package accounts

import (
	"context"
	"fmt"
	"net/mail"
	"strconv"
	"strings"
	"time"

	"gomail/internal/db"
	"gomail/internal/mailstore"
	"github.com/google/uuid"
)

// GoMailProvider implements MailProvider for the user's own local account —
// direct function calls against the database and Maildir store, no network
// round-trip. This is what the webmail client uses for "your own" mailbox;
// Phase 9's JMAP server exposes the same data over HTTP for third-party
// clients, but the webmail's internal path stays this direct route since it's
// strictly faster for same-process access.
type GoMailProvider struct {
	database *db.DB
	store    *mailstore.Store
	user     *db.User
}

func NewGoMailProvider(database *db.DB, store *mailstore.Store, user *db.User) *GoMailProvider {
	return &GoMailProvider{database: database, store: store, user: user}
}

func (p *GoMailProvider) ListFolders(_ context.Context) ([]Folder, error) {
	names, err := p.database.ListMailboxNames(p.user.ID)
	if err != nil {
		return nil, err
	}
	var folders []Folder
	for _, name := range names {
		entries, err := p.database.ListMailboxEntries(p.user.ID, name)
		if err != nil {
			continue
		}
		unread := 0
		for _, e := range entries {
			if !strings.Contains(e.Flags, "\\Seen") {
				unread++
			}
		}
		folders = append(folders, Folder{
			ID:          name,
			DisplayName: name,
			Type:        folderType(name),
			UnreadCount: unread,
			TotalCount:  len(entries),
		})
	}
	return folders, nil
}

func (p *GoMailProvider) ListMessages(_ context.Context, folderID string, opts ListOpts) ([]MessageHeader, error) {
	entries, err := p.database.ListMailboxEntries(p.user.ID, folderID)
	if err != nil {
		return nil, err
	}

	// Newest first, matching typical mail client default sort.
	for i, j := 0, len(entries)-1; i < j; i, j = i+1, j-1 {
		entries[i], entries[j] = entries[j], entries[i]
	}

	start := opts.Offset
	if start > len(entries) {
		start = len(entries)
	}
	end := len(entries)
	if opts.Limit > 0 && start+opts.Limit < end {
		end = start + opts.Limit
	}
	page := entries[start:end]

	var headers []MessageHeader
	for _, e := range page {
		raw, err := p.store.Read(e.EMLPath)
		if err != nil {
			continue
		}
		headers = append(headers, headerFromRaw(strconv.Itoa(e.UID), folderID, raw, e.Flags, e.SizeBytes))
	}
	return headers, nil
}

func (p *GoMailProvider) GetMessage(_ context.Context, folderID, messageID string) (*FullMessage, error) {
	entries, err := p.database.ListMailboxEntries(p.user.ID, folderID)
	if err != nil {
		return nil, err
	}
	uid, _ := strconv.Atoi(messageID)
	for _, e := range entries {
		if e.UID == uid {
			raw, err := p.store.Read(e.EMLPath)
			if err != nil {
				return nil, err
			}
			hdr := headerFromRaw(messageID, folderID, raw, e.Flags, e.SizeBytes)
			return &FullMessage{MessageHeader: hdr, Raw: raw}, nil
		}
	}
	return nil, db.ErrNotFound
}

// SendMessage delivers locally if the recipient is a GoMail user on this
// instance, otherwise stages it in the outbound queue — same routing logic
// SMTP submission uses, exposed here so webmail compose doesn't need to loop
// back through the SMTP port to send its own account's mail.
func (p *GoMailProvider) SendMessage(_ context.Context, msg *OutgoingMessage) error {
	raw := buildRFC5322(p.user.Email, msg)

	for _, to := range msg.To {
		domain := domainOf(to)
		localDomain, err := p.database.LookupDomainByName(domain)
		if err == nil && localDomain != nil {
			if recipUser, err := p.database.LookupUserByEmail(to); err == nil {
				if _, err := p.store.Deliver(recipUser.ID, recipUser.Email, "INBOX", raw); err != nil {
					return fmt.Errorf("local delivery to %s failed: %w", to, err)
				}
				continue
			}
		}

		_, queuePath, err := p.store.WriteQueueFile(raw)
		if err != nil {
			return fmt.Errorf("staging outbound message: %w", err)
		}
		entry := &db.OutboundQueueEntry{
			ID:            uuid.NewString(),
			UserID:        p.user.ID,
			FromAddress:   p.user.Email,
			ToAddress:     to,
			EMLPath:       queuePath,
			NextAttemptAt: time.Now().UTC(),
		}
		if err := p.database.InsertOutboundQueueEntry(entry); err != nil {
			return fmt.Errorf("enqueueing outbound message to %s: %w", to, err)
		}
	}
	return nil
}

func (p *GoMailProvider) SetFlags(_ context.Context, folderID, messageID string, flags []string) error {
	entries, err := p.database.ListMailboxEntries(p.user.ID, folderID)
	if err != nil {
		return err
	}
	uid, _ := strconv.Atoi(messageID)
	for _, e := range entries {
		if e.UID == uid {
			return p.database.UpdateMailboxFlags(e.ID, strings.Join(flags, " "))
		}
	}
	return db.ErrNotFound
}

// Move re-delivers the message into the destination folder and removes it
// from the source — GoMail's Maildir store has no native "move" primitive
// (each mailbox is its own directory tree), so this is copy+delete rather
// than an atomic rename. Acceptable since both halves are local and fast;
// a future optimization could hardlink instead of re-encrypting.
func (p *GoMailProvider) Move(ctx context.Context, folderID, messageID, destFolderID string) error {
	full, err := p.GetMessage(ctx, folderID, messageID)
	if err != nil {
		return err
	}
	if _, err := p.store.Deliver(p.user.ID, p.user.Email, destFolderID, full.Raw); err != nil {
		return fmt.Errorf("delivering to destination folder: %w", err)
	}
	return p.Delete(ctx, folderID, messageID)
}

func (p *GoMailProvider) Delete(_ context.Context, folderID, messageID string) error {
	entries, err := p.database.ListMailboxEntries(p.user.ID, folderID)
	if err != nil {
		return err
	}
	uid, _ := strconv.Atoi(messageID)
	for _, e := range entries {
		if e.UID == uid {
			return p.database.DeleteMailboxEntry(e.ID)
		}
	}
	return db.ErrNotFound
}

// Sync for the local provider is a no-op in the SyncResult sense — the
// caller already has live DB access via ListMessages, there's no remote
// state to reconcile. Implemented to satisfy the interface for callers that
// treat every linked account uniformly (the future unified-inbox sync loop).
func (p *GoMailProvider) Sync(_ context.Context, _ string) (*SyncResult, error) {
	return &SyncResult{NewCursor: ""}, nil
}

// ── Helpers ───────────────────────────────────────────────────────────────────

func folderType(name string) string {
	switch strings.ToUpper(name) {
	case "INBOX":
		return "inbox"
	case "SENT":
		return "sent"
	case "DRAFTS":
		return "drafts"
	case "TRASH":
		return "trash"
	case "JUNK":
		return "junk"
	default:
		return "custom"
	}
}

func headerFromRaw(id, folderID string, raw []byte, flags string, size int64) MessageHeader {
	h := MessageHeader{ID: id, FolderID: folderID, SizeBytes: size}
	if flags != "" {
		h.Flags = strings.Fields(flags)
	}
	msg, err := mail.ReadMessage(strings.NewReader(string(raw)))
	if err == nil {
		h.From = msg.Header.Get("From")
		h.To = msg.Header.Get("To")
		h.Subject = msg.Header.Get("Subject")
		h.Date = msg.Header.Get("Date")
	}
	return h
}

func domainOf(email string) string {
	parts := strings.SplitN(email, "@", 2)
	if len(parts) == 2 {
		return parts[1]
	}
	return ""
}

func buildRFC5322(from string, msg *OutgoingMessage) []byte {
	var b strings.Builder
	b.WriteString("From: " + from + "\r\n")
	b.WriteString("To: " + strings.Join(msg.To, ", ") + "\r\n")
	if len(msg.CC) > 0 {
		b.WriteString("Cc: " + strings.Join(msg.CC, ", ") + "\r\n")
	}
	b.WriteString("Subject: " + msg.Subject + "\r\n")
	b.WriteString("Date: " + time.Now().Format(time.RFC1123Z) + "\r\n")
	b.WriteString("\r\n")
	b.WriteString(msg.Body)
	b.WriteString("\r\n")
	return []byte(b.String())
}