// Package config loads the agent's configuration from environment variables.
package config

import (
	"errors"
	"os"
	"regexp"
	"strings"
)

var masterKeyPattern = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)

// Config holds the agent's runtime configuration.
type Config struct {
	MasterURL string // MASTER_URL, wss://host:port/agent
	MasterKey string // MASTER_KEY, fingerprint shown in the master UI
	Token     string // AGENT_TOKEN, shown once when the agent was added
	SelfID    string // SELF_ID, defaults to the hostname (= container ID prefix)
	LogLevel  string // LOG_LEVEL, default info
}

// Load reads and validates the agent configuration. It fails fast so a
// misconfigured agent never starts dialling.
func Load() (*Config, error) {
	cfg := &Config{
		MasterURL: os.Getenv("MASTER_URL"),
		MasterKey: os.Getenv("MASTER_KEY"),
		Token:     os.Getenv("AGENT_TOKEN"),
		SelfID:    os.Getenv("SELF_ID"),
		LogLevel:  os.Getenv("LOG_LEVEL"),
	}
	switch {
	case cfg.MasterURL == "":
		return nil, errors.New("MASTER_URL is required")
	case !strings.HasPrefix(cfg.MasterURL, "wss://"):
		return nil, errors.New("MASTER_URL must start with wss://")
	case cfg.MasterKey == "":
		return nil, errors.New("MASTER_KEY is required")
	case !masterKeyPattern.MatchString(cfg.MasterKey):
		return nil, errors.New("MASTER_KEY must look like sha256:<64 hex>")
	case cfg.Token == "":
		return nil, errors.New("AGENT_TOKEN is required")
	}
	if cfg.SelfID == "" {
		cfg.SelfID, _ = os.Hostname()
	}
	if cfg.LogLevel == "" {
		cfg.LogLevel = "info"
	}
	return cfg, nil
}