package postgres

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5/pgxpool"

	"lambdamail/protocols/internal/application/port"
)

// Conversations reads the mailbox as conversations rather than as single
// messages. Writing is MailStore's job, as for every other change.
type Conversations struct {
	pool  *pgxpool.Pool
	store *MailStore
}

func NewConversations(pool *pgxpool.Pool) *Conversations {
	return &Conversations{pool: pool, store: NewMailStore(pool)}
}

// scopeRow is one message that counts towards a conversation.
type scopeRow struct {
	threadID     uuid.UUID
	uid          uint32
	folder       string
	folderID     string
	subject      string
	sender       string
	name         string
	snippet      string
	receivedAt   time.Time
	hasAttach    bool
	seen         bool
	flagged      bool
	answeredFlag bool
	own          bool
}

// scopeSQL selects the messages of the given conversations that belong in a
// view of one folder: that folder's own messages, and the rest of the
// conversation wherever it is filed, except what has been thrown away. Trash,
// Junk and Drafts are left out of a conversation seen from elsewhere - a
// reply still being written, or one deleted, is not part of the thread a reader
// is looking at - and are the whole story when that is the folder viewed.
const scopeSQL = `
	SELECT COALESCE(e.thread_id, e.id), e.uid, fo.name, fo.id::text,
	       COALESCE(e.subject, ''), e.sender_address::text,
	       COALESCE(e.from_display_name, ''), COALESCE(e.snippet, ''),
	       e.received_at, e.has_attachments,
	       EXISTS (SELECT 1 FROM message_flags f WHERE f.message_id = e.id AND f.received_at = e.received_at AND f.flag = '\Seen'),
	       EXISTS (SELECT 1 FROM message_flags f WHERE f.message_id = e.id AND f.received_at = e.received_at AND f.flag = '\Flagged'),
	       EXISTS (SELECT 1 FROM message_flags f WHERE f.message_id = e.id AND f.received_at = e.received_at AND f.flag = '\Answered'),
	       e.sender_address::text = mb.email_address::text
	  FROM email_messages e
	  JOIN folders fo ON fo.id = e.folder_id
	  JOIN mailboxes mb ON mb.id = e.mailbox_id
	 WHERE e.mailbox_id = $1
	   AND e.expunged_at IS NULL
	   AND COALESCE(e.thread_id, e.id) = ANY($3::uuid[])
	   AND (fo.id::text = $2
	        OR (COALESCE(fo.special_use, '') NOT IN ('trash', 'junk', 'drafts')
	            AND lower(fo.name) NOT IN ('trash', 'junk', 'drafts')))
	 ORDER BY e.received_at ASC, e.uid ASC`

func (c *Conversations) scope(ctx context.Context, mailboxID, folderID string, threads []uuid.UUID) (map[uuid.UUID][]scopeRow, error) {
	rows, err := c.pool.Query(ctx, scopeSQL, mailboxID, folderID, threads)
	if err != nil {
		return nil, fmt.Errorf("read the conversations: %w", err)
	}
	defer rows.Close()
	out := make(map[uuid.UUID][]scopeRow, len(threads))
	for rows.Next() {
		var r scopeRow
		var uid int64
		if err := rows.Scan(&r.threadID, &uid, &r.folder, &r.folderID, &r.subject, &r.sender, &r.name,
			&r.snippet, &r.receivedAt, &r.hasAttach, &r.seen, &r.flagged, &r.answeredFlag, &r.own); err != nil {
			return nil, err
		}
		r.uid = uint32(uid)
		out[r.threadID] = append(out[r.threadID], r)
	}
	return out, rows.Err()
}

func (c *Conversations) ListThreads(
	ctx context.Context, mailboxID, folderName, search string, limit, offset int,
) ([]port.WebmailThread, error) {
	if limit <= 0 || limit > 200 {
		limit = 50
	}
	if offset < 0 {
		offset = 0
	}
	folderID, err := c.store.ResolveFolder(ctx, mailboxID, folderName)
	if errors.Is(err, port.ErrFolderMissing) {
		return []port.WebmailThread{}, nil
	}
	if err != nil {
		return nil, err
	}

	// The page is chosen first, by the newest message each conversation has in
	// this folder, and only then are those conversations read in full.
	rows, err := c.pool.Query(ctx, `
		SELECT COALESCE(thread_id, id)
		  FROM email_messages
		 WHERE folder_id = $1 AND expunged_at IS NULL
		   AND ($2 = '' OR subject ILIKE '%' || $2 || '%'
		                OR sender_address::text ILIKE '%' || $2 || '%'
		                OR snippet ILIKE '%' || $2 || '%')
		 GROUP BY COALESCE(thread_id, id)
		 ORDER BY max(received_at) DESC, max(uid) DESC
		 LIMIT $3 OFFSET $4`, folderID, search, limit, offset)
	if err != nil {
		return nil, fmt.Errorf("list conversations: %w", err)
	}
	var page []uuid.UUID
	for rows.Next() {
		var id uuid.UUID
		if err := rows.Scan(&id); err != nil {
			rows.Close()
			return nil, err
		}
		page = append(page, id)
	}
	rows.Close()
	if err := rows.Err(); err != nil {
		return nil, err
	}
	if len(page) == 0 {
		return []port.WebmailThread{}, nil
	}

	byThread, err := c.scope(ctx, mailboxID, folderID, page)
	if err != nil {
		return nil, err
	}
	out := make([]port.WebmailThread, 0, len(page))
	for _, id := range page {
		if t, ok := summarise(id, byThread[id], folderID); ok {
			out = append(out, t)
		}
	}
	return out, nil
}

// summarise folds a conversation's messages into its list row. It reports
// false for a conversation with nothing in the folder viewed.
func summarise(id uuid.UUID, msgs []scopeRow, folderID string) (port.WebmailThread, bool) {
	var latestHere *scopeRow
	for i := range msgs {
		if msgs[i].folderID == folderID {
			latestHere = &msgs[i] // oldest first, so the last one wins
		}
	}
	if latestHere == nil {
		return port.WebmailThread{}, false
	}

	t := port.WebmailThread{
		ThreadID: id.String(), UID: latestHere.uid, Subject: latestHere.subject,
		SenderAddress: latestHere.sender, FromName: latestHere.name, Snippet: latestHere.snippet,
		ReceivedAt: latestHere.receivedAt, MessageCount: len(msgs),
		Answered:     answered(msgs),
		Participants: participants(msgs),
	}
	for _, m := range msgs {
		if !m.seen {
			t.UnseenCount++
		}
		t.Flagged = t.Flagged || m.flagged
		t.HasAttachments = t.HasAttachments || m.hasAttach
	}
	t.Seen = t.UnseenCount == 0
	return t, true
}

// answered reports whether the last thing someone else wrote has been replied
// to - by the flag, or by a message of the owner's that came after it.
func answered(msgs []scopeRow) bool {
	lastIncoming := -1
	for i, m := range msgs {
		if !m.own {
			lastIncoming = i
		}
	}
	if lastIncoming < 0 {
		return false
	}
	if msgs[lastIncoming].answeredFlag {
		return true
	}
	for _, m := range msgs[lastIncoming+1:] {
		if m.own {
			return true
		}
	}
	return false
}

// participants lists who wrote, in the order they first did, at most four.
func participants(msgs []scopeRow) []port.WebmailParticipant {
	seen := map[string]bool{}
	var out []port.WebmailParticipant
	for _, m := range msgs {
		key := strings.ToLower(m.sender)
		if seen[key] || len(out) == 4 {
			continue
		}
		seen[key] = true
		name := m.name
		if name == "" {
			name = m.sender
		}
		out = append(out, port.WebmailParticipant{Name: name, Address: m.sender, Me: m.own})
	}
	return out
}

func (c *Conversations) ThreadMessages(
	ctx context.Context, mailboxID, folderName, threadID string,
) ([]port.WebmailThreadMessage, error) {
	id, err := uuid.Parse(threadID)
	if err != nil {
		return nil, ErrMessageNotFound
	}
	folderID, err := c.store.ResolveFolder(ctx, mailboxID, folderName)
	if errors.Is(err, port.ErrFolderMissing) {
		return nil, ErrMessageNotFound
	}
	if err != nil {
		return nil, err
	}
	byThread, err := c.scope(ctx, mailboxID, folderID, []uuid.UUID{id})
	if err != nil {
		return nil, err
	}
	msgs := byThread[id]
	if len(msgs) == 0 {
		// Another mailbox's conversation and one that does not exist look alike.
		return nil, ErrMessageNotFound
	}

	out := make([]port.WebmailThreadMessage, 0, len(msgs))
	for i, m := range msgs {
		out = append(out, port.WebmailThreadMessage{
			UID: m.uid, Folder: m.folder, Subject: m.subject, SenderAddress: m.sender, FromName: m.name,
			Snippet: m.snippet, ReceivedAt: m.receivedAt, HasAttachments: m.hasAttach,
			Seen: m.seen, Flagged: m.flagged, Own: m.own,
			Answered: !m.own && (m.answeredFlag || ownAfter(msgs, i)),
		})
	}
	sort.SliceStable(out, func(a, b int) bool { return out[a].ReceivedAt.Before(out[b].ReceivedAt) })
	return out, nil
}

func ownAfter(msgs []scopeRow, i int) bool {
	for _, m := range msgs[i+1:] {
		if m.own {
			return true
		}
	}
	return false
}

// MarkAnsweredByMessageID sets \Answered on the message a reply was written to.
func (c *Conversations) MarkAnsweredByMessageID(ctx context.Context, mailboxID, messageID string) error {
	messageID = strings.Trim(strings.TrimSpace(messageID), "<>")
	if messageID == "" {
		return nil
	}
	rows, err := c.pool.Query(ctx, `
		SELECT fo.id::text, e.uid
		  FROM email_messages e JOIN folders fo ON fo.id = e.folder_id
		 WHERE e.mailbox_id = $1 AND e.message_id_header = $2 AND e.expunged_at IS NULL
		   AND COALESCE(fo.special_use, '') NOT IN ('sent', 'drafts', 'trash')`, mailboxID, messageID)
	if err != nil {
		return fmt.Errorf("find the message that was answered: %w", err)
	}
	type target struct {
		folder string
		uid    int64
	}
	var targets []target
	for rows.Next() {
		var t target
		if err := rows.Scan(&t.folder, &t.uid); err != nil {
			rows.Close()
			return err
		}
		targets = append(targets, t)
	}
	rows.Close()
	for _, t := range targets {
		if err := func() error {
			_, e := c.store.SetFlags(ctx, t.folder, uint32(t.uid), port.FlagOpAdd, []string{`\Answered`}, 0)
			return e
		}(); err != nil {
			return fmt.Errorf("flag the answered message: %w", err)
		}
	}
	return nil
}