import { defaultAbiCoder } from "@ethersproject/abi";
import { Provider } from "@ethersproject/abstract-provider";
import { BigNumber } from "@ethersproject/bignumber";
import { BytesLike } from "@ethersproject/bytes";
import { Contract } from "@ethersproject/contracts";
import { id } from "@ethersproject/hash";

/**
 * Compute an EIP-1967 slot for the specified name. The proxy contract used by
 * `hardhat-deploy` implements EIP-1967 (Standard Proxy Storage Slot).
 *
 * <https://eips.ethereum.org/EIPS/eip-1967>.
 */
function slot(name: string): BytesLike {
  return defaultAbiCoder.encode(["bytes32"], [BigNumber.from(id(name)).sub(1)]);
}

const IMPLEMENTATION_STORAGE_SLOT = slot("eip1967.proxy.implementation");
const OWNER_STORAGE_SLOT = slot("eip1967.proxy.admin");

/**
 * Returns the address of the implementation of an EIP-1967-compatible proxy
 * from its address.
 *
 * @param proxy Address of the proxy contract.
 * @returns The address of the contract storing the proxy implementation.
 */
export async function implementationAddress(
  provider: Provider,
  proxy: string,
): Promise<string> {
  const [implementation] = defaultAbiCoder.decode(
    ["address"],
    await provider.getStorageAt(proxy, IMPLEMENTATION_STORAGE_SLOT),
  );
  return implementation;
}

/**
 * Returns the address of the implementation of an EIP-1967-compatible proxy
 * from its address.
 *
 * @param proxy Address of the proxy contract.
 * @returns The address of the administrator of the proxy.
 */
export async function ownerAddress(
  provider: Provider,
  proxy: string,
): Promise<string> {
  const [owner] = defaultAbiCoder.decode(
    ["address"],
    await provider.getStorageAt(proxy, OWNER_STORAGE_SLOT),
  );
  return owner;
}

/**
 * EIP-173 proxy ABI in "human-readable ABI" format. The proxy used by the
 * deployment plugin implements this interface, and copying it here avoids
 * pulling in `hardhat` as a dependency for just this ABI.
 *
 * <https://eips.ethereum.org/EIPS/eip-173#specification>
 */
export const EIP173_PROXY_ABI = [
  "event OwnershipTransferred(address indexed previousOwner, address indexed newOwner)",
  "function owner() view external returns(address)",
  "function transferOwnership(address newOwner) external",
  "function supportsInterface(bytes4 interfaceID) external view returns (bool)",
];

/**
 * Returns the proxy interface for the specified address.
 *
 * @param contract The proxy contract to return a proxy interface for.
 * @returns A Ethers.js contract instance for interacting with the proxy.
 */
export function proxyInterface(contract: Contract): Contract {
  return new Contract(
    contract.address,
    EIP173_PROXY_ABI,
    contract.signer ?? contract.provider,
  );
}