{
  "id": "contract_payable_fallback",
  "version": "2.0.0",
  "category": "advanced_features",
  "subcategory": "fallback",
  "difficulty": "medium",
  "title": "Payable Fallback - Send BNB to Contract",
  "natural_language_templates": [
    "Send {amount} BNB to the contract at {contract_address}",
    "Transfer {amount} BNB to contract {contract_address} without calling any function",
    "I want to send {amount} BNB directly to {contract_address}",
    "Send {amount} BNB to {contract_address} (no function call)"
  ],
  "description": [
    "Send BNB directly to a contract without calling any specific function.",
    "This will trigger the contract's receive() or fallback() function.",
    "",
    "Technical context:",
    "- When you send BNB to a contract without calldata, it triggers receive() if it exists",
    "- If receive() doesn't exist, it triggers fallback() if it's payable",
    "- The transaction 'to' field is the contract address",
    "- The 'value' field contains the BNB amount to send",
    "- The 'data' field should be empty (0x) or omitted",
    "- Recommended gas limit: 100000",
    "",
    "Fallback vs Receive:",
    "- receive() external payable: Called when BNB is sent with empty calldata",
    "- fallback() external payable: Called when function doesn't exist or as fallback for receive()",
    "- At least one must be payable for the contract to receive BNB",
    "",
    "Key considerations:",
    "- Do NOT include any function call data",
    "- Set transaction 'value' to the BNB amount (in wei)",
    "- Leave 'data' field empty or set to '0x'",
    "- The contract must have a payable receive() or fallback() function",
    "",
    "Success criteria:",
    "- Transaction executes successfully",
    "- Correct contract address is used",
    "- Correct BNB amount is sent",
    "- No function call data (empty data field)",
    "- Contract balance increases by the sent amount"
  ],
  "blockchain": {
    "chain": "BSC",
    "network": "mainnet"
  },
  "parameters": {
    "contract_address": {
      "type": "address",
      "role": "contract",
      "description": "Contract address with payable fallback/receive",
      "generation": {
        "method": "from_env",
        "env_key": "fallback_receiver_address",
        "comment": "Use dynamically deployed FallbackReceiver contract from environment"
      }
    },
    "amount": {
      "type": "number",
      "unit": "BNB",
      "description": "Amount of BNB to send",
      "generation": {
        "method": "random",
        "min": 0.001,
        "max": 0.05,
        "decimals": 4
      },
      "role": "transfer_amount"
    }
  },
  "validation": {
    "pre_conditions": [
      {
        "type": "contract_exists",
        "description": "Contract must exist",
        "address": "{contract_address}"
      },
      {
        "type": "sufficient_balance",
        "description": "Agent must have sufficient BNB balance",
        "required": "{amount}"
      }
    ],
    "post_conditions": [
      {
        "type": "transaction_success",
        "weight": 0.3,
        "description": "Transaction executed successfully"
      },
      {
        "type": "contract_address",
        "weight": 0.2,
        "description": "Transaction sent to correct contract",
        "expected": "{contract_address}"
      },
      {
        "type": "value_sent",
        "weight": 0.2,
        "description": "Correct BNB amount sent",
        "expected": "{amount}"
      },
      {
        "type": "empty_data",
        "weight": 0.15,
        "description": "No function call data (empty or 0x)",
        "expected": "empty"
      },
      {
        "type": "balance_increase",
        "weight": 0.15,
        "description": "Contract balance increased by sent amount",
        "expected": "{amount}"
      }
    ]
  },
  "metadata": {
    "tags": [
      "fallback",
      "receive",
      "payable",
      "direct_transfer",
      "advanced"
    ],
    "estimated_gas": 100000,
    "requires_contract": true,
    "contract_requirements": {
      "contract_type": "FallbackReceiver",
      "required_functions": [
        "receive() or fallback()"
      ],
      "note": "Tests understanding of fallback/receive functions"
    },
    "educational_value": "Understanding fallback/receive is important for contract interactions and DeFi protocols"
  }
}