package util

import "fmt"

// R-553 — a decision must never be made by reading a customer-facing Hungarian word.
//
// Five places in this product branched on their own copy (`strings.Contains(err.Error(), "kötelező")`
// and friends). The day that copy is translated — localisation slice 2 — every one of them silently
// takes the other branch: an install error becomes a 500, a quota failure reads as "unknown cause".
//
// KindErrorf is the fix in one line: it produces the EXACT same message bytes as `fmt.Errorf` while
// carrying a sentinel that `errors.Is` can test. The message is display; the sentinel is the decision.
//
//	return util.KindErrorf(ErrRequiredField, "a(z) %q mező kitöltése kötelező", label)
//	...
//	if errors.Is(err, stacks.ErrRequiredField) { status = http.StatusBadRequest }
//
// Deliberately NOT `fmt.Errorf("%w: …")`: that prepends the sentinel's own text and would change the
// sentence the customer reads, which a localisation-adjacent change may never do.
func KindErrorf(kind error, format string, a ...interface{}) error {
	return &kindError{kind: kind, msg: fmt.Sprintf(format, a...)}
}

// KindError wraps an existing message (a string built elsewhere) with its kind, bytes unchanged.
func KindError(kind error, msg string) error { return &kindError{kind: kind, msg: msg} }

type kindError struct {
	kind error
	msg  string
}

func (e *kindError) Error() string { return e.msg }

// Unwrap is what makes errors.Is(err, kind) true. It deliberately returns the KIND, not a cause
// chain: the message is a leaf, and the kind is the only thing a caller may branch on.
func (e *kindError) Unwrap() error { return e.kind }