nsatoshi
fd575000fe
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113 lines
3.8 KiB
TypeScript
113 lines
3.8 KiB
TypeScript
/**
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* MT760 — Issue of a Demand Guarantee / Standby Letter of Credit
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* (arch §4.2 Banking Instrument Layer + §6 Instrument Terms Hash).
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*
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* SWIFT FIN message. This is the issuance leg of the two-phase
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* commit. Output is deterministic so the planHash anchored on-chain
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* can be reproduced by any party with access to the InstrumentTerms.
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*
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* Reference: SWIFT FIN Category 7 User Handbook, MT760 format;
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* Emirates Islamic Bank beneficiary-format SBLC template.
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*/
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import { createHash } from "crypto";
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import type { InstrumentTerms } from "../../types/plan";
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export interface Mt760Message {
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sender: string;
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receiver: string;
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messageReference: string;
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fin: string;
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fields: Record<string, string>;
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}
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function formatAmount(amount: number, currency: string): string {
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// SWIFT FIN amount: 3-letter currency + 15n,2d (max), decimal comma.
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if (amount < 0) throw new Error("MT760: amount must be non-negative");
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return `${currency}${amount.toFixed(2).replace(".", ",")}`;
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}
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function yyMMdd(iso: string): string {
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// Accept YYYY-MM-DD and return YYMMDD.
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const m = /^(\d{4})-(\d{2})-(\d{2})$/.exec(iso);
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if (!m) throw new Error(`MT760: expiryDate must be YYYY-MM-DD, got '${iso}'`);
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return `${m[1].slice(2)}${m[2]}${m[3]}`;
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}
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/**
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* Render an MT760 from an InstrumentTerms record. Uses the
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* block-structured FIN format (Block 1/2/4/5). Tag codes:
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*
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* :20: Transaction reference number
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* :23: Further identification
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* :27: Sequence of total (here: 1/1)
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* :30: Date of issue
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* :40C: Applicable rules (URDG 758, UCP 600)
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* :31D: Date and place of expiry
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* :50: Applicant
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* :52A: Issuing bank (BIC)
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* :59: Beneficiary name + account
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* :32B: Amount
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* :77C: Details of guarantee
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* :72Z: Sender to receiver info
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*/
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export function generateMt760(
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terms: InstrumentTerms,
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opts: { transactionReference: string; issueDate: string },
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): Mt760Message {
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const sender = terms.issuingBankBIC;
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const receiver = terms.beneficiaryBankBIC;
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const field32B = formatAmount(terms.amount, terms.currency);
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const field31D = `${yyMMdd(terms.expiryDate)}${terms.placeOfPresentation.toUpperCase()}`;
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const fields: Record<string, string> = {
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"20": opts.transactionReference,
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"23": "ISSUE OF STANDBY LETTER OF CREDIT",
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"27": "1/1",
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"30": yyMMdd(opts.issueDate),
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"40C": terms.governingLaw,
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"31D": field31D,
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"50": terms.applicant,
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"52A": terms.issuingBankBIC,
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"59": [terms.beneficiaryName, terms.beneficiaryAccount].filter(Boolean).join("\n"),
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"32B": field32B,
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"77C": [
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`TEMPLATE/${terms.templateRef}`,
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`TEMPLATE_HASH/${terms.templateHash}`,
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`TENOR/${terms.tenor}`,
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].join("\n"),
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"72Z": `GOVLAW/${terms.governingLaw}`,
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};
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// Build FIN block 4 body with :tag:value sequences.
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const block4 = Object.entries(fields)
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.map(([tag, value]) => `:${tag}:${value}`)
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.join("\n");
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const block1 = `{1:F01${sender.padEnd(12, "X")}0000000000}`;
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const block2 = `{2:I760${receiver.padEnd(12, "X")}N}`;
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const block4Wrapped = `{4:\n${block4}\n-}`;
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const block5 = `{5:{CHK:${checksum(block4)}}}`;
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const fin = `${block1}${block2}${block4Wrapped}${block5}`;
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return { sender, receiver, messageReference: opts.transactionReference, fin, fields };
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}
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/**
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* Deterministic SHA-256 over the canonical field list. Matches
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* InstrumentTerms.templateHash when all 11 required fields are filled
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* in with the SBLC template values.
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*/
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export function messageHash(msg: Mt760Message): string {
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const canonical = Object.entries(msg.fields)
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.sort(([a], [b]) => a.localeCompare(b))
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.map(([k, v]) => `${k}=${v}`)
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.join("\n");
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return createHash("sha256").update(canonical).digest("hex");
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}
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function checksum(block4Body: string): string {
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return createHash("sha256").update(block4Body).digest("hex").slice(0, 12).toUpperCase();
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}
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