feat: migrate metrics command from CLI

Move AI metrics tracking command from core/cli cmd/ai into go-ai
where the metrics backend lives.

Co-Authored-By: Virgil <virgil@lethean.io>

cmd/metrics/cmd.go

@@ -0,0 +1,135 @@
+// Package metrics implements the metrics viewing command.
+package metrics
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"forge.lthn.ai/core/go-ai/ai"
+	"forge.lthn.ai/core/go/pkg/cli"
+	"forge.lthn.ai/core/go/pkg/i18n"
+)
+
+func init() {
+	cli.RegisterCommands(AddMetricsCommand)
+}
+
+var (
+	metricsSince string
+	metricsJSON  bool
+)
+
+var metricsCmd = &cli.Command{
+	Use:   "metrics",
+	Short: i18n.T("cmd.ai.metrics.short"),
+	Long:  i18n.T("cmd.ai.metrics.long"),
+	RunE: func(cmd *cli.Command, args []string) error {
+		return runMetrics()
+	},
+}
+
+func initMetricsFlags() {
+	metricsCmd.Flags().StringVar(&metricsSince, "since", "7d", i18n.T("cmd.ai.metrics.flag.since"))
+	metricsCmd.Flags().BoolVar(&metricsJSON, "json", false, i18n.T("common.flag.json"))
+}
+
+// AddMetricsCommand adds the 'metrics' command to the parent.
+func AddMetricsCommand(parent *cli.Command) {
+	initMetricsFlags()
+	parent.AddCommand(metricsCmd)
+}
+
+func runMetrics() error {
+	since, err := parseDuration(metricsSince)
+	if err != nil {
+		return cli.Err("invalid --since value %q: %v", metricsSince, err)
+	}
+
+	sinceTime := time.Now().Add(-since)
+	events, err := ai.ReadEvents(sinceTime)
+	if err != nil {
+		return cli.WrapVerb(err, "read", "metrics")
+	}
+
+	if metricsJSON {
+		summary := ai.Summary(events)
+		output, err := json.MarshalIndent(summary, "", "  ")
+		if err != nil {
+			return cli.Wrap(err, "marshal JSON output")
+		}
+		cli.Text(string(output))
+		return nil
+	}
+
+	summary := ai.Summary(events)
+
+	cli.Blank()
+	cli.Print("%s %s\n", cli.DimStyle.Render("Period:"), metricsSince)
+	total, _ := summary["total"].(int)
+	cli.Print("%s %d\n", cli.DimStyle.Render("Total events:"), total)
+	cli.Blank()
+
+	// By type
+	if byType, ok := summary["by_type"].([]map[string]any); ok && len(byType) > 0 {
+		cli.Print("%s\n", cli.DimStyle.Render("By type:"))
+		for _, entry := range byType {
+			cli.Print("  %-30s %v\n", entry["key"], entry["count"])
+		}
+		cli.Blank()
+	}
+
+	// By repo
+	if byRepo, ok := summary["by_repo"].([]map[string]any); ok && len(byRepo) > 0 {
+		cli.Print("%s\n", cli.DimStyle.Render("By repo:"))
+		for _, entry := range byRepo {
+			cli.Print("  %-30s %v\n", entry["key"], entry["count"])
+		}
+		cli.Blank()
+	}
+
+	// By agent
+	if byAgent, ok := summary["by_agent"].([]map[string]any); ok && len(byAgent) > 0 {
+		cli.Print("%s\n", cli.DimStyle.Render("By contributor:"))
+		for _, entry := range byAgent {
+			cli.Print("  %-30s %v\n", entry["key"], entry["count"])
+		}
+		cli.Blank()
+	}
+
+	if len(events) == 0 {
+		cli.Text(i18n.T("cmd.ai.metrics.none_found"))
+	}
+
+	return nil
+}
+
+// parseDuration parses a human-friendly duration like "7d", "24h", "30d".
+func parseDuration(s string) (time.Duration, error) {
+	if len(s) < 2 {
+		return 0, fmt.Errorf("invalid duration: %s", s)
+	}
+
+	unit := s[len(s)-1]
+	value := s[:len(s)-1]
+
+	var n int
+	if _, err := fmt.Sscanf(value, "%d", &n); err != nil {
+		return 0, fmt.Errorf("invalid duration: %s", s)
+	}
+
+	if n <= 0 {
+		return 0, fmt.Errorf("duration must be positive: %s", s)
+	}
+
+	switch unit {
+	case 'd':
+		return time.Duration(n) * 24 * time.Hour, nil
+	case 'h':
+		return time.Duration(n) * time.Hour, nil
+	case 'm':
+		return time.Duration(n) * time.Minute, nil
+	default:
+		return 0, fmt.Errorf("unknown unit %c in duration: %s", unit, s)
+	}
+}