Add counters draft client API

Signed-off-by: Tomasz Pietrek <[email protected]>

Author: Jarema

adr/ADR-49.md

@@ -226,31 +226,38 @@ In this case a dedicated light weight Counter client to begin with would be adde
 > This is just an idea at present, the client will be fleshed out later in the development cycle.
 
 ```go
-// Creates a new counter abstraction bound to a Stream
-func NewCounter(stream jetstream.Stream) (Counter, error)
-
-// Parses a messages received from a consumer into a counter entry
-func ParseMessage(msg jetstream.Msg) (Entry, error)
-
-// Entry holds helpers for parsing the values in counters
-type Entry interface {
-	// Value parses the value as a big.Int
-	Value() (big.Int, error)
-	
-// The messages that contributed to the Value
-	Messages() []jetstream.Msg
-}
+``package counters
+
+import "math/big"
 
-// Increments and loads 
 type Counter interface {
-    // Increments a counter by delta
-    func Increment(subject string, value int64) (Entry, error)
-	
-    // Loads the value from the stream subject, options to supply a specific seq/time for example
-    func Load(subject string, opts ...LoadOption) (Entry, error)
-
-    // Loads a group of subjects from the same stream using a direct batch get, performs the
-    // calculation to combine these numbers client side
-    func LoadMulti(subjects []string, opts ...LoadOptions) ([]Entry, error)
+     /// Adds or subtracts a value from the counter, returning the new value.
+	 Add(counter string, value big.Int) (big.Int, error)
+     /// Load retrieves the current value of the counter, using direct get with no headers.
+	 Load(counter string) (big.Int, error)
+     /// LoadMultiple retrieves the current values of multiple counters, using direct get with no headers.
+     /// It allows using wildcards in the counter names.
+	 LoadMultiple(counters []string) (Values, error)
+     /// Get retrieves the current value of a counter, including its sources.
+	 GetEntry(counter string) (Entry, error)
+	 /// GetMany retrieves the current values of multiple counters, including their sources.
+     /// It allows using wildcards in the counter names.
+	 GetEntries(counters []string) (Entries, error)
 }
-```
+
+type Entry struct {
+	Value big.Int
+    // TODO: maybe there is a prettier way to represent the sources.
+    // For now, we're using the server representation.
+	Sources  map[string]map[string]string
+
+}
+
+// Allows iterating over multiple counters values.
+type Values struct {}
+
+
+// Allows iterating over multiple counter Entries.
+type Entries struct {}
+
+`