First commit

backend/internal/pkg/timezone/timezone.go

@@ -0,0 +1,124 @@
+// Package timezone provides global timezone management for the application.
+// Similar to PHP's date_default_timezone_set, this package allows setting
+// a global timezone that affects all time.Now() calls.
+package timezone
+
+import (
+	"fmt"
+	"log"
+	"time"
+)
+
+var (
+	// location is the global timezone location
+	location *time.Location
+	// tzName stores the timezone name for logging/debugging
+	tzName string
+)
+
+// Init initializes the global timezone setting.
+// This should be called once at application startup.
+// Example timezone values: "Asia/Shanghai", "America/New_York", "UTC"
+func Init(tz string) error {
+	if tz == "" {
+		tz = "Asia/Shanghai" // Default timezone
+	}
+
+	loc, err := time.LoadLocation(tz)
+	if err != nil {
+		return fmt.Errorf("invalid timezone %q: %w", tz, err)
+	}
+
+	// Set the global Go time.Local to our timezone
+	// This affects time.Now() throughout the application
+	time.Local = loc
+	location = loc
+	tzName = tz
+
+	log.Printf("Timezone initialized: %s (UTC offset: %s)", tz, getUTCOffset(loc))
+	return nil
+}
+
+// getUTCOffset returns the current UTC offset for a location
+func getUTCOffset(loc *time.Location) string {
+	_, offset := time.Now().In(loc).Zone()
+	hours := offset / 3600
+	minutes := (offset % 3600) / 60
+	if minutes < 0 {
+		minutes = -minutes
+	}
+	sign := "+"
+	if hours < 0 {
+		sign = "-"
+		hours = -hours
+	}
+	return fmt.Sprintf("%s%02d:%02d", sign, hours, minutes)
+}
+
+// Now returns the current time in the configured timezone.
+// This is equivalent to time.Now() after Init() is called,
+// but provided for explicit timezone-aware code.
+func Now() time.Time {
+	if location == nil {
+		return time.Now()
+	}
+	return time.Now().In(location)
+}
+
+// Location returns the configured timezone location.
+func Location() *time.Location {
+	if location == nil {
+		return time.Local
+	}
+	return location
+}
+
+// Name returns the configured timezone name.
+func Name() string {
+	if tzName == "" {
+		return "Local"
+	}
+	return tzName
+}
+
+// StartOfDay returns the start of the given day (00:00:00) in the configured timezone.
+func StartOfDay(t time.Time) time.Time {
+	loc := Location()
+	t = t.In(loc)
+	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc)
+}
+
+// Today returns the start of today (00:00:00) in the configured timezone.
+func Today() time.Time {
+	return StartOfDay(Now())
+}
+
+// EndOfDay returns the end of the given day (23:59:59.999999999) in the configured timezone.
+func EndOfDay(t time.Time) time.Time {
+	loc := Location()
+	t = t.In(loc)
+	return time.Date(t.Year(), t.Month(), t.Day(), 23, 59, 59, 999999999, loc)
+}
+
+// StartOfWeek returns the start of the week (Monday 00:00:00) for the given time.
+func StartOfWeek(t time.Time) time.Time {
+	loc := Location()
+	t = t.In(loc)
+	weekday := int(t.Weekday())
+	if weekday == 0 {
+		weekday = 7 // Sunday is day 7
+	}
+	return time.Date(t.Year(), t.Month(), t.Day()-weekday+1, 0, 0, 0, 0, loc)
+}
+
+// StartOfMonth returns the start of the month (1st day 00:00:00) for the given time.
+func StartOfMonth(t time.Time) time.Time {
+	loc := Location()
+	t = t.In(loc)
+	return time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, loc)
+}
+
+// ParseInLocation parses a time string in the configured timezone.
+func ParseInLocation(layout, value string) (time.Time, error) {
+	return time.ParseInLocation(layout, value, Location())
+}