orca/src/renderer/src/lib/scroll-cache.ts

import type { editor, ISelection } from 'monaco-editor'

// Why: 20 entries covers a typical working set of open/recently-viewed files.
// Eviction only means losing a scroll position (user sees top of file), not a
// correctness bug, so a conservative cap is fine.
const CACHE_MAX_ENTRIES = 20

// Why: Module-scoped Maps grow unboundedly as unique file keys accumulate.
// Cap them with a simple LRU eviction: after each set, if the map exceeds
// this limit, delete the oldest entry (Maps iterate in insertion order).
// `maxEntries` is optional so consumers with their own Maps (like
// CombinedDiffViewer) can use different limits.
export function setWithLRU<K, V>(
  map: Map<K, V>,
  key: K,
  value: V,
  maxEntries: number = CACHE_MAX_ENTRIES
): void {
  // Re-insert to refresh insertion order (move to end).
  map.delete(key)
  map.set(key, value)
  if (map.size > maxEntries) {
    // Why: Use the iterator's `.done` property rather than checking
    // `value !== undefined`, because K could legitimately be `undefined`
    // in a generic Map — the undefined check would skip valid evictions.
    const first = map.keys().next()
    if (!first.done) {
      map.delete(first.value)
    }
  }
}

// Why: A single shared Map for scroll positions across all editor components.
// Module-scoped so it survives component unmount/remount without triggering
// React re-renders (unlike Zustand, which would broadcast state changes on
// every scroll event even though no component renders from scroll position).
export const scrollTopCache = new Map<string, number>()

// Why: Same rationale as scrollTopCache — module-scoped avoids Zustand
// re-renders on every cursor or selection change.
export const editorSelectionCache = new Map<string, readonly ISelection[]>()

// Why: PDFs store a pdf.js location in PDF user space, not a scrollTop — page
// layout is rebuilt at a scale that depends on container width, so a pixel
// offset restores to the wrong place at a different zoom or pane width.
export type PdfViewPosition = { pageNumber: number; top: number; left: number }
export const pdfViewPositionCache = new Map<string, PdfViewPosition>()

// Why: switching tabs unmounts the media element, so playback time (seconds)
// must outlive it or the clip restarts from zero on return.
export const mediaPlaybackPositionCache = new Map<string, number>()

// Why: Diff editors need more than a numeric scroll offset to restore the same
// working context. Monaco's diff view state also carries cursor/selection state
// for both sides plus diff model state, which matches VS Code's restore path
// more closely than Orca's previous scroll-only cache.
export const diffViewStateCache = new Map<string, editor.IDiffEditorViewState>()