Refactor usage of thread elements in gr-diff

Unify all calls to threadEl.getAttribute() in gr-diff-utils.

Change-Id: Iea805a8885d2fa222329ec841fd931d4b5369010
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element.ts b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element.ts
index 2f85a0b..912d59e 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element.ts
@@ -306,7 +306,7 @@
     return this.getContentTdByLine(line, side, row);
   }
 
-  getLineElByNumber(lineNumber: string | number, side?: Side) {
+  getLineElByNumber(lineNumber: LineNumber, side?: Side) {
     const sideSelector = side ? '.' + side : '';
     return this.diffElement.querySelector(
       `.lineNum[data-value="${lineNumber}"]${sideSelector}`
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-diff-highlight.ts b/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-diff-highlight.ts
index 08a567b..c788d76 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-diff-highlight.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-highlight/gr-diff-highlight.ts
@@ -30,6 +30,7 @@
 import {GrSelectionActionBox} from '../gr-selection-action-box/gr-selection-action-box';
 import {GrDiffBuilderElement} from '../gr-diff-builder/gr-diff-builder-element';
 import {FILE} from '../gr-diff/gr-diff-line';
+import {getRange, getSide} from '../gr-diff/gr-diff-utils';
 
 interface SidedRange {
   side: Side;
@@ -199,13 +200,9 @@
   }
 
   _indexForThreadEl(threadEl: HTMLElement) {
-    const side = threadEl.getAttribute('comment-side') as Side;
-    const rangeString = threadEl.getAttribute('range');
-    if (!rangeString) return undefined;
-    const range = JSON.parse(rangeString) as CommentRange;
-
-    if (!range) return undefined;
-
+    const side = getSide(threadEl);
+    const range = getRange(threadEl);
+    if (!side || !range) return undefined;
     return this._indexOfCommentRange(side, range);
   }
 
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
index 4b4f429..2223734 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
@@ -24,7 +24,12 @@
 import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {htmlTemplate} from './gr-diff-host_html';
 import {GerritNav} from '../../core/gr-navigation/gr-navigation';
-import {rangesEqual} from '../gr-diff/gr-diff-utils';
+import {
+  getLine,
+  getRange,
+  getSide,
+  rangesEqual,
+} from '../gr-diff/gr-diff-utils';
 import {appContext} from '../../../services/app-context';
 import {
   getParentIndex,
@@ -808,11 +813,7 @@
       throw new Error(`Unknown side: ${commentSide}`);
     }
     function matchesRange(threadEl: GrCommentThread) {
-      const rangeAtt = threadEl.getAttribute('range');
-      const threadRange = rangeAtt
-        ? (JSON.parse(rangeAtt) as CommentRange)
-        : undefined;
-      return rangesEqual(threadRange, range);
+      return rangesEqual(getRange(threadEl), range);
     }
 
     const filteredThreadEls = this._filterThreadElsForLocation(
@@ -830,21 +831,18 @@
   ) {
     function matchesLeftLine(threadEl: GrCommentThread) {
       return (
-        threadEl.getAttribute('comment-side') === Side.LEFT &&
-        threadEl.getAttribute('line-num') === String(lineInfo.beforeNumber)
+        getSide(threadEl) === Side.LEFT &&
+        getLine(threadEl) === lineInfo.beforeNumber
       );
     }
     function matchesRightLine(threadEl: GrCommentThread) {
       return (
-        threadEl.getAttribute('comment-side') === Side.RIGHT &&
-        threadEl.getAttribute('line-num') === String(lineInfo.afterNumber)
+        getSide(threadEl) === Side.RIGHT &&
+        getLine(threadEl) === lineInfo.afterNumber
       );
     }
     function matchesFileComment(threadEl: GrCommentThread) {
-      return (
-        threadEl.getAttribute('comment-side') === side &&
-        threadEl.getAttribute('line-num') === FILE
-      );
+      return getSide(threadEl) === side && getLine(threadEl) === FILE;
     }
 
     // Select the appropriate matchers for the desired side and line
@@ -855,7 +853,7 @@
     if (side === Side.RIGHT) {
       matchers.push(matchesRightLine);
     }
-    if (lineInfo.afterNumber === 'FILE' || lineInfo.beforeNumber === 'FILE') {
+    if (lineInfo.afterNumber === FILE || lineInfo.beforeNumber === FILE) {
       matchers.push(matchesFileComment);
     }
     return threadEls.filter(threadEl =>
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.ts b/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.ts
index 03740ba..08c8226 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.ts
@@ -30,6 +30,7 @@
 import {DiffInfo} from '../../../types/diff';
 import {Side} from '../../../constants/constants';
 import {GrDiffBuilderElement} from '../gr-diff-builder/gr-diff-builder-element';
+import {getSide, isThreadEl} from '../gr-diff/gr-diff-utils';
 
 /**
  * Possible CSS classes indicating the state of selection. Dynamically added/
@@ -96,10 +97,10 @@
   }
 
   _handleDownOnRangeComment(node: Element) {
-    if (node?.nodeName?.toLowerCase() === 'gr-comment-thread') {
+    if (isThreadEl(node)) {
       this._setClasses([
         SelectionClass.COMMENT,
-        node.getAttribute('comment-side') === Side.LEFT
+        getSide(node) === Side.LEFT
           ? SelectionClass.LEFT
           : SelectionClass.RIGHT,
       ]);
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
index 8984dc8..b13b3c5 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
@@ -17,6 +17,7 @@
 
 import {CommentRange} from '../../../types/common';
 import {FILE, LineNumber} from './gr-diff-line';
+import {Side} from '../../../constants/constants';
 
 /**
  * Compare two ranges. Either argument may be falsy, but will only return
@@ -46,3 +47,47 @@
   const lineNumber = Number(lineNumberStr);
   return Number.isInteger(lineNumber) ? lineNumber : null;
 }
+
+export function getLine(threadEl: HTMLElement): LineNumber {
+  const lineAtt = threadEl.getAttribute('line-num');
+  if (!lineAtt || lineAtt === 'FILE') return FILE;
+  const line = Number(lineAtt);
+  if (isNaN(line)) throw new Error(`cannot parse line number: ${lineAtt}`);
+  if (line < 1) throw new Error(`line number smaller than 1: ${line}`);
+  return line;
+}
+
+export function getSide(threadEl: HTMLElement): Side | undefined {
+  const sideAtt = threadEl.getAttribute('comment-side');
+  if (!sideAtt) {
+    console.warn('comment thread without side');
+    return undefined;
+  }
+  if (sideAtt !== Side.LEFT && sideAtt !== Side.RIGHT)
+    throw Error(`unexpected value for side: ${sideAtt}`);
+  return sideAtt as Side;
+}
+
+export function getRange(threadEl: HTMLElement): CommentRange | undefined {
+  const rangeAtt = threadEl.getAttribute('range');
+  if (!rangeAtt) return undefined;
+  const range = JSON.parse(rangeAtt) as CommentRange;
+  if (!range.start_line) throw new Error(`invalid range: ${rangeAtt}`);
+  return range;
+}
+
+// TODO: This type should be exposed to gr-diff clients in a separate type file.
+// For Gerrit these are instances of GrCommentThread, but other gr-diff users
+// have different HTML elements in use for comment threads.
+// TODO: Also document the required HTML attritbutes that thread elements must
+// have, e.g. 'comment-side', 'range', 'line-num', 'data-value'.
+export interface GrDiffThreadElement extends HTMLElement {
+  rootId: string;
+}
+
+export function isThreadEl(node: Node): node is GrDiffThreadElement {
+  return (
+    node.nodeType === Node.ELEMENT_NODE &&
+    (node as Element).classList.contains('comment-thread')
+  );
+}
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
index d8d6115..472a6bd 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
@@ -27,8 +27,16 @@
 import {GestureEventListeners} from '@polymer/polymer/lib/mixins/gesture-event-listeners';
 import {LegacyElementMixin} from '@polymer/polymer/lib/legacy/legacy-element-mixin';
 import {htmlTemplate} from './gr-diff_html';
-import {FILE, LineNumber} from './gr-diff-line';
-import {getLineNumber, rangesEqual} from './gr-diff-utils';
+import {LineNumber} from './gr-diff-line';
+import {
+  getLine,
+  getLineNumber,
+  getRange,
+  getSide,
+  GrDiffThreadElement,
+  isThreadEl,
+  rangesEqual,
+} from './gr-diff-utils';
 import {getHiddenScroll} from '../../../scripts/hiddenscroll';
 import {isMergeParent, patchNumEquals} from '../../../utils/patch-set-util';
 import {customElement, observe, property} from '@polymer/decorators';
@@ -53,7 +61,7 @@
   PolymerDomWrapper,
 } from '../../../types/types';
 import {CommentRangeLayer} from '../gr-ranged-comment-layer/gr-ranged-comment-layer';
-import {DiffViewMode, Side, CommentSide} from '../../../constants/constants';
+import {CommentSide, DiffViewMode, Side} from '../../../constants/constants';
 import {KeyLocations} from '../gr-diff-processor/gr-diff-processor';
 import {FlattenedNodesObserver} from '@polymer/polymer/lib/utils/flattened-nodes-observer';
 import {PolymerDeepPropertyChange} from '@polymer/polymer/interfaces';
@@ -67,30 +75,6 @@
 const FULL_CONTEXT = -1;
 const LIMITED_CONTEXT = 10;
 
-function getSide(threadEl: GrCommentThread): Side | undefined {
-  const sideAtt = threadEl.getAttribute('comment-side');
-  if (!sideAtt) {
-    console.warn('comment thread without side');
-    return undefined;
-  }
-  if (sideAtt !== 'left' && sideAtt !== 'right')
-    throw Error(`unexpected value for side: ${sideAtt}`);
-  return sideAtt as Side;
-}
-
-function isThreadEl(node: Node): node is GrCommentThread {
-  return (
-    node.nodeType === Node.ELEMENT_NODE &&
-    (node as Element).classList.contains('comment-thread')
-  );
-}
-
-// TODO(TS): Replace by proper GrCommentThread once converted.
-type GrCommentThread = PolymerElement & {
-  rootId: string;
-  range: CommentRange;
-};
-
 const COMMIT_MSG_PATH = '/COMMIT_MSG';
 /**
  * 72 is the unofficial length standard for git commit messages.
@@ -383,17 +367,16 @@
   // TODO(brohlfs): Rewrite gr-diff to be agnostic of GrCommentThread, because
   // other users of gr-diff may use different comment widgets.
   _updateRanges(
-    addedThreadEls: GrCommentThread[],
-    removedThreadEls: GrCommentThread[]
+    addedThreadEls: GrDiffThreadElement[],
+    removedThreadEls: GrDiffThreadElement[]
   ) {
     function commentRangeFromThreadEl(
-      threadEl: GrCommentThread
+      threadEl: GrDiffThreadElement
     ): CommentRangeLayer | undefined {
       const side = getSide(threadEl);
       if (!side) return undefined;
-      const rangeAtt = threadEl.getAttribute('range');
-      if (!rangeAtt) return undefined;
-      const range = JSON.parse(rangeAtt) as CommentRange;
+      const range = getRange(threadEl);
+      if (!range) return undefined;
 
       return {side, range, hovering: false, rootId: threadEl.rootId};
     }
@@ -437,12 +420,12 @@
     for (const threadEl of threadEls) {
       const side = getSide(threadEl);
       if (!side) continue;
-      const lineNum = threadEl.getAttribute('line-num') || FILE;
-      const commentRange = threadEl.range || {};
+      const lineNum = getLine(threadEl);
+      const commentRange = getRange(threadEl);
       keyLocations[side][lineNum] = true;
       // Add start_line as well if exists,
       // the being and end of the range should not be collapsed.
-      if (commentRange.start_line) {
+      if (commentRange?.start_line) {
         keyLocations[side][commentRange.start_line] = true;
       }
     }
@@ -450,7 +433,7 @@
   }
 
   // Dispatch events that are handled by the gr-diff-highlight.
-  _redispatchHoverEvents(addedThreadEls: GrCommentThread[]) {
+  _redispatchHoverEvents(addedThreadEls: HTMLElement[]) {
     for (const threadEl of addedThreadEls) {
       threadEl.addEventListener('mouseenter', () => {
         threadEl.dispatchEvent(
@@ -895,11 +878,11 @@
       // for each line from the start.
       let lastEl;
       for (const threadEl of addedThreadEls) {
-        const lineNumString = threadEl.getAttribute('line-num') || 'FILE';
+        const lineNum = getLine(threadEl);
         const commentSide = getSide(threadEl);
         if (!commentSide) continue;
         const lineEl = this.$.diffBuilder.getLineElByNumber(
-          lineNumString,
+          lineNum,
           commentSide
         );
         // When the line the comment refers to does not exist, log an error
@@ -909,7 +892,7 @@
           console.error(
             'thread attached to line ',
             commentSide,
-            lineNumString,
+            lineNum,
             ' which does not exist.'
           );
           continue;