// Minimal protobuf wire decoder for Tron's `Transaction.raw` — what a dapp
// hands us as `raw_data_hex`. The approval overlay MUST be built from these
// bytes (the thing that actually gets signed), never from the dapp's
// `raw_data` JSON, which can say anything.
//
// Field numbers from protocol/core/Tron.proto:
//   Transaction.raw: 1 ref_block_bytes, 3 ref_block_num, 4 ref_block_hash,
//     8 expiration, 9 auths, 10 data, 11 contract (repeated), 12 scripts,
//     14 timestamp, 18 fee_limit
//   Transaction.Contract: 1 type (enum), 2 parameter (google.protobuf.Any),
//     3 provider, 4 ContractName, 5 Permission_id
//   Any: 1 type_url (string), 2 value (bytes)
//   TransferContract: 1 owner_address, 2 to_address, 3 amount
//   TransferAssetContract: 1 asset_name, 2 owner_address, 3 to_address, 4 amount
//   TriggerSmartContract: 1 owner_address, 2 contract_address, 3 call_value,
//     4 data, 5 call_token_value, 6 token_id
//   Every other contract type puts owner_address in field 1.

const CONTRACT_TYPES = {
  0: "AccountCreateContract", 1: "TransferContract", 2: "TransferAssetContract",
  3: "VoteAssetContract", 4: "VoteWitnessContract", 5: "WitnessCreateContract",
  6: "AssetIssueContract", 8: "WitnessUpdateContract", 9: "ParticipateAssetIssueContract",
  10: "AccountUpdateContract", 11: "FreezeBalanceContract", 12: "UnfreezeBalanceContract",
  13: "WithdrawBalanceContract", 14: "UnfreezeAssetContract", 15: "UpdateAssetContract",
  16: "ProposalCreateContract", 17: "ProposalApproveContract", 18: "ProposalDeleteContract",
  19: "SetAccountIdContract", 20: "CustomContract", 30: "CreateSmartContract",
  31: "TriggerSmartContract", 33: "UpdateSettingContract", 41: "ExchangeCreateContract",
  42: "ExchangeInjectContract", 43: "ExchangeWithdrawContract", 44: "ExchangeTransactionContract",
  45: "UpdateEnergyLimitContract", 46: "AccountPermissionUpdateContract", 48: "ClearABIContract",
  49: "UpdateBrokerageContract", 51: "ShieldedTransferContract", 52: "MarketSellAssetContract",
  53: "MarketCancelOrderContract", 54: "FreezeBalanceV2Contract", 55: "UnfreezeBalanceV2Contract",
  56: "WithdrawExpireUnfreezeContract", 57: "DelegateResourceContract",
  58: "UnDelegateResourceContract", 59: "CancelAllUnfreezeV2Contract",
};
// Contract types that hand control of the account or its resources to a
// third party — the overlay stresses these.
const DANGEROUS_TYPES = new Set([46, 57]);

const TRC20_SELECTORS = {
  a9059cbb: { name: "transfer", args: ["to", "amount"] },
  "095ea7b3": { name: "approve", args: ["spender", "amount"] },
  "23b872dd": { name: "transferFrom", args: ["from", "to", "amount"] },
  "39509351": { name: "increaseAllowance", args: ["spender", "amount"] },
};
const UINT256_MAX = (1n << 256n) - 1n;

module.exports = function makeTronDecode({ sha256, base58check }) {
  const hexToBytes = (h) => {
    const s = String(h || "").replace(/^0x/i, "");
    if (!/^[0-9a-f]*$/i.test(s) || s.length % 2) throw new Error("raw_data_hex is not hex");
    const out = new Uint8Array(s.length / 2);
    for (let i = 0; i < out.length; i++) out[i] = parseInt(s.slice(i * 2, i * 2 + 2), 16);
    return out;
  };
  const bytesToHex = (b) => Array.from(b, (x) => x.toString(16).padStart(2, "0")).join("");

  // Split a message into { field, wire, value } records. Varints come back
  // as BigInt, length-delimited fields as Uint8Array views.
  function readFields(bytes) {
    const out = [];
    let off = 0;
    const varint = () => {
      let v = 0n, shift = 0n;
      for (;;) {
        if (off >= bytes.length) throw new Error("truncated varint");
        const b = bytes[off++];
        v |= BigInt(b & 0x7f) << shift;
        if ((b & 0x80) === 0) return v;
        shift += 7n;
        if (shift > 70n) throw new Error("varint too long");
      }
    };
    while (off < bytes.length) {
      const key = varint();
      const field = Number(key >> 3n), wire = Number(key & 7n);
      if (wire === 0) out.push({ field, wire, value: varint() });
      else if (wire === 1) { if (off + 8 > bytes.length) throw new Error("truncated fixed64"); out.push({ field, wire, value: bytes.subarray(off, off + 8) }); off += 8; }
      else if (wire === 2) { const n = Number(varint()); if (off + n > bytes.length) throw new Error("truncated bytes"); out.push({ field, wire, value: bytes.subarray(off, off + n) }); off += n; }
      else if (wire === 5) { if (off + 4 > bytes.length) throw new Error("truncated fixed32"); out.push({ field, wire, value: bytes.subarray(off, off + 4) }); off += 4; }
      else throw new Error("unsupported wire type " + wire);
    }
    return out;
  }
  const one = (fields, n) => fields.find((f) => f.field === n);
  const bytesOf = (fields, n) => { const f = one(fields, n); return f && f.wire === 2 ? f.value : null; };
  const numOf = (fields, n) => { const f = one(fields, n); return f && f.wire === 0 ? f.value : null; };

  // 21-byte Tron address (0x41 || h20) → "T…" base58check. Anything else is
  // returned as hex so the overlay never hides a malformed field.
  function addr(b) {
    if (!b) return null;
    if (b.length === 21 && b[0] === 0x41) { try { return base58check.encodeCheck(b); } catch {} }
    return "0x" + bytesToHex(b);
  }
  // EVM-style 32-byte word → Tron address (last 20 bytes, 0x41 prefix).
  function wordToAddr(word) {
    const out = new Uint8Array(21); out[0] = 0x41; out.set(word.subarray(12, 32), 1);
    return addr(out);
  }
  const wordToBig = (word) => { let v = 0n; for (const x of word) v = (v << 8n) | BigInt(x); return v; };

  function decodeTrc20(data) {
    if (!data || data.length < 4) return null;
    const sel = bytesToHex(data.subarray(0, 4));
    const spec = TRC20_SELECTORS[sel];
    if (!spec) return { selector: sel, name: null };
    const words = [];
    for (let i = 4; i + 32 <= data.length; i += 32) words.push(data.subarray(i, i + 32));
    if (words.length < spec.args.length) return { selector: sel, name: spec.name, malformed: true };
    const out = { selector: sel, name: spec.name };
    spec.args.forEach((a, i) => { out[a] = a === "amount" ? wordToBig(words[i]) : wordToAddr(words[i]); });
    if (out.amount != null) out.unlimited = out.amount >= (1n << 255n) || out.amount === UINT256_MAX;
    return out;
  }

  function decodeContract(fields) {
    const typeNum = Number(numOf(fields, 1) ?? 0n);
    const typeName = CONTRACT_TYPES[typeNum] || `Contract#${typeNum}`;
    const any = bytesOf(fields, 2);
    const c = { type: typeNum, typeName, dangerous: DANGEROUS_TYPES.has(typeNum), owner: null, permissionId: Number(numOf(fields, 5) ?? 0n) };
    if (!any) return c;
    const anyFields = readFields(any);
    const value = bytesOf(anyFields, 2);
    if (!value) return c;
    const vf = readFields(value);
    if (typeNum === 1) {                                   // TransferContract
      c.owner = addr(bytesOf(vf, 1)); c.to = addr(bytesOf(vf, 2)); c.amount = numOf(vf, 3) ?? 0n;
    } else if (typeNum === 2) {                            // TransferAssetContract
      const name = bytesOf(vf, 1);
      c.assetName = name ? Buffer.from(name).toString("utf8") : null;
      c.owner = addr(bytesOf(vf, 2)); c.to = addr(bytesOf(vf, 3)); c.amount = numOf(vf, 4) ?? 0n;
    } else if (typeNum === 31) {                           // TriggerSmartContract
      c.owner = addr(bytesOf(vf, 1)); c.contract = addr(bytesOf(vf, 2));
      c.callValue = numOf(vf, 3) ?? 0n;
      const data = bytesOf(vf, 4);
      c.data = data ? bytesToHex(data) : "";
      c.call = decodeTrc20(data);
    } else {
      c.owner = addr(bytesOf(vf, 1));
    }
    return c;
  }

  // Full decode. Throws on malformed input so the caller refuses to sign.
  function decodeRawData(rawDataHex) {
    const bytes = hexToBytes(rawDataHex);
    if (!bytes.length) throw new Error("raw_data_hex is empty");
    const fields = readFields(bytes);
    const contracts = fields.filter((f) => f.field === 11 && f.wire === 2).map((f) => decodeContract(readFields(f.value)));
    if (!contracts.length) throw new Error("raw_data_hex carries no contract");
    const memo = bytesOf(fields, 10);
    return {
      txid: bytesToHex(sha256(bytes)),
      contracts,
      expiration: Number(numOf(fields, 8) ?? 0n),
      timestamp: Number(numOf(fields, 14) ?? 0n),
      feeLimit: numOf(fields, 18) ?? null,
      memo: memo ? Buffer.from(memo).toString("utf8") : null,
    };
  }

  return { decodeRawData, decodeTrc20, readFields, CONTRACT_TYPES };
};