package storage

import (
	"context"
	"fmt"
)

// ListNonASCIISubjects returns emails whose subject contains at least one
// non-ASCII byte.
//
// Why a second lister next to ListRawEncodedSubjects: that one only matches the
// RFC 2047 encoded-word pattern (`=?charset?B|Q?...?=`) and therefore cannot
// find the second mojibake class at all — headers that were written with raw
// 8-bit Windows-1252/ISO-8859-1 bytes and no encoded-word syntax. Those rows
// contain no `=?...?=` marker; the only cheap SQL signal is "has bytes > 0x7F".
//
// The prefilter is `subject ~ '[^[:ascii:]]'`. Note that the obvious
// alternative `octet_length(subject) <> length(subject)` is WRONG here: in a
// SQL_ASCII database (which the production archive uses) length() counts bytes,
// so that condition is never true and the query silently returns nothing.
// The regex class works byte-wise in SQL_ASCII and char-wise in UTF8.
//
// The caller must narrow the result down with mailparser.NeedsCharsetRepair —
// the vast majority of non-ASCII subjects are perfectly valid UTF-8 and must
// not be touched.
//
// tenantID nil = all tenants. limit <= 0 = no limit.
func (s *Store) ListNonASCIISubjects(ctx context.Context, tenantID *int64, limit int) ([]SubjectRow, error) {
	if s.db == nil {
		return nil, fmt.Errorf("storage: list non-ascii subjects: no database configured")
	}

	query := `SELECT id, tenant_id, COALESCE(subject, '')
	          FROM emails
	          WHERE subject IS NOT NULL
	            AND subject ~ '[^[:ascii:]]'`
	args := []interface{}{}
	if tenantID != nil {
		args = append(args, *tenantID)
		query += fmt.Sprintf(" AND tenant_id = $%d", len(args))
	}
	query += " ORDER BY received_at ASC"
	if limit > 0 {
		args = append(args, limit)
		query += fmt.Sprintf(" LIMIT $%d", len(args))
	}

	rows, err := s.db.Query(ctx, query, args...)
	if err != nil {
		return nil, fmt.Errorf("storage: list non-ascii subjects: %w", err)
	}
	defer rows.Close()

	var out []SubjectRow
	for rows.Next() {
		var r SubjectRow
		if err := rows.Scan(&r.ID, &r.TenantID, &r.Subject); err != nil {
			return nil, fmt.Errorf("storage: list non-ascii subjects: scan: %w", err)
		}
		out = append(out, r)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("storage: list non-ascii subjects: rows: %w", err)
	}
	return out, nil
}