// Copyright 2009 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 main

import (
	"bytes"
	"compress/zlib"
	"debug/dwarf"
	"debug/elf"
	"encoding/binary"
	"fmt"
	"io"
	"strings"
)

// DWARF is a copy of Go's debug/elf func (f *File) DWARF().
// it has been forked here to prevent relocations from being applied
// prior to DWARF .debug_info parsing.
//
// See #15 for more details.
func DWARF(f *elf.File) (*dwarf.Data, error) {
	dwarfSuffix := func(s *elf.Section) string {
		switch {
		case strings.HasPrefix(s.Name, ".debug_"):
			return s.Name[7:]
		case strings.HasPrefix(s.Name, ".zdebug_"):
			return s.Name[8:]
		default:
			return ""
		}

	}
	// sectionData gets the data for s, checks its size, and
	// applies any applicable relations.
	sectionData := func(i int, s *elf.Section) ([]byte, error) {
		b, err := s.Data()
		if err != nil && uint64(len(b)) < s.Size {
			return nil, err
		}

		if len(b) >= 12 && string(b[:4]) == "ZLIB" {
			dlen := binary.BigEndian.Uint64(b[4:12])
			dbuf := make([]byte, dlen)
			r, err := zlib.NewReader(bytes.NewBuffer(b[12:]))
			if err != nil {
				return nil, err
			}
			if _, err := io.ReadFull(r, dbuf); err != nil {
				return nil, err
			}
			if err := r.Close(); err != nil {
				return nil, err
			}
			b = dbuf
		}

		// NOTE: removed relocations from original code here

		return b, nil
	}

	// There are many DWARf sections, but these are the ones
	// the debug/dwarf package started with.
	var dat = map[string][]byte{"abbrev": nil, "info": nil, "str": nil, "line": nil, "ranges": nil}
	for i, s := range f.Sections {
		suffix := dwarfSuffix(s)
		if suffix == "" {
			continue
		}
		if _, ok := dat[suffix]; !ok {
			continue
		}
		b, err := sectionData(i, s)
		if err != nil {
			return nil, err
		}
		dat[suffix] = b
	}

	d, err := dwarf.New(dat["abbrev"], nil, nil, dat["info"], dat["line"], nil, dat["ranges"], dat["str"])
	if err != nil {
		return nil, err
	}

	// Look for DWARF4 .debug_types sections and DWARF5 sections.
	for i, s := range f.Sections {
		suffix := dwarfSuffix(s)
		if suffix == "" {
			continue
		}
		if _, ok := dat[suffix]; ok {
			// Already handled.
			continue
		}

		b, err := sectionData(i, s)
		if err != nil {
			return nil, err
		}

		if suffix == "types" {
			if err := d.AddTypes(fmt.Sprintf("types-%d", i), b); err != nil {
				return nil, err
			}
		} else {
			if err := d.AddSection(".debug_"+suffix, b); err != nil {
				return nil, err
			}
		}
	}

	return d, nil
}