chain-studio-flow-editor/lib/src/model/layout_store.dart

// Layout sidecar — node positions persisted alongside a flow.
//
// Position metadata is intentionally kept OUT of the flow
// YAML. Reasons:
//
//   1. The YAML is what `fai run` consumes, what gets
//      tamper-checked against the audit log, and what shows
//      up in pull requests. It should describe behaviour
//      only, not where a node happened to be on a screen.
//
//   2. Two operators viewing the same flow may legitimately
//      want different layouts. The sidecar is per-user (and
//      can be re-laid-out fresh from any host).
//
//   3. If the sidecar is missing or corrupt, the graph view
//      falls back to a deterministic auto-layout. The flow
//      itself never breaks.
//
// Storage layout:
//
//   ~/.fai/data/flows/.layout/<flow-name>.json
//
// One file per flow. JSON shape:
//
//   {
//     "version": 1,
//     "positions": {
//       "<step-id>": { "x": 120.0, "y": 80.0 }
//     }
//   }

import 'dart:convert';
import 'dart:io';

class FlowLayout {
  final Map<String, NodePosition> positions;
  const FlowLayout({this.positions = const {}});

  factory FlowLayout.empty() => const FlowLayout();

  Map<String, dynamic> toJson() => {
    'version': 1,
    'positions': {
      for (final entry in positions.entries)
        entry.key: {'x': entry.value.x, 'y': entry.value.y},
    },
  };

  factory FlowLayout.fromJson(Map<String, dynamic> json) {
    final raw = json['positions'];
    if (raw is! Map) return FlowLayout.empty();
    final positions = <String, NodePosition>{};
    for (final entry in raw.entries) {
      final v = entry.value;
      if (v is! Map) continue;
      final x = (v['x'] as num?)?.toDouble();
      final y = (v['y'] as num?)?.toDouble();
      if (x == null || y == null) continue;
      positions[entry.key.toString()] = NodePosition(x, y);
    }
    return FlowLayout(positions: positions);
  }

  FlowLayout withPosition(String stepId, NodePosition pos) {
    return FlowLayout(positions: {...positions, stepId: pos});
  }

  FlowLayout withoutStep(String stepId) {
    return FlowLayout(
      positions: {
        for (final entry in positions.entries)
          if (entry.key != stepId) entry.key: entry.value,
      },
    );
  }
}

class NodePosition {
  final double x;
  final double y;
  const NodePosition(this.x, this.y);

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

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

/// On-disk persistence for [FlowLayout]. Synchronous I/O is
/// fine — these files are tiny (a few KB at most) and the
/// graph view loads / saves them at well-defined moments
/// (open file, drag end), not in the render loop.
class LayoutStore {
  /// Directory `~/.fai/data/flows/.layout/`, created on first
  /// write. Hidden so it doesn't show up in `fai admin
  /// flows list` style enumerations.
  static String defaultDir() {
    final home =
        Platform.environment['HOME'] ??
        Platform.environment['USERPROFILE'] ??
        '.';
    return '$home/.fai/data/flows/.layout';
  }

  /// Load the layout for [flowName]. Returns an empty layout
  /// if the sidecar doesn't exist yet (first time the flow is
  /// opened in the graph view), or if it fails to parse.
  static FlowLayout loadSync(String flowName) {
    try {
      final file = File('${defaultDir()}/$flowName.json');
      if (!file.existsSync()) return FlowLayout.empty();
      final raw = file.readAsStringSync();
      final json = jsonDecode(raw);
      if (json is! Map<String, dynamic>) return FlowLayout.empty();
      return FlowLayout.fromJson(json);
    } catch (_) {
      return FlowLayout.empty();
    }
  }

  /// Persist [layout] for [flowName]. Atomic via write-rename
  /// so a crash mid-write leaves the previous good copy
  /// intact.
  static void saveSync(String flowName, FlowLayout layout) {
    final dir = Directory(defaultDir());
    if (!dir.existsSync()) dir.createSync(recursive: true);
    final final_ = File('${dir.path}/$flowName.json');
    final tmp = File('${dir.path}/$flowName.json.tmp');
    tmp.writeAsStringSync(
      const JsonEncoder.withIndent('  ').convert(layout.toJson()),
      flush: true,
    );
    tmp.renameSync(final_.path);
  }

  /// Remove the sidecar — call this when the operator
  /// deletes a flow so we don't leak stale layouts.
  static void deleteSync(String flowName) {
    final file = File('${defaultDir()}/$flowName.json');
    if (file.existsSync()) file.deleteSync();
  }
}