package main

// 本机目录的访问范围（docs/design/21-knowledge-sources.md §4.3）。
// 允许的根目录写死在代码中，不接受平台传来的配置。

import (
	"os"
	"path/filepath"
	"sort"
	"strings"

	"golang.org/x/sys/unix"
)

var allowedRoots = []string{"/home", "/mnt", "/media"}

// ruleProblem 按 §4.3 检查一个已解析符号链接的绝对路径，通过时返回空字符串。
func ruleProblem(real string, roots []string) string {
	if !filepath.IsAbs(real) || filepath.Clean(real) != real {
		return "路径必须是规范的绝对路径"
	}
	root := ""
	for _, r := range roots {
		if real == r || strings.HasPrefix(real, r+"/") {
			root = r
			break
		}
	}
	if root == "" {
		return "只能选择 " + strings.Join(roots, "、") + " 下的目录"
	}
	if real == root {
		return "不能选择 " + root + " 本身，请选择其中的子目录"
	}
	rest := strings.Split(strings.TrimPrefix(real, root+"/"), "/")
	if root == "/home" && len(rest) == 1 {
		return "不能选择用户主目录本身，请选择其中的子目录"
	}
	if hasHidden(real) {
		return "不能选择隐藏目录（以 . 开头）或其中的目录"
	}
	return ""
}

func hasHidden(p string) bool {
	for _, seg := range strings.Split(p, "/") {
		if strings.HasPrefix(seg, ".") {
			return true
		}
	}
	return false
}

// inBrowseRange：逐级选择目录时可以进入的范围（允许的根目录本身与 home 目录本身也可以进入，但不能选择）
func inBrowseRange(real string, roots []string) bool {
	if hasHidden(real) {
		return false
	}
	for _, r := range roots {
		if real == r || strings.HasPrefix(real, r+"/") {
			return true
		}
	}
	return false
}

// checkError 带状态码的检查失败
type checkError struct {
	State   string // not_allowed | path_missing
	Message string
}

func (e *checkError) Error() string { return e.Message }

// checkSource 检查要登记（或解析出的）本机目录，返回解析符号链接后的真实路径
func checkSource(p string, roots []string) (string, *checkError) {
	if !filepath.IsAbs(p) {
		return "", &checkError{"not_allowed", "请填写绝对路径"}
	}
	p = filepath.Clean(p)
	if hasHidden(p) {
		return "", &checkError{"not_allowed", "不能选择隐藏目录（以 . 开头）或其中的目录"}
	}
	real, err := filepath.EvalSymlinks(p)
	if err != nil {
		return "", &checkError{"path_missing", "目录不存在：" + p}
	}
	if msg := ruleProblem(real, roots); msg != "" {
		if real != p {
			msg += "（实际位置：" + real + "）"
		}
		return "", &checkError{"not_allowed", msg}
	}
	st, err := os.Stat(real)
	if err != nil {
		return "", &checkError{"path_missing", "目录不存在：" + p}
	}
	if !st.IsDir() {
		return "", &checkError{"not_allowed", "不是目录：" + p}
	}
	if unix.Access(real, unix.R_OK|unix.X_OK) != nil {
		return "", &checkError{"not_allowed", "挂载服务没有读取这个目录的权限：" + p}
	}
	return real, nil
}

type browseEntry struct {
	Name       string `json:"name"`
	Path       string `json:"path"`
	Selectable bool   `json:"selectable"`
	Reason     string `json:"reason,omitempty"`
}

type browseResult struct {
	Path    string        `json:"path"`
	Parent  string        `json:"parent"`
	Entries []browseEntry `json:"entries"`
}

const maxBrowseEntries = 2000

// browse 列出可选择的子目录：隐藏以 . 开头的，标出不能选择的及原因。path 为空时列出允许的根目录。
func browse(p string, roots []string) (*browseResult, *checkError) {
	if p == "" || p == "/" {
		res := &browseResult{Path: "", Parent: "", Entries: []browseEntry{}}
		for _, r := range roots {
			if st, err := os.Stat(r); err == nil && st.IsDir() {
				res.Entries = append(res.Entries, browseEntry{Name: r, Path: r, Reason: "请进入后选择子目录"})
			}
		}
		return res, nil
	}
	if !filepath.IsAbs(p) {
		return nil, &checkError{"not_allowed", "请填写绝对路径"}
	}
	p = filepath.Clean(p)
	real, err := filepath.EvalSymlinks(p)
	if err != nil {
		return nil, &checkError{"path_missing", "目录不存在：" + p}
	}
	if hasHidden(p) || !inBrowseRange(real, roots) {
		return nil, &checkError{"not_allowed", "只能浏览 " + strings.Join(roots, "、") + " 下的目录"}
	}
	f, err := os.Open(real)
	if err != nil {
		return nil, &checkError{"not_allowed", "没有读取权限：" + p}
	}
	names, err := f.Readdirnames(-1)
	f.Close()
	if err != nil {
		return nil, &checkError{"not_allowed", "无法读取目录：" + p}
	}
	sort.Strings(names)
	parent := filepath.Dir(p)
	isRoot := false
	for _, r := range roots {
		if p == r {
			isRoot = true
		}
	}
	if isRoot {
		parent = ""
	}
	res := &browseResult{Path: p, Parent: parent, Entries: []browseEntry{}}
	for _, name := range names {
		if strings.HasPrefix(name, ".") {
			continue
		}
		child := filepath.Join(p, name)
		st, err := os.Stat(child)
		if err != nil || !st.IsDir() {
			continue
		}
		e := browseEntry{Name: name, Path: child, Selectable: true}
		childReal, err := filepath.EvalSymlinks(child)
		if err != nil {
			continue
		}
		if msg := ruleProblem(childReal, roots); msg != "" {
			e.Selectable, e.Reason = false, msg
		} else if unix.Access(childReal, unix.R_OK|unix.X_OK) != nil {
			e.Selectable, e.Reason = false, "没有读取权限"
		}
		if childReal != child && e.Selectable {
			e.Reason = "链接到 " + childReal
		}
		res.Entries = append(res.Entries, e)
		if len(res.Entries) >= maxBrowseEntries {
			break
		}
	}
	return res, nil
}