Enable budget changes over time

Makefile

@@ -9,7 +9,7 @@ VERSION ?= ${TRAVIS_TAG}
 endif
 VERSION ?= $(shell git rev-parse --verify HEAD)
 VERSION_FLAGS := -ldflags='-s -w -X github.com/johnstarich/sage/consts.Version=${VERSION}'
-LINT_VERSION=1.21.0
+LINT_VERSION=1.22.2
 
 # Ensure there's at least an empty bindata file when executing a target
 ENSURE_STUB := $(shell [[ -f ./server/bindata.go ]] || { mkdir -p web/build && GO111MODULE=on go generate ./server; })
@@ -34,7 +34,19 @@ lint-fix:
 
 .PHONY: test
 test:
-	./coverage.sh
+	set -e; \
+	tmpfile=$$(mktemp); \
+	trap 'rm -f "$$tmpfile"' EXIT; \
+	go test ./... -race -cover -coverprofile "$$tmpfile" >&2; \
+	coverage=$$(go tool cover -func "$$tmpfile" | tail -1 | awk '{print $$3}'); \
+	printf '##########################\n' >&2; \
+	printf '### Coverage is %6s ###\n' "$$coverage" >&2; \
+	printf '##########################\n' >&2; \
+	echo "$$coverage"; \
+	if [[ -n "$$COVERALLS_TOKEN" ]]; then \
+		go get github.com/mattn/goveralls; \
+		goveralls -coverprofile="$$tmpfile" -service=travis-ci -repotoken "$$COVERALLS_TOKEN"; \
+	fi
 
 .PHONY: build
 build: static

budget/budget.go

@@ -0,0 +1,164 @@
+package budget
+
+import (
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/pkg/errors"
+
+	"github.com/shopspring/decimal"
+)
+
+// Budget is a monthly budget tracker for a particular year
+type Budget interface {
+	Year() int
+	NextYear() Budget
+
+	Month(month time.Month) Accounts
+	SetMonth(month time.Month, account string, budget decimal.Decimal) error
+	RemoveMonth(month time.Month, account string) error
+}
+
+type budget struct {
+	mu sync.RWMutex
+
+	BudgetYear int
+	Months     map[time.Month]Accounts
+}
+
+// Accounts is a mapping from account names to budget amounts
+type Accounts map[string]decimal.Decimal
+
+func (a Accounts) set(account string, budget decimal.Decimal) {
+	a[strings.ToLower(account)] = budget
+}
+
+func (a Accounts) remove(account string) {
+	delete(a, strings.ToLower(account))
+}
+
+func (a Accounts) Get(account string) decimal.Decimal {
+	return a[strings.ToLower(account)]
+}
+
+// New returns a budget that's bound to a given year.
+// Every year can have monthly budgets for various accounts. Each new month copies the previous
+// month of budgets automatically.
+func New(year int) Budget {
+	return &budget{
+		BudgetYear: year,
+		Months:     make(map[time.Month]Accounts),
+	}
+}
+
+// NextYear creates a new budget for the following year, inheriting the latest budgets in 'b'
+func (b *budget) NextYear() Budget {
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	next := New(b.Year() + 1).(*budget)
+	// don't need to lock 'next' since nobody else has a reference to it yet
+	next.Months[time.January] = make(Accounts)
+	copyAccounts(next.Months[time.January], b.Month(time.December))
+	return next
+}
+
+func (b *budget) Month(month time.Month) Accounts {
+	if _, exists := b.Months[month]; exists {
+		b.mu.RLock()
+		defer b.mu.RUnlock()
+		return b.Months[month]
+	}
+	return b.allMonths()[month-1]
+}
+
+func (b *budget) allMonths() []Accounts {
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	months := make([]Accounts, time.December)
+	var previousAccounts Accounts
+	for i := range months {
+		accounts, exists := b.Months[time.Month(i+1)]
+		if !exists {
+			accounts = previousAccounts
+		}
+		months[i] = accounts
+		previousAccounts = accounts
+	}
+	return months
+}
+
+func (b *budget) SetMonth(month time.Month, account string, budget decimal.Decimal) error {
+	return b.setMonth(time.Now, month, account, budget)
+}
+
+func (b *budget) setMonth(getTime func() time.Time, month time.Month, account string, budget decimal.Decimal) error {
+	if month < time.January || month > time.December {
+		return errors.Errorf("Invalid month: %d", month)
+	}
+	if account == "" {
+		return errors.New("Account must be specified")
+	}
+
+	b.ensureMonth(getTime, month)
+	b.mu.Lock()
+	b.Months[month].set(account, budget)
+	b.mu.Unlock()
+	return nil
+}
+
+func (b *budget) ensureMonth(getTime func() time.Time, month time.Month) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	_, exists := b.Months[month]
+	switch {
+	case !exists:
+		accounts := make(Accounts)
+		for i := month - 1; i >= time.January; i-- {
+			if _, monthExists := b.Months[i-1]; monthExists {
+				copyAccounts(accounts, b.Months[i-1])
+				break
+			}
+		}
+		b.Months[month] = accounts
+	case exists && month < time.December:
+		// copy current budgets to following month, so SetMonth doesn't actually change more than one month's budgets
+		now := getTime()
+		if now.Year() > b.BudgetYear || (now.Year() == b.BudgetYear && now.Month() > month) {
+			_, nextExists := b.Months[month+1]
+			if !nextExists {
+				b.Months[month+1] = make(Accounts)
+				copyAccounts(b.Months[month+1], b.Months[month])
+			}
+		}
+	}
+}
+
+func (b *budget) RemoveMonth(month time.Month, account string) error {
+	return b.removeMonth(time.Now, month, account)
+}
+
+func (b *budget) removeMonth(getTime func() time.Time, month time.Month, account string) error {
+	if month < time.January || month > time.December {
+		return errors.Errorf("Invalid month: %d", month)
+	}
+	if account == "" {
+		return errors.New("Account must be specified")
+	}
+
+	b.ensureMonth(getTime, month)
+	b.mu.Lock()
+	b.Months[month].remove(account)
+	b.mu.Unlock()
+	return nil
+}
+
+func (b *budget) Year() int {
+	return b.BudgetYear
+}
+
+func copyAccounts(dest, src Accounts) {
+	for account, budget := range src {
+		dest[account] = budget
+	}
+}