refactor: split monolithic state into context-based modules

Extract image, desktop, mobile, and config state into separate context
providers to improve modularity and reduce unnecessary re-renders.

Signed-off-by: Sped0n <hi@sped0n.com>

assets/ts/mobile/state.ts

@@ -0,0 +1,78 @@
+import {
+  createComponent,
+  createContext,
+  createSignal,
+  useContext,
+  type Accessor,
+  type JSX,
+  type Setter
+} from 'solid-js'
+import invariant from 'tiny-invariant'
+
+import { useImageState } from '../imageState'
+import { decrement, increment } from '../utils'
+
+export interface MobileState {
+  index: Accessor<number>
+  isOpen: Accessor<boolean>
+  isAnimating: Accessor<boolean>
+  isScrollLocked: Accessor<boolean>
+}
+
+export type MobileStateContextType = readonly [
+  MobileState,
+  {
+    readonly setIndex: Setter<number>
+    readonly incIndex: () => void
+    readonly decIndex: () => void
+    readonly setIsOpen: Setter<boolean>
+    readonly setIsAnimating: Setter<boolean>
+    readonly setIsScrollLocked: Setter<boolean>
+  }
+]
+
+const MobileStateContext = createContext<MobileStateContextType>()
+
+export function MobileStateProvider(props: { children?: JSX.Element }): JSX.Element {
+  const imageState = useImageState()
+
+  const [index, setIndex] = createSignal(-1)
+  const [isOpen, setIsOpen] = createSignal(false)
+  const [isAnimating, setIsAnimating] = createSignal(false)
+  const [isScrollLocked, setIsScrollLocked] = createSignal(false)
+
+  const updateIndex = (stride: 1 | -1): void => {
+    const length = imageState().length
+    if (length <= 0) return
+    setIndex((current) =>
+      stride === 1 ? increment(current, length) : decrement(current, length)
+    )
+  }
+
+  return createComponent(MobileStateContext.Provider, {
+    value: [
+      { index, isOpen, isAnimating, isScrollLocked },
+      {
+        setIndex,
+        incIndex: () => {
+          updateIndex(1)
+        },
+        decIndex: () => {
+          updateIndex(-1)
+        },
+        setIsOpen,
+        setIsAnimating,
+        setIsScrollLocked
+      }
+    ],
+    get children() {
+      return props.children
+    }
+  })
+}
+
+export function useMobileState(): MobileStateContextType {
+  const context = useContext(MobileStateContext)
+  invariant(context, 'undefined mobile context')
+  return context
+}