// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:collection';
import 'dart:math';
import 'dart:typed_data';

import 'constants.dart' as constants;
import 'elf.dart';
import 'reader.dart';

int _initialLengthValue(Reader reader) {
  final length = reader.readBytes(4);
  if (length == 0xffffffff) {
    throw FormatException('64-bit DWARF format detected');
  } else if (length > 0xfffffff0) {
    throw FormatException('Unrecognized reserved initial length value');
  }
  return length;
}

enum _Tag {
  compileUnit,
  inlinedSubroutine,
  subprogram,
}

const _tags = <int, _Tag>{
  0x11: _Tag.compileUnit,
  0x1d: _Tag.inlinedSubroutine,
  0x2e: _Tag.subprogram,
};

const _tagStrings = <_Tag, String>{
  _Tag.compileUnit: 'DW_TAG_compile_unit',
  _Tag.inlinedSubroutine: 'DW_TAG_inlined_subroutine',
  _Tag.subprogram: 'DW_TAG_subroutine',
};

enum _AttributeName {
  abstractOrigin,
  artificial,
  callColumn,
  callFile,
  callLine,
  compilationDirectory,
  declarationColumn,
  declarationFile,
  declarationLine,
  highProgramCounter,
  lowProgramCounter,
  inline,
  name,
  producer,
  sibling,
  statementList,
}

const _attributeNames = <int, _AttributeName>{
  0x01: _AttributeName.sibling,
  0x03: _AttributeName.name,
  0x10: _AttributeName.statementList,
  0x11: _AttributeName.lowProgramCounter,
  0x12: _AttributeName.highProgramCounter,
  0x1b: _AttributeName.compilationDirectory,
  0x20: _AttributeName.inline,
  0x25: _AttributeName.producer,
  0x31: _AttributeName.abstractOrigin,
  0x34: _AttributeName.artificial,
  0x39: _AttributeName.declarationColumn,
  0x3a: _AttributeName.declarationFile,
  0x3b: _AttributeName.declarationLine,
  0x57: _AttributeName.callColumn,
  0x58: _AttributeName.callFile,
  0x59: _AttributeName.callLine,
};

const _attributeNameStrings = <_AttributeName, String>{
  _AttributeName.sibling: 'DW_AT_sibling',
  _AttributeName.name: 'DW_AT_name',
  _AttributeName.statementList: 'DW_AT_stmt_list',
  _AttributeName.lowProgramCounter: 'DW_AT_low_pc',
  _AttributeName.highProgramCounter: 'DW_AT_high_pc',
  _AttributeName.compilationDirectory: 'DW_AT_comp_dir',
  _AttributeName.inline: 'DW_AT_inline',
  _AttributeName.producer: 'DW_AT_producer',
  _AttributeName.abstractOrigin: 'DW_AT_abstract_origin',
  _AttributeName.artificial: 'DW_AT_artificial',
  _AttributeName.declarationColumn: 'DW_AT_decl_column',
  _AttributeName.declarationFile: 'DW_AT_decl_file',
  _AttributeName.declarationLine: 'DW_AT_decl_line',
  _AttributeName.callColumn: 'DW_AT_call_column',
  _AttributeName.callFile: 'DW_AT_call_file',
  _AttributeName.callLine: 'DW_AT_call_line',
};

enum _AttributeForm {
  address,
  constant,
  flag,
  reference4,
  sectionOffset,
  string,
}

const _attributeForms = <int, _AttributeForm>{
  0x01: _AttributeForm.address,
  0x08: _AttributeForm.string,
  0x0c: _AttributeForm.flag,
  0x0f: _AttributeForm.constant,
  0x13: _AttributeForm.reference4,
  0x17: _AttributeForm.sectionOffset,
};

const _attributeFormStrings = <_AttributeForm, String>{
  _AttributeForm.address: 'DW_FORM_addr',
  _AttributeForm.string: 'DW_FORM_string',
  _AttributeForm.flag: 'DW_FORM_flag',
  _AttributeForm.constant: 'DW_FORM_udata',
  _AttributeForm.reference4: 'DW_FORM_ref4',
  _AttributeForm.sectionOffset: 'DW_FORM_sec_offset',
};

class _Attribute {
  final _AttributeName name;
  final _AttributeForm form;

  _Attribute._(this.name, this.form);

  static _Attribute? fromReader(Reader reader) {
    final nameInt = reader.readLEB128EncodedInteger();
    final formInt = reader.readLEB128EncodedInteger();
    if (nameInt == 0 && formInt == 0) return null;
    if (!_attributeNames.containsKey(nameInt)) {
      throw FormatException('Unexpected DW_AT value 0x${paddedHex(nameInt)}');
    }
    if (!_attributeForms.containsKey(formInt)) {
      throw FormatException('Unexpected DW_FORM value 0x${paddedHex(formInt)}');
    }
    return _Attribute._(_attributeNames[nameInt]!, _attributeForms[formInt]!);
  }

  Object read(Reader reader, CompilationUnitHeader header) {
    switch (form) {
      case _AttributeForm.string:
        return reader.readNullTerminatedString();
      case _AttributeForm.flag:
        return reader.readByte() != 0;
      case _AttributeForm.address:
        return reader.readBytes(header.addressSize);
      case _AttributeForm.sectionOffset:
        return reader.readBytes(4);
      case _AttributeForm.constant:
        return reader.readLEB128EncodedInteger();
      case _AttributeForm.reference4:
        return reader.readBytes(4);
    }
  }

  String valueToString(Object value, [CompilationUnit? unit]) {
    switch (form) {
      case _AttributeForm.string:
        return value as String;
      case _AttributeForm.flag:
        return value.toString();
      case _AttributeForm.address:
        return '0x' + paddedHex(value as int, unit?.header.addressSize ?? 0);
      case _AttributeForm.sectionOffset:
        return paddedHex(value as int, 4);
      case _AttributeForm.constant:
        return value.toString();
      case _AttributeForm.reference4:
        final intValue = value as int;
        final unresolvedValue = paddedHex(intValue, 4);
        final name = unit?.nameOfOrigin(intValue) ?? '<unresolved>';
        return '0x$unresolvedValue (origin: $name)';
    }
  }
}

class _Abbreviation {
  final int code;
  final _Tag tag;
  final bool children;
  final List<_Attribute> attributes;

  _Abbreviation._(this.code, this.tag, this.children, this.attributes);

  // Constants from the DWARF specification.
  static const _dwChildrenNo = 0x00;
  static const _dwChildrenYes = 0x01;

  static _Abbreviation? fromReader(Reader reader) {
    final code = reader.readLEB128EncodedInteger();
    if (code == 0) return null;
    final tagInt = reader.readLEB128EncodedInteger();
    if (!_tags.containsKey(tagInt)) {
      throw FormatException('Unexpected DW_TAG value 0x${paddedHex(tagInt)}');
    }
    final tag = _tags[tagInt]!;
    final childrenByte = reader.readByte();
    if (childrenByte != _dwChildrenNo && childrenByte != _dwChildrenYes) {
      throw FormatException('Expected DW_CHILDREN_no or DW_CHILDREN_yes: '
          '$childrenByte');
    }
    final children = childrenByte == _dwChildrenYes;
    final attributes = reader.readRepeated(_Attribute.fromReader).toList();
    return _Abbreviation._(code, tag, children, attributes);
  }

  void writeToStringBuffer(StringBuffer buffer) {
    buffer
      ..write('    Tag: ')
      ..writeln(_tagStrings[tag])
      ..write('    Children: ')
      ..writeln(children ? 'DW_CHILDREN_yes' : 'DW_CHILDREN_no')
      ..writeln('    Attributes:');
    for (final attribute in attributes) {
      buffer
        ..write('      ')
        ..write(_attributeNameStrings[attribute.name]!)
        ..write(': ')
        ..writeln(_attributeFormStrings[attribute.form]!);
    }
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

class _AbbreviationsTable {
  final Map<int, _Abbreviation> _abbreviations;

  _AbbreviationsTable._(this._abbreviations);

  bool containsKey(int code) => _abbreviations.containsKey(code);
  _Abbreviation? operator [](int code) => _abbreviations[code];

  static _AbbreviationsTable? fromReader(Reader reader) {
    final abbreviations = Map.fromEntries(reader
        .readRepeated(_Abbreviation.fromReader)
        .map((abbr) => MapEntry(abbr.code, abbr)));
    return _AbbreviationsTable._(abbreviations);
  }

  void writeToStringBuffer(StringBuffer buffer) {
    buffer
      ..writeln('Abbreviations table:')
      ..writeln();
    _abbreviations.forEach((key, abbreviation) {
      buffer
        ..write('  ')
        ..write(key)
        ..writeln(':');
      abbreviation.writeToStringBuffer(buffer);
      buffer.writeln();
    });
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// A DWARF Debug Information Entry (DIE).
class DebugInformationEntry {
  // The index of the entry in the abbreviation table for this DIE.
  final int code;
  final Map<_Attribute, Object> attributes;
  final Map<int, DebugInformationEntry> children;

  DebugInformationEntry._(this.code, this.attributes, this.children);

  static DebugInformationEntry? fromReader(
      Reader reader, CompilationUnitHeader header) {
    final code = reader.readLEB128EncodedInteger();
    // DIEs with an abbreviation table index of 0 are list end markers.
    if (code == 0) return null;
    if (!header.abbreviations.containsKey(code)) {
      throw FormatException('Unknown abbreviation code 0x${paddedHex(code)}');
    }
    final abbreviation = header.abbreviations[code]!;
    final attributes = <_Attribute, Object>{};
    for (final attribute in abbreviation.attributes) {
      attributes[attribute] = attribute.read(reader, header);
    }
    final children = <int, DebugInformationEntry>{};
    if (abbreviation.children) {
      children.addEntries(reader.readRepeatedWithOffsets(
          (r) => DebugInformationEntry.fromReader(r, header),
          absolute: true));
    }
    return DebugInformationEntry._(code, attributes, children);
  }

  _Attribute? _namedAttribute(_AttributeName name) {
    for (final attribute in attributes.keys) {
      if (attribute.name == name) {
        return attribute;
      }
    }
    return null;
  }

  bool containsKey(_AttributeName name) => _namedAttribute(name) != null;

  Object? operator [](_AttributeName name) => attributes[_namedAttribute(name)];

  int? get sectionOffset => this[_AttributeName.statementList] as int?;

  int? get abstractOrigin => this[_AttributeName.abstractOrigin] as int?;

  int? get lowPC => this[_AttributeName.lowProgramCounter] as int?;

  int? get highPC => this[_AttributeName.highProgramCounter] as int?;

  bool get isArtificial => (this[_AttributeName.artificial] ?? false) as bool;

  bool containsPC(int virtualAddress) =>
      (lowPC ?? 0) <= virtualAddress && virtualAddress < (highPC ?? -1);

  String? get name => this[_AttributeName.name] as String?;

  int? get callFileIndex => this[_AttributeName.callFile] as int?;

  int? get callLine => this[_AttributeName.callLine] as int?;

  int? get callColumn => this[_AttributeName.callColumn] as int?;

  List<CallInfo>? callInfo(
      CompilationUnit unit, LineNumberProgram lineNumberProgram, int address) {
    String callFilename(int index) =>
        lineNumberProgram.header.filesInfo[index]?.name ?? '<unknown file>';
    if (!containsPC(address)) return null;

    final tag = unit.header.abbreviations[code]!.tag;
    final inlined = tag == _Tag.inlinedSubroutine;
    for (final child in children.values) {
      final callInfo = child.callInfo(unit, lineNumberProgram, address);
      if (callInfo == null) continue;

      if (tag == _Tag.compileUnit) return callInfo;

      return callInfo
        ..add(DartCallInfo(
            function: unit.nameOfOrigin(abstractOrigin ?? -1),
            inlined: inlined,
            internal: isArtificial,
            filename: callFilename(child.callFileIndex ?? -1),
            line: child.callLine ?? 0,
            column: child.callColumn ?? 0));
    }

    if (tag == _Tag.compileUnit) return null;

    final filename = lineNumberProgram.filename(address)!;
    final line = lineNumberProgram.lineNumber(address)!;
    final column = lineNumberProgram.column(address)!;
    return [
      DartCallInfo(
          function: unit.nameOfOrigin(abstractOrigin ?? -1),
          inlined: inlined,
          internal: isArtificial,
          filename: filename,
          line: line,
          column: column)
    ];
  }

  void writeToStringBuffer(StringBuffer buffer,
      {CompilationUnit? unit, String indent = ''}) {
    buffer
      ..write(indent)
      ..write('Abbreviation code: ')
      ..write(code)
      ..writeln('):');
    attributes.forEach((attribute, value) {
      buffer
        ..write(indent)
        ..write('  ')
        ..write(_attributeNameStrings[attribute.name]!)
        ..write(' => ')
        ..writeln(attribute.valueToString(value, unit));
    });
    if (children.isNotEmpty) {
      buffer
        ..write(indent)
        ..write('Children (')
        ..write(children.length)
        ..writeln('):');
      final sortedChildren = children.entries.toList()
        ..sort((kv1, kv2) => Comparable.compare(kv1.key, kv2.key));
      for (var i = 0; i < sortedChildren.length; i++) {
        final offset = sortedChildren[i].key;
        final child = sortedChildren[i].value;
        buffer
          ..write(indent)
          ..write('Child ')
          ..write(i)
          ..write(' (at offset 0x')
          ..write(paddedHex(offset))
          ..writeln('):');
        child.writeToStringBuffer(buffer, unit: unit, indent: indent + '  ');
      }
    }
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

class CompilationUnitHeader {
  final int size;
  final int version;
  final int abbreviationsOffset;
  final int addressSize;
  final _AbbreviationsTable abbreviations;

  CompilationUnitHeader._(this.size, this.version, this.abbreviationsOffset,
      this.addressSize, this.abbreviations);

  static CompilationUnitHeader? fromReader(
      Reader reader, Map<int, _AbbreviationsTable> abbreviationsTables) {
    final size = _initialLengthValue(reader);
    // An empty unit is an ending marker.
    if (size == 0) return null;
    final version = reader.readBytes(2);
    if (version != 2) {
      throw FormatException('Expected DWARF version 2, got $version');
    }
    final abbreviationsOffset = reader.readBytes(4);
    final abbreviationsTable = abbreviationsTables[abbreviationsOffset];
    if (abbreviationsTable == null) {
      throw FormatException('No abbreviation table found for offset '
          '0x${paddedHex(abbreviationsOffset, 4)}');
    }
    final addressSize = reader.readByte();
    return CompilationUnitHeader._(
        size, version, abbreviationsOffset, addressSize, abbreviationsTable);
  }

  void writeToStringBuffer(StringBuffer buffer) {
    buffer
      ..writeln('Compilation unit:')
      ..write('  Size: ')
      ..writeln(size)
      ..write('  Version: ')
      ..writeln(version)
      ..write('  Abbreviations offset: 0x')
      ..writeln(paddedHex(abbreviationsOffset, 4))
      ..write('  Address size: ')
      ..writeln(addressSize)
      ..writeln();
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// A class representing a DWARF compilation unit.
class CompilationUnit {
  CompilationUnitHeader header;
  Map<int, DebugInformationEntry> referenceTable;

  CompilationUnit._(this.header, this.referenceTable);

  static CompilationUnit? fromReader(
      Reader reader, Map<int, _AbbreviationsTable> abbreviationsTables) {
    final header =
        CompilationUnitHeader.fromReader(reader, abbreviationsTables);
    if (header == null) return null;

    final referenceTable = Map.fromEntries(reader.readRepeatedWithOffsets(
        (r) => DebugInformationEntry.fromReader(r, header),
        absolute: true));
    _addChildEntries(referenceTable);
    return CompilationUnit._(header, referenceTable);
  }

  static void _addChildEntries(Map<int, DebugInformationEntry> table) {
    final workList = Queue<MapEntry<int, DebugInformationEntry>>();
    for (final die in table.values) {
      workList.addAll(die.children.entries);
    }
    while (workList.isNotEmpty) {
      final kv = workList.removeFirst();
      final offset = kv.key;
      final child = kv.value;
      table[offset] = child;
      workList.addAll(child.children.entries);
    }
  }

  Iterable<CallInfo>? callInfo(LineNumberInfo lineNumberInfo, int address) {
    for (final die in referenceTable.values) {
      final lineNumberProgram = lineNumberInfo[die.sectionOffset ?? -1];
      if (lineNumberProgram == null) continue;
      final callInfo = die.callInfo(this, lineNumberProgram, address);
      if (callInfo != null) return callInfo;
    }
    return null;
  }

  String nameOfOrigin(int offset) {
    final origin = referenceTable[offset];
    if (origin == null) {
      throw ArgumentError(
          '${paddedHex(offset)} is not the offset of an abbreviated unit');
    }
    return origin[_AttributeName.name] as String;
  }

  void writeToStringBuffer(StringBuffer buffer) {
    header.writeToStringBuffer(buffer);
    referenceTable.forEach((offset, die) {
      buffer
        ..write('Debug information entry at offset 0x')
        ..write(paddedHex(offset))
        ..writeln(':');
      die.writeToStringBuffer(buffer, unit: this);
      buffer.writeln();
    });
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// A class representing a DWARF `.debug_info` section.
class DebugInfo {
  final List<CompilationUnit> units;

  DebugInfo._(this.units);

  static DebugInfo fromReader(
      Reader reader, Map<int, _AbbreviationsTable> abbreviationsTable) {
    final units = reader
        .readRepeated(
            (r) => CompilationUnit.fromReader(reader, abbreviationsTable))
        .toList();
    return DebugInfo._(units);
  }

  Iterable<CallInfo>? callInfo(LineNumberInfo lineNumberInfo, int address) {
    for (final unit in units) {
      final callInfo = unit.callInfo(lineNumberInfo, address);
      if (callInfo != null) return callInfo;
    }
    return null;
  }

  void writeToStringBuffer(StringBuffer buffer) {
    for (final unit in units) {
      unit.writeToStringBuffer(buffer);
      buffer.writeln();
    }
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

class FileEntry {
  final String name;
  final int directoryIndex;
  final int lastModified;
  final int size;

  FileEntry._(this.name, this.directoryIndex, this.lastModified, this.size);

  static FileEntry? fromReader(Reader reader) {
    final name = reader.readNullTerminatedString();
    // An empty null-terminated string marks the table end.
    if (name == '') return null;
    final directoryIndex = reader.readLEB128EncodedInteger();
    final lastModified = reader.readLEB128EncodedInteger();
    final size = reader.readLEB128EncodedInteger();
    return FileEntry._(name, directoryIndex, lastModified, size);
  }

  @override
  String toString() => 'File name: $name\n'
      '  Directory index: $directoryIndex\n'
      '  Last modified: $lastModified\n'
      '  Size: $size\n';
}

class FileInfo {
  final Map<int, FileEntry> _files;

  FileInfo._(this._files);

  static FileInfo fromReader(Reader reader) {
    final offsetFiles = reader.readRepeated(FileEntry.fromReader).toList();
    final files = <int, FileEntry>{};
    for (var i = 0; i < offsetFiles.length; i++) {
      // File entries are one-based, not zero-based.
      files[i + 1] = offsetFiles[i];
    }
    return FileInfo._(files);
  }

  bool containsKey(int index) => _files.containsKey(index);
  FileEntry? operator [](int index) => _files[index];

  void writeToStringBuffer(StringBuffer buffer) {
    if (_files.isEmpty) {
      buffer.writeln('No file information.');
      return;
    }

    final indexHeader = 'Entry';
    final dirIndexHeader = 'Dir';
    final modifiedHeader = 'Time';
    final sizeHeader = 'Size';
    final nameHeader = 'Name';

    final indexStrings = _files
        .map((int i, FileEntry f) => MapEntry<int, String>(i, i.toString()));
    final dirIndexStrings = _files.map((int i, FileEntry f) =>
        MapEntry<int, String>(i, f.directoryIndex.toString()));
    final modifiedStrings = _files.map((int i, FileEntry f) =>
        MapEntry<int, String>(i, f.lastModified.toString()));
    final sizeStrings = _files.map(
        (int i, FileEntry f) => MapEntry<int, String>(i, f.size.toString()));

    final maxIndexLength = indexStrings.values
        .fold(indexHeader.length, (int acc, String s) => max(acc, s.length));
    final maxDirIndexLength = dirIndexStrings.values
        .fold(dirIndexHeader.length, (int acc, String s) => max(acc, s.length));
    final maxModifiedLength = modifiedStrings.values
        .fold(modifiedHeader.length, (int acc, String s) => max(acc, s.length));
    final maxSizeLength = sizeStrings.values
        .fold(sizeHeader.length, (int acc, String s) => max(acc, s.length));

    buffer.writeln('File information:');

    buffer
      ..write(' ')
      ..write(indexHeader.padRight(maxIndexLength));
    buffer
      ..write(' ')
      ..write(dirIndexHeader.padRight(maxDirIndexLength));
    buffer
      ..write(' ')
      ..write(modifiedHeader.padRight(maxModifiedLength));
    buffer
      ..write(' ')
      ..write(sizeHeader.padRight(maxSizeLength));
    buffer
      ..write(' ')
      ..writeln(nameHeader);

    for (final index in _files.keys) {
      buffer
        ..write(' ')
        ..write(indexStrings[index]!.padRight(maxIndexLength));
      buffer
        ..write(' ')
        ..write(dirIndexStrings[index]!.padRight(maxDirIndexLength));
      buffer
        ..write(' ')
        ..write(modifiedStrings[index]!.padRight(maxModifiedLength));
      buffer
        ..write(' ')
        ..write(sizeStrings[index]!.padRight(maxSizeLength));
      buffer
        ..write(' ')
        ..writeln(_files[index]!.name);
    }
  }

  @override
  String toString() {
    var buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

class LineNumberState {
  final bool defaultIsStatement;

  late int address;
  late int fileIndex;
  late int line;
  late int column;
  late bool isStatement;
  late bool basicBlock;
  late bool endSequence;

  LineNumberState(this.defaultIsStatement) {
    reset();
  }

  void reset() {
    address = 0;
    fileIndex = 1;
    line = 1;
    column = 0;
    isStatement = defaultIsStatement;
    basicBlock = false;
    endSequence = false;
  }

  LineNumberState clone() {
    final clone = LineNumberState(defaultIsStatement);
    clone.address = address;
    clone.fileIndex = fileIndex;
    clone.line = line;
    clone.column = column;
    clone.isStatement = isStatement;
    clone.basicBlock = basicBlock;
    clone.endSequence = endSequence;
    return clone;
  }

  @override
  String toString() => 'Current line number state machine registers:\n'
      '  Address: ${paddedHex(address)}\n'
      '  File index: $fileIndex\n'
      '  Line number: $line\n'
      '  Column number: $column\n'
      "  Is ${isStatement ? "" : "not "}a statement.\n"
      "  Is ${basicBlock ? "" : "not "}at the beginning of a basic block.\n"
      "  Is ${endSequence ? "" : "not "}just after the end of a sequence.";
}

class LineNumberProgramHeader {
  final int size;
  final int version;
  final int headerLength;
  final int minimumInstructionLength;
  final bool defaultIsStatement;
  final int lineBase;
  final int lineRange;
  final int opcodeBase;
  final Map<int, int> standardOpcodeLengths;
  final List<String> includeDirectories;
  final FileInfo filesInfo;

  LineNumberProgramHeader._(
      this.size,
      this.version,
      this.headerLength,
      this.minimumInstructionLength,
      this.defaultIsStatement,
      this.lineBase,
      this.lineRange,
      this.opcodeBase,
      this.standardOpcodeLengths,
      this.includeDirectories,
      this.filesInfo);

  static LineNumberProgramHeader? fromReader(Reader reader) {
    final size = _initialLengthValue(reader);
    if (size == 0) return null;
    final version = reader.readBytes(2);

    final headerLength = reader.readBytes(4);
    // We'll need this later as a double-check that we've read the entire
    // header.
    final headerStart = reader.offset;
    final minimumInstructionLength = reader.readByte();
    final isStmtByte = reader.readByte();
    if (isStmtByte < 0 || isStmtByte > 1) {
      throw FormatException(
          'Unexpected value for default_is_stmt: $isStmtByte');
    }
    final defaultIsStatement = isStmtByte == 1;
    final lineBase = reader.readByte(signed: true);
    final lineRange = reader.readByte();
    final opcodeBase = reader.readByte();
    final standardOpcodeLengths = <int, int>{};
    // Standard opcode numbering starts at 1.
    for (var i = 1; i < opcodeBase; i++) {
      standardOpcodeLengths[i] = reader.readLEB128EncodedInteger();
    }
    final includeDirectories = <String>[];
    while (!reader.done) {
      final directory = reader.readNullTerminatedString();
      if (directory == '') break;
      includeDirectories.add(directory);
    }
    if (reader.done) {
      throw FormatException('Unterminated directory entry');
    }
    final filesInfo = FileInfo.fromReader(reader);

    // Header length doesn't include the 2-byte version or 4-byte length fields.
    if (reader.offset != headerStart + headerLength) {
      throw FormatException('At offset ${reader.offset} after header, '
          'expected to be at offset ${headerStart + headerLength}');
    }

    return LineNumberProgramHeader._(
        size,
        version,
        headerLength,
        minimumInstructionLength,
        defaultIsStatement,
        lineBase,
        lineRange,
        opcodeBase,
        standardOpcodeLengths,
        includeDirectories,
        filesInfo);
  }

  void writeToStringBuffer(StringBuffer buffer) {
    buffer
      ..write('  Size: ')
      ..writeln(size)
      ..write('  Version: ')
      ..writeln(version)
      ..write('  Header length: ')
      ..writeln(headerLength)
      ..write('  Min instruction length: ')
      ..writeln(minimumInstructionLength)
      ..write('  Default value of is_stmt: ')
      ..writeln(defaultIsStatement)
      ..write('  Line base: ')
      ..writeln(lineBase)
      ..write('  Line range: ')
      ..writeln(lineRange)
      ..write('  Opcode base: ')
      ..writeln(opcodeBase)
      ..writeln('Standard opcode lengths:');
    for (var i = 1; i < opcodeBase; i++) {
      buffer
        ..write('    Opcode ')
        ..write(i)
        ..write(': ')
        ..writeln(standardOpcodeLengths[i]);
    }

    if (includeDirectories.isEmpty) {
      buffer.writeln('No include directories.');
    } else {
      buffer.writeln('Include directories:');
      for (final dir in includeDirectories) {
        buffer
          ..write('    ')
          ..writeln(dir);
      }
    }

    filesInfo.writeToStringBuffer(buffer);
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// A class representing a DWARF line number program.
class LineNumberProgram {
  final LineNumberProgramHeader header;
  final List<LineNumberState> calculatedMatrix;
  final Map<int, LineNumberState> cachedLookups;

  LineNumberProgram._(this.header, this.calculatedMatrix) : cachedLookups = {};

  static LineNumberProgram? fromReader(Reader reader) {
    final header = LineNumberProgramHeader.fromReader(reader);
    if (header == null) return null;
    final calculatedMatrix = _readOpcodes(reader, header).toList();
    if (calculatedMatrix.isEmpty) {
      throw FormatException('No line number information generated by program');
    }
    return LineNumberProgram._(header, calculatedMatrix);
  }

  static Iterable<LineNumberState> _readOpcodes(
      Reader reader, LineNumberProgramHeader header) sync* {
    final state = LineNumberState(header.defaultIsStatement);

    void applySpecialOpcode(int opcode) {
      final adjustedOpcode = opcode - header.opcodeBase;
      state.address = adjustedOpcode ~/ header.lineRange;
      state.line += header.lineBase + (adjustedOpcode % header.lineRange);
    }

    while (!reader.done) {
      final opcode = reader.readByte();
      if (opcode >= header.opcodeBase) {
        applySpecialOpcode(opcode);
        continue;
      }
      switch (opcode) {
        case 0: // Extended opcodes
          final extendedLength = reader.readByte();
          final subOpcode = reader.readByte();
          switch (subOpcode) {
            case 0:
              throw FormatException('Attempted to execute extended opcode 0');
            case 1: // DW_LNE_end_sequence
              state.endSequence = true;
              yield state.clone();
              state.reset();
              break;
            case 2: // DW_LNE_set_address
              // The length includes the subopcode.
              final valueLength = extendedLength - 1;
              assert(valueLength == 4 || valueLength == 8);
              final newAddress = reader.readBytes(valueLength);
              state.address = newAddress;
              break;
            case 3: // DW_LNE_define_file
              throw FormatException(
                  'DW_LNE_define_file instruction not handled');
            default:
              throw FormatException(
                  'Extended opcode $subOpcode not in DWARF 2');
          }
          break;
        case 1: // DW_LNS_copy
          yield state.clone();
          state.basicBlock = false;
          break;
        case 2: // DW_LNS_advance_pc
          final increment = reader.readLEB128EncodedInteger();
          state.address += header.minimumInstructionLength * increment;
          break;
        case 3: // DW_LNS_advance_line
          state.line += reader.readLEB128EncodedInteger(signed: true);
          break;
        case 4: // DW_LNS_set_file
          state.fileIndex = reader.readLEB128EncodedInteger();
          break;
        case 5: // DW_LNS_set_column
          state.column = reader.readLEB128EncodedInteger();
          break;
        case 6: // DW_LNS_negate_stmt
          state.isStatement = !state.isStatement;
          break;
        case 7: // DW_LNS_set_basic_block
          state.basicBlock = true;
          break;
        case 8: // DW_LNS_const_add_pc
          applySpecialOpcode(255);
          break;
        case 9: // DW_LNS_fixed_advance_pc
          state.address += reader.readBytes(2);
          break;
        default:
          throw FormatException('Standard opcode $opcode not in DWARF 2');
      }
    }
  }

  bool containsKey(int address) {
    assert(calculatedMatrix.last.endSequence);
    return address >= calculatedMatrix.first.address &&
        address < calculatedMatrix.last.address;
  }

  LineNumberState? operator [](int address) {
    if (cachedLookups.containsKey(address)) return cachedLookups[address];

    if (!containsKey(address)) return null;

    // Since the addresses are generated in increasing order, we can do a
    // binary search to find the right state.
    assert(calculatedMatrix.isNotEmpty);
    var minIndex = 0;
    var maxIndex = calculatedMatrix.length - 1;
    while (true) {
      if (minIndex == maxIndex || minIndex + 1 == maxIndex) {
        final found = calculatedMatrix[minIndex];
        cachedLookups[address] = found;
        return found;
      }
      final index = minIndex + ((maxIndex - minIndex) ~/ 2);
      final compared = calculatedMatrix[index].address.compareTo(address);
      if (compared == 0) {
        return calculatedMatrix[index];
      } else if (compared < 0) {
        minIndex = index;
      } else if (compared > 0) {
        maxIndex = index;
      }
    }
  }

  String? filename(int address) =>
      header.filesInfo[this[address]?.fileIndex ?? -1]?.name;

  int? lineNumber(int address) => this[address]?.line;

  int? column(int address) => this[address]?.column;

  void writeToStringBuffer(StringBuffer buffer) {
    header.writeToStringBuffer(buffer);

    buffer.writeln('Results of line number program:');
    for (final state in calculatedMatrix) {
      buffer.writeln(state);
    }
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// A class representing a DWARF .debug_line section.
class LineNumberInfo {
  final Map<int, LineNumberProgram> programs;

  LineNumberInfo._(this.programs);

  static LineNumberInfo fromReader(Reader reader) {
    final programs = Map.fromEntries(
        reader.readRepeatedWithOffsets(LineNumberProgram.fromReader));
    return LineNumberInfo._(programs);
  }

  bool containsKey(int address) => programs.containsKey(address);
  LineNumberProgram? operator [](int address) => programs[address];

  void writeToStringBuffer(StringBuffer buffer) {
    programs.forEach((offset, program) {
      buffer
        ..write('Line number program @ 0x')
        ..writeln(paddedHex(offset));
      program.writeToStringBuffer(buffer);
    });
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// Represents the information for a call site.
abstract class CallInfo {
  /// Whether this call site is considered internal (i.e. not located in either
  /// user or library Dart source code).
  bool get isInternal => true;
}

/// Represents the information for a call site located in Dart source code.
class DartCallInfo extends CallInfo {
  final bool inlined;
  final bool internal;
  final String function;
  final String filename;
  final int line;
  final int column;

  DartCallInfo(
      {this.inlined = false,
      this.internal = false,
      required this.function,
      required this.filename,
      required this.line,
      required this.column});

  @override
  bool get isInternal => internal;

  @override
  int get hashCode => Object.hash(
        inlined,
        internal,
        function,
        filename,
        line,
        column,
      );

  @override
  bool operator ==(Object other) =>
      other is DartCallInfo &&
      inlined == other.inlined &&
      internal == other.internal &&
      function == other.function &&
      filename == other.filename &&
      line == other.line &&
      column == other.column;

  void writeToStringBuffer(StringBuffer buffer) {
    buffer
      ..write(function)
      ..write(' (')
      ..write(filename);
    if (line > 0) {
      buffer
        ..write(':')
        ..write(line);
      if (column > 0) {
        buffer
          ..write(':')
          ..write(column);
      }
    }
    buffer.write(')');
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}

/// Represents the information for a call site located in a Dart stub.
class StubCallInfo extends CallInfo {
  final String name;
  final int offset;

  StubCallInfo({required this.name, required this.offset});

  @override
  int get hashCode => Object.hash(name, offset);

  @override
  bool operator ==(Object other) =>
      other is StubCallInfo && name == other.name && offset == other.offset;

  @override
  String toString() => '$name+0x${offset.toRadixString(16)}';
}

/// The instructions section in which a program counter address is located.
enum InstructionsSection { none, vm, isolate }

/// A program counter address viewed as an offset into the appropriate
/// instructions section of a Dart snapshot.
class PCOffset {
  final int offset;
  final InstructionsSection section;

  PCOffset(this.offset, this.section);

  /// The virtual address for this [PCOffset] in [dwarf].
  int virtualAddressIn(Dwarf dwarf) => dwarf.virtualAddressOf(this);

  /// The call information found for this [PCOffset] in [dwarf].
  ///
  /// Returns null if the PCOffset is invalid for the given DWARF information.
  ///
  /// If [includeInternalFrames] is false, then only information corresponding
  /// to user or library code is returned.
  Iterable<CallInfo>? callInfoFrom(Dwarf dwarf,
          {bool includeInternalFrames = false}) =>
      dwarf.callInfoFor(dwarf.virtualAddressOf(this),
          includeInternalFrames: includeInternalFrames);

  @override
  int get hashCode => Object.hash(offset, section);

  @override
  bool operator ==(Object other) =>
      other is PCOffset && offset == other.offset && section == other.section;

  @override
  String toString() => 'PCOffset($section, $offset)';
}

/// The DWARF debugging information for a Dart snapshot.
class Dwarf {
  final Elf _elf;
  final Map<int, _AbbreviationsTable> _abbreviationsTables;
  final DebugInfo _debugInfo;
  final LineNumberInfo _lineNumberInfo;

  /// Virtual address of the start of the VM instructions section in the DWARF
  /// information.
  final int vmStartAddress;

  /// Virtual address of the start of the isolate instructions section in the
  /// DWARF information.
  final int isolateStartAddress;

  Dwarf._(this._elf, this._abbreviationsTables, this._debugInfo,
      this._lineNumberInfo, this.vmStartAddress, this.isolateStartAddress);

  /// Attempts to load the DWARF debugging information from the reader.
  ///
  /// Returns a [Dwarf] object if the load succeeds, otherwise returns null.
  static Dwarf? fromReader(Reader reader) {
    // Currently, the only DWARF-containing format we recognize is ELF.
    final elf = Elf.fromReader(reader);
    if (elf == null) return null;
    return Dwarf._loadSectionsFromElf(reader, elf);
  }

  /// Attempts to load the DWARF debugging information from the given bytes.
  ///
  /// Returns a [Dwarf] object if the load succeeds, otherwise returns null.
  static Dwarf? fromBytes(Uint8List bytes) =>
      Dwarf.fromReader(Reader.fromTypedData(bytes));

  /// Attempts to load the DWARF debugging information from the file at [path].
  ///
  /// Returns a [Dwarf] object if the load succeeds, otherwise returns null.
  static Dwarf? fromFile(String path) =>
      Dwarf.fromReader(Reader.fromFile(path));

  static Dwarf _loadSectionsFromElf(Reader reader, Elf elf) {
    final abbrevSection = elf.namedSections('.debug_abbrev').single;
    final abbrevReader = abbrevSection.refocusedCopy(reader);
    final abbreviationsTables = Map.fromEntries(
        abbrevReader.readRepeatedWithOffsets(_AbbreviationsTable.fromReader));

    final lineNumberSection = elf.namedSections('.debug_line').single;
    final lineNumberInfo =
        LineNumberInfo.fromReader(lineNumberSection.refocusedCopy(reader));

    final infoSection = elf.namedSections('.debug_info').single;
    final debugInfo = DebugInfo.fromReader(
        infoSection.refocusedCopy(reader), abbreviationsTables);

    final vmStartSymbol = elf.dynamicSymbolFor(constants.vmSymbolName);
    if (vmStartSymbol == null) {
      throw FormatException(
          'Expected a dynamic symbol with name ${constants.vmSymbolName}');
    }
    final vmStartAddress = vmStartSymbol.value;

    final isolateStartSymbol =
        elf.dynamicSymbolFor(constants.isolateSymbolName);
    if (isolateStartSymbol == null) {
      throw FormatException(
          'Expected a dynamic symbol with name ${constants.isolateSymbolName}');
    }
    final isolateStartAddress = isolateStartSymbol.value;

    return Dwarf._(elf, abbreviationsTables, debugInfo, lineNumberInfo,
        vmStartAddress, isolateStartAddress);
  }

  /// The build ID for the debugging information.
  ///
  /// Returns null if there is no build ID information recorded.
  String? get buildId {
    final sections = _elf.namedSections(constants.buildIdSectionName);
    if (sections.isEmpty) return null;
    final note = sections.single as Note;
    if (note.type != constants.buildIdNoteType) return null;
    if (note.name != constants.buildIdNoteName) return null;
    return note.description
        .map((i) => i.toRadixString(16).padLeft(2, '0'))
        .join();
  }

  /// The call information for the given virtual address. There may be
  /// multiple [CallInfo] objects returned for a single virtual address when
  /// code has been inlined.
  ///
  /// Returns null if the given address is invalid for the DWARF information.
  ///
  /// If [includeInternalFrames] is false, then only information corresponding
  /// to user or library code is returned.
  Iterable<CallInfo>? callInfoFor(int address,
      {bool includeInternalFrames = false}) {
    var calls = _debugInfo.callInfo(_lineNumberInfo, address);
    if (calls == null) {
      final symbol = _elf.staticSymbolAt(address);
      if (symbol != null) {
        final offset = address - symbol.value;
        calls = <CallInfo>[StubCallInfo(name: symbol.name, offset: offset)];
      }
    }
    if (!includeInternalFrames) {
      return calls?.where((CallInfo c) => !c.isInternal);
    }
    return calls;
  }

  /// The virtual address in this DWARF information for the given [PCOffset].
  int virtualAddressOf(PCOffset pcOffset) {
    switch (pcOffset.section) {
      case InstructionsSection.none:
        // This address is already virtualized, so we don't need to change it.
        return pcOffset.offset;
      case InstructionsSection.vm:
        return pcOffset.offset + vmStartAddress;
      case InstructionsSection.isolate:
        return pcOffset.offset + isolateStartAddress;
      default:
        throw 'Unexpected value for instructions section';
    }
  }

  void writeToStringBuffer(StringBuffer buffer) {
    buffer
      ..writeln('----------------------------------------')
      ..writeln('         Abbreviation tables')
      ..writeln('----------------------------------------')
      ..writeln();
    _abbreviationsTables.forEach((offset, table) {
      buffer
        ..write('(Offset ')
        ..write(paddedHex(offset, 4))
        ..write(') ');
      table.writeToStringBuffer(buffer);
    });
    buffer
      ..writeln('----------------------------------------')
      ..writeln('          Debug information')
      ..writeln('----------------------------------------')
      ..writeln();
    _debugInfo.writeToStringBuffer(buffer);
    buffer
      ..writeln('----------------------------------------')
      ..writeln('        Line number information')
      ..writeln('----------------------------------------')
      ..writeln();
    _lineNumberInfo.writeToStringBuffer(buffer);
  }

  String dumpFileInfo() {
    final buffer = StringBuffer();
    _elf.writeToStringBuffer(buffer);
    buffer.writeln();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    writeToStringBuffer(buffer);
    return buffer.toString();
  }
}