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

//go:build freebsd && (amd64 || arm64 || riscv64)

package debug

import (
	"encoding/binary"
	"syscall"
	"unsafe"

	"golang.org/x/sys/unix"
)

// FreeBSD TRAP_* si_code values (sys/signal.h).  A breakpoint (INT3, BRK,
// EBREAK) arrives as TRAP_BRKPT on every supported architecture; TRAP_TRACE
// is shared by the completed single-step and the hardware watchpoint hit,
// so the watchpoint layer disambiguates from the debug registers.
const (
	trapBRKPT = 1 // TRAP_BRKPT
	trapTRACE = 2 // TRAP_TRACE
)

// StopReason describes why the debuggee stopped.
type StopReason int

const (
	StopNone       StopReason = iota
	StopBreakpoint            // software breakpoint hit
	StopWatchpoint            // hardware watchpoint triggered
	StopSingleStep            // single-step completed
	StopSignal                // stopped by a signal
	StopExited                // process exited
)

// StopInfo returns the reason the debuggee stopped and the faulting address
// (for watchpoints, the watched address that was accessed).  FreeBSD has no
// PTRACE_GETSIGINFO; the stop's signal information comes from PT_LWPINFO,
// whose pl_siginfo carries the siginfo the kernel delivered.  A ptrace stop
// with no signal behind it (a completed single-step, the initial attach)
// fills no siginfo at all.
func (s *Session) StopInfo() (StopReason, uint64) {
	if s.exited {
		return StopExited, 0
	}
	var info unix.PtraceLwpInfoStruct
	if err := unix.PtraceLwpInfo(s.pid, &info); err != nil {
		return StopNone, 0
	}
	// The siginfo layout is the FreeBSD siginfo_t: three leading ints
	// (signo, errno, code), then the union, 8-byte aligned, whose _fault
	// member puts the address at byte offset 16.  The read is byte-wise
	// because the blob's alignment is not guaranteed.
	si := (*[64]byte)(unsafe.Pointer(&info.Siginfo))
	signo := int32(binary.LittleEndian.Uint32(si[0:4]))
	code := int32(binary.LittleEndian.Uint32(si[8:12]))
	switch {
	case signo == 0:
		// A pure ptrace stop: single-step completion, attach, or the
		// events the kernel resolves internally.
		return StopSingleStep, 0
	case signo != int32(syscall.SIGTRAP):
		return StopSignal, uint64(code)
	case code == trapBRKPT:
		return StopBreakpoint, 0
	case code == trapTRACE:
		addr := binary.LittleEndian.Uint64(si[16:24])
		return archStopTrace(s, addr)
	default:
		return StopSingleStep, 0
	}
}