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libs/web/tracker/application/src/lib/stores/board.reducers.ts

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+import {
+  BoardColumn,
+  BoardFilter,
+  IssueStatus,
+  IssueSummary,
+} from '@task-stream/web/tracker/domain';
+
+/** Pure board transformations (unit tested). */
+
+export function findIssue(
+  columns: BoardColumn[],
+  issueId: string,
+): IssueSummary | undefined {
+  for (const column of columns) {
+    const issue = column.issues.find((i) => i.id === issueId);
+    if (issue) return issue;
+  }
+  return undefined;
+}
+
+export function matchesFilter(
+  issue: IssueSummary,
+  filter: BoardFilter | null,
+): boolean {
+  if (!filter) return true;
+  if (filter.assigneeId && issue.assignee?.id !== filter.assigneeId)
+    return false;
+  if (filter.releaseId && issue.release?.id !== filter.releaseId) return false;
+  if (filter.area && issue.area !== filter.area) return false;
+  return true;
+}
+
+/** Removes the issue wherever it is and puts `next` (if any) on top of its status column. */
+export function placeIssue(
+  columns: BoardColumn[],
+  issueId: string,
+  next: IssueSummary | null,
+): BoardColumn[] {
+  return columns.map((column) => {
+    const had = column.issues.some((i) => i.id === issueId);
+    let issues = had
+      ? column.issues.filter((i) => i.id !== issueId)
+      : column.issues;
+    let total = column.total - (had ? 1 : 0);
+    if (next && next.status === column.status) {
+      issues = [next, ...issues];
+      total += 1;
+    }
+    return had || issues !== column.issues
+      ? { ...column, issues, total }
+      : column;
+  });
+}
+
+/** Optimistic move. */
+export function moveIssue(
+  columns: BoardColumn[],
+  issueId: string,
+  to: IssueStatus,
+): BoardColumn[] {
+  const issue = findIssue(columns, issueId);
+  return issue
+    ? placeIssue(columns, issueId, { ...issue, status: to })
+    : columns;
+}
+
+/** Merges a realtime change, ignoring stale versions and issues outside the filter. */
+export function applyIssueChange(
+  columns: BoardColumn[],
+  issue: IssueSummary,
+  filter: BoardFilter | null,
+): BoardColumn[] {
+  const current = findIssue(columns, issue.id);
+  if (current && current.version > issue.version) return columns;
+  return placeIssue(
+    columns,
+    issue.id,
+    matchesFilter(issue, filter) ? issue : null,
+  );
+}