import {
  ConvexReactClient,
  useConvex,
  useMutation,
  useQuery,
  Watch,
} from "convex/react";
import { Content, Editor, Extension, JSONContent } from "@tiptap/core";
import * as collab from "@tiptap/pm/collab";
import { Step } from "@tiptap/pm/transform";
import { useCallback, useMemo, useState } from "react";
import { SyncApi } from "../client";

// How many steps we will attempt to sync in one request.
const MAX_STEPS_SYNC = 1000;
const SNAPSHOT_DEBOUNCE_MS = 1000;

export type UseSyncOptions = {
  onSyncError?: (error: Error) => void;
  snapshotDebounceMs?: number;
  debug?: boolean;
};

export function useTiptapSync(
  syncApi: SyncApi,
  id: string,
  opts?: UseSyncOptions
) {
  const log: typeof console.log = opts?.debug ? console.debug : () => {};
  const convex = useConvex();
  const initial = useInitialState(syncApi, id);
  const extension = useMemo(() => {
    const { loading, ...initialState } = initial;
    if (loading || !initialState.initialContent) return null;
    return syncExtension(convex, id, syncApi, initialState, opts);
    // // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [convex, id, initial.loading, initial.initialContent]);
  const submitSnapshot = useMutation(
    syncApi.submitSnapshot
  ).withOptimisticUpdate((localQueryStore, args) => {
    // This update will allow the useInitialState to respond immediately to
    // creating documents, as if it came from the server.
    const existing = localQueryStore.getQuery(syncApi.getSnapshot, { id });
    if (!existing?.content) {
      localQueryStore.setQuery(
        syncApi.getSnapshot,
        { id },
        {
          version: args.version,
          content: args.content,
        }
      );
    }
    const version = localQueryStore.getQuery(syncApi.latestVersion, { id });
    if (version === null) {
      localQueryStore.setQuery(syncApi.latestVersion, { id }, args.version);
    }
  });
  const create = useCallback(
    async (content: JSONContent) => {
      log("Creating new document", { id });
      await submitSnapshot({
        id,
        version: 1,
        content: JSON.stringify(content),
      });
    },
    [convex, id]
  );
  if (initial.loading) {
    return {
      extension: null,
      isLoading: true,
      initialContent: null,
      /**
       * Create the document without waiting to hear from the server.
       * Warning: Only call this if you just created the document id.
       * It's safer to wait until loading is false.
       * It's also best practice to pass in the same initial content everywhere,
       * so if two clients create the same document id, they'll both end up
       * with the same initial content. Otherwise the second client will
       * throw an exception on the snapshot creation.
       */
      create,
    } as const;
  }
  if (!initial.initialContent) {
    return {
      extension: null,
      isLoading: false,
      initialContent: null,
      create,
    } as const;
  }
  return {
    extension: extension!,
    isLoading: false,
    initialContent: initial.initialContent,
  } as const;
}

export function syncExtension(
  convex: ConvexReactClient,
  id: string,
  syncApi: SyncApi,
  initialState: InitialState,
  opts?: UseSyncOptions
) {
  const log: typeof console.log = opts?.debug ? console.debug : () => {};
  let snapshotTimer: NodeJS.Timeout | undefined;
  const trySubmitSnapshot = (version: number, content: string) => {
    if (snapshotTimer) {
      clearTimeout(snapshotTimer);
    }
    snapshotTimer = setTimeout(() => {
      void convex
        .mutation(syncApi.submitSnapshot, { id, version, content })
        .catch(opts?.onSyncError);
    }, opts?.snapshotDebounceMs ?? SNAPSHOT_DEBOUNCE_MS);
  };

  let active: boolean = false;
  let pending:
    | { resolve: () => void; reject: () => void; promise: Promise<void> }
    | undefined;
  let watch: Watch<number | null> | undefined;

  async function trySync(editor: Editor) {
    const serverVersion = watch?.localQueryResult();
    if (serverVersion === undefined) {
      return;
    }
    if (serverVersion && serverVersion > collab.getVersion(editor.state)) {
      clearTimeout(snapshotTimer);
      snapshotTimer = undefined;
    }
    if (active) {
      if (!pending) {
        let resolve = () => {};
        let reject = () => {};
        const promise = new Promise<void>((res, rej) => {
          resolve = res;
          reject = rej;
        });
        pending = { resolve, reject, promise };
      }
      return pending.promise;
    }
    active = true;

    try {
      if (
        await doSync(
          editor,
          convex,
          syncApi,
          id,
          serverVersion,
          initialState,
          opts?.debug
        )
      ) {
        const version = collab.getVersion(editor.state);
        const content = JSON.stringify(editor.state.doc.toJSON());
        if (collab.sendableSteps(editor.state)) {
          throw new Error("Synced but still have sendable steps");
        }
        trySubmitSnapshot(version, content);
      }
    } catch (error) {
      if (opts?.onSyncError) {
        opts.onSyncError(error as Error);
      } else {
        throw error;
      }
    } finally {
      active = false;
      if (pending) {
        const { resolve, reject } = pending;
        pending = undefined;
        trySync(editor).then(resolve, reject);
      }
    }
  }

  let unsubscribe: (() => void) | undefined;

  return Extension.create({
    name: "convex-sync",
    onDestroy() {
      log("destroying");
      unsubscribe?.();
    },
    onCreate() {
      if (initialState.restoredSteps?.length) {
        // TODO: verify that restoring local steps works
        log("Restoring local steps", initialState.restoredSteps);
        const tr = this.editor.state.tr;
        for (const step of initialState.restoredSteps) {
          tr.step(Step.fromJSON(this.editor.schema, step));
        }
        this.editor.view.dispatch(tr);
      }
      watch = convex.watchQuery(syncApi.latestVersion, { id });
      unsubscribe = watch.onUpdate(() => {
        void trySync(this.editor);
      });
      void trySync(this.editor);
    },
    onUpdate() {
      void trySync(this.editor);
    },
    addProseMirrorPlugins() {
      log("Adding collab plugin", {
        version: initialState.initialVersion,
      });
      return [
        collab.collab({
          version: initialState.initialVersion,
        }),
      ];
    },
  });
}

async function doSync(
  editor: Editor,
  convex: ConvexReactClient,
  syncApi: SyncApi,
  id: string,
  serverVersion: number | null,
  initialState: InitialState,
  debug?: boolean
) {
  const log: typeof console.log = debug ? console.debug : () => {};
  if (serverVersion === null) {
    if (initialState.initialVersion <= 1) {
      // This is a new document, so we can create it on the server.
      // Note: this should only happen if the initial version is loaded from
      // a local cache. Creating a new document on the client will set the
      // initial version to 1 optimistically.
      log("Syncing new document", { id });
      await convex.mutation(syncApi.submitSnapshot, {
        id,
        version: initialState.initialVersion,
        content: JSON.stringify(initialState.initialContent),
      });
    } else {
      // TODO: Handle deletion gracefully
      throw new Error("Syncing a document that doesn't exist server-side");
    }
  }
  const version = collab.getVersion(editor.state);
  if (serverVersion !== null && serverVersion > version) {
    log("Updating to server version", {
      id,
      version,
      serverVersion,
    });
    const steps = await convex.query(syncApi.getSteps, {
      id,
      version,
    });
    receiveSteps(
      editor,
      steps.steps.map((step) => Step.fromJSON(editor.schema, JSON.parse(step))),
      steps.clientIds
    );
  }
  let anyChanges = false;
  while (true) {
    const sendable = collab.sendableSteps(editor.state);
    if (!sendable) {
      break;
    }
    const steps = sendable.steps
      .slice(0, MAX_STEPS_SYNC)
      .map((step) => JSON.stringify(step.toJSON()));
    log("Sending steps", { steps, version: sendable.version });
    const result = await convex.mutation(syncApi.submitSteps, {
      id,
      steps,
      version: sendable.version,
      clientId: sendable.clientID,
    });
    if (result.status === "synced") {
      anyChanges = true;
      // We replay the steps locally to avoid refetching them.
      receiveSteps(
        editor,
        steps.map((step) => Step.fromJSON(editor.schema, JSON.parse(step))),
        steps.map(() => sendable.clientID)
      );
      log("Synced", {
        steps,
        version,
        newVersion: collab.getVersion(editor.state),
      });
      continue;
    }
    if (result.status === "needs-rebase") {
      receiveSteps(
        editor,
        result.steps.map((step) =>
          Step.fromJSON(editor.schema, JSON.parse(step))
        ),
        result.clientIds
      );
      log("Rebased", {
        steps,
        newVersion: collab.getVersion(editor.state),
      });
    }
  }
  return anyChanges;
}

function receiveSteps(
  editor: Editor,
  steps: Step[],
  clientIds: (string | number)[]
) {
  editor.view.dispatch(
    collab.receiveTransaction(editor.state, steps, clientIds, {
      mapSelectionBackward: true,
    })
  );
}

type InitialState = {
  initialContent: Content;
  initialVersion: number;
  restoredSteps?: object[];
};

export function useInitialState(
  syncApi: SyncApi,
  id: string,
  cacheKeyPrefix?: string
) {
  const [initial, setInitial] = useState<InitialState | undefined>(() =>
    getCachedState(id, cacheKeyPrefix)
  );
  let data = initial;
  const serverInitial = useQuery(
    syncApi.getSnapshot,
    initial ? "skip" : { id }
  );
  const [loading, setLoading] = useState(!initial);
  if (loading && serverInitial) {
    setLoading(false);
  }
  if (!initial && serverInitial && serverInitial.content !== null) {
    data = {
      initialContent: JSON.parse(serverInitial.content) as Content,
      initialVersion: serverInitial.version,
    };
    setInitial(data);
  }

  if (data) {
    return {
      loading: false,
      ...data,
    };
  }
  if (!loading) {
    // We couldn't find it locally or on the server.
    // We could dynamically create a new document here,
    // not sure if that's generally the right pattern (vs. explicit creation).
    return {
      loading: false,
      initialContent: null,
    };
  }
  return {
    loading: true,
  };
}

function getCachedState(
  id: string,
  cacheKeyPrefix?: string
): InitialState | undefined {
  // TODO: Verify that this works
  const cacheKey = `${cacheKeyPrefix ?? "convex-sync"}-${id}`;
  const cache = sessionStorage.getItem(cacheKey);
  if (cache) {
    const { content, version, steps } = JSON.parse(cache);
    return {
      initialContent: content as Content,
      initialVersion: Number(version),
      restoredSteps: (steps ?? []) as object[],
    };
  }
}