package config

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

// Config is the runtime configuration, populated from the environment.
// Everything here is deployment shape; the things that get tuned mid-challenge
// (start date, targets) live in the data file instead, so changing a target
// does not mean a redeploy.
type Config struct {
	Addr     string
	BaseURL  string // public origin, e.g. https://fit.scottyah.com
	DataPath string // JSON file on the mounted volume
	TZ       *time.Location
}

// Load reads configuration from the environment, applying defaults. It returns
// an error only for settings that have no safe default.
func Load() (*Config, error) {
	c := &Config{
		Addr:     env("ADDR", ":8080"),
		BaseURL:  strings.TrimRight(env("BASE_URL", "http://localhost:8080"), "/"),
		DataPath: env("DATA_PATH", "data/fit.json"),
	}

	// The whole app is date arithmetic, so a wrong timezone silently logs
	// entries against the wrong day. Fail loudly rather than fall back to UTC.
	tzName := env("TZ_NAME", "America/Los_Angeles")
	loc, err := time.LoadLocation(tzName)
	if err != nil {
		return nil, fmt.Errorf("TZ_NAME %q: %w", tzName, err)
	}
	c.TZ = loc

	return c, nil
}

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