feat: add maplibre subpackage for type-safe MapLibre GL JS maps

Provides a Go API for interactive maps within Via applications:
- Plugin serves vendored MapLibre GL JS v4.7.1 assets
- Map struct with pre/post-render source, layer, marker, popup management
- Viewport signal sync (center, zoom, bearing, pitch) via hidden inputs
- FlyTo, SetCenter, SetZoom and other viewport setters via ExecScript
- Idempotent init script with SPA cleanup via MutationObserver
- Example app demonstrating markers, GeoJSON layers, and FlyTo actions

maplibre/types.go

@@ -0,0 +1,175 @@
+package maplibre
+
+import "encoding/json"
+
+// LngLat represents a geographic coordinate.
+type LngLat struct {
+	Lng float64
+	Lat float64
+}
+
+// Options configures the initial map state.
+type Options struct {
+	// Style is the map style URL (required).
+	Style string
+
+	Center  LngLat
+	Zoom    float64
+	Bearing float64
+	Pitch   float64
+	MinZoom float64
+	MaxZoom float64
+
+	// CSS dimensions for the map container. Defaults: "100%", "400px".
+	Width  string
+	Height string
+}
+
+// GeoJSONSource provides inline GeoJSON data to MapLibre.
+// Data should be a GeoJSON-marshalable value (struct, map, or json.RawMessage).
+type GeoJSONSource struct {
+	Data any
+}
+
+func (s GeoJSONSource) toJS() string {
+	data, _ := json.Marshal(s.Data)
+	return `{"type":"geojson","data":` + string(data) + `}`
+}
+
+// VectorSource references a vector tile source.
+type VectorSource struct {
+	URL   string
+	Tiles []string
+}
+
+func (s VectorSource) toJS() string {
+	obj := map[string]any{"type": "vector"}
+	if s.URL != "" {
+		obj["url"] = s.URL
+	}
+	if len(s.Tiles) > 0 {
+		obj["tiles"] = s.Tiles
+	}
+	b, _ := json.Marshal(obj)
+	return string(b)
+}
+
+// RasterSource references a raster tile source.
+type RasterSource struct {
+	URL      string
+	Tiles    []string
+	TileSize int
+}
+
+func (s RasterSource) toJS() string {
+	obj := map[string]any{"type": "raster"}
+	if s.URL != "" {
+		obj["url"] = s.URL
+	}
+	if len(s.Tiles) > 0 {
+		obj["tiles"] = s.Tiles
+	}
+	if s.TileSize > 0 {
+		obj["tileSize"] = s.TileSize
+	}
+	b, _ := json.Marshal(obj)
+	return string(b)
+}
+
+// sourceJSON converts a source value to its JS object literal string.
+func sourceJSON(src any) string {
+	switch s := src.(type) {
+	case GeoJSONSource:
+		return s.toJS()
+	case VectorSource:
+		return s.toJS()
+	case RasterSource:
+		return s.toJS()
+	default:
+		b, _ := json.Marshal(src)
+		return string(b)
+	}
+}
+
+// Layer describes a MapLibre style layer.
+type Layer struct {
+	ID          string
+	Type        string
+	Source      string
+	SourceLayer string
+	Paint       map[string]any
+	Layout      map[string]any
+	Filter      any
+	MinZoom     float64
+	MaxZoom     float64
+
+	// Before inserts this layer before the given layer ID in the stack.
+	Before string
+}
+
+func (l Layer) toJS() string {
+	obj := map[string]any{
+		"id":   l.ID,
+		"type": l.Type,
+	}
+	if l.Source != "" {
+		obj["source"] = l.Source
+	}
+	if l.SourceLayer != "" {
+		obj["source-layer"] = l.SourceLayer
+	}
+	if l.Paint != nil {
+		obj["paint"] = l.Paint
+	}
+	if l.Layout != nil {
+		obj["layout"] = l.Layout
+	}
+	if l.Filter != nil {
+		obj["filter"] = l.Filter
+	}
+	if l.MinZoom > 0 {
+		obj["minzoom"] = l.MinZoom
+	}
+	if l.MaxZoom > 0 {
+		obj["maxzoom"] = l.MaxZoom
+	}
+	b, _ := json.Marshal(obj)
+	return string(b)
+}
+
+// Marker describes a map marker.
+type Marker struct {
+	LngLat    LngLat
+	Color     string
+	Draggable bool
+	Popup     *Popup
+}
+
+// Popup describes a map popup.
+//
+// Content is rendered as HTML via MapLibre's setHTML. Do not pass untrusted
+// user input without sanitizing it first.
+type Popup struct {
+	Content         string // HTML content
+	LngLat          LngLat
+	HideCloseButton bool   // true removes the close button (MapLibre shows it by default)
+	MaxWidth        string
+}
+
+// sourceEntry pairs a source ID with its JS representation for pre-render accumulation.
+type sourceEntry struct {
+	id string
+	js string
+}
+
+// markerEntry pairs a marker ID with its definition for pre-render accumulation.
+type markerEntry struct {
+	id     string
+	marker Marker
+}
+
+// popupEntry pairs a popup ID with its definition for pre-render accumulation.
+type popupEntry struct {
+	id    string
+	popup Popup
+}