package service

import (
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"strings"

	"github.com/emersion/go-imap/v2"
	"github.com/emersion/go-imap/v2/imapclient"
	gomessage "github.com/emersion/go-message"
	_ "github.com/emersion/go-message/charset"
	"github.com/jackc/pgx/v5/pgxpool"
)

// FetchmailConfig holds IMAP server configuration.
type FetchmailConfig struct {
	Host     string
	Port     int
	User     string
	Password string
	UseTLS   bool
	Folder   string
}

// LoadFetchmailConfig loads IMAP settings from environment variables.
func LoadFetchmailConfig() *FetchmailConfig {
	cfg := &FetchmailConfig{
		Port:   993,
		UseTLS: true,
		Folder: "INBOX",
	}
	cfg.Host = os.Getenv("IMAP_HOST")
	cfg.User = os.Getenv("IMAP_USER")
	cfg.Password = os.Getenv("IMAP_PASSWORD")
	if v := os.Getenv("IMAP_FOLDER"); v != "" {
		cfg.Folder = v
	}
	if os.Getenv("IMAP_TLS") == "false" {
		cfg.UseTLS = false
		if cfg.Port == 993 {
			cfg.Port = 143
		}
	}
	return cfg
}

// FetchAndProcessEmails connects to IMAP, fetches unseen emails, and creates
// mail.message records in the database. Matches emails to existing threads
// via In-Reply-To/References headers.
// Mirrors: odoo/addons/fetchmail/models/fetchmail.py fetch_mail()
func FetchAndProcessEmails(ctx context.Context, pool *pgxpool.Pool) error {
	cfg := LoadFetchmailConfig()
	if cfg.Host == "" {
		return nil // IMAP not configured
	}

	addr := fmt.Sprintf("%s:%d", cfg.Host, cfg.Port)

	var c *imapclient.Client
	var err error
	if cfg.UseTLS {
		c, err = imapclient.DialTLS(addr, nil)
	} else {
		c, err = imapclient.DialInsecure(addr, nil)
	}
	if err != nil {
		return fmt.Errorf("fetchmail: connect to %s: %w", addr, err)
	}
	defer c.Close()

	if err := c.Login(cfg.User, cfg.Password).Wait(); err != nil {
		return fmt.Errorf("fetchmail: login as %s: %w", cfg.User, err)
	}

	if _, err := c.Select(cfg.Folder, nil).Wait(); err != nil {
		return fmt.Errorf("fetchmail: select %s: %w", cfg.Folder, err)
	}

	// Search unseen
	criteria := &imap.SearchCriteria{
		NotFlag: []imap.Flag{imap.FlagSeen},
	}
	searchData, err := c.Search(criteria, nil).Wait()
	if err != nil {
		return fmt.Errorf("fetchmail: search: %w", err)
	}

	seqSet := searchData.All
	if seqSet == nil {
		return nil
	}

	// Fetch envelope + body
	fetchOpts := &imap.FetchOptions{
		Envelope:    true,
		BodySection: []*imap.FetchItemBodySection{{}},
	}
	msgs, err := c.Fetch(seqSet, fetchOpts).Collect()
	if err != nil {
		return fmt.Errorf("fetchmail: fetch: %w", err)
	}

	var processed int
	for _, msg := range msgs {
		if err := processOneEmail(ctx, pool, msg); err != nil {
			log.Printf("fetchmail: process error: %v", err)
			continue
		}
		processed++
	}

	// Mark as seen
	if processed > 0 {
		storeFlags := &imap.StoreFlags{
			Op:    imap.StoreFlagsAdd,
			Flags: []imap.Flag{imap.FlagSeen},
		}
		if _, err := c.Store(seqSet, storeFlags, nil).Collect(); err != nil {
			log.Printf("fetchmail: mark seen error: %v", err)
		}
		log.Printf("fetchmail: processed %d new emails", processed)
	}

	return nil
}

func processOneEmail(ctx context.Context, pool *pgxpool.Pool, buf *imapclient.FetchMessageBuffer) error {
	env := buf.Envelope
	if env == nil {
		return fmt.Errorf("no envelope")
	}

	subject := env.Subject
	messageID := env.MessageID
	inReplyTo := env.InReplyTo
	date := env.Date

	var fromEmail, fromName string
	if len(env.From) > 0 {
		fromEmail = fmt.Sprintf("%s@%s", env.From[0].Mailbox, env.From[0].Host)
		fromName = env.From[0].Name
	}

	// Extract body from body section
	var bodyText string
	bodyBytes := buf.FindBodySection(&imap.FetchItemBodySection{})
	if bodyBytes != nil {
		bodyText = parseEmailBody(bodyBytes)
	}
	if bodyText == "" {
		bodyText = "(no body)"
	}

	// Find author partner by email
	var authorID int64
	pool.QueryRow(ctx,
		`SELECT id FROM res_partner WHERE LOWER(email) = LOWER($1) LIMIT 1`, fromEmail,
	).Scan(&authorID)

	// Thread matching via In-Reply-To
	var parentModel string
	var parentResID int64
	if len(inReplyTo) > 0 && inReplyTo[0] != "" {
		pool.QueryRow(ctx,
			`SELECT model, res_id FROM mail_message
			 WHERE message_id = $1 AND model IS NOT NULL AND res_id IS NOT NULL
			 LIMIT 1`, inReplyTo[0],
		).Scan(&parentModel, &parentResID)
	}

	// Fallback: match by subject
	if parentModel == "" && subject != "" {
		clean := subject
		for _, prefix := range []string{"Re: ", "RE: ", "Fwd: ", "FW: ", "AW: "} {
			clean = strings.TrimPrefix(clean, prefix)
		}
		pool.QueryRow(ctx,
			`SELECT model, res_id FROM mail_message
			 WHERE subject = $1 AND model IS NOT NULL AND res_id IS NOT NULL
			 ORDER BY id DESC LIMIT 1`, clean,
		).Scan(&parentModel, &parentResID)
	}

	_, err := pool.Exec(ctx,
		`INSERT INTO mail_message
		 (subject, body, message_type, email_from, author_id, model, res_id,
		  date, message_id, create_uid, write_uid, create_date, write_date)
		 VALUES ($1, $2, 'email', $3, $4, $5, $6, $7, $8, 1, 1, NOW(), NOW())`,
		subject, bodyText,
		fmt.Sprintf("%s <%s>", fromName, fromEmail),
		nilIfZero(authorID),
		nilIfEmpty(parentModel),
		nilIfZero(parentResID),
		date,
		messageID,
	)
	return err
}

func parseEmailBody(raw []byte) string {
	entity, err := gomessage.Read(strings.NewReader(string(raw)))
	if err != nil {
		return string(raw) // fallback: raw text
	}

	if mr := entity.MultipartReader(); mr != nil {
		var htmlBody, textBody string
		for {
			part, err := mr.NextPart()
			if err != nil {
				break
			}
			ct, _, _ := part.Header.ContentType()
			body, _ := io.ReadAll(part.Body)
			switch {
			case strings.HasPrefix(ct, "text/html"):
				htmlBody = string(body)
			case strings.HasPrefix(ct, "text/plain"):
				textBody = string(body)
			}
		}
		if htmlBody != "" {
			return htmlBody
		}
		return textBody
	}

	// Single part
	body, _ := io.ReadAll(entity.Body)
	return string(body)
}

func nilIfZero(v int64) interface{} {
	if v == 0 {
		return nil
	}
	return v
}

func nilIfEmpty(v string) interface{} {
	if v == "" {
		return nil
	}
	return v
}

// RegisterFetchmailCron ensures the message_id column exists for thread matching.
func RegisterFetchmailCron(ctx context.Context, pool *pgxpool.Pool) {
	pool.Exec(ctx, `ALTER TABLE mail_message ADD COLUMN IF NOT EXISTS message_id VARCHAR(255)`)
	pool.Exec(ctx, `CREATE INDEX IF NOT EXISTS idx_mail_message_message_id ON mail_message(message_id)`)
	log.Println("fetchmail: ready (IMAP config via IMAP_HOST/IMAP_USER/IMAP_PASSWORD env vars)")
}