From 668ae1bd9db918b97d5c0229948ffe44bb9defe9 Mon Sep 17 00:00:00 2001
From: Ishan Jain <contact@ishanjain.me>
Date: Wed, 20 Jul 2022 15:11:10 +0530
Subject: [PATCH] read table row count

---
 src/main.rs   | 45 ++++++++++++++++++++++++++++++++++++++++++---
 src/schema.rs |  2 +-
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 379502e..d73b1d6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -12,7 +12,7 @@ fn main() -> Result<()> {
     match args.len() {
         0 | 1 => bail!("Missing <database path> and <command>"),
         2 => bail!("Missing <command>"),
-        _ => {}
+        _ => (),
     }
 
     // Read database file into database
@@ -85,8 +85,47 @@ fn main() -> Result<()> {
                 print!("{} ", schema.name);
             }
         }
-        _ => bail!("Missing or invalid command passed: {}", command),
-    }
 
+        v => {
+            // Assume it's valid SQL
+            let table_name = v.split_whitespace().last().unwrap();
+
+            let db_page_size = u16::from_be_bytes([database[16], database[17]]);
+
+            // Parse page header from database
+            let page_header = PageHeader::parse(&database[100..108])?;
+
+            // Obtain all cell pointers
+            let cell_pointers = database[108..]
+                .chunks_exact(2)
+                .take(page_header.number_of_cells.into())
+                .map(|bytes| u16::from_be_bytes(bytes.try_into().unwrap()));
+
+            // Obtain all records from column 5
+            #[allow(unused_variables)]
+            let schemas = cell_pointers
+                .into_iter()
+                .map(|cell_pointer| {
+                    let stream = &database[cell_pointer as usize..];
+                    let (_, offset) = parse_varint(stream);
+                    let (rowid, read_bytes) = parse_varint(&stream[offset..]);
+
+                    parse_record(&stream[offset + read_bytes..], 5)
+                        .map(|record| Schema::parse(record).expect("Invalid record"))
+                })
+                .collect::<Result<Vec<_>>>()?;
+
+            let schema = schemas
+                .into_iter()
+                .find(|schema| schema.table_name == table_name)
+                .unwrap();
+
+            let table_page_offset = db_page_size as usize * (schema.root_page as usize - 1);
+            let page_header =
+                PageHeader::parse(&database[table_page_offset..table_page_offset + 8]).unwrap();
+
+            println!("{}", page_header.number_of_cells);
+        }
+    }
     Ok(())
 }
diff --git a/src/schema.rs b/src/schema.rs
index 120c0b0..e157886 100644
--- a/src/schema.rs
+++ b/src/schema.rs
@@ -3,7 +3,7 @@ pub struct Schema {
     pub kind: String,
     pub name: String,
     pub table_name: String,
-    root_page: u8,
+    pub root_page: u8,
     sql: String,
 }