Implement groundwork for challenge 13.

src/parser.rs

@@ -0,0 +1,65 @@
+use std::collections::HashMap;
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum Token {
+    Identifier(String),
+    Equal,
+    Ampersand,
+}
+
+pub type Tokens = Vec<Token>;
+
+pub fn parse_key_value(text: &str) -> HashMap<String, String> {
+    /* Parses foo=bar&baz=qux&zap=zazzle into respective hashmap. */
+    let mut tokens: Tokens = vec![];
+    let mut result = HashMap::new();
+    tokens = scan(text, 0, tokens);
+    for token_chunk in tokens.chunks(4) {
+        match &token_chunk[..] {
+            [Token::Identifier(key), Token::Equal, Token::Identifier(value), Token::Ampersand] => {
+                result.insert(key.to_string(), value.to_string());
+            }
+            [Token::Identifier(key), Token::Equal, Token::Identifier(value)] => {
+                result.insert(key.to_string(), value.to_string());
+            }
+            _ => panic!("Could not parse {:?}", token_chunk),
+        };
+    }
+    result
+}
+
+fn scan(code: &str, mut ix: usize, mut tokens: Tokens) -> Tokens {
+    if ix == code.len() {
+        return tokens;
+    }
+
+    let c: char = code[ix..ix + 1].chars().next().unwrap();
+    if c.is_ascii_alphanumeric() || SPECIAL_CHARS.contains(&c) {
+        return scan_identifier(code, ix, tokens);
+    } else if c == '&' {
+        tokens.push(Token::Ampersand);
+    } else if c == '=' {
+        tokens.push(Token::Equal);
+    } else {
+        panic!("Unexpected char '{}' at index {}", c, ix);
+    }
+    ix += 1;
+    scan(code, ix, tokens)
+}
+
+fn scan_identifier(code: &str, mut ix: usize, mut tokens: Tokens) -> Tokens {
+    let start_ix = ix;
+    let mut chars = code[ix..].chars();
+    while let Some(c) = chars.next() {
+        if c.is_ascii_alphanumeric() || SPECIAL_CHARS.contains(&c) {
+            ix += 1;
+        } else {
+            break;
+        }
+    }
+    let token = Token::Identifier(code[start_ix..ix].to_string());
+    tokens.push(token);
+    scan(code, ix, tokens)
+}
+
+const SPECIAL_CHARS: &[char] = &['.', '@'];