import {
  type GetBlockErrorType,
  getBlock,
} from '../../actions/public/getBlock.js'
import type { Client } from '../../clients/createClient.js'
import type { Transport } from '../../clients/transports/createTransport.js'
import type { ErrorType } from '../../errors/utils.js'
import type { Account } from '../../types/account.js'
import type { Chain } from '../../types/chain.js'

export type GetL2BlockNumberAtTimestampParameters = {
  /** L2 block timestamp. */
  timestamp: bigint
}

export type GetL2BlockNumberAtTimestampReturnType = bigint

export type GetL2BlockNumberAtTimestampErrorType = GetBlockErrorType | ErrorType

/**
 * Gets the L2 block number for a timestamp using the latest L2 block and its parent.
 *
 * @param client - Client to use.
 * @param parameters - {@link GetL2BlockNumberAtTimestampParameters}
 * @returns L2 block number.
 */
export async function getL2BlockNumberAtTimestamp(
  client: Client<Transport, Chain | undefined, Account | undefined>,
  parameters: GetL2BlockNumberAtTimestampParameters,
): Promise<GetL2BlockNumberAtTimestampReturnType> {
  const latest = await getBlock(client)
  if (latest.number === null)
    throw new Error('Latest L2 block number is unavailable.')
  if (latest.timestamp === undefined)
    throw new Error('Latest L2 block timestamp is unavailable.')
  if (latest.number === 0n)
    throw new Error('Cannot derive L2 block time from genesis block.')

  const parent = await getBlock(client, { blockNumber: latest.number - 1n })
  if (parent.timestamp === undefined)
    throw new Error('Parent L2 block timestamp is unavailable.')

  const blockTime = latest.timestamp - parent.timestamp
  if (blockTime === 0n) throw new Error('L2 block time is zero.')

  const timeDiff = latest.timestamp - parameters.timestamp
  if (timeDiff < 0n)
    throw new Error('Timestamp is in the future relative to L2 head.')
  if (timeDiff % blockTime !== 0n)
    throw new Error('Timestamp does not align with the L2 block time.')

  const blocksToLookBack = timeDiff / blockTime
  if (blocksToLookBack > latest.number)
    throw new Error('Timestamp predates L2 genesis.')

  return latest.number - blocksToLookBack
}