package catalogue

import (
	"errors"
	"regexp"
)

// A key this controller does not know, in a manifest (novox/hq ADR 0262).
//
// Registration refuses it, as it always has. A manifest the store already holds was registered by a newer
// controller, and is read by this one after a rollback: refusing it there failed the whole catalogue, and
// with it every plan and every send. Dropping the key silently would be worse — a module running without
// something its manifest says. So the manifest is read, the module is left out of every machine's
// declaration by name, and the controller raises a condition until it is updated.

// UnknownFieldError is a key a manifest has that this controller does not know, wherever it is: at the
// top of the manifest or inside a block (a state, an offer, a data item's backup, an own secret, a verb).
// Typed, because the blocks' decoders wrap the decoder's words in their own.
type UnknownFieldError struct {
	Field string
	err   error
}

func (e *UnknownFieldError) Error() string { return e.err.Error() }
func (e *UnknownFieldError) Unwrap() error { return e.err }

// unknownFieldText is how the JSON decoder words a key its target does not have.
var unknownFieldText = regexp.MustCompile(`^json: unknown field "([^"]*)"$`)

// typedUnknown is err as an UnknownFieldError when it is the decoder refusing an unknown key, else err.
func typedUnknown(err error) error {
	if err == nil {
		return nil
	}
	if m := unknownFieldText.FindStringSubmatch(err.Error()); m != nil {
		return &UnknownFieldError{Field: m[1], err: err}
	}
	return err
}

// asUnknownField is the unknown key err is about, at any depth, or nil.
func asUnknownField(err error) *UnknownFieldError {
	var u *UnknownFieldError
	if errors.As(typedUnknown(err), &u) {
		return u
	}
	return nil
}

// UnknownFieldReason is why a module whose stored manifest has a key this controller does not know is
// left out of a machine's declaration, or "" when it has none.
func UnknownFieldReason(m Manifest) string {
	if m.unknown == "" {
		return ""
	}
	return m.Module + " uses a field this controller does not know (" + m.unknown + "); it is left out " +
		"until the controller is updated (novox/hq ADR 0262)"
}