trainsim/lib/context.ts

type ContextStore = Record<string, any>;

const defaultContext: ContextStore = {};
const contextStack: ContextStore[] = [defaultContext];

const debug = JSON.parse(localStorage.getItem("debug") || "false");

export function setDefaultContext(context: ContextStore) {
  Object.assign(defaultContext, context);
}

export function withContext<T>(context: ContextStore, fn: () => T): T {
  contextStack.push(context);
  try {
    return fn();
  } finally {
    contextStack.pop();
  }
}

export const ctx = new Proxy(
  {},
  {
    get(_, prop: string) {
      for (let i = contextStack.length - 1; i >= 0; i--) {
        if (prop in contextStack[i]) return contextStack[i][prop];
      }
      if (prop in defaultContext) return defaultContext[prop];
      throw new Error(`Context variable '${prop}' is not defined.`);
    },
  },
) as Record<string, unknown>;

export function getContext() {
  return ctx;
}
export function getContextItem<T>(prop: string): T {
  return ctx[prop] as T;
}
export function getContextItemOrDefault<T>(prop: string, defaultValue: T): T {
  try {
    return ctx[prop] as T;
  } catch {
    return defaultValue;
  }
}
export function setContextItem<T>(prop: string, value: T) {
  Object.assign(contextStack[contextStack.length - 1] ?? defaultContext, {
    [prop]: value,
  });
}

if (debug) {
  setInterval(() => {
    let ctxEl = document.getElementById("context");
    if (!ctxEl) {
      ctxEl = document.createElement("div");
      ctxEl.id = "context";
      document.body.append(ctxEl);
    }
    ctxEl.innerHTML = "";
    const div = document.createElement("div");
    const pre = document.createElement("pre");
    const h3 = document.createElement("h3");
    h3.textContent = "Default";
    div.append(h3);
    pre.textContent = safeStringify(defaultContext);
    div.append(pre);
    ctxEl.append(div);
    for (const [idx, ctx] of contextStack.entries()) {
      const div = document.createElement("div");
      const pre = document.createElement("pre");
      const h3 = document.createElement("h3");
      h3.textContent = "CTX " + idx;
      div.append(h3);
      pre.textContent = safeStringify(ctx);
      div.append(pre);
      ctxEl.append(div);
    }
  }, 1000);
}

function safeStringify(obj: any) {
  const seen = new WeakSet();
  return JSON.stringify(obj, (key, value) => {
    if (typeof value === "object" && value !== null) {
      if (seen.has(value)) {
        return "[Circular]"; // Replace circular references
      }
      seen.add(value);
    }
    return value;
  }, 2);
}