//! A dimension a set is narrowed by, rendered as a list of values.
//!
//! The fourth phase-B emitter, beside [`form`](crate::form),
//! [`list`](crate::list) and [`meter`](crate::meter). Same split as those: this
//! owns the structure of the panel and the app owns the routes. A value's
//! identifier leaves in `data-facet-value`, which is the hook an app wires its
//! own request onto, exactly as [`list`](crate::list) writes `data-column` and
//! lets the app decide what pressing a heading calls.
//!
//! # Why this is markup and not only CSS
//!
//! Phase A's rule is that an app keeps its markup and gains the classes, and
//! that rule works because the markup already existed. Here it mostly does not:
//! a facet panel is the shape MNW's discover page reached by writing a tick box
//! and a chevron per row because filtering and browsing were two mechanisms, and
//! the whole point of [`makeover_layout::Selecting::Subtree`] is that they stop
//! being two. There is nothing to keep.
//!
//! # The one thing drawn that no flat control has
//!
//! An exclude affordance beside each value, in a subtree facet only. It is a
//! visible control rather than a modifier or a long press, and that was ruled
//! rather than chosen here: a gesture a terminal cannot express is a gesture
//! half the renderers leave out, and an affordance nothing teaches is one users
//! do not find. The glyph is this renderer's pick, and it takes the standing
//! preference for the heavier, simpler mark.
//!
//! # What the depth does and does not do
//!
//! `--facet-depth` carries the tree level as a number, and the indent rule
//! multiplies it by one geometry step. That keeps the whole tree one flat list
//! in the DOM rather than nested lists, which is what lets a renderer draw the
//! same description as a breadcrumb or a column of panes without the markup
//! disagreeing. It is not a size: the number is the level, and the step is
//! `makeover-geometry`'s.

use crate::form::escape_into;
use crate::{Emit, class, push_class};
use makeover_layout::{Depth, Facet, FacetValue, Selecting, Standing};
use std::fmt::Write as _;

/// The classes this module can put in markup.
///
/// [`crate::list::ROW_PART_CLASSES`]' obligation, and it exists for the same
/// reason: every class here is also ruled by [`facet_rules`], so the vocabulary
/// seal picks them up from the generated sheet, and this list is what a test
/// checks that against.
pub const FACET_CLASSES: &[&str] = &[
    "facet",
    "facet-name",
    "facet-values",
    "facet-value",
    "facet-take",
    "facet-count",
    "facet-prune",
];

/// The name a selection mode goes by in `data-selecting`.
///
/// An attribute rather than a class, for `data-selector`'s reason on a selector
/// group: the mode changes what the panel *means*, not how one value is
/// painted, and a class there would read as the styling hook the value's class
/// actually is.
#[must_use]
pub const fn selecting_name(mode: Selecting) -> &'static str {
    match mode {
        Selecting::OneOf => "one-of",
        Selecting::AnyOf => "any-of",
        Selecting::Range => "range",
        Selecting::Text => "text",
        Selecting::Subtree => "subtree",
        // A mode added to the description since this renderer was built.
        // `Selecting` is `#[non_exhaustive]`, and an unknown mode reads as the
        // one that offers no values and prunes nothing: drawing a value list
        // for a mode whose values mean something else is the worse mistake.
        _ => "unknown",
    }
}

/// The name a standing goes by in `data-standing`.
#[must_use]
pub const fn standing_name(standing: Standing) -> &'static str {
    match standing {
        Standing::Open => "open",
        Standing::Taken => "taken",
        Standing::Inherited => "inherited",
        Standing::Pruned => "pruned",
        // Unknown reads as open, which is the state that claims nothing about
        // the set.
        _ => "open",
    }
}

/// A facet as a labelled list of values.
///
/// ```
/// use makeover_layout::{Facet, FacetValue, Selecting, Standing};
/// use makeover_webview::{Emit, facet::facet_html};
///
/// let values = [
///     FacetValue::new("music", "Music")
///         .standing(Standing::Taken)
///         .counted(128)
///         .at(0, true),
///     FacetValue::new("music/synths", "Synths").at(1, false),
/// ];
/// let facet = Facet::new("Tag", Selecting::Subtree, &values);
/// let html = facet_html(&facet, &Emit::default());
///
/// assert!(html.contains(r#"data-selecting="subtree""#));
/// assert!(html.contains(r#"data-facet-value="music/synths""#));
/// // A subtree is the one mode that offers a way to prune a branch out.
/// assert!(html.contains("facet-prune"));
/// ```
///
/// A [`Selecting::Text`] or [`Selecting::Range`] facet lists nothing, so what
/// comes back is the panel and its name with an empty list inside it. That is
/// deliberate rather than an empty string: the app puts its own box in the
/// panel, and the panel is what gives the box the group label and the shared
/// geometry.
#[must_use]
pub fn facet_html(facet: &Facet<'_>, opts: &Emit) -> String {
    let mut html = String::new();
    facet_html_into(facet, opts, &mut html);
    html
}

/// A facet, written into a buffer the caller already has.
///
/// [`facet_html`]'s streaming form, byte-identical to it.
pub fn facet_html_into(facet: &Facet<'_>, opts: &Emit, out: &mut String) {
    out.push_str("<div class=\"");
    push_class(out, "facet", opts);
    out.push_str("\" role=\"group\" data-selecting=\"");
    out.push_str(selecting_name(facet.mode));
    // The gutter an indenting renderer reserves before it draws anything, so
    // the panel does not widen as deeper values arrive. "First paint is final
    // paint" applied to a tree.
    let _ = write!(out, "\" style=\"--facet-reach: {}\">", facet.reach());

    out.push_str("<p class=\"");
    push_class(out, "facet-name", opts);
    out.push_str("\">");
    escape_into(facet.name, out);
    out.push_str("</p>");

    out.push_str("<ul class=\"");
    push_class(out, "facet-values", opts);
    out.push_str("\">");
    if facet.mode.offers_values() {
        for value in facet.values {
            value_html_into(facet, value, opts, out);
        }
    }
    out.push_str("</ul></div>");
}

fn value_html_into(facet: &Facet<'_>, value: &FacetValue<'_>, opts: &Emit, out: &mut String) {
    out.push_str("<li class=\"");
    push_class(out, "facet-value", opts);
    out.push_str("\" data-standing=\"");
    out.push_str(standing_name(value.standing));
    let _ = write!(out, "\" style=\"--facet-depth: {}\">", value.depth);

    out.push_str("<button type=\"button\" class=\"");
    push_class(out, "facet-take", opts);
    out.push_str("\" data-facet-value=\"");
    escape_into(value.value, out);
    // `aria-pressed` and not `aria-selected`: the values are toggles over a set
    // rather than options in a listbox, and an inherited value is pressed in
    // fact even though nobody pressed it. That is `Standing::in_force`, which
    // exists so a renderer does not have to know which of the two it has.
    out.push_str("\" aria-pressed=\"");
    out.push_str(if value.standing.in_force() {
        "true\""
    } else {
        "false\""
    });
    // A branch that opens says so, so a reader is told there is more before
    // pressing rather than after.
    if value.branching {
        out.push_str(" aria-expanded=\"");
        out.push_str(if value.standing.in_force() {
            "true\""
        } else {
            "false\""
        });
    }
    out.push('>');
    escape_into(value.label, out);

    // Absent rather than zero when it was not measured, which is the
    // description's own position: a written zero reads as "none of them".
    if let Some(count) = value.count {
        out.push_str("<span class=\"");
        push_class(out, "facet-count", opts);
        let _ = write!(out, "\">{count}</span>");
    }
    out.push_str("</button>");

    if facet.mode.prunes() {
        out.push_str("<button type=\"button\" class=\"");
        push_class(out, "facet-prune", opts);
        out.push_str("\" data-facet-value=\"");
        escape_into(value.value, out);
        out.push_str("\" aria-pressed=\"");
        out.push_str(if value.standing == Standing::Pruned {
            "true\""
        } else {
            "false\""
        });
        // The accessible name is built here rather than described, for
        // `meter_text`'s reason: a tooltip wants a sentence and a terminal
        // wants a glyph, and a description shipping either would choose for
        // both.
        out.push_str(" aria-label=\"Exclude ");
        escape_into(value.label, out);
        // The heavier, simpler mark. It is the glyph and not a class, because a
        // renderer that swaps it is not changing what the control means.
        out.push_str("\">\u{2715}</button>");
    }

    out.push_str("</li>");
}

/// The rules for a facet panel.
///
/// Depth comes from the description: a value at rest sits as
/// [`Depth::Flat`] and a taken one is held in, which is
/// [`makeover_layout::Selector::chosen`]'s shape for a segment and is the same
/// sentence — this one is picked, so it is pressed. Nothing here states a
/// colour or a size; the indent is a count multiplied by a geometry step, and
/// the step is the one variable this crate is allowed to read.
pub(crate) fn facet_rules(opts: &Emit) -> String {
    let mut css = String::new();
    let panel = class("facet", opts);
    let name = class("facet-name", opts);
    let values = class("facet-values", opts);
    let value = class("facet-value", opts);
    let take = class("facet-take", opts);
    let count = class("facet-count", opts);
    let prune = class("facet-prune", opts);

    // The name of the dimension. A caption, and captions are legitimately
    // muted: it was never going to answer a press.
    let _ = writeln!(css, ".{name} {{\n    color: var(--content-muted);\n}}");

    // The list undoes the bullet a browser adds, for `row_rules`' reason: a
    // described set of tags is not a bulleted list and rendered as one because
    // nothing said otherwise.
    let _ = writeln!(
        css,
        ".{values} {{\n    list-style: none;\n    margin: 0;\n    padding: 0;\n}}"
    );

    // The indent is the level times one step. `--facet-depth` is written per
    // value and `--facet-reach` per panel; the panel one reserves the gutter so
    // nothing moves as deeper values arrive.
    let _ = writeln!(
        css,
        ".{value} {{\n    padding-inline-start: calc(var(--facet-depth, 0) * var(--space-tight, 0.5rem));\n}}"
    );

    let _ = writeln!(
        css,
        ".{panel} {{\n    min-inline-size: calc(var(--facet-reach, 0) * var(--space-tight, 0.5rem));\n}}"
    );

    // The value's own control. Flat at rest, held in when it is in force, and
    // that is the segmented control's sentence rather than a new one.
    css.push_str(&crate::depth_rule(&take, Depth::Flat));
    css.push_str(&crate::interactive_rules(&take, Depth::Flat, opts));
    css.push_str(&crate::depth_rule(
        &format!("{take}[aria-pressed=\"true\"]"),
        Depth::Well,
    ));

    // A pruned branch reads one step back and stays live: pressing it takes the
    // prune off, so it may not wear `content-muted`. `Standing::intent` is
    // where that is decided.
    let _ = writeln!(
        css,
        ".{value}[data-standing=\"pruned\"] .{take} {{\n    color: var(--{});\n}}",
        Standing::Pruned.intent()
    );

    // Inherited is in force and was not chosen. It reads as the thing itself,
    // like a taken value, and the difference is carried by the attribute for
    // whoever wants it rather than by a colour claiming something.
    let _ = writeln!(css, ".{count} {{\n    color: var(--content-muted);\n}}");

    css.push_str(&crate::depth_rule(&prune, Depth::Flat));
    css.push_str(&crate::interactive_rules(&prune, Depth::Flat, opts));
    css.push_str(&crate::depth_rule(
        &format!("{prune}[aria-pressed=\"true\"]"),
        Depth::Well,
    ));

    css
}

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

    fn tag_values() -> [FacetValue<'static>; 3] {
        [
            FacetValue::new("music", "Music")
                .standing(Standing::Taken)
                .counted(128)
                .at(0, true),
            FacetValue::new("music/synths", "Synths")
                .standing(Standing::Inherited)
                .at(1, false),
            FacetValue::new("music/drums", "Drums")
                .standing(Standing::Pruned)
                .at(1, false),
        ]
    }

    #[test]
    fn a_streamed_facet_is_the_facet_the_other_form_returns() {
        let opts = Emit {
            class_prefix: "mk-",
            ..Emit::default()
        };
        let values = tag_values();
        for facet in [
            Facet::new("Tag", Selecting::Subtree, &values),
            Facet::new("Type", Selecting::AnyOf, &values),
            Facet::new("Search", Selecting::Text, &[]),
        ] {
            let mut streamed = String::new();
            facet_html_into(&facet, &opts, &mut streamed);
            assert_eq!(streamed, facet_html(&facet, &opts));
        }
    }

    #[test]
    fn only_a_subtree_draws_an_exclude_affordance() {
        // The one control a flat facet has no use for: excluding a value there
        // is the same fact as not picking it.
        let values = tag_values();
        let subtree = facet_html(
            &Facet::new("Tag", Selecting::Subtree, &values),
            &Emit::default(),
        );
        assert!(subtree.contains("facet-prune"));
        assert!(subtree.contains(r#"aria-label="Exclude Drums""#));

        let flat = facet_html(
            &Facet::new("Type", Selecting::AnyOf, &values),
            &Emit::default(),
        );
        assert!(!flat.contains("facet-prune"));
    }

    #[test]
    fn an_inherited_value_reads_as_pressed_without_having_been_pressed() {
        // The distinction `Standing` has four members for. A renderer given a
        // bool marks every descendant of a taken branch or marks none, and both
        // are wrong on screen.
        let values = tag_values();
        let html = facet_html(
            &Facet::new("Tag", Selecting::Subtree, &values),
            &Emit::default(),
        );
        let synths = html
            .split("<li")
            .find(|chunk| chunk.contains("music/synths"))
            .expect("the inherited value");
        assert!(synths.contains(r#"data-standing="inherited""#));
        assert!(synths.contains(r#"aria-pressed="true""#));

        let drums = html
            .split("<li")
            .find(|chunk| chunk.contains("music/drums"))
            .expect("the pruned value");
        // Pruned is a decision and it is not in force, so the take control is
        // not pressed and the prune control is.
        assert!(drums.contains(r#"data-standing="pruned""#));
        assert!(drums.contains(r#"aria-pressed="false""#));
        assert!(drums.contains(r#"aria-label="Exclude Drums""#));
    }

    #[test]
    fn a_mode_that_lists_nothing_still_renders_its_panel() {
        // The app puts its own box in; the panel is what gives it the group
        // label and the shared geometry.
        let html = facet_html(
            &Facet::new("Search", Selecting::Text, &[]),
            &Emit::default(),
        );
        assert!(html.contains("facet-name"));
        assert!(html.contains(r#"data-selecting="text""#));
        assert!(!html.contains("facet-take"));
    }

    #[test]
    fn an_unmeasured_count_emits_no_number_at_all() {
        // A written zero reads as "none of them", which is a different claim
        // from "not counted".
        let values = [FacetValue::of("Ambient")];
        let html = facet_html(
            &Facet::new("Tag", Selecting::AnyOf, &values),
            &Emit::default(),
        );
        assert!(!html.contains("facet-count"));

        let counted = [FacetValue::of("Ambient").counted(0)];
        let html = facet_html(
            &Facet::new("Tag", Selecting::AnyOf, &counted),
            &Emit::default(),
        );
        assert!(html.contains(">0</span>"));
    }

    #[test]
    fn the_gutter_is_reserved_from_the_deepest_value_before_anything_is_drawn() {
        // "First paint is final paint" applied to a tree: a gutter widened as
        // deeper values arrive is the reflow that rule forbids.
        let values = tag_values();
        let html = facet_html(
            &Facet::new("Tag", Selecting::Subtree, &values),
            &Emit::default(),
        );
        assert!(html.contains("--facet-reach: 1"));
        assert!(html.contains("--facet-depth: 0"));
        assert!(html.contains("--facet-depth: 1"));
    }

    #[test]
    fn labels_and_identifiers_are_escaped_like_every_other_string() {
        // Both arrive from the app, and a tag path is user-supplied on a system
        // where a user names their own tags.
        let values = [FacetValue::new("a&b", "A & B")];
        let html = facet_html(
            &Facet::new("T<ag>", Selecting::AnyOf, &values),
            &Emit::default(),
        );
        assert!(html.contains("A &amp; B"));
        assert!(html.contains(r#"data-facet-value="a&amp;b""#));
        assert!(html.contains("T&lt;ag&gt;"));
        assert!(!html.contains("<ag>"));
    }

    #[test]
    fn every_class_this_module_emits_is_one_the_stylesheet_rules() {
        // `ROW_PART_CLASSES`' obligation: a class this crate writes and the
        // sheet does not rule is invisible to the dead-vocabulary seal.
        let names = crate::vocabulary::names(&Emit::default());
        for name in FACET_CLASSES {
            assert!(
                names.contains(&crate::class(name, &Emit::default())),
                "{name} is not in the vocabulary"
            );
        }
    }

    #[test]
    fn the_prefix_reaches_every_class_in_the_markup() {
        // A prefixed build claims its own names, and the emitted CSS selects
        // descendants: miss one and the rule stops matching.
        let opts = Emit {
            class_prefix: "mo-",
            ..Emit::default()
        };
        let values = tag_values();
        let html = facet_html(&Facet::new("Tag", Selecting::Subtree, &values), &opts);
        for name in FACET_CLASSES {
            assert!(html.contains(&format!("mo-{name}")), "{name} is unprefixed");
        }
    }
}