Add declarative map swipe (layer compare) feature

[Copilot]

• Add viewer/data/appdef.split.json demo (with SwipePrimaryLabel/SwipeSecondaryLabel demo labels: "Capital Cities" and "Natural Landmarks")
• Fix Issue 1 & 3: Secondary layers not shown / wrong layers on swipe activation
• Fix Issue 4: Swipe control monopolizes mouse input
• Fix Issue 5: Add useIsMapSwipeActive() public hook
• Fix TS2352 build error in test/components/map-providers/context.spec.tsx
• Fix swipe does nothing on first activation: move activateMapSwipe lazy-init override from dead generic.ts_ to the actual MapGuideMapProviderContext in mapguide.ts
• Fix broken state when swipe invoked from secondary map: restrict MapSwipe command enabled to primary-map-only
• Fix "Duplicate item added to a unique collection" OL error when switching maps while swipe is active: auto-deactivate swipe (and dispatch setMapSwipeMode(false)) in setProviderState before the detach/attach map switch
• Replace any types in IReduxStoreRef with properly typed Readonly<IApplicationState> (via ReduxStore) and ReduxDispatch
• Rename useActiveSwipePair → useMapSwipeInfo: returns IMapSwipeInfo | undefined, bundling the pair (IMapSwipePair) and an isSwipePrimary flag together so callers no longer need to compute primary-map membership separately
• Add optional primaryLabel/secondaryLabel fields to IMapSwipePair, read from SwipePrimaryLabel/SwipeSecondaryLabel MapGroup extension properties in the appdef (defaults to i18n strings "Primary" / "Secondary")
• Render primary and secondary labels in the swipe overlay: primary label shown top-left, secondary label shown top-right, alongside the "Close Comparison" button centred above the divider
• Fix runtime-added layers on the secondary map not appearing in swipe mode: added getSwipeableLayers() to MgLayerSetGroupBase (returns both base map layers and _customLayers); activateMapSwipe now uses this for both primary and secondary maps so layers added at runtime after initial load are correctly clipped and shown
• Route mouse interactions (clicks, selections) to the correct map in swipe mode: added getEffectiveMapNameAtPixel(pixelX) to base.ts which checks if swipe is active and returns the secondary map name when the click pixel is past the swipe divider, ensuring feature selection and other mouse events target the correct map side
• Layer manager swipe support: when swipe mode is active, the layer manager presents a map selector dropdown listing the primary and secondary maps, allowing the user to add/remove/manage layers for either map in the pair
• Add test/api/layer-set-group-swipe.spec.ts — 14 unit tests for MgLayerSetGroupBase swipe mechanics: getSwipeableLayers(), transferLayerOut/In, apply() isolation, and end-to-end primary-to-secondary layer transfer scenario
• Add test/containers/add-manage-layers.spec.tsx — React component tests for AddManageLayersContainer in swipe mode, covering: dropdown visibility/placement, map selection, blank-screen prevention when secondary unvisited, correct onLayerAdded dispatch target, and refreshSwipeClips()/transferLayerToSwipeSecondary() call expectations

Original prompt

---

This section details on the original issue you should resolve

<issue_title>The absence of Map-Sweeper Features</issue_title>
<issue_description>Hi Jack

I wanted to request the addition of a map-sweeper feature to the web GIS viewer. The map-sweeper would be a valuable enhancement that allows users to compare two different map layers side by side, facilitating visual analysis and making the viewer even more versatile.

Feature Description:
The map-sweeper feature should enable users to interactively slide a horizontal bar across the map viewer- between the and the , revealing two map layers simultaneously, This allows for easy comparison between two datasets or map themes, aiding in identifying patterns, changes, and relationships between the layers.

compare between tow Arial photos or Photogrammetric background layers . This feature would greatly benefit researchers and analysts who need to compare between tow layers.

This feature will allow users to:

1. Compare current and proposed zoning maps to assess the potential impact of new developments.
2. Environmental researchers could analyze changes in land cover by comparing satellite imagery from different time periods.
3. Emergency responders could overlay real-time data, such as Earthquake, on top of a base map to make informed decisions during crisis situations.

I'm enthusiastic about this feature and willing to contribute to its development. As an experienced front-end developer, I can assist with testing, and documentation to help bring this enhancement to life.

I understand the demands on your time as a project maintainer and appreciate your consideration of this request. Thank you for your dedication to maintaining the mapguide-react-layout-viewer and for fostering a collaborative open-source community.

Looking forward to hearing your thoughts on adding the map-sweeper feature.

</issue_description>

<agent_instructions>Come up with a declarative solution whereby we declare two maps in an appdef document to be part of a "pair" along with a new toolbar/menu widget that when invoked, toggles the current map into a side-by-side split view.

To avoid confusion which map to show in un-split mode, one side of the "pair" needs to declare that they're the "primary" map.

The underlying OpenLayers viewer already has the APIs and primitives to build such functionality (see example: https://openlayers.org/en/latest/examples/layer-swipe.html).

We want to bring such functionality into our viewer in a declarative manner by defining such features in the appdef the viewer will load from.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes The absence of Map-Sweeper Features #1475

---

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[jumpinjackie]

@copilot For an easy demo of this feature, pls add a variant of the existing appdef at viewer/data/appdef.generic.json called viewer/data/appdef.split.json and include a split map pair setup of the "Australia" map. Give each map in the pair a separate GeoJSON layer with a different set of features, such that when we activate split mode, we can see these 2 different GeoJSON layers side-by-side and be able to swipe between them.

[Copilot]

@copilot For an easy demo of this feature, pls add a variant of the existing appdef at viewer/data/appdef.generic.json called viewer/data/appdef.split.json and include a split ma...

Added viewer/data/appdef.split.json in commit 68e4107.

The demo appdef sets up a swipe pair on the Australia map with two distinct GeoJSON inline layers:

• Primary map ("Australia") — orange circle markers (🟠) for 8 Australian capital cities (Sydney, Melbourne, Brisbane, Perth, Adelaide, Hobart, Darwin, Canberra), with popups showing state, role, and population
• Secondary map ("AustraliaCompare") — green circle markers (🟢) for 8 Australian natural landmarks (Great Barrier Reef, Uluru-Kata Tjuta, Blue Mountains, Kakadu NP, Daintree Rainforest, Great Ocean Road, Ningaloo Reef, Cape York Peninsula), with popups showing type, world heritage status, and area

Both maps use OpenStreetMap as the basemap. The Map Swipe button appears first in the Toolbar and FileMenu containers. Clicking it toggles the swipe slider, which lets you drag to reveal one layer set vs the other side-by-side.

To try it out: load the generic viewer with ?resource=data/appdef.split.json (e.g. generic-demo/index.html?resource=data/appdef.split.json).

[coveralls]

coverage: 37.763% (+0.7%) from 37.045%
when pulling 881f432 on copilot/add-map-sweeper-feature
into e3020d5 on master.

[jumpinjackie]

@copilot I have updated the generic layout template to include a toolbar button for layer swipe command. Invoking the command brings up the layer swipe mode, but I have noticed a few issues.

1. Invoking the swipe command does nothing. It just shows the swipe control, but the two maps are not side-by-side.

2. I notice AustraliaCompare (the secondary map) is a switchable map. Nothing wrong with that. I change to AustraliaCompare and I can see its map and overlay layers.

3. Where it starts to become interesting is the moment is switch to AustraliaCompare and switch back to Australia, the swipe command does something, just not what I expect. It now shows AustraliaCompare on the right vs nothing on the left

4. When the swipe control is active, it monopolizes all mouse input. I lose the ability to pan, zoom and interact with vector features on either side. This does not help, we need to retain the ability to do such mouse interactions while the swipe is active.

5. I'd like a public hook that let's components of interest know if a layer swipe is active. I want to use this hook in my generic layout to disable the swipe toolbar button if a swipe is active, and enable it again when it is inactive.

[Copilot]

@copilot I have updated the generic layout template to include a toolbar button for layer swipe command. Invoking the command brings up the layer swipe mode, but I have noticed a few...

Fixed in commit 0caa22f. Here's what was addressed:

Issue 1 & 3 — Swipe shows wrong/missing layers:
Two root causes were found and fixed:

1. The secondary map's layer set group wasn't initialized until you first visited that map. GenericMapProviderContext now overrides activateMapSwipe to lazily initialize the secondary map from the Redux store (injected by MapContextProvider via a new setReduxStore method on the interface).
2. OL's prerender/postrender canvas clip does not propagate through LayerGroup to its children — the OSM basemap is wrapped in a LayerGroup, so it wasn't clipping at all and was covering primary map features. Fixed with getLeafLayersForClip() which recursively flattens LayerGroup → leaf layers. Additionally, the primary map's layers are now also clipped to the left side (not just secondary to the right), giving a clean split view.

Issue 4 — Swipe control monopolizes mouse input:
The full-screen invisible <input type="range"> that covered the entire map has been replaced with a narrow draggable divider strip using pointer capture (onPointerDown/onPointerMove/onPointerUp with setPointerCapture). The outer overlay uses pointer-events: none so pan, zoom, and feature interaction all work normally outside the divider area.

Issue 5 — Public hook for swipe active state:
Added useIsMapSwipeActive() hook (exported from map-viewer-swipe.tsx). The generic layout already uses it to show the comparison button in highlighted ("primary") state while swipe is active.

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[jumpinjackie]

@copilot You have a TS build error. Pls fix.

ERROR in /home/runner/work/mapguide-react-layout/mapguide-react-layout/test/components/map-providers/context.spec.tsx
14:52-16:24
[tsl] ERROR in /home/runner/work/mapguide-react-layout/mapguide-react-layout/test/components/map-providers/context.spec.tsx(14,53)
      TS2352: Conversion of type '{ setReduxStore: () => void; }' to type 'IMapProviderContext' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
  Type '{ setReduxStore: () => void; }' is missing the following properties from type 'IMapProviderContext': isReady, getProviderName, isDigitizing, getActiveTool, and 70 more.
ts-loader-default_e3b0c44298fc1c14

[Copilot]

@copilot You have a TS build error. Pls fix.

...

Fixed in commit 2ef6fc1. Changed the mock cast to as unknown as IMapProviderContext to satisfy TypeScript's strict conversion check (TS2352 requires going through unknown when the source type doesn't sufficiently overlap with the target).

[jumpinjackie]

@copilot It's kind of almost there. The only issues I see remaining are:

1. Invoking the swipe command still does nothing until you have done a map switch to the secondary map first and then back to the primary.

2. If you invoke the swipe command with the secondary map as the active map, the view goes horribly out of whack. I'm not sure if it's extremely zoomed in or panned to some nonsensical coordinate. Either way the map is all white and the internal map state looks to be in an unrecoverable state that requires a full browser reload.

[Copilot]

@copilot 2 steps forward, 1 step back it seems.

In the layer manager UI when swipe mode is active, I can now add layers *only if the primary map is the selected map in the dropdow...

Fixed in commit 4f94892. Two root causes were addressed:

1 — Stale closure in AddFileLayer.onAddFileLayer (add-layer.tsx):
The React.useCallback was missing props.onLayerAdded, addLayerName, and locale from its dependency array. This meant the callback captured the onLayerAdded from before swipe was activated (where isSwipeActive = false and targetMapName = primaryMapName). Any layer added with the secondary map selected would silently use the stale handler — dispatching to primary and never calling transferLayerToSwipeSecondary(). Added the missing deps so the callback is recreated when the target map changes.

2 — apply() scoping bug (layer-set-group-base.ts):
apply() counted ALL IS_EXTERNAL=true layers on the OL map as currentLayers. With swipe active, the secondary map's custom layers (e.g. Natural Landmarks GeoJSON) were also on the OL map with IS_EXTERNAL=true. This caused a size mismatch vs primary's Redux layers, triggering a full invalidation that removed secondary's layers from the OL map. Fixed by filtering currentLayers to only layers owned by this._customLayers (this layer set group), ignoring secondary swipe layers.

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[jumpinjackie]

@copilot Still is not happening. Can you add tests cases that lay down your expectations on the expected states of maps and layers in swipe mode?

[Copilot]

@copilot Still is not happening. Can you add tests cases that lay down your expectations on the expected states of maps and layers in swipe mode?

Added 14 unit tests in test/api/layer-set-group-swipe.spec.ts (commit 08aadde) documenting the expected states of maps and layers in swipe mode:

getSwipeableLayers() — returns mainSet layers + _customLayers combined (the full set available for clipping)

transferLayerOut() / transferLayerIn() — removing from primary's tracking leaves the OL layer on the map; transferLayerIn on secondary makes the layer appear in getSwipeableLayers()

Primary-to-secondary transfer (the "add layer to secondary" scenario):
After transferLayerOut("userFile") on primary + transferLayerIn("userFile", olLayer, order) on secondary:

• primaryGroup.hasLayer("userFile") → false
• secondaryGroup.hasLayer("userFile") → true
• primaryGroup.getSwipeableLayers() does NOT contain the layer
• secondaryGroup.getSwipeableLayers() DOES contain the layer
• The OL layer remains on the OL map throughout (never removed during tracking transfer)

apply() isolation — when secondary layers sit on the OL map during swipe, primaryGroup.apply() does not remove them (they're filtered out because _customLayers[name] is null for primary group)

All 14 tests pass. These tests confirm the LayerSetGroupBase mechanics are correct; the investigation continues to identify if the remaining issue is at the React component / async-closure layer.

[jumpinjackie]

@copilot Now can you extend the tests to also cover the React components representing the layer manager and see if the current expectations still hold?

[Copilot]

@copilot Now can you extend the tests to also cover the React components representing the layer manager and see if the current expectations still hold?

Done in commit 284b92b. Added test/containers/add-manage-layers.spec.tsx with 21 tests covering both the layer API and the React component layer:

test/api/layer-set-group-swipe.spec.ts (already merged, 14 tests) — LayerSetGroupBase mechanics: getSwipeableLayers, transferLayerOut/In, apply() isolation, end-to-end transfer scenario.

test/containers/add-manage-layers.spec.tsx (new, 21 tests):

No-swipe scenario:

• Renders TabSet without the "Layers for:" dropdown
• Returns empty when primary map is uninitialised (layers === undefined)
• Shows primary map's layers in Manage Layers tab

Swipe-active scenario:

• "Layers for:" dropdown appears above the TabSet with primary + secondary options
• Dropdown defaults to primary (active) map
• Switching to secondary shows that map's layers; switching back shows primary's
• Shows "No Layers" state when secondary is selected but has no layers
• Does NOT go blank (TabSet still renders) when secondary map has never been visited

onLayerAdded contract tests — triggered via the mock AddLayer's simulated click:

• Primary selected → dispatches MAP_LAYER_ADDED with primaryMapName + calls viewer.refreshSwipeClips()
• Secondary selected → dispatches MAP_LAYER_ADDED with secondaryMapName + calls viewer.transferLayerToSwipeSecondary(layerName)
• Swipe inactive → dispatches with activeMapName, calls no swipe methods

Parameterized targetMapName derivation — 5 input combinations confirming the isSwipeActive ? (selected ?? active) : active logic is correct in all cases.

All 646 tests in the suite pass.

[jumpinjackie]

@copilot Additional findings from a fresh start, doing these steps first. Hopefully should give you more context to find the underlying issue.

1. Turn on swipe mode
2. Open the layer manager

Case 1

1. Ensure dropdown is set to primary map
2. Add geojson layer to map

Expect: Layer is visually on the left (primary) map only and is visible in the manage layers tab
Get: Expectations met

3. Ensure dropdown in set to secondary map
4. Add same geojson layer to map

Expect: Layer is visually on the right (secondary) map only and is visible in the manage layers tab
Get: Add fails because "A layer named xxxx already exists". This make no sense as a layer of this name should only exist on the left (primary) map, not the right (secondary) map.

Case 2

1. Ensure dropdown is set to secondary map
2. Add geojson layer to map

Expect: Layer is visually on the right (secondary) map only and is visible in the manage layers tab
Get: Layer is not visually on either map but is visible in the manage layers tab.

3. Ensure dropdown is set to primary map
4. Add geojson layer to map

Expect: Layer is visually on the left (primary) map only and is visible in the manage layers tab
Get: Layer is visually on both maps, instead of just on the left (primary) side and is visible in the manage layers tab

[Copilot]

@copilot Additional findings from a fresh start, doing these steps first. Hopefully should give you more context to find the underlying issue.

1. Turn on swipe mode
   ...

Fixed in commit 96de392.

Root cause: viewer.getLayerManager() always returned the primary/active map's layer manager regardless of which map was selected in the dropdown. This caused both cases:

• Case 1 — adding the same layer name to secondary after primary: the primary's _customLayers already had that name → "LAYER_NAME_EXISTS"
• Case 2 — adding to secondary first: the layer got tracked in primary's _customLayers but dispatched to secondary's Redux state → primary's apply() saw the mismatch and removed the OL layer from the map; subsequent adds to primary then had the layer on both sides

Fix:

1. getLayerManager(mapName?) now actually uses mapName — when mapName is a known non-active layer set (as is always the case once swipe is active), it returns that map's layer manager directly. This means secondaryLayerSet.addLayer(...) is called instead of primaryLayerSet.addLayer(...), bypassing the primary name check entirely.
2. AddLayer, AddWmsLayer, and AddWfsLayer accept an optional targetLayerManager prop. AddManageLayersContainer computes this as viewer.getLayerManager(secondaryMapName) when secondary is selected.
3. onLayerAdded is now simplified — always calls refreshSwipeClips() when swipe is active (no more transferLayerToSwipeSecondary; the layer is already in the correct layer set from the start).

All 647 tests pass.

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[jumpinjackie]

@copilot I can get added layers to show on both primary and secondary maps if I do the following:

1. Load the viewer
2. Enter swipe mode
3. Open the Layer Manager UI
4. Ensure the dropdown is set to the primary map
5. Add the layer
6. See the layer visually added to the left (primary) map and visible in the Manage Layers tab.
7. Ensure the dropdown is set to the secondary map
8. Add the layer
9. See no layer visually added to the right (secondary) map, but visible in the Manage Layers tab.
10. Exit swipe mode
11. Switch to the secondary map
12. Switch back to the primary map
13. Re-activate swipe mode

After doing this, the added layers are visible on their respective maps. So whatever internal state the maps are in at step 9 is different from the internal state the maps are in after step 13. Whatever steps 10, 11, 12, 13 are doing, it looks like step 8 should be doing some/all of.

[Copilot]

@copilot I can get added layers to show on both primary and secondary maps if I do the following:

1. Load the viewer
   ...

Fixed in commit 6499c2c. Two root causes identified and addressed:

Bug 1 — z-order (Case 2, step 2 invisible layer):
When a layer was added to the secondary layer manager while swipe was active, addLayerFromParsedFeatures added it directly to the primary OL map (since getLayerManagerForLayerSet always uses this._map). Then refreshSwipeClips() removed the secondary base layers (OSM) via deactivateMapSwipe() and re-added them in activateMapSwipe(). The old code skipped layers already on the map (if (!currentMapLayers.includes(topLayer))), so the custom layer stayed in place while OSM was appended after it — covering the GeoJSON layer with the base map tiles.

Fix: activateMapSwipe now always removes-then-re-adds each secondary layer, preserving the getSwipeableLayers() order (base layers first, custom layers on top).

Bug 2 — apply() name collision (Case 1 "layer already exists" / Case 2 step 3 appearing on both sides):
apply()'s currentLayers filter was _customLayers[name] != null. When primary had "gisborne.geojson" (layer1) and secondary also had "gisborne.geojson" (layer2) — both different OL objects on the same primary canvas — both matched the filter (same name, primary's _customLayers entry was non-null for both). This gave currentLayers.length=2 vs layers.length=1 → full invalidation → secondary's layer2 was removed from the OL map.

Fix: Filter now uses object identity: _customLayers[name]?.layer === l.layer, ensuring only layers actually owned by this layer set group are counted.

A new test in test/api/layer-set-group-swipe.spec.ts explicitly documents the same-name/different-object scenario for Bug 2.

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