// Package config reads the service's settings from the environment.
package config

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

// Config is the whole configuration surface. Environment only: a control plane is deployed, not
// hand-run, and a settings file is one more thing to keep in sync with the deployment.
type Config struct {
	Addr string
	// DSN is the Postgres connection string. Empty is allowed and means "start unready": the
	// service answers liveness and reports on /readyz why it cannot serve.
	//
	// ⚠ It carries a password. It is read from the environment, never logged, and never echoed
	// into an error message.
	DSN string
	// TrustedOrigins are origins besides our own that may make unsafe requests.
	TrustedOrigins []string
	// SessionIdleTTL is how long a session survives without use; SessionMaxAge is the ceiling no
	// amount of use can extend.
	SessionIdleTTL time.Duration
	SessionMaxAge  time.Duration
	// Migrate applies pending migrations at boot. Off by default: a rollout should migrate once,
	// deliberately, not once per replica.
	Migrate bool
}

// Load reads the environment.
func Load() (Config, error) {
	c := Config{
		Addr:           env("TM_PLATFORM_ADDR", "127.0.0.1:8080"),
		DSN:            os.Getenv("TM_PLATFORM_DSN"),
		SessionIdleTTL: 14 * 24 * time.Hour,
		SessionMaxAge:  90 * 24 * time.Hour,
		Migrate:        os.Getenv("TM_PLATFORM_MIGRATE") == "1",
	}
	if raw := os.Getenv("TM_PLATFORM_TRUSTED_ORIGINS"); raw != "" {
		for _, o := range strings.Split(raw, ",") {
			if o = strings.TrimSpace(o); o != "" {
				c.TrustedOrigins = append(c.TrustedOrigins, o)
			}
		}
	}
	var err error
	if c.SessionIdleTTL, err = duration("TM_PLATFORM_SESSION_IDLE", c.SessionIdleTTL); err != nil {
		return Config{}, err
	}
	if c.SessionMaxAge, err = duration("TM_PLATFORM_SESSION_MAX_AGE", c.SessionMaxAge); err != nil {
		return Config{}, err
	}
	if c.SessionIdleTTL > c.SessionMaxAge {
		return Config{}, fmt.Errorf("config: session idle TTL %s exceeds max age %s", c.SessionIdleTTL, c.SessionMaxAge)
	}
	return c, nil
}

func env(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}

func duration(key string, def time.Duration) (time.Duration, error) {
	raw := os.Getenv(key)
	if raw == "" {
		return def, nil
	}
	d, err := time.ParseDuration(raw)
	if err != nil {
		return 0, fmt.Errorf("config: %s: %w", key, err)
	}
	if d <= 0 {
		return 0, fmt.Errorf("config: %s must be positive", key)
	}
	return d, nil
}