// Package filter provides message filtering configuration.
// It is used to restrict which messages are processed by the answer workers.
//
// NOTE: IMAP Search Limitations
// IMAP SEARCH (RFC 3501 §6.4.4) uses case-insensitive substring matching for
// text fields.
// A filter like From: "alice@example.com" would match:
//   - alice@example.com
//   - malice@example.com
//   - alice@example.com.evil.org
//
// For this reason, server-side IMAP filters should be considered
// performance optimizations only, not security controls. Use the
// [Filters.Senders] allowlist for exact sender matching.
//
// [RFC 3501 §6.4.4]:
// https://datatracker.ietf.org/doc/html/rfc3501#section-6.4.4
package filter

import "strings"

// Filters holds message filtering configuration for IMAP searches
// and sender verification.
type Filters struct {
	// Body contains keywords that must appear in the message body.
	Body []string `yaml:"body"`
	// From filters messages by the From header field.
	From string `yaml:"from"`
	// Senders is an allowlist of email addresses permitted to receive
	// replies. If empty, all senders are allowed.
	Senders []string `yaml:"allowed_senders"`
	// Subject filters messages by the Subject header field.
	Subject string `yaml:"subject"`
	// To filters messages by the To header field.
	To string `yaml:"to"`
}

// MatchSender checks if the sender is in the allowed list.
// Returns true if the allowlist is empty (allow all) or if the sender matches.
// Comparison is case-insensitive and ignores leading/trailing whitespace.
func (f *Filters) MatchSender(sender string) bool {
	if len(f.Senders) == 0 {
		return true
	}
	sender = strings.ToLower(strings.TrimSpace(sender))
	for _, allowed := range f.Senders {
		if strings.ToLower(strings.TrimSpace(allowed)) == sender {
			return true
		}
	}
	return false
}