novy-syndicate/src/runtime/dataspace.ts

import { KeyedDictionary, preserves } from '@preserves/core';
import { AnyValue, Assertion, Entity, Handle, LocalAction, Ref, Turn } from 'runtime/actor';

import { fromObserve, Observe } from '../gen/dataspace';
import { DBind, DDiscard, DLit, Pattern, DCompound, CArr, CDict, CRec } from '../gen/dataspacePatterns';

export { asObserve, fromObserve, toObserve, Observe, $Observe } from '../gen/dataspace';
export * from '../gen/dataspacePatterns';

// Q. Why keep "Observe"? Why not do the clever trick of asserting the
// observer, and having the dataspace read the implicit pattern it's
// interested in off its attenuator?
//
// A. (1) Because we want to have the possibility of more than one
// variety of pattern language. For example, here we have a simple
// label match, but we'll quickly want something about as rich as the
// pattern language in attenuators. And later, we could easily want
// something with, perhaps, as much power as RELAX-NG or similar. (2)
// Because we want to have onlookers have some hope of seeing whether
// a pattern of interest to them is being observed, and if we used
// attenuators to match, we'd have to expose visibility into
// attenuators into the pattern language. See next question. (3)
// Because reflection on attenuators is a big, heavy hammer, and it's
// better to be explicit about patterns! Also, some attenuations
// happen behind a veil of secrecy - they're not all open for the
// world to read about. Actors may proxy communications in arbitrary,
// secret ways.
//
// Q. What kinds of constraints on the pattern language are there?
//
// A. It should be fast to evaluate; ideally, JITtable? It should
// allow patterns on patterns, to some degree. This is for two
// reasons: we occasionally want to observe observers, and we
// frequently want to use attenuators limit the kinds of patterns that
// a principal may observe. As such, it's good to choose a language
// that enforced some kind of normal forms for its patterns, so
// observer-observers and attenuator patterns don't have to deal with
// spurious variation.

export class Dataspace implements Partial<Entity> {
    assert(turn: Turn, rec: Assertion, handle: Handle): void {
        console.log(preserves`ds ${turn.activeFacet.id} assert ${rec} ${handle}`);
        throw new Error("Full dataspaces not implemented");
    }

    retract(turn: Turn, upstreamHandle: Handle): void {
        console.log(preserves`ds ${turn.activeFacet.id} retract ${upstreamHandle}`);
        throw new Error("Full dataspaces not implemented");
    }

    message(turn: Turn, rec: Assertion): void {
        console.log(preserves`ds ${turn.activeFacet.id} message ${rec}`);
        throw new Error("Full dataspaces not implemented");
    }
}

export function during(f: (t: Turn, a: Assertion) => Promise<LocalAction | null>): Partial<Entity> {
    const assertionMap = new Map<Handle, LocalAction | 'dead'>();
    return {
        assert(t: Turn, a: Assertion, h: Handle): void {
            f(t, a).then(g => {
                if (g === null) g = _t => {};
                switch (assertionMap.get(h)) {
                    case void 0:
                        assertionMap.set(h, g);
                        break;
                    case 'dead':
                        assertionMap.delete(h);
                        t.freshen(g);
                        break;
                    default:
                        console.error('during: Duplicate handle in assert: ' + h);
                        break;
                }
            });
        },
        retract(t: Turn, h: Handle): void {
            const g = assertionMap.get(h);
            switch (g) {
                case void 0:
                    assertionMap.set(h, 'dead');
                    break;
                case 'dead':
                    console.error('during: Duplicate handle in retract: ' + h);
                    break;
                default:
                    assertionMap.delete(h);
                    g(t);
            }
        },
    };
}

export function observe(t: Turn, ds: Ref, pattern: Pattern, e: Partial<Entity>): Handle {
    return t.assert(ds, fromObserve(Observe({ pattern, observer: t.ref(e) })));
}

export namespace P {
    export function discard(): Pattern {
        return Pattern.DDiscard(DDiscard());
    }
    export function bind(name: string, pattern: Pattern = discard()): Pattern {
        return Pattern.DBind(DBind({name: Symbol.for(name), pattern}));
    }
    export function lit(value: AnyValue): Pattern {
        return Pattern.DLit(DLit(value));
    }
    export function rec(label: AnyValue, ...fields: Pattern[]): Pattern {
        const members = new KeyedDictionary<number, Pattern, Ref>();
        fields.forEach((f, i) => {
            if (f._variant !== 'DDiscard') members.set(i, f);
        });
        return Pattern.DCompound(DCompound.rec({
            ctor: CRec({ label, arity: fields.length }),
            members,
        }));
    }
    export function arr(...entries: Pattern[]): Pattern {
        const members = new KeyedDictionary<number, Pattern, Ref>();
        entries.forEach((f, i) => {
            if (f._variant !== 'DDiscard') members.set(i, f);
        });
        return Pattern.DCompound(DCompound.arr({
            ctor: CArr(entries.length),
            members,
        }));
    }
    export function dict(...entries: [AnyValue, Pattern][]): Pattern {
        const members = new KeyedDictionary<AnyValue, Pattern, Ref>();
        entries.forEach(([k, p]) => members.set(k, p));
        return Pattern.DCompound(DCompound.dict({
            ctor: CDict(),
            members,
        }));
    }
}