From 35e8c56437bc6e35bf83431904856d20103bdbf9 Mon Sep 17 00:00:00 2001
From: Chris Howey <chris@howey.me>
Date: Wed, 7 Oct 2015 10:09:42 -0500
Subject: [PATCH] Add date range support

---
 src/ledger/date.go | 101 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 src/ledger/date.go

diff --git a/src/ledger/date.go b/src/ledger/date.go
new file mode 100644
index 00000000..a380e751
--- /dev/null
+++ b/src/ledger/date.go
@@ -0,0 +1,101 @@
+package ledger
+
+import "time"
+
+// TransactionsInDateRange returns a new array of transactions that are in the date range
+// specified by start and end. The returned list contains transactions on the same day as start
+// but does not include any transactions on the day of end.
+func TransactionsInDateRange(trans []*Transaction, start, end time.Time) []*Transaction {
+	newlist := make([]*Transaction, 0)
+
+	start = start.Add(-1 * time.Second)
+
+	for _, tran := range trans {
+		if tran.Date.After(start) && tran.Date.Before((end)) {
+			newlist = append(newlist, tran)
+		}
+	}
+
+	return newlist
+}
+
+type Period string
+
+const (
+	PeriodMonth   Period = "Monthly"
+	PeriodQuarter Period = "Quarterly"
+	PeriodYear    Period = "Yearly"
+)
+
+func getDateBoundaries(per Period, start, end time.Time) []time.Time {
+	var incMonth, incYear int
+	var periodStart time.Time
+
+	switch per {
+	case PeriodMonth:
+		incMonth = 1
+		periodStart = time.Date(start.Year(), start.Month(), 1, 0, 0, 0, 0, time.UTC)
+	case PeriodQuarter:
+		incMonth = 3
+		switch start.Month() {
+		case time.January, time.February, time.March:
+			periodStart = time.Date(start.Year(), time.January, 1, 0, 0, 0, 0, time.UTC)
+		case time.April, time.May, time.June:
+			periodStart = time.Date(start.Year(), time.April, 1, 0, 0, 0, 0, time.UTC)
+		case time.July, time.August, time.September:
+			periodStart = time.Date(start.Year(), time.July, 1, 0, 0, 0, 0, time.UTC)
+		default:
+			periodStart = time.Date(start.Year(), time.October, 1, 0, 0, 0, 0, time.UTC)
+		}
+	case PeriodYear:
+		incYear = 1
+		periodStart = time.Date(start.Year(), time.January, 1, 0, 0, 0, 0, time.UTC)
+	}
+
+	boundaries := []time.Time{periodStart}
+	for periodStart.Before(end) {
+		periodStart = periodStart.AddDate(incYear, incMonth, 0)
+		boundaries = append(boundaries, periodStart)
+	}
+
+	return boundaries
+}
+
+type RangeType string
+
+const (
+	RangeSnapshot  RangeType = "Snapshot"
+	RangePartition RangeType = "Partition"
+)
+
+type RangeBalance struct {
+	Start, End time.Time
+	Balances   []*Account
+}
+
+// BalancesByPeriod will return the account balances for each period.
+func BalancesByPeriod(trans []*Transaction, per Period, rType RangeType) []*RangeBalance {
+	results := make([]*RangeBalance, 0)
+	if len(trans) < 1 {
+		return results
+	}
+
+	tStart := trans[0].Date
+	tEnd := trans[len(trans)-1].Date
+
+	boundaries := getDateBoundaries(per, tStart, tEnd)
+
+	bStart := boundaries[0]
+	for _, boundary := range boundaries[1:] {
+		bEnd := boundary
+
+		bTrans := TransactionsInDateRange(trans, bStart, bEnd)
+		results = append(results, &RangeBalance{Start: bStart, End: bEnd, Balances: GetBalances(bTrans, []string{})})
+
+		if rType == RangePartition {
+			bStart = bEnd
+		}
+	}
+
+	return results
+}