//! Static gain-curve display (visualisation only): output level vs input level for the channel
//! currently selected in the plot. Plots the full channel transfer for the wet path:
//! `out = (in + pre_gain) + gain_reduction(in + pre_gain) + makeup`. Mix is not folded in (the
//! curve shows the wet/100% path, matching the GR-meter convention); output is clamped at 0 dBFS.

use nih_plug_egui::egui::{self, pos2, vec2, Align2, Color32, CornerRadius, FontId, Sense, Stroke};

use crate::dsp::compressor::Compressor;
use crate::params::Codename206Params;

/// Side length of the square plot.
const CURVE_SIZE: f32 = 150.0;
/// dB extent of both axes (bottom/left = FLOOR_DB, top/right = 0 dBFS).
const FLOOR_DB: f32 = -60.0;

pub(super) fn draw(ui: &mut egui::Ui, params: &Codename206Params, selected: usize) {
    let labels = ["LOW", "MID", "HIGH", "ALL"];
    let ch = selected.min(3);
    let cp = match ch {
        0 => &params.low,
        1 => &params.mid,
        2 => &params.high,
        _ => &params.all,
    };
    let pre = cp.pre_gain_db.value();
    let threshold = cp.threshold_db.value();
    let ratio = cp.ratio.value();
    let knee = cp.knee_db.value();
    let makeup = cp.makeup_db.value();

    ui.label(format!("Curve: {}", labels[ch]));
    let (rect, _) = ui.allocate_exact_size(vec2(CURVE_SIZE, CURVE_SIZE), Sense::hover());
    let p = ui.painter_at(rect);
    p.rect_filled(rect, CornerRadius::ZERO, Color32::from_rgb(16, 16, 20));

    let inset = 2.0;
    let (left, right, top, bottom) =
        (rect.left() + inset, rect.right() - inset, rect.top() + inset, rect.bottom() - inset);
    let w = right - left;
    let h = bottom - top;
    let x_for = |db: f32| left + (db - FLOOR_DB) / -FLOOR_DB * w;
    let y_for = |db: f32| bottom - (db - FLOOR_DB) / -FLOOR_DB * h;

    // Unity reference (out = in), bottom-left to top-right.
    p.line_segment([pos2(left, bottom), pos2(right, top)], Stroke::new(1.0, Color32::from_gray(45)));
    // Threshold marker on the input axis — shifted left by pre-gain (the comp sees in + pre).
    let tx = x_for((threshold - pre).clamp(FLOOR_DB, 0.0));
    p.line_segment([pos2(tx, top), pos2(tx, bottom)], Stroke::new(1.0, Color32::from_rgb(80, 60, 45)));

    // Full wet transfer: drive into the comp, then makeup. (Mix not folded in.)
    let n = 96;
    let mut pts = Vec::with_capacity(n + 1);
    for i in 0..=n {
        let in_db = FLOOR_DB + (i as f32 / n as f32) * -FLOOR_DB; // external input, -60..0
        let driven = in_db + pre;
        let gr = Compressor::gain_computer(driven, threshold, ratio, knee); // <= 0 dB
        let out_db = (driven + gr + makeup).clamp(FLOOR_DB, 0.0);
        pts.push(pos2(x_for(in_db), y_for(out_db)));
    }
    p.add(egui::Shape::line(pts, Stroke::new(1.6, Color32::from_rgb(120, 200, 160))));

    // Corner dB ticks.
    p.text(pos2(left + 1.0, top + 1.0), Align2::LEFT_TOP, "0", FontId::proportional(9.0), Color32::from_gray(90));
    p.text(pos2(left + 1.0, bottom - 1.0), Align2::LEFT_BOTTOM, "-60", FontId::proportional(9.0), Color32::from_gray(90));
}