# Development

This page describes the protocol adopted for the AMDC firmware code development.

The AMDC firmware code base uses: [git](https://git-scm.com/) for version control; [semantic versioning](https://semver.org/) for release labeling.

```{tip}
Read about **semantic versioning** on the main **[semver.org](https://semver.org/)** website.
This greatly helps to explain the concepts below.
```

## Branches in git

```{image} images/amdc-git-branch-flow.svg
:width: 100%
```

All development intended to impact a future release is done on topic branches from the latest `develop` branch.
This applies to bug fixes, feature additions, and/or major changes.
The `develop` branch is **not stable** -- the latest commits to `develop` might yield unstable code which is still in testing.

Regular open-source development practice is followed -- pull requests (PRs) are used to review new code and then eventually are merged into `develop`.

- Merges into `develop` should use `Squash and Merge` via GitHub's online interface.
- Merges into release branches should use the simple `Merge` commit via GitHub's online interface.

Each PR should be small enough to reasonably review -- if a PR has too many files changed or covers too large of scope, the developer will be asked to reduce the PR size by creating multiple smaller PRs.

## Releases

Per semantic versioning, there are three types of releases:

1. Major
2. Minor
3. Bug fix

To create a release, a snapshot of the code is taken and labeled as: `vA.B.C` where `A` denotes the *major* release number, `B` denotes the *minor* number, and `C` denotes the *bug fix* number. For example, a release might be called `v1.0.0` or `v1.5.12`.

A so-called **release branch** refers to a labeled major and minor release, but unspecified bug fix.
The naming pattern is: `vA.B.x` where `A` and `B` are numbers and `x` denotes any bug fix number.
For example, the initial release branch is called `v1.0.x`.

### Procedure

```{tip}
Refer to the diagram above for a graphical representation of how the git branching should work.
```

The procedure for creating a new release is mostly common for all three types (major, minor, bug fix):

1. Update code via topic branches which are based on `develop` and merge updates into `develop`
2. Ensure development has stablized on the `develop` branch
3. Ensure thorough testing of the latest `develop` branch code
4. Create a final commit to `develop` where the `./CHANGELOG.md` file is updated with documentation about the new release

Now, depending on which type of release, the procedure differs:

#### Bug Fix

For a new bug fix release, a release branch should already exist.
To publish the bug fix, simply merge the bug fix from `develop` into the appropriate release branches.
This should be done via a PR on GitHub and the PR should perform a regular merge commit, not a `Squash + Merge`.

```{attention}
You might need to merge the bug fix into multiple release branches, depending on how widespread the bug is.

Always merge in one direction, from `develop` to the release branches.
```

Occasionally, a bug might need to be fixed in a previous release branch, but does not exist in the latest `develop` branch.
In this case, do not change `develop` -- simply fix the bug where it needs to be fixed.
This is depicted in the above diagram as the `hotfix1` branch.

#### Minor or Major

For a new minor or major release, a new release branch needs to be created.

1. Create a new release branch from `develop` and call it `vA.B.x`
2. Update GitHub's default repo branch to be the latest release branch which was just created
3. Update the documentation website to reflect the minor or major (breaking) changes

### Tag and Release

After following the above steps, the release branch(es) will hold the latest stable code release.
Users which checkout the release branch will have access to the code.

To complete the release, git tag(s) need to be created and GitHub release(s) need to be created.

1. Create git tag(s) pointing to the merge commit(s) on the release branch(es). If the new code was only merged to one release branch, only one tag will be created. However, if a bug fix was merged to multiple release branches, then the appropriate version number should be used to tag each merge commit.
2. For each new git tag, create a GitHub Release with the same name as the tag and include a description of the changes per the changelog contents.