// Import for testing
import { log } from 'console';
// This is so that we can see `console.log`s when we run `jest`

// Import Mongo
import MongoDB from 'mongodb';

// Import UUID
import { v4 as genUniqueId } from 'uuid';

// Import state
import dbState from '../dbState';

// Import types
import CollectionInterface from '../types/CollectionInterface';
import CollectionProcedure from '../coconut-types/CollectionProcedure';
import CollectionOpts from '../types/CollectionOpts';
import Id from '../types/Id';
import Query from '../types/Query';
import PaginatedResponse from '../types/PaginatedResponse';

// Import helpers
import initCollection from '../helpers/initCollection';
import processFindResult from '../helpers/processFindResult';
import getLockCollectionName from '../helpers/getLockCollectionName';
import getLockCollectionOpts from '../helpers/getLockCollectionOpts';
import pollResource, { PollingError } from '../helpers/pollResource';

// Import constants
import LOCK_POLL_INTERVAL_MS from '../constants/LOCK_POLL_INTERVAL_MS';
import DEFAULT_LOCK_TTL_MS from '../constants/DEFAULT_LOCK_TTL_MS';

/*------------------------------------------------------------------------*/
/*                               Collection                               */
/*------------------------------------------------------------------------*/

class Collection<DocumentType extends { [k: string]: any }> implements
  CollectionInterface<DocumentType> {
  // Name of this collection
  private collectionName: string;

  // Name of the unique key for the unique index (if one exists)
  private uniqueKey?: string; // can only be 'id' for concurrent

  // Promise that resolves with the mongo collection
  private collection: Promise<MongoDB.Collection<MongoDB.Document>>;

  // Whether the collection supports concurrency
  private supportConcurrency = false;

  // The collection of locks
  private lockCollection?: Promise<MongoDB.Collection<MongoDB.Document>>;

  // The maximum time that a lock can be in place
  private lockTimeToLiveMS: number;

  // The id of the 'server' using this Collection, for use with locks
  private serverId?: string; // uuid

  // If true, this collection uses TTL
  private usesTTL: boolean = false;

  /**
   * Create a new Collection
   * @author Gabe Abrams
   * @param collectionName the collection name
   * @param options the options for the collection (used when
   *   creating it)
   * @param [options.uniqueIndexKey] the name of the unique index
   *   (only created if included)
   * @param [options.expireAfterSeconds=no expiry] if unique index is
   *   created, this is the number of seconds before items on each key expire
   * @param [options.indexKeys] the names of keys to build
   *   secondary indexes on
   */
  public constructor(
    collectionName: string,
    options: CollectionOpts = {},
  ) {
    // Save collection name
    this.collectionName = collectionName;

    // Remember unique index
    this.uniqueKey = options.uniqueIndexKey;

    // Make sure init has been called first
    if (
      !dbState.schemaVersionTag
      || !dbState.initDB
    ) {
      // Init hasn't been called yet
      // eslint-disable-next-line no-console
      log('DCE-MANGO: Collection class instance created before initMango was called. Fatal error. Exiting.');
      process.exit(1);
    }

    // Remember if using TTL
    this.usesTTL = Boolean(options.expireAfterSeconds);

    // Initialize and save the promise so other functions can wait for the
    //   initialization to complete
    this.collection = initCollection(collectionName, options);

    if (options.supportConcurrency) {
      this.supportConcurrency = true;
      if (!this.uniqueKey) {
        throw new Error('A collection without a `uniqueIndexKey` cannot support concurrency.');
      }
      const lockCollectionName = getLockCollectionName(collectionName);
      const lockCollectionOpts = getLockCollectionOpts(options.atomicUpdateTimeoutMs);

      this.serverId = genUniqueId();
      this.lockCollection = initCollection(lockCollectionName, lockCollectionOpts);
      this.lockTimeToLiveMS = options.atomicUpdateTimeoutMs ?? DEFAULT_LOCK_TTL_MS;
    }
  }

  /*------------------------------------------------------------------------*/
  /*                            Getter Functions                            */
  /*------------------------------------------------------------------------*/

  /**
   * Get whether the collection supports concurrency or not.
   * @author Benedikt Arnarsson
   * @returns boolean indicating whether the collection supports concurrency.
   */
  public getSupportConcurrency() {
    return this.supportConcurrency;
  }

  /*------------------------------------------------------------------------*/
  /*                            Public Functions                            */
  /*------------------------------------------------------------------------*/

  /**
   * Run a query
   * @author Gabe Abrams
   * @param query the query to run
   * @param [includeMongoTimestamp] if true, include the timestamp
   *   in the mongo objects
   * @returns documents
   */
  public async find(
    query: Query,
    includeMongoTimestamp?: boolean,
  ): Promise<DocumentType[]> {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Get the list of matching items
    const items = await collection.find(query).toArray();

    // Filter out internal ids and add timestamps
    const processedItems: unknown[] = items.map((item) => {
      return processFindResult(item, includeMongoTimestamp);
    });

    return (
      items
        ? processedItems
        : []
    ) as DocumentType[];
  }

  /**
   * Run a query with pagination
   * @author Yuen Ler Chow
   * @param query the query to run
   * @param perPage the number of items per page
   * @param pageNumber the page number to return, 1-indexed
   * @param [includeMongoTimestamp] if true, include the timestamp
   *   in the mongo objects
   * @param [sortKey] the key to sort by, or _id if not provided
   * @param [sortDescending] if true, sort descending
   * @returns documents
   */
  public async findPaged(
    opts: {
      query: Query,
      perPage?: number,
      pageNumber?: number,
      includeMongoTimestamp?: boolean,
      sortKey?: string,
      sortDescending?: boolean,
    },
  ): Promise<PaginatedResponse<DocumentType>> {
    const {
      query,
      perPage = 10,
      pageNumber = 1,
      includeMongoTimestamp,
      sortKey = '_id',
      sortDescending,
    } = opts;

    if (pageNumber < 1) {
      throw new Error('Page number must be at least 1');
    }
    if (perPage < 1) {
      throw new Error('Per page must be at least 1');
    }

    // Wait for initialization to complete
    const collection = await this.collection;

    // Get the list of matching items for the specified page
    const items = await (
      collection
        .find(query)
        .sort({ [sortKey]: sortDescending ? -1 : 1 })
        .skip(perPage * (pageNumber - 1))
        // Get 1 extra item to check if there is another page
        .limit(perPage + 1)
        .toArray()
    );

    const hasAnotherPage = items.length > perPage;

    // Remove the extra item if there is another page
    if (hasAnotherPage) {
      items.pop();
    }

    // Filter out internal ids and add timestamps
    const processedItems: unknown[] = items.map((item) => {
      return processFindResult(item, includeMongoTimestamp);
    });

    return {
      items: (
        items
          ? processedItems
          : []
      ) as DocumentType[],
      currentPageNumber: pageNumber,
      perPage,
      hasAnotherPage,
    };
  }

  /**
   * Find elements then only return the values for one specific property from
   *   each item
   * @author Gabe Abrams
   * @param query the query to run
   * @param prop the name of the property to extract
   * @param [excludeFalsy] if true, exclude falsy values
   * @returns array of values of the property
   */
  public async findAndExtractProp(
    query: Query,
    prop: string,
    excludeFalsy?: boolean,
  ): Promise<any[]> {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Get the list of matching items
    const items = await collection.find(
      query,
      {
        projection: { [prop]: 1 },
      },
    ).toArray();

    // Only return the value of the prop, filter falsy values if requested
    return (
      items
        .map((item) => {
          return item[prop];
        })
        .filter((item) => {
          return (!excludeFalsy || item);
        })
    );
  }

  /**
   * Count the number of matching elements
   * @author Gabe Abrams
   * @param query the query to run
   * @returns number of documents that match
   */
  public async count(query: Query): Promise<number> {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Count
    const count = await collection.countDocuments(query);
    return count;
  }

  /**
   * List distinct values for a property in a collection
   * @author Gabe Abrams
   * @param prop the property to list distinct values for
   * @param [query] the query to run. If excluded, all distinct
   *  values are included
   * @returns array of distinct values
   */
  public async distinct(
    prop: string,
    query?: Query,
  ): Promise<any[]> {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Get distinct values
    const distinctValues = await collection.distinct(
      prop,
      query ?? {},
    );
    return distinctValues;
  }

  /**
   * Increment value of an integer for an object (doesn't reset TTL)
   * @author Gabe Abrams
   * @param id id of the object to increment
   * @param prop property to increment
   */
  public async increment(id: Id, prop: string) {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Increment
    return collection.findOneAndUpdate(
      {
        id,
      },
      {
        $inc: {
          [prop]: 1,
        },
      },
    );
  }

  /**
   * Increment value of an integer for an object, found by a query (doesn't reset TTL)
   * @author Gabe Abrams
   * @param query query to find the object to increment
   * @param prop property to increment
   */
  public async incrementByQuery(
    query: { [k: string]: any },
    prop: string,
  ) {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Increment
    return collection.findOneAndUpdate(
      query,
      {
        $inc: {
          [prop]: 1,
        },
      },
    );
  }

  /**
   * Add/update object values in an entry in the collection. The entry must
   *   already exist (doesn't reset TTL)
   * @author Gabe Abrams
   * @param query query to apply to find the object to update
   * @param updates map of updates: { prop => value } where prop is
   *   the potentially nested name of the property
   *   (e.g. "age" or "profile.age")
   */
  public async updatePropValues(
    query: Query,
    updates: Query,
  ) {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Perform update
    return collection.findOneAndUpdate(
      query,
      {
        $set: updates,
      },
    );
  }

  /**
   * Add an object to an array in an object (doesn't reset TTL)
   * @author Gabe Abrams
   * @param id the id of the object to modify
   * @param arrayProp the name of the array to insert into
   * @param obj the object to insert into the array
   */
  public async push(
    id: Id,
    arrayProp: string,
    obj: any,
  ) {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Push
    return collection.findOneAndUpdate(
      {
        id,
      },
      {
        $push: {
          [arrayProp]: obj,
        } as any,
      },
    );
  }

  /**
   * Filter an array of objects or primitives in an entry in the collection (doesn't reset TTL)
   * @author Gabe Abrams
   * @param opts object containing all args
   * @param opts.id the id of the object to modify
   * @param opts.arrayProp the name of the array to filter
   * @param [opts.compareProp] the name of the array entry prop to compare.
   * @param opts.compareValue the value of the array entry prop to filter
   *   out
   */
  public async filterOut(
    opts: {
      id: Id,
      arrayProp: string,
      compareProp?: string,
      compareValue: any,
    },
  ) {
    const {
      id,
      arrayProp,
      compareProp,
      compareValue,
    } = opts;

    // Wait for initialization to complete
    const collection = await this.collection;

    // Perform update
    if (!compareProp) {
      return collection.findOneAndUpdate(
        {
          id,
        },
        {
          $pull: {
            [arrayProp]: compareValue,
          } as any, // Cast is required because mongodb lib uses an improper type
        },
      );
    }
    return collection.findOneAndUpdate(
      {
        id,
      },
      {
        $pull: {
          [arrayProp]: {
            [compareProp]: compareValue,
          },
        } as any, // Cast is required because mongodb lib uses an improper type
      },
    );
  }

  /**
   * Write a record to the collection (DOES reset TTL)
   * @author Gabe Abrams
   * @param obj the object to insert
   */
  public async insert(obj: DocumentType) {
    // Remove stuff from object
    const updatedObj = obj;
    delete (updatedObj as any).mongoTimestamp;

    // If using TTL, add last updated field
    if (this.usesTTL) {
      (updatedObj as any).lastUpdatedForTTL = (new Date()).toISOString();
    }

    // Wait for initialization to complete
    const collection = await this.collection;

    // Check if we are inserting uniquely
    if (this.uniqueKey) {
      // Unique! Use replacement
      const query = {
        // Cast obj to any to force allowing this operation
        [this.uniqueKey]: (updatedObj as any)[this.uniqueKey],
      };

      await collection.updateOne(
        query, // Query to find the option to replace
        { $set: updatedObj }, // Type of update is a "set" operation
        { upsert: true }, // Choose to replace
      );
    } else {
      // Not unique. Just insert
      await collection.insertOne(updatedObj);
    }
  }

  /**
   * Delete the first document that matches the query in the collection
   * @author Gabe Abrams
   * @param query the query that will match the item
   */
  public async delete(query: Query) {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Delete the object
    await collection.deleteOne(query);
  }

  /**
   * Delete all documents that match the query in the collection
   * @author Gabe Abrams
   * @param query the query that will match the items to delete
   */
  public async deleteAll(query: Query) {
    // Wait for initialization to complete
    const collection = await this.collection;

    // Delete all matches
    await collection.deleteMany(query);
  }

  /*------------------------------------------------------------------------*/
  /*                           Concurrent Methods                           */
  /*------------------------------------------------------------------------*/

  /**
   * Creates a lock in the lock collection, to make sure modifications aren't made to the document with id=id.
   * @author Benedikt Arnarsson
   * @param id the 'id' of the document we want to lock.
   */
  private async lock(id: Id) {
    if (!this.supportConcurrency) {
      throw new Error('Cannot call lock on a Collection without concurrency support!');
    }
    const lockCollection = await this.lockCollection;
    const { serverId } = this;

    // Creating the lock with the document Id and serverId
    const lock = {
      id,
      serverId,
    };

    /**
     * Process of acquiring the lock from the lock-collection, used by pollResource.
     * @author Benedikt Arnarsson
     * @returns the Lock which is needed for concurrent process, must be of type Promise<MongoDB.UpdateResult>
     */
    const callResource = async () => {
      // Using updateOne w/ setOnInsert & upsert will make it only insert when there is no lock with same document Id
      return lockCollection.updateOne(
        // TODO: add time of insertion
        { id },
        { $setOnInsert: lock },
        { upsert: true },
      );
    };

    /**
     * Process of validating that we acquired the lock from the lock-collection, used by pollResource.
     * @author Benedikt Arnarsson
     * @param res the output of acquiring the resource, in this case the lock.
     * @returns boolean indicating whether we successfully acquired the lock.
     */
    const validateResult = (res: MongoDB.UpdateResult) => {
      return res.upsertedCount > 0;
    };

    // Initiate pollResource
    const result = await pollResource({
      callResource,
      validateResult,
      waitForMS: LOCK_POLL_INTERVAL_MS,
      // FIXME: when multiple servers are working
      // Add some randomness here so other servers can acquire lock
      timeOut: 2 * this.lockTimeToLiveMS,
    });

    // Logging
    if ((process.env.MANGO_LOG_LEVEL ?? '').toLowerCase() === 'info') {
      log(`Locking on ${serverId} (${this.collectionName}):\n\t- upserted: ${result.upsertedCount}\n\t- matched: ${result.matchedCount}\n\t- modified: ${result.modifiedCount}`);
    }
  }

  /**
   * Inverse of lock operation. Unlock a document which you have locked.
   * @author Benedikt Arnarsson
   * @param id the 'id' of the document that is being unlocked.
   */
  private async unlock(id: Id) {
    if (!this.supportConcurrency) {
      throw new Error('Cannot call unlock on a Collection without concurrency support!');
    }
    const lockCollection = await this.lockCollection;
    const { serverId } = this;

    // Only deletes a lock with the same id *and* serverId
    await lockCollection.deleteOne({ id, serverId });

    // Logging
    if ((process.env.MANGO_LOG_LEVEL ?? '').toLowerCase() === 'info') {
      log(`Unlocked document ${id}, with ${serverId} (${this.collectionName})`);
    }
  }

  /**
   * Given a function representing a set of operations on the collection and a set of ids to lock,
   * will run the function such that other collections cannot make modifications while the function runs.
   * For use in situations with multiple concurrent servers using the same database.
   * @author Benedikt Arnarsson
   * @param opts object containing all parameters
   * @param opts.idOrIdsToLock the one Id or list of Ids to lock for the procedure provided.
   * @param opts.procedure the procedure that is being wrapped in the lock-unlock calls
   * @returns the result of opts.procedure
   */
  public async runAtomicProcedure<Result>(
    opts: {
      idOrIdsToLock: Id | Id[],
      procedure: CollectionProcedure<DocumentType, Result>,
    },
  ): Promise<Result> {
    if (!this.supportConcurrency) {
      throw new Error('Cannot call runAtomicProcedure on a Collection without concurrency support!');
    }

    // Destructure
    const {
      idOrIdsToLock,
      procedure,
    } = opts;

    const collection = await this.collection;

    const ids = (
      Array.isArray(idOrIdsToLock)
        ? idOrIdsToLock
        : [idOrIdsToLock]
    );
    const query = Object.fromEntries([
      [this.uniqueKey, { $in: ids }],
    ]);

    // Get the list of matching items
    const items = await collection.find(query).toArray();

    // Filter out internal ids
    const uniqueIndexValues: unknown[] = (
      items
        ? items.map((item) => {
          return item[this.uniqueKey];
        })
        : []
    );

    let result: Result;
    try {
      // Lock all items
      await Promise.all(
        uniqueIndexValues.map(async (uniqueIndexValue) => {
          await this.lock(uniqueIndexValue as Id);
        }),
      );
      // Execute the procedure
      result = await procedure(this);
    } catch (err) {
      if (err instanceof PollingError) {
        throw new PollingError('Exceeded timeout when attempting to lock for atomic procedure.');
      } else {
        const errMsg = 'Failed to complete atomic procedure:';
        err.message = `${errMsg} ${err.message}`;
        throw err;
      }
    } finally {
      // Unlock all items
      await Promise.all(
        uniqueIndexValues.map(async (uniqueIndexValue) => {
          await this.unlock(uniqueIndexValue as Id);
        }),
      );
    }

    return result;
  }
}

export default Collection;