/// SPDX-License-Identifier: GPL-3.0-or-later
/// SPDX-FileCopyrightText: Copyright © 2016-2024 Tony Garnock-Jones <tonyg@leastfixedpoint.com>

// Basically Macaroons [1] in a Dataspace context
//
// [1]: Birgisson, Arnar, Joe Gibbs Politz, Úlfar Erlingsson, Ankur
// Taly, Michael Vrable, and Mark Lentczner. “Macaroons: Cookies with
// Contextual Caveats for Decentralized Authorization in the Cloud.”
// In Network and Distributed System Security Symposium. San Diego,
// California: Internet Society, 2014.

import { mac } from './cryptography.js';
import { Bytes, decode, encode, is, neverEmbeddedType, Value, fromJS } from '@preserves/core';
import * as S from '../gen/sturdy.js';
import * as G from '../gen/gatekeeper.js';
export * from '../gen/sturdy.js';

export type SturdyValue = Value<S._embedded>;

export const KEY_LENGTH = 16; // 128 bits

export function embeddedNotAllowed(): never {
    throw new Error("Embedded Ref not permitted in SturdyRef");
}

export function sturdyEncode(v: SturdyValue): Bytes {
    return encode<S._embedded>(v, {
        canonical: true,
        includeAnnotations: false,
        embeddedEncode: neverEmbeddedType,
    });
}

export function sturdyDecode(bs: Bytes): SturdyValue {
    return decode<S._embedded>(bs, {
        includeAnnotations: false,
        embeddedDecode: neverEmbeddedType,
    });
}

export function sturdyBind(
    oid: SturdyValue,
    secretKey: Bytes,
    target: S._embedded,
    observer?: S._embedded,
): G.Bind {
    return G.Bind({
        description: G.Description({
            stepType: fromJS(S.SturdyStepType()) as symbol,
            detail: fromJS(S.SturdyDescriptionDetail({ oid, key: secretKey })),
        }),
        target,
        observer: (observer === void 0) ? G.BindObserver.absent() : G.BindObserver.present(observer),
    });
}

type RefAndBind = { ref: S.SturdyRef, bind: G.Bind };
export function mint(oid: SturdyValue, secretKey: Bytes): S.SturdyRef;
export function mint(oid: SturdyValue, secretKey: Bytes, target: S._embedded, observer?: S._embedded): RefAndBind;
export function mint(
    oid: SturdyValue,
    secretKey: Bytes,
    target?: S._embedded,
    observer?: S._embedded,
): S.SturdyRef | RefAndBind {
    const ref = S.SturdyRef(S.Parameters({
        oid,
        sig: mac(secretKey, sturdyEncode(oid)),
        caveats: S.CaveatsField.absent(),
    }));
    if (target === void 0) return ref;
    return { ref, bind: sturdyBind(oid, secretKey, target, observer) };
}

function chainMac(key: Bytes, caveats: S.Caveat[]): Bytes {
    return caveats.reduce((key, c) => mac(key, sturdyEncode(S.fromCaveat(c))), key);
}

export function caveatChain(r: S.SturdyRef): S.Caveat[] {
    switch (r.parameters.caveats._variant) {
        case "present": return r.parameters.caveats.caveats;
        case "absent": return [];
        case "invalid": throw new Error("Invalid caveats on sturdyref");
    }
}

export function attenuate(r: S.SturdyRef, ... a: S.Caveat[]): S.SturdyRef {
    if (a.length === 0) return r;
    return S.SturdyRef(S.Parameters({
        oid: r.parameters.oid,
        caveats: S.CaveatsField.present([... caveatChain(r), ... a]),
        sig: chainMac(r.parameters.sig, a),
    }));
}

export function validate(r: S.SturdyRef, secretKey: Bytes): boolean {
    const sig = chainMac(mac(secretKey, sturdyEncode(r.parameters.oid)), caveatChain(r));
    return is(sig, r.parameters.sig);
}