Make klog start --resume fall back to previous record

Resolves #266.

In case there is no record at the current date, `klog start --resume`
now falls back to the previous record for determining the last entry
summary. E.g., for this file:

```
2020-01-01
    14:00-15:00 Something
```

Say today was `2020-01-02` + `13:39`, then `klog start --resume` would
yield:

```
2020-01-01
    14:00-15:00 Something

2020-01-02
    13:39-? Something
```

Previously, the newly created entry wouldn’t have had a summary.

CHANGELOG.md

@@ -4,6 +4,8 @@
 ## Next up
 - **[ FEATURE ]** Add new command `klog switch`, that stops a previously
   ongoing activity (open time range), and starts a new one.
+- **[ FEATURE ]** `klog start --resume` now falls back to the previous
+  record for determining the last entry summary.
 
 ## v6.1
 - **[ FEATURE ]** Add new flag `klog start --resume`, which takes over the

klog/app/cli/start.go

@@ -5,6 +5,8 @@ import (
 	"github.com/jotaen/klog/klog/app"
 	"github.com/jotaen/klog/klog/app/cli/lib"
 	"github.com/jotaen/klog/klog/parser/reconciling"
+	"github.com/jotaen/klog/klog/parser/txt"
+	"github.com/jotaen/klog/klog/service"
 )
 
 type Start struct {
@@ -34,14 +36,16 @@ func (opt *Start) Run(ctx app.Context) app.Error {
 	ctx.Config().DefaultShouldTotal.Map(func(s klog.ShouldTotal) {
 		additionalData.ShouldTotal = s
 	})
+	spy := PreviousRecordSpy{}
 	return lib.Reconcile(ctx, lib.ReconcileOpts{OutputFileArgs: opt.OutputFileArgs, WarnArgs: opt.WarnArgs},
 		[]reconciling.Creator{
+			spy.phonyCreator(date),
 			reconciling.NewReconcilerAtRecord(date),
 			reconciling.NewReconcilerForNewRecord(date, opt.DateFormat(ctx.Config()), additionalData),
 		},
 
 		func(reconciler *reconciling.Reconciler) error {
-			summary, sErr := opt.Summary(reconciler.Record)
+			summary, sErr := opt.Summary(reconciler.Record, spy.PreviousRecord)
 			if sErr != nil {
 				return sErr
 			}
@@ -50,7 +54,8 @@ func (opt *Start) Run(ctx app.Context) app.Error {
 	)
 }
 
-func (opt *Start) Summary(r klog.Record) (klog.EntrySummary, app.Error) {
+func (opt *Start) Summary(currentRecord klog.Record, previousRecord klog.Record) (klog.EntrySummary, app.Error) {
+	// Check for conflicting flags.
 	if opt.SummaryText != nil && opt.Resume {
 		return nil, app.NewErrorWithCode(
 			app.LOGICAL_ERROR,
@@ -59,12 +64,51 @@ func (opt *Start) Summary(r klog.Record) (klog.EntrySummary, app.Error) {
 			nil,
 		)
 	}
+
+	// Return summary flag, if specified.
 	if opt.SummaryText != nil {
 		return opt.SummaryText, nil
 	}
-	entriesCount := len(r.Entries())
-	if opt.Resume && entriesCount > 0 {
-		return r.Entries()[entriesCount-1].Summary(), nil
+
+	// Skip if resume flag wasn’t specified.
+	if !opt.Resume {
+		return nil, nil
+	}
+
+	// Return summary of last entry from current record, if it has any entries.
+	if len(currentRecord.Entries()) > 0 {
+		return lastEntrySummary(currentRecord), nil
 	}
+
+	// Return summary of last entry from previous record, if exists.
+	if previousRecord != nil {
+		return lastEntrySummary(previousRecord), nil
+	}
+
 	return nil, nil
 }
+
+func lastEntrySummary(r klog.Record) klog.EntrySummary {
+	entriesCount := len(r.Entries())
+	return r.Entries()[entriesCount-1].Summary()
+}
+
+type PreviousRecordSpy struct {
+	PreviousRecord klog.Record
+}
+
+// phonyCreator is a no-op “pass-through” creator, whose only purpose it is to hook into
+// the reconciler-creation mechanism, to get a handle on the records for determining
+// the previous record.
+func (p *PreviousRecordSpy) phonyCreator(currentDate klog.Date) reconciling.Creator {
+	return func(records []klog.Record, _ []txt.Block) *reconciling.Reconciler {
+		for _, r := range service.Sort(records, false) {
+			if r.Date().IsAfterOrEqual(currentDate) {
+				continue
+			}
+			p.PreviousRecord = r
+			return nil
+		}
+		return nil
+	}
+}

klog/app/cli/start_test.go

@@ -264,7 +264,7 @@ default_rounding = 60m
 }
 
 func TestStartWithResume(t *testing.T) {
-	t.Run("No previous entry -> Empty entry summary", func(t *testing.T) {
+	t.Run("No previous entry, no previous record -> Empty entry summary", func(t *testing.T) {
 		state, err := NewTestingContext()._SetRecords(`1623-12-13
 `)._SetNow(1623, 12, 13, 12, 49)._Run((&Start{
 			Resume: true,
@@ -275,6 +275,25 @@ func TestStartWithResume(t *testing.T) {
 `, state.writtenFileContents)
 	})
 
+	t.Run("No previous entry, but previous record -> Take over from previous record", func(t *testing.T) {
+		state, err := NewTestingContext()._SetRecords(`
+1623-12-12
+    14:00 - 15:00 Did something
+    10m Some activity
+`)._SetNow(1623, 12, 13, 12, 49)._Run((&Start{
+			Resume: true,
+		}).Run)
+		require.Nil(t, err)
+		assert.Equal(t, `
+1623-12-12
+    14:00 - 15:00 Did something
+    10m Some activity
+
+1623-12-13
+    12:49 - ? Some activity
+`, state.writtenFileContents)
+	})
+
 	t.Run("No previous entry summary -> Empty entry summary", func(t *testing.T) {
 		state, err := NewTestingContext()._SetRecords(`1623-12-13
     8:13 - 9:44