tensor/plot/plot_test.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package plot

import (
	"math"
	"os"
	"path/filepath"
	"strings"
	"testing"

	"sourcedock.dev/petrbalvin/tensor/internal/core"
)

func sampleChart() Chart {
	pts1 := make([]Point, 0, 50)
	pts2 := make([]Point, 0, 50)
	for i := range 50 {
		x := float64(i) / 49
		pts1 = append(pts1, Point{X: x, Y: x * x})
		pts2 = append(pts2, Point{X: x, Y: math.Sqrt(x)})
	}
	return Chart{
		Title:  "Test <chart>",
		XLabel: "x", YLabel: "y",
		Series: []Series{{Name: "quadratic", Points: pts1}, {Name: "sqrt", Points: pts2}},
	}
}

func TestWriteSVG(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "out.svg")
	if err := sampleChart().WriteSVG(path); err != nil {
		t.Fatal(err)
	}
	body, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	s := string(body)
	if !strings.HasPrefix(s, "<?xml") {
		t.Fatal("the SVG lacks the XML declaration")
	}
	if got := strings.Count(s, "<polyline"); got != 2 {
		t.Fatalf("%d polylines, want 2", got)
	}
	if strings.Count(s, "&lt;") != 1 {
		t.Fatal("the title was not escaped")
	}
	// Determinism: the same chart renders byte for byte the same file.
	path2 := filepath.Join(dir, "out2.svg")
	if err := sampleChart().WriteSVG(path2); err != nil {
		t.Fatal(err)
	}
	again, err := os.ReadFile(path2)
	if err != nil {
		t.Fatal(err)
	}
	if string(body) != string(again) {
		t.Fatal("the rendering is not deterministic")
	}
}

func TestWriteSVGErrors(t *testing.T) {
	dir := t.TempDir()
	one := Chart{Series: []Series{{Name: "only", Points: []Point{{X: 0, Y: 0}, {X: 1, Y: 1}}}}}
	one.Series[0].Points = one.Series[0].Points[:1]
	if err := one.WriteSVG(filepath.Join(dir, "bad.svg")); err == nil {
		t.Fatal("a single point must fail")
	}
	empty := Chart{Series: []Series{{Name: "none"}}}
	if err := empty.WriteSVG(filepath.Join(dir, "bad.svg")); err == nil {
		t.Fatal("an empty series must fail")
	}
	// A series built by hand is the caller's own: the constructor's
	// non-finite refusal still has to hold at the rendering door, or
	// the deterministic contract would publish a polyline carrying the
	// literal NaN no renderer draws.
	for _, pt := range []Point{{X: math.NaN(), Y: 0}, {X: 0, Y: math.Inf(1)}, {X: math.Inf(-1), Y: 1}} {
		nan := Chart{Series: []Series{{Name: "broken", Points: []Point{{X: 0, Y: 0}, pt, {X: 2, Y: 1}}}}}
		if err := nan.WriteSVG(filepath.Join(dir, "bad.svg")); err == nil {
			t.Fatalf("the non-finite point %+v was rendered", pt)
		}
	}
	// An axis range with an infinite or unordered span falls back to
	// the data's own bounds instead of mapping every point through a
	// division the format cannot evaluate.
	for _, r := range [][2]float64{{0, math.Inf(1)}, {math.Inf(-1), 0}, {2, 1}, {math.NaN(), 1}} {
		c := sampleChart()
		c.YRange = r
		path := filepath.Join(dir, "range.svg")
		if err := c.WriteSVG(path); err != nil {
			t.Fatalf("the range %v was refused instead of falling back: %v", r, err)
		}
		body, err := os.ReadFile(path)
		if err != nil {
			t.Fatal(err)
		}
		if s := string(body); strings.Contains(s, "NaN") || strings.Contains(s, "Inf") {
			t.Fatalf("the range %v leaked a non-finite coordinate into the rendering", r)
		}
	}
}

func mustFromFloats(t *testing.T, values []float64, shape ...int) *core.Array {
	t.Helper()
	a, err := core.FromFloats(values, shape...)
	if err != nil {
		t.Fatal(err)
	}
	return a
}

func TestLine(t *testing.T) {
	xs := mustFromFloats(t, []float64{0, 1, 2, 3}, 4)
	ys := mustFromFloats(t, []float64{0, 1, 4, 9}, 4)
	s, err := Line("quadratic", xs, ys)
	if err != nil {
		t.Fatal(err)
	}
	if s.Name != "quadratic" || len(s.Points) != 4 || s.Points[3] != (Point{X: 3, Y: 9}) {
		t.Fatalf("the series is wrong: %+v", s)
	}
}

func TestLineValidation(t *testing.T) {
	xs := mustFromFloats(t, []float64{0, 1, 2}, 3)
	ys := mustFromFloats(t, []float64{0, 1, 4}, 3)
	if _, err := Line("mismatch", xs, mustFromFloats(t, []float64{0, 1}, 2)); err == nil {
		t.Fatal("a length mismatch must fail")
	}
	if _, err := Line("matrix", mustFromFloats(t, []float64{1, 2, 3, 4}, 2, 2), ys); err == nil {
		t.Fatal("a rank-2 array must fail")
	}
	if _, err := Line("empty", mustFromFloats(t, nil, 0), mustFromFloats(t, nil, 0)); err == nil {
		t.Fatal("an empty array must fail")
	}
	if _, err := Line("nil", nil, ys); err == nil {
		t.Fatal("a nil array must fail")
	}
	if _, err := Line("nan", xs, mustFromFloats(t, []float64{0, 1, math.NaN()}, 3)); err == nil {
		t.Fatal("a non-finite point must fail")
	}
}

func TestTick(t *testing.T) {
	if tick(2) != "2" {
		t.Fatalf("tick(2) = %q", tick(2))
	}
	if tick(0.25) != "0.25" {
		t.Fatalf("tick(0.25) = %q", tick(0.25))
	}
	if tick(1e-7) != "1e-07" {
		t.Fatalf("tick(1e-7) = %q", tick(1e-7))
	}
}

// TestSeriesColourCycle pins the colour cycle element for element: the
// seven Viridis samples are part of the deterministic output, so an
// accidental edit must fall over here, and the cycle must wrap at the
// palette's own length.
func TestSeriesColourCycle(t *testing.T) {
	want := [7]string{
		"#440154",
		"#482a79",
		"#3d4d8a",
		"#2f6c8e",
		"#23888e",
		"#20a486",
		"#43bf71",
	}
	if seriesColours != want {
		t.Fatalf("series colours = %v, want %v", seriesColours, want)
	}
	for i := range len(seriesColours) {
		if colour(i) != seriesColours[i] {
			t.Fatalf("colour(%d) = %s, want %s", i, colour(i), seriesColours[i])
		}
		if colour(i+len(seriesColours)) != seriesColours[i] {
			t.Fatalf("colour(%d) does not wrap onto colour(%d)", i+len(seriesColours), i)
		}
	}
}