#include "harness.hpp"

#include <plot/input/controller.hpp>
#include <plot/plot/plot.hpp>
#include <plot/data/array_series.hpp>
#include <plot/data/stream_series.hpp>

#include <cmath>
#include <limits>
#include <utility>
#include <vector>

namespace {

using plot::f32;
using plot::f64;
using plot::u32;

constexpr u32 kShift = static_cast<u32>(plot::input::Mod::Shift);
constexpr u32 kCtrl = static_cast<u32>(plot::input::Mod::Ctrl);
constexpr u32 kNoAxis = ~u32{0};

/// A 800x400 plot with one x axis spanning [0, 100] and the controller attached.
struct Fixture {
  plot::Plot plot;
  u32 ax = kNoAxis;
  u32 ay = kNoAxis;
  plot::input::Controller controller{plot};

  Fixture() {
    plot.set_viewport({0.0f, 0.0f, 800.0f, 400.0f});
    ax = plot.add_x_axis({"t", {0.0, 100.0}, false, plot::AxisPlace::Bottom, false});
    controller.set_viewport({0.0f, 0.0f, 800.0f, 400.0f});
  }
};

f32 screen_x_of(const plot::Plot& p, u32 axis, f64 data) {
  return static_cast<f32>(p.x_transform(axis).to_screen_x(data));
}

}  // namespace

PLOT_TEST(wheel_zoom_keeps_data_under_cursor_fixed) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, true, plot::AxisPlace::Bottom, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const f32 cursor_x = 200.0f;
  const f64 before = p.x_transform(ax).to_data_x(cursor_x);
  plot::input::WheelEvent w{cursor_x, 100.0f, 0.0f, 1.0f, 0};
  c.on_wheel(w);
  const f64 after = p.x_transform(ax).to_data_x(cursor_x);
  PLOT_CHECK_NEAR(before, after, 1e-6);
  PLOT_CHECK(plot::Range{p.x_range(ax)}.span() < 100.0);  // zoomed in
}

PLOT_TEST(left_drag_pans_without_changing_span) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, true, plot::AxisPlace::Bottom, false});
  const u32 ay = p.add_y_axis({"v", {-1.0, 1.0}, true, plot::AxisPlace::Left, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const double span_before = p.x_range(ax).span();
  const f64 grabbed = p.x_transform(ax).to_data_x(100.0f);  // data under the press point
  c.on_pointer({100, 100, 0, 0, plot::input::Button::Left, 0, true, true, false});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::Pan);
  c.on_pointer({180, 130, 80, 30, plot::input::Button::Left, 0, true, false, false});
  c.on_pointer({180, 130, 0, 0, plot::input::Button::Left, 0, false, false, true});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::None);
  PLOT_CHECK_NEAR(p.x_range(ax).span(), span_before, 1e-9);  // span unchanged
  // Assert the INVARIANT, not a pixel fraction. Grab-and-drag means the data
  // grabbed at the press point is under the pointer afterwards. Pixels map to
  // data through layout().axes, NOT the whole viewport: the viewport model makes
  // dragged data lag the cursor by the label-strip fraction, a defect no
  // pixel-fraction assertion can see because it certifies its own arithmetic.
  PLOT_CHECK_NEAR(p.x_transform(ax).to_data_x(180.0f), grabbed, 1e-9);
  PLOT_CHECK(p.y_range(ay).max > 1.0);  // moving down raises y range
  PLOT_CHECK(!p.x_axis(ax).auto_scale);  // a pan is a user choice, not a fit
}

PLOT_TEST(shift_drag_box_zooms_to_selection) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 800.0}, true, plot::AxisPlace::Bottom, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const u32 e_shift = 1u << 0;  // Mod::Shift
  const f64 want_lo = p.x_transform(ax).to_data_x(100.0f);
  const f64 want_hi = p.x_transform(ax).to_data_x(300.0f);
  c.on_pointer({100, 50, 0, 0, plot::input::Button::Left, e_shift, true, true, false});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::BoxZoom);
  c.on_pointer({300, 150, 200, 100, plot::input::Button::Left, e_shift, true, false, false});
  PLOT_CHECK_NEAR(c.selection_rect().x, 100.0, 1e-6);
  PLOT_CHECK_NEAR(c.selection_rect().w, 200.0, 1e-6);
  c.on_pointer({300, 150, 0, 0, plot::input::Button::Left, e_shift, false, false, true});
  // The box frames exactly the data it encloses: the ranges come from the axes
  // transform, and the selection is clamped to layout().axes, not the viewport.
  PLOT_CHECK_NEAR(p.x_range(ax).min, want_lo, 1e-6);
  PLOT_CHECK_NEAR(p.x_range(ax).max, want_hi, 1e-6);
}

PLOT_TEST(box_zoom_uses_release_position_without_a_move) {
  // A host that reports only a press and a release -- no motion event between
  // them -- MUST still frame the box the release describes: the release position
  // is authoritative for the end of the gesture.
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 800.0}, true, plot::AxisPlace::Bottom, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const f64 want_lo = p.x_transform(ax).to_data_x(100.0f);
  const f64 want_hi = p.x_transform(ax).to_data_x(300.0f);
  c.on_pointer({100, 50, 0, 0, plot::input::Button::Left, kShift, true, true, false});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::BoxZoom);
  // No move: selection_ is still 0x0 until the release supplies the far corner.
  c.on_pointer({300, 150, 0, 0, plot::input::Button::Left, kShift, false, false, true});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::None);
  PLOT_CHECK_NEAR(p.x_range(ax).min, want_lo, 1e-6);
  PLOT_CHECK_NEAR(p.x_range(ax).max, want_hi, 1e-6);
  PLOT_CHECK(!p.x_axis(ax).auto_scale);  // a box zoom is a user choice, not a fit
}

PLOT_TEST(auto_scale_disabled_by_user_interaction) {
  // A wheel zoom or pan MUST clear auto_scale on the affected axis so the range
  // the user chose is not snapped back by the next autoscale.
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, true, plot::AxisPlace::Bottom, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  c.on_wheel({400.0f, 200.0f, 0.0f, 1.0f, 0});
  PLOT_CHECK(!p.x_axis(ax).auto_scale);
}

// --- resolutions of the brief's ambiguity, pinned ------------------------

PLOT_TEST(box_zoom_below_threshold_is_a_click) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 800.0}, false, plot::AxisPlace::Bottom, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  c.on_pointer({100, 50, 0, 0, plot::input::Button::Left, kShift, true, true, false});
  c.on_pointer({102, 52, 2, 2, plot::input::Button::Left, kShift, true, false, false});
  c.on_pointer({102, 52, 0, 0, plot::input::Button::Left, kShift, false, false, true});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::None);
  PLOT_CHECK_NEAR(p.x_range(ax).min, 0.0, 1e-9);
  PLOT_CHECK_NEAR(p.x_range(ax).max, 800.0, 1e-9);
}

PLOT_TEST(shift_wheel_zooms_x_only) {
  Fixture f;
  f.ay = f.plot.add_y_axis({"v", {-1.0, 1.0}, false, plot::AxisPlace::Left, false});
  f.controller.on_wheel({400.0f, 200.0f, 0.0f, 1.0f, kShift});
  PLOT_CHECK(f.plot.x_range(f.ax).span() < 100.0);
  PLOT_CHECK_NEAR(f.plot.y_range(f.ay).span(), 2.0, 1e-9);
}

PLOT_TEST(ctrl_wheel_zooms_y_only) {
  Fixture f;
  f.ay = f.plot.add_y_axis({"v", {-1.0, 1.0}, false, plot::AxisPlace::Left, false});
  f.controller.on_wheel({400.0f, 200.0f, 0.0f, 1.0f, kCtrl});
  PLOT_CHECK_NEAR(f.plot.x_range(f.ax).span(), 100.0, 1e-9);
  PLOT_CHECK(f.plot.y_range(f.ay).span() < 2.0);
}

PLOT_TEST(hovered_cursor_only_inside_plot_area) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, false, plot::AxisPlace::Bottom, false});
  const u32 cid = p.add_cursor(50.0, plot::Color::hex(0xFF0000));
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const f32 sx = screen_x_of(p, ax, 50.0);
  c.on_pointer({sx, 200, 0, 0, plot::input::Button::Left, 0, false, false, false});
  PLOT_CHECK(c.hovered_cursor() == cid);
  // The left label strip is outside the plot area.
  c.on_pointer({10, 200, 0, 0, plot::input::Button::Left, 0, false, false, false});
  PLOT_CHECK(c.hovered_cursor() == plot::kInvalid);
  c.on_pointer({sx, 200, 0, 0, plot::input::Button::Left, 0, false, false, false});
  PLOT_CHECK(c.hovered_cursor() == cid);
}

PLOT_TEST(ctrl_drag_moves_the_nearest_cursor) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, false, plot::AxisPlace::Bottom, false});
  const u32 cid = p.add_cursor(20.0, plot::Color::hex(0xFF0000));
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const f32 sx = screen_x_of(p, ax, 20.0);
  c.on_pointer({sx, 200, 0, 0, plot::input::Button::Left, kCtrl, true, true, false});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::MoveCursor);
  c.on_pointer({sx + 100, 200, 100, 0, plot::input::Button::Left, kCtrl, true, false, false});
  c.on_pointer({sx + 100, 200, 0, 0, plot::input::Button::Left, kCtrl, false, false, true});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::None);
  PLOT_CHECK(p.cursor(cid).x > 20.0);
  PLOT_CHECK_NEAR(p.cursor(cid).x, p.x_transform(ax).to_data_x(sx + 100), 1e-9);
}

PLOT_TEST(middle_drag_on_x_strip_zooms_x_only) {
  Fixture f;
  f.ay = f.plot.add_y_axis({"v", {-1.0, 1.0}, true, plot::AxisPlace::Left, false});
  const plot::PlotLayout& l = f.plot.layout();
  const f32 strip_x = l.axes.x + 0.5f * l.axes.w;
  const f32 strip_y = l.x_label_area.y + 0.5f * l.x_label_area.h;
  f.controller.on_pointer({strip_x, strip_y, 0, 0, plot::input::Button::Middle, 0, true, true, false});
  PLOT_CHECK(f.controller.drag_mode() == plot::input::DragMode::AxisZoomX);
  // Same sign convention as the wheel: a positive dy zooms in.
  f.controller.on_pointer({strip_x, strip_y + 20, 0, 20, plot::input::Button::Middle, 0, true, false, false});
  f.controller.on_pointer({strip_x, strip_y + 20, 0, 0, plot::input::Button::Middle, 0, false, false, true});
  // 20 px of drag is a tenth of a decade: the span is 10^(-20/200) of its
  // former self. A pixel is not a wheel notch, so this pins the magnitude.
  PLOT_CHECK_NEAR(f.plot.x_range(f.ax).span(), 100.0 * std::pow(10.0, -20.0 / 200.0), 1e-6);
  PLOT_CHECK_NEAR(f.plot.y_range(f.ay).span(), 2.0, 1e-9);
  PLOT_CHECK(!f.plot.x_axis(f.ax).auto_scale);
  PLOT_CHECK(f.plot.y_axis(f.ay).auto_scale);  // the untouched y axis keeps auto scale
}

PLOT_TEST(middle_drag_on_y_strip_zooms_y_only) {
  Fixture f;
  f.ay = f.plot.add_y_axis({"v", {-1.0, 1.0}, false, plot::AxisPlace::Left, false});
  const plot::PlotLayout& l = f.plot.layout();
  const f32 strip_x = l.y_label_area.x + 0.5f * l.y_label_area.w;
  const f32 strip_y = l.axes.y + 0.5f * l.axes.h;
  f.controller.on_pointer({strip_x, strip_y, 0, 0, plot::input::Button::Middle, 0, true, true, false});
  PLOT_CHECK(f.controller.drag_mode() == plot::input::DragMode::AxisZoomY);
  f.controller.on_pointer({strip_x, strip_y + 20, 0, 20, plot::input::Button::Middle, 0, true, false, false});
  f.controller.on_pointer({strip_x, strip_y + 20, 0, 0, plot::input::Button::Middle, 0, false, false, true});
  PLOT_CHECK_NEAR(f.plot.x_range(f.ax).span(), 100.0, 1e-9);
  PLOT_CHECK_NEAR(f.plot.y_range(f.ay).span(), 2.0 * std::pow(10.0, -20.0 / 200.0), 1e-6);
}

PLOT_TEST(key_plus_zooms_in_about_the_centre) {
  Fixture f;
  const f64 mid_before = 0.5 * (f.plot.x_range(f.ax).min + f.plot.x_range(f.ax).max);
  f.controller.on_key({plot::input::kKeyZoomIn, 0, true});
  PLOT_CHECK(f.plot.x_range(f.ax).span() < 100.0);
  PLOT_CHECK_NEAR(0.5 * (f.plot.x_range(f.ax).min + f.plot.x_range(f.ax).max), mid_before, 1e-9);
  const f64 span_after = f.plot.x_range(f.ax).span();
  f.controller.on_key({plot::input::kKeyZoomIn, 0, false});  // key-up is ignored
  PLOT_CHECK_NEAR(f.plot.x_range(f.ax).span(), span_after, 1e-12);
}

PLOT_TEST(key_minus_zooms_out) {
  Fixture f;
  f.controller.on_key({plot::input::kKeyZoomOut, 0, true});
  PLOT_CHECK(f.plot.x_range(f.ax).span() > 100.0);
}

/// A host can hand the controller a coordinate that is not a number: ImGui reports
/// (-FLT_MAX, -FLT_MAX) for "no mouse position", and any host can produce a NaN out
/// of a degenerate mapping of its own. The pan arithmetic runs through the axis
/// transforms, so such a value would leave a range that is not a range -- and
/// because a gesture that sets a range also clears auto scale, panning and zooming
/// could not bring it back.
PLOT_TEST(non_finite_pointer_does_not_move_a_range) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, true, plot::AxisPlace::Bottom, false});
  const u32 ay = p.add_y_axis({"v", {-1.0, 1.0}, true, plot::AxisPlace::Left, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  const plot::Range xr = p.x_range(ax);
  const plot::Range yr = p.y_range(ay);

  c.on_pointer({100, 100, 0, 0, plot::input::Button::Left, 0, true, true, false});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::Pan);

  const float inf = std::numeric_limits<float>::infinity();
  const float nan = std::numeric_limits<float>::quiet_NaN();
  const float sentinel = -std::numeric_limits<float>::max();  // ImGui's "no pointer"

  // The pointer-left-the-window sentinel arrives at the unrepresentable end of the
  // axis, so scaling and differencing it is a 1e35 pan. It must read as no
  // movement at all.
  c.on_pointer({sentinel, sentinel, inf, -inf, plot::input::Button::Left, 0, true, false, false});
  PLOT_CHECK(std::isfinite(p.x_range(ax).min) && std::isfinite(p.x_range(ax).max));
  PLOT_CHECK(std::isfinite(p.y_range(ay).min) && std::isfinite(p.y_range(ay).max));
  PLOT_CHECK_NEAR(p.x_range(ax).min, xr.min, 1e-9);
  PLOT_CHECK_NEAR(p.x_range(ax).max, xr.max, 1e-9);
  PLOT_CHECK_NEAR(p.y_range(ay).min, yr.min, 1e-9);
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::Pan);  // still the same drag

  // A usable position with an unusable delta is no movement either, and a later
  // usable position is not differenced against the sentinel.
  c.on_pointer({180, 130, inf, nan, plot::input::Button::Left, 0, true, false, false});
  PLOT_CHECK_NEAR(p.x_range(ax).min, xr.min, 1e-9);
  PLOT_CHECK_NEAR(p.x_range(ax).max, xr.max, 1e-9);
  PLOT_CHECK_NEAR(p.y_range(ay).min, yr.min, 1e-9);
  c.on_pointer({220, 160, 40, 30, plot::input::Button::Left, 0, true, false, false});
  PLOT_CHECK(std::isfinite(p.x_range(ax).min));  // a real move still pans
  PLOT_CHECK(p.x_range(ax).min < xr.min);

  // The buttons in a sanitised event still act: the release ends the drag.
  c.on_pointer({220, 160, 0, 0, plot::input::Button::Left, 0, false, false, true});
  PLOT_CHECK(c.drag_mode() == plot::input::DragMode::None);
}

PLOT_TEST(non_finite_wheel_does_not_break_a_range) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, true, plot::AxisPlace::Bottom, false});
  const u32 ay = p.add_y_axis({"v", {-1.0, 1.0}, true, plot::AxisPlace::Left, false});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});

  const float inf = std::numeric_limits<float>::infinity();
  const float nan = std::numeric_limits<float>::quiet_NaN();

  // A zoom is anchored at the data coordinate under the pointer, so a position that
  // is not a number must not become the anchor: the axis would be re-centred on
  // NaN, which no gesture could undo. The fallback is a real coordinate and the
  // zoom still happens. (A *finite* sentinel -- ImGui's `-FLT_MAX` for "no pointer"
  // -- is not the controller's to interpret: finite coordinates are legal input.
  // The adapter translates that one; see tests/test_imgui_widget.cpp.)
  const double span_before = p.x_range(ax).span();
  c.on_wheel({nan, nan, 0.0f, 1.0f, 0});
  PLOT_CHECK(std::isfinite(p.x_range(ax).min) && std::isfinite(p.x_range(ax).max));
  PLOT_CHECK(std::isfinite(p.y_range(ay).min) && std::isfinite(p.y_range(ay).max));
  PLOT_CHECK(std::fabs(p.x_range(ax).min) < 1e6 && std::fabs(p.x_range(ax).max) < 1e6);
  PLOT_CHECK(p.x_range(ax).span() < span_before);

  // A non-finite amount is no zoom at all -- and, just as important, it must not
  // touch the axes. A *zeroed* amount would be a zero-notch zoom (a factor of
  // exactly one): the range would survive, but the range setters it runs through
  // clear auto scale, so one garbage wheel would quietly disarm auto-fit.
  p.set_x_auto_scale(ax, true);
  p.set_y_auto_scale(ay, true);
  const plot::Range xr = p.x_range(ax);
  const plot::Range yr = p.y_range(ay);
  c.on_wheel({400.0f, 200.0f, 0.0f, nan, 0});
  c.on_wheel({400.0f, 200.0f, 0.0f, inf, 0});
  PLOT_CHECK_NEAR(p.x_range(ax).min, xr.min, 1e-12);
  PLOT_CHECK_NEAR(p.x_range(ax).max, xr.max, 1e-12);
  PLOT_CHECK_NEAR(p.y_range(ay).min, yr.min, 1e-12);
  PLOT_CHECK(p.x_axis(ax).auto_scale);
  PLOT_CHECK(p.y_axis(ay).auto_scale);
}

PLOT_TEST(key_f_auto_fits_traces) {
  plot::Plot p;
  p.set_viewport({0, 0, 800, 400});
  const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, false, plot::AxisPlace::Bottom, false});
  const u32 ay = p.add_y_axis({"v", {-1.0, 1.0}, false, plot::AxisPlace::Left, false});
  std::vector<f32> ys(51);
  for (u64 i = 0; i < ys.size(); ++i) ys[i] = static_cast<f32>(i) * 0.1f;  // 0.0 .. 5.0
  plot::data::ArraySeries s(std::move(ys), 0.0, 1.0);                       // x = 0 .. 50
  p.add_trace({&s, plot::Color::hex(0x4FA3FF), 1.5f, 0, 0});
  plot::input::Controller c(p);
  c.set_viewport({0, 0, 800, 400});
  c.on_key({plot::input::kKeyFit, 0, true});
  PLOT_CHECK(p.x_range(ax).min < 0.0);
  PLOT_CHECK(p.x_range(ax).max < 100.0);  // fitted to the series' 0..50
  PLOT_CHECK(p.y_range(ay).min < 0.0);
  PLOT_CHECK(p.y_range(ay).max > 1.0);  // fitted to the series' 0..5
  PLOT_CHECK(p.x_axis(ax).auto_scale);  // a fit re-arms auto scale
  PLOT_CHECK(p.y_axis(ay).auto_scale);
}

// --- tolerances are logical, coordinates are device pixels -------------------

/// The grab radius is a distance the user aims with, so it must be the same
/// *physical* distance at any DPI: the controller compares device-pixel coordinates
/// against `logical * Plot::ui_scale()`. The press positions below are the same
/// logical distance (0.9 and 1.1 of the 5 px radius) from the cursor at both scales,
/// so the same press grabs -- and the same press just outside does not.
PLOT_TEST(grab_radius_scales_with_dpi) {
  for (const f32 scale : {1.0f, 2.0f}) {
    plot::Plot p;
    p.set_ui_scale(scale);
    p.set_viewport({0, 0, 800.0f * scale, 400.0f * scale});
    const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, false, plot::AxisPlace::Bottom, false});
    const u32 cid = p.add_cursor(50.0, plot::Color::hex(0xFF0000));
    plot::input::Controller c(p);
    c.set_viewport({0, 0, 800.0f * scale, 400.0f * scale});
    PLOT_CHECK_NEAR(p.ui_scale(), scale, 1e-6);

    const f32 sx = screen_x_of(p, ax, 50.0);
    const f32 inside = 0.9f * 5.0f * scale;   // logical: within the grab radius
    const f32 outside = 1.1f * 5.0f * scale;  // logical: just past it
    c.on_pointer({sx + inside, 200.0f * scale, 0, 0, plot::input::Button::Left, 0, false, false,
                  false});
    PLOT_CHECK(c.hovered_cursor() == cid);
    c.on_pointer({sx + outside, 200.0f * scale, 0, 0, plot::input::Button::Left, 0, false, false,
                  false});
    PLOT_CHECK(c.hovered_cursor() == plot::kInvalid);
    // ...and a ctrl-drag at that same logical distance opens a cursor move, which is
    // the gesture the radius actually gates.
    c.on_pointer({sx + inside, 200.0f * scale, 0, 0, plot::input::Button::Left, kCtrl, true, true,
                  false});
    PLOT_CHECK(c.drag_mode() == plot::input::DragMode::MoveCursor);
  }
}

/// The box-zoom click threshold is a hand movement too: a selection the user
/// perceives as a few pixels is a click at any DPI, so both dimensions are compared
/// against `logical * Plot::ui_scale()`.
PLOT_TEST(box_zoom_click_threshold_scales_with_dpi) {
  for (const f32 scale : {1.0f, 2.0f}) {
    plot::Plot p;
    p.set_ui_scale(scale);
    p.set_viewport({0, 0, 800.0f * scale, 400.0f * scale});
    const u32 ax = p.add_x_axis({"t", {0.0, 800.0}, true, plot::AxisPlace::Bottom, false});
    plot::input::Controller c(p);
    c.set_viewport({0, 0, 800.0f * scale, 400.0f * scale});
    const plot::Range before = p.x_range(ax);

    // 3 logical px on each side: a click, at both scales.
    const f32 x0 = 100.0f * scale;
    const f32 y0 = 50.0f * scale;
    const f32 small = 3.0f * scale;
    c.on_pointer({x0, y0, 0, 0, plot::input::Button::Left, kShift, true, true, false});
    c.on_pointer({x0 + small, y0 + small, small, small, plot::input::Button::Left, kShift, true,
                  false, false});
    c.on_pointer({x0 + small, y0 + small, 0, 0, plot::input::Button::Left, kShift, false, false,
                  true});
    PLOT_CHECK_NEAR(p.x_range(ax).min, before.min, 1e-9);
    PLOT_CHECK_NEAR(p.x_range(ax).max, before.max, 1e-9);

    // 5 logical px on each side: a box, at both scales.
    const f32 large = 5.0f * scale;
    c.on_pointer({x0, y0, 0, 0, plot::input::Button::Left, kShift, true, true, false});
    c.on_pointer({x0 + large, y0 + large, large, large, plot::input::Button::Left, kShift, true,
                  false, false});
    c.on_pointer({x0 + large, y0 + large, 0, 0, plot::input::Button::Left, kShift, false, false,
                  true});
    PLOT_CHECK(p.x_range(ax).min > before.min);
    PLOT_CHECK(p.x_range(ax).max < before.max);
  }
}

// --------------------------------------------- live x follow (spec §12)
//
// The gestures on an axis that is following live data. Every path below already
// existed; what is new is that none of them disarms following, and that the ranges
// they set are read by `Plot::set_x_range` as a span and an offset behind the live
// edge rather than as absolute positions.

namespace {

/// A streaming plot under the controller: one `StreamSeries` on one x axis, 800x400,
/// with `push` samples already produced and acquired. The axis starts 10 units wide;
/// a case arms following when it needs it, so "Off is the default" is the state every
/// case here starts from.
struct LiveFixture {
  plot::data::StreamSeries series;
  plot::Plot graph;
  plot::input::Controller controller{graph};
  u32 ax = 0;
  u32 ay = 0;

  explicit LiveFixture(u64 retain, u64 push) : series(retain, 0.0, 1.0) {
    graph.set_viewport({0.0f, 0.0f, 800.0f, 400.0f});
    ax = graph.add_x_axis({"t", {0.0, 10.0}, false, plot::AxisPlace::Bottom, false});
    ay = graph.add_y_axis({"v", {-1.0, 1.0}, false, plot::AxisPlace::Left, false});
    graph.add_trace({&series, plot::Color::hex(0x4FA3FF), 1.5f, ax, ay});
    feed(push);
    controller.set_viewport({0.0f, 0.0f, 800.0f, 400.0f});
  }

  void feed(u64 n) {
    for (u64 i = 0; i < n; ++i) series.push(0.0f);
    series.acquire();
  }
  void live() { graph.set_x_follow(ax, plot::XFollow::Live); }
  f64 newest() const { return series.x_bounds().max; }
  plot::Range xr() const { return graph.x_range(ax); }
};

/// The centre of the x label strip: outside `axes`, which is where a zoom's anchor
/// falls back to the live edge, and where the middle-drag x zoom is aimed anyway.
plot::input::WheelEvent strip_wheel(const plot::Plot& p, f32 notches) {
  const plot::Rect strip = std::as_const(p).layout().x_label_area;
  return {strip.x + 0.5f * strip.w, strip.y + 0.5f * strip.h, 0.0f, notches, 0};
}

/// One left drag of `dx` device pixels across the axes, through the controller.
void drag(plot::input::Controller& c, const plot::Rect& axes, f32 dx) {
  const f32 x = axes.x + 0.5f * axes.w;
  const f32 y = axes.y + 0.5f * axes.h;
  c.on_pointer({x, y, 0.0f, 0.0f, plot::input::Button::Left, 0, true, true, false});
  c.on_pointer({x + dx, y, dx, 0.0f, plot::input::Button::Left, 0, true, false, false});
  c.on_pointer({x + dx, y, 0.0f, 0.0f, plot::input::Button::Left, 0, false, false, true});
}

}  // namespace

/// The regression §12 exists for. Today a wheel zoom clears the x axis' auto scale,
/// and a live plot then stops following the newest sample for good: the window stays
/// where the zoom left it while the stream walks out of it. Under `Live` the span
/// shrinks, following stays armed, and the window keeps ending where it ended --
/// which is asserted by *both* halves below, because the edge is the newest sample
/// only for a zoom anchored on it.
PLOT_TEST(wheel_zoom_keeps_following) {
  LiveFixture f(200, 40);
  f.graph.set_x_auto_scale(f.ax, true);  // the only way to follow before this feature
  f.graph.layout();
  f.live();
  const f64 span_before = f.xr().span();
  const plot::Rect axes = std::as_const(f.graph).layout().axes;

  // A notch from outside `axes` anchors on the live edge, so the window still ends
  // at the newest sample afterwards -- and goes on doing so as data arrives.
  f.controller.on_wheel(strip_wheel(f.graph, 1.0f));
  PLOT_CHECK(f.xr().span() < span_before);
  PLOT_CHECK_NEAR(f.xr().max, f.newest(), 1e-9);
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Live);
  f.feed(20);
  f.graph.layout();
  PLOT_CHECK_NEAR(f.xr().max, f.newest(), 1e-9);
  const f64 zoomed = f.xr().span();

  // A notch from inside `axes` anchors on the data under the pointer, which pushes
  // the window back from the edge by what the zoom chose -- and it still follows:
  // that distance is constant as the stream advances, so the newest sample is the
  // same distance off the right edge on every frame instead of drifting away.
  f.controller.on_wheel({axes.x + 0.5f * axes.w, axes.y + 0.5f * axes.h, 0.0f, 1.0f, 0});
  PLOT_CHECK_NEAR(f.xr().span(), zoomed * std::exp(-0.15), 1e-9);
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Live);
  const f64 behind = f.newest() - f.xr().max;
  PLOT_CHECK(behind > 0.0);
  f.feed(25);
  f.graph.layout();
  PLOT_CHECK_NEAR(f.newest() - f.xr().max, behind, 1e-9);
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Live);
}

/// Two half-notches are one full notch, because the wheel *multiplies* the span: an
/// additive step would give `2 * (span - d/2) != span - d`. The two fixtures have
/// identical state, so the comparison is exact -- and the pinned value says which
/// arithmetic produced it.
PLOT_TEST(wheel_zoom_is_relative) {
  LiveFixture a(200, 40);
  LiveFixture b(200, 40);
  a.live();
  b.live();
  PLOT_CHECK_NEAR(a.xr().span(), b.xr().span(), 1e-12);  // same state to start from

  a.controller.on_wheel(strip_wheel(a.graph, 0.5f));
  a.controller.on_wheel(strip_wheel(a.graph, 0.5f));
  b.controller.on_wheel(strip_wheel(b.graph, 1.0f));
  PLOT_CHECK_NEAR(a.xr().span(), b.xr().span(), 1e-9);
  PLOT_CHECK_NEAR(b.xr().span(), 10.0 * std::exp(-0.15), 1e-9);
  PLOT_CHECK(a.xr().span() < 10.0);
  // Each window still ends at its own live edge, so the relative zoom kept following.
  PLOT_CHECK_NEAR(a.xr().max, a.newest(), 1e-9);
  PLOT_CHECK_NEAR(b.xr().max, b.newest(), 1e-9);
  PLOT_CHECK(a.graph.x_follow(a.ax) == plot::XFollow::Live);
  PLOT_CHECK(b.graph.x_follow(b.ax) == plot::XFollow::Live);
}

/// Panning a live plot moves the window, not the scale: the offset grows by the
/// drag's data delta, the span is untouched, and following is still armed. Dragging
/// right reveals earlier data, which for a live window means moving back from the
/// edge -- and the window then keeps that distance as the stream advances.
PLOT_TEST(mouse_pan_shifts_the_offset_and_preserves_the_span) {
  LiveFixture f(200, 40);
  f.live();
  const f64 span = f.xr().span();
  const plot::Rect axes = std::as_const(f.graph).layout().axes;
  const f32 dx = 60.0f;
  drag(f.controller, axes, dx);

  const f64 want = static_cast<f64>(dx) / static_cast<f64>(axes.w) * span;
  PLOT_CHECK_NEAR(f.graph.x_offset(f.ax), want, 1e-9);
  PLOT_CHECK_NEAR(f.xr().span(), span, 1e-9);
  PLOT_CHECK_NEAR(f.xr().max, f.newest() - want, 1e-9);
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Live);
  PLOT_CHECK(f.controller.drag_mode() == plot::input::DragMode::None);

  f.feed(20);
  f.graph.layout();
  PLOT_CHECK_NEAR(f.graph.x_offset(f.ax), want, 1e-9);
  PLOT_CHECK_NEAR(f.xr().span(), span, 1e-9);
  PLOT_CHECK_NEAR(f.xr().max, f.newest() - want, 1e-9);
}

/// Dragging toward the live edge stops at it: the offset clamps at 0, so the window
/// ends at the newest sample instead of turning inside out -- the failure an
/// unclamped offset would produce, and one no gesture could undo.
PLOT_TEST(pan_cannot_pass_the_live_edge) {
  LiveFixture f(200, 40);
  f.live();
  const plot::Rect axes = std::as_const(f.graph).layout().axes;
  drag(f.controller, axes, 100.0f);  // back from the edge
  PLOT_CHECK(f.graph.x_offset(f.ax) > 0.0);
  const f64 span = f.xr().span();

  drag(f.controller, axes, -300.0f);  // hard toward it, past it
  PLOT_CHECK_NEAR(f.graph.x_offset(f.ax), 0.0, 1e-9);
  PLOT_CHECK_NEAR(f.xr().max, f.newest(), 1e-9);
  PLOT_CHECK_NEAR(f.xr().span(), span, 1e-9);
  PLOT_CHECK(f.xr().min < f.xr().max);  // a real window, not an inverted one
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Live);
}

/// The point of an offset: a user who scrolled back keeps seeing what they scrolled
/// to. The window advances by exactly what the stream advanced, so the sample at its
/// right edge is the same one frame after frame, and the span is unchanged.
PLOT_TEST(offset_survives_new_samples) {
  LiveFixture f(200, 48);
  f.live();
  f.graph.set_x_offset(f.ax, 10.0);
  const f64 span = f.xr().span();
  const f64 newest0 = f.newest();
  const f64 edge_sample = f.xr().max;
  PLOT_CHECK_NEAR(edge_sample, newest0 - 10.0, 1e-9);

  for (int i = 0; i < 4; ++i) {
    f.feed(5);
    f.graph.layout();
    PLOT_CHECK_NEAR(f.graph.x_offset(f.ax), 10.0, 1e-9);
    PLOT_CHECK_NEAR(f.xr().span(), span, 1e-9);
    PLOT_CHECK_NEAR(f.xr().max - edge_sample, f.newest() - newest0, 1e-9);
    // ...and it lands on a sample, so the same sample is at the right edge rather
    // than the window having crept between two of them.
    PLOT_CHECK_NEAR((f.xr().max - newest0) / f.series.dx(),
                    std::round((f.xr().max - newest0) / f.series.dx()), 1e-9);
  }
  PLOT_CHECK_NEAR(f.xr().max, f.newest() - 10.0, 1e-9);
}

/// The pre-existing behaviour, pinned so the mode is provably opt-in: on an `Off`
/// axis a gesture clears auto scale and the window then stays exactly where the
/// gesture left it, however much data arrives. That is what following replaces, and
/// it is still what an untouched plot does -- the six other controller cases above
/// are about this path.
PLOT_TEST(off_plot_zoom_and_pan_are_unchanged) {
  LiveFixture f(200, 40);
  f.graph.set_x_auto_scale(f.ax, true);
  f.graph.layout();  // today's implicit "follow": fit the retained window
  const plot::Range fitted = f.xr();
  const plot::Rect axes = std::as_const(f.graph).layout().axes;

  const f32 px = axes.x + 0.3f * axes.w;
  const f64 under = f.graph.x_transform(f.ax).to_data_x(px);
  f.controller.on_wheel({px, axes.y + 0.5f * axes.h, 0.0f, 1.0f, 0});
  PLOT_CHECK_NEAR(f.graph.x_transform(f.ax).to_data_x(px), under, 1e-9);  // anchor still
  PLOT_CHECK(f.xr().span() < fitted.span());
  PLOT_CHECK(!f.graph.x_axis(f.ax).auto_scale);  // a gesture is still a user choice
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Off);  // and arms nothing

  const f64 span = f.xr().span();
  const f64 grabbed = f.graph.x_transform(f.ax).to_data_x(axes.x + 0.25f * axes.w);
  drag(f.controller, axes, 60.0f);
  PLOT_CHECK_NEAR(f.xr().span(), span, 1e-9);
  PLOT_CHECK_NEAR(f.graph.x_transform(f.ax).to_data_x(axes.x + 0.25f * axes.w + 60.0f), grabbed,
                  1e-9);

  // Frozen: the stream walks on and the window does not move. This is the pre-fix
  // behaviour, and the reason `Live` exists.
  const plot::Range frozen = f.xr();
  f.feed(30);
  f.graph.layout();
  PLOT_CHECK_NEAR(f.xr().min, frozen.min, 1e-9);
  PLOT_CHECK_NEAR(f.xr().max, frozen.max, 1e-9);
  PLOT_CHECK(f.graph.x_follow(f.ax) == plot::XFollow::Off);
}

/// The deferred DPI item from the UI-scale task: the middle-drag axis zoom's gain was
/// per *device* pixel, so the same physical drag zoomed twice as much at 2x. The gain
/// is now logical -- 200 logical px is one decade -- and the drag delta is converted
/// through the plot's scale, so the same physical drag zooms the same amount at either
/// scale. The wheel is in notches, a unit that is already device-independent, so it
/// must *not* be converted: one notch scales the span by the same factor at both.
PLOT_TEST(drag_zoom_is_logical_the_wheel_is_not_scaled) {
  for (const f32 scale : {1.0f, 2.0f}) {
    plot::Plot p;
    p.set_ui_scale(scale);
    p.set_viewport({0.0f, 0.0f, 800.0f * scale, 400.0f * scale});
    const u32 ax = p.add_x_axis({"t", {0.0, 100.0}, false, plot::AxisPlace::Bottom, false});
    plot::input::Controller c(p);
    c.set_viewport({0.0f, 0.0f, 800.0f * scale, 400.0f * scale});

    const plot::PlotLayout& l = p.layout();
    const f32 strip_x = l.axes.x + 0.5f * l.axes.w;
    const f32 strip_y = l.x_label_area.y + 0.5f * l.x_label_area.h;
    const f32 drag_px = 20.0f * scale;  // 20 *logical* px at both scales
    c.on_pointer({strip_x, strip_y, 0, 0, plot::input::Button::Middle, 0, true, true, false});
    PLOT_CHECK(c.drag_mode() == plot::input::DragMode::AxisZoomX);
    c.on_pointer({strip_x, strip_y + drag_px, 0, drag_px, plot::input::Button::Middle, 0, true, false,
                  false});
    c.on_pointer({strip_x, strip_y + drag_px, 0, 0, plot::input::Button::Middle, 0, false, false,
                  true});
    PLOT_CHECK_NEAR(p.x_range(ax).span(), 100.0 * std::pow(10.0, -20.0 / 200.0), 1e-6);

    const f64 span_before = p.x_range(ax).span();
    c.on_wheel({400.0f * scale, 200.0f * scale, 0.0f, 1.0f, 0});
    PLOT_CHECK_NEAR(p.x_range(ax).span(), span_before * std::exp(-0.15), 1e-9);
  }
}