signalstats/src/lib/db-cache.ts

import { deserialize, serialize } from "seroval";
import { createEffect, createMemo, createRoot, on } from "solid-js";
import { dbHash } from "~/db";
import { hashString } from "./hash";

export const DATABASE_HASH_PREFIX = "database";

// clear the cache on new session so that selecting a different database does not result in wrong cache entries
const clearDbCache = () => {
  for (let i = 0, len = localStorage.length; i < len; i++) {
    const key = localStorage.key(i);

    if (key?.startsWith(DATABASE_HASH_PREFIX)) {
      localStorage.removeItem(key);
    }
  }
};

let prevDbHash = dbHash();

createRoot(() => {
  createEffect(() => {
    on(
      dbHash,
      (currentDbHash) => {
        if (currentDbHash && currentDbHash !== prevDbHash) {
          prevDbHash = currentDbHash;
          clearDbCache();
        }
      },
      {
        defer: true,
      },
    );
  });
});

class LocalStorageCacheAdapter {
  keys = new Set<string>(
    Object.keys(localStorage).filter((key) => key.startsWith(this.prefix)),
  );
  prefix = "database";
  // TODO: real way of detecting if the db is loaded, on loading the db and opfs (if persisted db?)
  #dbLoaded = createMemo(() => !!dbHash());

  #createKey(cacheName: string, key: string): string {
    return `${this.prefix}-${cacheName}-${key}`;
  }

  set(cacheName: string, key: string, value: unknown) {
    const fullKey = this.#createKey(cacheName, key);
    this.keys.add(fullKey);

    try {
      localStorage.setItem(fullKey, serialize(value));
    } catch (error: unknown) {
      if (
        error instanceof DOMException &&
        error.name === "QUOTA_EXCEEDED_ERR"
      ) {
        console.error("Storage quota exceeded, not caching new function calls");
      } else {
        console.error(error);
      }
    }
  }

  has(cacheName: string, key: string): boolean {
    if (this.#dbLoaded()) {
      return this.keys.has(this.#createKey(cacheName, key));
    }

    console.info("No database loaded");

    return false;
  }

  get<R>(cacheName: string, key: string): R | undefined {
    if (this.#dbLoaded()) {
      const item = localStorage.getItem(this.#createKey(cacheName, key));

      if (item) {
        return deserialize(item) as R;
      }
    } else {
      console.info("No database loaded");
    }
  }
}

const cache = new LocalStorageCacheAdapter();

const createHashKey = (...args: unknown[]) => {
  let stringToHash = "";

  for (const arg of args) {
    switch (typeof arg) {
      case "string":
        stringToHash += arg;
        break;
      case "number":
      case "bigint":
      case "symbol":
      case "function":
        stringToHash += arg.toString();
        break;
      case "boolean":
      case "undefined":
        stringToHash += String(arg);
        break;
      case "object":
        stringToHash += JSON.stringify(arg);
        break;
    }
  }

  return hashString(stringToHash);
};

export const cached = <T extends unknown[], R, TT>(
  fn: (...args: T) => R,
  self?: ThisType<TT>,
): ((...args: T) => R) => {
  const cacheName = hashString(fn.toString()).toString();

  // important to return a promise on follow-up calls even if the data is immediately available
  let isPromise: boolean;

  return (...args: T) => {
    const cacheKey = createHashKey(...args).toString();

    const cachedValue = cache.get<R>(cacheName, cacheKey);

    if (cachedValue) {
      return (isPromise ? Promise.resolve(cachedValue) : cachedValue) as R;
    }

    let newValue: R;

    if (self) {
      newValue = fn.apply(self, args);
    } else {
      newValue = fn(...args);
    }

    const promisified = Promise.resolve(newValue);

    isPromise = promisified == newValue;

    void promisified.then((result) => {
      if (result !== undefined) {
        cache.set(cacheName, cacheKey, result);
      }
    });

    return newValue;
  };
};