package models

import (
	"database/sql/driver"
	"fmt"
	"strings"
	"time"
	_ "time/tzdata" // Europe/Warsaw must resolve on hosts without zoneinfo.
)

// Location is the time zone the programme runs in. Timestamps are stored in
// UTC (TIMESTAMPTZ) and shown in this zone; a date or time typed without an
// offset is read in it.
var Location = mustLoadLocation("Europe/Warsaw")

func mustLoadLocation(name string) *time.Location {
	loc, err := time.LoadLocation(name)
	if err != nil {
		panic(fmt.Sprintf("jz.bm: load location %s: %v", name, err))
	}
	return loc
}

// DateLayout is the textual form of a Date.
const DateLayout = "2006-01-02"

// dateTimeLayouts are the forms ParseDateTime accepts. RFC 3339 carries its
// own offset; the others are wall-clock times in Location.
var dateTimeLayouts = []string{
	"2006-01-02T15:04",
	"2006-01-02 15:04",
	"2006-01-02T15:04:05",
	"2006-01-02 15:04:05",
}

// ParseDateTime reads an RFC 3339 timestamp, or a wall-clock time
// ("2026-10-03 08:00") in Location.
func ParseDateTime(s string) (time.Time, error) {
	s = strings.TrimSpace(s)
	if t, err := time.Parse(time.RFC3339, s); err == nil {
		return t, nil
	}
	for _, layout := range dateTimeLayouts {
		if t, err := time.ParseInLocation(layout, s, Location); err == nil {
			return t, nil
		}
	}
	return time.Time{}, fmt.Errorf("jz.bm: %q is not a date and time", s)
}

// ParseDate reads a YYYY-MM-DD calendar date.
func ParseDate(s string) (time.Time, error) {
	t, err := time.ParseInLocation(DateLayout, strings.TrimSpace(s), Location)
	if err != nil {
		return time.Time{}, fmt.Errorf("jz.bm: %q is not a YYYY-MM-DD date", s)
	}
	return t, nil
}

// DateTime is a TIMESTAMPTZ column held as RFC 3339 text in Location
// ("2026-10-03T08:00:00+02:00").
//
// It is a string type rather than time.Time because the admin form has no
// date picker and lagoon.Fill cannot write text into a time.Time field, while
// cabana treats any struct-typed field as a relation. A string type is filled
// from the form's text input, and Value checks and normalises it.
// TODO: requires SummerCMS change (a datetime form field type and Fill
// support for time.Time) to use time.Time here.
type DateTime string

// NewDateTime returns t as a DateTime in Location.
func NewDateTime(t time.Time) DateTime {
	return DateTime(t.In(Location).Format(time.RFC3339))
}

// Time parses the value.
func (d DateTime) Time() (time.Time, error) { return ParseDateTime(string(d)) }

// MustTime parses the value and returns the zero time when it does not parse.
// Values read from the database always parse.
func (d DateTime) MustTime() time.Time {
	t, _ := d.Time()
	return t
}

// Valid reports whether the value parses.
func (d DateTime) Valid() bool {
	_, err := d.Time()
	return err == nil
}

// Value stores the instant in UTC. An empty value is SQL NULL.
func (d DateTime) Value() (driver.Value, error) {
	if strings.TrimSpace(string(d)) == "" {
		return nil, nil
	}
	t, err := d.Time()
	if err != nil {
		return nil, err
	}
	return t.UTC(), nil
}

// Scan reads a TIMESTAMPTZ (or its text) and normalises it to Location.
func (d *DateTime) Scan(src any) error {
	switch v := src.(type) {
	case nil:
		*d = ""
	case time.Time:
		*d = NewDateTime(v)
	case string:
		return d.scanText(v)
	case []byte:
		return d.scanText(string(v))
	default:
		return fmt.Errorf("jz.bm: cannot scan %T into DateTime", src)
	}
	return nil
}

func (d *DateTime) scanText(s string) error {
	if strings.TrimSpace(s) == "" {
		*d = ""
		return nil
	}
	t, err := ParseDateTime(s)
	if err != nil {
		// Postgres text output: "2026-10-03 06:00:00+00".
		t, err = time.Parse("2006-01-02 15:04:05-07", s)
		if err != nil {
			return err
		}
	}
	*d = NewDateTime(t)
	return nil
}

// Date is a DATE column held as YYYY-MM-DD text, for the same reason as
// DateTime.
type Date string

// NewDate returns the calendar date of t in Location.
func NewDate(t time.Time) Date { return Date(t.In(Location).Format(DateLayout)) }

// Time returns midnight of the date in Location.
func (d Date) Time() (time.Time, error) { return ParseDate(string(d)) }

// Valid reports whether the value is a YYYY-MM-DD date.
func (d Date) Valid() bool {
	_, err := d.Time()
	return err == nil
}

// Value stores the date as text; Postgres casts it to DATE. An empty value is
// SQL NULL.
func (d Date) Value() (driver.Value, error) {
	if strings.TrimSpace(string(d)) == "" {
		return nil, nil
	}
	t, err := d.Time()
	if err != nil {
		return nil, err
	}
	return t.Format(DateLayout), nil
}

// Scan reads a DATE. The driver hands it over as midnight UTC, so the
// calendar fields are taken as they are, without a zone conversion.
func (d *Date) Scan(src any) error {
	switch v := src.(type) {
	case nil:
		*d = ""
	case time.Time:
		*d = Date(v.Format(DateLayout))
	case string:
		*d = Date(strings.TrimSpace(v))
		if len(*d) > len(DateLayout) {
			*d = (*d)[:len(DateLayout)]
		}
	case []byte:
		return d.Scan(string(v))
	default:
		return fmt.Errorf("jz.bm: cannot scan %T into Date", src)
	}
	return nil
}