import useSWRSubscription from "swr/subscription"
import { getDynamicBuilder, getLookupFn } from "@polkadot-api/metadata-builders"
import { distinct, filter, map, mergeMap } from "rxjs"

import { useUnstableProvider } from "./UnstableProvider"
import { useMetadata } from "./MetadataProvider"

export const useEraIndex = () => {
    const { chainHead$, chainId } = useUnstableProvider()
    const metadata = useMetadata()
    const { data: eraIndex } = useSWRSubscription(
        chainHead$ && chainId && metadata
            ? ["eraIndex", chainHead$, chainId, metadata]
            : null,
        ([_, chainHead$, chainId, metadata], { next }) => {
            const { finalized$, storage$ } = chainHead$
            const subscription = finalized$.pipe(
                filter(Boolean),
                mergeMap((blockInfo) => {
                    const builder = getDynamicBuilder(getLookupFn(metadata))
                    const eraIndex = builder.buildStorage("Staking", "ActiveEra")
                    return storage$(blockInfo?.hash, "value", () =>
                        eraIndex?.keys.enc()
                    ).pipe(
                        filter(Boolean),
                        distinct(),
                        map((value) => eraIndex?.value.dec(value))
                    )
                }),
            )
            .subscribe({
                next(eraIndex) {
                    next(null, eraIndex)
                },
                error: next,
            })
            return () => subscription.unsubscribe()
        }
    )
    return eraIndex;
}