Help+man+LibManual: Move argument handling to LibManual

This deduplicates argument handling logic from Help and man and makes it
more modular for future use cases. The argument handling works as
before: two arguments specify section and page (in this order), one
argument specifies either a page (the first section that it's found in
is used) or a path to a manpage markdown file.

Userland/Libraries/LibManual/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(SOURCES
+    Node.cpp
     PageNode.cpp
     Path.cpp
     SectionNode.cpp

Userland/Libraries/LibManual/Node.cpp

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Node.h"
+#include "PageNode.h"
+#include "SectionNode.h"
+#include <AK/Assertions.h>
+#include <AK/LexicalPath.h>
+#include <AK/Optional.h>
+#include <AK/StringView.h>
+#include <LibCore/File.h>
+#include <LibCore/Stream.h>
+#include <LibManual/Path.h>
+
+namespace Manual {
+
+ErrorOr<NonnullRefPtr<PageNode>> Node::try_create_from_query(Vector<StringView, 2> const& query_parameters)
+{
+    if (query_parameters.size() > 2)
+        return Error::from_string_literal("Queries longer than 2 strings are not supported yet");
+
+    auto query_parameter_iterator = query_parameters.begin();
+
+    if (query_parameter_iterator.is_end())
+        // BUG! No query was given.
+        VERIFY_NOT_REACHED();
+
+    auto first_query_parameter = *query_parameter_iterator;
+    ++query_parameter_iterator;
+    if (query_parameter_iterator.is_end()) {
+        // [/path/to/docs.md]
+        auto path_from_query = LexicalPath { first_query_parameter };
+        if (path_from_query.is_absolute()
+            && path_from_query.is_child_of(manual_base_path)
+            && path_from_query.extension() == "md"sv) {
+            auto section_directory = path_from_query.parent();
+            auto man_string_location = section_directory.basename().find("man"sv);
+            if (!man_string_location.has_value())
+                return Error::from_string_literal("Page is inside invalid section");
+            auto section_name = section_directory.basename().substring_view(man_string_location.value() + 3);
+            auto section = TRY(SectionNode::try_create_from_number(section_name));
+            return try_make_ref_counted<PageNode>(section, TRY(String::from_utf8(path_from_query.title())));
+        }
+
+        // [page] (in any section)
+        Optional<NonnullRefPtr<PageNode>> maybe_page;
+        for (auto const& section : sections) {
+            auto const page = TRY(try_make_ref_counted<PageNode>(section, TRY(String::from_utf8(first_query_parameter))));
+            if (Core::File::exists(TRY(page->path()))) {
+                maybe_page = page;
+                break;
+            }
+        }
+        if (maybe_page.has_value())
+            return maybe_page.release_value();
+        return Error::from_string_literal("Page not found");
+    }
+    // [section] [name]
+    auto second_query_parameter = *query_parameter_iterator;
+    auto section = TRY(SectionNode::try_create_from_number(first_query_parameter));
+    auto const page = TRY(try_make_ref_counted<PageNode>(section, TRY(String::from_utf8(second_query_parameter))));
+    if (Core::File::exists(TRY(page->path())))
+        return page;
+    return Error::from_string_literal("Page doesn't exist in section");
+}
+
+}

Userland/Libraries/LibManual/Node.h

@@ -25,6 +25,13 @@ public:
     virtual ErrorOr<String> name() const = 0;
     virtual bool is_page() const { return false; }
     virtual bool is_open() const { return false; }
+
+    // Backend for the command-line argument format that Help and man accept. Handles:
+    // [/path/to/documentation.md] (no second argument)
+    // [page] (no second argument) - will find first section with that page
+    // [section] [page]
+    // Help can also (externally) handle search queries, which is not possible (yet) in man.
+    static ErrorOr<NonnullRefPtr<PageNode>> try_create_from_query(Vector<StringView, 2> const& query_parameters);
 };
 
 }

Userland/Libraries/LibManual/SectionNode.cpp

@@ -13,6 +13,17 @@
 
 namespace Manual {
 
+ErrorOr<NonnullRefPtr<SectionNode>> SectionNode::try_create_from_number(StringView section)
+{
+    auto maybe_section_number = section.to_uint<u32>();
+    if (!maybe_section_number.has_value())
+        return Error::from_string_literal("Section is not a number");
+    auto section_number = maybe_section_number.release_value();
+    if (section_number > number_of_sections)
+        return Error::from_string_literal("Section number too large");
+    return sections[section_number - 1];
+}
+
 ErrorOr<String> SectionNode::path() const
 {
     return String::formatted("{}/{}{}", manual_base_path, top_level_section_prefix, m_section);

Userland/Libraries/LibManual/SectionNode.h

@@ -37,6 +37,8 @@ public:
     virtual bool is_open() const override { return m_open; }
     void set_open(bool open);
 
+    static ErrorOr<NonnullRefPtr<SectionNode>> try_create_from_number(StringView section_number);
+
 protected:
     String m_section;
     String m_name;