// Package envelope provides types and functions for working with Nostr protocol
// websocket messages. It defines the Envelope type representing a Nostr message
// and offers utilities for creating, parsing, and validating standardized message
// formats.
package envelope

// Envelope represents a Nostr websocket message.
type Envelope []byte

// GetLabel extracts the message label from an envelope.
// Returns the label as a byte slice or an error if the envelope is malformed.
func GetLabel(env Envelope) ([]byte, error) {
	// begin walking byte slice
	i, n := 0, len(env)

	// skip whitespace before '['
	for i < n && isSpace(env[i]) {
		i++
	}

	// expect '['
	if i >= n || env[i] != '[' {
		return nil, ErrInvalidEnvelope
	}
	i++

	// skip whitespace before '"'
	for i < n && isSpace(env[i]) {
		i++
	}

	// expect '"'
	if i >= n || env[i] != '"' {
		return nil, ErrInvalidEnvelope
	}
	i++

	// scan label: [A-Z]+ terminated by '"'
	start := i
	for i < n && env[i] != '"' { // do until end or '"' is reached
		if env[i] < 'A' || env[i] > 'Z' { // character is not [A-Z]
			return nil, ErrInvalidEnvelope
		}
		i++
	}

	if i == n || i == start { // a label was not found in the previous loop
		return nil, ErrInvalidEnvelope
	}

	return env[start:i], nil
}

func isSpace(b byte) bool {
	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
}

// GetStandardLabels returns a set of standard Nostr websocket message labels
func GetStandardLabels() map[string]struct{} {
	return map[string]struct{}{
		"EVENT":  {},
		"REQ":    {},
		"CLOSE":  {},
		"CLOSED": {},
		"EOSE":   {},
		"NOTICE": {},
		"OK":     {},
		"AUTH":   {},
	}
}

// IsStandardLabel checks if the given label is a standard Nostr websocket message label
func IsStandardLabel(label string) bool {
	labels := GetStandardLabels()
	_, ok := labels[label]
	return ok
}