1 files changed, 115 insertions, 0 deletions
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..d6a1e12
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,115 @@
+#[repr(u8)]
+enum WALRingType {
+    Full,
+    First,
+    Middle,
+    Last
+}
+
+struct WALRingBlob {
+    crc32: u32,
+    rsize: u32,
+    rtype: WALRingType,
+    // payload follows
+}
+
+type WALFileId = u32;
+type WALPos = u64;
+type WALWrite = (WALPos, Box<[u8]>);
+
+pub struct WALState {
+    pub base: WALPos,
+    pub last: WALPos,
+    pub block_nbit: u8,
+    pub file_nbit: u8,
+}
+
+pub struct WALWriter {
+    state: WALState,
+    block_buffer: Box<[u8]>,
+    block_size: u32,
+    file_size: u64,
+}
+
+impl WALWriter {
+    pub fn new(state: WALState) -> Self {
+        let mut b = Vec::new();
+        let block_size = 1 << (state.block_nbit as u32);
+        let file_size = 1 << (state.file_nbit as u64);
+        b.resize(block_size as usize, 0);
+        WALWriter{
+            state,
+            block_buffer: b.into_boxed_slice(),
+            block_size,
+            file_size,
+        }
+    }
+
+    pub fn grow(&mut self, records: &[Box<[u8]>]) -> Vec<WALWrite> {
+        let mut res = Vec::new();
+        let msize = std::mem::size_of::<WALRingBlob>() as u32;
+        // the global offest of the begining of the block
+        // the start of the unwritten data
+        let mut bbuff_start = self.state.last as u32 & (self.block_size - 1);
+        // the end of the unwritten data
+        let mut bbuff_cur = bbuff_start;
+
+        for _rec in records {
+            let mut rec = &_rec[..];
+            let mut rsize = rec.len() as u32;
+            let mut started = false;
+            while rsize > 0 {
+                let remain = self.block_size - bbuff_cur;
+                if remain > msize {
+                    let d = remain - msize;
+                    let blob = unsafe {std::mem::transmute::<*mut u8, &mut WALRingBlob>(
+                        &mut self.block_buffer[bbuff_cur as usize] as *mut u8)};
+                    if d >= rsize {
+                        // the remaining rec fits in the block
+                        let payload = rec;
+                        blob.crc32 = crc::crc32::checksum_ieee(payload);
+                        blob.rsize = rsize;
+                        blob.rtype = if started {WALRingType::Last} else {WALRingType::Full};
+                        rsize = 0;
+                        &mut self.block_buffer[bbuff_cur as usize..].copy_from_slice(payload);
+                        bbuff_cur += rsize;
+                    } else {
+                        // the remaining block can only accommodate partial rec
+                        let payload = &rec[..d as usize];
+                        blob.crc32 = crc::crc32::checksum_ieee(payload);
+                        blob.rsize = d;
+                        blob.rtype = if started {WALRingType::Middle} else {
+                            started = true;
+                            WALRingType::First
+                        };
+                        rsize -= d;
+                        &mut self.block_buffer[bbuff_cur as usize..].copy_from_slice(payload);
+                        bbuff_cur += d;
+                        rec = &rec[d as usize..];
+                    }
+                } else {
+                    // add padding space by moving the point to the end of the block
+                    bbuff_cur = self.block_size;
+                }
+                if bbuff_cur == self.block_size {
+                    res.push((self.state.last,
+                             self.block_buffer[bbuff_start as usize..]
+                                .to_vec().into_boxed_slice()));
+                    self.state.last += (self.block_size - bbuff_start) as u64;
+                    bbuff_start = 0;
+                    bbuff_cur = 0;
+                }
+            }
+        }
+        if bbuff_cur > bbuff_start {
+            res.push((self.state.last,
+                     self.block_buffer[bbuff_start as usize..bbuff_cur as usize]
+                        .to_vec().into_boxed_slice()));
+            self.state.last += (bbuff_cur - bbuff_start) as u64;
+        }
+        res
+    }
+}
+
+struct WALReader {
+}