3 files changed, 115 insertions, 3 deletions

diff --git a/mardown/ast_header.go b/mardown/ast_header.go
index 07d7e1c..1526efa 100644
--- a/mardown/ast_header.go
+++ b/mardown/ast_header.go
@@ -25,7 +25,7 @@ func (a *astHeader) Eval() (template.HTML, error) {
 	return template.HTML(fmt.Sprintf("<h%d>%s</h%d>", a.level, content, a.level)), nil
 }
 
-func header(lxs lexers) (block, error) {
+func header(lxs lexers) (*astHeader, error) {
 	b := &astHeader{level: uint(len(lxs.Current().Value))}
 	var err error
 	b.content, err = paragraph(lxs, true)
diff --git a/mardown/ast_modifier.go b/mardown/ast_modifier.go
new file mode 100644
index 0000000..e505aef
--- /dev/null
+++ b/mardown/ast_modifier.go
@@ -0,0 +1,104 @@
+package mardown
+
+import (
+	"errors"
+	"fmt"
+	"html/template"
+)
+
+var (
+	ErrInternalError         = errors.New("internal error")
+	ErrInvalidModifier       = errors.Join(ErrInvalidParagraph, errors.New("invalid modifier organization"))
+	ErrInvalidTypeInModifier = errors.Join(ErrInvalidParagraph, errors.New("invalid type in modifier"))
+)
+
+type modifierTag string
+
+const (
+	boldTag modifierTag = "b"
+	emTag   modifierTag = "em"
+	codeTag modifierTag = "code"
+)
+
+type astModifier struct {
+	symbols string
+	tag     modifierTag
+	content []block
+	parent  *astModifier
+}
+
+func (a *astModifier) Eval() (template.HTML, error) {
+	var content template.HTML
+	for _, c := range a.content {
+		ct, err := c.Eval()
+		if err != nil {
+			return "", err
+		}
+		content += ct
+	}
+	return template.HTML(fmt.Sprintf("<%s>%s</%s>", a.tag, content, a.tag)), nil
+}
+
+func modifier(lxs lexers) (*astModifier, error) {
+	current := lxs.Current().Value
+	mod := modifierDetect(current)
+	modInside := mod
+	if len(mod.content) > 0 {
+		var ok bool
+		modInside, ok = mod.content[0].(*astModifier)
+		if modInside.content != nil && !ok {
+			return nil, ErrInternalError
+		}
+		// getting the last modifier
+		for len(modInside.content) > 0 {
+			modInside, ok = modInside.content[0].(*astModifier)
+			if modInside.content != nil && !ok {
+				return nil, ErrInternalError
+			}
+		}
+	}
+	n := len(modInside.symbols)
+	var s string
+	for lxs.Next() {
+		switch lxs.Current().Type {
+		case lexerLiteral:
+			s += lxs.Current().Value
+		case lexerModifier:
+			if len(lxs.Current().Value) < n {
+				return nil, ErrInvalidModifier
+			}
+			if lxs.Current().Value[:n] != modInside.symbols {
+				return nil, ErrInvalidModifier
+			}
+			modInside.content = append(modInside.content, astLiteral(s))
+			s = ""
+			modInside = modInside.parent
+		default:
+			return nil, ErrInvalidTypeInModifier
+		}
+	}
+	return mod, nil
+}
+
+func modifierDetect(val string) *astModifier {
+	mod := new(astModifier)
+	if len(val) == 1 {
+		mod.symbols = val
+		if val == "`" {
+			mod.tag = codeTag
+		} else {
+			mod.tag = emTag
+		}
+		return mod
+	}
+	if val[:2] == "**" || val[:2] == "__" {
+		mod.symbols = val
+		mod.tag = boldTag
+	} else {
+		mod = modifierDetect(val[:1])
+		next := modifierDetect(val[1:])
+		next.parent = mod
+		mod.content = append(mod.content, next)
+	}
+	return mod
+}
diff --git a/mardown/ast_paragraph.go b/mardown/ast_paragraph.go
index 04f2086..3c8f985 100644
--- a/mardown/ast_paragraph.go
+++ b/mardown/ast_paragraph.go
@@ -47,7 +47,11 @@ func paragraph(lxs lexers, oneLine bool) (*astParagraph, error) {
 		case lexerLiteral, lexerHeader:
 			tree.content = append(tree.content, astLiteral(lxs.Current().Value))
 		case lexerModifier:
-			//TODO: handle
+			mod, err := modifier(lxs)
+			if err != nil {
+				return nil, err
+			}
+			tree.content = append(tree.content, mod)
 		case lexerQuote:
 			//TODO: handle
 		case lexerEscape:
@@ -62,7 +66,11 @@ func paragraph(lxs lexers, oneLine bool) (*astParagraph, error) {
 				lxs.current-- // because we do not use it before the next
 				return tree, nil
 			}
-			//TODO: handle
+			mod, err := modifier(lxs)
+			if err != nil {
+				return nil, err
+			}
+			tree.content = append(tree.content, mod)
 		}
 	}
 	return tree, nil