triplex/serial/serial_test.go

// Copyright (c) 2026 Micha Hoiting

package serial_test

import (
	"errors"
	"fmt"
	"testing"
	"testing/quick"

	"git.hoiting.org/micha/triplex/serial"
)

// Property: Decode(Encode(code)) == code (for valid codes)
func TestEncodeDecodeRoundtrip(t *testing.T) {
	f := func(idx uint32) bool {
		if idx >= serial.MaxIndex {
			return true
		}

		code, err := serial.Decode(idx)
		if err != nil {
			return false
		}

		idx2, err := serial.Encode(code)
		if err != nil {
			return false
		}

		return idx == idx2
	}

	if err := quick.Check(f, nil); err != nil {
		t.Fatalf("Encode/Decode roundtrip failed: %v", err)
	}
}

// Property: Decode(Encode(Decode(i))) == Decode(i) (idempotent on valid indices)
func TestDecodeEncodeDecodeIdempotent(t *testing.T) {
	f := func(idx uint32) bool {
		if idx >= serial.MaxIndex {
			return true
		}

		code1, err := serial.Decode(idx)
		if err != nil {
			return true // decode may reject indices (e.g. forbidden pair)
		}

		idx2, err := serial.Encode(code1)
		if err != nil {
			return false
		}

		code2, err := serial.Decode(idx2)
		if err != nil {
			return false
		}

		return code1 == code2
	}

	if err := quick.Check(f, nil); err != nil {
		t.Fatalf("Decode/Encode/Decode idempotence failed: %v", err)
	}
}

// Property: forbidden first three letters are never returned by Decode
func TestForbiddenTripletsNeverDecoded(t *testing.T) {
	f := func(idx uint32) bool {
		if idx >= serial.MaxIndex {
			return true
		}

		code, err := serial.Decode(idx)
		if err != nil {
			return true // decode may reject indices
		}

		l1 := code[0]
		l2 := code[1]
		l3 := code[2]

		return !serial.IsForbiddenTriplet(l1, l2, l3)
	}

	if err := quick.Check(f, nil); err != nil {
		t.Fatalf("Forbidden triplets appeared in Decode: %v", err)
	}
}

// Optional: basic check for format LLL-NNN-LC
func TestDecodedFormatLooksCorrect(t *testing.T) {
	f := func(idx uint32) bool {
		if idx >= serial.MaxIndex {
			return true
		}

		code, err := serial.Decode(idx)
		if err != nil {
			return true
		}

		if len(code) != 10 {
			return false
		}
		if code[3] != '-' || code[7] != '-' {
			return false
		}

		// letters at positions 0,1,2,8,9
		for _, p := range []int{0, 1, 2, 8, 9} {
			if code[p] < 'A' || code[p] > 'Z' {
				return false
			}
		}

		// digits at positions 4,5,6
		for _, p := range []int{4, 5, 6} {
			if code[p] < '0' || code[p] > '9' {
				return false
			}
		}

		return true
	}

	if err := quick.Check(f, nil); err != nil {
		t.Fatalf("Decoded format property failed: %v", err)
	}
}

func TestEncodeDecodeRoundtripSpecificIndex11223344(t *testing.T) {
	baseIdx := uint32(0x11223344)
	idx := baseIdx % serial.MaxIndex

	code, err := serial.Decode(idx)
	if err != nil {
		t.Fatalf("Decode failed for idx %d (derived from 0x11223344): %v", idx, err)
	}

	idx2, err := serial.Encode(code)
	if err != nil {
		t.Fatalf("Encode failed for code %q: %v", code, err)
	}

	if idx2 != idx {
		t.Fatalf("roundtrip mismatch: got %d, want %d", idx2, idx)
	}
}

func TestDecodeOutOfRangeAtMaxIndex(t *testing.T) {
	_, err := serial.Decode(serial.MaxIndex)
	if !errors.Is(err, serial.ErrIndexOutOfRange) {
		t.Fatalf("expected index out of range error, got: %v", err)
	}
}

func TestDecodeOutOfRangeAtMaxIndexPlusHundred(t *testing.T) {
	_, err := serial.Decode(serial.MaxIndex + 100)
	if !errors.Is(err, serial.ErrIndexOutOfRange) {
		t.Fatalf("expected index out of range error, got: %v", err)
	}
}

func TestEncodeRejectsOldFormatWithThirdDash(t *testing.T) {
	_, err := serial.Encode("AA-100-AA")
	if !errors.Is(err, serial.ErrInvalidFormat) {
		t.Fatalf("expected invalid format error, got: %v", err)
	}
}

func TestEncodeRejectsLowercaseLetters(t *testing.T) {
	_, err := serial.Encode("AAa-100-AA")
	if !errors.Is(err, serial.ErrInvalidLetters) {
		t.Fatalf("expected invalid letters error, got: %v", err)
	}
}

func TestEncodeRejectsInvalidChecksum(t *testing.T) {
	_, err := serial.Encode("AAA-100-AB")
	if !errors.Is(err, serial.ErrInvalidChecksum) {
		t.Fatalf("expected invalid checksum error, got: %v", err)
	}
}

func TestEncodeRejectsNonDigitInNumber(t *testing.T) {
	_, err := serial.Encode("AAA-1A0-AA")
	if !errors.Is(err, serial.ErrInvalidNumber) {
		t.Fatalf("expected invalid number error, got: %v", err)
	}
}

func TestRandomCodeRoundtrip(t *testing.T) {
	for i := 0; i < 100; i++ {
		code, idx, err := serial.RandomCode()
		if err != nil {
			t.Fatalf("RandomCode failed: %v", err)
		}

		idx2, err := serial.Encode(code)
		if err != nil {
			t.Fatalf("Encode failed for random code %q: %v", code, err)
		}

		if idx2 != idx {
			t.Fatalf("returned idx mismatch: got %d, want %d", idx, idx2)
		}

		decoded, err := serial.Decode(idx)
		if err != nil {
			t.Fatalf("Decode failed for idx %d: %v", idx, err)
		}

		if decoded != code {
			t.Fatalf("random roundtrip mismatch: got %q, want %q", decoded, code)
		}
	}
}

func TestRandomCodeInvokesInUseCallback(t *testing.T) {
	called := false

	code, idx, err := serial.RandomCode(func(candidate uint32) bool {
		called = true
		return false
	})
	if err != nil {
		t.Fatalf("RandomCode failed: %v", err)
	}
	if !called {
		t.Fatalf("expected in-use callback to be called")
	}

	idx2, err := serial.Encode(code)
	if err != nil {
		t.Fatalf("Encode failed for random code %q: %v", code, err)
	}
	if idx2 != idx {
		t.Fatalf("returned idx mismatch: got %d, want %d", idx, idx2)
	}
}

func TestRandomCodeFailsWhenAllIndicesInUse(t *testing.T) {
	_, _, err := serial.RandomCode(func(candidate uint32) bool {
		return true
	})
	if !errors.Is(err, serial.ErrNoAvailableIndex) {
		t.Fatalf("expected no available index error, got: %v", err)
	}
}

func TestRandomCodeWithOptionsMaxAttempts(t *testing.T) {
	_, _, err := serial.RandomCodeWithOptions(serial.RandomCodeOptions{
		MaxAttempts: 1,
		IsInUse: func(candidate uint32) bool {
			return true
		},
	})
	if !errors.Is(err, serial.ErrNoAvailableIndex) {
		t.Fatalf("expected no available index error, got: %v", err)
	}
}

func TestRandomCodeWithOptionsRandomSourceFailure(t *testing.T) {
	_, _, err := serial.RandomCodeWithOptions(serial.RandomCodeOptions{
		RandomIndex: func(max uint32) (uint32, error) {
			return 0, fmt.Errorf("rng down")
		},
	})
	if !errors.Is(err, serial.ErrRandomSourceFailed) {
		t.Fatalf("expected random source failed error, got: %v", err)
	}
}