package pgmonitor

import (
	"context"
	"errors"
	"fmt"
	"time"

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

// Service provides PostgreSQL observability and maintenance helpers (control plane instance scope).
type Service struct {
	pool  *pgxpool.Pool
	cache *ttlCache
}

// NewService constructs a metrics service for the API PostgreSQL pool.
func NewService(pool *pgxpool.Pool) *Service {
	if pool == nil {
		return nil
	}
	return &Service{
		pool:  pool,
		cache: newTTLCache(10 * time.Second),
	}
}

// Pool exposes the underlying pool for job workers.
func (s *Service) Pool() *pgxpool.Pool {
	if s == nil {
		return nil
	}
	return s.pool
}

// Overview returns cached instance-level stats.
func (s *Service) Overview(ctx context.Context) (Overview, error) {
	if s == nil || s.pool == nil {
		return Overview{}, errors.New("pgmonitor: postgres not configured")
	}
	if v, ok := s.cache.get("overview"); ok {
		if o, ok := v.(Overview); ok {
			return o, nil
		}
	}
	o, err := s.fetchOverview(ctx)
	if err != nil {
		return Overview{}, err
	}
	s.cache.set("overview", o)
	return o, nil
}

// Locks returns active / blocking locks.
func (s *Service) Locks(ctx context.Context) ([]LockRow, error) {
	if s == nil || s.pool == nil {
		return nil, errors.New("pgmonitor: postgres not configured")
	}
	if v, ok := s.cache.get("locks"); ok {
		if rows, ok := v.([]LockRow); ok {
			return rows, nil
		}
	}
	rows, err := queryLocks(ctx, s.pool)
	if err != nil {
		return nil, err
	}
	s.cache.set("locks", rows)
	return rows, nil
}

// Tables returns top tables by size with I/O stats.
func (s *Service) Tables(ctx context.Context, limit int) ([]TableStat, error) {
	if s == nil || s.pool == nil {
		return nil, errors.New("pgmonitor: postgres not configured")
	}
	key := fmt.Sprintf("tables:%d", limit)
	if v, ok := s.cache.get(key); ok {
		if rows, ok := v.([]TableStat); ok {
			return rows, nil
		}
	}
	rows, err := queryTables(ctx, s.pool, limit)
	if err != nil {
		return nil, err
	}
	s.cache.set(key, rows)
	return rows, nil
}