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

package core

import (
	"math"
	"testing"
)

// TestEinsumGeneralReductions pins patterns only the general engine
// reaches: reduction-only axes, implicit output, arbitrary order.
func TestEinsumGeneralReductions(t *testing.T) {
	a, _ := FromFloats([]float64{1, 2, 3, 4, 5, 6}, 2, 3)
	// "ij->i": row sums.
	rs, err := Einsum("ij->i", a)
	if err != nil {
		t.Fatalf("ij->i: %v", err)
	}
	if rs.FloatAt(0) != 6 || rs.FloatAt(1) != 15 {
		t.Fatalf("row sums = (%g, %g), want (6, 15)", rs.FloatAt(0), rs.FloatAt(1))
	}
	// "ij->j": column sums.
	cs, err := Einsum("ij->j", a)
	if err != nil {
		t.Fatalf("ij->j: %v", err)
	}
	for j, want := range []float64{5, 7, 9} {
		if cs.FloatAt(j) != want {
			t.Fatalf("col sum %d = %g, want %g", j, cs.FloatAt(j), want)
		}
	}
	// Implicit output: "ij,jk" == "ij,jk->ik".
	b, _ := FromFloats([]float64{1, 0, 0, 1, 2, -1}, 3, 2)
	m1, err := Einsum("ij,jk", a, b)
	if err != nil {
		t.Fatalf("implicit: %v", err)
	}
	m2, _ := Einsum("ij,jk->ik", a, b)
	if !sameValues(m1, m2) {
		t.Fatal("implicit output differs from explicit")
	}
	// Output order "ij->ji" through the general engine as well.
	tr, err := Einsum("ij->ji", a)
	if err != nil {
		t.Fatalf("ij->ji: %v", err)
	}
	if tr.FloatAt(0) != 1 || tr.FloatAt(1) != 4 || tr.FloatAt(2) != 2 {
		t.Fatalf("transpose wrong: %v %v %v", tr.FloatAt(0), tr.FloatAt(1), tr.FloatAt(2))
	}
}

func sameValues(a, b *Array) bool {
	if a.Len() != b.Len() {
		return false
	}
	for i := range a.Len() {
		if a.Dtype() == Complex {
			if a.ComplexAt(i) != b.ComplexAt(i) {
				return false
			}
		} else if a.FloatAt(i) != b.FloatAt(i) {
			return false
		}
	}
	return true
}

// TestEinsumEllipsis pins batched and broadcast patterns.
func TestEinsumEllipsis(t *testing.T) {
	// Batched matmul "...ij,...jk->...ik" against the manual loop.
	av := make([]float64, 2*3*4)
	bv := make([]float64, 2*4*5)
	for i := range av {
		av[i] = float64(i%7) - 3
	}
	for i := range bv {
		bv[i] = float64(i%5) - 2
	}
	a, _ := FromFloats(av, 2, 3, 4)
	b, _ := FromFloats(bv, 2, 4, 5)
	got, err := Einsum("...ij,...jk->...ik", a, b)
	if err != nil {
		t.Fatalf("ellipsis batched: %v", err)
	}
	if got.NDim() != 3 || got.Shape()[0] != 2 || got.Shape()[1] != 3 || got.Shape()[2] != 5 {
		t.Fatalf("shape %v, want (2, 3, 5)", got.Shape())
	}
	for bt := range 2 {
		for i := range 3 {
			for k := range 5 {
				want := 0.0
				for j := range 4 {
					want += a.FloatAt((bt*3+i)*4+j) * b.FloatAt((bt*4+j)*5+k)
				}
				if math.Abs(got.FloatAt((bt*3+i)*5+k)-want) > 1e-12 {
					t.Fatalf("batched [%d,%d,%d] = %g, want %g", bt, i, k, got.FloatAt((bt*3+i)*5+k), want)
				}
			}
		}
	}
	// Broadcast: (1, 4) x (2, 4) -> (2, ...) inner product per batch.
	u, _ := FromFloats([]float64{1, 2, 3, 4}, 4)
	v, _ := FromFloats([]float64{1, 0, 0, 0, 0, 1, 0, 0}, 2, 4)
	dots, err := Einsum("i,...i->...", u, v)
	if err != nil {
		t.Fatalf("broadcast dots: %v", err)
	}
	if dots.Shape()[0] != 2 || dots.FloatAt(0) != 1 || dots.FloatAt(1) != 2 {
		t.Fatalf("broadcast dots = %v %v", dots.FloatAt(0), dots.FloatAt(1))
	}
}

// TestEinsumDiagonalGeneral pins repeated labels through the engine.
func TestEinsumDiagonalGeneral(t *testing.T) {
	a, _ := FromFloats([]float64{1, 2, 3, 4}, 2, 2)
	// "ii->i" still hits the fast path; "iij->ij" only the engine can.
	b, _ := FromFloats([]float64{
		1, 2, 3, 4, 5, 6, 7, 8,
	}, 2, 2, 2)
	out, err := Einsum("iij->ij", b)
	if err != nil {
		t.Fatalf("iij->ij: %v", err)
	}
	if out.Shape()[0] != 2 || out.Shape()[1] != 2 {
		t.Fatalf("shape %v, want (2, 2)", out.Shape())
	}
	// element [i][j] = b[i][i][j].
	for i := range 2 {
		for j := range 2 {
			want := b.FloatAt((i*2+i)*2 + j)
			if out.FloatAt(i*2+j) != want {
				t.Fatalf("out[%d][%d] = %g, want %g", i, j, out.FloatAt(i*2+j), want)
			}
		}
	}
	// Bad specs stay errors.
	if _, err := Einsum("ij->jj", a); err == nil {
		t.Fatal("repeated output label accepted")
	}
	if _, err := Einsum("ij->k", a); err == nil {
		t.Fatal("unknown output label accepted")
	}
}

// TestEinsumSlotSplitWideWorkload pins the parallel slot walk's chunk
// cursor. The general engine hands every worker a contiguous chunk of
// output slots and each worker rebuilds the cursor of its own first slot
// from the slot index, so the walk must return the same bits however the
// slots are split. Both workloads hold thousands of slots, and the split
// is asserted before it is compared so a shrunken workload cannot
// quietly fall back to the single-chunk walk.
func TestEinsumSlotSplitWideWorkload(t *testing.T) {
	const workers = 4
	cases := []struct {
		spec     string
		shapes   [][]int
		sumTotal int // product of the summed labels' sizes
	}{
		// 64·8·8·4 = 16384 slots and nothing summed, so the cursor is
		// the only source of every operand offset.
		{"ij,kl->ijkl", [][]int{{64, 8}, {8, 4}}, 1},
		// 64·16 = 1024 slots of 8·8·3 = 192 visits: the sum runs inside
		// the worker that owns the slot.
		{"ik,kj,jl->il", [][]int{{64, 8}, {8, 8}, {8, 16}}, 64},
	}
	prev := NumWorkers()
	defer SetNumCPU(prev)
	for _, tc := range cases {
		for _, dt := range []Dtype{Int, Float} {
			operands := make([]*Array, len(tc.shapes))
			for i, shape := range tc.shapes {
				operands[i] = einsumOperand(t, dt, shape...)
			}
			SetNumCPU(1)
			want, err := Einsum(tc.spec, operands...)
			if err != nil {
				t.Fatalf("%s/%s: %v", tc.spec, dt, err)
			}
			// The dispatch splits only while a worker's chunk reaches
			// the visit floor, so assert the workload still does.
			perSlot := tc.sumTotal * len(operands)
			minSlots := 1
			if perSlot < einsumSlotFloor {
				minSlots = (einsumSlotFloor + perSlot - 1) / perSlot
			}
			slots := want.Len()
			if chunk := (slots + workers - 1) / workers; chunk < minSlots {
				t.Fatalf("%s/%s: %d slots no longer split at %d workers: chunk %d below the %d-slot floor",
					tc.spec, dt, slots, workers, chunk, minSlots)
			}
			// A pure outer product is the product of one element of each
			// operand, so its corners are checked against that definition:
			// the comparison below cannot pass on a walk that is wrong in
			// every chunk.
			if tc.sumTotal == 1 {
				for _, c := range [][4]int{{0, 0, 0, 0}, {7, 3, 5, 1}, {63, 7, 7, 3}} {
					var x, y, g float64
					if dt == Int {
						xi, _ := IntAt(operands[0], c[0], c[1])
						yi, _ := IntAt(operands[1], c[2], c[3])
						gi, _ := IntAt(want, c[0], c[1], c[2], c[3])
						x, y, g = float64(xi), float64(yi), float64(gi)
					} else {
						x, _ = FloatAt(operands[0], c[0], c[1])
						y, _ = FloatAt(operands[1], c[2], c[3])
						g, _ = FloatAt(want, c[0], c[1], c[2], c[3])
					}
					if g != x*y {
						t.Fatalf("%s/%s: slot %v = %v, want %v·%v = %v",
							tc.spec, dt, c, g, x, y, x*y)
					}
				}
			}
			SetNumCPU(workers)
			got, err := Einsum(tc.spec, operands...)
			if err != nil {
				t.Fatalf("%s/%s: split walk: %v", tc.spec, dt, err)
			}
			if !einsumBitsEqual(got, want) {
				t.Fatalf("%s/%s: the split walk disagrees with the serial one at element %d",
					tc.spec, dt, firstDifferingSlot(got, want))
			}
		}
	}
}

// firstDifferingSlot returns the flat index of the first element on
// which two results disagree, or -1 when none does: a failure names one
// element instead of printing two whole payloads.
func firstDifferingSlot(a, b *Array) int {
	if a.Len() != b.Len() || a.Dtype() != b.Dtype() {
		return -1
	}
	for i := range a.Len() {
		switch a.dt {
		case Int:
			if a.ints[i] != b.ints[i] {
				return i
			}
		case Float32:
			if a.floats32[i] != b.floats32[i] {
				return i
			}
		case Float:
			if a.floats[i] != b.floats[i] {
				return i
			}
		case Complex:
			if a.complexes[i] != b.complexes[i] {
				return i
			}
		}
	}
	return -1
}