still in progress but want to go to laptop

src/encoding.rs

@@ -1,34 +1,81 @@
+/// 5 bits
+#[derive(Clone, Copy)]
 struct ZChar(u8);
-struct ZsciiChar(u8);
 
-struct ZsciiString(Vec<ZsciiChar>);
+/// technically 10 bits, but top two unused so they are dropped
+#[derive(PartialEq, Clone, Copy)]
+pub struct ZsciiChar(u8);
+
+pub type ZsciiString = Vec<ZsciiChar>;
 
 /// Returns:
 /// - a result that wraps a ZsciiString, erroring if the slice terminates before the string ends
 /// - a usize indicating how many bytes were consumed
-
-pub fn decode_zchars(zchars: &[u8]) -> Option<(ZsciiString, usize)> {
+pub fn decode_zchars(
+    zchars: &[u8], 
+    alphabet_table: Option<&[u8]>, 
+    abbreviations_table: &[u8],
+) -> Option<(ZsciiString, usize)> {
     fn cut_string(zchars: &[u8]) -> Option<Vec<u16>> {
-        for (i, word) in zchars.chunks_exact(2).map(|c| u16::from_be_bytes([c[0], c[1]])).enumerate() {
+        let mut out = Vec::new();
+        for word in zchars.chunks_exact(2).map(|c| u16::from_be_bytes([c[0], c[1]])) {
+            out.push(word);
+            if 0x8000 & word != 0 {
+                return Some(out);
+            }
+        }
+        None
+    }
+
+    /// requires: alphabet_num < 3, 5 < char_idx < 32, !(alphabet_num = 2 AND char_idx = 6)
+    fn index_alphabet(
+        alphabet_table: Option<&[u8]>, 
+        alphabet_number: usize, 
+        ZChar(char_idx): ZChar,
+        zchars: &mut impl Iterator<Item = ZChar>,
+    ) -> Option<ZsciiChar> {
+        let default_alphabet: [[ZsciiChar; 26]; 3] = [
+            b"abcdefghijklmnopqrstuvwxyz".map(ZsciiChar), 
+            b"ABCDEFGHIJKLMNOPQRSTUVWXYZ".map(ZsciiChar), 
+            br#"  0123456789.,!?_#'"/\-:()"#.map(ZsciiChar)
+        ];
+        if alphabet_number == 2 && char_idx == 7 {
+            Some(ZsciiChar(13))
+        } else if alphabet_number == 2 && char_idx == 6 {
+            todo!()
+        } else if let Some(alphabet_table) = alphabet_table {
+            todo!()
+        } else {
+            Some(default_alphabet[alphabet_number][char_idx as usize - 6])
+        }
+    }
+
+    let zwords = cut_string(zchars)?;
+    let consumed_length = zwords.len() * 2;
+    let mut zchars = zwords.iter()
+        .flat_map(|word| [
+            (word >> 10) & 0x1f,
+            (word >> 5) & 0x1f,
+            word & 0x1f
+        ])
+        .map(|word| ZChar(word as u8))
+        .peekable();
+
+    let mut out = Vec::new();
+    let mut current_alphabet = 0;
+    while let Some(char) = zchars.next() {
+        match char {
+            ZChar(0) => out.push(ZsciiChar(32)),
+            ZChar(1..=3) => todo!("abbreviations"),
+            ZChar(4..=5) => if zchars.peek().is_some_and(|&ZChar(n)| n > 5) {
+                if let Some(zc) = index_alphabet(alphabet_table, char.0 as usize - 3, zchars.next().unwrap(), &mut zchars) { out.push(zc) }
+            },
+            ZChar(_) => if let Some(zc) = index_alphabet(alphabet_table, 0, char, &mut zchars) {
+                out.push(zc)
+            }
         }
     }
-    let zchars = slice_string(zchars);
-    // let mut index: usize = 0;
-    // let mut out = Vec::new();
-    // loop {
-    //     let word = u16::from_be_bytes([zchars[index], zchars[index + 1]]);
-    //     let end_bit_set = word & 0x8000 != 0;
-    //     let chars = [
-    //         (word & (0b11111 << 10)) >> 10,
-    //         (word & (0b11111 << 5)) >> 5,
-    //         (word & (0b11111 << 0)) >> 0,
-    //     ].map(|c| ZChar(c as u8));
-    //     out.extend(chars);
-    //     index += 2;
-    //     if index >= zchars.len() - 1 { break (Err(out), index); }
-    //     if end_bit_set { break (Ok(out), index); }
-    //     // TODO: finish
-    // }
+    Some((out, consumed_length))
 }