import MongoCollection from './MongoCollection';

function mongoFieldToParseSchemaField(type) {
  if (type[0] === '*') {
    return {
      type: 'Pointer',
      targetClass: type.slice(1),
    };
  }
  if (type.startsWith('relation<')) {
    return {
      type: 'Relation',
      targetClass: type.slice('relation<'.length, type.length - 1),
    };
  }
  switch (type) {
    case 'number':   return {type: 'Number'};
    case 'string':   return {type: 'String'};
    case 'boolean':  return {type: 'Boolean'};
    case 'date':     return {type: 'Date'};
    case 'map':
    case 'object':   return {type: 'Object'};
    case 'array':    return {type: 'Array'};
    case 'geopoint': return {type: 'GeoPoint'};
    case 'file':     return {type: 'File'};
    case 'bytes':    return {type: 'Bytes'};
  }
}

const nonFieldSchemaKeys = ['_id', '_metadata', '_client_permissions'];
function mongoSchemaFieldsToParseSchemaFields(schema) {
  var fieldNames = Object.keys(schema).filter(key => nonFieldSchemaKeys.indexOf(key) === -1);
  var response = fieldNames.reduce((obj, fieldName) => {
    obj[fieldName] = mongoFieldToParseSchemaField(schema[fieldName])
    return obj;
  }, {});
  response.ACL = {type: 'ACL'};
  response.createdAt = {type: 'Date'};
  response.updatedAt = {type: 'Date'};
  response.objectId = {type: 'String'};
  return response;
}

const emptyCLPS = Object.freeze({
  find: {},
  get: {},
  create: {},
  update: {},
  delete: {},
  addField: {},
});

const defaultCLPS = Object.freeze({
  find: {'*': true},
  get: {'*': true},
  create: {'*': true},
  update: {'*': true},
  delete: {'*': true},
  addField: {'*': true},
});

function mongoSchemaToParseSchema(mongoSchema) {
  let clps = defaultCLPS;
  if (mongoSchema._metadata && mongoSchema._metadata.class_permissions) {
    clps = {...emptyCLPS, ...mongoSchema._metadata.class_permissions};
  }
  return {
    className: mongoSchema._id,
    fields: mongoSchemaFieldsToParseSchemaFields(mongoSchema),
    classLevelPermissions: clps,
  };
}

function _mongoSchemaQueryFromNameQuery(name: string, query) {
  return _mongoSchemaObjectFromNameFields(name, query);
}

function _mongoSchemaObjectFromNameFields(name: string, fields) {
  let object = { _id: name };
  if (fields) {
    Object.keys(fields).forEach(key => {
      object[key] = fields[key];
    });
  }
  return object;
}

// Returns a type suitable for inserting into mongo _SCHEMA collection.
// Does no validation. That is expected to be done in Parse Server.
function parseFieldTypeToMongoFieldType({ type, targetClass }) {
  switch (type) {
    case 'Pointer':  return `*${targetClass}`;
    case 'Relation': return `relation<${targetClass}>`;
    case 'Number':   return 'number';
    case 'String':   return 'string';
    case 'Boolean':  return 'boolean';
    case 'Date':     return 'date';
    case 'Object':   return 'object';
    case 'Array':    return 'array';
    case 'GeoPoint': return 'geopoint';
    case 'File':     return 'file';
  }
}

// Returns { code, error } if invalid, or { result }, an object
// suitable for inserting into _SCHEMA collection, otherwise.
function mongoSchemaFromFieldsAndClassNameAndCLP(fields, className, classLevelPermissions) {

  let mongoObject = {
    _id: className,
    objectId: 'string',
    updatedAt: 'string',
    createdAt: 'string'
  };

  for (let fieldName in fields) {
    mongoObject[fieldName] = parseFieldTypeToMongoFieldType(fields[fieldName]);
  }

  if (typeof classLevelPermissions !== 'undefined') {
    mongoObject._metadata = mongoObject._metadata || {};
    if (!classLevelPermissions) {
      delete mongoObject._metadata.class_permissions;
    } else {
      mongoObject._metadata.class_permissions = classLevelPermissions;
    }
  }

  return mongoObject;
}

class MongoSchemaCollection {
  _collection: MongoCollection;

  constructor(collection: MongoCollection) {
    this._collection = collection;
  }

  _fetchAllSchemasFrom_SCHEMA() {
    return this._collection._rawFind({})
    .then(schemas => schemas.map(mongoSchemaToParseSchema));
  }

  _fechOneSchemaFrom_SCHEMA(name: string) {
    return this._collection._rawFind(_mongoSchemaQueryFromNameQuery(name), { limit: 1 }).then(results => {
      if (results.length === 1) {
        return mongoSchemaToParseSchema(results[0]);
      } else {
        throw undefined;
      }
    });
  }

  // Atomically find and delete an object based on query.
  findAndDeleteSchema(name: string) {
    return this._collection._mongoCollection.findAndRemove(_mongoSchemaQueryFromNameQuery(name), []);
  }

  // Returns a promise that is expected to resolve with the newly created schema, in Parse format.
  // If the class already exists, returns a promise that rejects with DUPLICATE_VALUE as the reason.
  addSchema(name: string, fields, classLevelPermissions) {
    let mongoSchema = mongoSchemaFromFieldsAndClassNameAndCLP(fields, name, classLevelPermissions);
    let mongoObject = _mongoSchemaObjectFromNameFields(name, mongoSchema);
    return this._collection.insertOne(mongoObject)
    .then(result => mongoSchemaToParseSchema(result.ops[0]))
    .catch(error => {
      if (error.code === 11000) { //Mongo's duplicate key error
        throw new Parse.Error(Parse.Error.DUPLICATE_VALUE, 'Class already exists.');
      } else {
        throw error;
      }
    });
  }

  updateSchema(name: string, update) {
    return this._collection.updateOne(_mongoSchemaQueryFromNameQuery(name), update);
  }

  upsertSchema(name: string, query: string, update) {
    return this._collection.upsertOne(_mongoSchemaQueryFromNameQuery(name, query), update);
  }

  // Add a field to the schema. If database does not support the field
  // type (e.g. mongo doesn't support more than one GeoPoint in a class) reject with an "Incorrect Type"
  // Parse error with a desciptive message. If the field already exists, this function must
  // not modify the schema, and must reject with DUPLICATE_VALUE error.
  // If this is called for a class that doesn't exist, this function must create that class.

  // TODO: throw an error if an unsupported field type is passed. Deciding whether a type is supported
  // should be the job of the adapter. Some adapters may not support GeoPoint at all. Others may
  // Support additional types that Mongo doesn't, like Money, or something.

  // TODO: don't spend an extra query on finding the schema if the type we are trying to add isn't a GeoPoint.
  addFieldIfNotExists(className: string, fieldName: string, type: string) {
    return this._fechOneSchemaFrom_SCHEMA(className)
    .then(schema => {
      // The schema exists. Check for existing GeoPoints.
      if (type.type === 'GeoPoint') {
        // Make sure there are not other geopoint fields
        if (Object.keys(schema.fields).some(existingField => schema.fields[existingField].type === 'GeoPoint')) {
          throw new Parse.Error(Parse.Error.INCORRECT_TYPE, 'MongoDB only supports one GeoPoint field in a class.');
        }
      }
      return;
    }, error => {
      // If error is undefined, the schema doesn't exist, and we can create the schema with the field.
      // If some other error, reject with it.
      if (error === undefined) {
        return;
      }
      throw error;
    })
    .then(() => {
      // We use $exists and $set to avoid overwriting the field type if it
      // already exists. (it could have added inbetween the last query and the update)
      return this.upsertSchema(
        className,
        { [fieldName]: { '$exists': false } },
        { '$set' : { [fieldName]: parseFieldTypeToMongoFieldType(type) } }
      );
    });
  }
}

// Exported for testing reasons and because we haven't moved all mongo schema format
// related logic into the database adapter yet.
MongoSchemaCollection._TESTmongoSchemaToParseSchema = mongoSchemaToParseSchema

export default MongoSchemaCollection