feat: add analytics CLI for skill usage stats

bun run analytics reads ~/.gstack/analytics/skill-usage.jsonl and shows
top skills, per-repo breakdown, hook fire stats, and daily timeline.
Supports --period 7d/30d/all. Handles missing/empty/malformed data.

22 unit tests cover parsing, filtering, formatting, and edge cases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/analytics.ts

@@ -0,0 +1,190 @@
+#!/usr/bin/env bun
+/**
+ * analytics — CLI for viewing gstack skill usage statistics.
+ *
+ * Reads ~/.gstack/analytics/skill-usage.jsonl and displays:
+ *   - Top skills by invocation count
+ *   - Per-repo skill breakdown
+ *   - Safety hook fire events
+ *
+ * Usage:
+ *   bun run scripts/analytics.ts [--period 7d|30d|all]
+ */
+
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+
+export interface AnalyticsEvent {
+  skill: string;
+  ts: string;
+  repo: string;
+  event?: string;
+  pattern?: string;
+}
+
+const ANALYTICS_FILE = path.join(os.homedir(), '.gstack', 'analytics', 'skill-usage.jsonl');
+
+/**
+ * Parse JSONL content into AnalyticsEvent[], skipping malformed lines.
+ */
+export function parseJSONL(content: string): AnalyticsEvent[] {
+  const events: AnalyticsEvent[] = [];
+  for (const line of content.split('\n')) {
+    const trimmed = line.trim();
+    if (!trimmed) continue;
+    try {
+      const obj = JSON.parse(trimmed);
+      if (typeof obj === 'object' && obj !== null && typeof obj.ts === 'string') {
+        events.push(obj as AnalyticsEvent);
+      }
+    } catch {
+      // skip malformed lines
+    }
+  }
+  return events;
+}
+
+/**
+ * Filter events by period. Supports "7d", "30d", and "all".
+ */
+export function filterByPeriod(events: AnalyticsEvent[], period: string): AnalyticsEvent[] {
+  if (period === 'all') return events;
+
+  const match = period.match(/^(\d+)d$/);
+  if (!match) return events;
+
+  const days = parseInt(match[1], 10);
+  const cutoff = new Date(Date.now() - days * 24 * 60 * 60 * 1000);
+
+  return events.filter(e => {
+    const d = new Date(e.ts);
+    return !isNaN(d.getTime()) && d >= cutoff;
+  });
+}
+
+/**
+ * Format a report string from a list of events.
+ */
+export function formatReport(events: AnalyticsEvent[], period: string = 'all'): string {
+  const skillEvents = events.filter(e => e.event !== 'hook_fire');
+  const hookEvents = events.filter(e => e.event === 'hook_fire');
+
+  const lines: string[] = [];
+  lines.push('gstack skill usage analytics');
+  lines.push('\u2550'.repeat(39));
+  lines.push('');
+
+  const periodLabel = period === 'all' ? 'all time' : `last ${period.replace('d', ' days')}`;
+  lines.push(`Period: ${periodLabel}`);
+
+  // Top Skills
+  const skillCounts = new Map<string, number>();
+  for (const e of skillEvents) {
+    skillCounts.set(e.skill, (skillCounts.get(e.skill) || 0) + 1);
+  }
+
+  if (skillCounts.size > 0) {
+    lines.push('');
+    lines.push('Top Skills');
+
+    const sorted = [...skillCounts.entries()].sort((a, b) => b[1] - a[1]);
+    const maxName = Math.max(...sorted.map(([name]) => name.length + 1)); // +1 for /
+    const maxCount = Math.max(...sorted.map(([, count]) => String(count).length));
+
+    for (const [name, count] of sorted) {
+      const label = `/${name}`;
+      const suffix = `${count} invocation${count === 1 ? '' : 's'}`;
+      const dotLen = Math.max(2, 25 - label.length - suffix.length);
+      const dots = ' ' + '.'.repeat(dotLen) + ' ';
+      lines.push(`  ${label}${dots}${suffix}`);
+    }
+  }
+
+  // By Repo
+  const repoSkills = new Map<string, Map<string, number>>();
+  for (const e of skillEvents) {
+    if (!repoSkills.has(e.repo)) repoSkills.set(e.repo, new Map());
+    const m = repoSkills.get(e.repo)!;
+    m.set(e.skill, (m.get(e.skill) || 0) + 1);
+  }
+
+  if (repoSkills.size > 0) {
+    lines.push('');
+    lines.push('By Repo');
+
+    const sortedRepos = [...repoSkills.entries()].sort((a, b) => a[0].localeCompare(b[0]));
+    for (const [repo, skills] of sortedRepos) {
+      const parts = [...skills.entries()]
+        .sort((a, b) => b[1] - a[1])
+        .map(([s, c]) => `${s}(${c})`);
+      lines.push(`  ${repo}: ${parts.join(' ')}`);
+    }
+  }
+
+  // Safety Hook Events
+  const hookCounts = new Map<string, number>();
+  for (const e of hookEvents) {
+    if (e.pattern) {
+      hookCounts.set(e.pattern, (hookCounts.get(e.pattern) || 0) + 1);
+    }
+  }
+
+  if (hookCounts.size > 0) {
+    lines.push('');
+    lines.push('Safety Hook Events');
+
+    const sortedHooks = [...hookCounts.entries()].sort((a, b) => b[1] - a[1]);
+    for (const [pattern, count] of sortedHooks) {
+      const suffix = `${count} fire${count === 1 ? '' : 's'}`;
+      const dotLen = Math.max(2, 25 - pattern.length - suffix.length);
+      const dots = ' ' + '.'.repeat(dotLen) + ' ';
+      lines.push(`  ${pattern}${dots}${suffix}`);
+    }
+  }
+
+  // Total
+  const totalSkills = skillEvents.length;
+  const totalHooks = hookEvents.length;
+  lines.push('');
+  lines.push(`Total: ${totalSkills} skill invocation${totalSkills === 1 ? '' : 's'}, ${totalHooks} hook fire${totalHooks === 1 ? '' : 's'}`);
+
+  return lines.join('\n');
+}
+
+function main() {
+  // Parse --period flag
+  let period = 'all';
+  const args = process.argv.slice(2);
+  for (let i = 0; i < args.length; i++) {
+    if (args[i] === '--period' && i + 1 < args.length) {
+      period = args[i + 1];
+      i++;
+    }
+  }
+
+  // Read file
+  if (!fs.existsSync(ANALYTICS_FILE)) {
+    console.log('No analytics data found.');
+    process.exit(0);
+  }
+
+  const content = fs.readFileSync(ANALYTICS_FILE, 'utf-8').trim();
+  if (!content) {
+    console.log('No analytics data found.');
+    process.exit(0);
+  }
+
+  const events = parseJSONL(content);
+  if (events.length === 0) {
+    console.log('No analytics data found.');
+    process.exit(0);
+  }
+
+  const filtered = filterByPeriod(events, period);
+  console.log(formatReport(filtered, period));
+}
+
+if (import.meta.main) {
+  main();
+}