import std/[json, nre, os, sequtils, strtabs, strutils]
import docopt

type
  CombinedConfig* = object
    docopt*: Table[string, Value]
    json*: JsonNode

template walkFieldDefs*(t: NimNode, body: untyped) =
  let tTypeImpl = t.getTypeImpl

  var nodeToItr: NimNode
  if tTypeImpl.typeKind == ntyObject: nodeToItr = tTypeImpl[2]
  elif tTypeImpl.typeKind == ntyTypeDesc: nodeToItr = tTypeImpl.getType[1].getType[2]
  else: error $t & " is not an object or type desc (it's a " & $tTypeImpl.typeKind & ")."

  for fieldDef {.inject.} in nodeToItr.children:
    # ignore AST nodes that are not field definitions
    if fieldDef.kind == nnkIdentDefs:
      let fieldIdent {.inject.} = fieldDef[0]
      let fieldType {.inject.} = fieldDef[1]
      body

    elif fieldDef.kind == nnkSym:
      let fieldIdent {.inject.} = fieldDef
      let fieldType {.inject.} = fieldDef.getType
      body


# TODO: Generic config loader
# macro loadConfig*(filePath: string, cfgType: typed, args: Table[string, docopt.Value): untyped =
#   result = newNimNode(nnkObjConstr).(cfgType)
#
#   var idx = 0
#   cfgType.walkFieldDefs:
#     let valLookup = quote do: `getVal`(

proc initCombinedConfig*(
    filename: string,
    docopt: Table[string, Value] = initTable[string, Value]()
  ): CombinedConfig =

  result = CombinedConfig(docopt: docopt, json: parseFile(filename))

proc findConfigFile*(name: string, otherLocations: seq[string] = @[]): string =
  let cfgLocations = @[
    $getEnv(name.strip(chars = {'.'}).toUpper()),
    $getEnv("HOME") / name ] & otherLocations

  result = cfgLocations.foldl(if fileExists(b): b else: a, "")
  if result == "" or not fileExists(result):
    raise newException(ValueError, "could not find configuration file")

proc getVal*(cfg: CombinedConfig, key: string): string =
  let argKey = "--" & key
  let envKey = key.replace('-', '_').toUpper
  let jsonKey = key.replace(re"(-\w)", proc (m: RegexMatch): string = ($m)[1..1].toUpper)

  if cfg.docopt.contains(argKey) and cfg.docopt[argKey]: return $cfg.docopt[argKey]
  elif existsEnv(envKey): return getEnv(envKey)
  elif cfg.json.hasKey(jsonKey):
    let node = cfg.json[jsonKey]
    case node.kind
    of JString: return node.getStr
    of JInt: return $node.getInt
    of JFloat: return $node.getFloat
    of JBool: return $node.getBool
    of JNull: return ""
    of JObject: return $node
    of JArray: return $node
  else: raise newException(ValueError, "cannot find a configuration value for \"" & key & "\"")

proc getVal*(cfg: CombinedConfig, key, default: string): string =
  try: return getVal(cfg, key)
  except: return default

proc getJson*(cfg: CombinedConfig, key: string): JsonNode =
  let argKey = "--" & key
  let envKey = key.replace('-', '_').toUpper
  let jsonKey = key.replace(re"(-\w)", proc (m: RegexMatch): string = ($m)[1..1].toUpper)

  if cfg.docopt.contains(argKey) and cfg.docopt[argKey]: return parseJson($cfg.docopt[argKey])
  elif existsEnv(envKey): return parseJson(getEnv(envKey))
  elif cfg.json.hasKey(jsonKey): return cfg.json[jsonKey]
  else: raise newException(ValueError, "cannot find a configuration value for \"" & key & "\"")

proc getJson*(cfg: CombinedConfig, key: string, default: JsonNode): JsonNode =
  try: return getJson(cfg, key)
  except: return default

proc loadEnv*(): StringTableRef =
  result = newStringTable()

  for k, v in envPairs():
    result[k] = v