import { type mastodon } from "masto";
import { Accessor, createEffect, createResource } from "solid-js";
import { createStore } from "solid-js/store";

type TimelineFetchTips = {
  direction?: "new" | "old";
};

type Timeline = {
  list(params: {
    readonly limit?: number;
  }): mastodon.Paginator<mastodon.v1.Status[], unknown>;
};

export function useTimeline(
  timeline: Accessor<Timeline>,
  cfg?: {
    /**
     * Use full refresh mode. This mode ignores paging, it will refetch the specified number
     * of toots at every refetch().
     */
    fullRefresh?: number;
  },
) {
  let otl: Timeline | undefined;
  let npager: mastodon.Paginator<mastodon.v1.Status[], unknown> | undefined;
  let opager: mastodon.Paginator<mastodon.v1.Status[], unknown> | undefined;
  const [snapshot, { refetch }] = createResource<
    {
      records: mastodon.v1.Status[];
      direction: "new" | "old" | "items";
      tlChanged: boolean;
    },
    [Timeline],
    TimelineFetchTips | undefined
  >(
    () => [timeline()] as const,
    async ([tl], info) => {
      let tlChanged = false;
      if (otl !== tl) {
        npager = opager = undefined;
        otl = tl;
        tlChanged = true;
      }
      const fullRefresh = cfg?.fullRefresh;
      if (typeof fullRefresh !== "undefined") {
        const records = await tl
          .list({
            limit: fullRefresh,
          })
          .next();
        return {
          direction: "items",
          records: records.value ?? [],
          end: records.done,
          tlChanged,
        };
      }
      const direction =
        typeof info.refetching !== "boolean"
          ? (info.refetching?.direction ?? "old")
          : "old";
      if (direction === "old") {
        if (!opager) {
          opager = tl.list({}).setDirection("next");
        }
        const next = await opager.next();
        return {
          direction,
          records: next.value ?? [],
          end: next.done,
          tlChanged,
        };
      } else {
        if (!npager) {
          npager = tl.list({}).setDirection("prev");
        }
        const next = await npager.next();
        const page = next.value ?? [];
        return { direction, records: page, end: next.done, tlChanged };
      }
    },
  );

  const [store, setStore] = createStore([] as mastodon.v1.Status[]);

  createEffect(() => {
    const shot = snapshot();
    if (!shot) return;
    const { direction, records, tlChanged } = shot;
    if (tlChanged) {
      setStore(() => []);
    }
    if (direction === "new") {
      setStore((x) => [...records, ...x]);
    } else if (direction === "old") {
      setStore((x) => [...x, ...records]);
    } else if (direction === "items") {
      setStore(() => records);
    }
  });

  return [
    store,
    snapshot,
    {
      refetch,
      mutate: setStore,
    },
  ] as const;
}

export function createTimelineSnapshot(
  timeline: Accessor<Timeline>,
  limit: Accessor<number>,
) {
  const [shot, {refetch}] = createResource(
    () => [timeline(), limit()] as const,
    async ([tl, limit]) => {
      const ls = await tl.list({ limit }).next();
      return ls.value?.map((x) => [x]) ?? [];
    },
  );

  const [snapshot, setSnapshot] = createStore([] as mastodon.v1.Status[][]);

  createEffect(() => {
    const nls = shot();
    if (!nls) return;
    const ols = Array.from(snapshot);
    // The algorithm below assumes the snapshot is not changing
    for (let i = 0; i < nls.length; i++) {
      if (i >= ols.length) {
        setSnapshot(i, nls[i]);
      } else {
        if (nls[i].length !== ols[i].length) {
          setSnapshot(i, nls[i]);
        } else {
          const oth = ols[i],
            nth = nls[i];
          for (let j = 0; j < oth.length; j++) {
            const ost = oth[j],
              nst = nth[j];
            for (const key of Object.keys(
              nst,
            ) as unknown as (keyof mastodon.v1.Status)[]) {
              if (ost[key] !== nst[key]) {
                setSnapshot(i, j, key, nst[key]);
              }
            }
          }
        }
      }
    }
  });

  return [snapshot, shot, {
    refetch,
    mutate: setSnapshot
  }] as const;
}

export function createTimeline(timeline: Accessor<Timeline>) {
  // TODO
}