refactor(chart): introduce hybrid domain architecture

src/components/interaction/viewportInteractionState.test.ts

@@ -0,0 +1,76 @@
+import { describe, expect, it } from 'vitest'
+
+import { ViewportInteractionStateMachine } from './viewportInteractionState'
+
+const gesture = {
+  trackIndex: 2,
+  independent: true,
+  startX: 10,
+  startY: 20,
+  pointerId: 7,
+  kind: 'box' as const,
+  xDomain: [0, 100] as [number, number],
+  yDomains: { track: [-1, 1] as [number, number] },
+}
+
+describe('ViewportInteractionStateMachine', () => {
+  it('accepts one gesture and rejects a conflicting start', () => {
+    const machine = new ViewportInteractionStateMachine()
+
+    expect(machine.begin(gesture)).toBe(true)
+    expect(machine.begin({ ...gesture, pointerId: 8 })).toBe(false)
+    expect(machine.state).toMatchObject({ kind: 'box', pointerId: 7 })
+  })
+
+  it('rejects moves and completion from a different pointer', () => {
+    const machine = new ViewportInteractionStateMachine()
+    machine.begin(gesture)
+
+    expect(machine.move(8, { currentX: 30, currentY: 40 })).toBeNull()
+    expect(machine.finish(8, { currentX: 30, currentY: 40 })).toBeNull()
+    expect(machine.state?.currentX).toBe(10)
+  })
+
+  it('updates a valid pointer, completes it, and returns to idle', () => {
+    const machine = new ViewportInteractionStateMachine()
+    machine.begin({ ...gesture, kind: 'pan' })
+
+    expect(machine.move(7, { currentX: 30, currentY: 40 })).toMatchObject({
+      kind: 'pan',
+      currentX: 30,
+      currentY: 40,
+    })
+    expect(machine.finish(7, { currentX: 50, currentY: 60 })).toMatchObject({
+      kind: 'pan',
+      currentX: 50,
+      currentY: 60,
+    })
+    expect(machine.state).toBeNull()
+  })
+
+  it('only cancels the owning pointer and supports explicit reset', () => {
+    const machine = new ViewportInteractionStateMachine()
+    machine.begin(gesture)
+
+    expect(machine.cancel(8)).toBe(false)
+    expect(machine.state).not.toBeNull()
+    expect(machine.cancel(7)).toBe(true)
+    expect(machine.state).toBeNull()
+
+    machine.begin(gesture)
+    machine.reset()
+    expect(machine.state).toBeNull()
+  })
+
+  it('returns defensive copies from its state getter', () => {
+    const machine = new ViewportInteractionStateMachine()
+    machine.begin(gesture)
+    const snapshot = machine.state!
+    snapshot.currentX = 99
+    snapshot.xDomain[0] = 50
+    snapshot.yDomains.track![0] = 50
+
+    expect(machine.state).toMatchObject({ currentX: 10, xDomain: [0, 100] })
+    expect(machine.state?.yDomains.track).toEqual([-1, 1])
+  })
+})