package caddytls

import (
	"bytes"
	"crypto/tls"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"

	"github.com/caddyserver/caddy"
)

func init() {
	caddy.RegisterModule(caddy.Module{
		Name: "tls.certificates.load_folders",
		New:  func() interface{} { return folderLoader{} },
	})
}

// folderLoader loads certificates and their associated keys from disk
// by recursively walking the specified directories, looking for PEM
// files which contain both a certificate and a key.
type folderLoader []string

// LoadCertificates loads all the certificates+keys in the directories
// listed in fl from all files ending with .pem. This method of loading
// certificates expects the certificate and key to be bundled into the
// same file.
func (fl folderLoader) LoadCertificates() ([]tls.Certificate, error) {
	var certs []tls.Certificate
	for _, dir := range fl {
		err := filepath.Walk(dir, func(fpath string, info os.FileInfo, err error) error {
			if err != nil {
				return fmt.Errorf("unable to traverse into path: %s", fpath)
			}
			if info.IsDir() {
				return nil
			}
			if !strings.HasSuffix(strings.ToLower(info.Name()), ".pem") {
				return nil
			}

			cert, err := x509CertFromCertAndKeyPEMFile(fpath)
			if err != nil {
				return err
			}

			certs = append(certs, cert)

			return nil
		})
		if err != nil {
			return nil, err
		}
	}
	return certs, nil
}

func x509CertFromCertAndKeyPEMFile(fpath string) (tls.Certificate, error) {
	bundle, err := ioutil.ReadFile(fpath)
	if err != nil {
		return tls.Certificate{}, err
	}

	certBuilder, keyBuilder := new(bytes.Buffer), new(bytes.Buffer)
	var foundKey bool // use only the first key in the file

	for {
		// Decode next block so we can see what type it is
		var derBlock *pem.Block
		derBlock, bundle = pem.Decode(bundle)
		if derBlock == nil {
			break
		}

		if derBlock.Type == "CERTIFICATE" {
			// Re-encode certificate as PEM, appending to certificate chain
			pem.Encode(certBuilder, derBlock)
		} else if derBlock.Type == "EC PARAMETERS" {
			// EC keys generated from openssl can be composed of two blocks:
			// parameters and key (parameter block should come first)
			if !foundKey {
				// Encode parameters
				pem.Encode(keyBuilder, derBlock)

				// Key must immediately follow
				derBlock, bundle = pem.Decode(bundle)
				if derBlock == nil || derBlock.Type != "EC PRIVATE KEY" {
					return tls.Certificate{}, fmt.Errorf("%s: expected elliptic private key to immediately follow EC parameters", fpath)
				}
				pem.Encode(keyBuilder, derBlock)
				foundKey = true
			}
		} else if derBlock.Type == "PRIVATE KEY" || strings.HasSuffix(derBlock.Type, " PRIVATE KEY") {
			// RSA key
			if !foundKey {
				pem.Encode(keyBuilder, derBlock)
				foundKey = true
			}
		} else {
			return tls.Certificate{}, fmt.Errorf("%s: unrecognized PEM block type: %s", fpath, derBlock.Type)
		}
	}

	certPEMBytes, keyPEMBytes := certBuilder.Bytes(), keyBuilder.Bytes()
	if len(certPEMBytes) == 0 {
		return tls.Certificate{}, fmt.Errorf("%s: failed to parse PEM data", fpath)
	}
	if len(keyPEMBytes) == 0 {
		return tls.Certificate{}, fmt.Errorf("%s: no private key block found", fpath)
	}

	cert, err := tls.X509KeyPair(certPEMBytes, keyPEMBytes)
	if err != nil {
		return tls.Certificate{}, fmt.Errorf("%s: making X509 key pair: %v", fpath, err)
	}

	return cert, nil
}