added support for :excerpt(max, withEllipsis?) fields modifier

tools/rest/excerpt_modifier.go

@@ -0,0 +1,131 @@
+package rest
+
+import (
+	"errors"
+	"regexp"
+	"strings"
+
+	"github.com/pocketbase/pocketbase/tools/list"
+	"github.com/spf13/cast"
+	"golang.org/x/net/html"
+)
+
+var whitespaceRegex = regexp.MustCompile(`\s+`)
+
+var excludeTags = []string{
+	"head", "style", "script", "iframe", "embed", "applet", "object",
+	"svg", "img", "picture", "dialog", "template", "button", "form",
+	"textarea", "input", "select", "option",
+}
+
+var inlineTags = []string{
+	"a", "abbr", "acronym", "b", "bdo", "big", "br", "button",
+	"cite", "code", "em", "i", "label", "q", "small", "span",
+	"strong", "strike", "sub", "sup", "time",
+}
+
+var _ FieldModifier = (*excerptModifier)(nil)
+
+type excerptModifier struct {
+	max          int  // approximate max excerpt length
+	withEllipsis bool // if enabled will add ellipsis when the plain text length > max
+}
+
+// newExcerptModifier validates the specified raw string arguments and
+// initializes a new excerptModifier.
+//
+// This method is usually invoked in initModifer().
+func newExcerptModifier(args ...string) (*excerptModifier, error) {
+	totalArgs := len(args)
+
+	if totalArgs == 0 {
+		return nil, errors.New("max argument is required - expected (max, withEllipsis?)")
+	}
+
+	if totalArgs > 2 {
+		return nil, errors.New("too many arguments - expected (max, withEllipsis?)")
+	}
+
+	max := cast.ToInt(args[0])
+	if max == 0 {
+		return nil, errors.New("max argument must be > 0")
+	}
+
+	var withEllipsis bool
+	if totalArgs > 1 {
+		withEllipsis = cast.ToBool(args[1])
+	}
+
+	return &excerptModifier{max, withEllipsis}, nil
+}
+
+// Modify implements the [FieldModifier.Modify] interface method.
+//
+// It returns a plain text excerpt/short-description from a formatted
+// html string (non-string values are kept untouched).
+func (m *excerptModifier) Modify(value any) (any, error) {
+	strValue, ok := value.(string)
+	if !ok {
+		// not a string -> return as it is without applying the modifier
+		// (we don't throw an error because the modifier could be applied for a missing expand field)
+		return value, nil
+	}
+
+	var builder strings.Builder
+
+	doc, err := html.Parse(strings.NewReader(strValue))
+	if err != nil {
+		return "", err
+	}
+
+	var isNotEmpty bool
+	var needSpace bool
+
+	// for all node types and more details check
+	// https://pkg.go.dev/golang.org/x/net/html#Parse
+	var stripTags func(*html.Node)
+	stripTags = func(n *html.Node) {
+		switch n.Type {
+		case html.TextNode:
+			if txt := strings.TrimSpace(whitespaceRegex.ReplaceAllString(n.Data, " ")); txt != "" {
+				if isNotEmpty && needSpace {
+					needSpace = false
+					builder.WriteString(" ")
+				}
+
+				builder.WriteString(txt)
+
+				if !isNotEmpty {
+					isNotEmpty = true
+				}
+			}
+		case html.ElementNode:
+			if !needSpace && !list.ExistInSlice(n.Data, inlineTags) {
+				needSpace = true
+			}
+		}
+
+		if builder.Len() > m.max {
+			return
+		}
+
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			if c.Type != html.ElementNode || !list.ExistInSlice(c.Data, excludeTags) {
+				stripTags(c)
+			}
+		}
+	}
+	stripTags(doc)
+
+	result := builder.String()
+
+	if len(result) > m.max {
+		result = strings.TrimSpace(result[:m.max])
+
+		if m.withEllipsis {
+			result += "..."
+		}
+	}
+
+	return result, nil
+}