Advertising is an $800 billion industry controlled by 3 companies.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract X402AdEngine {

    struct AdServe {
        address publisher;
        address advertiser;
        uint256 amount;
        bytes32 impressionHash;
        uint256 timestamp;
    }

    mapping(bytes32 => AdServe) public adReceipts;

    event AdServed(
        bytes32 indexed receiptId,
        address indexed publisher,
        address indexed advertiser,
        uint256 amount
    );

    function serveAd(
        address publisher,
        bytes32 impressionHash
    ) external payable returns (bytes32 receiptId) {
        receiptId = keccak256(
            abi.encodePacked(
                publisher,
                msg.sender,
                impressionHash,
                block.timestamp
            )
        );

        // Instant publisher payout
        payable(publisher).transfer(msg.value);

        // Cryptographic proof of display
        adReceipts[receiptId] = AdServe({
            publisher: publisher,
            advertiser: msg.sender,
            amount: msg.value,
            impressionHash: impressionHash,
            timestamp: block.timestamp
        });

        emit AdServed(receiptId, publisher, msg.sender, msg.value);
    }

    function verifyAdServe(bytes32 receiptId)
        external
        view
        returns (AdServe memory)
    {
        return adReceipts[receiptId];
    }
}