# Pipeline Network Diagram Editor — Implementation Plan

A desktop diagram editor for drawing **pipeline networks** (water lines, power lines,
gas, etc.), built with **PyQt6** on the **QGraphicsView / QGraphicsScene** framework.

## Tool selection (research outcome)

| Candidate | Verdict |
|-----------|---------|
| **QGraphicsView framework (chosen)** | Maximum control over custom SVG nodes, typed ports, orthogonal grid routing, arc crossings, flow animation. Mature, high item-count performance. |
| QtNodes (paceholder/nodeeditor) | Dataflow-centric, fixed node visuals, v3 breaking API — poor fit for grid-routed pipeline networks. |
| QuickQanava (QML) | Modern but connection routing in QML is the hard part; less control over orthogonal/arc routing. |

Bindings: **PyQt6 6.10** (apt, works with Python 3.14). Tests: **pytest + pytest-qt**,
headless via `QT_QPA_PLATFORM=offscreen`.

Sources:
- <https://github.com/paceholder/nodeeditor>
- <https://github.com/cneben/QuickQanava>
- <https://doc.qt.io/qt-6/qtwidgets-graphicsview-elasticnodes-example.html>
- <https://www.qt.io/blog/2017/01/19/should-you-be-using-qgraphicsview>

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## Phase 0 — Project scaffolding
- [ ] Repo layout, `requirements.txt`, `README.md`, `.gitignore`
- [ ] `pipeline_editor` package skeleton + `__main__` entry point
- [ ] pytest config + headless conftest (QApplication fixture)

## Phase 1 — Domain model (no UI)
- [ ] `PropertyType` enum: string, int, float, bool, enum, color, catalogue_item, catalogue_items, value_list
- [ ] `Property` + `PropertyGroup` (grouped, editable/readonly, validation)
- [ ] `Catalogue` / `CatalogueItem` registry
- [ ] `PortRelation` registry (water/power/gas...) with color schemes + compatibility rules
- [ ] `Port` (id, name, relation, side/offset, direction)
- [ ] `NodeModel`, `EdgeModel` (ids, geometry, style, property groups)
- [ ] `DiagramDocument` — holds nodes/edges, emits change signals
- [ ] JSON serialization / deserialization (round-trip)

## Phase 2 — Node library (feature #1)
- [ ] Bundled SVG node graphics (pump, tank, valve, junction, source, sink, transformer…)
- [ ] `NodeTemplate` = SVG + port configuration, organized into groups
- [ ] Left dock `NodePanel`: grouped tree with vector previews
- [ ] Drag-and-drop node template → canvas creates a node

## Phase 3 — Canvas, scene & nodes
- [ ] `CanvasView`: zoom (wheel), pan, fit-to-view, rubber-band select
- [ ] Grid background (dots/lines), configurable size, snap-to-grid
- [ ] `NodeItem`: renders SVG, movable, selectable, edges follow on move
- [ ] Multi-select move, delete

## Phase 4 — Ports & edges (features #2, #3, #5)
- [ ] Focused node reveals `PortItem` handles
- [ ] Port relation coloring + connection-compatibility feedback
- [ ] Drag from port → other node's port (or self) creates an edge
- [ ] Orthogonal routing along rectangular grid
- [ ] Config option: draw **arc** at line intersections/crossings
- [ ] `EdgeItem` styles: line style, head/tail decorations (arrow, circle, diamond, none)

## Phase 5 — Property panel (feature #4)
- [ ] Right dock `PropertyPanel`: grouped property editors
- [ ] Editor widgets per type (string/int/float/bool/enum/color/catalogue/list)
- [ ] Two-way binding: edit → model → view refresh
- [ ] Geometry/title (presentation) group + physics group (length, diameter, flow rate, flow type)

## Phase 6 — Mock calculation & flow animation
- [ ] `FlowSolver`: mock flow distribution across edges (conservation-ish heuristic)
- [ ] Per-edge flow value + direction
- [ ] `FlowAnimator`: animate direction (marching dashes) and volume (speed/width)
- [ ] Play/pause/stop controls

## Phase 7 — Editing UX & configuration (added features)
- [ ] Undo/redo via `QUndoStack` (add/move/delete/connect/edit)
- [ ] Copy / paste / duplicate / delete
- [ ] Save / Open / New document (JSON)
- [ ] Export canvas to PNG / SVG
- [ ] Config dialog: grid size, snap, arc-on-crossing, color scheme, animation speed
- [ ] Multiple color schemes (light/dark + relation palettes)
- [ ] Toolbar + menus + status bar + keyboard shortcuts

## Phase 8 — Tests (typical scenarios)
- [ ] Model: properties, catalogue, relations, serialization round-trip
- [ ] Routing: orthogonal path + arc-crossing generation
- [ ] Flow solver: conservation & direction on a small network
- [ ] Scene: create node via drop, connect ports, move node moves edge, delete cascades
- [ ] Property panel: edit propagates to model
- [ ] Undo/redo of add/move/connect/delete

## Phase 9 — Polish
- [ ] README with run/test instructions and screenshots
- [ ] Final pass: lint, docstrings, sample document