// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package verify

import (
	"os"
	"os/exec"
	"testing"
)

// goobjFoldMainSrc is the Go side of the SSE regression.  The kernel
// XOR-folds 16-byte blocks and sums the tail bytes through the amd64 SSE
// families; main derives the same value in Go and panics on any divergence
// before printing the deterministic line the baseline and the gasm-linked
// binaries must agree on.
const goobjFoldMainSrc = `package main

import "encoding/binary"

func fold(buf []byte, seed uint64) uint64

func main() {
	buf := []byte("gasm link parity vector kernel! 0123456789abcdef tail")
	low, high := uint64(0), uint64(0)
	for i := 0; i+16 <= len(buf); i += 16 {
		low ^= binary.LittleEndian.Uint64(buf[i:])
		high ^= binary.LittleEndian.Uint64(buf[i+8:])
	}
	tail := uint64(0)
	for _, b := range buf[len(buf)-len(buf)%16:] {
		tail += uint64(b)
	}
	const k = 0x9e3779b97f4a7c15
	want := (low + high + tail) * k ^ 0xabcdef
	if got := fold(buf, 0xabcdef); got != want {
		panic("fold")
	}
	println("ok", fold(buf, 0xabcdef))
}
`

// TestGOOBJLinkFoldKernel proves the amd64 SSE families are proven end to
// end: the kernel assembles by gasm into a GOOBJ object, substitutes
// byte-wise into a real go build archive, relinks with cmd/link and the
// linked binary computes the same fold as the toolchain-built one, run
// natively on amd64 hosts.
func TestGOOBJLinkFoldKernel(t *testing.T) {
	if testing.Short() {
		t.Skip("builds the gasm binary and links Go programs")
	}
	if os.Getenv("GASM_LINK_PARITY") == "" {
		t.Skip("deliberate verification: set GASM_LINK_PARITY=1 (just link-parity)")
	}
	goBin, err := exec.LookPath("go")
	if err != nil {
		t.Skip("no Go toolchain available")
	}
	gasmBin := buildLinkParityGasm(t, goBin)
	t.Run("amd64", func(t *testing.T) {
		goobjLinkKernel(t, goBin, gasmBin, "amd64", "linkfold_amd64.s", goobjFoldMainSrc)
	})
}