package mail

import (
	"fmt"
	"io"
	"sort"
	"time"

	"github.com/emersion/go-imap"
	"github.com/emersion/go-imap/client"
)

type IMAPConfig struct {
	Host     string
	Port     int
	Security string // tls | starttls
	Username string
	Password string
}

type Client struct {
	c *client.Client
}

func Dial(cfg IMAPConfig) (*Client, error) {
	addr := fmt.Sprintf("%s:%d", cfg.Host, cfg.Port)
	var (
		ic  *client.Client
		err error
	)
	switch cfg.Security {
	case "tls":
		ic, err = client.DialTLS(addr, nil)
	case "starttls":
		ic, err = client.Dial(addr)
		if err == nil {
			err = ic.StartTLS(nil)
		}
	default:
		return nil, fmt.Errorf("unknown imap security %q", cfg.Security)
	}
	if err != nil {
		return nil, err
	}
	if err := ic.Login(cfg.Username, cfg.Password); err != nil {
		ic.Logout()
		return nil, err
	}
	return &Client{c: ic}, nil
}

func (c *Client) Logout() error { return c.c.Logout() }

func (c *Client) SelectFolder(folder string) (uint32, uint32, error) {
	mbox, err := c.c.Select(folder, true) // read-only select
	if err != nil {
		return 0, 0, err
	}
	var maxUID uint32
	if mbox.Messages > 0 {
		// UIDNext-1 is an upper bound for the highest existing UID.
		if mbox.UidNext > 0 {
			maxUID = mbox.UidNext - 1
		}
	}
	return mbox.UidValidity, maxUID, nil
}

func (c *Client) fetchByUIDSet(folder string, set *imap.SeqSet, full bool) ([]Message, error) {
	if _, err := c.c.Select(folder, true); err != nil {
		return nil, err
	}
	section := &imap.BodySectionName{Peek: true} // entire message, no \Seen side-effect
	items := []imap.FetchItem{imap.FetchUid, section.FetchItem()}

	msgCh := make(chan *imap.Message, 16)
	done := make(chan error, 1)
	go func() { done <- c.c.UidFetch(set, items, msgCh) }()

	var out []Message
	for m := range msgCh {
		r := m.GetBody(section)
		if r == nil {
			continue
		}
		raw, _ := io.ReadAll(r)
		parsed, err := ParseMessage(m.Uid, raw)
		if err != nil {
			return nil, err
		}
		if !full {
			parsed.Attachments = nil
			parsed.BodyText = ""
		}
		out = append(out, parsed)
	}
	if err := <-done; err != nil {
		return nil, err
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Header.UID > out[j].Header.UID })
	return out, nil
}

func (c *Client) FetchHeaders(folder string, uids []uint32) ([]Header, error) {
	set := new(imap.SeqSet)
	if len(uids) == 0 {
		set.AddRange(1, 0) // 1:* — all
	} else {
		for _, u := range uids {
			set.AddNum(u)
		}
	}
	msgs, err := c.fetchByUIDSet(folder, set, false)
	if err != nil {
		return nil, err
	}
	return headersOf(msgs), nil
}

func (c *Client) FetchHeadersRange(folder string, sinceUID, beforeUID uint32, limit int) ([]Header, error) {
	set := new(imap.SeqSet)
	lo := sinceUID + 1
	if sinceUID == 0 {
		lo = 1
	}
	hi := uint32(0) // '*'
	if beforeUID > 1 {
		hi = beforeUID - 1
	}
	set.AddRange(lo, hi)
	msgs, err := c.fetchByUIDSet(folder, set, false)
	if err != nil {
		return nil, err
	}
	h := headersOf(msgs)
	if limit > 0 && len(h) > limit {
		h = h[:limit]
	}
	return h, nil
}

func (c *Client) FetchFull(folder string, uid uint32) (Message, error) {
	set := new(imap.SeqSet)
	set.AddNum(uid)
	msgs, err := c.fetchByUIDSet(folder, set, true)
	if err != nil {
		return Message{}, err
	}
	if len(msgs) == 0 {
		return Message{}, fmt.Errorf("uid %d not found in %s", uid, folder)
	}
	return msgs[0], nil
}

type SearchCriteria struct {
	From            string
	SubjectContains string
	Text            string
	Since           time.Time
	Before          time.Time
}

func (c *Client) Search(folder string, sc SearchCriteria, limit int) ([]Header, error) {
	if _, err := c.c.Select(folder, true); err != nil {
		return nil, err
	}
	crit := imap.NewSearchCriteria()
	if sc.From != "" {
		crit.Header.Add("From", sc.From)
	}
	if sc.SubjectContains != "" {
		crit.Header.Add("Subject", sc.SubjectContains)
	}
	if sc.Text != "" {
		crit.Text = []string{sc.Text}
	}
	if !sc.Since.IsZero() {
		crit.Since = sc.Since
	}
	if !sc.Before.IsZero() {
		crit.Before = sc.Before
	}
	uids, err := c.c.UidSearch(crit)
	if err != nil {
		return nil, err
	}
	if len(uids) == 0 {
		return nil, nil
	}
	return c.FetchHeaders(folder, uids)
}

func headersOf(msgs []Message) []Header {
	out := make([]Header, 0, len(msgs))
	for _, m := range msgs {
		out = append(out, m.Header)
	}
	return out
}