Resourceとキャッシュを一緒に考えたい

index.tsx

import React, { Suspense, useState, useCallback, ChangeEvent } from "react";
import ReactDOM from "react-dom";
import { createService } from "./Service";

interface User {
  id: number;
  name: string;
}

let count = 0;
function fetchUser(id: User["id"]): Promise<User> {
  return new Promise((resolve) =>
    setTimeout(() => resolve({ id, name: `user ${id} ${++count}` }), 3000)
  );
}

const UserService = createService(fetchUser);

const UserComponent: React.FC<{ id: number }> = ({ id }) => {
  const user = UserService.useResource(id).read();
  return (
    <pre>
      <code>{JSON.stringify(user, null, 2)}</code>
    </pre>
  );
};

const Wrapper: React.FC<{ defaultId: number }> = ({ defaultId }) => {
  const [id, setId] = useState(defaultId);
  const [tmpId, setTmpId] = useState(id);
  const handleChange = useCallback(
    (event: ChangeEvent<HTMLInputElement>) =>
      setTmpId(event.target.valueAsNumber),
    [setTmpId]
  );
  const applyChange = useCallback(() => setId(tmpId), [setId, tmpId]);
  const buster = UserService.useCacheBuster(id);
  return (
    <div>
      <input type="number" onChange={handleChange} value={tmpId}></input>
      <button type="button" onClick={applyChange}>
        apply
      </button>
      <button type="button" onClick={buster}>
        cache busting for {id}
      </button>
      <Suspense fallback={<div>loading...</div>}>
        <UserComponent id={id} />
      </Suspense>
    </div>
  );
};

const Root = () => {
  return (
    <UserService.VersionProvider>
      <div>
        <Wrapper defaultId={0} />
        <Wrapper defaultId={100} />
      </div>
    </UserService.VersionProvider>
  );
};

const rootEl = document.createElement("div");
rootEl.id = "root";
document.body.appendChild(rootEl);
// @ts-ignore
ReactDOM.createRoot(document.getElementById("root")!).render(<Root />);

Resource.ts

// https://gist.github.com/fsubal/b1ab80acb82763c28a3d92ed8f2010af
type Status = "pending" | "success" | "error";

export default class Resource<T> {
  static from<T>(promise: Promise<T>): Resource<T> {
    return new this(promise);
  }

  private status: Status;

  private result: T | undefined;

  private suspender: Promise<void>;

  private constructor(promise: Promise<T>) {
    this.status = "pending";
    this.suspender = promise.then(
      (r) => {
        this.status = "success";
        this.result = r;
      },
      (e) => {
        this.status = "error";
        this.result = e;
      }
    );
  }

  read(): T {
    switch (this.status) {
      case "pending": {
        throw this.suspender;
      }

      case "error": {
        throw this.result;
      }

      case "success": {
        return this.result!;
      }

      default: {
        throw new RangeError(
          `invariant status: ${JSON.stringify(this.status)}`
        );
      }
    }
  }
}

Service.ts

import React, {
  createContext,
  useContext,
  useReducer,
  useCallback,
  createElement,
} from "react";
import Resource from "./Resource";

interface Service<T, K> {
  VersionProvider: React.FC;
  useCacheBuster(id: K): () => void;
  useResource(id: K): Resource<T>;
}

export function createService<T, K>(
  fetcher: (key: K) => Promise<T>
): Service<T, K> {
  const VersionContext = createContext({
    version: 0,
    updateVersion: () => {},
  });
  const resourceMap = new Map<K, Resource<T>>();
  function clearCache(key: K): void {
    resourceMap.delete(key);
  }

  return {
    VersionProvider: ((props) => {
      const [version, updateVersion] = useReducer((v) => v + 1, 0);
      const value = { version, updateVersion };
      return createElement(VersionContext.Provider, {
        value,
        ...props,
      });
    }) as React.FC,

    useCacheBuster(key: K): () => void {
      const { updateVersion } = useContext(VersionContext);
      return useCallback((): void => {
        clearCache(key);
        updateVersion();
      }, [key, updateVersion]);
    },

    useResource(key: K): Resource<T> {
      // re-render on version update
      const _ignore = useContext(VersionContext);
      if (resourceMap.has(key)) {
        return resourceMap.get(key)!;
      }

      const resource = Resource.from(fetcher(key));
      resourceMap.set(key, resource);
      return resource;
    },
  };
}

参考文献このあたり（Resourceは丸々持ってきてる）
https://qiita.com/uhyo/items/4a6315bfccf387407631
https://gist.github.com/fsubal/b1ab80acb82763c28a3d92ed8f2010af

真面目に条件付きリクエストする方が得なのではないか