// FILE: ./internal/providers/openmeteo/time.go
package openmeteo

import (
	"fmt"
	"strings"
	"time"
)

// ParseTime parses timestamps as returned by Open-Meteo.
//
// Open-Meteo commonly returns timestamps in one of these forms:
//
//   - RFC3339 / RFC3339Nano with an explicit timezone suffix, e.g.
//     "2026-01-10T18:30:00Z" or "2026-01-10T12:30:00-06:00"
//
//   - A local time string WITHOUT a timezone suffix, typically:
//     "YYYY-MM-DDTHH:MM" (and sometimes "YYYY-MM-DDTHH:MM:SS")
//     In that case, the timezone is provided separately via the top-level
//     "timezone" field (IANA name) and/or "utc_offset_seconds".
//
// Parsing strategy:
//
//  1. If the timestamp includes a timezone suffix (RFC3339/RFC3339Nano),
//     treat it as authoritative.
//
//  2. Otherwise, attempt to interpret the timestamp in the provided IANA
//     timezone name (if loadable), then fall back to a fixed zone derived
//     from utcOffsetSeconds.
//
// This helper lives in internal/providers so BOTH sources and normalizers can
// share Open-Meteo quirks without duplicating logic.
func ParseTime(s string, tz string, utcOffsetSeconds int) (time.Time, error) {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}, fmt.Errorf("empty time")
	}

	// If the server returned a timezone-aware RFC3339 timestamp, accept it.
	if t, err := time.Parse(time.RFC3339Nano, s); err == nil {
		return t, nil
	}
	if t, err := time.Parse(time.RFC3339, s); err == nil {
		return t, nil
	}

	// Open-Meteo "local timestamp" formats (no timezone suffix).
	// Commonly "2006-01-02T15:04"; sometimes seconds are present.
	layouts := []string{
		"2006-01-02T15:04:05",
		"2006-01-02T15:04",
	}

	// Prefer the IANA timezone name if it's valid on this system.
	if tz = strings.TrimSpace(tz); tz != "" {
		if loc, err := time.LoadLocation(tz); err == nil {
			for _, layout := range layouts {
				if t, err := time.ParseInLocation(layout, s, loc); err == nil {
					return t, nil
				}
			}
		}
	}

	// Fall back to a fixed zone derived from the offset seconds.
	zoneName := tz
	if zoneName == "" {
		zoneName = "open-meteo"
	}
	loc := time.FixedZone(zoneName, utcOffsetSeconds)

	for _, layout := range layouts {
		if t, err := time.ParseInLocation(layout, s, loc); err == nil {
			return t, nil
		}
	}

	return time.Time{}, fmt.Errorf("unsupported open-meteo timestamp format: %q", s)
}