shep 0.16.1

//! The shared cells the redesigned panes draw magnitude with.
//!
//! Every one returns a `String` rather than a `Line` or a `Span`: the
//! caller owns the styling, and a pure string is testable against a
//! literal the way `flock::mark` already is.
//!
//! Deliberately not `ratatui::widgets::Sparkline` or `Gauge`. This module
//! builds its rows by hand so column widths stay fixed and a row stays a
//! string a test can assert on, which those widgets take away.

use crate::output::width::text_columns;

/// The eight sparkline steps, low to high.
const STEPS: [char; 8] = [
    '\u{2581}', '\u{2582}', '\u{2583}', '\u{2584}', '\u{2585}', '\u{2586}', '\u{2587}', '\u{2588}',
];

/// How many of `cells` a `gauge`'d bar fills, given `value` over `ceiling`.
///
/// Shared by [`gauge`] and by callers that draw the fill and the tail as two
/// separately-styled spans and so need the split point without re-deriving
/// it. `None`, zero, and any ceiling a value cannot be measured against give
/// zero: the bar says "no ceiling set" rather than guessing a denominator. A
/// value above its ceiling saturates at `cells` rather than overflowing it.
#[must_use]
pub fn gauge_fill(value: u64, ceiling: Option<u64>, cells: usize) -> usize {
    match ceiling {
        Some(ceiling) if ceiling > 0 => {
            let scaled = (value as f64 / ceiling as f64 * cells as f64).round();
            (scaled as usize).min(cells)
        }
        _ => 0,
    }
}

/// A horizontal bar of `cells`, filled in proportion to `value` over
/// `ceiling` and padded with the light shade.
///
/// See [`gauge_fill`] for the no-ceiling and overflow cases.
#[must_use]
pub fn gauge(value: u64, ceiling: Option<u64>, cells: usize) -> String {
    let filled = gauge_fill(value, ceiling, cells);
    let mut out = String::with_capacity(cells * 3);
    out.extend(std::iter::repeat_n('\u{2588}', filled));
    out.extend(std::iter::repeat_n('\u{2591}', cells - filled));
    out
}

/// The newest `cells` samples, one cell each, scaled against `ceiling`.
///
/// Padded on the left with spaces when there are fewer samples than cells,
/// so the line grows into the column from the right as history arrives.
/// No samples at all is blank rather than a flat line at the floor: a flat
/// line reads as measured and idle, and blank reads as not measured yet.
/// A sample above `ceiling` saturates at the tallest step rather than
/// overflowing it, the same way [`gauge_fill`] saturates a value above its
/// own ceiling.
///
/// `ceiling` is the caller's to choose, and the choice is the whole design
/// of this cell. Scaling each row to its OWN peak makes every row fill its
/// column, so an idle sheep and a busy one look identical, which is the
/// discontinuity the design's opening problem statement exists to fix.
/// Scaling every row to a fixed 100% of a core makes an ordinary flock draw
/// ten flat lines, since real processes mostly sit near zero. What works for
/// a table is one ceiling shared by every row and set by the data: see
/// [`super::super::app::App::cpu_ceiling`], which takes the busiest sheep in
/// the window and floors it so an idle flock's rounding noise is not
/// amplified into a shape.
#[must_use]
pub fn sparkline(samples: &[f32], cells: usize, ceiling: f32) -> String {
    if samples.is_empty() || cells == 0 {
        return " ".repeat(cells);
    }
    let window = &samples[samples.len().saturating_sub(cells)..];
    let mut out = String::with_capacity(cells * 3);
    for _ in window.len()..cells {
        out.push(' ');
    }
    let ceiling = if ceiling > 0.0 { ceiling } else { 1.0 };
    for sample in window {
        let clamped = sample.clamp(0.0, ceiling);
        let scaled = (clamped / ceiling * (STEPS.len() - 1) as f32).round();
        let step = (scaled as usize).min(STEPS.len() - 1);
        out.push(STEPS[step]);
    }
    out
}

/// A half-block area chart: `rows` rows of `cols` cells, oldest sample
/// leftmost, top row first.
///
/// Sixteen steps in eight rows. For a sample of value `v` the column's
/// height in half-steps is `h = round(v / ceiling * rows * 2)`; for row `r`
/// counted from the top, `s = h - (rows - 1 - r) * 2`, and the cell is `█`
/// when `s >= 2`, `▄` when `s == 1`, and blank otherwise.
///
/// Left-padded like [`sparkline`], and blank rather than a floor line with
/// no samples, for the reasons that function's own doc gives.
///
/// A sample at or above `ceiling` fills its column, the same way
/// [`gauge_fill`] saturates a value above its own ceiling: the row match
/// below sends any height at or past the top row's floor to the same `█`
/// arm regardless of how far past it the sample sits, so there is nothing
/// for an explicit clamp to add on that side. A negative sample is a
/// different case, one this function does need to get right even though no
/// caller today produces one: the `as usize` cast on the line below sends it
/// to a height of `0` (a saturating cast, not a wrapping one), which reads as
/// blank rather than as a spurious full column.
#[must_use]
pub fn chart(samples: &[f32], ceiling: f32, cols: usize, rows: usize) -> Vec<String> {
    // A zero `cols` or `rows` degrades through the general path below with
    // no guard needed: don't re-add one without a test proving it wrong.
    let window = &samples[samples.len().saturating_sub(cols)..];
    let pad = cols - window.len();
    let ceiling = if ceiling > 0.0 { ceiling } else { 1.0 };
    let steps = rows * 2;
    let heights: Vec<usize> = window
        .iter()
        .map(|sample| (sample / ceiling * steps as f32).round() as usize)
        .collect();
    (0..rows)
        .map(|row| {
            let floor = (rows - 1 - row) * 2;
            let mut line = " ".repeat(pad);
            for height in &heights {
                line.push(match height.saturating_sub(floor) {
                    0 => ' ',
                    1 => '\u{2584}',
                    _ => '\u{2588}',
                });
            }
            line
        })
        .collect()
}

/// A rule of exactly `cells` box-drawing horizontals.
///
/// `status::rule_line` is its only non-test caller today.
#[must_use]
pub fn rule(cells: usize) -> String {
    "\u{2500}".repeat(cells)
}

/// A section band: the two-block marker, the label, and padding to `cells`.
///
/// The caller styles it; this only lays it out. Truncates rather than
/// overflowing, since a band that runs past its `Rect` shifts the row.
#[must_use]
// Called by `view::mod`'s `section_band`.
pub fn band(label: &str, cells: usize) -> String {
    let head = format!(" \u{2588}\u{2588} {label}");
    let drawn: usize = text_columns(&head);
    if drawn >= cells {
        return super::flock::fit(&head, cells as u16);
    }
    let mut out = head;
    out.extend(std::iter::repeat_n(' ', cells - drawn));
    out
}

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

    #[test]
    fn a_gauge_fills_from_the_left_and_pads_with_the_light_shade() {
        assert_eq!(gauge(0, Some(100), 10), "░░░░░░░░░░");
        assert_eq!(gauge(50, Some(100), 10), "█████░░░░░");
        assert_eq!(gauge(100, Some(100), 10), "██████████");
    }

    #[test]
    fn a_gauge_over_its_ceiling_is_full_rather_than_wider() {
        assert_eq!(gauge(250, Some(100), 10), "██████████");
    }

    #[test]
    fn a_gauge_with_no_ceiling_is_all_tail() {
        assert_eq!(gauge(48, None, 10), "░░░░░░░░░░");
    }

    #[test]
    fn a_zero_ceiling_is_all_tail_rather_than_a_division_by_zero() {
        assert_eq!(gauge(48, Some(0), 10), "░░░░░░░░░░");
    }

    #[test]
    fn a_gauge_rounds_to_the_nearest_cell() {
        // 4 of 10 cells: 44% rounds down, 45% rounds up.
        assert_eq!(gauge(44, Some(100), 10), "████░░░░░░");
        assert_eq!(gauge(45, Some(100), 10), "█████░░░░░");
    }

    #[test]
    fn a_chart_at_the_ceiling_fills_every_row() {
        assert_eq!(chart(&[100.0], 100.0, 1, 4), ["█", "█", "█", "█"]);
    }

    #[test]
    fn a_chart_at_half_the_ceiling_fills_the_bottom_half() {
        assert_eq!(chart(&[50.0], 100.0, 1, 4), [" ", " ", "█", "█"]);
    }

    /// The half-block is the whole point of the cell: four rows carry eight
    /// steps, not four.
    #[test]
    fn an_odd_half_step_draws_the_lower_half_block() {
        assert_eq!(chart(&[12.5], 100.0, 1, 4), [" ", " ", " ", "▄"]);
    }

    #[test]
    fn a_chart_over_its_ceiling_fills_its_column() {
        assert_eq!(chart(&[250.0], 100.0, 1, 2), ["█", "█"]);
    }

    /// The `as usize` cast that turns a height into a row count saturates a
    /// negative value to zero rather than wrapping it, so a negative sample
    /// reads as blank rather than as a spurious full column. Nothing today
    /// produces a negative sample; this pins the cast anyway.
    #[test]
    fn a_negative_sample_reads_as_blank() {
        assert_eq!(chart(&[-50.0], 100.0, 1, 2), [" ", " "]);
    }

    /// Left-padded like `sparkline`, so the chart grows into its column from
    /// the right as history arrives rather than stretching to fit.
    #[test]
    fn a_chart_shorter_than_its_columns_pads_on_the_left() {
        assert_eq!(chart(&[100.0], 100.0, 3, 1), ["  █"]);
    }

    #[test]
    fn a_chart_longer_than_its_columns_keeps_the_newest() {
        assert_eq!(chart(&[100.0, 0.0, 0.0], 100.0, 2, 1), ["  "]);
    }

    /// No samples is blank rather than a floor line, for `sparkline`'s reason:
    /// a flat line reads as measured and idle, blank reads as not measured yet.
    /// `chart` has no empty-samples branch to mutate today, so this guards a
    /// future one: if a later change adds an explicit `is_empty` arm mirroring
    /// `sparkline`'s and gets it wrong, this is the test that would catch it.
    #[test]
    fn an_empty_chart_is_blank_rather_than_a_floor_line() {
        assert_eq!(chart(&[], 100.0, 3, 2), ["   ", "   "]);
    }

    #[test]
    fn a_sparkline_is_one_cell_per_sample_scaled_to_a_fixed_ceiling() {
        assert_eq!(sparkline(&[0.0, 50.0, 100.0], 3, 100.0), "▁▅█");
    }

    #[test]
    fn a_sparkline_over_its_ceiling_is_full_rather_than_wider() {
        assert_eq!(sparkline(&[250.0], 4, 100.0), "   █");
    }

    #[test]
    fn a_sparkline_shorter_than_its_cells_pads_on_the_left() {
        assert_eq!(sparkline(&[100.0], 4, 100.0), "   █");
    }

    #[test]
    fn a_sparkline_longer_than_its_cells_keeps_the_newest() {
        assert_eq!(sparkline(&[100.0, 0.0, 0.0], 2, 100.0), "▁▁");
    }

    #[test]
    fn an_empty_sparkline_is_blank_rather_than_a_flat_line() {
        // A flat line at the floor reads as measured-and-idle. Blank reads
        // as no data yet, which is what twenty seconds after start is.
        assert_eq!(sparkline(&[], 4, 100.0), "    ");
    }

    #[test]
    fn a_flat_sparkline_sits_at_the_floor() {
        assert_eq!(sparkline(&[0.0, 0.0, 0.0], 3, 100.0), "▁▁▁");
    }

    #[test]
    fn two_rows_at_different_loads_render_differently() {
        // The bug this fix closes: scaling each row to its own peak made an
        // idle sheep and a busy one both fill their column, so a reader
        // could not tell them apart. Scaling both to the same ceiling means
        // an idle row and a busy row read as idle and busy.
        let idle = sparkline(&[0.5, 0.5, 0.5], 3, 100.0);
        let busy = sparkline(&[80.0, 80.0, 80.0], 3, 100.0);
        assert_ne!(idle, busy);
        assert_eq!(idle, "▁▁▁");
    }

    #[test]
    fn a_shared_ceiling_keeps_a_busy_row_taller_than_a_quiet_one() {
        // The point of taking the ceiling from the caller: both rows are
        // scaled by the same number, so their heights can be compared with
        // each other. Scaled to their own peaks these two would be
        // identical, which is the failure this replaced.
        let ceiling = 40.0;
        assert_eq!(sparkline(&[4.0, 4.0, 4.0], 3, ceiling), "▂▂▂");
        assert_eq!(sparkline(&[40.0, 40.0, 40.0], 3, ceiling), "███");
    }

    #[test]
    fn a_ceiling_of_zero_does_not_divide_by_zero() {
        assert_eq!(sparkline(&[0.0, 1.0], 2, 0.0), "▁█");
    }

    #[test]
    fn a_rule_is_exactly_its_cells() {
        assert_eq!(rule(4), "────");
        assert_eq!(rule(0), "");
    }

    #[test]
    fn a_band_marks_its_label_and_pads_to_width() {
        assert_eq!(band("FLOCK", 20), " ██ FLOCK           ");
    }

    #[test]
    fn a_band_narrower_than_its_label_truncates_rather_than_overflowing() {
        assert_eq!(band("FLOCK", 6), " ██ F…");
    }
}