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

package tensor

import (
	"os"
	"path/filepath"
	"runtime"
	"testing"
)

// The leak harness. A kernel that returns must leave nothing behind:
// every parallel worker joined, every buffer handed back or
// unreachable, no reference parked in a package global. Go garbage
// collects, so a leak here means unbounded growth, not a lost block,
// and the check is the same shape either way: run the heavy paths,
// force collection, and require the goroutine count and the live heap
// to come back to where they started. The buffers sync.Pool hoards are
// released by the collections the check forces first.

// leakOps is the representative load: parallel kernels across every
// domain, the ones that spawn workers and the ones that allocate
// scratch proportional to the input, plus the untrusted-input readers.
// The data is sized so that a single retained buffer per round shows up
// far above the tolerance below: the vectors are 2 MiB and the matrix
// 32 KiB, while the tolerance is a fraction of a megabyte.
func leakOps(t *testing.T) []func() {
	t.Helper()
	const bigN = 1 << 18 // 2 MiB of float64
	big := randA(t, 31, bigN)
	med := randA(t, 32, 1<<16)
	sq := mustA(t, med.RawFloats()[:64*64], 64, 64)
	// Symmetric, diagonally dominant: both factorisations stay stable.
	mm := sq.RawFloats()
	for i := range 64 {
		for j := range 64 {
			mm[i*64+j] = (mm[i*64+j] + mm[j*64+i]) / 2
		}
		mm[i*64+i] += 20
	}
	sig := randA(t, 33, 1<<14)
	// Files the readers must refuse: a header that lies about its sizes
	// and a table header with no data behind it. Reading them allocates
	// nothing beyond the few dozen bytes they contain, and nothing may
	// stay behind either.
	dir := t.TempDir()
	hostileNC := filepath.Join(dir, "hostile.nc")
	if err := os.WriteFile(hostileNC, hostileOracleHeader(), 0o644); err != nil {
		t.Fatal(err)
	}
	hostileFITS := filepath.Join(dir, "hostile.fits")
	if err := os.WriteFile(hostileFITS, hostileOracleTable(), 0o644); err != nil {
		t.Fatal(err)
	}
	return []func(){
		func() { _, _ = Add(big, big) },
		func() { _, _ = Mul(big, big) },
		func() { _, _ = MatMul2D(sq, sq) },
		func() { _, _ = Einsum("ij,jk->ik", sq, sq) },
		func() { _, _ = Sort(big) },
		func() { _, _ = ArgSort(big) },
		func() { _, _ = FFT(sig) },
		func() { _, _, _, _ = SVD(sq) },
		func() { _, _, _ = Eigen(sq) },
		func() { _, _ = Inv(sq) },
		func() { _, _ = Cholesky(sq) },
		func() { _, _, _ = QR(sq) },
		func() { _, _, _ = WelchPSD(sig, 1000, 256, 128, "hann") },
		func() { _, _ = SavitzkyGolay(sig, 21, 3) },
		func() { _, _ = DWT(sig, 4) },
		func() { _, _ = CWT(sig, Morlet, []float64{1, 2, 4, 8, 16}, 1) },
		func() { _, _ = SobolPoints(1<<12, 8, 0) },
		func() { _, _ = HaltonPoints(1<<12, 8, 0) },
		func() { _, _ = Gradient1D(sig, 1) },
		func() { _, _ = Laplacian(sq, 1, 1) },
		func() {
			_, _ = IntegrateODE(func(t float64, y *Array) (*Array, error) {
				return MulF(y, -1), nil
			}, 0, 5, mustA(t, []float64{1}, 1), ODEOptions{MaxSteps: 100000})
		},
		func() { _, _, _, _ = LoadNetCDF(hostileNC) },
		func() { _, _ = LoadFITSTable(hostileFITS) },
		func() { _, _ = LoadHDF5(filepath.Join("io", "testdata", "h5", "fixture.h5")) },
		func() {
			_, _ = LinearRegression(mustA(t, randA(t, 34, 4096).RawFloats(), 4096, 1),
				randA(t, 35, 4096))
		},
	}
}

// liveHeap returns the live heap after forcing every reclaimable byte
// to be collected twice: sync.Pool keeps one victim generation, so two
// rounds are what it takes for pooled buffers to be unreachable.
func liveHeap() (heap uint64, goroutines int) {
	runtime.GC()
	runtime.GC()
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	return m.HeapAlloc, runtime.NumGoroutine()
}

// leakBlock runs one measurement block over the given operations and
// returns the live heap and goroutine count after it, so the leak
// detector itself can be measured by the same instrument it uses.
func leakBlock(ops []func(), rounds int) (heap uint64, goroutines int) {
	for range rounds {
		for _, op := range ops {
			op()
		}
	}
	return liveHeap()
}

// TestLeakHarnessDetectsLeaks is the harness's self-check: the same
// block measurement run over an operation that deliberately retains
// half a megabyte per round must fail, so a regression that empties
// the comparison or flips its direction cannot pass silently.
func TestLeakHarnessDetectsLeaks(t *testing.T) {
	var retained [][]float64
	leaky := []func(){
		func() { retained = append(retained, make([]float64, 64<<10)) },
	}
	leakBlock(leaky, 3) // settle, as the real harness does
	first, _ := leakBlock(leaky, 10)
	second, _ := leakBlock(leaky, 10)
	// The closure must stay reachable through the second block's
	// collections: without a later use, the caller's slot is dead
	// during the call and the collector would free exactly the data
	// the self-check means to catch.
	runtime.KeepAlive(leaky)
	if second <= first+256<<10 {
		t.Fatalf("the leak harness measured %d then %d bytes: a 5 MiB retention over 10 rounds went undetected", first, second)
	}
}

func TestNoResourceLeaks(t *testing.T) {
	ops := leakOps(t)
	if len(ops) == 0 {
		t.Fatal("the leak harness has no operations: a refactor emptied leakOps and the measurement below would pass vacuously")
	}
	run := func(rounds int) {
		for range rounds {
			for _, op := range ops {
				op()
			}
		}
	}
	// Caches, pooled buffers and lazy tables settle in the first block.
	// The measurement then compares successive blocks rather than the
	// whole run against a baseline: a leak retains data per round and
	// grows steadily block over block, while the runtime's own
	// structures settle. Comparing endpoint to start once is what let
	// a leak of a few hundred kilobytes per block hide under the
	// settling curve.
	const (
		block     = 10
		tolerance = 256 << 10
	)
	run(3)
	run(block)
	prev, g0 := liveHeap()
	for range 2 {
		run(block)
		heap, g := liveHeap()
		if heap > prev+tolerance {
			t.Errorf("live heap grew from %d to %d bytes over %d rounds of the facade load (tolerance %d): something retains data per round",
				prev, heap, block, tolerance)
		}
		if g > g0 {
			t.Errorf("goroutines grew from %d to %d over %d rounds of the facade load: a worker did not return",
				g0, g, block)
		}
		prev = heap
	}
}