// ---------------------------------------------------------------------------
// Atlas texture helpers: decode the baked sheet into a Pixi texture and slice
// per-entry sub-textures from it on demand (cached).
// ---------------------------------------------------------------------------

import { Rectangle, Texture } from 'pixi.js'
import type { AtlasEntry } from './contract'

/** Decode a data URL (or any image URL) into a nearest-neighbour Texture, so the
 *  baked pixel art stays crisp under the renderer's uniform zoom. */
export async function loadTexture(url: string): Promise<Texture> {
  const img = new Image()
  // Request CORS so a remote atlas (e.g. an atproto PDS blob) can be uploaded to
  // WebGL without tainting the canvas. Harmless for same-origin `data:`/`blob:`
  // URLs (the editor's case), required for cross-origin http(s) URLs.
  img.crossOrigin = 'anonymous'
  img.src = url
  await img.decode()
  const tex = Texture.from(img)
  tex.source.scaleMode = 'nearest'
  return tex
}

/** A lazily-built, cached lookup from atlas entry id → its sub-texture of the
 *  baked sheet. Returns null when there is no atlas (colour-only / failed bake)
 *  so callers can skip art that isn't available. */
export interface AtlasSlicer {
  texFor: (id: number) => Texture | null
  /** Destroy every interned sub-texture (NOT the underlying atlas source). */
  destroy: () => void
}

export function makeAtlasSlicer(atlas: Texture | null, entries: AtlasEntry[]): AtlasSlicer {
  const cache = new Map<number, Texture>()
  return {
    texFor(id) {
      if (!atlas) return null
      let t = cache.get(id)
      if (!t) {
        const e = entries[id]
        if (!e) return null
        t = new Texture({ source: atlas.source, frame: new Rectangle(e.x, e.y, e.w, e.h) })
        cache.set(id, t)
      }
      return t
    },
    destroy() {
      for (const t of cache.values()) t.destroy(false)
      cache.clear()
    },
  }
}