WIP: Backends added, Archive backend created

new/src/client/offline_client.rs

@@ -0,0 +1,58 @@
+use crate::config::Config;
+use crate::client::ClientAtBlock;
+use crate::error::OfflineClientAtBlockError;
+use subxt_metadata::Metadata;
+use std::sync::Arc;
+
+#[derive(Clone, Debug)]
+pub struct OfflineClient<T: Config> {
+    /// The configuration for this client.
+    config: T,
+}
+
+impl<T: Config> OfflineClient<T> {
+    /// Create a new [`OfflineClient`] with the given configuration.
+    pub fn new(config: T) -> Self {
+        OfflineClient {
+            config,
+        }
+    }
+
+    /// Pick the block height at which to operate. This references data from the
+    /// [`OfflineClient`] it's called on, and so cannot outlive it.
+    pub fn at(
+        &self,
+        block_number: u32,
+    ) -> Result<ClientAtBlock<OfflineClientAtBlock, T>, OfflineClientAtBlockError> {
+        let spec_version = self
+            .config
+            .spec_version_for_block_number(block_number)
+            .ok_or(OfflineClientAtBlockError::SpecVersionNotFound { block_number })?;
+
+        let metadata = self
+            .config
+            .metadata_for_spec_version(spec_version)
+            .ok_or(OfflineClientAtBlockError::MetadataNotFound { spec_version })?;
+
+        Ok(ClientAtBlock::new(OfflineClientAtBlock {
+            metadata,
+        }))
+    }
+}
+
+pub struct OfflineClientAtBlock {
+    metadata: Arc<Metadata>,
+}
+
+/// This represents an offline-only client at a specific block.
+#[doc(hidden)]
+pub trait OfflineClientAtBlockT {
+    /// Get the metadata appropriate for this block.
+    fn metadata(&self) -> &Metadata;
+}
+
+impl OfflineClientAtBlockT for OfflineClientAtBlock {
+    fn metadata(&self) -> &Metadata {
+        &self.metadata
+    }
+}