// Package policy holds pure enforcement functions: address matching,
// inbound filtering, and (in a later phase) outbound checks.
package policy

import (
	"errors"
	"fmt"
	"net/mail"
	"strings"
)

// NormalizeAddr lower-cases an address and strips any display name/brackets.
func NormalizeAddr(addr string) string {
	addr = strings.TrimSpace(addr)
	if a, err := mail.ParseAddress(addr); err == nil {
		return strings.ToLower(a.Address)
	}
	return strings.ToLower(strings.Trim(addr, "<> "))
}

// MatchAddress reports whether addr matches any whitelist entry.
// Entries beginning with '@' match a whole domain; others match exactly.
func MatchAddress(entries []string, addr string) bool {
	norm := NormalizeAddr(addr)
	if norm == "" {
		return false
	}
	at := strings.LastIndex(norm, "@")
	domain := ""
	if at >= 0 {
		domain = norm[at:] // includes '@'
	}
	for _, e := range entries {
		e = strings.ToLower(strings.TrimSpace(e))
		if strings.HasPrefix(e, "@") {
			if e == domain {
				return true
			}
			continue
		}
		if e == norm {
			return true
		}
	}
	return false
}

// ValidWhitelistAddress reports an error if s is not a usable whitelist entry.
// Accepted forms: a bare address "local@domain", or a domain wildcard "@domain".
// The domain must contain at least one dot. Display-name forms ("Bob <b@x>")
// are rejected because the store keeps the raw string, which would never match.
func ValidWhitelistAddress(s string) error {
	s = strings.TrimSpace(s)
	if s == "" {
		return errors.New("address must not be empty")
	}
	bad := fmt.Errorf("invalid address %q: expected local@domain or @domain", s)
	if strings.HasPrefix(s, "@") {
		domain := s[1:]
		if domain == "" || strings.Contains(domain, "@") || !strings.Contains(domain, ".") {
			return bad
		}
		return nil
	}
	addr, err := mail.ParseAddress(s)
	if err != nil || !strings.EqualFold(addr.Address, s) {
		return bad // parse failure or a display-name/extra-token form
	}
	at := strings.LastIndex(addr.Address, "@")
	if at < 1 || !strings.Contains(addr.Address[at+1:], ".") {
		return bad
	}
	return nil
}