# Author: Simon-Pierre Boucher
# Mail: contact@spboucher.ai
"""Hand-rolled ERC-20 event decoding — no ABI library.

An ERC-20 transfer is a contract call emitting:
    Transfer(address indexed from, address indexed to, uint256 value)

In the log:
    topics[0] = keccak256("Transfer(address,address,uint256)")
    topics[1] = from, left-padded to 32 bytes (indexed params live in topics)
    topics[2] = to,   left-padded to 32 bytes
    data      = value as one 32-byte big-endian word (non-indexed)
"""

from decimal import Decimal

TRANSFER_TOPIC = (
    "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"
)


def topic_address(topic):
    """A 32-byte topic holding an address: the address is the last 20 bytes."""
    return "0x" + topic[-40:].lower()


def word_uint(hexdata):
    if hexdata in (None, "0x", ""):
        return 0
    return int(hexdata, 16)


def format_amount(raw, decimals):
    """Human-readable amount from raw integer units (raw may be str or int)."""
    q = Decimal(int(raw)) / (Decimal(10) ** decimals)
    return format(q.normalize(), "f")


def decode_transfer(chain, log, token_meta, timestamp):
    """Normalize one raw Transfer log into the canonical cross-chain event."""
    return {
        "chain": chain,
        "block": int(log["blockNumber"], 16),
        "block_hash": (log.get("blockHash") or "").lower() or None,
        "tx_hash": log["transactionHash"].lower(),
        "log_index": int(log["logIndex"], 16),
        "timestamp": timestamp,
        "token": log["address"].lower(),
        "symbol": token_meta["symbol"],
        "from": topic_address(log["topics"][1]),
        "to": topic_address(log["topics"][2]),
        # uint256 overflows SQLite's int64 — store raw units as TEXT
        "amount": str(word_uint(log["data"])),
        "decimals": token_meta["decimals"],
    }