[PM-6556] reintroduce policy reduction for multi-org accounts (#8409)

libs/common/src/tools/generator/abstractions/generator-strategy.abstraction.ts

@@ -1,3 +1,5 @@
+import { Observable } from "rxjs";
+
 import { PolicyType } from "../../../admin-console/enums";
 // FIXME: use index.ts imports once policy abstractions and models
 // implement ADR-0002
@@ -21,13 +23,16 @@ export abstract class GeneratorStrategy<Options, Policy> {
   /** Length of time in milliseconds to cache the evaluator */
   cache_ms: number;
 
-  /** Creates an evaluator from a generator policy.
+  /** Operator function that converts a policy collection observable to a single
+   *   policy evaluator observable.
    * @param policy The policy being evaluated.
    * @returns the policy evaluator. If `policy` is is `null` or `undefined`,
    * then the evaluator defaults to the application's limits.
    * @throws when the policy's type does not match the generator's policy type.
    */
-  evaluator: (policy: AdminPolicy) => PolicyEvaluator<Policy, Options>;
+  toEvaluator: () => (
+    source: Observable<AdminPolicy[]>,
+  ) => Observable<PolicyEvaluator<Policy, Options>>;
 
   /** Generates credentials from the given options.
    * @param options The options used to generate the credentials.

libs/common/src/tools/generator/default-generator.service.spec.ts

@@ -4,7 +4,7 @@
  */
 
 import { mock } from "jest-mock-extended";
-import { BehaviorSubject, firstValueFrom } from "rxjs";
+import { BehaviorSubject, firstValueFrom, map, pipe } from "rxjs";
 
 import { FakeSingleUserState, awaitAsync } from "../../../spec";
 import { PolicyService } from "../../admin-console/abstractions/policy/policy.service.abstraction";
@@ -20,12 +20,12 @@ import { PasswordGenerationOptions } from "./password";
 
 import { DefaultGeneratorService } from ".";
 
-function mockPolicyService(config?: { state?: BehaviorSubject<Policy> }) {
+function mockPolicyService(config?: { state?: BehaviorSubject<Policy[]> }) {
   const service = mock<PolicyService>();
 
   // FIXME: swap out the mock return value when `getAll$` becomes available
-  const stateValue = config?.state ?? new BehaviorSubject<Policy>(null);
-  service.get$.mockReturnValue(stateValue);
+  const stateValue = config?.state ?? new BehaviorSubject<Policy[]>([null]);
+  service.getAll$.mockReturnValue(stateValue);
 
   // const stateValue = config?.state ?? new BehaviorSubject<Policy[]>(null);
   // service.getAll$.mockReturnValue(stateValue);
@@ -46,7 +46,9 @@ function mockGeneratorStrategy(config?: {
     // the value from `config`.
     durableState: jest.fn(() => durableState),
     policy: config?.policy ?? PolicyType.DisableSend,
-    evaluator: jest.fn(() => config?.evaluator ?? mock<PolicyEvaluator<any, any>>()),
+    toEvaluator: jest.fn(() =>
+      pipe(map(() => config?.evaluator ?? mock<PolicyEvaluator<any, any>>())),
+    ),
   });
 
   return strategy;
@@ -94,9 +96,7 @@ describe("Password generator service", () => {
 
       await firstValueFrom(service.evaluator$(SomeUser));
 
-      // FIXME: swap out the expect when `getAll$` becomes available
-      expect(policy.get$).toHaveBeenCalledWith(PolicyType.PasswordGenerator);
-      //expect(policy.getAll$).toHaveBeenCalledWith(PolicyType.PasswordGenerator, SomeUser);
+      expect(policy.getAll$).toHaveBeenCalledWith(PolicyType.PasswordGenerator, SomeUser);
     });
 
     it("should map the policy using the generation strategy", async () => {
@@ -112,21 +112,22 @@ describe("Password generator service", () => {
 
     it("should update the evaluator when the password generator policy changes", async () => {
       // set up dependencies
-      const state = new BehaviorSubject<Policy>(null);
+      const state = new BehaviorSubject<Policy[]>([null]);
       const policy = mockPolicyService({ state });
       const strategy = mockGeneratorStrategy();
       const service = new DefaultGeneratorService(strategy, policy);
 
-      // model responses for the observable update
+      // model responses for the observable update. The map is called multiple times,
+      // and the array shift ensures reference equality is maintained.
       const firstEvaluator = mock<PolicyEvaluator<any, any>>();
-      strategy.evaluator.mockReturnValueOnce(firstEvaluator);
       const secondEvaluator = mock<PolicyEvaluator<any, any>>();
-      strategy.evaluator.mockReturnValueOnce(secondEvaluator);
+      const evaluators = [firstEvaluator, secondEvaluator];
+      strategy.toEvaluator.mockReturnValueOnce(pipe(map(() => evaluators.shift())));
 
       // act
       const evaluator$ = service.evaluator$(SomeUser);
       const firstResult = await firstValueFrom(evaluator$);
-      state.next(null);
+      state.next([null]);
       const secondResult = await firstValueFrom(evaluator$);
 
       // assert
@@ -142,9 +143,7 @@ describe("Password generator service", () => {
       await firstValueFrom(service.evaluator$(SomeUser));
       await firstValueFrom(service.evaluator$(SomeUser));
 
-      // FIXME: swap out the expect when `getAll$` becomes available
-      expect(policy.get$).toHaveBeenCalledTimes(1);
-      //expect(policy.getAll$).toHaveBeenCalledTimes(1);
+      expect(policy.getAll$).toHaveBeenCalledTimes(1);
     });
 
     it("should cache the password generator policy for each user", async () => {
@@ -155,9 +154,8 @@ describe("Password generator service", () => {
       await firstValueFrom(service.evaluator$(SomeUser));
       await firstValueFrom(service.evaluator$(AnotherUser));
 
-      // FIXME: enable this test when `getAll$` becomes available
-      // expect(policy.getAll$).toHaveBeenNthCalledWith(1, PolicyType.PasswordGenerator, SomeUser);
-      // expect(policy.getAll$).toHaveBeenNthCalledWith(2, PolicyType.PasswordGenerator, AnotherUser);
+      expect(policy.getAll$).toHaveBeenNthCalledWith(1, PolicyType.PasswordGenerator, SomeUser);
+      expect(policy.getAll$).toHaveBeenNthCalledWith(2, PolicyType.PasswordGenerator, AnotherUser);
     });
   });
 

libs/common/src/tools/generator/default-generator.service.ts

@@ -1,4 +1,4 @@
-import { firstValueFrom, map, share, timer, ReplaySubject, Observable } from "rxjs";
+import { firstValueFrom, share, timer, ReplaySubject, Observable } from "rxjs";
 
 // FIXME: use index.ts imports once policy abstractions and models
 // implement ADR-0002
@@ -44,14 +44,12 @@ export class DefaultGeneratorService<Options, Policy> implements GeneratorServic
   }
 
   private createEvaluator(userId: UserId) {
-    // FIXME: when it becomes possible to get a user-specific policy observable
-    // (`getAll$`) update this code to call it instead of `get$`.
-    const policies$ = this.policy.get$(this.strategy.policy);
+    const evaluator$ = this.policy.getAll$(this.strategy.policy, userId).pipe(
+      // create the evaluator from the policies
+      this.strategy.toEvaluator(),
 
       // cache evaluator in a replay subject to amortize creation cost
       // and reduce GC pressure.
-    const evaluator$ = policies$.pipe(
-      map((policy) => this.strategy.evaluator(policy)),
       share({
         connector: () => new ReplaySubject(1),
         resetOnRefCountZero: () => timer(this.strategy.cache_ms),

libs/common/src/tools/generator/passphrase/passphrase-generator-policy.spec.ts

@@ -0,0 +1,51 @@
+import { PolicyType } from "../../../admin-console/enums";
+// FIXME: use index.ts imports once policy abstractions and models
+// implement ADR-0002
+import { Policy } from "../../../admin-console/models/domain/policy";
+import { PolicyId } from "../../../types/guid";
+
+import { DisabledPassphraseGeneratorPolicy, leastPrivilege } from "./passphrase-generator-policy";
+
+function createPolicy(
+  data: any,
+  type: PolicyType = PolicyType.PasswordGenerator,
+  enabled: boolean = true,
+) {
+  return new Policy({
+    id: "id" as PolicyId,
+    organizationId: "organizationId",
+    data,
+    enabled,
+    type,
+  });
+}
+
+describe("leastPrivilege", () => {
+  it("should return the accumulator when the policy type does not apply", () => {
+    const policy = createPolicy({}, PolicyType.RequireSso);
+
+    const result = leastPrivilege(DisabledPassphraseGeneratorPolicy, policy);
+
+    expect(result).toEqual(DisabledPassphraseGeneratorPolicy);
+  });
+
+  it("should return the accumulator when the policy is not enabled", () => {
+    const policy = createPolicy({}, PolicyType.PasswordGenerator, false);
+
+    const result = leastPrivilege(DisabledPassphraseGeneratorPolicy, policy);
+
+    expect(result).toEqual(DisabledPassphraseGeneratorPolicy);
+  });
+
+  it.each([
+    ["minNumberWords", 10],
+    ["capitalize", true],
+    ["includeNumber", true],
+  ])("should take the %p from the policy", (input, value) => {
+    const policy = createPolicy({ [input]: value });
+
+    const result = leastPrivilege(DisabledPassphraseGeneratorPolicy, policy);
+
+    expect(result).toEqual({ ...DisabledPassphraseGeneratorPolicy, [input]: value });
+  });
+});

libs/common/src/tools/generator/passphrase/passphrase-generator-policy.ts

@@ -1,3 +1,8 @@
+import { PolicyType } from "../../../admin-console/enums";
+// FIXME: use index.ts imports once policy abstractions and models
+// implement ADR-0002
+import { Policy } from "../../../admin-console/models/domain/policy";
+
 /** Policy options enforced during passphrase generation. */
 export type PassphraseGeneratorPolicy = {
   minNumberWords: number;
@@ -11,3 +16,24 @@ export const DisabledPassphraseGeneratorPolicy: PassphraseGeneratorPolicy = Obje
   capitalize: false,
   includeNumber: false,
 });
+
+/** Reduces a policy into an accumulator by accepting the most restrictive
+ *  values from each policy.
+ *  @param acc the accumulator
+ *  @param policy the policy to reduce
+ *  @returns the most restrictive values between the policy and accumulator.
+ */
+export function leastPrivilege(
+  acc: PassphraseGeneratorPolicy,
+  policy: Policy,
+): PassphraseGeneratorPolicy {
+  if (policy.type !== PolicyType.PasswordGenerator) {
+    return acc;
+  }
+
+  return {
+    minNumberWords: Math.max(acc.minNumberWords, policy.data.minNumberWords ?? acc.minNumberWords),
+    capitalize: policy.data.capitalize || acc.capitalize,
+    includeNumber: policy.data.includeNumber || acc.includeNumber,
+  };
+}

libs/common/src/tools/generator/passphrase/passphrase-generator-strategy.spec.ts

@@ -4,6 +4,7 @@
  */
 
 import { mock } from "jest-mock-extended";
+import { of, firstValueFrom } from "rxjs";
 
 import { PolicyType } from "../../../admin-console/enums";
 // FIXME: use index.ts imports once policy abstractions and models
@@ -21,17 +22,8 @@ import { PassphraseGeneratorOptionsEvaluator, PassphraseGeneratorStrategy } from
 const SomeUser = "some user" as UserId;
 
 describe("Password generation strategy", () => {
-  describe("evaluator()", () => {
-    it("should throw if the policy type is incorrect", () => {
-      const strategy = new PassphraseGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
-        type: PolicyType.DisableSend,
-      });
-
-      expect(() => strategy.evaluator(policy)).toThrow(new RegExp("Mismatched policy type\\. .+"));
-    });
-
-    it("should map to the policy evaluator", () => {
+  describe("toEvaluator()", () => {
+    it("should map to the policy evaluator", async () => {
       const strategy = new PassphraseGeneratorStrategy(null, null);
       const policy = mock<Policy>({
         type: PolicyType.PasswordGenerator,
@@ -42,7 +34,8 @@ describe("Password generation strategy", () => {
         },
       });
 
-      const evaluator = strategy.evaluator(policy);
+      const evaluator$ = of([policy]).pipe(strategy.toEvaluator());
+      const evaluator = await firstValueFrom(evaluator$);
 
       expect(evaluator).toBeInstanceOf(PassphraseGeneratorOptionsEvaluator);
       expect(evaluator.policy).toMatchObject({
@@ -52,13 +45,18 @@ describe("Password generation strategy", () => {
       });
     });
 
-    it("should map `null` to a default policy evaluator", () => {
+    it.each([[[]], [null], [undefined]])(
+      "should map `%p` to a disabled password policy evaluator",
+      async (policies) => {
         const strategy = new PassphraseGeneratorStrategy(null, null);
-      const evaluator = strategy.evaluator(null);
+
+        const evaluator$ = of(policies).pipe(strategy.toEvaluator());
+        const evaluator = await firstValueFrom(evaluator$);
 
         expect(evaluator).toBeInstanceOf(PassphraseGeneratorOptionsEvaluator);
         expect(evaluator.policy).toMatchObject(DisabledPassphraseGeneratorPolicy);
-    });
+      },
+    );
   });
 
   describe("durableState", () => {

libs/common/src/tools/generator/passphrase/passphrase-generator-strategy.ts

@@ -1,18 +1,19 @@
+import { map, pipe } from "rxjs";
+
 import { GeneratorStrategy } from "..";
 import { PolicyType } from "../../../admin-console/enums";
-// FIXME: use index.ts imports once policy abstractions and models
-// implement ADR-0002
-import { Policy } from "../../../admin-console/models/domain/policy";
 import { StateProvider } from "../../../platform/state";
 import { UserId } from "../../../types/guid";
 import { PASSPHRASE_SETTINGS } from "../key-definitions";
 import { PasswordGenerationServiceAbstraction } from "../password/password-generation.service.abstraction";
+import { reduceCollection } from "../reduce-collection.operator";
 
 import { PassphraseGenerationOptions } from "./passphrase-generation-options";
 import { PassphraseGeneratorOptionsEvaluator } from "./passphrase-generator-options-evaluator";
 import {
   DisabledPassphraseGeneratorPolicy,
   PassphraseGeneratorPolicy,
+  leastPrivilege,
 } from "./passphrase-generator-policy";
 
 const ONE_MINUTE = 60 * 1000;
@@ -23,6 +24,7 @@ export class PassphraseGeneratorStrategy
 {
   /** instantiates the password generator strategy.
    *  @param legacy generates the passphrase
+   *  @param stateProvider provides durable state
    */
   constructor(
     private legacy: PasswordGenerationServiceAbstraction,
@@ -39,26 +41,17 @@ export class PassphraseGeneratorStrategy
     return PolicyType.PasswordGenerator;
   }
 
+  /** {@link GeneratorStrategy.cache_ms} */
   get cache_ms() {
     return ONE_MINUTE;
   }
 
-  /** {@link GeneratorStrategy.evaluator} */
-  evaluator(policy: Policy): PassphraseGeneratorOptionsEvaluator {
-    if (!policy) {
-      return new PassphraseGeneratorOptionsEvaluator(DisabledPassphraseGeneratorPolicy);
-    }
-
-    if (policy.type !== this.policy) {
-      const details = `Expected: ${this.policy}. Received: ${policy.type}`;
-      throw Error("Mismatched policy type. " + details);
-    }
-
-    return new PassphraseGeneratorOptionsEvaluator({
-      minNumberWords: policy.data.minNumberWords,
-      capitalize: policy.data.capitalize,
-      includeNumber: policy.data.includeNumber,
-    });
+  /** {@link GeneratorStrategy.toEvaluator} */
+  toEvaluator() {
+    return pipe(
+      reduceCollection(leastPrivilege, DisabledPassphraseGeneratorPolicy),
+      map((policy) => new PassphraseGeneratorOptionsEvaluator(policy)),
+    );
   }
 
   /** {@link GeneratorStrategy.generate} */

libs/common/src/tools/generator/password/password-generator-policy.spec.ts

@@ -0,0 +1,55 @@
+import { PolicyType } from "../../../admin-console/enums";
+// FIXME: use index.ts imports once policy abstractions and models
+// implement ADR-0002
+import { Policy } from "../../../admin-console/models/domain/policy";
+import { PolicyId } from "../../../types/guid";
+
+import { DisabledPasswordGeneratorPolicy, leastPrivilege } from "./password-generator-policy";
+
+function createPolicy(
+  data: any,
+  type: PolicyType = PolicyType.PasswordGenerator,
+  enabled: boolean = true,
+) {
+  return new Policy({
+    id: "id" as PolicyId,
+    organizationId: "organizationId",
+    data,
+    enabled,
+    type,
+  });
+}
+
+describe("leastPrivilege", () => {
+  it("should return the accumulator when the policy type does not apply", () => {
+    const policy = createPolicy({}, PolicyType.RequireSso);
+
+    const result = leastPrivilege(DisabledPasswordGeneratorPolicy, policy);
+
+    expect(result).toEqual(DisabledPasswordGeneratorPolicy);
+  });
+
+  it("should return the accumulator when the policy is not enabled", () => {
+    const policy = createPolicy({}, PolicyType.PasswordGenerator, false);
+
+    const result = leastPrivilege(DisabledPasswordGeneratorPolicy, policy);
+
+    expect(result).toEqual(DisabledPasswordGeneratorPolicy);
+  });
+
+  it.each([
+    ["minLength", 10, "minLength"],
+    ["useUpper", true, "useUppercase"],
+    ["useLower", true, "useLowercase"],
+    ["useNumbers", true, "useNumbers"],
+    ["minNumbers", 10, "numberCount"],
+    ["useSpecial", true, "useSpecial"],
+    ["minSpecial", 10, "specialCount"],
+  ])("should take the %p from the policy", (input, value, expected) => {
+    const policy = createPolicy({ [input]: value });
+
+    const result = leastPrivilege(DisabledPasswordGeneratorPolicy, policy);
+
+    expect(result).toEqual({ ...DisabledPasswordGeneratorPolicy, [expected]: value });
+  });
+});

libs/common/src/tools/generator/password/password-generator-policy.ts

@@ -1,3 +1,8 @@
+import { PolicyType } from "../../../admin-console/enums";
+// FIXME: use index.ts imports once policy abstractions and models
+// implement ADR-0002
+import { Policy } from "../../../admin-console/models/domain/policy";
+
 /** Policy options enforced during password generation. */
 export type PasswordGeneratorPolicy = {
   /** The minimum length of generated passwords.
@@ -48,3 +53,25 @@ export const DisabledPasswordGeneratorPolicy: PasswordGeneratorPolicy = Object.f
   useSpecial: false,
   specialCount: 0,
 });
+
+/** Reduces a policy into an accumulator by accepting the most restrictive
+ *  values from each policy.
+ *  @param acc the accumulator
+ *  @param policy the policy to reduce
+ *  @returns the most restrictive values between the policy and accumulator.
+ */
+export function leastPrivilege(acc: PasswordGeneratorPolicy, policy: Policy) {
+  if (policy.type !== PolicyType.PasswordGenerator || !policy.enabled) {
+    return acc;
+  }
+
+  return {
+    minLength: Math.max(acc.minLength, policy.data.minLength ?? acc.minLength),
+    useUppercase: policy.data.useUpper || acc.useUppercase,
+    useLowercase: policy.data.useLower || acc.useLowercase,
+    useNumbers: policy.data.useNumbers || acc.useNumbers,
+    numberCount: Math.max(acc.numberCount, policy.data.minNumbers ?? acc.numberCount),
+    useSpecial: policy.data.useSpecial || acc.useSpecial,
+    specialCount: Math.max(acc.specialCount, policy.data.minSpecial ?? acc.specialCount),
+  };
+}

libs/common/src/tools/generator/password/password-generator-strategy.spec.ts

@@ -4,6 +4,7 @@
  */
 
 import { mock } from "jest-mock-extended";
+import { of, firstValueFrom } from "rxjs";
 
 import { PolicyType } from "../../../admin-console/enums";
 // FIXME: use index.ts imports once policy abstractions and models
@@ -24,17 +25,8 @@ import {
 const SomeUser = "some user" as UserId;
 
 describe("Password generation strategy", () => {
-  describe("evaluator()", () => {
-    it("should throw if the policy type is incorrect", () => {
-      const strategy = new PasswordGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
-        type: PolicyType.DisableSend,
-      });
-
-      expect(() => strategy.evaluator(policy)).toThrow(new RegExp("Mismatched policy type\\. .+"));
-    });
-
-    it("should map to the policy evaluator", () => {
+  describe("toEvaluator()", () => {
+    it("should map to a password policy evaluator", async () => {
       const strategy = new PasswordGeneratorStrategy(null, null);
       const policy = mock<Policy>({
         type: PolicyType.PasswordGenerator,
@@ -49,7 +41,8 @@ describe("Password generation strategy", () => {
         },
       });
 
-      const evaluator = strategy.evaluator(policy);
+      const evaluator$ = of([policy]).pipe(strategy.toEvaluator());
+      const evaluator = await firstValueFrom(evaluator$);
 
       expect(evaluator).toBeInstanceOf(PasswordGeneratorOptionsEvaluator);
       expect(evaluator.policy).toMatchObject({
@@ -63,13 +56,18 @@ describe("Password generation strategy", () => {
       });
     });
 
-    it("should map `null`  to a default policy evaluator", () => {
+    it.each([[[]], [null], [undefined]])(
+      "should map `%p` to a disabled password policy evaluator",
+      async (policies) => {
         const strategy = new PasswordGeneratorStrategy(null, null);
-      const evaluator = strategy.evaluator(null);
+
+        const evaluator$ = of(policies).pipe(strategy.toEvaluator());
+        const evaluator = await firstValueFrom(evaluator$);
 
         expect(evaluator).toBeInstanceOf(PasswordGeneratorOptionsEvaluator);
         expect(evaluator.policy).toMatchObject(DisabledPasswordGeneratorPolicy);
-    });
+      },
+    );
   });
 
   describe("durableState", () => {

libs/common/src/tools/generator/password/password-generator-strategy.ts

@@ -1,11 +1,11 @@
+import { map, pipe } from "rxjs";
+
 import { GeneratorStrategy } from "..";
 import { PolicyType } from "../../../admin-console/enums";
-// FIXME: use index.ts imports once policy abstractions and models
-// implement ADR-0002
-import { Policy } from "../../../admin-console/models/domain/policy";
 import { StateProvider } from "../../../platform/state";
 import { UserId } from "../../../types/guid";
 import { PASSWORD_SETTINGS } from "../key-definitions";
+import { reduceCollection } from "../reduce-collection.operator";
 
 import { PasswordGenerationOptions } from "./password-generation-options";
 import { PasswordGenerationServiceAbstraction } from "./password-generation.service.abstraction";
@@ -13,6 +13,7 @@ import { PasswordGeneratorOptionsEvaluator } from "./password-generator-options-
 import {
   DisabledPasswordGeneratorPolicy,
   PasswordGeneratorPolicy,
+  leastPrivilege,
 } from "./password-generator-policy";
 
 const ONE_MINUTE = 60 * 1000;
@@ -43,26 +44,12 @@ export class PasswordGeneratorStrategy
     return ONE_MINUTE;
   }
 
-  /** {@link GeneratorStrategy.evaluator} */
-  evaluator(policy: Policy): PasswordGeneratorOptionsEvaluator {
-    if (!policy) {
-      return new PasswordGeneratorOptionsEvaluator(DisabledPasswordGeneratorPolicy);
-    }
-
-    if (policy.type !== this.policy) {
-      const details = `Expected: ${this.policy}. Received: ${policy.type}`;
-      throw Error("Mismatched policy type. " + details);
-    }
-
-    return new PasswordGeneratorOptionsEvaluator({
-      minLength: policy.data.minLength,
-      useUppercase: policy.data.useUpper,
-      useLowercase: policy.data.useLower,
-      useNumbers: policy.data.useNumbers,
-      numberCount: policy.data.minNumbers,
-      useSpecial: policy.data.useSpecial,
-      specialCount: policy.data.minSpecial,
-    });
+  /** {@link GeneratorStrategy.toEvaluator} */
+  toEvaluator() {
+    return pipe(
+      reduceCollection(leastPrivilege, DisabledPasswordGeneratorPolicy),
+      map((policy) => new PasswordGeneratorOptionsEvaluator(policy)),
+    );
   }
 
   /** {@link GeneratorStrategy.generate} */

libs/common/src/tools/generator/reduce-collection.operator.spec.ts

@@ -0,0 +1,33 @@
+/**
+ * include structuredClone in test environment.
+ * @jest-environment ../../../../shared/test.environment.ts
+ */
+
+import { of, firstValueFrom } from "rxjs";
+
+import { reduceCollection } from "./reduce-collection.operator";
+
+describe("reduceCollection", () => {
+  it.each([[null], [undefined], [[]]])(
+    "should return the default value when the collection is %p",
+    async (value: number[]) => {
+      const reduce = (acc: number, value: number) => acc + value;
+      const source$ = of(value);
+
+      const result$ = source$.pipe(reduceCollection(reduce, 100));
+      const result = await firstValueFrom(result$);
+
+      expect(result).toEqual(100);
+    },
+  );
+
+  it("should reduce the collection to a single value", async () => {
+    const reduce = (acc: number, value: number) => acc + value;
+    const source$ = of([1, 2, 3]);
+
+    const result$ = source$.pipe(reduceCollection(reduce, 0));
+    const result = await firstValueFrom(result$);
+
+    expect(result).toEqual(6);
+  });
+});

libs/common/src/tools/generator/reduce-collection.operator.ts

@@ -0,0 +1,20 @@
+import { map, OperatorFunction } from "rxjs";
+
+/**
+ * An observable operator that reduces an emitted collection to a single object,
+ * returning a default if all items are ignored.
+ * @param reduce The reduce function to apply to the filtered collection. The
+ *  first argument is the accumulator, and the second is the current item. The
+ *  return value is the new accumulator.
+ * @param defaultValue The default value to return if the collection is empty. The
+ *   default value is also the initial value of the accumulator.
+ */
+export function reduceCollection<Item, Accumulator>(
+  reduce: (acc: Accumulator, value: Item) => Accumulator,
+  defaultValue: Accumulator,
+): OperatorFunction<Item[], Accumulator> {
+  return map((values: Item[]) => {
+    const reduced = (values ?? []).reduce(reduce, structuredClone(defaultValue));
+    return reduced;
+  });
+}

libs/common/src/tools/generator/username/catchall-generator-strategy.spec.ts

@@ -1,4 +1,5 @@
 import { mock } from "jest-mock-extended";
+import { of, firstValueFrom } from "rxjs";
 
 import { PolicyType } from "../../../admin-console/enums";
 // FIXME: use index.ts imports once policy abstractions and models
@@ -12,39 +13,26 @@ import { CATCHALL_SETTINGS } from "../key-definitions";
 import { CatchallGeneratorStrategy, UsernameGenerationServiceAbstraction } from ".";
 
 const SomeUser = "some user" as UserId;
-
-describe("Email subaddress list generation strategy", () => {
-  describe("evaluator()", () => {
-    it("should throw if the policy type is incorrect", () => {
-      const strategy = new CatchallGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
-        type: PolicyType.DisableSend,
-      });
-
-      expect(() => strategy.evaluator(policy)).toThrow(new RegExp("Mismatched policy type\\. .+"));
-    });
-
-    it("should map to the policy evaluator", () => {
-      const strategy = new CatchallGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
+const SomePolicy = mock<Policy>({
   type: PolicyType.PasswordGenerator,
   data: {
     minLength: 10,
   },
-      });
+});
 
-      const evaluator = strategy.evaluator(policy);
-
-      expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
-      expect(evaluator.policy).toMatchObject({});
-    });
-
-    it("should map `null` to a default policy evaluator", () => {
+describe("Email subaddress list generation strategy", () => {
+  describe("toEvaluator()", () => {
+    it.each([[[]], [null], [undefined], [[SomePolicy]], [[SomePolicy, SomePolicy]]])(
+      "should map any input (= %p) to the default policy evaluator",
+      async (policies) => {
         const strategy = new CatchallGeneratorStrategy(null, null);
-      const evaluator = strategy.evaluator(null);
+
+        const evaluator$ = of(policies).pipe(strategy.toEvaluator());
+        const evaluator = await firstValueFrom(evaluator$);
 
         expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
-    });
+      },
+    );
   });
 
   describe("durableState", () => {

libs/common/src/tools/generator/username/catchall-generator-strategy.ts

@@ -1,5 +1,6 @@
+import { map, pipe } from "rxjs";
+
 import { PolicyType } from "../../../admin-console/enums";
-import { Policy } from "../../../admin-console/models/domain/policy";
 import { StateProvider } from "../../../platform/state";
 import { UserId } from "../../../types/guid";
 import { GeneratorStrategy } from "../abstractions";
@@ -41,18 +42,9 @@ export class CatchallGeneratorStrategy
     return ONE_MINUTE;
   }
 
-  /** {@link GeneratorStrategy.evaluator} */
-  evaluator(policy: Policy) {
-    if (!policy) {
-      return new DefaultPolicyEvaluator<CatchallGenerationOptions>();
-    }
-
-    if (policy.type !== this.policy) {
-      const details = `Expected: ${this.policy}. Received: ${policy.type}`;
-      throw Error("Mismatched policy type. " + details);
-    }
-
-    return new DefaultPolicyEvaluator<CatchallGenerationOptions>();
+  /** {@link GeneratorStrategy.toEvaluator} */
+  toEvaluator() {
+    return pipe(map((_) => new DefaultPolicyEvaluator<CatchallGenerationOptions>()));
   }
 
   /** {@link GeneratorStrategy.generate} */

libs/common/src/tools/generator/username/eff-username-generator-strategy.spec.ts

@@ -1,4 +1,5 @@
 import { mock } from "jest-mock-extended";
+import { of, firstValueFrom } from "rxjs";
 
 import { PolicyType } from "../../../admin-console/enums";
 // FIXME: use index.ts imports once policy abstractions and models
@@ -12,39 +13,26 @@ import { EFF_USERNAME_SETTINGS } from "../key-definitions";
 import { EffUsernameGeneratorStrategy, UsernameGenerationServiceAbstraction } from ".";
 
 const SomeUser = "some user" as UserId;
-
-describe("EFF long word list generation strategy", () => {
-  describe("evaluator()", () => {
-    it("should throw if the policy type is incorrect", () => {
-      const strategy = new EffUsernameGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
-        type: PolicyType.DisableSend,
-      });
-
-      expect(() => strategy.evaluator(policy)).toThrow(new RegExp("Mismatched policy type\\. .+"));
-    });
-
-    it("should map to the policy evaluator", () => {
-      const strategy = new EffUsernameGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
+const SomePolicy = mock<Policy>({
   type: PolicyType.PasswordGenerator,
   data: {
     minLength: 10,
   },
-      });
+});
 
-      const evaluator = strategy.evaluator(policy);
-
-      expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
-      expect(evaluator.policy).toMatchObject({});
-    });
-
-    it("should map `null` to a default policy evaluator", () => {
+describe("EFF long word list generation strategy", () => {
+  describe("toEvaluator()", () => {
+    it.each([[[]], [null], [undefined], [[SomePolicy]], [[SomePolicy, SomePolicy]]])(
+      "should map any input (= %p) to the default policy evaluator",
+      async (policies) => {
         const strategy = new EffUsernameGeneratorStrategy(null, null);
-      const evaluator = strategy.evaluator(null);
+
+        const evaluator$ = of(policies).pipe(strategy.toEvaluator());
+        const evaluator = await firstValueFrom(evaluator$);
 
         expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
-    });
+      },
+    );
   });
 
   describe("durableState", () => {

libs/common/src/tools/generator/username/eff-username-generator-strategy.ts

@@ -1,5 +1,6 @@
+import { map, pipe } from "rxjs";
+
 import { PolicyType } from "../../../admin-console/enums";
-import { Policy } from "../../../admin-console/models/domain/policy";
 import { StateProvider } from "../../../platform/state";
 import { UserId } from "../../../types/guid";
 import { GeneratorStrategy } from "../abstractions";
@@ -41,18 +42,9 @@ export class EffUsernameGeneratorStrategy
     return ONE_MINUTE;
   }
 
-  /** {@link GeneratorStrategy.evaluator} */
-  evaluator(policy: Policy) {
-    if (!policy) {
-      return new DefaultPolicyEvaluator<EffUsernameGenerationOptions>();
-    }
-
-    if (policy.type !== this.policy) {
-      const details = `Expected: ${this.policy}. Received: ${policy.type}`;
-      throw Error("Mismatched policy type. " + details);
-    }
-
-    return new DefaultPolicyEvaluator<EffUsernameGenerationOptions>();
+  /** {@link GeneratorStrategy.toEvaluator} */
+  toEvaluator() {
+    return pipe(map((_) => new DefaultPolicyEvaluator<EffUsernameGenerationOptions>()));
   }
 
   /** {@link GeneratorStrategy.generate} */

libs/common/src/tools/generator/username/forwarder-generator-strategy.spec.ts

@@ -1,6 +1,11 @@
 import { mock } from "jest-mock-extended";
+import { of, firstValueFrom } from "rxjs";
 
 import { FakeStateProvider, mockAccountServiceWith } from "../../../../spec";
+import { PolicyType } from "../../../admin-console/enums";
+// FIXME: use index.ts imports once policy abstractions and models
+// implement ADR-0002
+import { Policy } from "../../../admin-console/models/domain/policy";
 import { CryptoService } from "../../../platform/abstractions/crypto.service";
 import { EncryptService } from "../../../platform/abstractions/encrypt.service";
 import { StateProvider } from "../../../platform/state";
@@ -29,6 +34,12 @@ class TestForwarder extends ForwarderGeneratorStrategy<ApiOptions> {
 
 const SomeUser = "some user" as UserId;
 const AnotherUser = "another user" as UserId;
+const SomePolicy = mock<Policy>({
+  type: PolicyType.PasswordGenerator,
+  data: {
+    minLength: 10,
+  },
+});
 
 describe("ForwarderGeneratorStrategy", () => {
   const encryptService = mock<EncryptService>();
@@ -63,11 +74,17 @@ describe("ForwarderGeneratorStrategy", () => {
     });
   });
 
-  it("evaluator returns the default policy evaluator", () => {
-    const strategy = new TestForwarder(null, null, null);
+  describe("toEvaluator()", () => {
+    it.each([[[]], [null], [undefined], [[SomePolicy]], [[SomePolicy, SomePolicy]]])(
+      "should map any input (= %p) to the default policy evaluator",
+      async (policies) => {
+        const strategy = new TestForwarder(encryptService, keyService, stateProvider);
 
-    const result = strategy.evaluator(null);
+        const evaluator$ = of(policies).pipe(strategy.toEvaluator());
+        const evaluator = await firstValueFrom(evaluator$);
 
-    expect(result).toBeInstanceOf(DefaultPolicyEvaluator);
+        expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
+      },
+    );
   });
 });

libs/common/src/tools/generator/username/forwarder-generator-strategy.ts

@@ -1,5 +1,6 @@
+import { map, pipe } from "rxjs";
+
 import { PolicyType } from "../../../admin-console/enums";
-import { Policy } from "../../../admin-console/models/domain/policy";
 import { CryptoService } from "../../../platform/abstractions/crypto.service";
 import { EncryptService } from "../../../platform/abstractions/encrypt.service";
 import { KeyDefinition, SingleUserState, StateProvider } from "../../../platform/state";
@@ -81,8 +82,8 @@ export abstract class ForwarderGeneratorStrategy<
   /** Determine where forwarder configuration is stored  */
   protected abstract readonly key: KeyDefinition<Options>;
 
-  /** {@link GeneratorStrategy.evaluator} */
-  evaluator = (_policy: Policy) => {
-    return new DefaultPolicyEvaluator<Options>();
+  /** {@link GeneratorStrategy.toEvaluator} */
+  toEvaluator = () => {
+    return pipe(map((_) => new DefaultPolicyEvaluator<Options>()));
   };
 }

libs/common/src/tools/generator/username/subaddress-generator-strategy.spec.ts

@@ -1,4 +1,5 @@
 import { mock } from "jest-mock-extended";
+import { of, firstValueFrom } from "rxjs";
 
 import { PolicyType } from "../../../admin-console/enums";
 // FIXME: use index.ts imports once policy abstractions and models
@@ -12,39 +13,26 @@ import { SUBADDRESS_SETTINGS } from "../key-definitions";
 import { SubaddressGeneratorStrategy, UsernameGenerationServiceAbstraction } from ".";
 
 const SomeUser = "some user" as UserId;
-
-describe("Email subaddress list generation strategy", () => {
-  describe("evaluator()", () => {
-    it("should throw if the policy type is incorrect", () => {
-      const strategy = new SubaddressGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
-        type: PolicyType.DisableSend,
-      });
-
-      expect(() => strategy.evaluator(policy)).toThrow(new RegExp("Mismatched policy type\\. .+"));
-    });
-
-    it("should map to the policy evaluator", () => {
-      const strategy = new SubaddressGeneratorStrategy(null, null);
-      const policy = mock<Policy>({
+const SomePolicy = mock<Policy>({
   type: PolicyType.PasswordGenerator,
   data: {
     minLength: 10,
   },
-      });
+});
 
-      const evaluator = strategy.evaluator(policy);
-
-      expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
-      expect(evaluator.policy).toMatchObject({});
-    });
-
-    it("should map `null` to a default policy evaluator", () => {
+describe("Email subaddress list generation strategy", () => {
+  describe("toEvaluator()", () => {
+    it.each([[[]], [null], [undefined], [[SomePolicy]], [[SomePolicy, SomePolicy]]])(
+      "should map any input (= %p) to the default policy evaluator",
+      async (policies) => {
         const strategy = new SubaddressGeneratorStrategy(null, null);
-      const evaluator = strategy.evaluator(null);
+
+        const evaluator$ = of(policies).pipe(strategy.toEvaluator());
+        const evaluator = await firstValueFrom(evaluator$);
 
         expect(evaluator).toBeInstanceOf(DefaultPolicyEvaluator);
-    });
+      },
+    );
   });
 
   describe("durableState", () => {

libs/common/src/tools/generator/username/subaddress-generator-strategy.ts

@@ -1,5 +1,6 @@
+import { map, pipe } from "rxjs";
+
 import { PolicyType } from "../../../admin-console/enums";
-import { Policy } from "../../../admin-console/models/domain/policy";
 import { StateProvider } from "../../../platform/state";
 import { UserId } from "../../../types/guid";
 import { GeneratorStrategy } from "../abstractions";
@@ -41,18 +42,9 @@ export class SubaddressGeneratorStrategy
     return ONE_MINUTE;
   }
 
-  /** {@link GeneratorStrategy.evaluator} */
-  evaluator(policy: Policy) {
-    if (!policy) {
-      return new DefaultPolicyEvaluator<SubaddressGenerationOptions>();
-    }
-
-    if (policy.type !== this.policy) {
-      const details = `Expected: ${this.policy}. Received: ${policy.type}`;
-      throw Error("Mismatched policy type. " + details);
-    }
-
-    return new DefaultPolicyEvaluator<SubaddressGenerationOptions>();
+  /** {@link GeneratorStrategy.toEvaluator} */
+  toEvaluator() {
+    return pipe(map((_) => new DefaultPolicyEvaluator<SubaddressGenerationOptions>()));
   }
 
   /** {@link GeneratorStrategy.generate} */