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

package stats

import (
	"sourcedock.dev/petrbalvin/tensor/internal/core"
	"testing"
)

// TestPoissonDrawsZeroLambda pins the degenerate distribution: λ = 0
// must draw 0, never the −1 the multiplication loop used to hand back.
func TestPoissonDrawsZeroLambda(t *testing.T) {
	g := core.NewGenerator(7)
	out, err := PoissonDraws(g, 16, 0)
	if err != nil {
		t.Fatalf("PoissonDraws: %v", err)
	}
	for i := range 16 {
		if out.FloatAt(i) != 0 {
			t.Fatalf("draw %d = %g, want 0", i, out.FloatAt(i))
		}
	}
}

// TestChiSquareComplexRejects pins the dtype guard.
func TestChiSquareComplexRejects(t *testing.T) {
	obs, err := core.FromComplexes([]complex128{1, 2, 3}, 3)
	if err != nil {
		t.Fatalf("FromComplexes: %v", err)
	}
	exp, _ := core.FromFloats([]float64{1, 2, 3}, 3)
	if _, _, _, err := ChiSquareGoodnessOfFit(obs, exp); err == nil {
		t.Fatal("ChiSquareGoodnessOfFit accepted complex observed")
	}
	if _, _, _, err := ChiSquareGoodnessOfFit(exp, obs); err == nil {
		t.Fatal("ChiSquareGoodnessOfFit accepted complex expected")
	}
}

// TestBootstrapCIFreshArray pins the documented contract: a statistic
// that retains its argument must observe values frozen at call time,
// never the next resample's mutation through the shared buffer.
func TestBootstrapCIFreshArray(t *testing.T) {
	data, err := core.FromFloats([]float64{1, 2, 3, 4, 5, 6, 7, 8}, 8)
	if err != nil {
		t.Fatalf("FromFloats: %v", err)
	}
	type snapshot struct {
		arr  *core.Array
		mean float64
	}
	var kept []snapshot
	stat := func(a *core.Array) (float64, error) {
		m, err := core.Mean(a)
		if err != nil {
			return 0, err
		}
		kept = append(kept, snapshot{a, m})
		return m, nil
	}
	if _, _, err := BootstrapCI(data, stat, 0.9, 8, 42); err != nil {
		t.Fatalf("BootstrapCI: %v", err)
	}
	for i, s := range kept {
		m, err := core.Mean(s.arr)
		if err != nil {
			t.Fatalf("kept[%d] mean: %v", i, err)
		}
		if m != s.mean {
			t.Fatalf("kept[%d] mean drifted from %g to %g (buffer was mutated)", i, s.mean, m)
		}
	}
}