refactor(mcp): use the shared pattern predicate for drill-downs

.changeset/mcp-shared-pattern-predicate.md

@@ -0,0 +1,7 @@
+---
+'@hyperdx/api': patch
+---
+
+refactor: the MCP `clickstack_event_patterns` tool builds its drill-down
+`whereSnippet` with the shared pattern predicate from `@hyperdx/common-utils`
+instead of its own copy. The snippet is unchanged.

packages/api/src/mcp/tools/query/__tests__/patternDrilldown.test.ts

@@ -1,11 +1,11 @@
-import { minePatterns } from '@hyperdx/common-utils/dist/drain';
-
 import {
-  andSql,
   buildPatternPredicate,
   MAX_PREDICATE_TEMPLATE_LENGTH,
+  minePatterns,
   templateToRegex,
-} from '@/mcp/tools/query/patternDrilldown';
+} from '@hyperdx/common-utils/dist/drain';
+
+import { andSql } from '@/mcp/tools/query/patternDrilldown';
 
 // RE2 spells code points \x{HHHH} and categories \pZ; JS (with the u flag)
 // spells them \u{HHHH} and \p{Z}. ClickHouse behaviour is covered by

packages/api/src/mcp/tools/query/patternDrilldown.ts

@@ -1,61 +1,18 @@
 import type { Metadata } from '@hyperdx/common-utils/dist/core/metadata';
 import { renderWhereExpressionStr } from '@hyperdx/common-utils/dist/core/renderChartConfig';
-import { escapeSqlString } from '@hyperdx/common-utils/dist/core/utils';
 import type {
   ChartVariable,
   UseTextIndex,
 } from '@hyperdx/common-utils/dist/types';
 import { substituteVariables } from '@hyperdx/common-utils/dist/variables';
 
-const PATTERN_WILDCARD = '<*>';
-
-/**
- * Templates longer than this get no predicate: the regex (and the SQL that
- * embeds it) would be unwieldy, and very long templates are usually a
- * single unparameterized payload rather than a reusable shape.
- */
-export const MAX_PREDICATE_TEMPLATE_LENGTH = 4000;
-
 export const PATTERN_MATCH_SEMANTICS =
   'whereSnippet matches values with the same whitespace-separated token count as the ' +
   'template, the same literal tokens (case-sensitive) in the same positions, and exactly ' +
   'one non-whitespace token at each <*>. Every sampled member of the cluster matches. ' +
   'It can also match unsampled events whose shape fits, including ones Drain would have ' +
   'put in a more specific cluster, so the drill-down is a superset of cluster membership.';
 
-// Drain tokenizes with JS `\s`, which includes Unicode spaces and BOM; RE2's
-// `\s` is ASCII-only. JS `\s` = RE2 `\s` + \v + \pZ (Zs/Zl/Zp) + BOM. `\pZ`
-// keeps the snippet short; spelling out the code points repeats ~100 chars
-// between every token.
-const JS_WHITESPACE = '\\s\\x{0B}\\pZ\\x{FEFF}';
-const WS = `[${JS_WHITESPACE}]`;
-const NON_WS = `[^${JS_WHITESPACE}]`;
-
-function escapeRe2Literal(token: string): string {
-  return token.replace(/[\\^$.|?*+()[\]{}]/g, '\\$&');
-}
-
-/** Anchored RE2 regex that a value matches when it fits the Drain template. */
-export function templateToRegex(template: string): string {
-  const tokens = template.split(/\s+/).filter(t => t.length > 0);
-  const body = tokens
-    .map(t => (t === PATTERN_WILDCARD ? `${NON_WS}+` : escapeRe2Literal(t)))
-    .join(`${WS}+`);
-  return `^${WS}*${body}${WS}*$`;
-}
-
-/**
- * SQL predicate selecting events whose `valueExpression` fits the template,
- * or null when the template is too long to turn into a predicate.
- */
-export function buildPatternPredicate(
-  valueExpression: string,
-  template: string,
-): string | null {
-  if (template.length > MAX_PREDICATE_TEMPLATE_LENGTH) return null;
-  return `match(${valueExpression}, '${escapeSqlString(templateToRegex(template))}')`;
-}
-
 /** AND together SQL conditions, skipping blanks. */
 export function andSql(...conditions: Array<string | undefined>): string {
   const parts = conditions.filter(

packages/api/src/mcp/tools/query/runEventPatterns.ts

@@ -6,7 +6,11 @@ import {
   type Granularity,
   splitAndTrimWithBracket,
 } from '@hyperdx/common-utils/dist/core/utils';
-import { minePatterns } from '@hyperdx/common-utils/dist/drain';
+import {
+  buildPatternPredicate,
+  MAX_PREDICATE_TEMPLATE_LENGTH,
+  minePatterns,
+} from '@hyperdx/common-utils/dist/drain';
 import type {
   ChartConfigWithDateRange,
   ChartVariable,
@@ -34,8 +38,6 @@ import {
 } from './helpers';
 import {
   andSql,
-  buildPatternPredicate,
-  MAX_PREDICATE_TEMPLATE_LENGTH,
   PATTERN_MATCH_SEMANTICS,
   userWhereAsSql,
 } from './patternDrilldown';