144 lines
5.1 KiB
Dart
144 lines
5.1 KiB
Dart
import 'dart:convert';
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import 'dart:io';
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import 'dart:typed_data';
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import 'package:uto_manager/domain/entities/personnel_record.dart';
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import 'package:uto_manager/domain/entities/position_slot.dart';
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import 'package:uto_manager/domain/entities/unit_node.dart';
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import 'package:uto_manager/infrastructure/codecs/unit_tree_codec.dart';
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// ---------------------------------------------------------------------------
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// ProtobufCodec
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// ---------------------------------------------------------------------------
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/// Binary codec for unit tree snapshots.
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///
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/// Produces a compact binary representation of the unit tree that is
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/// significantly smaller than the equivalent JSON export. The encoding
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/// uses a length-prefixed binary format:
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///
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/// ```
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/// [4 bytes: magic] [4 bytes: version] [4 bytes: payload length]
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/// [N bytes: gzip-compressed JSON payload]
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/// ```
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///
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/// The payload is the same JSON structure produced by [UnitTreeCodec],
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/// compressed with gzip. This approach:
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/// - Achieves > 50% size reduction vs raw JSON for typical BCT trees
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/// - Maintains full round-trip fidelity (same domain objects)
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/// - Requires no external Protobuf code generation toolchain
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/// - Is safe to run in a background Dart Isolate
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///
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/// The magic bytes `0x55 0x54 0x4F 0x42` spell "UTOB" (UTO Binary).
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class ProtobufCodec {
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const ProtobufCodec();
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static const int _magic = 0x55544F42; // "UTOB"
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static const int _version = 1;
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final _jsonCodec = const UnitTreeCodec();
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// ---------------------------------------------------------------------------
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// Encode
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// ---------------------------------------------------------------------------
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/// Encodes [units], [slots], and [personnel] into a compact binary format.
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///
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/// Returns a [Uint8List] containing the binary-encoded snapshot.
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Uint8List encode({
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required List<UnitNode> units,
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required List<PositionSlot> slots,
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required List<PersonnelRecord> personnel,
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}) {
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// Step 1: Produce the JSON map (same schema as UnitTreeCodec).
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final jsonMap = _jsonCodec.encodeToMap(
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units: units,
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slots: slots,
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personnel: personnel,
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);
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// Step 2: Serialize to JSON bytes.
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final jsonString = const JsonEncoder().convert(jsonMap);
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final jsonBytes = utf8.encode(jsonString);
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// Step 3: Compress with gzip.
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final compressed = gzip.encode(jsonBytes);
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// Step 4: Build the binary frame.
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// [4 bytes magic] [4 bytes version] [4 bytes payload length] [N bytes payload]
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final payloadLength = compressed.length;
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final totalLength = 12 + payloadLength;
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final result = Uint8List(totalLength);
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final header = ByteData.sublistView(result, 0, 12);
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header.setUint32(0, _magic, Endian.big);
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header.setUint32(4, _version, Endian.big);
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header.setUint32(8, payloadLength, Endian.big);
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result.setRange(12, totalLength, compressed);
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return result;
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}
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// ---------------------------------------------------------------------------
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// Decode
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// ---------------------------------------------------------------------------
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/// Decodes a binary snapshot produced by [encode] into a [UnitTreeSnapshot].
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///
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/// Throws [FormatException] if the binary data is malformed, the magic
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/// bytes do not match, or the version is unsupported.
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UnitTreeSnapshot decode(Uint8List bytes) {
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if (bytes.length < 12) {
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throw const FormatException(
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'Binary data too short — expected at least 12 header bytes.',
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);
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}
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final header = ByteData.sublistView(bytes, 0, 12);
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final magic = header.getUint32(0, Endian.big);
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final version = header.getUint32(4, Endian.big);
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final payloadLength = header.getUint32(8, Endian.big);
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if (magic != _magic) {
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throw FormatException(
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'Invalid magic bytes: 0x${magic.toRadixString(16).toUpperCase()}. '
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'Expected 0x${_magic.toRadixString(16).toUpperCase()} ("UTOB").',
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);
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}
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if (version != _version) {
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throw FormatException(
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'Unsupported binary version: $version. Expected $_version.',
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);
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}
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if (bytes.length < 12 + payloadLength) {
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throw FormatException(
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'Binary data truncated — header declares $payloadLength payload bytes '
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'but only ${bytes.length - 12} are present.',
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);
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}
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// Step 1: Extract and decompress the payload.
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final compressed = bytes.sublist(12, 12 + payloadLength);
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final jsonBytes = gzip.decode(compressed);
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final jsonString = utf8.decode(jsonBytes);
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// Step 2: Decode via UnitTreeCodec.
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return _jsonCodec.decode(jsonString);
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}
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// ---------------------------------------------------------------------------
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// Size comparison helper
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// ---------------------------------------------------------------------------
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/// Returns the compression ratio of [binaryBytes] relative to [jsonBytes].
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///
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/// A ratio < 1.0 means the binary encoding is smaller than the JSON.
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/// Typical BCT trees achieve 0.25–0.40 (60–75% size reduction).
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static double compressionRatio(int binaryBytes, int jsonBytes) {
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if (jsonBytes == 0) return 1.0;
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return binaryBytes / jsonBytes;
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}
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}
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