import { erc20Abi, getContract, type Address, type PublicActions, type WalletClient } from 'viem';

type EnsureTokenApprovalDependencies = {
  client: WalletClient & PublicActions;
};

type EnsureTokenApprovalParams = {
  tokenAddress: Address;
  spenderAddress: Address;
  amount: bigint;
};

type EnsureTokenApprovalReturnType = {
  spenderAddress: Address;
  approved: boolean;
  transactionHash?: `0x${string}`;
  previousAllowance: bigint;
  newAllowance: bigint;
  wasAlreadyApproved: boolean;
};

/**
 * Ensures that the token is approved for the spender to spend the amount.
 * If the token is already approved for the amount, this function does nothing.
 * If the token is not approved for the amount, this function approves the token for the spender to spend the amount.
 *
 * @param dependencies - The dependencies for the function.
 * @param params - The parameters for the function.
 * @returns A promise that resolves with the approval result details.
 */
export async function ensureTokenApproval(
  dependencies: EnsureTokenApprovalDependencies,
  params: EnsureTokenApprovalParams,
): Promise<EnsureTokenApprovalReturnType> {
  const { client } = dependencies;
  const { tokenAddress, spenderAddress, amount } = params;

  if (!client.account) {
    throw new Error('Wallet client account not found for approval');
  }

  const tokenContract = getContract({
    abi: erc20Abi,
    address: tokenAddress,
    client,
  });

  const currentAllowance = await tokenContract.read.allowance([client.account.address, spenderAddress]);

  if (currentAllowance >= amount) {
    return {
      spenderAddress,
      approved: true,
      previousAllowance: currentAllowance,
      newAllowance: currentAllowance,
      wasAlreadyApproved: true,
    };
  }

  const approveTxHash = await tokenContract.write.approve([spenderAddress, amount], {
    account: client.account,
    chain: client.chain,
  });

  await client.waitForTransactionReceipt({ hash: approveTxHash });

  return {
    spenderAddress,
    approved: true,
    transactionHash: approveTxHash,
    previousAllowance: currentAllowance,
    newAllowance: amount,
    wasAlreadyApproved: false,
  };
}