Method accessed

packages/service-worker/worker/src/data.ts:168–215

(url: string)

  }

  accessed(url: string): void {
    // When a URL is accessed, its node needs to be moved to the head of the chain.
    // This is accomplished in two steps:
    //
    // 1) remove the node from its position within the chain.
    // 2) insert the node as the new head.
    //
    // Sometimes, a URL is accessed which has not been seen before. In this case, step 1 can
    // be skipped completely (which will grow the chain by one). Of course, if the node is
    // already the head, this whole operation can be skipped.
    if (this.state.head === url) {
      // The URL is already in the head position, accessing it is a no-op.
      return;
    }

    // Look up the node in the map, and construct a new entry if it's
    const node = this.state.map[url] || {url, next: null, previous: null};

    // Step 1: remove the node from its position within the chain, if it is in the chain.
    if (this.state.map[url] !== undefined) {
      this.remove(url);
    }

    // Step 2: insert the node at the head of the chain.

    // First, check if there's an existing head node. If there is, it has previous: null.
    // Its previous pointer should be set to the node we're inserting.
    if (this.state.head !== null) {
      this.state.map[this.state.head]!.previous = url;
    }

    // The next pointer of the node being inserted gets set to the old head, before the head
    // pointer is updated to this node.
    node.next = this.state.head;

    // The new head is the new node.
    this.state.head = url;

    // If there is no tail, then this is the first node, and is both the head and the tail.
    if (this.state.tail === null) {
      this.state.tail = url;
    }

    // Set the node in the map of nodes (if the URL has been seen before, this is a no-op)
    // and count the insertion.
    this.state.map[url] = node;
    this.state.count++;
  }
}

/**