interop/block: update documentation, fix GetTransaction

GetTransaction never worked with hash, it works with indexes.

pkg/interop/block/block.go

@@ -1,25 +1,30 @@
+/*
+Package block provides getters for Neo Block structure.
+*/
 package block
 
 import "github.com/nspcc-dev/neo-go/pkg/interop/transaction"
 
-// Package block provides function signatures that can be used inside
-// smart contracts that are written in the neo-go framework.
-
-// Block stubs a NEO block type.
+// Block represents a NEO block, it's an opaque data structure that you can get
+// data from only using functions from this package. It's similar in function to
+// the Block class in the Neo .net framework. To use it you need to get it via
+// blockchain.GetBlock function call.
 type Block struct{}
 
-// GetTransactionCount returns the number of recorded transactions in the given block.
+// GetTransactionCount returns the number of recorded transactions in the given
+// block. It uses `Neo.Block.GetTransactionCount` syscall internally.
 func GetTransactionCount(b Block) int {
 	return 0
 }
 
 // GetTransactions returns a slice of transactions recorded in the given block.
+// It uses `Neo.Block.GetTransactions` syscall internally.
 func GetTransactions(b Block) []transaction.Transaction {
 	return []transaction.Transaction{}
 }
 
-// GetTransaction returns a transaction from the given a block hash of the
-// transaction.
-func GetTransaction(b Block, hash []byte) transaction.Transaction {
+// GetTransaction returns transaction from the given block by its index. It
+// uses `Neo.Block.GetTransaction` syscall internally.
+func GetTransaction(b Block, index int) transaction.Transaction {
 	return transaction.Transaction{}
 }