seedpgp-web/src/lib/seedpgp.ts

import * as openpgp from "openpgp";
import { base45Encode, base45Decode } from "./base45";
import { crc16CcittFalse } from "./crc16";
import type { SeedPgpPlaintext, ParsedSeedPgpFrame } from "./types";

function nonEmptyTrimmed(s?: string): string | undefined {
    if (!s) return undefined;
    const t = s.trim();
    return t.length ? t : undefined;
}

export function normalizeMnemonic(words: string): string {
    return words.trim().toLowerCase().replace(/\s+/g, " ");
}

export function buildPlaintext(
    mnemonic: string,
    bip39PassphraseUsed: boolean,
    recipientFingerprints?: string[]
): SeedPgpPlaintext {
    const plain: SeedPgpPlaintext = {
        v: 1,
        t: "bip39",
        w: normalizeMnemonic(mnemonic),
        l: "en",
        pp: bip39PassphraseUsed ? 1 : 0,
    };
    if (recipientFingerprints && recipientFingerprints.length > 0) {
        plain.fpr = recipientFingerprints;
    }
    return plain;
}

export function frameEncode(pgpBinary: Uint8Array): string {
    const crc = crc16CcittFalse(pgpBinary);
    const b45 = base45Encode(pgpBinary);
    return `SEEDPGP1:0:${crc}:${b45}`;
}

export function frameParse(text: string): ParsedSeedPgpFrame {
    const s = text.trim().replace(/^["']|["']$/g, "").replace(/[\n\r\t]/g, "");
    if (!s.startsWith("SEEDPGP1:")) throw new Error("Missing SEEDPGP1: prefix");

    const parts = s.split(":");
    if (parts.length < 4) {
        throw new Error("Invalid frame format (need at least 4 colon-separated parts)");
    }

    const prefix = parts[0];
    const frame = parts[1];
    const crc16 = parts[2].toUpperCase();
    const b45 = parts.slice(3).join(":");

    if (prefix !== "SEEDPGP1") throw new Error("Invalid prefix");
    if (frame !== "0") throw new Error("Multipart frames not supported in this prototype");
    if (!/^[0-9A-F]{4}$/.test(crc16)) throw new Error("Invalid CRC16 format (must be 4 hex chars)");

    return { kind: "single", crc16, b45 };
}

export function frameDecodeToPgpBytes(frameText: string): Uint8Array {
    const f = frameParse(frameText);
    const pgp = base45Decode(f.b45);
    const crc = crc16CcittFalse(pgp);
    if (crc !== f.crc16) {
        throw new Error(`CRC16 mismatch! Expected: ${f.crc16}, Got: ${crc}. QR scan may be corrupted.`);
    }
    return pgp;
}

export async function encryptToSeedPgp(params: {
    plaintext: SeedPgpPlaintext;
    publicKeyArmored?: string;
    messagePassword?: string;
}): Promise<{ framed: string; pgpBytes: Uint8Array; recipientFingerprint?: string }> {
    const pub = nonEmptyTrimmed(params.publicKeyArmored);
    const pw = nonEmptyTrimmed(params.messagePassword);

    if (!pub && !pw) {
        throw new Error("Provide either a PGP public key or a message password (or both).");
    }

    let encryptionKeys: openpgp.PublicKey[] = [];
    let recipientFingerprint: string | undefined;

    if (pub) {
        const pubKey = await openpgp.readKey({ armoredKey: pub });
        try {
            await pubKey.getEncryptionKey();
        } catch {
            throw new Error("This public key has no usable encryption subkey (E).");
        }

        recipientFingerprint = pubKey.getFingerprint().toUpperCase();
        encryptionKeys = [pubKey];
    }

    const message = await openpgp.createMessage({ text: JSON.stringify(params.plaintext) });

    const encrypted = await openpgp.encrypt({
        message,
        encryptionKeys,
        passwords: pw ? [pw] : [],
        format: "binary",
        config: {
            preferredSymmetricAlgorithm: openpgp.enums.symmetric.aes256,
        },
    });

    const pgpBytes = new Uint8Array(encrypted as Uint8Array);
    return { framed: frameEncode(pgpBytes), pgpBytes, recipientFingerprint };
}

export async function decryptSeedPgp(params: {
    frameText: string;
    privateKeyArmored?: string;
    privateKeyPassphrase?: string;
    messagePassword?: string;
}): Promise<SeedPgpPlaintext> {
    const pgpBytes = frameDecodeToPgpBytes(params.frameText);
    const message = await openpgp.readMessage({ binaryMessage: pgpBytes });
    const encKeyIds: openpgp.KeyID[] = message.getEncryptionKeyIDs?.() ?? [];

    const privArmored = nonEmptyTrimmed(params.privateKeyArmored);
    const privPw = nonEmptyTrimmed(params.privateKeyPassphrase);
    const msgPw = nonEmptyTrimmed(params.messagePassword);

    let decryptionKeys: openpgp.PrivateKey[] = [];

    if (privArmored) {
        let privKey = await openpgp.readPrivateKey({ armoredKey: privArmored });

        if (!privKey.isDecrypted()) {
            if (!privPw) {
                throw new Error("Private key is still locked. Enter the private key passphrase.");
            }
            privKey = await openpgp.decryptKey({ privateKey: privKey, passphrase: privPw });
            if (!privKey.isDecrypted()) {
                throw new Error("Private key passphrase incorrect (key still locked).");
            }
        }

        // Preflight: validate the private key matches a recipient
        if (encKeyIds.length) {
            const dec = await privKey.getDecryptionKeys();
            const decArr = Array.isArray(dec) ? dec : [dec];
            const decKeyIds = decArr.map((k: any) => k.getKeyID().toHex().toUpperCase());
            const want = new Set(encKeyIds.map((kid: openpgp.KeyID) => kid.toHex().toUpperCase()));
            const matched = decKeyIds.some((id: string) => want.has(id));

            if (!matched) {
                throw new Error(
                    "This payload is not encrypted to the provided private key (no matching recipient KeyID)."
                );
            }
        }

        decryptionKeys = [privKey];
    }

    let decryptResult;
    try {
        const decryptOptions: any = {
            message,
            format: "utf8",
        };

        if (decryptionKeys.length > 0) {
            decryptOptions.decryptionKeys = decryptionKeys;
        }

        if (msgPw) {
            decryptOptions.passwords = [msgPw];
        }

        decryptResult = await openpgp.decrypt(decryptOptions);
    } catch (err: any) {
        console.error("SeedPGP: decrypt failed:", err.message);
        throw err;
    }

    const { data } = decryptResult;
    const obj = JSON.parse(data as string) as SeedPgpPlaintext;

    if (obj.v !== 1) throw new Error(`Unsupported version: ${obj.v}`);
    if (obj.t !== "bip39") throw new Error(`Unsupported type: ${obj.t}`);
    if (obj.l !== "en") throw new Error(`Unsupported language: ${obj.l}`);

    return obj;
}