package unreadMail

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/base64"
	"fmt"
	"git.gutmet.org/libUnreadMail/imap"
	"io"
	"io/ioutil"
	"mime"
	"mime/multipart"
	"mime/quotedprintable"
	"net/mail"
	"strconv"
	"strings"
)

type Parameters struct {
	Server string
	Port   int
	Cert   string
	User   string
	Passwd string
}

type Error string

func (err Error) Error() string {
	return string(err)
}

func validateParameters(p *Parameters) []error {
	var err []error
	p.Cert = strings.TrimSpace(p.Cert)
	p.User = strings.TrimSpace(p.User)
	p.Passwd = strings.TrimSpace(p.Passwd)

	if p.Server == "" {
		err = append(err, Error("Empty server address"))
	}
	if p.Port <= 0 || p.Port > 65535 {
		err = append(err, Error("Invalid port number: "+strconv.Itoa(p.Port)))
	}
	if p.Cert == "" {
		err = append(err, Error("Empty server cert"))
	}
	if p.User == "" {
		err = append(err, Error("Empty user"))
	}
	if p.Passwd == "" {
		err = append(err, Error("Empty passwd"))
	}
	return err
}

func tlsConnection(p *Parameters) (*tls.Conn, error) {
	roots := x509.NewCertPool()
	ok := roots.AppendCertsFromPEM([]byte(p.Cert))
	if !ok {
		return nil, Error("Failed to set up root cert")
	}
	conf := &tls.Config{RootCAs: roots}
	c, err := tls.Dial("tcp", fmt.Sprintf("%s:%d", p.Server, p.Port), conf)
	if err != nil {
		return nil, Error("Failed to dial")
	}
	return c, nil
}

func normalize(m []byte, encoding string) ([]byte, error) {
	var s []byte
	var err error
	if encoding == "quoted-printable" {
		s, err = ioutil.ReadAll(quotedprintable.NewReader(strings.NewReader(string(m))))
	} else if encoding == "base64" {
		s, err = ioutil.ReadAll(base64.NewDecoder(base64.StdEncoding, strings.NewReader(string(m))))
	} else {
		s = m
	}
	if err == io.ErrUnexpectedEOF {
		err = nil
	}
	return s, err
}

func decodeSubject(subject string) (string, error) {
	dec := new(mime.WordDecoder)
	return dec.DecodeHeader(subject)
}

func attachmentName(contentDisposition string) string {
	_, params, err := mime.ParseMediaType(contentDisposition)
	if filename, ok := params["filename"]; err == nil && ok {
		return filename
	} else {
		return ""
	}
}

func getPlainParts(mail *mail.Message) ([]string, []error) {
	parts := make([]string, 0)
	errs := make([]error, 0)
	mediaType, params, err := mime.ParseMediaType(mail.Header.Get("Content-Type"))
	_, hasBoundary := params["boundary"]
	if err == nil && strings.HasPrefix(mediaType, "multipart/") && hasBoundary {
		mr := multipart.NewReader(mail.Body, params["boundary"])
		for {
			p, err := mr.NextPart()
			if err == io.EOF {
				break
			}
			if err != nil {
				errs = append(errs, err)
			}
			if contentType := p.Header.Get("Content-Type"); !strings.HasPrefix(contentType, "text/plain") {
				parts = append(parts, "Non-plain part: "+contentType)
			} else if contentDisposition := p.Header.Get("Content-Disposition"); strings.HasPrefix(contentDisposition, "attachment") {
				if filename := attachmentName(contentDisposition); filename != "" {
					parts = append(parts, "Plain attachment: "+filename)
				}
			} else {
				body, _ := ioutil.ReadAll(p)
				encoding := p.Header.Get("Content-Transfer-Encoding")
				if encoding != "" {
					body, err = normalize(body, encoding)
					if err != nil {
						body = nil
						errs = append(errs, err)
					}
				}
				parts = append(parts, string(body))
			}
		}
	} else {
		// not a multipart message
		if strings.HasPrefix(mediaType, "text/plain") {
			encoding := mail.Header.Get("Content-Transfer-Encoding")
			body, _ := ioutil.ReadAll(mail.Body)
			if encoding != "" {
				body, err = normalize(body, encoding)
				if err != nil {
					body = nil
					errs = append(errs, err)
				}
			}
			parts = append(parts, string(body))
		} else if contentName := params["name"]; contentName != "" {
			parts = append(parts, contentName)
		}
	}
	return parts, errs
}

func Fetch(p *Parameters) ([]*mail.Message, []error) {
	errs := validateParameters(p)
	if len(errs) == 0 {
		conn, err := tlsConnection(p)
		if err != nil {
			errs = append(errs, err)
		} else {
			return imap.Fetch(conn, p.User, p.Passwd)
		}
	}
	return nil, errs
}

func FetchPlaintext(p *Parameters) ([]string, []error) {
	mails, errs := Fetch(p)
	mailsPlain := make([]string, 0)
	for _, mail := range mails {
		// check for mime parts
		parts, pErrs := getPlainParts(mail)
		errs = append(errs, pErrs...)
		date := mail.Header.Get("Date")
		from := mail.Header.Get("From")
		to := mail.Header.Get("To")
		subject, sErr := decodeSubject(mail.Header.Get("Subject"))
		if sErr != nil {
			errs = append(errs, sErr)
		}
		m := fmt.Sprintf("Date: %s\nFrom: %s\nTo: %s\nSubject: %s\n\n%s", date, from, to, subject, strings.Join(parts, "\n\n"))
		mailsPlain = append(mailsPlain, m)
	}
	return mailsPlain, errs
}