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import { AmountString, j2s, Logger } from "@gnu-taler/taler-util";
import { AuthMethod, Policy, PolicyProvider } from "./reducer-types.js";
const logger = new Logger("anastasis-core:policy-suggestion.ts");
/**
* Provider information used during provider/method mapping.
*/
export interface ProviderInfo {
url: string;
methodCost: Record<string, AmountString>;
}
export function suggestPolicies(
methods: AuthMethod[],
providers: ProviderInfo[],
): PolicySelectionResult {
const numMethods = methods.length;
if (numMethods === 0) {
throw Error("no methods");
}
let numSel: number;
if (numMethods <= 2) {
numSel = numMethods;
} else if (numMethods <= 4) {
numSel = numMethods - 1;
} else if (numMethods <= 6) {
numSel = numMethods - 2;
} else if (numMethods == 7) {
numSel = numMethods - 3;
} else {
numSel = 4;
}
const policies: Policy[] = [];
const selections = enumerateMethodSelections(numSel, numMethods);
logger.info(`selections: ${j2s(selections)}`);
for (const sel of selections) {
const p = assignProviders(policies, methods, providers, sel);
if (p) {
policies.push(p);
}
}
return {
policies,
policy_providers: providers.map((x) => ({
provider_url: x.url,
})),
};
}
/**
* Assign providers to a method selection.
*
* The evaluation of the assignment is made with respect to
* previously generated policies.
*/
function assignProviders(
existingPolicies: Policy[],
methods: AuthMethod[],
providers: ProviderInfo[],
methodSelection: number[],
): Policy | undefined {
const providerSelections = enumerateProviderMappings(
methodSelection.length,
providers.length,
);
let bestProvSel: ProviderSelection | undefined;
let bestDiversity = 0;
for (const provSel of providerSelections) {
// First, check if selection is even possible with the methods offered
let possible = true;
for (const methIndex in provSel) {
const provIndex = provSel[methIndex];
const meth = methods[methIndex];
const prov = providers[provIndex];
if (!prov.methodCost[meth.type]) {
possible = false;
break;
}
}
if (!possible) {
continue;
}
// Evaluate diversity, always prefer policies
// that increase diversity.
const providerSet = new Set<string>();
for (const pol of existingPolicies) {
for (const m of pol.methods) {
providerSet.add(m.provider);
}
}
for (const provIndex of provSel) {
const prov = providers[provIndex];
providerSet.add(prov.url);
}
const diversity = providerSet.size;
if (!bestProvSel || diversity > bestDiversity) {
bestProvSel = provSel;
bestDiversity = diversity;
}
// TODO: also evaluate costs and duplicates (same challenge at same provider)
}
if (!bestProvSel) {
return undefined;
}
return {
methods: bestProvSel.map((x, i) => ({
authentication_method: methodSelection[i],
provider: providers[x].url,
})),
};
}
type ProviderSelection = number[];
/**
* Compute provider mappings.
* Enumerates all n-combinations with repetition of m providers.
*/
function enumerateProviderMappings(n: number, m: number): ProviderSelection[] {
const selections: ProviderSelection[] = [];
const a = new Array(n);
const sel = (i: number, start: number = 0) => {
if (i === n) {
selections.push([...a]);
return;
}
for (let j = start; j < m; j++) {
a[i] = j;
sel(i + 1, j);
}
};
sel(0);
return selections;
}
interface PolicySelectionResult {
policies: Policy[];
policy_providers: PolicyProvider[];
}
type MethodSelection = number[];
/**
* Compute method selections.
* Enumerates all n-combinations without repetition of m methods.
*/
function enumerateMethodSelections(n: number, m: number): MethodSelection[] {
const selections: MethodSelection[] = [];
const a = new Array(n);
const sel = (i: number, start: number = 0) => {
if (i === n) {
selections.push([...a]);
return;
}
for (let j = start; j < m; j++) {
a[i] = j;
sel(i + 1, j + 1);
}
};
sel(0);
return selections;
}
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