//! The Askama entry point for a described Export CSV button.
//!
//! The first act taken through the pattern `27d5e5b8` ruled on: a described
//! fragment inside an Askama page, at the granularity of one primitive, in a
//! glue module that is a sibling of `widgets/` rather than a member of it. The
//! whole of the reasoning is in [`super::widgets`]; what is here is the first
//! thing it buys.
//!
//! # What it replaces
//!
//! `data-action="exportCsvButton" data-arg="/api/export/sales"
//! data-arg2="sales.csv"` — a class naming a behaviour plus the two things the
//! behaviour needed, positionally, repeated at five sites in four templates,
//! backed by a `window.exportCsvButton` global that fetched the URL, built an
//! anchor, set `download`, clicked it, and put the button's own label back
//! afterwards.
//!
//! [`Action::saving`] says all of it in one sentence: the answer to this call
//! is a file the reader keeps rather than a view. `htmx-glue.ts` performs it
//! once for everything that says so, which it already did for
//! [`super::buyer_contacts`], the one screen described before this. A terminal
//! renderer writes the file to disk from the same sentence without being told
//! which button this is.
//!
//! # One act, five call sites, and why the URL is a parameter
//!
//! The five exports differ in exactly two things: where the rows come from and
//! what the file is called. Both are facts about the caller rather than about
//! the control, so they are arguments and there is one function. Compare
//! `upload_field`, where the accept list is a fact about MNW and belongs to the
//! module: the test is whether a template would be writing the same literal
//! twice if it were not here.
//!
//! # The visual change, which is the ruling's accepted cost
//!
//! The templates wrote `class="btn-secondary text-sm"`. A described act emits
//! `class="button"`, so these five land on the design system's button. The
//! layout-only classes a caller needs (`broadcast-export`, `nowrap`) stay in
//! Askama on the element around it, where they were always a fact about that
//! page's layout rather than about the control.

use quasi_router::{Action, Node};

/// The route each export posts to, and the name the file is kept under.
///
/// A read would be a link the browser downloads by itself; these are posts,
/// because assembling the file is work the server does rather than a document
/// it already has, and `Action::saves` is independent of the verb for exactly
/// that reason.
///
/// `awaiting` because the whole file is assembled before any of it comes back.
/// Nothing countable to say about the wait: the row count is often known at the
/// call site and the byte count never is, and `layout::Awaiting` takes a
/// measurement rather than a stand-in for one.
#[must_use]
pub fn act(route: &str, filename: &str) -> Node {
    Node::act(
        "Export CSV",
        Action::post(route).saving(filename).awaiting(),
    )
}

/// The same act as a fragment, for a template to drop in place.
///
/// No shell and no region: this lands inside a document Askama has already
/// built, which is what every glue module here does.
#[must_use]
pub fn html(route: &str, filename: &str) -> String {
    use quasi_axum::Serves as _;

    quasi_webview::Webview::new().fragment(&act(route, filename))
}

#[cfg(test)]
mod tests {
    /// The three things `data-action` + two positional arguments used to say,
    /// said once. `data-saves` is the whole of the host's instruction.
    #[test]
    fn an_export_says_where_it_reads_from_and_what_the_file_is_called() {
        let html = super::html("/api/export/sales", "sales.csv");

        assert!(html.contains(r#"hx-post="/api/export/sales""#), "{html}");
        assert!(html.contains(r#"data-saves="sales.csv""#), "{html}");
        assert!(html.contains("Export CSV"), "{html}");
    }

    /// The mark that says the call waits. A file the server assembles is the
    /// report case `Action::awaiting` exists for, and the button locking itself
    /// is what the deleted global did by hand.
    #[test]
    fn an_export_says_it_waits() {
        let html = super::html("/api/export/sales", "sales.csv");

        assert!(html.contains("data-awaiting="), "{html}");
    }

    /// Nothing positional survives. The failure this replaced was a second
    /// argument drifting from the first at one of five sites, silently.
    #[test]
    fn no_call_site_carries_a_behaviour_by_name() {
        let html = super::html("/api/export/followers", "followers.csv");

        assert!(!html.contains("data-action"), "{html}");
        assert!(!html.contains("data-arg"), "{html}");
    }
}