# M4b task 12: approval posts in the state file

**Branch:** `m4b` (run `git switch m4b`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `gatewayd: state, the posts of open approvals, and the turn of a session`

## Goal

Two things the serve loop needs from `state.json` (M4b spec, sections 6 and 8):

- **Approval posts.** The posts of each approval shown and not yet ended, so that at the next
  start the ones left behind can be marked dead. The field is **optional**: an M4a state file
  loads unchanged. Like every other field, its ids must be valid, or the file is refused.
- **The turn of a session**: where an approval of that session goes (its thread).

## Files

- Copy: `crates/gatewayd/tests/state_approvals.rs`
- Modify: `crates/gatewayd/src/state.rs`, `docs/implementer-log.md`

## The changes, exactly

In `crates/gatewayd/src/state.rs`:

**1.** In `struct StateFile`, after `in_flight: Vec<InFlight>,`:

```rust
    /// Optional, so an M4a state file loads unchanged.
    #[serde(default)]
    approvals: Vec<ApprovalPosts>,
```

and after `struct StateFile`:

```rust
/// The posts of an approval shown in Mattermost and not yet ended (M4b spec, section 8).
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct ApprovalPosts {
    pub approval: u64,
    pub channel: String,
    /// First part first; the last is the one that is edited when it ends.
    pub posts: Vec<String>,
}
```

**2.** In `StateFile::problem`, after the `in_flight` loop and before `None`: each entry of
`approvals` must have a `valid_id` channel and at least one post, all `valid_id`; otherwise
`Some(format!("approval {}'s posts are not valid", shown.approval))`.

**3.** Four methods at the end of `impl State`, each saving (`self.save()`) when it changes
something, like the methods already there:

- `pub fn turn_of(&self, session: &str) -> Option<InFlight>`: the entry of `in_flight` with that
  session, cloned.
- `pub fn add_approval(&mut self, shown: ApprovalPosts) -> Result<(), StateError>`: remove any
  entry with the same `approval`, push this one, save.
- `pub fn remove_approval(&mut self, approval: u64) -> Result<(), StateError>`: remove the entries
  with that `approval`; save only if one was removed.
- `pub fn take_approvals(&mut self) -> Result<Vec<ApprovalPosts>, StateError>`: take them all out
  (`std::mem::take`); save only when there were some; return them. (As `take_in_flight` does.)

## Steps

- [ ] **1. Copy.** `git switch m4b`, then `cp docs/plans/M4b/files/crates/gatewayd/tests/state_approvals.rs crates/gatewayd/tests/`
- [ ] **2. See it fail.** `cargo test -p gatewayd --test state_approvals`. Expected: it does not
  compile.
- [ ] **3. Make the three changes.** Run `cargo fmt --all`.
- [ ] **4. See it pass.** `cargo test -p gatewayd --test state_approvals --test state --test serve_restart`.
  Expected: 4, 4 and 7 passed.
- [ ] **5. Run the gate.** `make gate`. Expected last line: `gate: ok`.
- [ ] **6. Log and commit.** `git add crates/gatewayd docs/implementer-log.md Cargo.lock && git commit`

## Done when

- The three suites pass; `make gate` prints `gate: ok`.