package format

import (
	"encoding/json"
	"errors"
	"fmt"
	"math"
	"strconv"
	"strings"
	"time"
)

type exifRecord struct {
	ImageWidth       int
	ImageHeight      int
	Orientation      int
	DateTimeOriginal string
	CreateDate       string
	Make             string
	Model            string
	LensModel        string
	FNumber          float64
	ExposureTime     float64
	ISO              int
}

// parseExif reads `exiftool -json -n` output for a single file.
func parseExif(data []byte) (Meta, error) {
	var recs []exifRecord
	if err := json.Unmarshal(data, &recs); err != nil {
		return Meta{}, fmt.Errorf("exiftool output: %w", err)
	}
	if len(recs) != 1 {
		return Meta{}, fmt.Errorf("exiftool output: %d records, want 1", len(recs))
	}
	e := recs[0]
	if e.ImageWidth == 0 || e.ImageHeight == 0 {
		return Meta{}, errors.New("exiftool output: no image dimensions")
	}
	m := Meta{Width: e.ImageWidth, Height: e.ImageHeight, Lens: e.LensModel, ISO: e.ISO}
	if e.Orientation >= 5 && e.Orientation <= 8 {
		m.Width, m.Height = m.Height, m.Width
	}
	m.Taken = exifTime(e.DateTimeOriginal)
	if m.Taken.IsZero() {
		m.Taken = exifTime(e.CreateDate)
	}
	m.Camera = camera(e.Make, e.Model)
	if e.FNumber > 0 {
		// Two significant figures, as f-numbers are written (0.95, 1.8, 5.6, 22);
		// exiftool -n reports the raw value, e.g. 1.779999971.
		m.Aperture = "f/" + strconv.FormatFloat(e.FNumber, 'g', 2, 64)
	}
	m.Shutter = shutter(e.ExposureTime)
	return m, nil
}

// exifTime parses "YYYY:MM:DD HH:MM:SS", ignoring any trailing subseconds or zone.
func exifTime(s string) time.Time {
	if len(s) < 19 {
		return time.Time{}
	}
	t, err := time.Parse("2006:01:02 15:04:05", s[:19])
	if err != nil {
		return time.Time{}
	}
	return t
}

func camera(maker, model string) string {
	maker, model = strings.TrimSpace(maker), strings.TrimSpace(model)
	if maker == "" {
		return model
	}
	if model == "" {
		return maker
	}
	brand := strings.ToLower(strings.Fields(maker)[0])
	if strings.Contains(strings.ToLower(model), brand) {
		return model
	}
	return maker + " " + model
}

func shutter(sec float64) string {
	switch {
	case sec <= 0:
		return ""
	case sec >= 1:
		return strconv.FormatFloat(sec, 'f', -1, 64) + "s"
	default:
		return "1/" + strconv.Itoa(int(math.Round(1/sec)))
	}
}