Add Carbon Period functionality (#78)

* Add Carbon Period functionality

* Add unit tests that check errors in carbon period

carbonPeriod.go

@@ -0,0 +1,35 @@
+package carbon
+
+import "errors"
+
+var (
+	ErrEndMustBeAfterStart = errors.New("end date must be after start date")
+	ErrDayAtLeast1         = errors.New("days must be at least 1")
+)
+
+// Period returns an array of Carbon dates by accepting start date, number of
+// days, and end date. Useful for generating a recurring dates.
+func Period(start *Carbon, days int, end *Carbon) ([]*Carbon, error) {
+	if end.Before(start.Time) {
+		return nil, ErrEndMustBeAfterStart
+	}
+	if days <= 0 {
+		return nil, ErrDayAtLeast1
+	}
+
+	want := make([]*Carbon, 0)
+
+	want = append(want, start)
+
+	next := start
+	for {
+		try := next.AddDays(days)
+
+		if try.Gte(end) {
+			return want, nil
+		}
+
+		want = append(want, try)
+		next = try
+	}
+}

carbonPeriod_test.go

@@ -0,0 +1,92 @@
+package carbon
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewPeriod(t *testing.T) {
+	start1, _ := Create(2022, time.April, 1, 23, 0, 0, 0, "UTC")
+	end1, _ := Create(2022, time.April, 30, 23, 0, 0, 0, "UTC")
+
+	days := 7
+
+	wantTime := make([]*Carbon, 0)
+	want1a, _ := Create(2022, time.April, 1, 23, 0, 0, 0, "UTC")
+	want1b, _ := Create(2022, time.April, 8, 23, 0, 0, 0, "UTC")
+	want1c, _ := Create(2022, time.April, 15, 23, 0, 0, 0, "UTC")
+	want1d, _ := Create(2022, time.April, 22, 23, 0, 0, 0, "UTC")
+	want1e, _ := Create(2022, time.April, 29, 23, 0, 0, 0, "UTC")
+	wantTime = append(wantTime, want1a)
+	wantTime = append(wantTime, want1b)
+	wantTime = append(wantTime, want1c)
+	wantTime = append(wantTime, want1d)
+	wantTime = append(wantTime, want1e)
+
+	type args struct {
+		start *Carbon
+		days  int
+		end   *Carbon
+	}
+
+	type want struct {
+		wantTime []*Carbon
+		error
+	}
+
+	tests := []struct {
+		name string
+		args args
+		//want []*Carbon
+		want
+	}{
+		{
+			name: "normal",
+			args: args{
+				start: start1,
+				days:  days,
+				end:   end1,
+			},
+			want: want{
+				wantTime: wantTime,
+				error:    nil,
+			},
+		},
+		{
+			name: "date to is before date start",
+			args: args{
+				start: end1,
+				days:  1,
+				end:   start1,
+			},
+			want: want{
+				wantTime: nil,
+				error:    ErrEndMustBeAfterStart,
+			},
+		},
+		{
+			name: "day is zero",
+			args: args{
+				start: start1,
+				days:  0,
+				end:   end1,
+			},
+			want: want{
+				wantTime: nil,
+				error:    ErrDayAtLeast1,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Period(tt.args.start, tt.args.days, tt.args.end)
+			assert.Equal(t, tt.want.error, err)
+
+			for key, val := range got {
+				assert.Equal(t, tt.want.wantTime[key], val)
+			}
+		})
+	}
+}

examples/period.go

@@ -0,0 +1,22 @@
+package examples
+
+import (
+	"fmt"
+
+	"github.com/uniplaces/carbon"
+)
+
+func period() {
+	t1, _ := carbon.Create(2012, 1, 1, 12, 0, 0, 0, "Lisbon/Rome")
+	t2, _ := carbon.Create(2012, 1, 31, 12, 0, 0, 0, "Lisbon/Rome")
+	days := 7
+
+	periods, err := carbon.Period(t1, days, t2)
+	if err != nil {
+		return
+	}
+
+	for _, val := range periods {
+		fmt.Println(val)
+	}
+}