// Package config 读取采购服务的启动配置。凭据只允许来自显式环境变量，避免把秘密写入代码或仓库。
package config

import (
	"errors"
	"fmt"
	"os"
	"strings"

	"golang.org/x/crypto/bcrypt"
)

const (
	adminUsernameEnv       = "CMBUYER_ADMIN_USERNAME"
	adminPasswordBcryptEnv = "CMBUYER_ADMIN_PASSWORD_BCRYPT"
	sessionSecretEnv       = "CMBUYER_SESSION_SECRET"
	cookieSecureEnv        = "CMBUYER_COOKIE_SECURE"
	databaseSourceEnv      = "CMBUYER_DATABASE_SOURCE"
	minimumSecretLength    = 32
)

// Config 是启动采购服务所需的最小安全配置。
type Config struct {
	AdminUsername       string
	AdminPasswordBcrypt string
	SessionSecret       []byte
	CookieSecure        bool
	DatabaseSource      string
}

// LoadFromEnv 从进程环境读取配置。错误只指出缺失或非法的变量名，绝不回显秘密。
func LoadFromEnv() (Config, error) {
	return Load(os.LookupEnv)
}

// Load 使用 lookup 读取配置，以便在不污染进程环境的情况下测试启动边界。
func Load(lookup func(string) (string, bool)) (Config, error) {
	username, err := required(lookup, adminUsernameEnv)
	if err != nil {
		return Config{}, err
	}

	passwordHash, err := required(lookup, adminPasswordBcryptEnv)
	if err != nil {
		return Config{}, err
	}
	if _, err := bcrypt.Cost([]byte(passwordHash)); err != nil {
		return Config{}, fmt.Errorf("%s is not a valid bcrypt hash", adminPasswordBcryptEnv)
	}

	secret, err := required(lookup, sessionSecretEnv)
	if err != nil {
		return Config{}, err
	}
	if len([]byte(secret)) < minimumSecretLength {
		return Config{}, fmt.Errorf("%s must be at least %d bytes", sessionSecretEnv, minimumSecretLength)
	}

	cookieSecure := false
	if value, present := lookup(cookieSecureEnv); present {
		switch value {
		case "true":
			cookieSecure = true
		case "false":
			cookieSecure = false
		default:
			return Config{}, fmt.Errorf("%s must be exactly true or false", cookieSecureEnv)
		}
	}
	databaseSource, err := required(lookup, databaseSourceEnv)
	if err != nil {
		return Config{}, err
	}

	return Config{
		AdminUsername:       username,
		AdminPasswordBcrypt: passwordHash,
		SessionSecret:       []byte(secret),
		CookieSecure:        cookieSecure,
		DatabaseSource:      databaseSource,
	}, nil
}

func required(lookup func(string) (string, bool), name string) (string, error) {
	value, present := lookup(name)
	if !present || strings.TrimSpace(value) == "" {
		return "", errors.New(name + " must be set")
	}

	return value, nil
}