import * as z from "zod";

export const VIDEO_PREFIX = "/videos/";
export const VIDEO_R2_PREFIX = "videos/";
export const SCRUB_MANIFEST = "scrub/manifest.json";

const idPattern = /^[a-z0-9][a-z0-9-]{0,63}$/;
const assetPattern =
  /^(?:master\.m3u8|poster\.jpg|captions\/[a-z]{2}\.vtt|scrub\/(?:manifest\.json|sheet-[0-9]{3}\.webp)|[1-9][0-9]{0,3}\/(?:index\.m3u8|init\.mp4|[0-9]{5}\.m4s))$/;

export interface VideoPath {
  id: string;
  version: string;
  asset: string;
}

/** `/videos/<id>/<version>/<asset>`; anything outside the prepared layout is refused before touching R2. */
export function parseVideoPath(pathname: string): VideoPath | null {
  if (!pathname.startsWith(VIDEO_PREFIX)) return null;
  const [id, version, ...rest] = pathname.slice(VIDEO_PREFIX.length).split("/");
  const asset = rest.join("/");
  if (!id || !version || !idPattern.test(id) || !idPattern.test(version) || !assetPattern.test(asset)) return null;
  return { id, version, asset };
}

export function contentTypeForAsset(asset: string): string {
  if (asset.endsWith(".m3u8")) return "application/vnd.apple.mpegurl";
  if (asset.endsWith(".jpg")) return "image/jpeg";
  if (asset.endsWith(".webp")) return "image/webp";
  if (asset.endsWith(".vtt")) return "text/vtt; charset=utf-8";
  if (asset.endsWith(".json")) return "application/json";
  return "video/mp4";
}

export function videoR2Key({ id, version, asset }: VideoPath): string {
  return `${VIDEO_R2_PREFIX}${id}/${version}/${asset}`;
}

export function videoUrl(id: string, version: string, asset: string): string {
  return `${VIDEO_PREFIX}${id}/${version}/${asset}`;
}

export const scrubManifestSchema = z.object({
  interval: z.number().positive(),
  count: z.number().int().positive(),
  frameWidth: z.number().int().positive(),
  frameHeight: z.number().int().positive(),
  columns: z.number().int().positive(),
  rows: z.number().int().positive(),
  sheets: z.array(z.string().regex(/^scrub\/sheet-[0-9]{3}\.webp$/)).min(1),
});
export type ScrubManifest = z.infer<typeof scrubManifestSchema>;

export interface ScrubFrame {
  sheet: string;
  x: number;
  y: number;
}

/** The sprite tile nearest `time`; tiles are taken every `interval` seconds starting at 0. */
export function scrubFrameAt(manifest: ScrubManifest, time: number): ScrubFrame {
  const index = Math.min(manifest.count - 1, Math.max(0, Math.round(time / manifest.interval)));
  const perSheet = manifest.columns * manifest.rows;
  const within = index % perSheet;
  return {
    sheet: manifest.sheets[Math.min(manifest.sheets.length - 1, Math.floor(index / perSheet))],
    x: (within % manifest.columns) * manifest.frameWidth,
    y: Math.floor(within / manifest.columns) * manifest.frameHeight,
  };
}