// Package postgres is anchorage's Postgres adapter: pgxpool lifecycle,
// schema migrations, and the concrete implementation of the store
// interfaces defined in internal/pkg/store.
package postgres

import (
	"context"
	"fmt"
	"time"

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

// PoolConfig is the subset of config.PostgresConfig the pool needs. Kept
// as a local struct so callers (tests, migrate subcommand) can construct
// one without importing the full config package.
type PoolConfig struct {
	DSN      string
	MaxConns int
}

// NewPool constructs a pgxpool.Pool and verifies connectivity with a ping.
//
// The caller is responsible for calling pool.Close() at shutdown. A zero
// or negative MaxConns falls back to pgxpool's default.
func NewPool(ctx context.Context, cfg PoolConfig) (*pgxpool.Pool, error) {
	if cfg.DSN == "" {
		return nil, fmt.Errorf("postgres dsn is required")
	}

	poolCfg, err := pgxpool.ParseConfig(cfg.DSN)
	if err != nil {
		return nil, fmt.Errorf("parse postgres dsn: %w", err)
	}

	if cfg.MaxConns > 0 {
		poolCfg.MaxConns = int32(cfg.MaxConns)
	}

	// Keep idle conns short so Postgres restarts don't wedge old tcp
	// connections that will never work again.
	poolCfg.MaxConnIdleTime = 5 * time.Minute
	poolCfg.MaxConnLifetime = 30 * time.Minute
	poolCfg.HealthCheckPeriod = 30 * time.Second

	pool, err := pgxpool.NewWithConfig(ctx, poolCfg)
	if err != nil {
		return nil, fmt.Errorf("open postgres pool: %w", err)
	}

	pingCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	if err := pool.Ping(pingCtx); err != nil {
		pool.Close()
		return nil, fmt.Errorf("ping postgres: %w", err)
	}

	return pool, nil
}