Add Ormin ORM support for BaraDB (Nim client)

clients/nim/ormin/ormin/dispatcher.nim

@@ -0,0 +1,71 @@
+## This module implements a little helper macro to ease
+## writing the dispatching logic for JSON based servers.
+
+import macros
+
+proc tbody(n: NimNode): NimNode =
+  # transforms::
+  #   f fields(a, "b")
+  # into::
+  #   f  a = %args["a"], b = %args["b"]
+  case n.kind
+  of nnkCallKinds:
+    result = copyNimNode(n)
+    result.add tbody(n[0])
+    for i in 1..<n.len:
+      let it = n[i]
+      if it.kind == nnkCall and $it[0] == "fields":
+        for j in 1..<it.len:
+          let field = it[j]
+          let s = if field.kind in {nnkStrLit..nnkTripleStrLit}: field.strVal
+                  else: $field
+          let arg = newTree(nnkPrefix, ident"%",
+            newTree(nnkBracketExpr, ident"arg", newLit(s)))
+          result.add newTree(nnkExprEqExpr, ident(s), arg)
+      else:
+        result.add tbody(it)
+  else:
+    result = copyNimNode(n)
+    for x in n: result.add tbody(x)
+
+macro createDispatcher*(name, n: untyped): untyped =
+  expectKind n, nnkStmtList
+  result = newStmtList()
+  let disp = newTree(nnkCaseStmt, ident"cmd")
+  template cmdProc(name, body) {.dirty.} =
+    proc name(arg: JsonNode): JsonNode = body
+  template callCmd(name) {.dirty.} =
+    result = name(arg)
+
+  for x in n:
+    if x.kind == nnkCall and x.len == 2 and
+        x[0].kind == nnkIdent and x[1].kind == nnkStmtList:
+      result.add getAst(cmdProc(x[0], tbody x[1]))
+      disp.add newTree(nnkOfBranch, newLit($x[0]),
+                       newStmtList(getAst(callCmd(x[0]))))
+    else:
+      # do not touch:
+      result.add n
+  disp.add newTree(nnkElse, newStmtList(newTree(nnkDiscardStmt, newEmptyNode())))
+
+  template dispatchProc(name, body) {.dirty.} =
+    proc dispatch(inp: JsonNode): JsonNode =
+      let arg = inp["arg"]
+      let cmd = inp["cmd"].getStr("")
+      body
+  result.add getAst(dispatchProc(name, disp))
+  when defined(debugDispatcherDsl):
+    echo repr result
+
+when isMainModule:
+  import json, db_sqlite
+
+  createDispatcher(dispatch):
+    insertCustomer:
+      echo "insert customer", fields(a, b, c)
+      result = arg
+    selectCustomers:
+      echo "select customer"
+      result = arg
+
+  echo dispatch(nil, %*{"cmd": "insertCustomer", "arg": [1, 2, 3]})