(yet another) modify git history to add a very first commit

I am modifying someone else's (non-git) code. I downloaded the original, ensued my modifications, and jumped the gun and made the modified version my first commit. This was a mistake, I should have added the original downloaded code as my first commit.


Then to add insult to injury, I added the original code as a branch off of my first edit.. In other words it is a big mess now :(


In simple terms, what I have looks like the blue graph below. C5 is the actual original code, C1,C2-C6 are my gradual modifications (C4 is redundant). I'd rather have the green be my history.





Any ideas how to modify history to accomplish this?


Thanks many,


sly

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Answer:

I have done this completely at the command-line, but am going to insert screenshots from SourceTree to illustrate what's going on.

First get the first 7 or 8 digits of commit id (50da9c3) from the C5 commit and put in on your clipboard or in textedit or something - you'll need it later

For confirmation, Here is our starting state:

Here are the steps to get where you want:

Create a new non-rooted branch to start building commits off of named base

git symbolic-ref HEAD refs/heads/base

Now remove all files and directories from git

git rm --cached -r .

Now that all the files are 'untracked' remove them from the local working directory

git clean -d --force

Now create a commit with nothing in it (this will be the commit on which everything else will be built).

git commit --allow-empty -m'Initial Commit'

Your tree should look like this now:

Now cherry pick the c5 commit (what you had on the clipboard)

git cherry-pick 50da9c3

Now re-root the master branch on to the base branch

git rebase --onto base --root master

Now you can delete the base and c4-c5 branches

git branch -d base

git branch -D c4-c5branch

Keep in mind the the 'Initial Commit' is an empty commit with no files, so don't be fooled. The C5 commit is actually the first content based commit.