Vue Render Context Implementation Challenge

Vue's render context is a fundamental concept that allows components to share data and functionality in a hierarchical manner. This challenge focuses on implementing a simplified version of this mechanism in TypeScript, enabling parent components to pass down information and child components to access it. Mastering render context is crucial for building reusable and maintainable Vue applications.

Problem Description

Your task is to implement a system that simulates Vue's render context mechanism. This involves creating a way for a parent component to provide data and functions that can be accessed by its descendant components, without explicitly passing props down through every intermediate component.

Key Requirements:

1. provide Functionality: A mechanism to "provide" a value (data or a function) from a parent component.
2. inject Functionality: A mechanism to "inject" or retrieve a provided value in a descendant component.
3. Hierarchical Access: Injected values should be accessible by any descendant component that calls inject with the correct key.
4. Scope: Provided values should be scoped to the component that provided them and its descendants.
5. TypeScript Support: The implementation must be written in TypeScript, leveraging its type safety features.

Expected Behavior:

• A component can call provide('key', value) to make value available under key.
• A descendant component can call inject('key') to retrieve the value that was provided by the nearest ancestor (or itself).
• If inject('key') is called and no ancestor has provided a value for key, it should return undefined (or a default value if specified, though this is not a primary requirement for this challenge).
• Updates to provided values should not automatically trigger re-renders in the injecting components without explicit mechanisms (similar to how Vue's context works; we're focusing on the provision/injection mechanism itself).

Edge Cases:

• Injecting a key that has not been provided by any ancestor.
• Multiple components providing the same key at different levels. The closest ancestor's value should be prioritized.

Examples

Example 1:

Consider a ParentComponent that provides a user's name, and a ChildComponent that injects and displays it.

// Assume a global context object or a similar mechanism to manage context
class ContextManager {
  private contextStack: Map<string, any>[] = [];

  provide(key: string, value: any): void {
    const currentContext = this.contextStack[this.contextStack.length - 1] || new Map();
    currentContext.set(key, value);
    if (this.contextStack.length === 0) {
      this.contextStack.push(currentContext);
    }
  }

  inject<T>(key: string): T | undefined {
    for (let i = this.contextStack.length - 1; i >= 0; i--) {
      const context = this.contextStack[i];
      if (context.has(key)) {
        return context.get(key) as T;
      }
    }
    return undefined;
  }

  enterComponent(): void {
    this.contextStack.push(new Map());
  }

  exitComponent(): void {
    this.contextStack.pop();
  }
}

// --- Simulated Component Structure ---

// Mock ParentComponent
function ParentComponent(this: any, props: { children: any[] }) {
  const contextManager = new ContextManager(); // Simplified for example

  this.name = "Alice";
  contextManager.enterComponent();
  contextManager.provide('userName', this.name);

  // Simulate rendering children
  let renderedOutput = `Parent: ${this.name}\n`;
  for (const child of props.children) {
    renderedOutput += child.render(); // Assume child has a render method
  }

  contextManager.exitComponent();
  return renderedOutput;
}

// Mock ChildComponent
function ChildComponent(this: any) {
  this.render = function() {
    const userName = contextManager.inject<string>('userName'); // Assuming contextManager is accessible
    return `  Child: Hello, ${userName}!\n`;
  };
  return this;
}

// --- Execution ---
const contextManager = new ContextManager(); // Global or passed instance

const parentInstance = new (ParentComponent as any)({
  children: [
    new (ChildComponent as any)()
  ]
});

console.log(parentInstance); // This would be a simplified representation of rendering

Input:

A nested component structure where ParentComponent provides 'userName' and ChildComponent injects it.

Output:

Parent: Alice
  Child: Hello, Alice!

Explanation:

ParentComponent provides 'userName' with the value 'Alice'. ChildComponent then successfully injects this value and uses it in its rendering.

Example 2:

Demonstrating overriding a provided value by a closer ancestor.

// Using the same ContextManager as above

// Mock GrandparentComponent
function GrandparentComponent(this: any, props: { children: any[] }) {
  this.value = "Grandparent";
  contextManager.enterComponent();
  contextManager.provide('sharedValue', this.value);

  let renderedOutput = `Grandparent: ${this.value}\n`;
  for (const child of props.children) {
    renderedOutput += child.render();
  }
  contextManager.exitComponent();
  return renderedOutput;
}

// Mock ParentComponent (within Grandparent)
function ParentComponentInner(this: any, props: { children: any[] }) {
  this.value = "Parent";
  contextManager.enterComponent();
  contextManager.provide('sharedValue', this.value); // Overrides grandparent's

  let renderedOutput = `  Parent: ${this.value}\n`;
  for (const child of props.children) {
    renderedOutput += child.render();
  }
  contextManager.exitComponent();
  return renderedOutput;
}

// Mock ChildComponent (within ParentInner)
function ChildComponentInner(this: any) {
  this.render = function() {
    const sharedValue = contextManager.inject<string>('sharedValue');
    return `    Child: Value is ${sharedValue}!\n`;
  };
  return this;
}

// --- Execution ---
const contextManager = new ContextManager(); // Global or passed instance

const grandparentInstance = new (GrandparentComponent as any)({
  children: [
    new (ParentComponentInner as any)({
      children: [
        new (ChildComponentInner as any)()
      ]
    })
  ]
});

console.log(grandparentInstance);

Input:

A tree of components: Grandparent -> ParentInner -> ChildInner. Both Grandparent and ParentInner provide a value for 'sharedValue'.

Output:

Grandparent: Grandparent
  Parent: Parent
    Child: Value is Parent!

Explanation:

Grandparent provides 'sharedValue' as "Grandparent". ParentInner also provides 'sharedValue' as "Parent". ChildInner, being a descendant of both, injects the value provided by its closest ancestor that provided it, which is ParentInner's "Parent".

Example 3: Injecting a non-existent key

// Using the same ContextManager as above

// Mock RootComponent
function RootComponent(this: any, props: { children: any[] }) {
  contextManager.enterComponent();
  // No provide calls here

  let renderedOutput = "Root:\n";
  for (const child of props.children) {
    renderedOutput += child.render();
  }
  contextManager.exitComponent();
  return renderedOutput;
}

// Mock LeafComponent
function LeafComponent(this: any) {
  this.render = function() {
    const nonExistentValue = contextManager.inject<number>('someNumber');
    return `  Leaf: Trying to inject someNumber: ${nonExistentValue}\n`;
  };
  return this;
}

// --- Execution ---
const contextManager = new ContextManager(); // Global or passed instance

const rootInstance = new (RootComponent as any)({
  children: [
    new (LeafComponent as any)()
  ]
});

console.log(rootInstance);

Input:

A RootComponent that does not provide any keys, and a LeafComponent that attempts to inject a non-existent key 'someNumber'.

Output:

Root:
  Leaf: Trying to inject someNumber: undefined

Explanation:

Since no ancestor component (including RootComponent and LeafComponent itself) has provided a value for 'someNumber', inject returns undefined.

Constraints

• The core logic for provide and inject should be implementable within a class or a set of functions that manage the context.
• The solution must be written in TypeScript.
• Focus on the mechanism of providing and injecting; no need to implement a full Vue component lifecycle or reactivity system.
• The context management should handle nested component structures correctly.

Notes

• Think about how Vue manages its context internally. It uses a context instance that is passed down the component tree. You'll need a similar mechanism to maintain the "current" context.
• Consider how to handle type safety when providing and injecting values. Using generics in your inject function will be beneficial.
• The examples use simplified mock components for demonstration. Your implementation should focus on the provide and inject functions and the underlying context management. You can assume a way to simulate component nesting and traversal for testing your solution.
• This challenge is about understanding and implementing the mechanism of context, not replicating Vue's entire rendering or reactivity pipeline.