jiang13-bbs/backend/markdown/hide.go

// Package markdown 提供帖子正文隐藏块（行级 BBCode [hide]…[/hide]）的解析、校验与脱敏。
package markdown

import (
	"errors"
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"unicode/utf8"
)

const (
	HideKindLogin    = "login"
	HideKindReply    = "reply"
	HideKindPoints   = "points"
	HideKindPassword = "password"
)

const (
	// MaxHidePasswordLen 密码可见块密码最大长度（字符）
	MaxHidePasswordLen = 64
	// MinHidePasswordLen 密码最小长度
	MinHidePasswordLen = 1
)

// HideBlock 正文中的一段隐藏内容
type HideBlock struct {
	Kind     string // login | reply | points | password
	Points   int    // 仅 points 有效
	Password string // 仅 password 有效（原文；脱敏输出时清空）
	Body     string // 块内 Markdown（不含开闭标记行）
	Start    int    // 开标记行在 lines 中的下标
	End      int    // 闭标记行在 lines 中的下标（含）
	Locked   bool   // 开标记是否已带 locked（脱敏输出）
	Index    int    // 在全文隐藏块列表中的下标（0-based）
}

// DerivedAccess 由正文隐藏块派生的帖级可见性
type DerivedAccess struct {
	Access string // public | login | reply | points | password | mixed
	Points int    // 所有积分块价格之和
}

// ViewerCaps 读者对隐藏块的能力（由 service 填充）
type ViewerCaps struct {
	Bypass           bool // 作者 / 版主
	LoggedIn         bool
	HasReplied       bool
	PointsPaid       bool         // 已支付本帖积分解锁
	PasswordUnlocked map[int]bool // 已凭密码解锁的隐藏块下标
}

var (
	ErrHideNested       = errors.New("隐藏块不可嵌套")
	ErrHideUnclosed     = errors.New("隐藏块未正确闭合")
	ErrHideInvalid      = errors.New("隐藏块语法无效")
	ErrHidePointsNeed   = errors.New("积分可见块须指定 1–100000 的积分")
	ErrHidePasswordNeed = errors.New("密码可见块须设置 1–64 字符且不含空格的密码")
)

// 开标记：整行 [hide <kind> …]；闭标记：整行 [/hide]
var hideOpenRe = regexp.MustCompile(`(?i)^\[hide(?:\s+(.+))?\]$`)

// ParseHideBlocks 扫描正文中的 [hide]…[/hide] 块（忽略代码围栏内伪语法）。
func ParseHideBlocks(content string) ([]HideBlock, error) {
	lines := splitLines(content)
	var blocks []HideBlock
	inCode := false
	i := 0
	for i < len(lines) {
		trimmed := strings.TrimSpace(lines[i])

		if strings.HasPrefix(trimmed, "```") {
			inCode = !inCode
			i++
			continue
		}
		if inCode {
			i++
			continue
		}

		if kind, pts, pwd, locked, ok := parseOpenMarker(trimmed); ok {
			j := i + 1
			bodyLines := make([]string, 0)
			foundClose := false
			innerCode := false
			for j < len(lines) {
				inner := strings.TrimSpace(lines[j])
				if strings.HasPrefix(inner, "```") {
					innerCode = !innerCode
					bodyLines = append(bodyLines, lines[j])
					j++
					continue
				}
				if innerCode {
					bodyLines = append(bodyLines, lines[j])
					j++
					continue
				}
				if _, _, _, _, isOpen := parseOpenMarker(inner); isOpen {
					return nil, ErrHideNested
				}
				if isCloseMarker(inner) {
					foundClose = true
					break
				}
				bodyLines = append(bodyLines, lines[j])
				j++
			}
			if !foundClose {
				return nil, ErrHideUnclosed
			}
			if kind == HideKindPoints {
				if pts < 1 || pts > 100000 {
					return nil, ErrHidePointsNeed
				}
			}
			if kind == HideKindPassword {
				// 已 locked 的脱敏行无密码，仅服务端原文必须带合法密码
				if !locked {
					if err := validatePassword(pwd); err != nil {
						return nil, err
					}
				}
			}
			blocks = append(blocks, HideBlock{
				Kind:     kind,
				Points:   pts,
				Password: pwd,
				Body:     strings.Join(bodyLines, "\n"),
				Start:    i,
				End:      j,
				Locked:   locked,
				Index:    len(blocks),
			})
			i = j + 1
			continue
		}

		if isCloseMarker(trimmed) {
			return nil, ErrHideInvalid
		}
		i++
	}
	return blocks, nil
}

// DeriveAccess 由隐藏块列表派生帖级 content_access / access_points
func DeriveAccess(blocks []HideBlock) DerivedAccess {
	if len(blocks) == 0 {
		return DerivedAccess{Access: "public", Points: 0}
	}
	kinds := map[string]struct{}{}
	totalPts := 0
	for _, b := range blocks {
		kinds[b.Kind] = struct{}{}
		if b.Kind == HideKindPoints {
			totalPts += b.Points
		}
	}
	if len(kinds) > 1 {
		return DerivedAccess{Access: "mixed", Points: totalPts}
	}
	for k := range kinds {
		return DerivedAccess{Access: k, Points: totalPts}
	}
	return DerivedAccess{Access: "public", Points: 0}
}

// DeriveAccessFromContent 解析并派生；校验失败返回 error
func DeriveAccessFromContent(content string) (DerivedAccess, error) {
	blocks, err := ParseHideBlocks(content)
	if err != nil {
		return DerivedAccess{}, err
	}
	return DeriveAccess(blocks), nil
}

// SanitizeForViewer 按读者能力脱敏：未满足条件的块清空正文并加 locked。
// 密码块即使已解锁，也不向读者回传明文密码（开标记写成 [hide password] 或 [hide password locked]）。
func SanitizeForViewer(content string, caps ViewerCaps) (sanitized string, fullyLocked bool) {
	blocks, err := ParseHideBlocks(content)
	if err != nil {
		return "", true
	}
	if len(blocks) == 0 {
		return content, strings.TrimSpace(content) == ""
	}
	if caps.Bypass {
		return content, false
	}

	lines := splitLines(content)
	var out []string
	cursor := 0
	anyVisible := false

	for _, b := range blocks {
		for i := cursor; i < b.Start; i++ {
			out = append(out, lines[i])
			if strings.TrimSpace(lines[i]) != "" {
				anyVisible = true
			}
		}

		if blockUnlocked(b, caps) {
			out = append(out, openMarkerLine(b.Kind, b.Points, "", false))
			if b.Body != "" {
				out = append(out, splitLines(b.Body)...)
				if strings.TrimSpace(b.Body) != "" {
					anyVisible = true
				}
			}
			out = append(out, "[/hide]")
		} else {
			out = append(out, openMarkerLine(b.Kind, b.Points, "", true))
			out = append(out, "[/hide]")
		}
		cursor = b.End + 1
	}
	for i := cursor; i < len(lines); i++ {
		out = append(out, lines[i])
		if strings.TrimSpace(lines[i]) != "" {
			anyVisible = true
		}
	}

	return strings.Join(out, "\n"), !anyVisible
}

// MatchPasswordBlocks 返回密码匹配的隐藏块下标
func MatchPasswordBlocks(content, password string) ([]int, error) {
	blocks, err := ParseHideBlocks(content)
	if err != nil {
		return nil, err
	}
	var hit []int
	for _, b := range blocks {
		if b.Kind != HideKindPassword {
			continue
		}
		if constantTimeEqual(b.Password, password) {
			hit = append(hit, b.Index)
		}
	}
	return hit, nil
}

// WrapContentAsHide 将整篇正文包进单一隐藏块（旧帖迁移用）
func WrapContentAsHide(kind string, points int, content string) string {
	body := strings.TrimRight(content, "\n")
	open := openMarkerLine(kind, points, "", false)
	if body == "" {
		return open + "\n[/hide]\n"
	}
	return open + "\n" + body + "\n[/hide]\n"
}

// HasHideBlocks 快速判断正文是否已含隐藏块（迁移幂等）
func HasHideBlocks(content string) bool {
	blocks, err := ParseHideBlocks(content)
	if err != nil {
		return strings.Contains(strings.ToLower(content), "[hide")
	}
	return len(blocks) > 0
}

func blockUnlocked(b HideBlock, caps ViewerCaps) bool {
	switch b.Kind {
	case HideKindLogin:
		return caps.LoggedIn
	case HideKindReply:
		return caps.HasReplied
	case HideKindPoints:
		return caps.PointsPaid
	case HideKindPassword:
		return caps.PasswordUnlocked != nil && caps.PasswordUnlocked[b.Index]
	default:
		return true
	}
}

// openMarkerLine 生成开标记。密码仅在原文存储时写入；对外脱敏输出传空 password。
func openMarkerLine(kind string, points int, password string, locked bool) string {
	var b strings.Builder
	b.WriteString("[hide ")
	b.WriteString(kind)
	if kind == HideKindPoints && points > 0 {
		b.WriteString("=")
		b.WriteString(strconv.Itoa(points))
	}
	if kind == HideKindPassword && password != "" && !locked {
		b.WriteString("=")
		b.WriteString(password)
	}
	if locked {
		b.WriteString(" locked")
	}
	b.WriteByte(']')
	return b.String()
}

// parseOpenMarker 解析 [hide <kind>[=arg] [locked]]
func parseOpenMarker(trimmed string) (kind string, points int, password string, locked bool, ok bool) {
	m := hideOpenRe.FindStringSubmatch(trimmed)
	if m == nil {
		return "", 0, "", false, false
	}
	rest := strings.TrimSpace(m[1])
	if rest == "" {
		return "", 0, "", false, false
	}
	parts := strings.Fields(rest)
	if len(parts) == 0 {
		return "", 0, "", false, false
	}

	head := parts[0]
	kind = head
	arg := ""
	if i := strings.IndexByte(head, '='); i >= 0 {
		kind = head[:i]
		arg = head[i+1:]
	}
	kind = strings.ToLower(kind)
	switch kind {
	case HideKindLogin, HideKindReply, HideKindPoints, HideKindPassword:
	default:
		return "", 0, "", false, false
	}

	idx := 1
	if kind == HideKindPoints {
		if arg == "" {
			return "", 0, "", false, false
		}
		n, err := strconv.Atoi(arg)
		if err != nil {
			return "", 0, "", false, false
		}
		points = n
	} else if kind == HideKindPassword {
		// [hide password=secret] 或脱敏 [hide password locked]
		if arg != "" {
			password = arg
		}
	} else if arg != "" {
		// login/reply 不应带 =arg
		return "", 0, "", false, false
	}

	for ; idx < len(parts); idx++ {
		if strings.EqualFold(parts[idx], "locked") {
			locked = true
		} else {
			return "", 0, "", false, false
		}
	}
	return kind, points, password, locked, true
}

func validatePassword(pwd string) error {
	if pwd == "" || strings.ContainsAny(pwd, " \t") {
		return ErrHidePasswordNeed
	}
	n := utf8.RuneCountInString(pwd)
	if n < MinHidePasswordLen || n > MaxHidePasswordLen {
		return ErrHidePasswordNeed
	}
	return nil
}

func isCloseMarker(trimmed string) bool {
	return strings.EqualFold(trimmed, "[/hide]")
}

func splitLines(s string) []string {
	if s == "" {
		return []string{}
	}
	s = strings.ReplaceAll(s, "\r\n", "\n")
	s = strings.ReplaceAll(s, "\r", "\n")
	return strings.Split(s, "\n")
}

// ValidateHideContent 校验正文隐藏块；失败返回用户可读错误
func ValidateHideContent(content string) error {
	_, err := ParseHideBlocks(content)
	if err == nil {
		return nil
	}
	switch {
	case errors.Is(err, ErrHideNested):
		return fmt.Errorf("隐藏块不可嵌套")
	case errors.Is(err, ErrHideUnclosed):
		return fmt.Errorf("隐藏块未正确闭合，请检查 [/hide] 标记")
	case errors.Is(err, ErrHidePointsNeed):
		return fmt.Errorf("积分可见块须指定 1–100000 的积分")
	case errors.Is(err, ErrHidePasswordNeed):
		return fmt.Errorf("密码可见块须设置 1–64 字符且不含空格的密码")
	case errors.Is(err, ErrHideInvalid):
		return fmt.Errorf("隐藏块语法无效")
	default:
		return err
	}
}

func constantTimeEqual(a, b string) bool {
	if len(a) != len(b) {
		return false
	}
	var v byte
	for i := 0; i < len(a); i++ {
		v |= a[i] ^ b[i]
	}
	return v == 0
}