// Device registry and desired state (AGENTS.md §7 devices/state, §11 Phase 2).
//
// The Control Service is the only writer of device config (SYSTEM_MAP.md).
// Every mutation appends to the audit log (FR-15), and nothing is ever
// hard-deleted (§10 rule 10).
package store

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

// ErrNotFound is returned when a device id does not exist.
var ErrNotFound = errors.New("device not found")

// Platform values allowed by the devices.platform CHECK constraint.
const (
	PlatformAndroid = "android"
	PlatformWindows = "windows"
)

// ValidPlatform reports whether p is one of the supported platforms.
func ValidPlatform(p string) bool {
	return p == PlatformAndroid || p == PlatformWindows
}

// Device is one registered device plus its desired state.
type Device struct {
	ID        int64
	Name      string
	Child     string
	Platform  string
	Topic     string
	Online    bool
	LastSeen  *time.Time
	CreatedAt time.Time
	UpdatedAt time.Time

	// Desired state, from the state table.
	Locked  bool
	Until   *time.Time
	StateAt time.Time
}

// AuditEntry is one row of the append-only audit log (FR-15).
type AuditEntry struct {
	ID         int64
	Actor      string
	Action     string
	DeviceID   *int64
	DeviceName string
	Detail     string
	CreatedAt  time.Time
}

// selectDevice is the shared projection for reading a device with its state.
const selectDevice = `
SELECT d.id, d.name, d.child, d.platform, d.topic, d.online, d.last_seen,
       d.created_at, d.updated_at,
       COALESCE(s.locked, 0), s.until, s.updated_at
FROM devices d
LEFT JOIN state s ON s.device_id = d.id`

func scanDevice(row interface {
	Scan(dest ...any) error
}) (*Device, error) {
	var (
		dev                      Device
		online                   int
		lastSeen, until, stateAt sql.NullString
		createdAt, updatedAt     sql.NullString
	)
	if err := row.Scan(
		&dev.ID, &dev.Name, &dev.Child, &dev.Platform, &dev.Topic, &online,
		&lastSeen, &createdAt, &updatedAt,
		&dev.Locked, &until, &stateAt,
	); err != nil {
		return nil, err
	}
	dev.Online = online != 0
	dev.LastSeen = parseTimePtr(lastSeen)
	dev.Until = parseTimePtr(until)
	if t := parseTime(createdAt.String); !t.IsZero() {
		dev.CreatedAt = t
	}
	if t := parseTime(updatedAt.String); !t.IsZero() {
		dev.UpdatedAt = t
	}
	if t := parseTime(stateAt.String); !t.IsZero() {
		dev.StateAt = t
	}
	return &dev, nil
}

// ListDevices returns every registered device with its desired state, in
// registration order. Expired locks are already cleared by ExpireLocks.
func (s *Store) ListDevices(ctx context.Context) ([]Device, error) {
	rows, err := s.db.QueryContext(ctx, selectDevice+` ORDER BY d.id`)
	if err != nil {
		return nil, fmt.Errorf("list devices: %w", err)
	}
	defer rows.Close()

	out := make([]Device, 0, 8)
	for rows.Next() {
		dev, err := scanDevice(rows)
		if err != nil {
			return nil, fmt.Errorf("scan device: %w", err)
		}
		out = append(out, *dev)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("list devices: %w", err)
	}
	return out, nil
}

// GetDevice returns one device with its state, or ErrNotFound.
func (s *Store) GetDevice(ctx context.Context, id int64) (*Device, error) {
	dev, err := scanDevice(s.db.QueryRowContext(ctx, selectDevice+` WHERE d.id = ?`, id))
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("get device: %w", err)
	}
	return dev, nil
}

// CreateDevice inserts a device and its initial (unlocked) state row, and
// appends one audit entry. The topic is derived from the name and the new id,
// so it is stable across renames.
func (s *Store) CreateDevice(ctx context.Context, name, child, platform, actor string) (*Device, error) {
	name = strings.TrimSpace(name)
	child = strings.TrimSpace(child)
	platform = strings.ToLower(strings.TrimSpace(platform))

	if name == "" {
		return nil, errors.New("device name is required")
	}
	if len(name) > 80 {
		return nil, errors.New("device name must be 80 characters or fewer")
	}
	if child == "" {
		return nil, errors.New("child is required")
	}
	if len(child) > 40 {
		return nil, errors.New("child must be 40 characters or fewer")
	}
	if !ValidPlatform(platform) {
		return nil, errors.New(`platform must be "android" or "windows"`)
	}

	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return nil, fmt.Errorf("create device: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	// The topic needs the new id, so insert with a placeholder then set it.
	res, err := tx.ExecContext(ctx,
		`INSERT INTO devices (name, child, platform, topic) VALUES (?, ?, ?, '')`,
		name, child, platform)
	if err != nil {
		return nil, fmt.Errorf("insert device: %w", err)
	}
	id, err := res.LastInsertId()
	if err != nil {
		return nil, fmt.Errorf("device id: %w", err)
	}
	topic := fmt.Sprintf("restrict/%s_%d/config", slug(name), id)
	if _, err := tx.ExecContext(ctx,
		`UPDATE devices SET topic = ? WHERE id = ?`, topic, id); err != nil {
		return nil, fmt.Errorf("set topic: %w", err)
	}
	if _, err := tx.ExecContext(ctx,
		`INSERT INTO state (device_id, locked, until) VALUES (?, 0, NULL)`, id); err != nil {
		return nil, fmt.Errorf("insert state: %w", err)
	}
	if err := insertAudit(ctx, tx, actor, "device.created", &id,
		fmt.Sprintf("%s (%s · %s)", name, child, platform)); err != nil {
		return nil, err
	}
	if err := tx.Commit(); err != nil {
		return nil, fmt.Errorf("commit device: %w", err)
	}
	return s.GetDevice(ctx, id)
}

// UpdateDevice renames or reassigns a device. The topic and id never change, so
// a device's MQTT identity is stable. It appends one audit entry.
func (s *Store) UpdateDevice(ctx context.Context, id int64, name, child, platform, actor string) (*Device, error) {
	name = strings.TrimSpace(name)
	child = strings.TrimSpace(child)
	platform = strings.ToLower(strings.TrimSpace(platform))

	if name == "" {
		return nil, errors.New("device name is required")
	}
	if len(name) > 80 {
		return nil, errors.New("device name must be 80 characters or fewer")
	}
	if child == "" {
		return nil, errors.New("child is required")
	}
	if len(child) > 40 {
		return nil, errors.New("child must be 40 characters or fewer")
	}
	if !ValidPlatform(platform) {
		return nil, errors.New(`platform must be "android" or "windows"`)
	}

	res, err := s.db.ExecContext(ctx,
		`UPDATE devices SET name = ?, child = ?, platform = ?, updated_at = datetime('now') WHERE id = ?`,
		name, child, platform, id)
	if err != nil {
		return nil, fmt.Errorf("update device: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return nil, fmt.Errorf("update device: %w", err)
	}
	if n == 0 {
		return nil, ErrNotFound
	}
	if err := s.Audit(ctx, actor, "device.updated", &id,
		fmt.Sprintf("%s (%s · %s)", name, child, platform)); err != nil {
		return nil, err
	}
	return s.GetDevice(ctx, id)
}

// SetDeviceLock writes the desired lock state for one device and appends one
// audit entry in the same transaction. When locked is false, until is ignored.
func (s *Store) SetDeviceLock(ctx context.Context, id int64, locked bool, until *time.Time, actor, action string) (*Device, error) {
	if !locked {
		until = nil
	}
	if locked && until != nil {
		t := until.UTC()
		until = &t
	}

	if _, err := s.GetDevice(ctx, id); err != nil {
		return nil, err
	}

	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return nil, fmt.Errorf("set state: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	var untilArg any
	detail := "unlocked"
	if locked {
		detail = "locked"
		if until != nil {
			untilArg = until.Format(time.RFC3339)
			detail = "locked until " + until.Format(time.RFC3339)
		} else {
			detail = "locked (no end time)"
		}
	}

	if _, err := tx.ExecContext(ctx, `
		INSERT INTO state (device_id, locked, until, updated_at)
		VALUES (?, ?, ?, datetime('now'))
		ON CONFLICT(device_id) DO UPDATE SET
			locked = excluded.locked,
			until = excluded.until,
			updated_at = datetime('now')`,
		id, boolToInt(locked), untilArg); err != nil {
		return nil, fmt.Errorf("set state: %w", err)
	}
	if err := insertAudit(ctx, tx, actor, action, &id, detail); err != nil {
		return nil, err
	}
	if err := tx.Commit(); err != nil {
		return nil, fmt.Errorf("commit state: %w", err)
	}
	return s.GetDevice(ctx, id)
}

// ExpireLocks unlocks every device whose timed lock has passed and appends one
// audit entry per device. It returns how many locks it cleared. It is safe to
// call often.
func (s *Store) ExpireLocks(ctx context.Context) (int, error) {
	now := time.Now().UTC().Format(time.RFC3339)
	rows, err := s.db.QueryContext(ctx,
		`SELECT device_id FROM state WHERE locked = 1 AND until IS NOT NULL AND until <= ?`, now)
	if err != nil {
		return 0, fmt.Errorf("expire locks: %w", err)
	}
	var ids []int64
	for rows.Next() {
		var id int64
		if err := rows.Scan(&id); err != nil {
			rows.Close()
			return 0, fmt.Errorf("scan expired lock: %w", err)
		}
		ids = append(ids, id)
	}
	if err := rows.Err(); err != nil {
		rows.Close()
		return 0, fmt.Errorf("expire locks: %w", err)
	}
	rows.Close()

	for _, id := range ids {
		if _, err := s.SetDeviceLock(ctx, id, false, nil, "system", "state.expired"); err != nil {
			return 0, err
		}
	}
	return len(ids), nil
}

// ListAudit returns the newest audit entries first (FR-15).
func (s *Store) ListAudit(ctx context.Context, limit int) ([]AuditEntry, error) {
	if limit <= 0 || limit > 500 {
		limit = 50
	}
	rows, err := s.db.QueryContext(ctx, `
		SELECT a.id, a.actor, a.action, a.device_id, COALESCE(d.name, ''),
		       COALESCE(a.detail, ''), a.created_at
		FROM audit a
		LEFT JOIN devices d ON d.id = a.device_id
		ORDER BY a.id DESC
		LIMIT ?`, limit)
	if err != nil {
		return nil, fmt.Errorf("list audit: %w", err)
	}
	defer rows.Close()

	out := make([]AuditEntry, 0, limit)
	for rows.Next() {
		var (
			e        AuditEntry
			deviceID sql.NullInt64
			created  sql.NullString
		)
		if err := rows.Scan(&e.ID, &e.Actor, &e.Action, &deviceID,
			&e.DeviceName, &e.Detail, &created); err != nil {
			return nil, fmt.Errorf("scan audit: %w", err)
		}
		if deviceID.Valid {
			id := deviceID.Int64
			e.DeviceID = &id
		}
		e.CreatedAt = parseTime(created.String)
		out = append(out, e)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("list audit: %w", err)
	}
	return out, nil
}

// insertAudit appends one audit row using the given executor (a transaction or
// the database handle), so callers can audit atomically with a state change.
func insertAudit(ctx context.Context, ex interface {
	ExecContext(context.Context, string, ...any) (sql.Result, error)
}, actor, action string, deviceID *int64, detail string) error {
	var id any
	if deviceID != nil {
		id = *deviceID
	}
	if _, err := ex.ExecContext(ctx,
		`INSERT INTO audit (actor, action, device_id, detail) VALUES (?, ?, ?, ?)`,
		actor, action, id, detail); err != nil {
		return fmt.Errorf("audit insert: %w", err)
	}
	return nil
}

func boolToInt(b bool) int {
	if b {
		return 1
	}
	return 0
}

// parseTime accepts the RFC3339 strings this package writes and the
// "YYYY-MM-DD HH:MM:SS" strings SQLite's datetime() writes.
func parseTime(s string) time.Time {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}
	}
	for _, layout := range []string{time.RFC3339, "2006-01-02 15:04:05", "2006-01-02T15:04:05Z"} {
		if t, err := time.Parse(layout, s); err == nil {
			return t.UTC()
		}
	}
	return time.Time{}
}

func parseTimePtr(ns sql.NullString) *time.Time {
	if !ns.Valid {
		return nil
	}
	t := parseTime(ns.String)
	if t.IsZero() {
		return nil
	}
	return &t
}

// slug makes a short ASCII token for an MQTT topic from a device name.
func slug(name string) string {
	var b strings.Builder
	lastUnderscore := false
	for _, r := range strings.ToLower(name) {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
			lastUnderscore = false
		default:
			if !lastUnderscore && b.Len() > 0 {
				b.WriteByte('_')
				lastUnderscore = true
			}
		}
	}
	out := strings.Trim(b.String(), "_")
	if out == "" {
		return "device"
	}
	return out
}