//! Column layout and row structure for lists and tables.
//!
//! The other half of phase B. [`form`](crate::form) renders a field; this
//! renders the frame a list of rows sits in: which columns exist, how wide they
//! are, which ones survive a narrow viewport, and the cell containers a row is
//! made of.
//!
//! # What this does not do
//!
//! It does not render a cell's contents. That is the crate's own limit, stated
//! in `makeover_layout`'s "Where the description stops": generate the boring
//! 80% so the bespoke 20% gets the attention. A goingson task row carries
//! delegated action hooks with argument substitution, four nested sub-renderers,
//! conditional state classes and aria labels built from data. A description
//! expressive enough to emit that is a templating language wearing a
//! description's name.
//!
//! So the split is the one [`Markup`] already draws for forms: this owns the
//! structure and the app owns what goes in it. What that removes from an app is
//! not small — cell order, cell classes, the grid tracks, and above all the
//! narrowing rules, which is where addressing columns by position goes wrong.
//!
//! # Why positions are the bug
//!
//! goingson hides its mobile columns with `nth-child(n+5)` against a
//! seven-column table, plus a separate `nth-child(3)`, plus two class-based
//! rules — the same fact said three ways, two of them positional. Insert a
//! column anywhere left of the cut and the wrong one disappears, silently,
//! because nothing in the stylesheet knows what column five *is*.
//! [`Priority`] is the fix: a renderer narrows by raising a cutoff, and never
//! by counting.

use crate::form::Markup;
use crate::{Emit, class};
use makeover_layout::{Column, Priority, RowPart, Width};
use std::fmt::Write as _;

/// The lengths the description deferred.
///
/// [`Width`] says `Content`, `Fixed` or `Fill` and deliberately carries no
/// magnitude, because a magnitude is a CSS answer and the description is read
/// by renderers that have no pixels. So the numbers arrive here instead, the
/// way a field's value arrives in [`Filling`](crate::form::Filling) rather than
/// in `Field`.
///
/// Looked up by column name, because an app's columns are not all one size:
/// goingson's task table has six distinct fixed widths.
#[derive(Debug, Clone, Copy, Default)]
pub struct Sizing<'a> {
    /// `(column name, CSS length)`. The length is the track for a
    /// [`Width::Fixed`] column and the floor for a [`Width::Fill`] one.
    pub lengths: &'a [(&'a str, &'a str)],
    /// Used for a column with no entry above. Empty means `auto`.
    pub fallback: &'a str,
}

impl Sizing<'_> {
    /// The length for a named column.
    fn length_for(&self, name: &str) -> &str {
        self.lengths
            .iter()
            .find(|(column, _)| *column == name)
            .map_or_else(
                || {
                    if self.fallback.is_empty() {
                        "auto"
                    } else {
                        self.fallback
                    }
                },
                |(_, length)| *length,
            )
    }

    /// The grid track for one column.
    fn track(&self, column: &Column<'_>) -> String {
        match column.width {
            Width::Content => "max-content".to_owned(),
            Width::Fixed => self.length_for(column.name).to_owned(),
            Width::Fill => format!("minmax({}, 1fr)", self.length_for(column.name)),
            // A width added to the description since this renderer was built.
            // `auto` is the track that makes no claim, which is the honest
            // answer to a claim this renderer cannot read.
            _ => "auto".to_owned(),
        }
    }
}

/// The class a cell of this column carries.
///
/// Derived from the column's own name, which is what makes the narrowing rules
/// addressable. `data-column` would do as well; a class is what both webview
/// apps already key their cell styling on.
#[must_use]
pub fn column_class(column: &Column<'_>, opts: &Emit) -> String {
    class(&format!("col-{}", column.name), opts)
}

/// The `grid-template-columns` value for the columns kept at `cutoff`.
///
/// Emitting only the surviving tracks is what keeps the track list and the
/// hiding in agreement. An app that hides a cell with `display: none` but
/// leaves its track in place gets a column of empty space, which is the other
/// half of goingson's mobile bug: its narrow rule drops to four tracks by hand
/// and has to be edited in step with the `nth-child` cut.
#[must_use]
pub fn grid_template_columns(
    columns: &[Column<'_>],
    sizing: &Sizing<'_>,
    cutoff: Priority,
) -> String {
    columns
        .iter()
        .filter(|column| column.kept_at(cutoff))
        .map(|column| sizing.track(column))
        .collect::<Vec<_>>()
        .join(" ")
}

/// The rules that narrow `selector` to the columns kept at `cutoff`.
///
/// Both halves together: the shortened track list, and `display: none` on each
/// dropped column *by its own class*. Nothing counts positions, so inserting a
/// column changes what is emitted rather than changing which column vanishes.
///
/// `selector` may be a selector list. A descendant is appended to each part
/// rather than to the whole, because appending to the whole changes what the
/// earlier parts match: `.head, .row > .col-x` reads as "`.head`, or a `.col-x`
/// inside `.row`", so `.head` itself would be hidden.
#[must_use]
pub fn narrowing_css(
    columns: &[Column<'_>],
    selector: &str,
    sizing: &Sizing<'_>,
    cutoff: Priority,
    opts: &Emit,
) -> String {
    let parts: Vec<&str> = selector.split(',').map(str::trim).collect();

    let mut css = format!(
        "{} {{\n    grid-template-columns: {};\n}}\n",
        parts.join(", "),
        grid_template_columns(columns, sizing, cutoff)
    );

    for column in columns.iter().filter(|c| !c.kept_at(cutoff)) {
        let class = column_class(column, opts);
        let targets: Vec<String> = parts
            .iter()
            .map(|part| format!("{part} > .{class}"))
            .collect();
        let _ = write!(css, "{} {{\n    display: none;\n}}\n", targets.join(",\n"));
    }
    css
}

/// One cell of a row.
///
/// The contents are [`Markup`] rather than text, and that is the whole shape of
/// this module: a cell holds whatever the app builds, and the app says so by
/// naming it. Escaping a cell here would be wrong as well as impossible — a
/// task row's description cell is five nested spans and a badge.
#[derive(Debug, Clone, Copy)]
pub struct Cell<'a> {
    /// Which column this fills, by name.
    pub column: &'a str,
    /// What kind of text it is, when it is text.
    ///
    /// Carries the row-part class the stylesheet half already emits, so a
    /// secondary cell says it is secondary in the description's own words
    /// rather than in the app's.
    pub part: Option<RowPart>,
    /// The contents. Trusted app markup.
    pub content: Markup<'a>,
}

impl<'a> Cell<'a> {
    /// A cell with no row part.
    #[must_use]
    pub const fn new(column: &'a str, content: Markup<'a>) -> Self {
        Self {
            column,
            part: None,
            content,
        }
    }
}

/// The class for a row part.
///
/// This comment used to say `RowPart` was the one closed enum left here, and
/// that gaining a member would stop this compiling — "the same lockstep break
/// `non_exhaustive` was added elsewhere to end". makeover-layout 0.9.0 ended
/// it: the enum gained [`RowPart::Tokens`] and `#[non_exhaustive]` in the same
/// release, so the prediction was paid off rather than waited for.
///
/// The fallback is what that costs. A member added upstream lands here as a
/// bare `row-part` with no rule of its own, which is a thing rendering plainly
/// rather than a build that stops. Grep this function when adopting a new
/// makeover-layout.
pub(crate) fn part_class(part: RowPart) -> &'static str {
    match part {
        RowPart::Primary => "row-primary",
        RowPart::Secondary => "row-secondary",
        RowPart::Meta => "row-meta",
        RowPart::Actions => "row-actions",
        RowPart::Tokens => "row-tokens",
        RowPart::Proportion => "row-proportion",
        _ => "row-part",
    }
}

/// A row's cells, in column order.
///
/// Ordered by the columns and not by the cells, so a row cannot silently
/// disagree with its table about what comes where. A column with no cell gets
/// an empty container, which keeps the grid aligned; a cell naming no column is
/// dropped, because there is nowhere to put it.
///
/// Emits the cells alone, not the row element. The row carries the app's
/// identity and hooks — `data-id`, a context-menu binding, a tabindex, its
/// state classes — and none of that is describable here.
///
/// # Not for a webview's scroll path
///
/// This has no consumer in either webview app, deliberately, and wiring one in
/// would be a mistake worth naming. goingson renders rows through a virtual
/// scroller whose `_render` calls its row builder **synchronously** while
/// scrolling; the code's own comment says scroll events fire at 60Hz+ and that
/// this is the hot path. Reaching Rust from there means an IPC round trip and
/// an `await` in that loop, per visible range, during a drag.
///
/// So this is for the hosts where rendering already happens in Rust: an axum
/// route, and the router when it lands. There the objection does not apply,
/// because nothing crosses a process boundary to reach it. A webview app should
/// take [`narrowing_css`] and [`column_class`] and keep building its own rows.
#[must_use]
pub fn cells_html(columns: &[Column<'_>], cells: &[Cell<'_>], opts: &Emit) -> String {
    let cell_class = class("cell", opts);
    let mut html = String::new();

    for column in columns {
        let found = cells.iter().find(|cell| cell.column == column.name);
        let mut classes = format!("{cell_class} {}", column_class(column, opts));
        if let Some(part) = found.and_then(|cell| cell.part) {
            let _ = write!(classes, " {}", class(part_class(part), opts));
        }
        let _ = write!(
            html,
            "<div class=\"{classes}\">{}</div>",
            found.map_or("", |cell| cell.content.0)
        );
    }
    html
}

#[cfg(test)]
mod tests {
    use super::*;

    fn columns() -> Vec<Column<'static>> {
        vec![
            Column {
                width: Width::Fill,
                priority: Priority::Essential,
                ..Column::new("description")
            },
            Column {
                width: Width::Fixed,
                priority: Priority::Secondary,
                ..Column::new("due")
            },
            Column {
                width: Width::Fixed,
                priority: Priority::Optional,
                ..Column::new("progress")
            },
        ]
    }

    fn sizing() -> Sizing<'static> {
        Sizing {
            lengths: &[
                ("description", "200px"),
                ("due", "110px"),
                ("progress", "100px"),
            ],
            fallback: "",
        }
    }

    #[test]
    fn a_fill_column_gets_a_floor_and_the_slack() {
        let tracks = grid_template_columns(&columns(), &sizing(), Priority::Optional);
        assert_eq!(tracks, "minmax(200px, 1fr) 110px 100px");
    }

    #[test]
    fn a_column_with_no_length_makes_no_claim() {
        let sizing = Sizing::default();
        let tracks = grid_template_columns(&columns(), &sizing, Priority::Optional);
        assert_eq!(tracks, "minmax(auto, 1fr) auto auto");
    }

    /// The point of the module. Raising the cutoff drops columns by what they
    /// are worth, and the track list shortens to match, so the two cannot
    /// disagree the way a hand-written `nth-child` cut and a hand-written
    /// track list can.
    #[test]
    fn raising_the_cutoff_drops_columns_and_their_tracks_together() {
        let columns = columns();

        let wide = grid_template_columns(&columns, &sizing(), Priority::Optional);
        assert_eq!(wide.split(' ').count(), 4); // minmax(200px, + 1fr) + 2

        let narrow = grid_template_columns(&columns, &sizing(), Priority::Secondary);
        assert_eq!(narrow, "minmax(200px, 1fr) 110px");

        let narrowest = grid_template_columns(&columns, &sizing(), Priority::Essential);
        assert_eq!(narrowest, "minmax(200px, 1fr)");
    }

    #[test]
    fn narrowing_hides_a_dropped_column_by_its_own_class_not_its_position() {
        let css = narrowing_css(
            &columns(),
            ".ui-mode-mobile .task-row",
            &sizing(),
            Priority::Secondary,
            &Emit::default(),
        );
        assert!(
            css.contains("grid-template-columns: minmax(200px, 1fr) 110px;"),
            "{css}"
        );
        assert!(
            css.contains(".ui-mode-mobile .task-row > .col-progress {"),
            "{css}"
        );
        assert!(!css.contains("nth-child"), "{css}");
        // The kept columns are not mentioned as hidden.
        assert!(!css.contains(".col-due {\n    display: none"), "{css}");
    }

    /// A selector list has to distribute, or the earlier parts of it get the
    /// child combinator appended to the whole and start matching things they
    /// never named. This hid an entire table header the first time it ran.
    #[test]
    fn a_selector_list_distributes_the_hidden_column() {
        let css = narrowing_css(
            &columns(),
            ".task-header-row, .task-row",
            &sizing(),
            Priority::Secondary,
            &Emit::default(),
        );
        assert!(
            css.contains(".task-header-row > .col-progress,\n.task-row > .col-progress {"),
            "{css}"
        );
        // The bare header selector must never appear as a hiding target.
        assert!(
            !css.contains(".task-header-row {\n    display: none"),
            "{css}"
        );
        assert!(
            css.contains(".task-header-row, .task-row {\n    grid-template-columns:"),
            "{css}"
        );
    }

    #[test]
    fn cells_follow_the_columns_and_carry_their_column_class() {
        let cells = [
            Cell {
                column: "due",
                part: Some(RowPart::Meta),
                content: Markup("tomorrow"),
            },
            Cell::new("description", Markup("<span>Ship it</span>")),
        ];
        let html = cells_html(&columns(), &cells, &Emit::default());

        // Column order, not cell order: description was passed second.
        let description = html.find("Ship it").expect("description cell");
        let due = html.find("tomorrow").expect("due cell");
        assert!(description < due, "{html}");

        assert!(
            html.contains(r#"<div class="cell col-description">"#),
            "{html}"
        );
        assert!(
            html.contains(r#"<div class="cell col-due row-meta">"#),
            "{html}"
        );
        // progress had no cell, so it is present and empty rather than absent,
        // or the grid would shift left by one.
        assert!(
            html.contains(r#"<div class="cell col-progress"></div>"#),
            "{html}"
        );
    }

    #[test]
    fn a_cell_naming_no_column_is_dropped() {
        let cells = [Cell::new("nonexistent", Markup("nowhere"))];
        let html = cells_html(&columns(), &cells, &Emit::default());
        assert!(!html.contains("nowhere"), "{html}");
    }

    #[test]
    fn the_class_prefix_reaches_the_cells_and_the_narrowing() {
        let opts = Emit {
            class_prefix: "mk-",
            ..Emit::default()
        };
        let cells = [Cell::new("due", Markup("x"))];
        assert!(
            cells_html(&columns(), &cells, &opts).contains("mk-cell mk-col-due"),
            "prefix missing"
        );
        assert!(
            narrowing_css(&columns(), ".t", &sizing(), Priority::Secondary, &opts)
                .contains(".mk-col-progress"),
            "prefix missing"
        );
    }
}