Duplicate downloading checking + fix startFromOffset

[treetrum]

Changes:

• Adds a simple check to see if a book has already been downloaded (by checking the local files existence + filesize) and if its already downloaded will abort the request to save time on reruns of the tool
• Fixes the behaviour of startFromOffset by offsetting the list of books we fetch instead of offsetting the individual book downloads
• Adds a new flag --duplicateHandling with options for either skip or overwrite to control the duplicate download check
• Updates the default for --totalDownloads to be Infinity
• Downloaded file names now include the unique amazon indentifier (ASIN) to hopefully prevent issues where different editions of the same book were being overwritten when they shared a file name. Should address Duplicate Books Handling #185 and Missing failed download message? Counts don't add up. #186

[HamsterExAstris]

Good news: the duplicate downloading checking appears to be working great.

Bad news: The startFromOffset changes appear to have broken something else. Where previously it found all ~2200-ish books in my account with no pagination parameters (just --baseUrl), it's now only finding 200 and then stopping.

| Found 200 books in total

[jsonbecker]

Can confirm the same-- the skipping of existing downloads work, the offset fix does not. Checking out e16378c alone was a huge improvement, so I wonder if it's worth reverting the offset fix into it's own PR.

[treetrum]

Thanks for the reports! I think I will split off the offset fix into its own PR then.

[treetrum]

I think I found the culprit of only downloading 200 books. Was a simple fix so will keep in this PR for now. @jsonbecker / @HamsterExAstris I would really appreciate if either of you could pull the latest and retest before I merge this?

[jsonbecker]

I didn't actually redownload, but it does appear to find the full count of books now and (and didn't download them because I have them).

[HamsterExAstris]

Can confirm the current version in the branch fixes the 200 book limit.

It looks like the duplicate handling is working too. I didn't think it was at first, but that's because the file names changed to append ASIN. I think that's a good idea because it fixes other issues reported when a user has multiple books with the same title; but it might cause some confusion over why duplicates aren't being skipped.

[warriordog]

The latest version works for me. Was able to download 3800 books with only 63 failures.