LibCore: Add a CConfigFile class, a simple INI file parser.

You open the configuration for an app like so:

    auto config = CConfigFile::get_for_app("MyApp");

This will then open ~/MyApp.ini and parse it for you.
Immediately start using it in Minesweeper to load the field size and mine
count from a config file.

LibCore/CConfigFile.cpp

@@ -0,0 +1,195 @@
+#include <LibCore/CConfigFile.h>
+#include <LibCore/CFile.h>
+#include <AK/StringBuilder.h>
+#include <stdio.h>
+#include <pwd.h>
+#include <unistd.h>
+
+Retained<CConfigFile> CConfigFile::get_for_app(const String& app_name)
+{
+    String home_path;
+    if (auto* home_env = getenv("HOME")) {
+        home_path = home_env;
+    } else {
+        uid_t uid = getuid();
+        if (auto* pwd = getpwuid(uid))
+            home_path = pwd->pw_dir;
+    }
+    if (home_path.is_empty())
+        home_path = String::format("/tmp");
+    auto path = String::format("%s/%s.ini", home_path.characters(), app_name.characters());
+    return adopt(*new CConfigFile(path));
+}
+
+CConfigFile::CConfigFile(const String& file_name)
+    : m_file_name(file_name)
+{
+	reparse();
+}
+
+CConfigFile::~CConfigFile()
+{
+	sync();
+}
+
+void CConfigFile::reparse()
+{
+	m_groups.clear();
+
+    CFile file(m_file_name);
+    if (!file.open(CIODevice::OpenMode::ReadOnly))
+        return;
+
+    HashMap<String, String>* current_group = nullptr;
+
+    while (file.can_read_line()) {
+        auto line = file.read_line(BUFSIZ);
+        auto* cp = (const char*)line.pointer();
+
+        while(*cp && (*cp == ' ' || *cp == '\t' || *cp == '\n'))
+			++cp;
+
+        switch (*cp) {
+			case '\0':// EOL...
+			case '#': // Comment, skip entire line.
+			case ';': // -||-
+				continue;
+            case '[': { // Start of new group.
+                StringBuilder builder;
+				++cp; // Skip the '['
+                while (*cp && (*cp != ']'))
+                    builder.append(*(cp++));
+                current_group = &m_groups.ensure(builder.to_string());
+				break;
+			}
+            default: { // Start of key{
+                StringBuilder key_builder;
+                StringBuilder value_builder;
+                while (*cp && (*cp != '='))
+                    key_builder.append(*(cp++));
+				++cp; // Skip the '='
+                while (*cp && (*cp != '\n'))
+                    value_builder.append(*(cp++));
+                if (!current_group) {
+					// We're not in a group yet, create one with the name ""...
+                    current_group = &m_groups.ensure("");
+				}
+                current_group->set(key_builder.to_string(), value_builder.to_string());
+			}
+		}
+	}
+}
+
+String CConfigFile::read_entry(const String& group, const String& key, const String& default_value) const
+{
+    if (!has_key(group, key)) {
+        const_cast<CConfigFile&>(*this).write_entry(group, key, default_value);
+        return default_value;
+    }
+    auto it = m_groups.find(group);
+    auto jt = it->value.find(key);
+    return jt->value;
+}
+
+int CConfigFile::read_num_entry(const String& group, const String &key, int default_value) const
+{
+    if (!has_key(group, key)) {
+        const_cast<CConfigFile&>(*this).write_num_entry(group, key, default_value);
+        return default_value;
+    }
+
+    bool ok;
+    int value = read_entry(group, key).to_uint(ok);
+    if (!ok)
+        return default_value;
+    return value;
+}
+
+bool CConfigFile::read_bool_entry(const String& group, const String &key, bool default_value) const
+{
+    return read_entry(group, key, default_value ? "1" : "0") == "1";
+}
+
+void CConfigFile::write_entry(const String& group, const String& key, const String& value)
+{
+    m_groups.ensure(group).ensure(key) = value;
+	m_dirty = true;
+}
+
+void CConfigFile::write_num_entry(const String& group, const String& key, int value)
+{
+    write_entry(group, key, String::format("%d", value));
+}
+
+bool CConfigFile::sync()
+{
+    if (!m_dirty)
+		return true;
+
+    FILE *fp = fopen(m_file_name.characters(), "wb");
+    if (!fp)
+		return false;
+
+    for (auto& it : m_groups) {
+        fprintf(fp, "[%s]\n", it.key.characters());
+        for (auto& jt : it.value)
+            fprintf(fp, "%s=%s\n", jt.key.characters(), jt.value.characters());
+        fprintf(fp, "\n");
+	}
+
+    fclose(fp);
+
+	m_dirty = false;
+	return true;
+}
+
+void CConfigFile::dump() const
+{
+    for (auto& it : m_groups) {
+        printf("[%s]\n", it.key.characters());
+        for (auto& jt : it.value)
+            printf("%s=%s\n", jt.key.characters(), jt.value.characters());
+        printf("\n");
+	}
+}
+
+Vector<String> CConfigFile::groups() const
+{
+    return m_groups.keys();
+}
+
+Vector<String> CConfigFile::keys(const String& group) const
+{
+    auto it = m_groups.find(group);
+    if (it == m_groups.end())
+        return { };
+    return it->value.keys();
+}
+
+bool CConfigFile::has_key(const String& group, const String& key) const
+{
+    auto it = m_groups.find(group);
+    if (it == m_groups.end())
+        return { };
+    return it->value.contains(key);
+}
+
+bool CConfigFile::has_group(const String& group) const
+{
+    return m_groups.contains(group);
+}
+
+void CConfigFile::remove_group(const String& group)
+{
+    m_groups.remove(group);
+	m_dirty = true;
+}
+
+void CConfigFile::remove_entry(const String& group, const String& key)
+{
+    auto it = m_groups.find(group);
+    if (it == m_groups.end())
+        return;
+    it->value.remove(key);
+	m_dirty = true;
+}