feat: new cron trigger

go.mod

@@ -18,6 +18,7 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/kr/pretty v0.1.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/robfig/cron/v3 v3.0.0 // indirect
 	golang.org/x/net v0.42.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 )

go.sum

@@ -17,6 +17,8 @@ github.com/nathan-osman/go-sunrise v1.1.0/go.mod h1:RcWqhT+5ShCZDev79GuWLayetpJp
 github.com/philhofer/fwd v1.1.1/go.mod h1:gk3iGcWd9+svBvR0sR+KPcfE+RNWozjowpeBVG3ZVNU=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/robfig/cron/v3 v3.0.0 h1:kQ6Cb7aHOHTSzNVNEhmp8EcWKLb4CbiMW9h9VyIhO4E=
+github.com/robfig/cron/v3 v3.0.0/go.mod h1:eQICP3HwyT7UooqI/z+Ov+PtYAWygg1TEWWzGIFLtro=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=

internal/scheduling/cron.go

@@ -0,0 +1,43 @@
+package scheduling
+
+import (
+	"fmt"
+	"hash/fnv"
+	"time"
+
+	"github.com/robfig/cron/v3"
+)
+
+// CronTrigger represents a trigger based on a cron expression.
+type CronTrigger struct {
+	expression string // required for hash
+	schedule   cron.Schedule
+}
+
+// NewCronTrigger creates a new CronTrigger from a cron expression.
+func NewCronTrigger(expression string) (*CronTrigger, error) {
+	// Use the standard cron parser
+	parser := cron.NewParser(cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow)
+	schedule, err := parser.Parse(expression)
+	if err != nil {
+		return nil, fmt.Errorf("invalid cron expression: %w", err)
+	}
+
+	return &CronTrigger{
+		expression: expression,
+		schedule:   schedule,
+	}, nil
+}
+
+// NextTime calculates the next occurrence of this cron trigger after the given time.
+func (t *CronTrigger) NextTime(now time.Time) *time.Time {
+	next := t.schedule.Next(now)
+	return &next
+}
+
+// Hash returns a stable hash value for the CronTrigger.
+func (t *CronTrigger) Hash() uint64 {
+	h := fnv.New64()
+	fmt.Fprintf(h, "cron:%s", t.expression)
+	return h.Sum64()
+}

internal/scheduling/cron_test.go

@@ -0,0 +1,131 @@
+package scheduling_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/Xevion/go-ha/internal/scheduling"
+)
+
+func TestCronTrigger(t *testing.T) {
+	// Use a fixed time for consistent testing
+	baseTime := time.Date(2025, 8, 2, 10, 30, 0, 0, time.UTC)
+
+	tests := []struct {
+		name     string
+		cron     string
+		now      time.Time
+		expected time.Time
+	}{
+		{
+			name:     "daily at 9am",
+			cron:     "0 9 * * *",
+			now:      baseTime,
+			expected: time.Date(2025, 8, 3, 9, 0, 0, 0, time.UTC),
+		},
+		{
+			name:     "every 15 minutes",
+			cron:     "*/15 * * * *",
+			now:      baseTime,
+			expected: time.Date(2025, 8, 2, 10, 45, 0, 0, time.UTC),
+		},
+		{
+			name: "weekdays at 8am (Saturday)",
+			// Base time is a Saturday, so next run should be Monday
+			cron:     "0 8 * * 1-5",
+			now:      time.Date(2025, 8, 2, 10, 30, 0, 0, time.UTC),
+			expected: time.Date(2025, 8, 4, 8, 0, 0, 0, time.UTC),
+		},
+		{
+			name: "weekdays at 8am (Sunday)",
+			// Base time is a Sunday, so next run should be Monday
+			cron:     "0 8 * * 1-5",
+			now:      time.Date(2025, 8, 3, 10, 30, 0, 0, time.UTC),
+			expected: time.Date(2025, 8, 4, 8, 0, 0, 0, time.UTC),
+		},
+
+		{
+			name:     "monthly on 1st",
+			cron:     "0 0 1 * *",
+			now:      baseTime,
+			expected: time.Date(2025, 9, 1, 0, 0, 0, 0, time.UTC),
+		},
+		{
+			name:     "specific time today",
+			cron:     "0 14 * * *",
+			now:      baseTime,
+			expected: time.Date(2025, 8, 2, 14, 0, 0, 0, time.UTC),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			trigger, err := scheduling.NewCronTrigger(tt.cron)
+			if err != nil {
+				t.Fatalf("Failed to create cron trigger: %v", err)
+			}
+
+			next := trigger.NextTime(tt.now)
+			if next == nil {
+				t.Fatal("Expected next time, got nil")
+			}
+
+			if !next.Equal(tt.expected) {
+				t.Errorf("Expected %v, got %v", tt.expected, *next)
+			}
+		})
+	}
+}
+
+func TestCronTriggerInvalid(t *testing.T) {
+	tests := []struct {
+		name       string
+		expression string
+	}{
+		{
+			name:       "bad pattern",
+			expression: "invalid",
+		},
+		{
+			name:       "requires 5 fields - too few",
+			expression: "4",
+		},
+		{
+			name:       "requires 5 fields - missing field",
+			expression: "0 9 * *",
+		},
+		{
+			name:       "too many fields",
+			expression: "0 9 * * * *",
+		},
+		{
+			name:       "invalid minute",
+			expression: "60 9 * * *",
+		},
+		{
+			name:       "invalid hour",
+			expression: "0 25 * * *",
+		},
+		{
+			name:       "invalid day of month",
+			expression: "0 9 32 * *",
+		},
+		{
+			name:       "invalid month",
+			expression: "0 9 * 13 *",
+		},
+		{
+			name:       "invalid day of week",
+			expression: "0 9 * * 7",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := scheduling.NewCronTrigger(tt.expression)
+			if err == nil {
+				t.Errorf("Expected error for invalid expression %q", tt.expression)
+			}
+		})
+	}
+}