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

package stats

import (
	"math"
	"strings"
	"testing"
)

// TestQuantile pins linear interpolation between order statistics.
func TestQuantile(t *testing.T) {
	a := mustFloats(t, []float64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 10)
	q, err := Quantile(a, []float64{0.25})
	if err != nil {
		t.Fatal(err)
	}
	// Linear interpolation: position 0.25*(9)=2.25 lands between 3 and 4.
	if v := q.FloatAt(0); math.Abs(v-3.25) > 1e-9 {
		t.Errorf("q25: %v, want 3.25", v)
	}
	med, _ := Quantile(a, []float64{0.5})
	if v := med.FloatAt(0); math.Abs(v-5.5) > 1e-9 {
		t.Errorf("median quantile: %v", v)
	}
}

// TestQuantileDegenerateInputs pins the guard that used to panic:
// Quantile on an empty sample.
func TestQuantileDegenerateInputs(t *testing.T) {
	empty := mustFloats(t, []float64{}, 0)
	if _, err := Quantile(empty, []float64{0.5}); err == nil {
		t.Error("Quantile empty: expected error")
	}
}

// TestBinCounts counts values in equally wide bins.
func TestBinCounts(t *testing.T) {
	vals := mustFloats(t, []float64{-3, 5, 12, 25}, 4)
	counts, err := BinCounts(vals, 2)
	if err != nil {
		t.Fatal(err)
	}
	if counts.Len() != 2 {
		t.Fatalf("counts len: %d", counts.Len())
	}
	if c1 := counts.FloatAt(0); c1 < 1 {
		t.Errorf("first bin empty: %v", counts.RawFloats())
	}
}

// TestComplexStatsErrors pins the refusals for complex input: no
// ordering, so no median, standard deviation or histogram.
func TestComplexStatsErrors(t *testing.T) {
	c := mustComplexes(t, []complex128{complex(1, 1)}, 1)

	if _, err := Median(c); err == nil || !strings.Contains(err.Error(), "no median") {
		t.Fatalf("Median complex: %v", err)
	}
	if _, err := Std(c); err == nil || !strings.Contains(err.Error(), "no float standard deviation") {
		t.Fatalf("Std complex: %v", err)
	}
	if _, _, err := Histogram(c, 2); err == nil || !strings.Contains(err.Error(), "no histogram") {
		t.Fatalf("Histogram complex: %v", err)
	}
}