remove regex dependency, rename constructor, implement Gemtext trait

src/line/header.rs

@@ -1,4 +1,8 @@
-use glib::{Regex, RegexCompileFlags, RegexMatchFlags};
+/// [Header](https://geminiprotocol.net/docs/gemtext-specification.gmi#heading-lines) tag
+/// * store as entire static chars array
+pub const TAG_H1: &str = "#";
+pub const TAG_H2: &str = "##";
+pub const TAG_H3: &str = "###";
 
 /// [Header](https://geminiprotocol.net/docs/gemtext-specification.gmi#heading-lines) type holder
 pub enum Level {
@@ -9,32 +13,78 @@ pub enum Level {
 
 /// [Header](https://geminiprotocol.net/docs/gemtext-specification.gmi#heading-lines) entity holder
 pub struct Header {
-    pub value: String,
     pub level: Level,
+    pub value: String,
 }
 
 impl Header {
     // Constructors
 
     /// Parse `Self` from line string
-    pub fn from(line: &str) -> Option<Self> {
-        // Parse line
-        let regex = Regex::split_simple(
-            r"^(#{1,3})\s*(.+)$",
-            line,
-            RegexCompileFlags::DEFAULT,
-            RegexMatchFlags::DEFAULT,
-        );
-
-        // Result
+    pub fn parse(line: &str) -> Option<Self> {
         Some(Self {
-            level: match regex.get(1)?.len() {
-                1 => Level::H1,
-                2 => Level::H2,
-                3 => Level::H3,
-                _ => return None,
-            },
-            value: regex.get(2)?.trim().to_string(),
+            level: line.to_level()?,
+            value: line.as_value()?.to_string(),
         })
     }
+
+    // Converters
+
+    /// Convert `Self` to [Gemtext](https://geminiprotocol.net/docs/gemtext-specification.gmi) line
+    pub fn to_source(&self) -> String {
+        self.value.to_source(&self.level)
+    }
+}
+
+pub trait Gemtext {
+    /// Get [Gemtext](https://geminiprotocol.net/docs/gemtext-specification.gmi) value from `Self`
+    fn as_value(&self) -> Option<&Self>;
+    /// 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<&Self> {
+        if let Some(h3) = self.strip_prefix(TAG_H3) {
+            if h3.trim_start().starts_with(TAG_H1) {
+                return None; // H4+
+            }
+            return Some(h3.trim());
+        }
+        if let Some(h2) = self.strip_prefix(TAG_H2) {
+            return Some(h2.trim());
+        }
+        if let Some(h1) = self.strip_prefix(TAG_H1) {
+            return Some(h1.trim());
+        }
+        None
+    }
+    fn to_level(&self) -> Option<Level> {
+        if let Some(h3) = self.strip_prefix(TAG_H3) {
+            if h3.trim_start().starts_with(TAG_H1) {
+                return None; // H4+
+            }
+            return Some(Level::H3);
+        }
+        if self.starts_with(TAG_H2) {
+            return Some(Level::H2);
+        }
+        if self.starts_with(TAG_H1) {
+            return Some(Level::H1);
+        }
+        None
+    }
+    fn to_source(&self, level: &Level) -> String {
+        format!(
+            "{} {}",
+            match level {
+                Level::H1 => TAG_H1,
+                Level::H2 => TAG_H2,
+                Level::H3 => TAG_H3,
+            },
+            self.trim()
+        )
+    }
 }