package runtimeconfig

import (
	"fmt"
	"net"
	"os"
	"strconv"
	"strings"
	"time"
)

const (
	defaultAPIAddress = "127.0.0.1:8081"
	defaultShutdown   = 10 * time.Second
	// defaultHeartbeatFile matches deploy/healthcheck-heartbeat.sh. See
	// docs/operations/WORKER_AGENT_HEALTHCHECK_CONTRACT.md.
	defaultHeartbeatFile = "/tmp/healthy"
)

// ServiceConfig contains only foundation runtime settings. Infrastructure credentials and
// datasource settings are deliberately not accepted by the service skeletons yet.
type ServiceConfig struct {
	ServiceName   string
	ListenAddress string
	ShutdownAfter time.Duration
	// HeartbeatFile is the liveness file a loop-driven service updates after
	// every completed iteration, read by the container healthcheck.
	HeartbeatFile string
}

func Load(serviceName string) (ServiceConfig, error) {
	if serviceName == "" {
		return ServiceConfig{}, fmt.Errorf("service name is required")
	}

	config := ServiceConfig{ServiceName: serviceName, ShutdownAfter: defaultShutdown}
	envPrefix := "PULSE_" + strings.ToUpper(serviceName)
	if serviceName == "api" {
		config.ListenAddress = valueOrDefault("PULSE_API_ADDR", defaultAPIAddress)
	} else {
		config.ListenAddress = valueOrDefault(envPrefix+"_ADDR", "")
	}
	if raw := os.Getenv(envPrefix + "_SHUTDOWN_TIMEOUT"); raw != "" {
		duration, err := time.ParseDuration(raw)
		if err != nil || duration <= 0 || duration > time.Minute {
			return ServiceConfig{}, fmt.Errorf("%s_SHUTDOWN_TIMEOUT must be a duration between 1ns and 1m", envPrefix)
		}
		config.ShutdownAfter = duration
	}
	if config.ListenAddress != "" {
		if err := validateListenAddress(config.ListenAddress); err != nil {
			return ServiceConfig{}, fmt.Errorf("%s_ADDR: %w", envPrefix, err)
		}
	}
	config.HeartbeatFile = valueOrDefault("PULSE_HEARTBEAT_FILE", defaultHeartbeatFile)
	if err := validateHeartbeatFile(config.HeartbeatFile); err != nil {
		return ServiceConfig{}, fmt.Errorf("PULSE_HEARTBEAT_FILE: %w", err)
	}
	return config, nil
}

// validateHeartbeatFile keeps the heartbeat path an ordinary absolute file path
// so a misconfigured value fails at startup instead of silently never being
// written, which the healthcheck would eventually punish as a hang.
func validateHeartbeatFile(path string) error {
	if !strings.HasPrefix(path, "/") || len(path) > 255 || strings.ContainsAny(path, "\x00\r\n") || strings.HasSuffix(path, "/") {
		return fmt.Errorf("must be an absolute file path of at most 255 characters")
	}
	return nil
}

func valueOrDefault(key, fallback string) string {
	if value := strings.TrimSpace(os.Getenv(key)); value != "" {
		return value
	}
	return fallback
}

func validateListenAddress(address string) error {
	host, portText, err := net.SplitHostPort(address)
	if err != nil || host == "" {
		return fmt.Errorf("must be host:port")
	}
	port, err := strconv.Atoi(portText)
	if err != nil || port < 1 || port > 65535 {
		return fmt.Errorf("port must be an integer between 1 and 65535")
	}
	return nil
}

func parseInt(value string) (int, error) { return strconv.Atoi(value) }