fix(tooltip): throw a better error when an invalid position is passed

* Throws a more informative error message when an invalid position is passed to the tooltip. Previously it would throw something along the lines of `Cannot read property 'originX' of undefined`.
* Moves the various tooltip switch statements to use an enum for easier validation.

Referencing angular#1959.

src/lib/tooltip/tooltip-errors.ts

@@ -0,0 +1,11 @@
+import {MdError} from '../core';
+
+/** Exception thrown when a tooltip has an invalid position. */
+export class MdTooltipInvalidPositionError extends MdError {
+  constructor(position: string, allowedPositions: string[]) {
+    super(
+      `Tooltip position "${position}" is invalid. The allowed position are: "` +
+      allowedPositions.join(', ') + '".'
+    );
+  }
+}

src/lib/tooltip/tooltip.spec.ts

@@ -155,20 +155,27 @@ describe('MdTooltip', () => {
         phaseName: '',
       }));
     }));
+
+    it('should throw when trying to assign an invalid position', () => {
+      expect(() => {
+        fixture.componentInstance.position = 'everywhere';
+        fixture.detectChanges();
+      }).toThrowError(/Tooltip position "everywhere" is invalid/);
+    });
   });
 });
 
 @Component({
   selector: 'app',
   template: `
     <button *ngIf="showButton"
-            [md-tooltip]="message" 
+            [md-tooltip]="message"
             [tooltip-position]="position">
       Button
     </button>`
 })
 class BasicTooltipDemo {
-  position: TooltipPosition = 'below';
+  position: string = 'below';
   message: string = initialTooltipMessage;
   showButton: boolean = true;
 }

src/lib/tooltip/tooltip.ts

@@ -24,11 +24,41 @@ import {
   OriginConnectionPosition,
   OVERLAY_PROVIDERS,
 } from '../core';
+import {MdTooltipInvalidPositionError} from './tooltip-errors';
 import {Observable} from 'rxjs/Observable';
 import {Subject} from 'rxjs/Subject';
 
 export type TooltipPosition = 'before' | 'after' | 'above' | 'below';
 
+const TOOLTIP_POSITION_CONFIG: {
+  [key: string]: {
+    origin: OriginConnectionPosition,
+    position: OverlayConnectionPosition,
+    transformOrigin: string
+  }
+} = {
+  before: {
+    origin: { originX: 'start', originY: 'center' },
+    position: { overlayX: 'end', overlayY: 'center' },
+    transformOrigin: 'right'
+  },
+  after: {
+    origin: { originX: 'end', originY: 'center' },
+    position: { overlayX: 'start', overlayY: 'center' },
+    transformOrigin: 'left'
+  },
+  above: {
+    origin: { originX: 'center', originY: 'top' },
+    position: { overlayX: 'center', overlayY: 'bottom' },
+    transformOrigin: 'bottom'
+  },
+  below: {
+    origin: { originX: 'center', originY: 'bottom' },
+    position: { overlayX: 'center', overlayY: 'top' },
+    transformOrigin: 'top'
+  }
+};
+
 /** Time in ms to delay before changing the tooltip visibility to hidden */
 export const TOUCHEND_HIDE_DELAY  = 1500;
 
@@ -59,6 +89,10 @@ export class MdTooltip {
   }
 
   set position(value: TooltipPosition) {
+    if (!TOOLTIP_POSITION_CONFIG.hasOwnProperty(value)) {
+      throw new MdTooltipInvalidPositionError(value, Object.keys(TOOLTIP_POSITION_CONFIG));
+    }
+
     if (value !== this._position) {
       this._position = value;
 
@@ -136,8 +170,8 @@ export class MdTooltip {
 
   /** Create the overlay config and position strategy */
   private _createOverlay(): void {
-    let origin = this._getOrigin();
-    let position = this._getOverlayPosition();
+    let origin = TOOLTIP_POSITION_CONFIG[this.position].origin;
+    let position = TOOLTIP_POSITION_CONFIG[this.position].position;
     let strategy = this._overlay.position().connectedTo(this._elementRef, origin, position);
     let config = new OverlayState();
     config.positionStrategy = strategy;
@@ -152,26 +186,6 @@ export class MdTooltip {
     this._tooltipInstance = null;
   }
 
-  /** Returns the origin position based on the user's position preference */
-  private _getOrigin(): OriginConnectionPosition {
-    switch (this.position) {
-      case 'before': return { originX: 'start',  originY: 'center' };
-      case 'after':  return { originX: 'end',    originY: 'center' };
-      case 'above':  return { originX: 'center', originY: 'top' };
-      case 'below':  return { originX: 'center', originY: 'bottom' };
-    }
-  }
-
-  /** Returns the overlay position based on the user's preference */
-  private _getOverlayPosition(): OverlayConnectionPosition {
-    switch (this.position) {
-      case 'before': return { overlayX: 'end',    overlayY: 'center' };
-      case 'after':  return { overlayX: 'start',  overlayY: 'center' };
-      case 'above':  return { overlayX: 'center', overlayY: 'bottom' };
-      case 'below':  return { overlayX: 'center', overlayY: 'top' };
-    }
-  }
-
   /** Updates the tooltip message and repositions the overlay according to the new message length */
   private _setTooltipMessage(message: string) {
     // Must wait for the message to be painted to the tooltip so that the overlay can properly
@@ -228,7 +242,7 @@ export class TooltipComponent {
   show(position: TooltipPosition): void {
     this._closeOnInteraction = false;
     this._visibility = 'visible';
-    this._setTransformOrigin(position);
+    this._transformOrigin = TOOLTIP_POSITION_CONFIG[position].transformOrigin;
 
     // Cancel the delayed hide if it is scheduled
     if (this._hideTimeoutId) {
@@ -258,16 +272,6 @@ export class TooltipComponent {
     return this._visibility === 'visible';
   }
 
-  /** Sets the tooltip transform origin according to the tooltip position */
-  _setTransformOrigin(value: TooltipPosition) {
-    switch (value) {
-      case 'before': this._transformOrigin = 'right'; break;
-      case 'after':  this._transformOrigin = 'left'; break;
-      case 'above':  this._transformOrigin = 'bottom'; break;
-      case 'below':  this._transformOrigin = 'top'; break;
-    }
-  }
-
   _afterVisibilityAnimation(e: AnimationTransitionEvent): void {
     if (e.toState === 'hidden' && !this.isVisible()) {
       this._onHide.next();