// Folder and bulk-action persistence for Phase 4 (FR-6, FR-9, FR-13).
//
// A message carries two location fields after migration v4: `folder`, the
// low-cardinality app view (inbox, delete, saved, replied), and `mailbox`, the
// exact Gmail IMAP label it currently lives in. The mailbox is what a restore
// needs, because a Gmail message gets a new UID in each label it appears in.
package store

import (
	"context"
	"database/sql"
	"fmt"
	"strings"
)

// UnclassifiedCategory is the triage bucket for messages whose latest
// classification is missing. It is a view, not a stored category.
const UnclassifiedCategory = "Unclassified"

// MessageFilter narrows the triage list. An empty Folder means every folder; an
// empty Category means every category. Unclassified selects messages with no
// usable classification.
type MessageFilter struct {
	Folder       string
	Category     string
	Unclassified bool
	Limit        int
}

// ListMessagesFiltered returns messages matching the filter, newest first,
// joined to their latest classification. It backs the inbox and folder views.
func (s *Store) ListMessagesFiltered(ctx context.Context, f MessageFilter) ([]MessageListItem, error) {
	if f.Limit < 1 {
		f.Limit = 200
	}
	var (
		where []string
		args  []any
	)
	if f.Folder != "" && f.Folder != "all" {
		where = append(where, "m.folder = ?")
		args = append(args, f.Folder)
	}
	switch {
	case f.Unclassified:
		where = append(where, "(c.id IS NULL OR c.category = '')")
	case f.Category != "":
		where = append(where, "c.category = ? COLLATE NOCASE")
		args = append(args, f.Category)
	}
	clause := ""
	if len(where) > 0 {
		clause = "WHERE " + strings.Join(where, " AND ")
	}

	q := `
SELECT
    m.id, m.gmail_id, COALESCE(m.thread_id, ''), COALESCE(m.from_addr, ''),
    COALESCE(m.to_addr, ''), COALESCE(m.subject, ''), COALESCE(m.body_text, ''),
    COALESCE(m.source_address, ''), COALESCE(m.date_sent, ''), m.received_at,
    COALESCE(m.imap_uid, 0), COALESCE(m.imap_uidvalidity, 0),
    COALESCE(m.folder, 'inbox'), COALESCE(m.mailbox, 'INBOX'),
    COALESCE(c.category, ''), COALESCE(c.importance, ''),
    COALESCE(c.action, ''), COALESCE(c.confidence, 0)
FROM messages m
LEFT JOIN classifications c ON c.id = (
    SELECT id FROM classifications WHERE message_id = m.id ORDER BY id DESC LIMIT 1
)
` + clause + `
ORDER BY COALESCE(NULLIF(m.date_sent, ''), m.received_at) DESC, m.id DESC
LIMIT ?`
	args = append(args, f.Limit)

	rows, err := s.db.QueryContext(ctx, q, args...)
	if err != nil {
		return nil, fmt.Errorf("list filtered messages: %w", err)
	}
	defer rows.Close()

	var out []MessageListItem
	for rows.Next() {
		var (
			item     MessageListItem
			dateSent string
			received string
		)
		if err := rows.Scan(
			&item.ID, &item.GmailID, &item.ThreadID, &item.FromAddr,
			&item.ToAddr, &item.Subject, &item.BodyText,
			&item.SourceAddress, &dateSent, &received,
			&item.IMAPUID, &item.IMAPUIDValidity, &item.Folder, &item.Mailbox,
			&item.Category, &item.Importance, &item.Action, &item.Confidence,
		); err != nil {
			return nil, fmt.Errorf("scan filtered message: %w", err)
		}
		item.DateSent = parseSQLTime(dateSent)
		item.ReceivedAt = parseSQLTime(received)
		item.HasClassification = item.Category != ""
		out = append(out, item)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("list filtered messages: %w", err)
	}
	return out, nil
}

// MessagesByIDs loads the messages with the given ids. Order is not significant.
func (s *Store) MessagesByIDs(ctx context.Context, ids []int64) ([]Message, error) {
	if len(ids) == 0 {
		return nil, nil
	}
	placeholders := make([]string, len(ids))
	args := make([]any, len(ids))
	for i, id := range ids {
		placeholders[i] = "?"
		args[i] = id
	}
	q := `
SELECT m.id, m.gmail_id, COALESCE(m.thread_id, ''), COALESCE(m.from_addr, ''),
       COALESCE(m.to_addr, ''), COALESCE(m.subject, ''), COALESCE(m.body_text, ''),
       COALESCE(m.source_address, ''), COALESCE(m.date_sent, ''), m.received_at,
       COALESCE(m.imap_uid, 0), COALESCE(m.imap_uidvalidity, 0),
       COALESCE(m.folder, 'inbox'), COALESCE(m.mailbox, 'INBOX')
FROM messages m
WHERE m.id IN (` + strings.Join(placeholders, ",") + `)`

	rows, err := s.db.QueryContext(ctx, q, args...)
	if err != nil {
		return nil, fmt.Errorf("load messages by id: %w", err)
	}
	defer rows.Close()

	var out []Message
	for rows.Next() {
		var (
			m        Message
			dateSent string
			received string
		)
		if err := rows.Scan(
			&m.ID, &m.GmailID, &m.ThreadID, &m.FromAddr, &m.ToAddr, &m.Subject,
			&m.BodyText, &m.SourceAddress, &dateSent, &received,
			&m.IMAPUID, &m.IMAPUIDValidity, &m.Folder, &m.Mailbox,
		); err != nil {
			return nil, fmt.Errorf("scan message by id: %w", err)
		}
		m.DateSent = parseSQLTime(dateSent)
		m.ReceivedAt = parseSQLTime(received)
		out = append(out, m)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("load messages by id: %w", err)
	}
	return out, nil
}

// SetMessageLocation records the app folder and Gmail label a message now lives
// in. It is called after a successful move; the database is only updated once
// the mailbox agrees, so a failed move leaves the list truthful.
func (s *Store) SetMessageLocation(ctx context.Context, id int64, folder, mailbox string) error {
	const q = `UPDATE messages SET folder = ?, mailbox = ? WHERE id = ?`
	if _, err := s.db.ExecContext(ctx, q, folder, mailbox, id); err != nil {
		return fmt.Errorf("set message %d location: %w", id, err)
	}
	return nil
}

// LatestClassifications returns the newest classification per message id.
func (s *Store) LatestClassifications(ctx context.Context, ids []int64) (map[int64]Classification, error) {
	out := map[int64]Classification{}
	if len(ids) == 0 {
		return out, nil
	}
	placeholders := make([]string, len(ids))
	args := make([]any, len(ids))
	for i, id := range ids {
		placeholders[i] = "?"
		args[i] = id
	}
	q := `
SELECT c.message_id, c.category, COALESCE(c.importance, ''), COALESCE(c.action, ''),
       COALESCE(c.confidence, 0), COALESCE(c.model, '')
FROM classifications c
WHERE c.id IN (
    SELECT MAX(id) FROM classifications WHERE message_id IN (` + strings.Join(placeholders, ",") + `)
    GROUP BY message_id
)`
	rows, err := s.db.QueryContext(ctx, q, args...)
	if err != nil {
		return nil, fmt.Errorf("latest classifications: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var c Classification
		if err := rows.Scan(&c.MessageID, &c.Category, &c.Importance, &c.Action, &c.Confidence, &c.Model); err != nil {
			return nil, fmt.Errorf("scan latest classification: %w", err)
		}
		out[c.MessageID] = c
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("latest classifications: %w", err)
	}
	return out, nil
}

// CountByFolder returns the number of messages in each app folder.
func (s *Store) CountByFolder(ctx context.Context) (map[string]int, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT COALESCE(folder, 'inbox'), COUNT(*) FROM messages GROUP BY 1`)
	if err != nil {
		return nil, fmt.Errorf("count by folder: %w", err)
	}
	defer rows.Close()
	out := map[string]int{}
	for rows.Next() {
		var (
			folder string
			n      int
		)
		if err := rows.Scan(&folder, &n); err != nil {
			return nil, fmt.Errorf("scan folder count: %w", err)
		}
		out[folder] = n
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("count by folder: %w", err)
	}
	return out, nil
}

// ActionLogEntry is one row of the append-only action log (FR-13).
type ActionLogEntry struct {
	ID        int64
	MessageID sql.NullInt64
	Action    string
	Actor     string
	Detail    string
	CreatedAt string
}

// RecentActions returns the newest action-log rows, newest first.
func (s *Store) RecentActions(ctx context.Context, limit int) ([]ActionLogEntry, error) {
	if limit < 1 {
		limit = 50
	}
	rows, err := s.db.QueryContext(ctx, `
SELECT id, message_id, action, COALESCE(actor, ''), COALESCE(detail, ''), created_at
FROM actions_log ORDER BY id DESC LIMIT ?`, limit)
	if err != nil {
		return nil, fmt.Errorf("recent actions: %w", err)
	}
	defer rows.Close()
	var out []ActionLogEntry
	for rows.Next() {
		var e ActionLogEntry
		if err := rows.Scan(&e.ID, &e.MessageID, &e.Action, &e.Actor, &e.Detail, &e.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan action log: %w", err)
		}
		out = append(out, e)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("recent actions: %w", err)
	}
	return out, nil
}