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

//go:build freebsd && amd64

package debug

import (
	"encoding/binary"
	"fmt"
	"unsafe"

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

// GetRegs reads the general-purpose registers of the stopped debuggee and
// converts the FreeBSD struct reg into the portable layout.
func (s *Session) GetRegs() (Regs, error) {
	var ur unix.Reg
	if err := unix.PtraceGetRegs(s.pid, &ur); err != nil {
		return Regs{}, fmt.Errorf("debug: PT_GETREGS: %w", err)
	}
	return Regs{
		R15:    uint64(ur.R15),
		R14:    uint64(ur.R14),
		R13:    uint64(ur.R13),
		R12:    uint64(ur.R12),
		R11:    uint64(ur.R11),
		R10:    uint64(ur.R10),
		R9:     uint64(ur.R9),
		R8:     uint64(ur.R8),
		RDI:    uint64(ur.Rdi),
		RSI:    uint64(ur.Rsi),
		RBP:    uint64(ur.Rbp),
		RBX:    uint64(ur.Rbx),
		RDX:    uint64(ur.Rdx),
		RCX:    uint64(ur.Rcx),
		RAX:    uint64(ur.Rax),
		RIP:    uint64(ur.Rip),
		CS:     uint64(ur.Cs),
		RFLAGS: uint64(ur.Rflags),
		RSP:    uint64(ur.Rsp),
		SS:     uint64(ur.Ss),
		FS:     uint64(ur.Fs),
		GS:     uint64(ur.Gs),
		DS:     uint64(ur.Ds),
		ES:     uint64(ur.Es),
	}, nil
}

// SetRegs writes the general-purpose registers of the stopped debuggee.
func (s *Session) SetRegs(regs *Regs) error {
	// Read-modify-write keeps the fields FreeBSD owns (trapno, err) intact.
	var ur unix.Reg
	if err := unix.PtraceGetRegs(s.pid, &ur); err != nil {
		return fmt.Errorf("debug: PT_GETREGS: %w", err)
	}
	ur.R15 = int64(regs.R15)
	ur.R14 = int64(regs.R14)
	ur.R13 = int64(regs.R13)
	ur.R12 = int64(regs.R12)
	ur.R11 = int64(regs.R11)
	ur.R10 = int64(regs.R10)
	ur.R9 = int64(regs.R9)
	ur.R8 = int64(regs.R8)
	ur.Rdi = int64(regs.RDI)
	ur.Rsi = int64(regs.RSI)
	ur.Rbp = int64(regs.RBP)
	ur.Rbx = int64(regs.RBX)
	ur.Rdx = int64(regs.RDX)
	ur.Rcx = int64(regs.RCX)
	ur.Rax = int64(regs.RAX)
	ur.Rip = int64(regs.RIP)
	ur.Cs = int64(regs.CS)
	ur.Rflags = int64(regs.RFLAGS)
	ur.Rsp = int64(regs.RSP)
	ur.Ss = int64(regs.SS)
	return unix.PtraceSetRegs(s.pid, &ur)
}

// FPRegs holds the x87 FPU and SSE (XMM) register state, the FXSAVE image
// the FreeBSD struct fpreg mirrors: XMM0-15 at the same offsets.
type FPRegs struct {
	XMM [16][16]byte // XMM0-15
}

// GetFPRegs retrieves the FPU/SSE register state via PT_GETFPREGS.  The
// FreeBSD struct fpreg mirrors the FXSAVE image: the x87 environment and
// stack in Env/Acc, XMM0-15 in Xacc.
func (s *Session) GetFPRegs() (FPRegs, error) {
	var fp FPRegs
	var fr unix.FpReg
	if err := unix.PtraceGetFpRegs(s.pid, &fr); err != nil {
		return fp, fmt.Errorf("debug: PT_GETFPREGS: %w", err)
	}
	for i := range 16 {
		copy(fp.XMM[i][:], fr.Xacc[i][:])
	}
	return fp, nil
}

// VectorRegs holds the YMM register state.
type VectorRegs struct {
	YMM [16][32]byte // YMM0-15 (full 256-bit values)
}

// The XSAVE area the PT_GETXSTATE request returns follows the architectural
// layout (Intel SDM vol 1, "XSAVE"): the 512-byte legacy FXSAVE image (x87
// state in 0-159, XMM0-15 in 160-511), then the 64-byte xsave header whose
// first 8 bytes are xstate_bv, then one component per set feature bit, each
// 64-byte aligned.  The YMM high halves are the first extended component,
// at offset 576; XFEATURE_STATE_BIT_AVX is bit 2 of xstate_bv.
const (
	xsaveXMMOffset    = 160
	xsaveHeaderOffset = 512
	xsaveBVOffset     = xsaveHeaderOffset
	ymmOffset         = xsaveHeaderOffset + 64 // 576
	ymmSize           = 256                    // 16 registers, 16 bytes each
	xfeatureMaskYMM   = 1 << 2
	xstateMaxBuffer   = 4096 // PT_GETXSTATE_INFO bounds the size far below this
)

// GetVectorRegs retrieves the YMM registers via PT_GETXSTATE.  The low
// (XMM) halves always come from the legacy image; the high halves are
// copied only when xstate_bv reports the AVX state, and read as zero
// otherwise.  When the request fails the FP image still provides correct
// XMM halves, so that is the fallback.
func (s *Session) GetVectorRegs() (VectorRegs, error) {
	var v VectorRegs
	buf := make([]byte, xstateMaxBuffer)
	n, _, errno := unix.Syscall6(
		unix.SYS_PTRACE,
		uintptr(unix.PT_GETXSTATE),
		uintptr(s.pid),
		0,
		uintptr(unsafe.Pointer(&buf[0])),
		0, 0,
	)
	if errno != 0 {
		fp, err := s.GetFPRegs()
		if err != nil {
			return v, err
		}
		for i := range 16 {
			copy(v.YMM[i][:16], fp.XMM[i][:])
		}
		return v, nil
	}
	for i := range 16 {
		copy(v.YMM[i][:16], buf[xsaveXMMOffset+16*i:xsaveXMMOffset+16*i+16])
	}
	if int(n) >= ymmOffset+ymmSize {
		if binary.LittleEndian.Uint64(buf[xsaveBVOffset:xsaveBVOffset+8])&xfeatureMaskYMM != 0 {
			for i := range 16 {
				copy(v.YMM[i][16:], buf[ymmOffset+16*i:ymmOffset+16*i+16])
			}
		}
	}
	return v, nil
}