package pgsql

import (
	"context"
	"fmt"
	"runtime/debug"
	"strings"

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

const (
	defaultApplicationPrefix = "relspecgo"
	postgresIdentifierMaxLen = 63
)

// BuildApplicationName returns a PostgreSQL application_name in the form:
// relspecgo/<version>[:<component>]
func BuildApplicationName(component string) string {
	appName := fmt.Sprintf("%s/%s", defaultApplicationPrefix, relspecVersion())
	component = strings.TrimSpace(component)
	if component != "" {
		appName = appName + ":" + component
	}
	if len(appName) > postgresIdentifierMaxLen {
		appName = appName[:postgresIdentifierMaxLen]
	}
	return appName
}

// ParseConfigWithApplicationName parses a connection string and applies a default
// application_name when one is not explicitly provided by the caller.
func ParseConfigWithApplicationName(connString, component string) (*pgx.ConnConfig, error) {
	cfg, err := pgx.ParseConfig(connString)
	if err != nil {
		return nil, err
	}

	if cfg.RuntimeParams == nil {
		cfg.RuntimeParams = map[string]string{}
	}

	if strings.TrimSpace(cfg.RuntimeParams["application_name"]) == "" {
		cfg.RuntimeParams["application_name"] = BuildApplicationName(component)
	}

	return cfg, nil
}

// Connect establishes a PostgreSQL connection with a default relspec
// application_name when the caller does not provide one in the DSN.
func Connect(ctx context.Context, connString, component string) (*pgx.Conn, error) {
	cfg, err := ParseConfigWithApplicationName(connString, component)
	if err != nil {
		return nil, err
	}

	return pgx.ConnectConfig(ctx, cfg)
}

func relspecVersion() string {
	info, ok := debug.ReadBuildInfo()
	if !ok {
		return "dev"
	}

	version := strings.TrimSpace(info.Main.Version)
	if version != "" && version != "(devel)" {
		return version
	}

	for _, setting := range info.Settings {
		if setting.Key == "vcs.revision" {
			revision := strings.TrimSpace(setting.Value)
			if len(revision) >= 7 {
				return revision[:7]
			}
			if revision != "" {
				return revision
			}
		}
	}

	return "dev"
}