swh-storage.

Update

• check occurrence existence for the origin
• occurrence does not exist, deal same as Initial import and stop.
• Retrieve last seen svn revision
• Checkout that revision, compute that revision's swh revision checksum
• Compare those, if mismatch, stop since the history has been altered.
• Otherwise iterate over logs from svn revision to head, and compute checksums and send for storage (the same as previous step in initial import).