Implement reading backwards from log file

2 files changed, 123 insertions, 6 deletions

diff --git a/tests/integration.rs b/tests/integration.rs
index 2c0a958..7fb3229 100644
--- a/tests/integration.rs
+++ b/tests/integration.rs
@@ -1,11 +1,16 @@
-use log_db::log_db::{Config, Record, RecordFieldType, RecordValue, DB};
+use env_logger;
+use log_db;
+use log_db::log_db::{Config, LogReader, Record, RecordFieldType, RecordValue, DB};
 use serial_test::serial;
+use std::fs;
+use std::path::Path;
 
 const TEST_DATA_DIR: &str = "test_db_data";
-const TEST_SEGMENT_SIZE: u64 = 1024 * 1024; // 1 MB
-const TEST_MEMTABLE_SIZE: u64 = 1024 * 1024; // 1 MB
+const TEST_RESOURCES_DIR: &str = "tests/resources";
+const TEST_SEGMENT_SIZE: usize = 1024 * 1024; // 1 MB
+const TEST_MEMTABLE_SIZE: usize = 1024 * 1024; // 1 MB
 
-#[derive(Eq, PartialEq, Clone)]
+#[derive(Eq, PartialEq, Clone, Debug)]
 enum Field {
     Id,
     Name,
@@ -35,7 +40,7 @@ fn test_initialize() {
 
 #[test]
 #[serial]
-fn test_upsert_to_empty_db() {
+fn test_upsert_and_get_with_memtable() {
     let mut db = DB::initialize(&Config {
         data_dir: TEST_DATA_DIR.to_string(),
         segment_size: TEST_SEGMENT_SIZE,
@@ -59,7 +64,7 @@ fn test_upsert_to_empty_db() {
     };
     db.upsert(&record).unwrap();
 
-    let result = db.get(Field::Id, RecordValue::Int(1)).unwrap().unwrap();
+    let result = db.get(&Field::Id, &RecordValue::Int(1)).unwrap().unwrap();
 
     // Check that the IDs match
     assert!(match (&result.values[0], &record.values[0]) {
@@ -73,6 +78,91 @@ fn test_upsert_to_empty_db() {
 
 #[test]
 #[serial]
+fn test_upsert_and_get_without_memtable() {
+    let _ = env_logger::builder().is_test(true).try_init();
+    let mut db = DB::initialize(&Config {
+        data_dir: TEST_DATA_DIR.to_string(),
+        segment_size: TEST_SEGMENT_SIZE,
+        memtable_size: 0, // Force log reads
+        fields: vec![
+            (Field::Id, RecordFieldType::Int),
+            (Field::Name, RecordFieldType::String),
+            (Field::Data, RecordFieldType::Bytes),
+        ],
+        primary_key: Field::Id,
+        secondary_keys: vec![],
+    })
+    .unwrap();
+
+    // Insert some records
+    let record0 = Record {
+        values: vec![
+            RecordValue::Int(0),
+            RecordValue::String("John".to_string()),
+            RecordValue::Bytes(vec![3, 4, 5]),
+        ],
+    };
+    db.upsert(&record0).unwrap();
+
+    let record1 = Record {
+        values: vec![
+            RecordValue::Int(1),
+            RecordValue::String("Alice".to_string()),
+            RecordValue::Bytes(vec![0, 1, 2]),
+        ],
+    };
+    db.upsert(&record1).unwrap();
+
+    let record2 = Record {
+        values: vec![
+            RecordValue::Int(1),
+            RecordValue::String("Bob".to_string()),
+            RecordValue::Bytes(vec![0, 1, 2]),
+        ],
+    };
+    db.upsert(&record2).unwrap();
+
+    let record3 = Record {
+        values: vec![
+            RecordValue::Int(2),
+            RecordValue::String("George".to_string()),
+            RecordValue::Bytes(vec![]),
+        ],
+    };
+    db.upsert(&record3).unwrap();
+
+    // Get with ID = 0
+    let result = db.get(&Field::Id, &RecordValue::Int(0)).unwrap().unwrap();
+
+    // Should match record0
+    assert!(match (&result.values[0], &record0.values[0]) {
+        (RecordValue::Int(a), RecordValue::Int(b)) => a == b,
+        _ => false,
+    });
+    assert!(match (&result.values[1], &record0.values[1]) {
+        (RecordValue::String(a), RecordValue::String(b)) => a == b,
+        _ => false,
+    });
+
+    // Get with ID = 1
+    let result = db.get(&Field::Id, &RecordValue::Int(1)).unwrap().unwrap();
+
+    // Should match record2
+    assert!(match (&result.values[0], &record2.values[0]) {
+        (RecordValue::Int(a), RecordValue::Int(b)) => a == b,
+        _ => false,
+    });
+    assert!(match (&result.values[1], &record2.values[1]) {
+        (RecordValue::String(a), RecordValue::String(b)) => a == b,
+        _ => false,
+    });
+
+    // Clean up
+    std::fs::remove_dir_all(TEST_DATA_DIR.to_string()).unwrap();
+}
+
+#[test]
+#[serial]
 fn test_upsert_fails_on_invalid_number_of_values() {
     let mut db = DB::initialize(&Config {
         data_dir: TEST_DATA_DIR.to_string(),
@@ -130,3 +220,30 @@ fn test_upsert_fails_on_invalid_value_type() {
     // Clean up
     std::fs::remove_dir_all(TEST_DATA_DIR.to_string()).unwrap();
 }
+
+#[test]
+#[serial]
+fn test_log_reader_fixture_db1() {
+    let _ = env_logger::builder().is_test(true).try_init();
+    let db_path = Path::new(TEST_RESOURCES_DIR).join("test_db1");
+    let mut file = fs::OpenOptions::new()
+        .read(true)
+        .open(&db_path)
+        .expect("Failed to open file");
+    let mut log_reader = LogReader::new(&mut file).unwrap();
+
+    // There are two records in the log with "schema": Int, Null
+
+    let last_record = log_reader.next().expect("Failed to read the last record");
+    assert!(match last_record.values.as_slice() {
+        [RecordValue::Int(10), RecordValue::Null] => true,
+        _ => false,
+    });
+
+    let first_record = log_reader.next().expect("Failed to read the first record");
+    assert!(match first_record.values.as_slice() {
+        // Note: the int value is equal to the escape byte
+        [RecordValue::Int(0x1D), RecordValue::Null] => true,
+        _ => false,
+    });
+}
diff --git a/tests/resources/test_db1 b/tests/resources/test_db1
new file mode 100644
index 0000000..e75edf5
--- /dev/null
+++ b/tests/resources/test_db1