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

package core

import (
	"math"
	"slices"
	"strconv"
	"strings"
	"testing"

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

// The general engine's slot walk and the axis folds the reduction-only
// specs dispatch to: their benchmarks, and the oracles that pin the
// walk's bits.

// einsumSlotSumOdometer steps every summed axis through one shared
// odometer. It is the oracle for the peeled kernel: a slot must hold
// exactly what this walk puts there, bit for bit.
func einsumSlotSumOdometer[T int64 | float64 | complex128](rv [][]T, out []T, slot int, base, off, coord, delta, sizes []int, total int) {
	nSum := len(sizes)
	copy(off, base)
	clear(coord[:nSum])
	acc := T(1)
	for p := range rv {
		acc *= rv[p][off[p]]
	}
	out[slot] += acc
	for range total - 1 {
		t := nSum - 1
		for t >= 0 {
			coord[t]++
			for p := range rv {
				off[p] += delta[p*nSum+t]
			}
			if coord[t] < sizes[t] {
				break
			}
			coord[t] = 0
			for p := range rv {
				off[p] -= delta[p*nSum+t] * sizes[t]
			}
			t--
		}
		acc = T(1)
		for p := range rv {
			acc *= rv[p][off[p]]
		}
		out[slot] += acc
	}
}

// einsumSlotSumF32Odometer is einsumSlotSumOdometer for a float32
// result, narrowing every addend into the slot as it arrives.
func einsumSlotSumF32Odometer(rv [][]float64, out []float32, slot int, base, off, coord, delta, sizes []int, total int) {
	nSum := len(sizes)
	copy(off, base)
	clear(coord[:nSum])
	acc := 1.0
	for p := range rv {
		acc *= rv[p][off[p]]
	}
	out[slot] = float32(float64(out[slot]) + acc)
	for range total - 1 {
		t := nSum - 1
		for t >= 0 {
			coord[t]++
			for p := range rv {
				off[p] += delta[p*nSum+t]
			}
			if coord[t] < sizes[t] {
				break
			}
			coord[t] = 0
			for p := range rv {
				off[p] -= delta[p*nSum+t] * sizes[t]
			}
			t--
		}
		acc = 1.0
		for p := range rv {
			acc *= rv[p][off[p]]
		}
		out[slot] = float32(float64(out[slot]) + acc)
	}
}

// einsumProbeFloats fills n elements with distinct values of mixed
// magnitude: any visit order other than the reference's moves addends
// across a rounding boundary and changes the low bits of the sum.
func einsumProbeFloats(n int) []float64 {
	v := make([]float64, n)
	for i := range v {
		v[i] = float64(i%11)*1.5 - 4 + math.Ldexp(1, i%17-8) + float64(i)/512
	}
	return v
}

// einsumSlotConfig is one slot-walk configuration: the axis extents, the
// per-operand cursor and the per-operand, per-axis strides.
type einsumSlotConfig struct {
	sizes []int
	base  []int
	delta []int
	reach []int
}

// configs walks the operand counts and the summed-axis counts, giving
// every kernel shape a configuration with in-bounds cursors; the
// zero-summed-axis shapes come last.
func einsumSlotConfigs() []einsumSlotConfig {
	var out []einsumSlotConfig
	for nOps := 1; nOps <= 5; nOps++ {
		for nSum := 1; nSum <= 3; nSum++ {
			cfg := einsumSlotConfig{
				sizes: make([]int, nSum),
				base:  make([]int, nOps),
				delta: make([]int, nOps*nSum),
				reach: make([]int, nOps),
			}
			for t := range nSum {
				cfg.sizes[t] = 2 + (t*5+nOps)%3
			}
			for p := range nOps {
				cfg.base[p] = p
				cfg.reach[p] = p
				for t := range nSum {
					cfg.delta[p*nSum+t] = 1 + (p*3+t)%4
					cfg.reach[p] += (cfg.sizes[t] - 1) * cfg.delta[p*nSum+t]
				}
			}
			out = append(out, cfg)
		}
	}
	for nOps := 1; nOps <= 4; nOps++ {
		cfg := einsumSlotConfig{
			base:  make([]int, nOps),
			delta: make([]int, nOps),
			reach: make([]int, nOps),
		}
		for p := range nOps {
			cfg.base[p] = p
			cfg.reach[p] = p
		}
		out = append(out, cfg)
	}
	return out
}

// slotTotal is the number of visits one slot's walk takes.
func (c einsumSlotConfig) slotTotal() int {
	total := 1
	for _, s := range c.sizes {
		total *= s
	}
	return total
}

// name spells the configuration for a failure message.
func (c einsumSlotConfig) name() string {
	return "ops=" + strconv.Itoa(len(c.base)) + "/sum=" + strconv.Itoa(len(c.sizes))
}

// einsumCheckSlotKernel runs one configuration through the peeled
// kernel and the odometer reference for a payload type and compares the
// two slots by the given identity, so every operand count and cursor
// reaches both loops.
func einsumCheckSlotKernel[T int64 | float64 | complex128](
	t *testing.T, label string, cfg einsumSlotConfig,
	mk func(reach []int) [][]T, same func(T, T) bool,
) {
	t.Helper()
	rv := mk(cfg.reach)
	got := make([]T, 1)
	want := make([]T, 1)
	nSum := len(cfg.sizes)
	einsumSlotSum(rv, got, 0, cfg.base, make([]int, len(cfg.base)), make([]int, nSum), cfg.delta, cfg.sizes, cfg.slotTotal())
	einsumSlotSumOdometer(rv, want, 0, cfg.base, make([]int, len(cfg.base)), make([]int, nSum), cfg.delta, cfg.sizes, cfg.slotTotal())
	if !same(got[0], want[0]) {
		t.Fatalf("%s %s: slot %v, want %v", label, cfg.name(), got[0], want[0])
	}
}

// einssumCheckSlotKernelF32 pins the float32 slot kernel, which narrows
// every addend into the slot, against its own odometer form.
func einssumCheckSlotKernelF32(t *testing.T, cfg einsumSlotConfig, mk func(reach []int) [][]float64) {
	t.Helper()
	rv := mk(cfg.reach)
	got := make([]float32, 1)
	want := make([]float32, 1)
	nSum := len(cfg.sizes)
	einsumSlotSumF32(rv, got, 0, cfg.base, make([]int, len(cfg.base)), make([]int, nSum), cfg.delta, cfg.sizes, cfg.slotTotal())
	einsumSlotSumF32Odometer(rv, want, 0, cfg.base, make([]int, len(cfg.base)), make([]int, nSum), cfg.delta, cfg.sizes, cfg.slotTotal())
	if math.Float32bits(got[0]) != math.Float32bits(want[0]) {
		t.Fatalf("float32 %s: slot %v, want %v", cfg.name(), got[0], want[0])
	}
}

// floatsPerReach builds one probe reader per operand, each long enough
// for that operand's whole walk.
func floatsPerReach(reach []int) [][]float64 {
	rv := make([][]float64, len(reach))
	for p, r := range reach {
		rv[p] = einsumProbeFloats(r + 1)
	}
	return rv
}

// TestEinsumSlotSumMatchesOdometer pins the peeled slot kernels against
// the odometer form across operand counts, summed-axis counts, axis
// extents and cursors, on every payload type the kernels serve. The
// distinct probe values make a moved addend visible in the low bits.
func TestEinsumSlotSumMatchesOdometer(t *testing.T) {
	configs := einsumSlotConfigs()
	for _, cfg := range configs {
		// The generic kernel, instantiated for each payload type.
		einsumCheckSlotKernel(t, "float", cfg, floatsPerReach,
			func(a, b float64) bool { return math.Float64bits(a) == math.Float64bits(b) })
		einsumCheckSlotKernel(t, "int", cfg,
			func(reach []int) [][]int64 {
				rv := make([][]int64, len(reach))
				for p, r := range reach {
					rv[p] = make([]int64, r+1)
					for i := range rv[p] {
						rv[p][i] = int64(i%13)*7 - 9
					}
				}
				return rv
			}, func(a, b int64) bool { return a == b })
		einsumCheckSlotKernel(t, "complex", cfg,
			func(reach []int) [][]complex128 {
				rv := make([][]complex128, len(reach))
				for p, r := range reach {
					rv[p] = make([]complex128, r+1)
					for i := range rv[p] {
						rv[p][i] = complex(float64(i%7)-3, float64(i%5)-2)
					}
				}
				return rv
			}, func(a, b complex128) bool {
				return math.Float64bits(real(a)) == math.Float64bits(real(b)) &&
					math.Float64bits(imag(a)) == math.Float64bits(imag(b))
			})
		einssumCheckSlotKernelF32(t, cfg, floatsPerReach)
	}
}

// einsumOperand builds a deterministic contiguous operand of the given
// dtype.
func einsumOperand(tb testing.TB, dt Dtype, shape ...int) *Array {
	tb.Helper()
	n := 1
	for _, d := range shape {
		n *= d
	}
	var a *Array
	var err error
	switch dt {
	case Int:
		v := make([]int64, n)
		for i := range v {
			v[i] = int64(i%9)*3 - 4 + int64(i)*7
		}
		a, err = FromInts(v, shape...)
	case Float32:
		v := make([]float32, n)
		for i := range v {
			v[i] = float32(i%7)*0.5 - 2 + float32(i)/64
		}
		a, err = FromFloat32s(v, shape...)
	case Complex:
		v := make([]complex128, n)
		for i := range v {
			v[i] = complex(float64(i%5)-2, float64(i%3)-1)
		}
		a, err = FromComplexes(v, shape...)
	default:
		a, err = FromFloats(einsumProbeFloats(n), shape...)
	}
	if err != nil {
		tb.Fatalf("operand %s %v: %v", dt, shape, err)
	}
	return a
}

// einsumStridedOperand builds a read-only view of the given shape whose
// axes step by the given strides over a longer payload.
func einsumStridedOperand(t testing.TB, dt Dtype, shape, strides []int) *Array {
	t.Helper()
	n := 1
	for d, s := range shape {
		n += (s - 1) * strides[d]
	}
	flat := einsumOperand(t, dt, n)
	view := &Array{shape: slices.Clone(shape), dt: dt, strides: slices.Clone(strides)}
	switch dt {
	case Int:
		view.ints = flat.RawInts()
	case Float32:
		view.floats32 = flat.RawFloat32s()
	case Complex:
		view.complexes = flat.RawComplexes()
	default:
		view.floats = flat.RawFloats()
	}
	return view
}

// einsumBitsEqual compares two results by dtype, shape and raw payload
// bits, so a NaN matches only its own bit pattern.
func einsumBitsEqual(a, b *Array) bool {
	if a.Dtype() != b.Dtype() || !slices.Equal(a.Shape(), b.Shape()) {
		return false
	}
	switch a.dt {
	case Int:
		return slices.Equal(a.RawInts(), b.RawInts())
	case Float32:
		return slices.EqualFunc(a.RawFloat32s(), b.RawFloat32s(), func(x, y float32) bool {
			return math.Float32bits(x) == math.Float32bits(y)
		})
	case Float:
		return slices.EqualFunc(a.RawFloats(), b.RawFloats(), func(x, y float64) bool {
			return math.Float64bits(x) == math.Float64bits(y)
		})
	case Complex:
		return slices.EqualFunc(a.RawComplexes(), b.RawComplexes(), func(x, y complex128) bool {
			return math.Float64bits(real(x)) == math.Float64bits(real(y)) &&
				math.Float64bits(imag(x)) == math.Float64bits(imag(y))
		})
	}
	return false
}

// TestEinsumSlotSplitMatchesSerial runs the whole dispatch with the
// worker pool as it stands and with it pinned to one worker, which
// walks every slot in one chunk. The slot walk must write the same bits
// either way, for every operand count, dtype and stride pattern the
// engine accepts.
func TestEinsumSlotSplitMatchesSerial(t *testing.T) {
	cases := []struct {
		spec   string
		shapes [][]int
	}{
		{"...ij,jk->...ik", [][]int{{4, 6, 5}, {5, 3}}},
		{"...ij,...jk->...ik", [][]int{{3, 4, 5}, {3, 5, 2}}},
		{"ik,kj,jl->il", [][]int{{6, 5}, {5, 4}, {4, 7}}},
		{"ijk->kji", [][]int{{3, 4, 5}}},
		{"ij,jk,kl->il", [][]int{{5, 4}, {4, 6}, {6, 3}}},
		{"ij,jk,lk->il", [][]int{{5, 4}, {4, 6}, {3, 6}}},
		{"i,...i->...", [][]int{{5}, {3, 5}}},
		{"...i,...i->...", [][]int{{2, 4}, {4}}},
		{"kji->k", [][]int{{3, 4, 5}}},
		{"iij->ij", [][]int{{4, 4, 3}}},
		{"ii->i", [][]int{{5, 5}}},
		{"...->...", [][]int{{3, 4}}},
		{"ij->i", [][]int{{7, 5}}},
		{"ab,bc->ac", [][]int{{6, 5}, {5, 4}}},
		{"ij,ij->", [][]int{{6, 5}, {6, 5}}},
	}
	for _, tc := range cases {
		for _, dt := range []Dtype{Int, Float32, Float, Complex} {
			ops := make([]*Array, len(tc.shapes))
			for i, shape := range tc.shapes {
				ops[i] = einsumOperand(t, dt, shape...)
			}
			want, werr := Einsum(tc.spec, ops...)
			restore := engine.SetNumWorkers(1)
			got, gerr := Einsum(tc.spec, ops...)
			engine.SetNumWorkers(restore)
			if werr != nil || gerr != nil {
				t.Fatalf("%s/%s: split error %v, serial error %v", tc.spec, dt, werr, gerr)
			}
			if !einsumBitsEqual(got, want) {
				t.Fatalf("%s/%s: split result %s differs from the serial walk %s",
					tc.spec, dt, got, want)
			}
		}
	}
	// A strided operand is gathered through the accessor on every dtype
	// the engine widens; the walk must read the view's own elements.
	for _, dt := range []Dtype{Int, Float32, Float, Complex} {
		ops := []*Array{
			einsumStridedOperand(t, dt, []int{3, 4}, []int{8, 2}),
			einsumOperand(t, dt, 3, 4),
		}
		want, werr := Einsum("ij,ij->i", ops...)
		restore := engine.SetNumWorkers(1)
		got, gerr := Einsum("ij,ij->i", ops...)
		engine.SetNumWorkers(restore)
		if werr != nil || gerr != nil {
			t.Fatalf("strided/%s: split error %v, serial error %v", dt, werr, gerr)
		}
		if !einsumBitsEqual(got, want) {
			t.Fatalf("strided/%s: split result %s differs from the serial walk %s", dt, got, want)
		}
	}
}

// TestEinsumSumAxesMatchesEngine pins the reduction-only dispatch to the
// general engine: "ij->i" and its relatives must fold to the same bits
// the engine's walk produced, for every shape, axis order and dtype. The
// float32 and complex operands stay with the engine by design and are
// compared here as well, so a later change to the dispatch cannot move
// them silently.
func TestEinsumSumAxesMatchesEngine(t *testing.T) {
	shapes := map[int][]int{2: {6, 5}, 3: {4, 6, 5}, 4: {3, 4, 6, 2}}
	specs := []string{
		"ij->i", "ij->j",
		"ijk->ij", "ijk->ik", "ijk->ji", "ijk->i", "ijk->j", "ijk->k",
		"kji->k", "kji->ki", "kji->jk",
		"ijkl->il", "ijkl->lj", "ijkl->ji", "ijkl->i", "ijkl->l",
	}
	for _, spec := range specs {
		lhsStr, rhsStr, ok := strings.Cut(spec, "->")
		shape, ok2 := shapes[len(lhsStr)]
		if !ok || !ok2 {
			continue
		}
		for _, dt := range []Dtype{Int, Float32, Float, Complex} {
			a := einsumOperand(t, dt, shape...)
			want, werr := einsumGeneral([]string{lhsStr}, rhsStr, true, []*Array{a})
			got, gerr := Einsum(spec, a)
			if werr != nil || gerr != nil {
				t.Fatalf("%s/%s %v: dispatch error %v, engine error %v", spec, dt, shape, gerr, werr)
			}
			if !einsumBitsEqual(got, want) {
				t.Fatalf("%s/%s %v: dispatched result %s differs from the engine %s",
					spec, dt, shape, got, want)
			}
		}
	}
}

// einsumDenseOf copies a view's logical elements into a contiguous
// array of the same dtype.
func einsumDenseOf(t *testing.T, a *Array) *Array {
	t.Helper()
	n := a.Len()
	var out *Array
	var err error
	switch a.dt {
	case Int:
		v := make([]int64, n)
		for i := range v {
			v[i] = a.ints[a.physIndex(i)]
		}
		out, err = FromInts(v, a.Shape()...)
	case Float32:
		v := make([]float32, n)
		for i := range v {
			v[i] = a.floats32[a.physIndex(i)]
		}
		out, err = FromFloat32s(v, a.Shape()...)
	case Complex:
		v := make([]complex128, n)
		for i := range v {
			v[i] = a.complexAt(i)
		}
		out, err = FromComplexes(v, a.Shape()...)
	default:
		v := make([]float64, n)
		for i := range v {
			v[i] = a.floatAt(i)
		}
		out, err = FromFloats(v, a.Shape()...)
	}
	if err != nil {
		t.Fatalf("dense copy of %s: %v", a, err)
	}
	return out
}

// TestEinsumStridedViewMatchesDense pins the engine's readers against a
// view's own elements: a strided operand must contract exactly as a
// dense array holding the same logical elements, for every dtype the
// engine widens. The patterns are the ones the engine owns; the table
// paths read payload windows and take contiguous operands only, as the
// Array contract states.
func TestEinsumStridedViewMatchesDense(t *testing.T) {
	for _, dt := range []Dtype{Int, Float32, Float, Complex} {
		view := einsumStridedOperand(t, dt, []int{3, 4}, []int{8, 2})
		dense := einsumDenseOf(t, view)
		other := einsumOperand(t, dt, 3, 4)
		vec := einsumOperand(t, dt, 4)
		for _, tc := range []struct {
			spec  string
			which []bool // true takes the strided view, false the dense operand
		}{
			{"ij->i", []bool{true}},
			{"ij->j", []bool{true}},
			{"ij,ij->i", []bool{true, false}},
			{"ij,ij->ji", []bool{true, false}},
			{"ij,kj->ik", []bool{true, false}},
			{"...i,i->...", []bool{true, false}},
		} {
			withView := make([]*Array, len(tc.which))
			withDense := make([]*Array, len(tc.which))
			for i, isView := range tc.which {
				if isView {
					withView[i], withDense[i] = view, dense
					continue
				}
				if tc.spec == "...i,i->..." {
					withView[i], withDense[i] = vec, vec
					continue
				}
				withView[i], withDense[i] = other, other
			}
			got, gerr := Einsum(tc.spec, withView...)
			want, werr := Einsum(tc.spec, withDense...)
			if werr != nil || gerr != nil {
				t.Fatalf("%s/%s: dense error %v, view error %v", tc.spec, dt, werr, gerr)
			}
			if !einsumBitsEqual(got, want) {
				t.Fatalf("%s/%s: view result %s differs from the dense array %s", tc.spec, dt, got, want)
			}
		}
	}
}

// benchEinsum measures one spec with the worker pool as it stands and
// with it pinned to one worker: the in-process A/B of the slot walk's
// split, where the pinned pool walks every slot in one chunk.
func benchEinsum(b *testing.B, spec string, ops ...*Array) {
	b.Run("pool", func(b *testing.B) {
		b.ReportAllocs()
		for b.Loop() {
			if _, err := Einsum(spec, ops...); err != nil {
				b.Fatal(err)
			}
		}
	})
	b.Run("one worker", func(b *testing.B) {
		restore := engine.SetNumWorkers(1)
		defer engine.SetNumWorkers(restore)
		b.ReportAllocs()
		for b.Loop() {
			if _, err := Einsum(spec, ops...); err != nil {
				b.Fatal(err)
			}
		}
	})
}

// BenchmarkEinsumEllipsisBatch is a contraction carrying a batch axis:
// the pattern the dispatch table cannot take, walked slot by slot.
func BenchmarkEinsumEllipsisBatch(b *testing.B) {
	a := benchMat(b, 11, 8, 48, 48)
	c := benchMat(b, 12, 48, 48)
	benchEinsum(b, "...ij,jk->...ik", a, c)
}

// BenchmarkEinsumEllipsisFloat32 is the same contraction on float32
// payloads: the operands widen into the walk and every addend narrows
// into the float32 slot.
func BenchmarkEinsumEllipsisFloat32(b *testing.B) {
	a := einsumOperand(b, Float32, 8, 48, 48)
	c := einsumOperand(b, Float32, 48, 48)
	benchEinsum(b, "...ij,jk->...ik", a, c)
}

// BenchmarkEinsumThreeOperandChain sums one shared label across three
// operands, the shape attention and tensordot patterns reduce to.
func BenchmarkEinsumThreeOperandChain(b *testing.B) {
	a := benchMat(b, 13, 16, 32)
	c := benchMat(b, 14, 32, 32)
	d := benchMat(b, 15, 32, 16)
	benchEinsum(b, "ik,kj,jl->il", a, c, d)
}

// BenchmarkEinsumSmallBatchedProduct is the small batched product the
// dispatch table's own batched kernel takes, kept as the fixed-cost
// control beside the general engine's shapes.
func BenchmarkEinsumSmallBatchedProduct(b *testing.B) {
	a := benchMat(b, 16, 4, 32, 32)
	c := benchMat(b, 17, 4, 32, 32)
	benchEinsum(b, "bij,bjk->bik", a, c)
}

// BenchmarkEinsumReduceOnly measures a reduction-only spec through the
// axis fold the dispatch now takes, against the same spec on the
// general engine, which is where it went before.
func BenchmarkEinsumReduceOnly(b *testing.B) {
	a := benchMat(b, 18, 512, 512)
	b.Run("axis fold", func(b *testing.B) {
		b.ReportAllocs()
		for b.Loop() {
			if _, err := Einsum("ij->i", a); err != nil {
				b.Fatal(err)
			}
		}
	})
	b.Run("general engine", func(b *testing.B) {
		b.ReportAllocs()
		for b.Loop() {
			if _, err := einsumGeneral([]string{"ij"}, "i", true, []*Array{a}); err != nil {
				b.Fatal(err)
			}
		}
	})
	b.Run("general engine, one worker", func(b *testing.B) {
		restore := engine.SetNumWorkers(1)
		defer engine.SetNumWorkers(restore)
		b.ReportAllocs()
		for b.Loop() {
			if _, err := einsumGeneral([]string{"ij"}, "i", true, []*Array{a}); err != nil {
				b.Fatal(err)
			}
		}
	})
}

// BenchmarkEinsumSlotKernelWalk is one slot's walk shaped like a
// contraction's, two operands over a summed axis of 48 with the second
// operand's cursor stepping a row: the peeled kernel against the
// odometer oracle, in one process.
func BenchmarkEinsumSlotKernelWalk(b *testing.B) {
	sizes := []int{48}
	base := []int{0, 0}
	delta := []int{1, 48}
	rv := [][]float64{einsumProbeFloats(48), einsumProbeFloats(48 * 48)}
	out := make([]float64, 1)
	off := make([]int, 2)
	coord := make([]int, 1)
	b.Run("peeled", func(b *testing.B) {
		for b.Loop() {
			einsumSlotSum(rv, out, 0, base, off, coord, delta, sizes, 48)
		}
	})
	b.Run("odometer", func(b *testing.B) {
		for b.Loop() {
			einsumSlotSumOdometer(rv, out, 0, base, off, coord, delta, sizes, 48)
		}
	})
}