// Package clientcert manages client (mutual-TLS) certificates: which
// certificate mitmux presents to an upstream server that requires one,
// selected by matching the request's hostname the same way scope rules
// do (see internal/scope) - substring match by default, or a regex - so
// the "which rule applies to this host" mental model stays identical
// throughout the tool.
package clientcert

import (
	"crypto/tls"
	"fmt"
	"regexp"
	"strings"
)

// Cert is one client certificate, scoped to hosts matching Pattern.
type Cert struct {
	ID      int64  `json:"id"`
	Enabled bool   `json:"enabled"`
	Name    string `json:"name"`
	Pattern string `json:"pattern"`
	IsRegex bool   `json:"is_regex"`
	CertPEM []byte `json:"cert_pem"`
	KeyPEM  []byte `json:"key_pem"`
}

func (c Cert) matches(host string) bool {
	if c.IsRegex {
		re, err := regexp.Compile(c.Pattern)
		if err != nil {
			return false
		}
		return re.MatchString(host)
	}
	return strings.Contains(strings.ToLower(host), strings.ToLower(c.Pattern))
}

// FindFor returns the first enabled cert whose pattern matches host, or
// nil if none applies - mitmux then just doesn't present a client
// certificate for that connection, same as if mutual TLS weren't
// configured at all. First-match-wins on ID order, same convention as
// match-and-replace rules' Position ordering, minus the extra field:
// client certs are keyed by host, not layered edits, so insertion order
// is a reasonable enough tiebreaker without adding one.
func FindFor(certs []Cert, host string) *Cert {
	for i := range certs {
		if certs[i].Enabled && certs[i].matches(host) {
			return &certs[i]
		}
	}
	return nil
}

// TLSCertificate parses c's PEM-encoded cert/key pair into the form
// crypto/tls needs to present it during a handshake.
func (c Cert) TLSCertificate() (tls.Certificate, error) {
	cert, err := tls.X509KeyPair(c.CertPEM, c.KeyPEM)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("parse client certificate %q: %w", c.Name, err)
	}
	return cert, nil
}