feat: implement burnless toil export command (closes #9)

- export toil events as CSV (default) or JSON
- optional --month flag to filter by month
- optional --output flag to write to a file instead of stdout
- includes cost_usd column calculated from DefaultCostModel
- CSV format compatible with Excel, Google Sheets

Author: Dinushi94

internal/cli/toil.go

@@ -18,6 +18,7 @@ func NewToilCmd() *cobra.Command {
 
 	toilCmd.AddCommand(newToilLogCmd())
 	toilCmd.AddCommand(newToilReportCmd())
+	toilCmd.AddCommand(newToilExportCmd())
 
 	return toilCmd
 }

internal/cli/toil_export.go

@@ -0,0 +1,142 @@
+package cli
+
+import (
+	"encoding/csv"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+
+	"github.com/burnless/burnless/internal/toil"
+
+	"github.com/spf13/cobra"
+)
+
+// NewToilExportCmd creates the "burnless toil export" command.
+func newToilExportCmd() *cobra.Command {
+	var (
+		format string
+		month  string
+		output string
+	)
+
+	cmd := &cobra.Command{
+		Use:          "export",
+		Short:        "Export toil events as CSV or JSON",
+		SilenceUsage: true,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return runToilExport(format, month, output)
+		},
+	}
+
+	cmd.Flags().StringVar(&format, "format", "csv", "Output format: csv or json")
+	cmd.Flags().StringVar(&month, "month", "", "Filter by month e.g. 2026-06 (default: all)")
+	cmd.Flags().StringVar(&output, "output", "", "File path to write to (default: stdout)")
+
+	return cmd
+}
+
+func runToilExport(format, month, output string) error {
+	dbPath, err := toil.DefaultDBPath()
+	if err != nil {
+		return fmt.Errorf("finding database path: %w", err)
+	}
+
+	store, err := toil.OpenStore(dbPath)
+	if err != nil {
+		return fmt.Errorf("opening toil database: %w", err)
+	}
+	defer func() { _ = store.Close() }()
+
+	events, err := store.All()
+	if err != nil {
+		return fmt.Errorf("reading toil events: %w", err)
+	}
+
+	// filter by month if specified
+	if month != "" {
+		events, err = toil.FilterByMonth(events, month)
+		if err != nil {
+			return err
+		}
+	}
+
+	if len(events) == 0 {
+		fmt.Fprintln(os.Stderr, "No toil events found.")
+		return nil
+	}
+
+	// determine output writer
+	var w io.Writer = os.Stdout
+	if output != "" {
+		f, err := os.Create(output)
+		if err != nil {
+			return fmt.Errorf("creating output file: %w", err)
+		}
+		defer func() { _ = f.Close() }()
+		w = f
+	}
+
+	model := toil.DefaultCostModel()
+
+	switch format {
+	case "csv":
+		return exportCSV(w, events, model)
+	case "json":
+		return exportJSON(w, events, model)
+	default:
+		return fmt.Errorf("unknown format %q — use csv or json", format)
+	}
+}
+
+func exportCSV(w io.Writer, events []toil.Event, model toil.CostModel) error {
+	cw := csv.NewWriter(w)
+	defer cw.Flush()
+
+	// header
+	if err := cw.Write([]string{
+		"id", "service", "task", "date",
+		"duration_minutes", "automatable", "trigger", "notes", "cost_usd",
+	}); err != nil {
+		return err
+	}
+
+	// rows
+	for _, e := range events {
+		cost := model.Cost(e)
+		if err := cw.Write([]string{
+			e.ID,
+			e.Service,
+			e.Task,
+			e.Date.Format("2006-01-02"),
+			strconv.Itoa(e.DurationMins),
+			strconv.FormatBool(e.Automatable),
+			e.Trigger,
+			e.Notes,
+			fmt.Sprintf("%.2f", cost),
+		}); err != nil {
+			return err
+		}
+	}
+
+	return cw.Error()
+}
+
+type exportRow struct {
+	toil.Event
+	CostUSD float64 `json:"cost_usd"`
+}
+
+func exportJSON(w io.Writer, events []toil.Event, model toil.CostModel) error {
+	rows := make([]exportRow, len(events))
+	for i, e := range events {
+		rows[i] = exportRow{
+			Event:   e,
+			CostUSD: model.Cost(e),
+		}
+	}
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "  ")
+	return enc.Encode(rows)
+}