// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package pe

import (
	"encoding/binary"
	"fmt"
	"internal/saferio"
	"io"
	"strconv"
)

// SectionHeader32 represents real PE COFF section header.
type SectionHeader32 struct {
	Name                 [8]uint8
	VirtualSize          uint32
	VirtualAddress       uint32
	SizeOfRawData        uint32
	PointerToRawData     uint32
	PointerToRelocations uint32
	PointerToLineNumbers uint32
	NumberOfRelocations  uint16
	NumberOfLineNumbers  uint16
	Characteristics      uint32
}

// fullName finds real name of section sh. Normally name is stored
// in sh.Name, but if it is longer then 8 characters, it is stored
// in COFF string table st instead.
func (sh *SectionHeader32) fullName(st StringTable) (string, error) {
	if sh.Name[0] != '/' {
		return cstring(sh.Name[:]), nil
	}
	i, err := strconv.Atoi(cstring(sh.Name[1:]))
	if err != nil {
		return "", err
	}
	return st.String(uint32(i))
}

// TODO(brainman): copy all IMAGE_REL_* consts from ldpe.go here

// Reloc represents a PE COFF relocation.
// Each section contains its own relocation list.
type Reloc struct {
	VirtualAddress   uint32
	SymbolTableIndex uint32
	Type             uint16
}

func readRelocs(sh *SectionHeader, r io.ReadSeeker) ([]Reloc, error) {
	if sh.NumberOfRelocations <= 0 {
		return nil, nil
	}
	_, err := r.Seek(int64(sh.PointerToRelocations), io.SeekStart)
	if err != nil {
		return nil, fmt.Errorf("fail to seek to %q section relocations: %v", sh.Name, err)
	}
	relocs := make([]Reloc, sh.NumberOfRelocations)
	err = binary.Read(r, binary.LittleEndian, relocs)
	if err != nil {
		return nil, fmt.Errorf("fail to read section relocations: %v", err)
	}
	return relocs, nil
}

// SectionHeader is similar to [SectionHeader32] with Name
// field replaced by Go string.
type SectionHeader struct {
	Name                 string
	VirtualSize          uint32
	VirtualAddress       uint32
	Size                 uint32
	Offset               uint32
	PointerToRelocations uint32
	PointerToLineNumbers uint32
	NumberOfRelocations  uint16
	NumberOfLineNumbers  uint16
	Characteristics      uint32
}

// Section provides access to PE COFF section.
type Section struct {
	SectionHeader
	Relocs []Reloc

	// Embed ReaderAt for ReadAt method.
	// Do not embed SectionReader directly
	// to avoid having Read and Seek.
	// If a client wants Read and Seek it must use
	// Open() to avoid fighting over the seek offset
	// with other clients.
	io.ReaderAt
	sr *io.SectionReader
}

// Data reads and returns the contents of the PE section s.
//
// If s.Offset is 0, the section has no contents,
// and Data will always return a non-nil error.
func (s *Section) Data() ([]byte, error) {
	return saferio.ReadDataAt(s.sr, uint64(s.Size), 0)
}

// Open returns a new ReadSeeker reading the PE section s.
//
// If s.Offset is 0, the section has no contents, and all calls
// to the returned reader will return a non-nil error.
func (s *Section) Open() io.ReadSeeker {
	return io.NewSectionReader(s.sr, 0, 1<<63-1)
}

// Section characteristics flags.
const (
	IMAGE_SCN_CNT_CODE               = 0x00000020
	IMAGE_SCN_CNT_INITIALIZED_DATA   = 0x00000040
	IMAGE_SCN_CNT_UNINITIALIZED_DATA = 0x00000080
	IMAGE_SCN_LNK_COMDAT             = 0x00001000
	IMAGE_SCN_MEM_DISCARDABLE        = 0x02000000
	IMAGE_SCN_MEM_EXECUTE            = 0x20000000
	IMAGE_SCN_MEM_READ               = 0x40000000
	IMAGE_SCN_MEM_WRITE              = 0x80000000
)