WIP cost calculation

utils/utils.go

@@ -1,8 +1,11 @@
 package utils
 
 import (
+	"bufio"
 	"crypto/rand"
 	"encoding/hex"
+	"io"
+	"os"
 )
 
 func GenerateSessionId(length int) string {
@@ -17,3 +20,41 @@ func GenerateSessionId(length int) string {
 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
+}