Hooks and mixins

/// Pre-events and lifecycle phases listed in `capabilities.hooks` call op
/// `hook`. Return `proceed`, `modify(payload)` or `cancel(reason)`.
fn hook(input: &Value) -> Value {
    let event = input["event"].as_str().unwrap_or("");
    if input["phase"].as_str().unwrap_or("before") != "before" {
        return reply::proceed(); // during/after/finished only observe
    }
    let mut p = input["payload"].clone();
    bump(&format!("hook:{event}"));
    match event {
        // Cancel: refuse sign-in for one domain.
        "login.before" if p["email"].as_str().is_some_and(|e| e.ends_with("@denied.test")) => reply::cancel("domain not allowed"),
        // Modify: tidy up the display name before the account is created.
        "client.before_register" => {
            p["display_name"] = json!(p["display_name"].as_str().unwrap_or("").trim().to_string());
            reply::modify(p)
        }
        // Own custom event (declared as `before:integration-guide:greeted`,
        // delivered with `event` = the bare name and `phase` = "before").
        "integration-guide:greeted" if p["name"] == "nobody" => reply::cancel("no greeting for nobody"),
        "order.before_place" => order_hook(input, p),
        _ => reply::proceed(),
    }
}

/// Mixins wrap a core route (`capabilities.mixins`). An `after` mixin may
/// change values of keys the response already has; new keys are dropped.
fn mixin(input: &Value) -> Value {
    let mut resp = input["response"].clone();
    // Opt-in per request so this example never changes other callers.
    let wanted = input["request"]["query"].as_str().unwrap_or("").contains("guide=1");
    if input["at"] == "after" && wanted {
        if let Some(c) = resp["city"].as_str() {
            resp["city"] = json!(c.to_uppercase());
        }
        return json!({ "response": resp });
    }
    json!({})
}