Add a wait-for-sync.sh script to be used in CI job

from #1127

scripts/wait-for-sync.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+
+set -euo pipefail
+
+# Wait until a node syncs with the rest of the blockchain!
+WAIT_FOR_BLOCK_NUMBER=${1:-0x0}
+RPC_URL=${2:-http://127.0.0.1:9933}
+COUNTER=1
+
+IS_SYNCING="true"
+while [ "$IS_SYNCING" == "true" ]; do
+    echo "INFO: $COUNTER - waiting for sync ..."
+    COUNTER=$((COUNTER + 1))
+    sleep 60
+
+    IS_SYNCING=$(curl --silent "$RPC_URL/health" | jq  -r '.isSyncing')
+done
+echo "INFO: blockchain health reported that it's not syncing anymore!"
+echo "INFO: will start comparing blocks numbers ......"
+
+
+LAST_BLOCK_NUMBER=0x0
+# Bash seems to support hex comparisons if numbers are prefixed wwith 0x
+# https://stackoverflow.com/a/13503150/1431647
+while [[ $LAST_BLOCK_NUMBER -lt $WAIT_FOR_BLOCK_NUMBER ]]; do
+    echo "INFO: Block Number from chain: $LAST_BLOCK_NUMBER < target: $WAIT_FOR_BLOCK_NUMBER"
+    # WARNING: using getBlockHash() instead of getFinalizedBlock() b/c PoW doesn't have finalization
+    LAST_BLOCK=$(curl --silent -H "Content-Type: application/json" \
+                  -d '{"id": 1, "jsonrpc": "2.0", "method": "chain_getBlockHash", "params": [] }' \
+                    "$RPC_URL" | jq -r '.result'
+    )
+
+    LAST_BLOCK_NUMBER=$(curl --silent -H "Content-Type: application/json" \
+         -d "{\"id\": 1, \"jsonrpc\": \"2.0\", \"method\": \"chain_getBlock\", \"params\": [\"$LAST_BLOCK\"] }" \
+        "$RPC_URL" | jq -r '.result.block.header.number')
+
+    if [ "$LAST_BLOCK_NUMBER" == "null" ]; then
+        LAST_BLOCK_NUMBER="0x0"
+        echo "INFO: retry fetching block info for $LAST_BLOCK"
+    fi
+
+    sleep 60
+done
+
+echo "DONE: node is fully in sync"
+echo "INFO: Block Number from chain: $LAST_BLOCK_NUMBER; target: $WAIT_FOR_BLOCK_NUMBER"
+
+exit 0