package core

import "testing"

func FuzzComputeBufferEditInvariants(f *testing.F) {
	f.Add("abc\ndef", "abc\nxyz")
	f.Add("", "x")
	f.Add("same", "same")
	f.Add("hello", "")

	f.Fuzz(func(t *testing.T, oldSource, newSource string) {
		edit, ok := computeBufferEdit(oldSource, newSource)

		if oldSource == newSource {
			if ok {
				t.Fatalf("expected no edit when strings are equal")
			}
			return
		}

		if !ok {
			t.Fatalf("expected edit for differing strings")
		}

		oldBytes := []byte(oldSource)
		newBytes := []byte(newSource)
		start := int(edit.StartByte)
		oldEnd := int(edit.OldEndByte)
		newEnd := int(edit.NewEndByte)

		if start < 0 || start > len(oldBytes) || start > len(newBytes) {
			t.Fatalf("invalid start byte: %d", start)
		}
		if oldEnd < start || oldEnd > len(oldBytes) {
			t.Fatalf("invalid old end byte: %d", oldEnd)
		}
		if newEnd < start || newEnd > len(newBytes) {
			t.Fatalf("invalid new end byte: %d", newEnd)
		}

		if string(oldBytes[:start]) != string(newBytes[:start]) {
			t.Fatalf("prefix before edit start must match")
		}
		if string(oldBytes[oldEnd:]) != string(newBytes[newEnd:]) {
			t.Fatalf("suffix after edit end must match")
		}

		sp := byteOffsetToPoint(oldBytes, start)
		op := byteOffsetToPoint(oldBytes, oldEnd)
		np := byteOffsetToPoint(newBytes, newEnd)

		if sp != edit.StartPoint {
			t.Fatalf("start point mismatch: got %+v want %+v", edit.StartPoint, sp)
		}
		if op != edit.OldEndPoint {
			t.Fatalf("old end point mismatch: got %+v want %+v", edit.OldEndPoint, op)
		}
		if np != edit.NewEndPoint {
			t.Fatalf("new end point mismatch: got %+v want %+v", edit.NewEndPoint, np)
		}
	})
}