// Summary and reporting persistence for Phase 7 (FR-10).
//
// The daily summary is built from the same classification data the triage list
// uses; it is stored once per date in the `summaries` table (AGENTS.md §7) and
// then delivered by email through Apprise.
package store

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

// CategoryCount is one bucket of the inbox overview: a category name and how
// many messages currently sit in it. The empty category is the unclassified
// bucket.
type CategoryCount struct {
	Category string
	Count    int
}

// CountByCategory returns message counts for one folder, grouped by each
// message's latest classification category. Messages with no usable
// classification are counted under the empty category name.
func (s *Store) CountByCategory(ctx context.Context, folder string) ([]CategoryCount, error) {
	const q = `
SELECT COALESCE(c.category, ''), COUNT(*)
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
)
WHERE (? = '' OR m.folder = ?)
GROUP BY 1
ORDER BY 2 DESC, 1 ASC`
	rows, err := s.db.QueryContext(ctx, q, folder, folder)
	if err != nil {
		return nil, fmt.Errorf("count by category: %w", err)
	}
	defer rows.Close()

	var out []CategoryCount
	for rows.Next() {
		var c CategoryCount
		if err := rows.Scan(&c.Category, &c.Count); err != nil {
			return nil, fmt.Errorf("scan category count: %w", err)
		}
		out = append(out, c)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("count by category: %w", err)
	}
	return out, nil
}

// MessagesByCategory returns the newest messages in a folder whose latest
// classification is one of categories, highest importance first. It backs the
// "what needs attention" list in the daily summary and the Hub answer.
func (s *Store) MessagesByCategory(ctx context.Context, folder string, categories []string, limit int) ([]MessageListItem, error) {
	if len(categories) == 0 {
		return nil, nil
	}
	if limit < 1 {
		limit = 20
	}
	placeholders := make([]string, len(categories))
	args := make([]any, 0, len(categories)+2)
	for i, c := range categories {
		placeholders[i] = "?"
		args = append(args, c)
	}
	// The importance rank puts high first; an unset importance sorts last.
	rank := `CASE LOWER(COALESCE(c.importance, ''))
        WHEN 'high' THEN 0 WHEN 'medium' THEN 1 WHEN 'low' THEN 2 ELSE 3 END`
	folderClause := ""
	if folder != "" {
		folderClause = "AND m.folder = ?"
		args = append(args, folder)
	}
	args = append(args, limit)

	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
)
WHERE c.category IN (` + strings.Join(placeholders, ",") + `) ` + folderClause + `
ORDER BY ` + rank + `, COALESCE(NULLIF(m.date_sent, ''), m.received_at) DESC, m.id DESC
LIMIT ?`
	rows, err := s.db.QueryContext(ctx, q, args...)
	if err != nil {
		return nil, fmt.Errorf("messages by category: %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 category 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("messages by category: %w", err)
	}
	return out, nil
}

// Summary is one stored daily summary (FR-10).
type Summary struct {
	ID          int64
	Date        string
	Text        string
	DeliveredTo string
	CreatedAt   string
}

// SaveSummary stores the summary for a date, replacing an earlier build for the
// same date so re-running the job does not duplicate rows. It returns the row id.
func (s *Store) SaveSummary(ctx context.Context, date, text, deliveredTo string) (int64, error) {
	const q = `
INSERT INTO summaries (date, text, delivered_to) VALUES (?, ?, ?)
ON CONFLICT (date) DO UPDATE SET
    text = excluded.text,
    delivered_to = excluded.delivered_to`
	if _, err := s.db.ExecContext(ctx, q, date, text, nullString(deliveredTo)); err != nil {
		return 0, fmt.Errorf("save summary %s: %w", date, err)
	}
	var id int64
	if err := s.db.QueryRowContext(ctx,
		`SELECT id FROM summaries WHERE date = ?`, date).Scan(&id); err != nil {
		return 0, fmt.Errorf("read summary id for %s: %w", date, err)
	}
	return id, nil
}

// MarkSummaryDelivered records the recipient once a summary has been emailed.
func (s *Store) MarkSummaryDelivered(ctx context.Context, id int64, deliveredTo string) error {
	if _, err := s.db.ExecContext(ctx,
		`UPDATE summaries SET delivered_to = ? WHERE id = ?`, nullString(deliveredTo), id); err != nil {
		return fmt.Errorf("mark summary %d delivered: %w", id, err)
	}
	return nil
}

// SummaryByDate loads one summary by its YYYY-MM-DD date. ok is false when none
// exists.
func (s *Store) SummaryByDate(ctx context.Context, date string) (Summary, bool, error) {
	row := s.db.QueryRowContext(ctx, `
SELECT id, date, text, COALESCE(delivered_to, ''), created_at
FROM summaries WHERE date = ?`, date)
	var sum Summary
	if err := row.Scan(&sum.ID, &sum.Date, &sum.Text, &sum.DeliveredTo, &sum.CreatedAt); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return Summary{}, false, nil
		}
		return Summary{}, false, fmt.Errorf("read summary %s: %w", date, err)
	}
	return sum, true, nil
}

// ListSummaries returns stored summaries, newest date first.
func (s *Store) ListSummaries(ctx context.Context, limit int) ([]Summary, error) {
	if limit < 1 {
		limit = 30
	}
	rows, err := s.db.QueryContext(ctx, `
SELECT id, date, text, COALESCE(delivered_to, ''), created_at
FROM summaries ORDER BY date DESC LIMIT ?`, limit)
	if err != nil {
		return nil, fmt.Errorf("list summaries: %w", err)
	}
	defer rows.Close()
	var out []Summary
	for rows.Next() {
		var sum Summary
		if err := rows.Scan(&sum.ID, &sum.Date, &sum.Text, &sum.DeliveredTo, &sum.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan summary: %w", err)
		}
		out = append(out, sum)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("list summaries: %w", err)
	}
	return out, nil
}

// DeleteSummary removes one stored report (AGENTS.md §5 "delete-report").
func (s *Store) DeleteSummary(ctx context.Context, id int64) error {
	if _, err := s.db.ExecContext(ctx, `DELETE FROM summaries WHERE id = ?`, id); err != nil {
		return fmt.Errorf("delete summary %d: %w", id, err)
	}
	return nil
}