//! The chrome as data. Axes, tick labels, gridline positions, the readout,
//! markers' and spans' places and the direct-label anchors are handed to the
//! host, which draws them in the DOM: crisp at any zoom, themed by the page's
//! tokens, and read by assistive technology. Text wears the page's ink
//! tokens; a series' colour only marks its key (a short line beside its
//! name).
//!
//! Positions are CSS pixels from the plot area's top-left corner. Every
//! list keeps its capacity, so a frame writes the chrome without allocating;
//! `labels_changed` tells the host when text (not just positions) changed.

use crate::annot::Tint;
use crate::label::Label;
use crate::layout::Rect;
use crate::view::Mode;
use alloc::vec::Vec;

/// Most ticks an axis carries.
pub const MAX_TICKS: usize = 32;

/// One tick: where, and its label. Gridlines go at the same positions.
#[derive(Clone, Copy, Debug, PartialEq, Default)]
pub struct Tick {
    /// Position along the axis (x for the time axis, y for a lane), CSS px.
    pub pos: f32,
    /// The label (in the axis's unit, prefix included in `Axis::unit`).
    pub label: Label,
}

/// An axis.
#[derive(Clone, Debug, PartialEq, Default)]
pub struct Axis {
    /// Ticks, in order.
    pub ticks: Vec<Tick>,
    /// The unit with its prefix ("mV", "ms", "m:ss").
    pub unit: Label,
    /// Whether any label or the unit changed since the last frame.
    pub labels_changed: bool,
}

impl Axis {
    /// An axis with room for [`MAX_TICKS`].
    pub fn new() -> Axis {
        Axis {
            ticks: Vec::with_capacity(MAX_TICKS),
            unit: Label::new(),
            labels_changed: true,
        }
    }

    /// Starts writing a frame's ticks.
    pub fn begin(&mut self) -> AxisWriter<'_> {
        AxisWriter {
            axis: self,
            n: 0,
            changed: false,
        }
    }
}

/// Writes an axis's ticks in place, noting whether any label changed.
pub struct AxisWriter<'a> {
    axis: &'a mut Axis,
    n: usize,
    changed: bool,
}

impl AxisWriter<'_> {
    /// Adds a tick; `write` fills its label.
    pub fn tick(&mut self, pos: f32, write: impl FnOnce(&mut Label)) {
        if self.n >= MAX_TICKS {
            return;
        }
        let mut l = Label::new();
        write(&mut l);
        if self.n < self.axis.ticks.len() {
            let t = &mut self.axis.ticks[self.n];
            if t.label != l {
                self.changed = true;
                t.label = l;
            }
            t.pos = pos;
        } else {
            self.axis.ticks.push(Tick { pos, label: l });
            self.changed = true;
        }
        self.n += 1;
    }

    /// Sets the unit and finishes.
    pub fn finish(self, unit: &Label) {
        let changed = self.changed || self.n != self.axis.ticks.len() || self.axis.unit != *unit;
        self.axis.ticks.truncate(self.n);
        self.axis.unit = *unit;
        self.axis.labels_changed = changed;
    }
}

/// A lane's chrome.
#[derive(Clone, Debug, PartialEq, Default)]
pub struct LaneChrome {
    /// Where the lane is.
    pub rect: Rect,
    /// Its vertical axis (positions are y).
    pub y: Axis,
    /// Its range this frame.
    pub lo: f64,
    /// Its range this frame.
    pub hi: f64,
    /// The y of zero, if zero is in range (a baseline).
    pub zero: Option<f32>,
}

/// One series at the cursor: the value first, the name after.
#[derive(Clone, Copy, Debug, PartialEq, Default)]
pub struct ReadoutRow {
    /// Lane.
    pub lane: u16,
    /// Series in the lane.
    pub series: u16,
    /// Its colour slot (for its key).
    pub slot: u8,
    /// The value at the cursor's sample ("—" when there is none).
    pub value: Label,
    /// The unit with prefix.
    pub unit: Label,
    /// Where the value is on screen (CSS px), NaN when none.
    pub y: f32,
    /// The value as a number.
    pub v: f64,
    /// When the cursor's pixel column holds more than one sample: their
    /// least and greatest (empty labels otherwise).
    pub col_min: Label,
    /// See `col_min`.
    pub col_max: Label,
}

/// The crosshair and its readout.
#[derive(Clone, Debug, PartialEq, Default)]
pub struct Readout {
    /// Whether there is a cursor.
    pub visible: bool,
    /// Its x (CSS px), snapped to the focused lane's nearest sample.
    pub x: f32,
    /// Its page time.
    pub t: f64,
    /// Its time, written on the time axis's terms with finer decimals.
    pub time: Label,
    /// The time's unit.
    pub time_unit: Label,
    /// The lane the cursor snaps to.
    pub focus_lane: u16,
    /// Every series of every lane at that time.
    pub rows: Vec<ReadoutRow>,
}

/// A marker or span on screen.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct MarkChrome {
    /// x of a marker, or a span's left edge (CSS px).
    pub x0: f32,
    /// A span's right edge (equal to `x0` for a marker).
    pub x1: f32,
    /// The host's id.
    pub id: u32,
    /// Its tint.
    pub tint: Tint,
}

/// Where a series' newest visible value is, for a direct label.
#[derive(Clone, Copy, Debug, PartialEq, Default)]
pub struct EndLabel {
    /// Lane.
    pub lane: u16,
    /// Series in the lane.
    pub series: u16,
    /// y (CSS px), NaN when nothing is visible.
    pub y: f32,
}

/// Everything the host draws around and over the canvas.
#[derive(Clone, Debug, PartialEq, Default)]
pub struct Chrome {
    /// Frames made.
    pub frame: u64,
    /// The mode.
    pub mode: Mode,
    /// The window shown (page times).
    pub window: (f64, f64),
    /// The time axis (positions are x).
    pub x: Axis,
    /// The lanes, top to bottom.
    pub lanes: Vec<LaneChrome>,
    /// The cursor's readout.
    pub readout: Readout,
    /// Markers on screen.
    pub markers: Vec<MarkChrome>,
    /// Spans on screen.
    pub spans: Vec<MarkChrome>,
    /// Direct-label anchors.
    pub ends: Vec<EndLabel>,
    /// The scope's trigger x (CSS px) when one is shown.
    pub trigger_x: Option<f32>,
    /// The trigger's level as y in its lane (CSS px).
    pub trigger_y: Option<f32>,
}

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

    #[test]
    fn writing_notes_label_changes() {
        let mut a = Axis::new();
        let mut w = a.begin();
        w.tick(1.0, |l| l.push_str("0"));
        w.tick(2.0, |l| l.push_str("5"));
        w.finish(&Label::of("s"));
        assert!(a.labels_changed);
        let cap = a.ticks.capacity();
        // Same labels, new positions: only positions change.
        let mut w = a.begin();
        w.tick(1.5, |l| l.push_str("0"));
        w.tick(2.5, |l| l.push_str("5"));
        w.finish(&Label::of("s"));
        assert!(!a.labels_changed);
        assert_eq!(a.ticks[1].pos, 2.5);
        let mut w = a.begin();
        w.tick(1.5, |l| l.push_str("0"));
        w.finish(&Label::of("s"));
        assert!(a.labels_changed);
        assert_eq!(a.ticks.len(), 1);
        assert_eq!(a.ticks.capacity(), cap);
    }
}