From 32ced351309a8b487f844d9e0b5f8ac49f17b625 Mon Sep 17 00:00:00 2001
From: Nathan Coad <nathan@thecoads.com>
Date: Thu, 29 Jan 2026 12:27:08 +1100
Subject: [PATCH] more metadata in reports

---
 internal/report/snapshots.go | 110 +++++++++++++++++++++++++++++++++--
 1 file changed, 106 insertions(+), 4 deletions(-)

diff --git a/internal/report/snapshots.go b/internal/report/snapshots.go
index 13d05c4..6a62b3a 100644
--- a/internal/report/snapshots.go
+++ b/internal/report/snapshots.go
@@ -6,6 +6,7 @@ import (
 	"database/sql"
 	"fmt"
 	"log/slog"
+	"math"
 	"os"
 	"path/filepath"
 	"sort"
@@ -748,7 +749,20 @@ func CreateTableReport(logger *slog.Logger, Database db.Database, ctx context.Co
 	}
 
 	if isDailySummary || isMonthlySummary {
-		addReportMetadataSheet(logger, xlsx)
+		meta := reportMetadata{
+			TableName:   tableName,
+			ReportType:  reportTypeFromTable(tableName),
+			GeneratedAt: time.Now(),
+			Duration:    time.Since(start),
+			RowCount:    rowCount,
+			ColumnCount: len(columns),
+			DBDriver:    Database.DB().DriverName(),
+		}
+		if windowStart, windowEnd, ok := reportWindowFromTable(tableName); ok {
+			meta.WindowStart = &windowStart
+			meta.WindowEnd = &windowEnd
+		}
+		addReportMetadataSheet(logger, xlsx, meta)
 	}
 
 	addTotalsChartSheet(logger, Database, ctx, xlsx, tableName)
@@ -1057,14 +1071,102 @@ func summaryReportOrder() []string {
 	}
 }
 
-func addReportMetadataSheet(logger *slog.Logger, xlsx *excelize.File) {
+type reportMetadata struct {
+	TableName   string
+	ReportType  string
+	GeneratedAt time.Time
+	Duration    time.Duration
+	RowCount    int
+	ColumnCount int
+	WindowStart *time.Time
+	WindowEnd   *time.Time
+	DBDriver    string
+}
+
+func reportTypeFromTable(tableName string) string {
+	switch {
+	case strings.HasPrefix(tableName, "inventory_daily_summary_"):
+		return "daily"
+	case strings.HasPrefix(tableName, "inventory_monthly_summary_"):
+		return "monthly"
+	default:
+		return "unknown"
+	}
+}
+
+func reportWindowFromTable(tableName string) (time.Time, time.Time, bool) {
+	if strings.HasPrefix(tableName, "inventory_daily_summary_") {
+		suffix := strings.TrimPrefix(tableName, "inventory_daily_summary_")
+		dayStart, err := time.ParseInLocation("20060102", suffix, time.Local)
+		if err != nil {
+			return time.Time{}, time.Time{}, false
+		}
+		return dayStart, dayStart.AddDate(0, 0, 1), true
+	}
+	if strings.HasPrefix(tableName, "inventory_monthly_summary_") {
+		suffix := strings.TrimPrefix(tableName, "inventory_monthly_summary_")
+		monthStart, err := time.ParseInLocation("200601", suffix, time.Local)
+		if err != nil {
+			return time.Time{}, time.Time{}, false
+		}
+		return monthStart, monthStart.AddDate(0, 1, 0), true
+	}
+	return time.Time{}, time.Time{}, false
+}
+
+func addReportMetadataSheet(logger *slog.Logger, xlsx *excelize.File, meta reportMetadata) {
 	sheetName := "Metadata"
 	if _, err := xlsx.NewSheet(sheetName); err != nil {
 		logger.Error("Error creating metadata sheet", "error", err)
 		return
 	}
-	xlsx.SetCellValue(sheetName, "A1", "ReportGeneratedAt")
-	xlsx.SetCellValue(sheetName, "B1", time.Now().Format(time.RFC3339))
+	rows := []struct {
+		key   string
+		value interface{}
+	}{
+		{"ReportTable", meta.TableName},
+		{"ReportType", meta.ReportType},
+		{"ReportGeneratedAt", meta.GeneratedAt.Format(time.RFC3339)},
+		{"ReportGeneratedAtUTC", meta.GeneratedAt.UTC().Format(time.RFC3339)},
+		{"ReportDuration", meta.Duration.String()},
+		{"ReportDurationSeconds", math.Round(meta.Duration.Seconds()*1000) / 1000},
+		{"RowCount", meta.RowCount},
+		{"ColumnCount", meta.ColumnCount},
+	}
+	if meta.WindowStart != nil && meta.WindowEnd != nil {
+		rows = append(rows,
+			struct {
+				key   string
+				value interface{}
+			}{"DataWindowStart", meta.WindowStart.Format(time.RFC3339)},
+			struct {
+				key   string
+				value interface{}
+			}{"DataWindowEnd", meta.WindowEnd.Format(time.RFC3339)},
+			struct {
+				key   string
+				value interface{}
+			}{"DataWindowTimezone", time.Local.String()},
+		)
+	}
+	if meta.DBDriver != "" {
+		rows = append(rows, struct {
+			key   string
+			value interface{}
+		}{"DatabaseDriver", meta.DBDriver})
+	}
+	if meta.Duration > 0 && meta.RowCount > 0 {
+		rows = append(rows, struct {
+			key   string
+			value interface{}
+		}{"RowsPerSecond", math.Round((float64(meta.RowCount)/meta.Duration.Seconds())*1000) / 1000})
+	}
+	for i, row := range rows {
+		cellKey := fmt.Sprintf("A%d", i+1)
+		cellVal := fmt.Sprintf("B%d", i+1)
+		xlsx.SetCellValue(sheetName, cellKey, row.key)
+		xlsx.SetCellValue(sheetName, cellVal, row.value)
+	}
 	if err := SetColAutoWidth(xlsx, sheetName); err != nil {
 		logger.Error("Error setting metadata auto width", "error", err)
 	}