# HG changeset patch
# User Sam <sam@basx.dev>
# Date 1680630144 -25200
# Node ID 4991475ee27db01b0618682e5a1a56823649ecd4
# Parent  13febe7978e5361618d1f47b6c59b0715d7326ec
add: build- and runtime configuration system with hot-code reload

diff -r 13febe7978e5 -r 4991475ee27d src/semicongine/config.nim
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/semicongine/config.nim	Wed Apr 05 00:42:24 2023 +0700
@@ -0,0 +1,114 @@
+import std/parsecfg
+import std/strutils
+import std/sequtils
+import std/parseutils
+import std/strformat
+import std/tables
+import std/os
+
+
+
+# build configuration
+# =====================
+
+# compile-time defines, usefull for build-dependent settings
+# can be overriden with compiler flags, e.g. -d:Foo=42 -d:Bar=false
+# pramas: {.intdefine.} {.strdefine.} {.booldefine.}
+
+# root of where config files will be searched
+# must be relative (to the directory of the binary)
+const DEBUG = not defined(release)
+const CONFIGROOT {.strdefine.}: string = "."
+assert not isAbsolute(CONFIGROOT)
+
+const CONFIGEXTENSION {.strdefine.}: string = "ini"
+
+# by default enable hot-reload of runtime-configuration only in debug builds
+const CONFIGHOTRELOAD {.booldefine.}: bool = DEBUG
+
+# milliseconds to wait between checks for config hotreload
+const CONFIGHOTRELOADINTERVAL {.intdefine.}: int = 1000
+
+
+when CONFIGHOTRELOAD:
+  var configUpdates: Channel[(string, Config)]
+  configUpdates.open()
+
+# runtime configuration
+# =====================
+# namespace is the path from the CONFIGROOT to the according config file without the file extension
+# a config file must always have the extension CONFIGEXTENSION
+# a fully qualified config identifier can be in the form {namespace}.{section}.{key}
+# {key} and {section} may not contain dots
+
+# a "namespace" is the path from the config root to an *.CONFIGEXTENSION file, without the file extension
+# config is a namespace <-> config mapping
+var theConfig: Table[string, Config]
+
+proc configRoot(): string =
+  joinPath(absolutePath(getAppDir()), CONFIGROOT)
+
+proc getFile(namespace: string): string =
+  joinPath(configRoot(), namespace & "." & CONFIGEXTENSION)
+
+iterator walkConfigNamespaces(): string =
+  for file in walkDirRec(dir=configRoot(), relative=true, checkDir=true):
+    if file.endsWith("." & CONFIGEXTENSION):
+      yield file[0 ..< ^(CONFIGEXTENSION.len + 1)]
+
+proc loadAllConfig(): Table[string, Config] =
+  for ns in walkConfigNamespaces():
+    result[ns] = ns.getFile().loadConfig()
+
+proc configStr(key: string, section="", namespace = ""): string =
+  var ns = namespace
+  if ns == "":
+    ns = "config"
+  when CONFIGHOTRELOAD:
+    while configUpdates.peek() > 0:
+      let (updatedNamespace, updatedConfig) = configUpdates.recv()
+      theConfig[updatedNamespace] = updatedConfig
+  if not theConfig.hasKey(ns):
+    raise newException(Exception, &"Namespace {ns} not found, available namespaces are {theConfig.keys().toSeq}")
+  theConfig[ns].getSectionValue(section, key)
+
+proc config*[T: int|float|string](key: string, section: string, namespace = "config"): T =
+  when T is int:
+    let value = configStr(key, section, namespace)
+    if parseInt(value, result) == 0:
+      raise newException(Exception, &"Unable to parse int from config {namespace}.{section}.{key}: {value}")
+  elif T is float:
+    let value = configStr(key, section, namespace)
+    if parseFloat(value, result) == 0:
+      raise newException(Exception, &"Unable to parse float from config {namespace}.{section}.{key}: {value}")
+  else:
+    result = configStr(key, section, namespace)
+
+proc config*[T: int|float|string](identifier: string): T =
+  # identifier can be in the form:
+  # {key}
+  # {section}.{key}
+  # {namespace}.{section}.{key}
+  let parts = identifier.rsplit(".", maxsplit=2)
+  if parts.len == 1: result = config[T](parts[0], "")
+  elif parts.len == 2: result = config[T](parts[1], parts[0])
+  elif parts.len == 3: result = config[T](parts[2], parts[1], parts[0])
+
+theConfig = loadAllConfig()
+
+when CONFIGHOTRELOAD == true:
+  import std/times
+
+  proc configFileWatchdog() {.thread.} =
+    var configModTimes: Table[string, Time]
+    while true:
+      for namespace in walkConfigNamespaces():
+        if not (namespace in configModTimes):
+          configModTimes[namespace] = Time()
+        let lastMod = namespace.getFile().getLastModificationTime()
+        if lastMod != configModTimes[namespace]:
+          configUpdates.send((namespace, namespace.getFile().loadConfig()))
+      sleep CONFIGHOTRELOADINTERVAL
+  var thethread: Thread[void]
+  createThread(thethread, configFileWatchdog)
+