import { assertAccountExists, decodeAccount, type FetchAccountConfig } from '@solana/accounts';
import { combineCodec, type FixedSizeCodec, type FixedSizeDecoder, type FixedSizeEncoder } from '@solana/codecs-core';
import { getStructDecoder, getStructEncoder } from '@solana/codecs-data-structures';
import { getU64Decoder, getU64Encoder } from '@solana/codecs-numbers';
import type { GetAccountInfoApi } from '@solana/rpc-api';
import type { Rpc } from '@solana/rpc-spec';
import type { Slot } from '@solana/rpc-types';

import { fetchEncodedSysvarAccount, SYSVAR_LAST_RESTART_SLOT_ADDRESS } from './sysvar';

type SysvarLastRestartSlotSize = 8;

/**
 * Information about the last restart slot (hard fork).
 *
 * The `LastRestartSlot` sysvar provides access to the last restart slot kept in the bank fork for
 * the slot on the fork that executes the current transaction. In case there was no fork it returns
 * `0`.
 */
export type SysvarLastRestartSlot = Readonly<{
    /** The last restart {@link Slot} */
    lastRestartSlot: Slot;
}>;

/**
 * Returns an encoder that you can use to encode a {@link SysvarLastRestartSlot} to a byte array
 * representing the `LastRestartSlot` sysvar's account data.
 */
export function getSysvarLastRestartSlotEncoder(): FixedSizeEncoder<SysvarLastRestartSlot, SysvarLastRestartSlotSize> {
    return getStructEncoder([['lastRestartSlot', getU64Encoder()]]) as FixedSizeEncoder<
        SysvarLastRestartSlot,
        SysvarLastRestartSlotSize
    >;
}

/**
 * Returns a decoder that you can use to decode a byte array representing the `LastRestartSlot`
 * sysvar's account data to a {@link SysvarLastRestartSlot}.
 */
export function getSysvarLastRestartSlotDecoder(): FixedSizeDecoder<SysvarLastRestartSlot, SysvarLastRestartSlotSize> {
    return getStructDecoder([['lastRestartSlot', getU64Decoder()]]) as FixedSizeDecoder<
        SysvarLastRestartSlot,
        SysvarLastRestartSlotSize
    >;
}

/**
 * Returns a codec that you can use to encode from or decode to {@link SysvarLastRestartSlot}
 *
 * @see {@link getSysvarLastRestartSlotDecoder}
 * @see {@link getSysvarLastRestartSlotEncoder}
 */
export function getSysvarLastRestartSlotCodec(): FixedSizeCodec<
    SysvarLastRestartSlot,
    SysvarLastRestartSlot,
    SysvarLastRestartSlotSize
> {
    return combineCodec(getSysvarLastRestartSlotEncoder(), getSysvarLastRestartSlotDecoder());
}

/**
 * Fetches the `LastRestartSlot` sysvar account using any RPC that supports the
 * {@link GetAccountInfoApi}.
 */
export async function fetchSysvarLastRestartSlot(
    rpc: Rpc<GetAccountInfoApi>,
    config?: FetchAccountConfig,
): Promise<SysvarLastRestartSlot> {
    const account = await fetchEncodedSysvarAccount(rpc, SYSVAR_LAST_RESTART_SLOT_ADDRESS, config);
    assertAccountExists(account);
    const decoded = decodeAccount(account, getSysvarLastRestartSlotDecoder());
    return decoded.data;
}