package syntax

import "testing"

func FuzzByteColToRuneIndexInvariants(f *testing.F) {
	f.Add("abc", 0)
	f.Add("aéb", 1)
	f.Add("こんにちは", 5)
	f.Add("", 0)

	f.Fuzz(func(t *testing.T, s string, col int) {
		line := []byte(s)
		idx := byteColToRuneIndex(line, col)

		runes := []rune(s)
		if idx < 0 || idx > len(runes) {
			t.Fatalf("rune index out of bounds: idx=%d len=%d", idx, len(runes))
		}

		if col <= 0 && idx != 0 {
			t.Fatalf("expected idx 0 for non-positive col, got %d", idx)
		}

		if col >= len(line) && idx != len(runes) {
			t.Fatalf("expected idx len(runes) for col>=len(bytes), got %d", idx)
		}

		if col > 0 && col < len(line) {
			expected := len([]rune(string(line[:col])))
			if idx != expected {
				t.Fatalf("expected idx %d got %d", expected, idx)
			}
		}
	})
}