import path from "path-browserify";
import { Sha256 } from "@aws-crypto/sha256-universal";
import { Buffer } from "buffer";
import { SPEC_URL, toHex } from "./util";

export interface PointerInfo {
  /** OID (currently, SHA256 hash) of actual blob contents. */
  oid: string;

  /** Actual blob size in bytes. */
  size: number;
}

export interface Pointer {
  info: PointerInfo;

  /** Absolute path to actual blob in LFS cache. */
  objectPath: string;
}

function isValidPointerInfo(val: Record<string, any>): val is PointerInfo {
  return val.oid.trim !== undefined && typeof val.size === "number";
}

export function readPointerInfo(content: Buffer): PointerInfo {
  const info = content
    .toString()
    .trim()
    .split("\n")
    .reduce((accum, line) => {
      const [k, v] = line.split(" ", 2);
      if (k === "oid") {
        accum[k] = v.split(":", 2)[1];
      } else if (k === "size") {
        accum[k] = parseInt(v, 10);
      }
      return accum;
    }, {} as Record<string, any>);

  if (isValidPointerInfo(info)) {
    return info;
  } else {
    throw new Error("LFS pointer is incomplete or cannot be read");
  }
}

interface PointerRequest {
  dir: string;
  gitdir?: string;
  content: Buffer;
}
export function readPointer({
  dir,
  gitdir = path.join(dir, ".git"),
  content,
}: PointerRequest): Pointer {
  const info = readPointerInfo(content);

  const objectPath = path.join(
    gitdir,
    "lfs",
    "objects",
    info.oid.substr(0, 2),
    info.oid.substr(2, 2),
    info.oid
  );

  return { info, objectPath };
}

/** Formats given PointerInfo for writing in Git tree. */
export function formatPointerInfo(info: PointerInfo): Buffer {
  const lines = [
    `version ${SPEC_URL}`,
    `oid sha256:${info.oid}`,
    `size ${info.size}`,
    "",
  ];
  return Buffer.from(lines.join("\n"));
}

export async function buildPointerInfo(content: Buffer): Promise<PointerInfo> {
  const size = content.byteLength;
  const hash = await crypto.subtle.digest("SHA-256", content);
  const oid = toHex(hash);
  return { oid, size };
}