package webclient

import (
	"bytes"
	"context"
	"fmt"
	"mime"
	"mime/multipart"
	"mime/quotedprintable"
	"net/mail"
	"net/textproto"
	"strings"
	"time"

	appCrypto "ghb.freebede.com/nahakubuilder/mailgosend/internal/crypto"
	"ghb.freebede.com/nahakubuilder/mailgosend/internal/models"
	"ghb.freebede.com/nahakubuilder/mailgosend/internal/storage"
)

// ComposeParams holds parsed compose form fields.
type ComposeParams struct {
	From       string   // "Display Name <email@host>"
	FromEmail  string   // bare email
	To         []string // each a valid RFC 5322 address
	CC         []string
	BCC        []string
	Subject    string
	BodyText   string
	InReplyTo  string
	References string
	MessageID  string // auto-generated if empty
}

// BuildRFC5322 creates a raw RFC 5322 message.
func BuildRFC5322(p *ComposeParams) ([]byte, error) {
	if p.MessageID == "" {
		randHex, err := appCrypto.RandomHex(16)
		if err != nil {
			return nil, fmt.Errorf("message-id random: %w", err)
		}
		fromDomain := "localhost"
		if idx := strings.LastIndex(p.FromEmail, "@"); idx >= 0 {
			fromDomain = p.FromEmail[idx+1:]
		}
		p.MessageID = "<" + randHex + "@" + fromDomain + ">"
	}

	var buf bytes.Buffer
	writeHeader := func(k, v string) {
		if v != "" {
			buf.WriteString(k + ": " + v + "\r\n")
		}
	}

	writeHeader("From", p.From)
	writeHeader("To", strings.Join(p.To, ", "))
	if len(p.CC) > 0 {
		writeHeader("Cc", strings.Join(p.CC, ", "))
	}
	writeHeader("Subject", mime.QEncoding.Encode("utf-8", p.Subject))
	writeHeader("Date", time.Now().UTC().Format(time.RFC1123Z))
	writeHeader("Message-Id", p.MessageID)
	writeHeader("MIME-Version", "1.0")
	if p.InReplyTo != "" {
		writeHeader("In-Reply-To", sanitizeHeaderValue(p.InReplyTo))
	}
	if p.References != "" {
		writeHeader("References", sanitizeHeaderValue(p.References))
	}

	// Write body as quoted-printable text/plain.
	mw := multipart.NewWriter(&buf)
	buf.WriteString("Content-Type: multipart/alternative; boundary=\"" + mw.Boundary() + "\"\r\n")
	buf.WriteString("\r\n")

	// text/plain part
	th := make(textproto.MIMEHeader)
	th.Set("Content-Type", "text/plain; charset=utf-8")
	th.Set("Content-Transfer-Encoding", "quoted-printable")
	pw, err := mw.CreatePart(th)
	if err != nil {
		return nil, fmt.Errorf("create text part: %w", err)
	}
	qw := quotedprintable.NewWriter(pw)
	if _, err := qw.Write([]byte(p.BodyText)); err != nil {
		return nil, fmt.Errorf("write body: %w", err)
	}
	if err := qw.Close(); err != nil {
		return nil, fmt.Errorf("close qp: %w", err)
	}

	if err := mw.Close(); err != nil {
		return nil, fmt.Errorf("close multipart: %w", err)
	}

	return buf.Bytes(), nil
}

// parseAddressList parses a comma-separated address string into valid email addresses.
// Returns only the bare email addresses (no display names in returned slice).
func parseAddressList(raw string) ([]string, error) {
	if strings.TrimSpace(raw) == "" {
		return nil, nil
	}
	addrs, err := mail.ParseAddressList(raw)
	if err != nil {
		// Try as a single address.
		addr, err2 := mail.ParseAddress(raw)
		if err2 != nil {
			return nil, fmt.Errorf("invalid address %q: %w", raw, err)
		}
		return []string{addr.Address}, nil
	}
	out := make([]string, 0, len(addrs))
	for _, a := range addrs {
		out = append(out, a.Address)
	}
	return out, nil
}

// addressListRFC formats a list of bare emails as RFC 5322 addresses.
func addressListRFC(emails []string) []string {
	out := make([]string, len(emails))
	for i, e := range emails {
		out[i] = e
	}
	return out
}

// deliverLocally saves a message to a local recipient's INBOX.
func (s *Server) deliverLocally(ctx context.Context, recipientEmail string, raw []byte, msg *storage.IncomingMessage) error {
	user, err := s.deps.DB.ResolveEmail(ctx, recipientEmail)
	if err != nil {
		return fmt.Errorf("resolve %s: %w", recipientEmail, err)
	}
	if user == nil || !user.Enabled {
		return fmt.Errorf("recipient %s not found or disabled", recipientEmail)
	}

	inbox, err := s.deps.DB.GetMailboxByType(ctx, user.ID, models.MailboxInbox)
	if err != nil || inbox == nil {
		return fmt.Errorf("inbox not found for %s", recipientEmail)
	}

	if _, err := s.deps.Store.SaveIncoming(ctx, user.ID, inbox.ID, msg); err != nil {
		return fmt.Errorf("save incoming: %w", err)
	}
	return nil
}

// saveSentCopy saves a copy of a sent message to the sender's Sent folder.
func (s *Server) saveSentCopy(ctx context.Context, senderID int64, raw []byte, msg *storage.IncomingMessage) error {
	sentBox, err := s.deps.DB.GetMailboxByType(ctx, senderID, models.MailboxSent)
	if err != nil || sentBox == nil {
		return fmt.Errorf("sent mailbox not found")
	}
	_, err = s.deps.Store.SaveIncoming(ctx, senderID, sentBox.ID, msg)
	return err
}

// enqueueForDelivery adds a message to the delivery queue for a remote recipient.
func (s *Server) enqueueForDelivery(ctx context.Context, fromEmail, toEmail string, raw []byte, msgID string) error {
	// Determine domain for queue domain_id (best effort, nil if not local).
	fromDomain := ""
	if idx := strings.LastIndex(fromEmail, "@"); idx >= 0 {
		fromDomain = fromEmail[idx+1:]
	}
	var domainID *int64
	if dom, err := s.deps.DB.GetDomain(ctx, fromDomain); err == nil && dom != nil {
		domainID = &dom.ID
	}

	maxAge := s.deps.Cfg.QueueMaxAgeHours
	if maxAge <= 0 {
		maxAge = 72
	}

	key, err := s.deps.Crypt.DeriveKeyGlobal("queue")
	if err != nil {
		return fmt.Errorf("queue key: %w", err)
	}
	rawEnc, err := appCrypto.Encrypt(key, raw)
	if err != nil {
		return fmt.Errorf("encrypt queue: %w", err)
	}

	domID := int64(0)
	if domainID != nil {
		domID = *domainID
	}
	_, err = s.deps.DB.EnqueueMessage(ctx, domID, fromEmail, toEmail, msgID, rawEnc, maxAge)
	return err
}

// sanitizeHeaderValue strips CR and LF from a header value to prevent injection.
func sanitizeHeaderValue(s string) string {
	return strings.Map(func(r rune) rune {
		if r == '\r' || r == '\n' {
			return -1
		}
		return r
	}, s)
}