allow user to configure timezone

refer #162

docs/blog/posts/localization.md

@@ -43,6 +43,12 @@ numbers in the default currency.
 Paisa also allows you to control the number of digits shown after the
 decimal point. By default, it's set to zero.
 
+### `time_zone`
+
+Paisa by default will try to use the system time zone. But if you
+deploy the application in a server, then you would have to set the
+time zone explicitly, as the server time zone might not be same as
+your local time zone. The time zone is used to parse and format dates.
 
 ## Journal
 

docs/reference/config.md

@@ -70,6 +70,13 @@ amount_alignment_column: 52
 # OPTIONAL, DEFAULT: en-IN
 locale: en-IN
 
+# The time zone used to parse and format dates. If not set, system
+# time zone will be used. Example values are Asia/Kolkata,
+# America/New_York, etc
+#
+# OPTIONAL, DEFAULT: system timezone
+time_zone: ""
+
 # First month of the financial year. This can be set to 1 to follow
 # January to December.
 #

internal/config/config.go

@@ -134,6 +134,7 @@ type Config struct {
 	DisplayPrecision           int          `json:"display_precision" yaml:"display_precision"`
 	AmountAlignmentColumn      int          `json:"amount_alignment_column" yaml:"amount_alignment_column"`
 	Locale                     string       `json:"locale" yaml:"locale"`
+	TimeZone                   string       `json:"time_zone" yaml:"time_zone"`
 	FinancialYearStartingMonth time.Month   `json:"financial_year_starting_month" yaml:"financial_year_starting_month"`
 	WeekStartingDay            time.Weekday `json:"week_starting_day" yaml:"week_starting_day"`
 	Strict                     BoolType     `json:"strict" yaml:"strict"`
@@ -159,6 +160,7 @@ type Config struct {
 
 var config Config
 var configPath string
+var location *time.Location
 
 var defaultConfig = Config{
 	Readonly:                   false,
@@ -167,6 +169,7 @@ var defaultConfig = Config{
 	DisplayPrecision:           0,
 	AmountAlignmentColumn:      52,
 	Locale:                     "en-IN",
+	TimeZone:                   "",
 	Budget:                     Budget{Rollover: Yes},
 	FinancialYearStartingMonth: 4,
 	Strict:                     No,
@@ -320,6 +323,16 @@ func LoadConfig(content []byte, cp string) error {
 		configPath = cp
 	}
 
+	if config.TimeZone == "" {
+		location = time.Local
+	} else {
+		location, err = time.LoadLocation(config.TimeZone)
+		if err != nil {
+			location = time.Local
+			return errors.New(fmt.Sprintf("Invalid time zone: %s\n%#v", config.TimeZone, err))
+		}
+	}
+
 	return nil
 }
 
@@ -393,3 +406,11 @@ func EnsureLogFilePath() (string, error) {
 func DefaultCurrency() string {
 	return config.DefaultCurrency
 }
+
+func TimeZone() *time.Location {
+	if location != nil {
+		return location
+	}
+
+	return time.Local
+}