refactor(chart): introduce hybrid domain architecture

src/components/interaction/viewportInteractionState.ts

@@ -0,0 +1,80 @@
+import type { ViewportSelectionState } from '../core/waveformChartTypes'
+
+export interface ViewportGestureStart {
+  trackIndex: number
+  independent: boolean
+  startX: number
+  startY: number
+  pointerId: number
+  kind: 'box' | 'pan'
+  xDomain: [number, number]
+  yDomains: Record<string, [number, number]>
+}
+
+export interface ViewportGesturePosition {
+  currentX: number
+  currentY: number
+}
+
+function cloneState(state: ViewportSelectionState | null): ViewportSelectionState | null {
+  if (!state) return null
+  return {
+    ...state,
+    xDomain: [...state.xDomain],
+    yDomains: Object.fromEntries(
+      Object.entries(state.yDomains).map(([key, domain]) => [key, [...domain] as [number, number]]),
+    ),
+  }
+}
+
+/** Owns the legal lifecycle of one active viewport pointer gesture. */
+export class ViewportInteractionStateMachine {
+  private current: ViewportSelectionState | null = null
+
+  get state(): ViewportSelectionState | null {
+    return cloneState(this.current)
+  }
+
+  begin(input: ViewportGestureStart): boolean {
+    if (this.current) return false
+    this.current = {
+      ...input,
+      currentX: input.startX,
+      currentY: input.startY,
+      xDomain: [...input.xDomain],
+      yDomains: Object.fromEntries(
+        Object.entries(input.yDomains).map(([key, domain]) => [
+          key,
+          [...domain] as [number, number],
+        ]),
+      ),
+    }
+    return true
+  }
+
+  move(pointerId: number, position: ViewportGesturePosition): ViewportSelectionState | null {
+    if (!this.current || this.current.pointerId !== pointerId) return null
+    this.current = { ...this.current, ...position }
+    return this.state
+  }
+
+  finish(pointerId: number, position: ViewportGesturePosition): ViewportSelectionState | null {
+    if (!this.current || this.current.pointerId !== pointerId) return null
+    this.current = { ...this.current, ...position }
+    const completed = this.state
+    this.current = null
+    return completed
+  }
+
+  cancel(pointerId?: number): boolean {
+    if (!this.current || (pointerId !== undefined && this.current.pointerId !== pointerId)) {
+      return false
+    }
+    this.current = null
+    return true
+  }
+
+  reset(): void {
+    this.current = null
+  }
+}