add missing file

src/validation.cairo

@@ -0,0 +1,60 @@
+use super::state::{Block, ChainState};
+
+#[generate_trait]
+impl BlockValidatorImpl of BlockValidator {
+    fn validate_and_apply(self: ChainState, block: Block) -> Result<ChainState, ByteArray> {
+        validate_prev_block_hash(@self, @block)?;
+        validate_proof_of_work(@self, @block)?;
+        validate_target(@self, @block)?;
+        validate_timestamp(@self, @block)?;
+
+        // validate_merkle_root
+        // validate_and_apply_transactions
+
+        let prev_timestamps = next_prev_timestamps(@self, @block);
+        let total_work = compute_total_work(@self, @block);
+        let (current_target, epoch_start_time) = adjust_difficulty(@self, @block);
+
+        Result::Ok(
+            ChainState { total_work, current_target, epoch_start_time, prev_timestamps, ..self, }
+        )
+    }
+}
+
+fn validate_prev_block_hash(self: @ChainState, block: @Block) -> Result<(), ByteArray> {
+    if self.best_block_hash == block.header.prev_block_hash {
+        Result::Ok(())
+    } else {
+        Result::Err("Invalid `prev_block_hash`. This block does not extend the current chain.")
+    }
+}
+
+fn validate_proof_of_work(self: @ChainState, block: @Block) -> Result<(), ByteArray> {
+    // TODO: implement
+    Result::Ok(())
+}
+
+fn validate_target(self: @ChainState, block: @Block) -> Result<(), ByteArray> {
+    // TODO: implement
+    Result::Ok(())
+}
+
+fn validate_timestamp(self: @ChainState, block: @Block) -> Result<(), ByteArray> {
+    // TODO: implement
+    Result::Ok(())
+}
+
+fn next_prev_timestamps(self: @ChainState, block: @Block) -> Span<u32> {
+    // TODO: implement
+    *self.prev_timestamps
+}
+
+fn compute_total_work(self: @ChainState, block: @Block) -> u256 {
+    // TODO: implement
+    *self.total_work
+}
+
+fn adjust_difficulty(self: @ChainState, block: @Block) -> (u32, u32) {
+    // TODO: implement
+    (*self.current_target, *self.epoch_start_time)
+}