jiang13-bbs/backend/markdown/hide.go

// Package markdown 提供帖子正文隐藏块（:::hide）的解析、校验与脱敏。
package markdown

import (
	"errors"
	"fmt"
	"strconv"
	"strings"
)

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

// HideBlock 正文中的一段隐藏内容
type HideBlock struct {
	Kind   string // login | reply | points
	Points int    // 仅 points 有效
	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）
}

// DerivedAccess 由正文隐藏块派生的帖级可见性
type DerivedAccess struct {
	Access string // public | login | reply | points | 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
}

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")
)

// ParseHideBlocks 扫描正文中的 :::hide 块（忽略代码围栏内伪语法）。
// 校验失败返回 error（用于 Create/Update）。
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, 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
				}
			}
			blocks = append(blocks, HideBlock{
				Kind:   kind,
				Points: pts,
				Body:   strings.Join(bodyLines, "\n"),
				Start:  i,
				End:    j,
				Locked: locked,
			})
			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。
// fullyLocked 表示读者当前看不到任何可见正文（整篇都在锁块里或公开区为空）。
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, ":::")
		} else {
			out = append(out, openMarkerLine(b.Kind, b.Points, true))
			out = append(out, ":::")
		}
		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
}

// 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:::\n"
	}
	return open + "\n" + body + "\n:::\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(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
	default:
		return true
	}
}

func openMarkerLine(kind string, points int, locked bool) string {
	var b strings.Builder
	b.WriteString(":::hide ")
	b.WriteString(kind)
	if kind == HideKindPoints && points > 0 {
		b.WriteByte(' ')
		b.WriteString(strconv.Itoa(points))
	}
	if locked {
		b.WriteString(" locked")
	}
	return b.String()
}

func parseOpenMarker(trimmed string) (kind string, points int, locked bool, ok bool) {
	if !strings.HasPrefix(trimmed, ":::hide") {
		return "", 0, false, false
	}
	rest := strings.TrimSpace(trimmed[len(":::hide"):])
	if rest == "" {
		return "", 0, false, false
	}
	parts := strings.Fields(rest)
	if len(parts) == 0 {
		return "", 0, false, false
	}
	kind = parts[0]
	switch kind {
	case HideKindLogin, HideKindReply, HideKindPoints:
	default:
		return "", 0, false, false
	}
	idx := 1
	if kind == HideKindPoints {
		if idx >= len(parts) {
			return "", 0, false, false
		}
		n, err := strconv.Atoi(parts[idx])
		if err != nil {
			return "", 0, false, false
		}
		points = n
		idx++
	}
	for ; idx < len(parts); idx++ {
		if parts[idx] == "locked" {
			locked = true
		} else {
			return "", 0, false, false
		}
	}
	return kind, points, locked, true
}

func isCloseMarker(trimmed string) bool {
	return trimmed == ":::"
}

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 ::: 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, ErrHideInvalid):
		return fmt.Errorf("隐藏块语法无效")
	default:
		return err
	}
}