# All files / model mutation.ts

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     /**
     * Copyright 2017 Google Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    import { Timestamp } from '../api/timestamp';
    import { SnapshotVersion } from '../core/snapshot_version';
    import { assert, fail } from '../util/assert';
    import * as misc from '../util/misc';

    import { Document, MaybeDocument, NoDocument } from './document';
    import { DocumentKey } from './document_key';
    import { FieldValue, ObjectValue, ServerTimestampValue } from './field_value';
    import { FieldPath } from './path';

    /**
     * Provides a set of fields that can be used to partially patch a document.
     * FieldMask is used in conjunction with ObjectValue.
     * Examples:
     *   foo - Overwrites foo entirely with the provided value. If foo is not
     *         present in the companion ObjectValue, the field is deleted.
     *   foo.bar - Overwrites only the field bar of the object foo.
     *             If foo is not an object, foo is replaced with an object
     *             containing foo
     */
    export class FieldMask {
      constructor(readonly fields: FieldPath[]) {
        // TODO(dimond): validation of FieldMask
      }

      isEqual(other: FieldMask): boolean {
        return misc.arrayEquals(this.fields, other.fields);
      }
    }

    /** Represents a transform within a TransformMutation. */
    export interface TransformOperation {
      isEqual(other: TransformOperation): boolean;
    }

    /** Transforms a value into a server-generated timestamp. */
    export class ServerTimestampTransform implements TransformOperation {
      private constructor() {}
      static instance = new ServerTimestampTransform();

      isEqual(other: TransformOperation): boolean {
        return other instanceof ServerTimestampTransform;
      }
    }

    /** A field path and the TransformOperation to perform upon it. */
    export class FieldTransform {
      constructor(
        readonly field: FieldPath,
        readonly transform: TransformOperation
      ) {}

      isEqual(other: FieldTransform): boolean {
        return (
          this.field.isEqual(other.field) && this.transform.isEqual(other.transform)
        );
      }
    }

    /** The result of successfully applying a mutation to the backend. */
    export class MutationResult {
      constructor(
        /**
         * The version at which the mutation was committed or null for a delete.
         */
        readonly version: SnapshotVersion | null,
        /**
         * The resulting fields returned from the backend after a
         * TransformMutation has been committed. Contains one FieldValue for each
         * FieldTransform that was in the mutation.
         *
         * Will be null if the mutation was not a TransformMutation.
         */
        readonly transformResults: FieldValue[] | null
      ) {}
    }

    export enum MutationType {
      Set,
      Patch,
      Transform,
      Delete
    }

    /**
     * Encodes a precondition for a mutation. This follows the model that the
     * backend accepts with the special case of an explicit "empty" precondition
     * (meaning no precondition).
     */
    export class Precondition {
      static readonly NONE = new Precondition();

      private constructor(
        readonly updateTime?: SnapshotVersion,
        readonly exists?: boolean
      ) {
        assert(
          updateTime === undefined || exists === undefined,
          'Precondition can specify "exists" or "updateTime" but not both'
        );
      }

      /** Creates a new Precondition with an exists flag. */
      static exists(exists: boolean) {
        return new Precondition(undefined, exists);
      }

      /** Creates a new Precondition based on a version a document exists at. */
      static updateTime(version: SnapshotVersion) {
        return new Precondition(version);
      }

      /** Returns whether this Precondition is empty. */
      get isNone(): boolean {
        return this.updateTime === undefined && this.exists === undefined;
      }

      /**
       * Returns true if the preconditions is valid for the given document
       * (or null if no document is available).
       */
      isValidFor(maybeDoc: MaybeDocument | null) {
        Iif (this.updateTime !== undefined) {
          return (
            maybeDoc instanceof Document &&
            maybeDoc.version.isEqual(this.updateTime)
          );
        } else if (this.exists !== undefined) {
          Eif (this.exists) {
            return maybeDoc instanceof Document;
          } else {
            return maybeDoc === null || maybeDoc instanceof NoDocument;
          }
        } else {
          assert(this.isNone, 'Precondition should be empty');
          return true;
        }
      }

      isEqual(other: Precondition) {
        return (
          misc.equals(this.updateTime, other.updateTime) &&
          this.exists === other.exists
        );
      }
    }

    /**
     * A mutation describes a self-contained change to a document. Mutations can
     * create, replace, delete, and update subsets of documents.
     *
     * Mutations not only act on the value of the document but also it version.
     * In the case of Set, Patch, and Transform mutations we preserve the existing
     * version. In the case of Delete mutations, we reset the version to 0.
     *
     * Here's the expected transition table.
     *
     * MUTATION           APPLIED TO            RESULTS IN
     *
     * SetMutation        Document(v3)          Document(v3)
     * SetMutation        NoDocument(v3)        Document(v0)
     * SetMutation        null                  Document(v0)
     * PatchMutation      Document(v3)          Document(v3)
     * PatchMutation      NoDocument(v3)        NoDocument(v3)
     * PatchMutation      null                  null
     * TransformMutation  Document(v3)          Document(v3)
     * TransformMutation  NoDocument(v3)        NoDocument(v3)
     * TransformMutation  null                  null
     * DeleteMutation     Document(v3)          NoDocument(v0)
     * DeleteMutation     NoDocument(v3)        NoDocument(v0)
     * DeleteMutation     null                  NoDocument(v0)
     *
     * Note that TransformMutations don't create Documents (in the case of being
     * applied to a NoDocument), even though they would on the backend. This is
     * because the client always combines the TransformMutation with a SetMutation
     * or PatchMutation and we only want to apply the transform if the prior
     * mutation resulted in a Document (always true for a SetMutation, but not
     * necessarily for a PatchMutation).
     *
     * ## Subclassing Notes
     *
     * Subclasses of Mutation need to implement applyToRemoteDocument() and
     * applyToLocalView() to implement the actual behavior of applying the mutation
     * to some source document.
     */
    export abstract class Mutation {
      readonly type: MutationType;
      readonly key: DocumentKey;
      readonly precondition: Precondition;

      /**
       * Applies this mutation to the given MaybeDocument or null for the purposes
       * of computing a new remote document. Both the input and returned documents
       * can be null.
       *
       * @param maybeDoc The document to mutate. The input document can be null if
       *     the client has no knowledge of the pre-mutation state of the document.
       * @param mutationResult The result of applying the mutation from the backend.
       * @return The mutated document. The returned document may be null, but only
       *     if maybeDoc was null and the mutation would not create a new document.
       */
      abstract applyToRemoteDocument(
        maybeDoc: MaybeDocument | null,
        mutationResult: MutationResult
      ): MaybeDocument | null;

      /**
       * Applies this mutation to the given MaybeDocument or null for the purposes
       * of computing the new local view of a document. Both the input and returned
       * documents can be null.
       *
       * @param maybeDoc The document to mutate. The input document can be null if
       *     the client has no knowledge of the pre-mutation state of the document.
       * @param baseDoc The state of the document prior to this mutation batch. The
       *     input document can be null if the client has no knowledge of the
       *     pre-mutation state of the document.
       * @param localWriteTime A timestamp indicating the local write time of the
       *     batch this mutation is a part of.
       * @return The mutated document. The returned document may be null, but only
       *     if maybeDoc was null and the mutation would not create a new document.
       */
      abstract applyToLocalView(
        maybeDoc: MaybeDocument | null,
        baseDoc: MaybeDocument | null,
        localWriteTime: Timestamp
      ): MaybeDocument | null;

      abstract isEqual(other: Mutation): boolean;

      protected verifyKeyMatches(maybeDoc: MaybeDocument | null): void {
        if (maybeDoc != null) {
          assert(
            maybeDoc.key.isEqual(this.key),
            'Can only apply a mutation to a document with the same key'
          );
        }
      }

      /**
       * Returns the version from the given document for use as the result of a
       * mutation. Mutations are defined to return the version of the base document
       * only if it is an existing document. Deleted and unknown documents have a
       * post-mutation version of SnapshotVersion.MIN.
       */
      protected static getPostMutationVersion(
        maybeDoc: MaybeDocument | null
      ): SnapshotVersion {
        if (maybeDoc instanceof Document) {
          return maybeDoc.version;
        } else {
          return SnapshotVersion.MIN;
        }
      }
    }

    /**
     * A mutation that creates or replaces the document at the given key with the
     * object value contents.
     */
    export class SetMutation extends Mutation {
      constructor(
        readonly key: DocumentKey,
        readonly value: ObjectValue,
        readonly precondition: Precondition
      ) {
        super();
      }

      readonly type: MutationType = MutationType.Set;

      applyToRemoteDocument(
        maybeDoc: MaybeDocument | null,
        mutationResult: MutationResult
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        assert(
          mutationResult.transformResults == null,
          'Transform results received by SetMutation.'
        );

        // Unlike applyToLocalView, if we're applying a mutation to a remote
        // document the server has accepted the mutation so the precondition must
        // have held.

        const version = Mutation.getPostMutationVersion(maybeDoc);
        return new Document(this.key, version, this.value, {
          hasLocalMutations: false
        });
      }

      applyToLocalView(
        maybeDoc: MaybeDocument | null,
        baseDoc: MaybeDocument | null,
        localWriteTime: Timestamp
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        Iif (!this.precondition.isValidFor(maybeDoc)) {
          return maybeDoc;
        }

        const version = Mutation.getPostMutationVersion(maybeDoc);
        return new Document(this.key, version, this.value, {
          hasLocalMutations: true
        });
      }

      isEqual(other: Mutation): boolean {
        return (
          other instanceof SetMutation &&
          this.key.isEqual(other.key) &&
          this.value.isEqual(other.value) &&
          this.precondition.isEqual(other.precondition)
        );
      }
    }

    /**
     * A mutation that modifies fields of the document at the given key with the
     * given values. The values are applied through a field mask:
     *
     *  * When a field is in both the mask and the values, the corresponding field
     *    is updated.
     *  * When a field is in neither the mask nor the values, the corresponding
     *    field is unmodified.
     *  * When a field is in the mask but not in the values, the corresponding field
     *    is deleted.
     *  * When a field is not in the mask but is in the values, the values map is
     *    ignored.
     */
    export class PatchMutation extends Mutation {
      constructor(
        readonly key: DocumentKey,
        readonly data: ObjectValue,
        readonly fieldMask: FieldMask,
        readonly precondition: Precondition
      ) {
        super();
      }

      readonly type: MutationType = MutationType.Patch;

      applyToRemoteDocument(
        maybeDoc: MaybeDocument | null,
        mutationResult: MutationResult
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        assert(
          mutationResult.transformResults == null,
          'Transform results received by PatchMutation.'
        );

        // TODO(mcg): Relax enforcement of this precondition
        //
        // We shouldn't actually enforce the precondition since it already passed on
        // the backend, but we may not have a local version of the document to
        // patch, so we use the precondition to prevent incorrectly putting a
        // partial document into our cache.
        if (!this.precondition.isValidFor(maybeDoc)) {
          return maybeDoc;
        }

        const version = Mutation.getPostMutationVersion(maybeDoc);
        const newData = this.patchDocument(maybeDoc);
        return new Document(this.key, version, newData, {
          hasLocalMutations: false
        });
      }

      applyToLocalView(
        maybeDoc: MaybeDocument | null,
        baseDoc: MaybeDocument | null,
        localWriteTime: Timestamp
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        if (!this.precondition.isValidFor(maybeDoc)) {
          return maybeDoc;
        }

        const version = Mutation.getPostMutationVersion(maybeDoc);
        const newData = this.patchDocument(maybeDoc);
        return new Document(this.key, version, newData, {
          hasLocalMutations: true
        });
      }

      isEqual(other: Mutation): boolean {
        return (
          other instanceof PatchMutation &&
          this.key.isEqual(other.key) &&
          this.fieldMask.isEqual(other.fieldMask) &&
          this.precondition.isEqual(other.precondition)
        );
      }

      /**
       * Patches the data of document if available or creates a new document. Note
       * that this does not check whether or not the precondition of this patch
       * holds.
       */
      private patchDocument(maybeDoc: MaybeDocument | null): ObjectValue {
        let data: ObjectValue;
        if (maybeDoc instanceof Document) {
          data = maybeDoc.data;
        } else {
          data = ObjectValue.EMPTY;
        }
        return this.patchObject(data);
      }

      private patchObject(data: ObjectValue): ObjectValue {
        for (const fieldPath of this.fieldMask.fields) {
          const newValue = this.data.field(fieldPath);
          if (newValue !== undefined) {
            data = data.set(fieldPath, newValue);
          } else {
            data = data.delete(fieldPath);
          }
        }
        return data;
      }
    }

    /**
     * A mutation that modifies specific fields of the document with transform
     * operations. Currently the only supported transform is a server timestamp, but
     * IP Address, increment(n), etc. could be supported in the future.
     *
     * It is somewhat similar to a PatchMutation in that it patches specific fields
     * and has no effect when applied to a null or NoDocument (see comment on
     * Mutation for rationale).
     */
    export class TransformMutation extends Mutation {
      readonly type: MutationType = MutationType.Transform;

      // NOTE: We set a precondition of exists: true as a safety-check, since we
      // always combine TransformMutations with a SetMutation or PatchMutation which
      // (if successful) should end up with an existing document.
      readonly precondition = Precondition.exists(true);

      constructor(
        readonly key: DocumentKey,
        readonly fieldTransforms: FieldTransform[]
      ) {
        super();
      }

      applyToRemoteDocument(
        maybeDoc: MaybeDocument | null,
        mutationResult: MutationResult
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        assert(
          mutationResult.transformResults != null,
          'Transform results missing for TransformMutation.'
        );
        const transformResults = mutationResult.transformResults!;

        // TODO(mcg): Relax enforcement of this precondition
        //
        // We shouldn't actually enforce the precondition since it already passed on
        // the backend, but we may not have a local version of the document to
        // patch, so we use the precondition to prevent incorrectly putting a
        // partial document into our cache.
        if (!this.precondition.isValidFor(maybeDoc)) {
          return maybeDoc;
        }

        const doc = this.requireDocument(maybeDoc);
        const newData = this.transformObject(doc.data, transformResults);
        return new Document(this.key, doc.version, newData, {
          hasLocalMutations: false
        });
      }

      applyToLocalView(
        maybeDoc: MaybeDocument | null,
        baseDoc: MaybeDocument | null,
        localWriteTime: Timestamp
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        if (!this.precondition.isValidFor(maybeDoc)) {
          return maybeDoc;
        }

        const doc = this.requireDocument(maybeDoc);
        const transformResults = this.localTransformResults(
          localWriteTime,
          baseDoc
        );
        const newData = this.transformObject(doc.data, transformResults);
        return new Document(this.key, doc.version, newData, {
          hasLocalMutations: true
        });
      }

      isEqual(other: Mutation): boolean {
        return (
          other instanceof TransformMutation &&
          this.key.isEqual(other.key) &&
          misc.arrayEquals(this.fieldTransforms, other.fieldTransforms) &&
          this.precondition.isEqual(other.precondition)
        );
      }

      /**
       * Asserts that the given MaybeDocument is actually a Document and verifies
       * that it matches the key for this mutation. Since we only support
       * transformations with precondition exists this method is guaranteed to be
       * safe.
       */
      private requireDocument(maybeDoc: MaybeDocument | null): Document {
        assert(
          maybeDoc instanceof Document,
          'Unknown MaybeDocument type ' + maybeDoc
        );
        const doc = maybeDoc! as Document;
        assert(
          doc.key.isEqual(this.key),
          'Can only transform a document with the same key'
        );
        return doc;
      }

      /**
       * Creates a list of "transform results" (a transform result is a field value
       * representing the result of applying a transform) for use when applying a
       * TransformMutation locally.
       *
       * @param localWriteTime The local time of the transform mutation (used to
       *     generate ServerTimestampValues).
       * @param baseDoc The document prior to applying this mutation batch.
       * @return The transform results list.
       */
      private localTransformResults(
        localWriteTime: Timestamp,
        baseDoc: MaybeDocument | null
      ): FieldValue[] {
        const transformResults = [] as FieldValue[];
        for (const fieldTransform of this.fieldTransforms) {
          const transform = fieldTransform.transform;
          Eif (transform instanceof ServerTimestampTransform) {
            let previousValue: FieldValue | null = null;

            if (baseDoc instanceof Document) {
              previousValue = baseDoc.field(fieldTransform.field) || null;
            }

            transformResults.push(
              new ServerTimestampValue(localWriteTime, previousValue)
            );
          } else {
            return fail('Encountered unknown transform: ' + transform);
          }
        }
        return transformResults;
      }

      private transformObject(
        data: ObjectValue,
        transformResults: FieldValue[]
      ): ObjectValue {
        assert(
          transformResults.length === this.fieldTransforms.length,
          'TransformResults length mismatch.'
        );

        for (let i = 0; i < this.fieldTransforms.length; i++) {
          const fieldTransform = this.fieldTransforms[i];
          const transform = fieldTransform.transform;
          const fieldPath = fieldTransform.field;
          Eif (transform instanceof ServerTimestampTransform) {
            data = data.set(fieldPath, transformResults[i]);
          } else {
            return fail('Encountered unknown transform: ' + transform);
          }
        }
        return data;
      }
    }

    /** A mutation that deletes the document at the given key. */
    export class DeleteMutation extends Mutation {
      constructor(readonly key: DocumentKey, readonly precondition: Precondition) {
        super();
      }

      readonly type: MutationType = MutationType.Delete;

      applyToRemoteDocument(
        maybeDoc: MaybeDocument | null,
        mutationResult: MutationResult
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        assert(
          mutationResult.transformResults == null,
          'Transform results received by DeleteMutation.'
        );

        // Unlike applyToLocalView, if we're applying a mutation to a remote
        // document the server has accepted the mutation so the precondition must
        // have held.

        return new NoDocument(this.key, SnapshotVersion.MIN);
      }

      applyToLocalView(
        maybeDoc: MaybeDocument | null,
        baseDoc: MaybeDocument | null,
        localWriteTime: Timestamp
      ): MaybeDocument | null {
        this.verifyKeyMatches(maybeDoc);

        Iif (!this.precondition.isValidFor(maybeDoc)) {
          return maybeDoc;
        }

        if (maybeDoc) {
          assert(
            maybeDoc.key.isEqual(this.key),
            'Can only apply mutation to document with same key'
          );
        }
        return new NoDocument(this.key, SnapshotVersion.forDeletedDoc());
      }

      isEqual(other: Mutation): boolean {
        return (
          other instanceof DeleteMutation &&
          this.key.isEqual(other.key) &&
          this.precondition.isEqual(other.precondition)
        );
      }
    }