package config

import (
	"errors"
	"fmt"
	"io"
	"net/url"
	"os"
	"path/filepath"
	"runtime"
	"strings"

	"golang.org/x/mod/modfile"
)

const (
	DefaultAPIBaseURL = "https://api.zhecent.com"

	APIBaseURLEnv = "LIGHTCORE_API_BASE_URL"
	TokenEnv      = "LIGHTCORE_SHOP_CRM_AGENT_TOKEN"
	EnvFileName   = ".env"

	maxEnvFileSize = 16 << 10
	modulePath     = "code.zhecent.com/open/shop-crm-agent"
)

type Config struct {
	APIBaseURL string
	Token      string
}

func Load() (Config, error) {
	envFile, err := DefaultEnvFile()
	if err != nil {
		return Config{}, err
	}
	return load(envFile, os.LookupEnv)
}

func Initialize(token string) (string, error) {
	envFile, err := DefaultEnvFile()
	if err != nil {
		return "", err
	}
	if err := writeEnvFile(envFile, token); err != nil {
		return "", err
	}
	return envFile, nil
}

func DefaultEnvFile() (string, error) {
	executable, executableErr := os.Executable()
	if executableErr == nil {
		if resolved, err := filepath.EvalSymlinks(executable); err == nil {
			executable = resolved
		}
	}

	workingDir, err := os.Getwd()
	if err != nil {
		return "", fmt.Errorf("定位 shop-crm-agent 仓库失败: %w", err)
	}
	return resolveEnvFile(executable, workingDir)
}

func resolveEnvFile(executable, workingDir string) (string, error) {
	binaryDir := filepath.Dir(executable)
	if filepath.Base(binaryDir) == "bin" {
		repoRoot := filepath.Dir(binaryDir)
		if isRepositoryRoot(repoRoot) {
			return filepath.Join(repoRoot, EnvFileName), nil
		}
	}
	if !isRepositoryRoot(workingDir) {
		return "", errors.New("无法定位 shop-crm-agent 仓库根目录，请从仓库根运行 CLI")
	}
	return filepath.Join(workingDir, EnvFileName), nil
}

func load(envFile string, lookupEnv func(string) (string, bool)) (Config, error) {
	apiBaseURL := DefaultAPIBaseURL
	if rawAPIBaseURL, exists := lookupEnv(APIBaseURLEnv); exists && strings.TrimSpace(rawAPIBaseURL) != "" {
		apiBaseURL = normalizeBaseURL(rawAPIBaseURL)
		if err := validateAPIBaseURL(apiBaseURL); err != nil {
			return Config{}, err
		}
	}

	if rawToken, exists := lookupEnv(TokenEnv); exists && strings.TrimSpace(rawToken) != "" {
		token, err := normalizeToken(rawToken)
		if err != nil {
			return Config{}, err
		}
		return Config{APIBaseURL: apiBaseURL, Token: token}, nil
	}
	if apiBaseURL != DefaultAPIBaseURL {
		return Config{}, fmt.Errorf("覆盖 %s 时必须同时设置 %s", APIBaseURLEnv, TokenEnv)
	}

	token, err := readEnvFile(envFile)
	if err != nil {
		return Config{}, err
	}
	return Config{APIBaseURL: apiBaseURL, Token: token}, nil
}

func readEnvFile(path string) (string, error) {
	pathInfo, err := os.Lstat(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return "", errors.New("CRM Agent 尚未初始化，请运行 shop-crm-agent init")
		}
		return "", fmt.Errorf("读取 CRM Agent .env 信息失败: %w", err)
	}
	if !pathInfo.Mode().IsRegular() {
		return "", errors.New("CRM Agent .env 必须是普通文件")
	}

	file, err := os.Open(path)
	if err != nil {
		return "", fmt.Errorf("打开 CRM Agent .env 失败: %w", err)
	}
	defer file.Close()

	info, err := file.Stat()
	if err != nil {
		return "", fmt.Errorf("读取 CRM Agent .env 信息失败: %w", err)
	}
	if !info.Mode().IsRegular() || !os.SameFile(pathInfo, info) {
		return "", errors.New("CRM Agent .env 必须是普通文件")
	}
	if runtime.GOOS != "windows" && info.Mode().Perm()&0o077 != 0 {
		return "", errors.New("CRM Agent .env 不得允许组或其他用户访问，请设置为 0600 权限")
	}

	data, err := io.ReadAll(io.LimitReader(file, maxEnvFileSize+1))
	if err != nil {
		return "", fmt.Errorf("读取 CRM Agent .env 失败: %w", err)
	}
	if len(data) > maxEnvFileSize {
		return "", errors.New("CRM Agent .env 超过 16 KiB 限制")
	}
	contents := strings.TrimSuffix(string(data), "\n")
	contents = strings.TrimSuffix(contents, "\r")
	if strings.ContainsAny(contents, "\r\n\x00") {
		return "", errors.New("CRM Agent .env 格式无效，请重新运行 shop-crm-agent init")
	}
	prefix := TokenEnv + "="
	if !strings.HasPrefix(contents, prefix) {
		return "", errors.New("CRM Agent .env 缺少凭证，请重新运行 shop-crm-agent init")
	}
	return normalizeToken(strings.TrimPrefix(contents, prefix))
}

func writeEnvFile(path, token string) error {
	return writeEnvFileWithReplace(path, token, replaceFile)
}

func writeEnvFileWithReplace(path, token string, replace func(string, string) error) error {
	token, err := normalizeToken(token)
	if err != nil {
		return err
	}
	contents := TokenEnv + "=" + token + "\n"
	if len(contents) > maxEnvFileSize {
		return errors.New("CRM Agent Token 超过 .env 大小限制")
	}
	if info, err := os.Lstat(path); err == nil {
		if !info.Mode().IsRegular() {
			return errors.New("CRM Agent .env 已存在且不是普通文件，拒绝覆盖")
		}
	} else if !errors.Is(err, os.ErrNotExist) {
		return fmt.Errorf("检查 CRM Agent .env 失败: %w", err)
	}

	tempFile, err := os.CreateTemp(filepath.Dir(path), EnvFileName+".tmp-*")
	if err != nil {
		return fmt.Errorf("创建 CRM Agent .env 临时文件失败: %w", err)
	}
	tempPath := tempFile.Name()
	defer func() {
		_ = tempFile.Close()
		_ = os.Remove(tempPath)
	}()
	if runtime.GOOS != "windows" {
		if err := tempFile.Chmod(0o600); err != nil {
			return fmt.Errorf("设置 CRM Agent .env 权限失败: %w", err)
		}
	}
	if _, err := io.WriteString(tempFile, contents); err != nil {
		return fmt.Errorf("写入 CRM Agent .env 失败: %w", err)
	}
	if err := tempFile.Sync(); err != nil {
		return fmt.Errorf("同步 CRM Agent .env 失败: %w", err)
	}
	if err := tempFile.Close(); err != nil {
		return fmt.Errorf("关闭 CRM Agent .env 失败: %w", err)
	}
	if err := replace(tempPath, path); err != nil {
		return fmt.Errorf("替换 CRM Agent .env 失败: %w", err)
	}
	return nil
}

func normalizeToken(value string) (string, error) {
	token := strings.TrimSpace(value)
	if token == "" {
		return "", errors.New("CRM Agent Token 不能为空")
	}
	if len(token) > maxEnvFileSize || strings.ContainsAny(token, "\r\n\x00") {
		return "", errors.New("CRM Agent Token 格式无效")
	}
	return token, nil
}

func normalizeBaseURL(value string) string {
	return strings.TrimRight(strings.TrimSpace(value), "/")
}

func validateAPIBaseURL(value string) error {
	parsed, err := url.Parse(value)
	if err != nil || parsed.Host == "" || (parsed.Scheme != "http" && parsed.Scheme != "https") {
		return errors.New("CRM Agent API Base URL 必须是有效的 http/https URL")
	}
	return nil
}

func isRepositoryRoot(path string) bool {
	data, err := os.ReadFile(filepath.Join(path, "go.mod"))
	if err != nil {
		return false
	}
	return modfile.ModulePath(data) == modulePath
}