ahab/README.md

# ahab

A wrapper around `docker compose` for our dockerized django projects, so the
same commands work in every repository.

## installing

You will need rust installed. Clone repo and run:
```bash
cargo install --path .
```

## what it makes of a project

`ahab status` prints the services it picked, the containers behind them, the
credentials it would use and what the store holds, reporting whatever it cannot
work out rather than stopping at the first thing:

```
$ ahab status
services: db, django
django: django (built from the project)
	container: 0a8b19e27634
postgres: db (postgres:18-alpine)
	container: 189d4d395d62
	user:      myproject
	database:  myproject_db
store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
	linked:    2
	`ahab link check` lists what a sandbox can still read
```

## seeing what it runs

`-v` prints each docker command as it runs, `--dry-run` prints the ones it would
run without running them, and `-q` prints only what was asked for, dropping the
progress along the way (compose's own progress included). All work before or
after the subcommand.

```bash
ahab -v django migrate
ahab --dry-run postgres import ./dump
ahab -q postgres dump ./dump
```

Nothing is written under `--dry-run`, filesystem included: `link add` and
`django make-command` say what they would do and leave the tree alone.

## exit codes

- `0` — it ran and had nothing to report
- `1` — it could not finish
- `2` — the arguments were wrong
- `4` — it ran fine and found something worth reporting, i.e.
  `link check --exit-code` with anything outside the store

## shell completion

`ahab completions <shell>` writes a completion script to stdout, for bash,
elvish, fish, powershell or zsh:

```bash
ahab completions zsh > ~/.local/share/zsh/completions/_ahab
eval "$(ahab completions zsh)"      # or one line in .zshrc, never goes stale
```

Completions are also generated during the build. They land in
`target/*/build/*/out/` by default, and `SHELL_COMPLETIONS_DIR_<SHELL>`
installs a single shell's file straight into place:

```bash
SHELL_COMPLETIONS_DIR_ZSH=~/.local/share/zsh/completions \
SHELL_COMPLETIONS_DIR_FISH=~/.config/fish/completions \
  cargo install --path .
```

`SHELL_COMPLETIONS_DIR` writes every shell into one directory instead.

## the compose file

`ahab` does not pass `-f`. docker compose finds the file itself, so set
docker's own `COMPOSE_FILE` when it is not in the working directory, including
its `base.yaml:override.yaml` form. A project's `.env` is a good place for it,
since docker reads that too:

```
COMPOSE_FILE=docker/docker-compose.yaml
```

## service detection

`ahab` finds the services it needs in `docker compose config`, so they can be
named anything:

- **postgres**: the service whose image is a postgres flavour, matching
  `postg`, `timescale`, `pgvector` or `citus`
- **django**: the service that both builds an image and sets
  `DJANGO_SETTINGS_MODULE`. Where more than one does — a worker beside the web
  service, say — the one publishing ports wins

If nothing matches, or two candidates cannot be told apart, `ahab` says so and
lists the services it looked at rather than guessing. Two services that both
build and set the settings module are ambiguous unless exactly one of them
publishes ports.

`POSTGRES_USER` and `POSTGRES_DB` are read off the detected postgres service, so
`dropdb`, `createdb`, `pg_restore` and `pg_dump` use the role and database the
project declares, falling back to `db` when it declares neither. Both have to
be names: `ahab` hands them to those tools as a role and a database, and libpq
reads a database name holding an `=` or a url as a whole connection string,
which would send a dump to whatever server it names. A value that could be read
as something other than a name is refused rather than passed on.

## django

```bash
ahab django run <cmd>                # in a fresh container, through the entrypoint
ahab django bash                     # shell in a fresh container
ahab django manage <args>            # manage.py
ahab django makemigrations
ahab django migrate <args>
ahab django shell
ahab django make-command <app> <name>
```

There is no `ahab django test`: which runner a project uses is the project's
choice, and `manage.py test` exits 0 having collected nothing when the tests are
written for pytest, so a wrong guess reads as a pass. Name the runner instead:

```bash
ahab django run pytest -x tests/
```

## postgres

```bash
ahab postgres dump <path>            # pg_dump, custom format
ahab postgres dump -F plain <path>   # pg_dump, plain sql
ahab postgres dump -F tar <path>     # pg_dump, tar
ahab postgres dump -F directory <d>  # pg_dump, a directory of files
ahab postgres dump -F cluster <path> # pg_dumpall, roles and all databases
ahab postgres dump -F plain -z <path> # any of them, gzipped
ahab postgres import <path>          # drop, create, then restore
ahab postgres psql <args>            # psql in the database container
```

A dump is written `0600` and under a name of its own until it is complete, then
renamed over the target: a cluster dump carries every role's password hash, and
the default `0644` would hand it to anyone else with an account on the machine.

`psql` passes its arguments through and only asks docker for a terminal when it
has one to hand over, so both of these work:

```bash
ahab postgres psql                          # interactive
ahab postgres psql -tAc 'select count(*) from auth_user' | wc -l
```

The format of a dump being imported is read from the file rather than its name.
A custom format dump starts with `PGDMP` and a tar one with `toc.dat`, both of
which go to `pg_restore`, as does a directory produced by `pg_dump -Fd`.
Anything else is treated as sql and fed to `psql` with `ON_ERROR_STOP` and
`--single-transaction`, so a bad file rolls back instead of half applying.
A whole cluster dump from `pg_dumpall` is recognised by its header and handled
differently again: it creates its own databases and carries role statements, so
the database is dropped but not recreated, the dump goes to `psql` connected to
`postgres`, and it runs without `ON_ERROR_STOP` because roles that already exist
report errors that are expected. Any error it does not expect is reported and
fails the import, since psql without `ON_ERROR_STOP` exits 0 having applied
only part of the dump. Gzipped dumps are decompressed on the way in, whichever
of the three they hold. A cluster that has never held the database yet is a
valid target either way, so importing into a fresh one works.

`import` stops the project before it starts, so an import that fails leaves it
stopped and says so: `docker compose up` brings it back.

## link

`ahab link` moves untracked paths out of the repository into an out-of-repo
store and symlinks them back, so a sandbox that mounts the repository sees a
dangling symlink instead of the contents, while the host resolves it as before.

```bash
ahab link add .env secrets/         # move out, leave symlinks behind
ahab link restore .env              # move it back into the repository
ahab link restore --all             # everything this repo has linked
ahab link list                      # what the store holds for this repository
ahab link check                     # what a sandbox can still read
ahab link check --porcelain         # `<code> <path>`, for scripts
ahab link check --exit-code         # exit 4 when anything is outside the store
```

`restore` is the inverse of `add`: the file moves out of the store and back to
where it was, and the store keeps nothing. A second checkout linking the same
path is left with a dangling symlink, since there is only ever one stored copy.

`list` says what state each stored path is in, which `check` cannot see because
it asks git about the repository rather than reading the store:

```
$ ahab link list
store: /home/you/.local/share/ahab/git.aflabs.org/urnik/afurnik
	linked:    .env
	shadowed:  config.local.py
	missing:   secrets/token
```

`missing` is a path whose symlink is gone, `shadowed` one that a real file took
back; either way the stored copy is the one nobody reads.

`restore --all` moves back the linked ones and says how many it left, since
there is nothing to undo for a path whose symlink is gone.

`-z` is the porcelain format for scripts that must survive any filename: entries
end with a NUL, and the two paths of a symlink leading elsewhere are separated
by one as well, the way `git status -z` reports a rename.

`check` looks at tracked paths too, since git tracks symlinks and one can lead
out of the repository without appearing in any untracked listing. `add` cannot
externalize a tracked path, so all `check` can do is report it, under the code
`T>`.

A symlink already leading out of the repository is not something `add` will
take: moving the link would move the pointer and leave the contents where they
are, so the store would hold a way back out while `check`, seeing a link into
the store, called the repository clean.

The store lives under
`${XDG_DATA_HOME:-$HOME/.local/share}/ahab/<host>/<owner>/<repo>/`, derived
from the git `origin` remote, or `_local/<checkout>` when there is no remote to
name it after. Its directories are created `0700`: it exists to hold what
should not be readable from the repository, and on a shared machine the default
`0755` would leave that to whoever else has an account. A store path derived
from a remote, or a checkout name, that needed characters replacing carries a
short fingerprint of the original, so two of them cannot land on one directory.

## configuration

Currently `ahab` respects the following environment variables.

- `AHAB_LINK_ROOT`: where `ahab link` keeps its store - the same as `--store`,
  which takes precedence, and defaults to `${XDG_DATA_HOME:-$HOME/.local/share}/ahab`.
  `ahab status` reads it too, so it reports the store the link commands use