package mov

import (
	"bytes"
	"encoding/binary"
	"errors"
	"os"
	"time"
)

const epochAdjust = 2082844800

// Created attempts to find a created time from the metadata in a .mov file.
func Created(path string) (time.Time, error) {
	var r time.Time
	f, err := os.Open(path)
	if err != nil {
		return r, err
	}
	defer f.Close()

	buf := [8]byte{}
	for {
		_, err := f.Read(buf[:])
		if err != nil {
			return r, err
		}
		if bytes.Equal(buf[4:8], []byte("moov")) {
			break
		} else {
			atomSize := binary.BigEndian.Uint32(buf[:])
			f.Seek(int64(atomSize)-8, 1)
		}
	}

	_, err = f.Read(buf[:])
	if err != nil {
		return r, err
	}

	s := string(buf[4:8])
	switch s {
	case "mvhd":
		if _, err := f.Seek(4, 1); err != nil {
			return r, err
		}
		_, err = f.Read(buf[:4])
		if err != nil {
			return r, err
		}
		i := int64(binary.BigEndian.Uint32(buf[:4]))
		c := i - epochAdjust
		u := time.Unix(c, 0).Local()
		return u, nil
	case "cmov":
		return r, errors.New("moov atom is compressed")
	default:
		return r, errors.New("expected to find 'mvhd' header, didn't")
	}
}