package clocktime

import (
	"fmt"
	"time"
)

// ClockTime represents a time of day without a date component (24-hour HH:MM:SS).
type ClockTime struct {
	Hour   int `json:"hour"`
	Minute int `json:"minute"`
	Second int `json:"second"`
}

// NewClockTime creates a ClockTime after validating component ranges.
func NewClockTime(hour, minute, second int) (ClockTime, error) {
	t := ClockTime{Hour: hour, Minute: minute, Second: second}
	if err := t.validate(); err != nil {
		return ClockTime{}, err
	}
	return t, nil
}

// ParseClockTime parses strict HH:MM:SS (RFC 3339 time-of-day subset).
func ParseClockTime(s string) (ClockTime, error) {
	return ClockTimeFromString(s)
}

// ClockTimeFromString parses a ClockTime from HH:MM:SS.
func ClockTimeFromString(s string) (ClockTime, error) {
	if s == "" {
		return ClockTime{}, fmt.Errorf("invalid time format: empty string")
	}
	parsed, err := time.Parse("15:04:05", s)
	if err != nil {
		return ClockTime{}, fmt.Errorf("invalid time format: %s", s)
	}
	return ClockTime{Hour: parsed.Hour(), Minute: parsed.Minute(), Second: parsed.Second()}, nil
}

// ClockTimeFromTime extracts the UTC time-of-day from t (sub-second precision truncated).
func ClockTimeFromTime(t time.Time) ClockTime {
	u := t.UTC()
	return ClockTime{Hour: u.Hour(), Minute: u.Minute(), Second: u.Second()}
}

func (t ClockTime) validate() error {
	if t.Hour < 0 || t.Hour > 23 || t.Minute < 0 || t.Minute > 59 || t.Second < 0 || t.Second > 59 {
		return fmt.Errorf("time out of range: %s", t.String())
	}
	return nil
}

// String returns HH:MM:SS with zero padding.
func (t ClockTime) String() string {
	return fmt.Sprintf("%02d:%02d:%02d", t.Hour, t.Minute, t.Second)
}

// Time returns a UTC time.Time anchored on 1970-01-01.
func (t ClockTime) Time() time.Time {
	return time.Date(1970, 1, 1, t.Hour, t.Minute, t.Second, 0, time.UTC)
}

// IsMidnight reports whether the time is exactly 00:00:00.
func (t ClockTime) IsMidnight() bool {
	return t.Hour == 0 && t.Minute == 0 && t.Second == 0
}

// IsZero reports whether the receiver pointer is nil. For optional fields use *ClockTime;
// midnight 00:00:00 is a valid value and is not considered zero.
func (t *ClockTime) IsZero() bool {
	return t == nil
}

// Equal reports whether two times are the same.
func (t ClockTime) Equal(other ClockTime) bool {
	return t.Hour == other.Hour && t.Minute == other.Minute && t.Second == other.Second
}

// Compare returns -1, 0, or 1 comparing t to other.
func (t ClockTime) Compare(other ClockTime) int {
	if t.Before(other) {
		return -1
	}
	if t.After(other) {
		return 1
	}
	return 0
}

// Before reports whether t is before other.
func (t ClockTime) Before(other ClockTime) bool {
	if t.Hour != other.Hour {
		return t.Hour < other.Hour
	}
	if t.Minute != other.Minute {
		return t.Minute < other.Minute
	}
	return t.Second < other.Second
}

// After reports whether t is after other.
func (t ClockTime) After(other ClockTime) bool {
	if t.Hour != other.Hour {
		return t.Hour > other.Hour
	}
	if t.Minute != other.Minute {
		return t.Minute > other.Minute
	}
	return t.Second > other.Second
}