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

//go:build linux

package debug

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

// 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
)

// siginfo_t layout (Linux): si_signo, si_errno, si_code, then union.
// The si_addr field is at offset 16 on all supported architectures.
type siginfoT struct {
	SiSigno int32
	SiErrno int32
	SiCode  int32
	_pad    [125]byte
}

const (
	trapBRKPT   = 1 // software breakpoint
	trapHWBRKPT = 4 // hardware watchpoint
)

// StopInfo returns the reason the debuggee stopped and the faulting address
// (for watchpoints, the watched address that was accessed).
func (s *Session) StopInfo() (StopReason, uint64) {
	if s.exited {
		return StopExited, 0
	}
	var info siginfoT
	_, _, errno := syscall.Syscall6(
		syscall.SYS_PTRACE,
		uintptr(syscall.PTRACE_GETSIGINFO),
		uintptr(s.pid),
		0,
		uintptr(unsafe.Pointer(&info)),
		0, 0,
	)
	if errno != 0 {
		return StopNone, 0
	}
	if info.SiSigno != int32(syscall.SIGTRAP) {
		return StopSignal, uint64(info.SiCode)
	}
	switch info.SiCode {
	case trapBRKPT:
		return StopBreakpoint, 0
	case trapHWBRKPT:
		// si_addr sits at struct offset 16 (12 bytes of signo/errno/code
		// plus 4 bytes of union alignment).  The siginfo buffer is only
		// 4-byte aligned, so the address is read byte-wise to keep the
		// load aligned on riscv64 and loong64.  What si_addr names is
		// architecture-specific (the data address on arm64, the
		// instruction pointer on x86), so the per-architecture
		// archWatchpointAddr resolves it to the watched address.
		addr := binary.LittleEndian.Uint64(info._pad[4:12])
		return StopWatchpoint, archWatchpointAddr(s, addr)
	default:
		return StopSingleStep, 0
	}
}