var Q = require('q');

/**
 * OKResource!
 * TODO Would be nicer to compose this with an existing resource
 * module, but haven't found a good fit. Should keep an eye on
 * 'resource' by bigcompany for an update.
 */
function OKResource(options) {
  if (!(this instanceof OKResource)) return new OKResource(options);
  options = options || {};
  if (!options.type)
    throw new Error('No resource type provided to OKResource')
  if (!options.schema)
    throw new Error('No schema provided to OKResource');
  if (!options.db)
    throw new Error('No DB provided to OKResource');

  var schema = options.schema;
  // Iterate through spec to find field which will act as the
  // resource id in da db.
  var idField = Object.keys(schema.spec).reduce(function(idField, prop) {
    var spec = schema.spec[prop];
    if (spec.id)
      idField = prop;
    return idField;
  // If schema has a prop called 'id', default to that one
  }, schema.id && 'id');
  if (!idField)
    throw new Error('Bad schema: no ID field');

  var type = options.type;
  this._db = options.db;

  // Define properties which are part of the API

  Object.defineProperty(this, 'schema', {
    value: schema,
    writable: false,
    enumerable: true
  });

  Object.defineProperty(this, 'spec', {
    value: schema.spec,
    writable: false,
    enumerable: true
  });

  Object.defineProperty(this, 'type', {
    value: type,
    writable: false,
    enumerable: true
  });

  Object.defineProperty(this, 'idField', {
    value: idField,
    writable: false,
    enumerable: true
  });
}

/**
 * Throws an error if data does not conform to schema
 */
OKResource.prototype.assertValid = function(data) {
  this.schema.assertValid(data);
};

OKResource.prototype.all = function() {
  return this._db.getAll(this.type);
};

OKResource.prototype.create = function(data) {
  data = data || {};
  var id = data[this.idField];
  return Q.promise(function(resolve, reject) {
    if (!id) {
      reject(new Error('Data does not contain ID property'));
    } else {
      this._db.create(this.type, data).then(resolve, reject);
    }
  });
};

OKResource.prototype.destroy = function(data) {
  data = data || {};
  var id = data[this.idField];
  return Q.promise(function(resolve, reject) {
    if (!id) {
      reject(new Error('Data does not contain ID property'));
    } else {
      this._db.remove(this.type, data.id, data).then(resolve, reject);
    }
  });
};

OKResource.prototype.find = function(query) {
  return Q.promise(function(resolve, reject) {
    if (!query) {
      throw new Error('No query given');
    } else {
      this._db.find(this.type, query).then(resolve, reject);
    }
  });
};

OKResource.prototype.get = function(id) {
  var db = this._db;
  var type = this.type;
  var idField = this.idField;
  return Q.promise(function(resolve, reject) {
    if (!id) {
      throw new Error('No ID given');
    } else {
      // We have the id, but we still need
      // to resolve which field is the id field
      // to match
      var query = {};
      query[idField] = id;
      db.get(type, query).then(resolve, reject);
    }
  });
};

OKResource.prototype.update = function(data) {
  data = data || {};
  var id = data[this.idField];
  var db = this._db;
  var type = this.type;
  var idField = this.idField;
  return Q.promise(function(resolve, reject) {
    if (!id) {
      reject(new Error('Data does not contain ID property'));
    } else {
      var query = {};
      query[idField] = data[idField];
      db.put(type, query, data).then(resolve, reject);;
    }
  });
};

OKResource.prototype.updateOrCreate = function(data) {
  data = data || {};
  var id = data[this.idField];
  var type = this.type;
  var db = this._db;
  var idField = this.idField;
  return Q.promise(function(resolve, reject) {
    if (!id) {
      reject(new Error('Cannot updateOrCreate without ID'));
    } else {
      db.get(type, data.id).then(function(cached) {
        var query = {};
        query[idField] = id;
        if (cached)
          db.put(type, query, data).then(resolve, reject);
        else
          db.create(type, data).then(resolve, reject);
      }, reject);
    }
  });
};

module.exports = OKResource;