package storage

import (
	"fmt"
	"net/url"
	"strings"
	"unicode"
)

// ObjectKeyFromCDNURL 将属于 cdnBase 的 HTTPS URL 转成原始 S3 对象 key。
// cdnBase 可省略 scheme，也可带 base path。外站或不属于 base path 的 URL
// 返回 owned=false 且不报错；格式非法或试图伪装路径的 URL 返回错误。
func ObjectKeyFromCDNURL(rawURL, cdnBase string) (key string, owned bool, err error) {
	base, err := parseCDNBase(cdnBase)
	if err != nil {
		return "", false, err
	}
	parsed, err := parseCDNURL(rawURL, false)
	if err != nil {
		return "", false, err
	}
	if !strings.EqualFold(parsed.Host, base.Host) {
		return "", false, nil
	}

	basePath := base.Path
	if basePath != "" {
		if parsed.Path == basePath {
			return "", false, fmt.Errorf("CDN URL does not contain an object key")
		}
		prefix := basePath + "/"
		if !strings.HasPrefix(parsed.Path, prefix) {
			return "", false, nil
		}
		key = strings.TrimPrefix(parsed.Path, prefix)
	} else {
		key = strings.TrimPrefix(parsed.Path, "/")
	}
	if key == "" {
		return "", false, fmt.Errorf("CDN URL does not contain an object key")
	}

	// 只去掉 cdnBase 的路径和前导分隔符；不添加或移除 bucket，也不 Clean，
	// 因而返回的解码路径仍是实际 S3 key。
	return key, true, nil
}

func parseCDNBase(cdnBase string) (*url.URL, error) {
	if cdnBase == "" {
		return nil, fmt.Errorf("CDN base URL is empty")
	}
	rawBase := cdnBase
	if strings.HasPrefix(rawBase, "//") {
		rawBase = "https:" + rawBase
	} else if !strings.Contains(rawBase, "://") {
		rawBase = "https://" + rawBase
	}
	return parseCDNURL(rawBase, true)
}

func parseCDNURL(rawURL string, isBase bool) (*url.URL, error) {
	if rawURL == "" {
		return nil, fmt.Errorf("URL is empty")
	}
	if strings.Contains(rawURL, `\`) || containsControl(rawURL) {
		return nil, fmt.Errorf("URL contains a backslash or control character")
	}
	parsed, err := url.Parse(rawURL)
	if err != nil {
		return nil, fmt.Errorf("parse URL: %w", err)
	}
	if !parsed.IsAbs() || !strings.EqualFold(parsed.Scheme, "https") || parsed.Host == "" ||
		parsed.Hostname() == "" || parsed.Opaque != "" {
		return nil, fmt.Errorf("URL must be an absolute HTTPS URL")
	}
	if parsed.User != nil {
		return nil, fmt.Errorf("URL must not contain userinfo")
	}
	if parsed.RawQuery != "" || parsed.ForceQuery {
		return nil, fmt.Errorf("URL must not contain a query")
	}
	if parsed.Fragment != "" || strings.Contains(rawURL, "#") {
		return nil, fmt.Errorf("URL must not contain a fragment")
	}

	// 必须在 url.Parse 的 Path 解码之外检查 EscapedPath：编码斜杠在 Path 中
	// 与普通分隔符无法区分，若放行会导致 CDN 与 S3 对 key 的解释不一致。
	escapedPath := strings.ToLower(parsed.EscapedPath())
	if strings.Contains(escapedPath, "%2f") || strings.Contains(escapedPath, "%5c") {
		return nil, fmt.Errorf("URL path contains an encoded slash or backslash")
	}
	if strings.Contains(parsed.Path, `\`) || containsControl(parsed.Path) {
		return nil, fmt.Errorf("URL path contains a backslash or control character")
	}

	if isBase && strings.HasSuffix(parsed.Path, "/") {
		// 配置中的 CDN base 允许一个末尾斜杠；其余空路径段仍会被拒绝。
		parsed.Path = strings.TrimSuffix(parsed.Path, "/")
		parsed.RawPath = ""
	}
	if parsed.Path == "" {
		if isBase {
			return parsed, nil
		}
		return nil, fmt.Errorf("URL path is empty")
	}
	if !strings.HasPrefix(parsed.Path, "/") {
		return nil, fmt.Errorf("URL path must be absolute")
	}
	for _, segment := range strings.Split(strings.TrimPrefix(parsed.Path, "/"), "/") {
		if segment == "" {
			return nil, fmt.Errorf("URL path contains an empty segment")
		}
		if segment == "." || segment == ".." {
			return nil, fmt.Errorf("URL path contains a dot segment")
		}
	}
	return parsed, nil
}

func containsControl(value string) bool {
	for _, r := range value {
		if unicode.IsControl(r) {
			return true
		}
	}
	return false
}