package utils

import (
	"bufio"
	"crypto/rand"
	"encoding/hex"
	"io"
	"os"
)

func GenerateSessionId(length int) string {
	bytes := make([]byte, length) // 16 bytes = 128 bits
	_, err := rand.Read(bytes)
	if err != nil {
		panic("failed to generate session ID")
	}
	return hex.EncodeToString(bytes)
}

func GenerateToken() string {
	return GenerateSessionId(16)
}

const match = "/Page\x00"

// Pages reads the given io.ByteReader until EOF is reached, returning the
// number of pages encountered.
func Pages(reader io.ByteReader) (pages int) {
	i := 0
	for {
		b, err := reader.ReadByte()
		if err != nil {
			return
		}
	check:
		switch match[i] {
		case 0:
			if !(b >= 'A' && b <= 'Z' || b >= 'a' && b <= 'z') {
				pages++
			}
			i = 0
			goto check
		case b:
			i++
		default:
			i = 0
		}
	}
}

// PagesAtPath opens a PDF file at the given file path, returning the number
// of pages found.
func CountPagesAtPath(path string) (pages int) {
	if reader, err := os.Open(path); err == nil {
		reader.Chdir()
		pages = Pages(bufio.NewReader(reader))
		reader.Close()
	}
	return
}