reorganize header component

src/line/header/gemtext.rs

@@ -0,0 +1,66 @@
+use super::Level;
+
+pub trait Gemtext {
+    /// Get [Gemtext](https://geminiprotocol.net/docs/gemtext-specification.gmi) value for `Self`
+    fn as_value(&self) -> Option<&str>;
+    /// Get parsed H1 header value for `Self`
+    fn as_h1_value(&self) -> Option<&str>;
+    /// Get parsed H2 header value `Self`
+    fn as_h2_value(&self) -> Option<&str>;
+    /// Get parsed H3 header value `Self`
+    fn as_h3_value(&self) -> Option<&str>;
+    /// Get parsed header value `Self` match `Level`
+    fn as_value_match_level(&self, level: Level) -> Option<&str>;
+    /// Convert `Self` to `Level`
+    fn to_level(&self) -> Option<Level>;
+    /// Convert `Self` to [Gemtext](https://geminiprotocol.net/docs/gemtext-specification.gmi) line
+    fn to_source(&self, level: &Level) -> String;
+}
+
+impl Gemtext for str {
+    fn as_value(&self) -> Option<&str> {
+        if let Some(value) = self.as_h1_value() {
+            return Some(value);
+        }
+        if let Some(value) = self.as_h2_value() {
+            return Some(value);
+        }
+        if let Some(value) = self.as_h3_value() {
+            return Some(value);
+        }
+        None
+    }
+    fn as_h1_value(&self) -> Option<&str> {
+        self.as_value_match_level(Level::H1)
+    }
+    fn as_h2_value(&self) -> Option<&str> {
+        self.as_value_match_level(Level::H2)
+    }
+    fn as_h3_value(&self) -> Option<&str> {
+        self.as_value_match_level(Level::H3)
+    }
+    fn as_value_match_level(&self, level: Level) -> Option<&str> {
+        if let Some(value) = self.strip_prefix(level.as_tag()) {
+            if value.trim_start().starts_with(Level::H1.as_tag()) {
+                return None;
+            }
+            return Some(value.trim());
+        }
+        None
+    }
+    fn to_level(&self) -> Option<Level> {
+        if self.as_h1_value().is_some() {
+            return Some(Level::H1);
+        }
+        if self.as_h2_value().is_some() {
+            return Some(Level::H2);
+        }
+        if self.as_h3_value().is_some() {
+            return Some(Level::H3);
+        }
+        None
+    }
+    fn to_source(&self, level: &Level) -> String {
+        format!("{} {}", level.as_tag(), self.trim())
+    }
+}