package dns

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"testing"
)

const (
	maxPrintableLabel = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789x"
	tooLongLabel      = maxPrintableLabel + "x"
)

var (
	longDomain = maxPrintableLabel[:53] + strings.TrimSuffix(
		strings.Join([]string{".", ".", ".", ".", "."}, maxPrintableLabel[:49]), ".")
	reChar              = regexp.MustCompile(`.`)
	i                   = -1
	maxUnprintableLabel = reChar.ReplaceAllStringFunc(maxPrintableLabel, func(ch string) string {
		if i++; i >= 32 {
			i = 0
		}
		return fmt.Sprintf("\\%03d", i)
	})
)

func TestUnpackDomainName(t *testing.T) {
	var cases = []struct {
		label          string
		input          string
		expectedOutput string
		expectedError  string
	}{
		{"empty domain",
			"\x00",
			".",
			""},
		{"long label",
			string(63) + maxPrintableLabel + "\x00",
			maxPrintableLabel + ".",
			""},
		{"unprintable label",
			string(63) + regexp.MustCompile(`\\[0-9]+`).ReplaceAllStringFunc(maxUnprintableLabel,
				func(escape string) string {
					n, _ := strconv.ParseInt(escape[1:], 10, 8)
					return string(n)
				}) + "\x00",
			maxUnprintableLabel + ".",
			""},
		{"long domain",
			string(53) + strings.Replace(longDomain, ".", string(49), -1) + "\x00",
			longDomain + ".",
			""},
		{"compression pointer",
			// an unrealistic but functional test referencing an offset _inside_ a label
			"\x03foo" + "\x05\x03com\x00" + "\x07example" + "\xC0\x05",
			"foo.\\003com\\000.example.com.",
			""},

		{"too long domain",
			string(54) + "x" + strings.Replace(longDomain, ".", string(49), -1) + "\x00",
			"x" + longDomain + ".",
			ErrLongDomain.Error()},
		{"too long by pointer",
			// a matryoshka doll name to get over 255 octets after expansion via internal pointers
			string([]byte{
				// 11 length values, first to last
				40, 37, 34, 31, 28, 25, 22, 19, 16, 13, 0,
				// 12 filler values
				120, 120, 120, 120, 120, 120, 120, 120, 120, 120, 120, 120,
				// 10 pointers, last to first
				192, 10, 192, 9, 192, 8, 192, 7, 192, 6, 192, 5, 192, 4, 192, 3, 192, 2, 192, 1,
			}),
			"",
			ErrLongDomain.Error()},
		{"long by pointer",
			// a matryoshka doll name _not_ exceeding 255 octets after expansion
			string([]byte{
				// 11 length values, first to last
				37, 34, 31, 28, 25, 22, 19, 16, 13, 10, 0,
				// 9 filler values
				120, 120, 120, 120, 120, 120, 120, 120, 120,
				// 10 pointers, last to first
				192, 10, 192, 9, 192, 8, 192, 7, 192, 6, 192, 5, 192, 4, 192, 3, 192, 2, 192, 1,
			}),
			"" +
				(`\"\031\028\025\022\019\016\013\010\000xxxxxxxxx` +
					`\192\010\192\009\192\008\192\007\192\006\192\005\192\004\192\003\192\002.`) +
				(`\031\028\025\022\019\016\013\010\000xxxxxxxxx` +
					`\192\010\192\009\192\008\192\007\192\006\192\005\192\004\192\003.`) +
				(`\028\025\022\019\016\013\010\000xxxxxxxxx` +
					`\192\010\192\009\192\008\192\007\192\006\192\005\192\004.`) +
				(`\025\022\019\016\013\010\000xxxxxxxxx` +
					`\192\010\192\009\192\008\192\007\192\006\192\005.`) +
				`\022\019\016\013\010\000xxxxxxxxx\192\010\192\009\192\008\192\007\192\006.` +
				`\019\016\013\010\000xxxxxxxxx\192\010\192\009\192\008\192\007.` +
				`\016\013\010\000xxxxxxxxx\192\010\192\009\192\008.` +
				`\013\010\000xxxxxxxxx\192\010\192\009.` +
				`\010\000xxxxxxxxx\192\010.` +
				`\000xxxxxxxxx.`,
			""},
		{"truncated name", "\x07example\x03", "", "dns: buffer size too small"},
		{"non-absolute name", "\x07example\x03com", "", "dns: buffer size too small"},
		{"compression pointer cycle",
			"\x03foo" + "\x03bar" + "\x07example" + "\xC0\x04",
			"",
			"dns: too many compression pointers"},
		{"reserved compression pointer 0b10", "\x07example\x80", "", "dns: bad rdata"},
		{"reserved compression pointer 0b01", "\x07example\x40", "", "dns: bad rdata"},
	}
	for _, test := range cases {
		output, idx, err := UnpackDomainName([]byte(test.input), 0)
		if test.expectedOutput != "" && output != test.expectedOutput {
			t.Errorf("%s: expected %s, got %s", test.label, test.expectedOutput, output)
		}
		if test.expectedError == "" && err != nil {
			t.Errorf("%s: expected no error, got %d %v", test.label, idx, err)
		} else if test.expectedError != "" && (err == nil || err.Error() != test.expectedError) {
			t.Errorf("%s: expected error %s, got %d %v", test.label, test.expectedError, idx, err)
		}
	}
}