package maintenance

import (
	"context"
	"errors"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
)

var (
	ErrNotFound      = errors.New("maintenance: window not found")
	ErrConflictOpen  = errors.New("maintenance: an open window already exists")
	ErrInvalidWindow = errors.New("maintenance: invalid schedule")
	ErrBadStatus     = errors.New("maintenance: invalid status transition")
)

const (
	StatusScheduled = "scheduled"
	StatusActive    = "active"
	StatusEnded     = "ended"
	StatusCancelled = "cancelled"
)

// Window 维护窗口行。
type Window struct {
	ID             int64      `json:"id"`
	ScheduledStart time.Time  `json:"scheduledStart"`
	ScheduledEnd   time.Time  `json:"scheduledEnd"`
	Message        string     `json:"message"`
	Status         string     `json:"status"`
	CreatedBy      *int64     `json:"createdBy,omitempty"`
	CreatedAt      time.Time  `json:"createdAt"`
	UpdatedAt      time.Time  `json:"updatedAt"`
	ActivatedAt    *time.Time `json:"activatedAt,omitempty"`
	EndedAt        *time.Time `json:"endedAt,omitempty"`
}

// Store 持久化接口。
type Store interface {
	GetOpen(ctx context.Context) (*Window, error)
	GetByID(ctx context.Context, id int64) (*Window, error)
	Insert(ctx context.Context, w Window) (Window, error)
	UpdateStatus(ctx context.Context, id int64, from, to string) (Window, error)
	ListRecent(ctx context.Context, limit int) ([]Window, error)
}

type pgStore struct {
	pool *pgxpool.Pool
}

func NewPGStore(pool *pgxpool.Pool) Store {
	return &pgStore{pool: pool}
}

func scanWindow(row pgx.Row) (Window, error) {
	var w Window
	var createdBy *int64
	var activated, ended *time.Time
	err := row.Scan(
		&w.ID, &w.ScheduledStart, &w.ScheduledEnd, &w.Message, &w.Status,
		&createdBy, &w.CreatedAt, &w.UpdatedAt, &activated, &ended,
	)
	if err != nil {
		return Window{}, err
	}
	w.CreatedBy = createdBy
	w.ActivatedAt = activated
	w.EndedAt = ended
	return w, nil
}

func (s *pgStore) GetOpen(ctx context.Context) (*Window, error) {
	w, err := scanWindow(s.pool.QueryRow(ctx, `
		SELECT id, scheduled_start, scheduled_end, message, status,
		       created_by, created_at, updated_at, activated_at, ended_at
		FROM maintenance_windows
		WHERE status IN ('scheduled', 'active')
		ORDER BY scheduled_start ASC
		LIMIT 1
	`))
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrNotFound
		}
		return nil, err
	}
	return &w, nil
}

func (s *pgStore) GetByID(ctx context.Context, id int64) (*Window, error) {
	w, err := scanWindow(s.pool.QueryRow(ctx, `
		SELECT id, scheduled_start, scheduled_end, message, status,
		       created_by, created_at, updated_at, activated_at, ended_at
		FROM maintenance_windows WHERE id = $1
	`, id))
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrNotFound
		}
		return nil, err
	}
	return &w, nil
}

func (s *pgStore) Insert(ctx context.Context, in Window) (Window, error) {
	w, err := scanWindow(s.pool.QueryRow(ctx, `
		INSERT INTO maintenance_windows (scheduled_start, scheduled_end, message, status, created_by)
		VALUES ($1, $2, $3, $4, $5)
		RETURNING id, scheduled_start, scheduled_end, message, status,
		          created_by, created_at, updated_at, activated_at, ended_at
	`, in.ScheduledStart, in.ScheduledEnd, in.Message, StatusScheduled, in.CreatedBy))
	if err != nil {
		// unique partial index → conflict
		if isUniqueViolation(err) {
			return Window{}, ErrConflictOpen
		}
		return Window{}, err
	}
	return w, nil
}

func (s *pgStore) UpdateStatus(ctx context.Context, id int64, from, to string) (Window, error) {
	var q string
	switch to {
	case StatusActive:
		q = `
			UPDATE maintenance_windows
			SET status = $2, updated_at = now(), activated_at = now()
			WHERE id = $1 AND status = $3
			RETURNING id, scheduled_start, scheduled_end, message, status,
			          created_by, created_at, updated_at, activated_at, ended_at`
	case StatusEnded, StatusCancelled:
		q = `
			UPDATE maintenance_windows
			SET status = $2, updated_at = now(), ended_at = now()
			WHERE id = $1 AND status = $3
			RETURNING id, scheduled_start, scheduled_end, message, status,
			          created_by, created_at, updated_at, activated_at, ended_at`
	default:
		return Window{}, ErrBadStatus
	}
	w, err := scanWindow(s.pool.QueryRow(ctx, q, id, to, from))
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return Window{}, ErrBadStatus
		}
		return Window{}, err
	}
	return w, nil
}

func (s *pgStore) ListRecent(ctx context.Context, limit int) ([]Window, error) {
	if limit <= 0 {
		limit = 20
	}
	rows, err := s.pool.Query(ctx, `
		SELECT id, scheduled_start, scheduled_end, message, status,
		       created_by, created_at, updated_at, activated_at, ended_at
		FROM maintenance_windows
		ORDER BY scheduled_start DESC
		LIMIT $1
	`, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := make([]Window, 0)
	for rows.Next() {
		w, err := scanWindow(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, w)
	}
	return out, rows.Err()
}

func isUniqueViolation(err error) bool {
	return err != nil && (contains(err.Error(), "uq_maintenance_windows_one_open") || contains(err.Error(), "unique"))
}

func contains(s, sub string) bool {
	return len(s) >= len(sub) && (s == sub || len(sub) == 0 || indexOf(s, sub) >= 0)
}

func indexOf(s, sub string) int {
	for i := 0; i+len(sub) <= len(s); i++ {
		if s[i:i+len(sub)] == sub {
			return i
		}
	}
	return -1
}