Roadbound-Map-Utility/lib/pages/map/vector/tile_pyramid_cache.dart

import 'dart:collection';
import 'dart:ui' as ui;

class _TileCoord {
  const _TileCoord(this.z, this.x, this.y);

  final int z;
  final int x;
  final int y;

  @override
  bool operator ==(Object other) =>
      other is _TileCoord && other.z == z && other.x == x && other.y == y;

  @override
  int get hashCode => Object.hash(z, x, y);
}

class CachedTile {
  CachedTile(this.image);

  final ui.Image image;
}

// Static tile pyramid image cache. Stores one rasterised ui.Image per
// deterministic pyramid tile coordinate (z, x, y).
class TilePyramidCache {
  TilePyramidCache._();

  static const int _maxEntries = 384;
  static const int _maxApproxBytes = 768 * 1024 * 1024;

  // Cap concurrent renders to avoid saturating the main isolate with
  // synchronous canvas recording. I/O (network/Hive) is still concurrent
  // up to this limit.
  static const int _maxConcurrent = 4;

  static final LinkedHashMap<_TileCoord, CachedTile> _cache =
      LinkedHashMap<_TileCoord, CachedTile>();

  static final Set<_TileCoord> _inFlight = <_TileCoord>{};
  static final Queue<_Queued> _queue = Queue<_Queued>();
  static int _active = 0;
  static bool Function(int z, int x, int y)? _queueFilter;

  static int _approxBytes = 0;

  static CachedTile? peek(int z, int x, int y) {
    final coord = _TileCoord(z, x, y);
    final tile = _cache.remove(coord);
    if (tile == null) return null;
    _cache[coord] = tile; // promote to MRU
    return tile;
  }

  static bool isInFlight(int z, int x, int y) =>
      _inFlight.contains(_TileCoord(z, x, y));

  // Queue a render for (z, x, y). No-op if already in flight.
  // render() produces the image; onReady() is called after it's stored.
  static void enqueue(
    int z,
    int x,
    int y,
    Future<ui.Image?> Function() render,
    void Function() onReady,
  ) {
    final coord = _TileCoord(z, x, y);
    if (_inFlight.contains(coord)) return;
    final filter = _queueFilter;
    if (filter != null && !filter(z, x, y)) return;
    _inFlight.add(coord);

    _queue.add(_Queued(coord: coord, render: render, onReady: onReady));
    _drain();
  }

  static void setQueueFilter(bool Function(int z, int x, int y)? filter) {
    _queueFilter = filter;
    _pruneQueue();
  }

  static void _drain() {
    while (_active < _maxConcurrent && _queue.isNotEmpty) {
      _active++;
      _run(_queue.removeFirst());
    }
  }

  static Future<void> _run(_Queued item) async {
    try {
      final image = await item.render();
      _inFlight.remove(item.coord);
      if (image == null) return;

      final filter = _queueFilter;
      if (filter != null && !filter(item.coord.z, item.coord.x, item.coord.y)) {
        image.dispose();
        return;
      }

      final existing = _cache.remove(item.coord);
      if (existing != null) {
        _approxBytes -= _estimateBytes(existing.image);
        existing.image.dispose();
      }

      _cache[item.coord] = CachedTile(image);
      _approxBytes += _estimateBytes(image);
      _trim();

      item.onReady();
    } catch (_) {
      _inFlight.remove(item.coord);
    } finally {
      _active--;
      _drain();
    }
  }

  static int _estimateBytes(ui.Image img) => img.width * img.height * 4;

  static void _trim() {
    while (_cache.length > _maxEntries || _approxBytes > _maxApproxBytes) {
      final key = _cache.keys.first;
      final tile = _cache.remove(key);
      if (tile == null) continue;
      _approxBytes -= _estimateBytes(tile.image);
      tile.image.dispose();
    }
  }

  static void _pruneQueue() {
    final filter = _queueFilter;
    if (filter == null || _queue.isEmpty) return;

    final kept = Queue<_Queued>();
    while (_queue.isNotEmpty) {
      final item = _queue.removeFirst();
      if (filter(item.coord.z, item.coord.x, item.coord.y)) {
        kept.add(item);
      } else {
        _inFlight.remove(item.coord);
      }
    }

    _queue.addAll(kept);
  }

  static void clear() {
    for (final tile in _cache.values) {
      tile.image.dispose();
    }
    _cache.clear();
    _inFlight.clear();
    _queue.clear();
    _active = 0;
    _approxBytes = 0;
    _queueFilter = null;
  }
}

class _Queued {
  const _Queued({
    required this.coord,
    required this.render,
    required this.onReady,
  });

  final _TileCoord coord;
  final Future<ui.Image?> Function() render;
  final void Function() onReady;
}