// Copyright (C) 2019 Marius Schellenberger

package scan

import (
	"bytes"
	"net/http"
	"os"
)

const (
	pdfT         = "application/pdf"
	jpegT        = "image/jpeg"
	pngT         = "image/png"
	bmpT         = "image/bmp"
	gifT         = "image/gif"
	webpT        = "image/webp"
	pnmT         = "image/x-portable-anymap"
	jp2T         = "image/jp2"
	tiffT        = "image/tiff"
	maxSniffSize = 512
)

type extendedSig struct {
	sig []byte
	ct  string
}

var extendedSigs = []extendedSig{
	{[]byte("P1\x0A"), pnmT},
	{[]byte("P2\x0A"), pnmT},
	{[]byte("P3\x0A"), pnmT},
	{[]byte("P4\x0A"), pnmT},
	{[]byte("P5\x0A"), pnmT},
	{[]byte("P6\x0A"), pnmT},
	{[]byte("P7\x0A"), pnmT},
	{[]byte("\x00\x00\x00\x0C\x6A\x50\x20\x20\x0D\x0A\x87\x0A\x00\x00\x00\x14\x66\x74\x79\x70\x6A\x70\x32"), jp2T},
	{[]byte("\x4d\x4d\x00\x2a"), tiffT},
	{[]byte("\x49\x49\x2a\x00"), tiffT},
}

func extendedContentType(buf []byte) string {
	for _, sig := range extendedSigs {
		if bytes.HasPrefix(buf, sig.sig) {
			return sig.ct
		}
	}
	return "application/octet-stream"
}

func isPDF(path string) bool {
	f, err := os.Open(path)
	if err != nil {
		return false
	}
	defer f.Close()
	buf := make([]byte, maxSniffSize)
	_, err = f.Read(buf)
	if err != nil {
		return false
	}
	return http.DetectContentType(buf) == pdfT
}

func isImage(path string) bool {
	f, err := os.Open(path)
	if err != nil {
		return false
	}
	defer f.Close()
	buf := make([]byte, maxSniffSize)
	_, err = f.Read(buf)
	if err != nil {
		return false
	}
	switch http.DetectContentType(buf) {
	case jpegT, pngT, bmpT, gifT, webpT:
		return true
	default:
		switch extendedContentType(buf) {
		case pnmT, jp2T, tiffT:
			return true
		}
	}
	return false
}