import
  std/[options, strutils, wordwrap],
  stew/shims/macros,
  confutils/[defs, cli_parser, config_file]

export
  defs, config_file, options

const
  useBufferedOutput = defined(nimscript)
  noColors = useBufferedOutput or defined(confutils_no_colors)
  hasCompletions = not defined(nimscript)
  descPadding = 6
  minNameWidth =  24 - descPadding

when not defined(nimscript):
  import
    os, terminal,
    confutils/shell_completion

type
  HelpAppInfo = ref object
    appInvocation: string
    copyrightBanner: string
    hasAbbrs: bool
    maxNameLen: int
    terminalWidth: int
    namesWidth: int

  CmdInfo = ref object
    name: string
    desc: string
    isHidden: bool
    opts: seq[OptInfo]

  OptKind = enum
    Discriminator
    CliSwitch
    Arg

  OptInfo = ref object
    name, abbr, desc, typename: string
    idx: int
    isHidden: bool
    defaultValue: string
    case kind: OptKind
    of Discriminator:
      isCommand: bool
      isImplicitlySelectable: bool
      subCmds: seq[CmdInfo]
      defaultSubCmd: int
    else:
      discard

const
  confutils_description_width {.intdefine.} = 80
  confutils_narrow_terminal_width {.intdefine.} = 36

proc getFieldName(caseField: NimNode): NimNode =
  result = caseField
  if result.kind == nnkIdentDefs: result = result[0]
  if result.kind == nnkPragmaExpr: result = result[0]
  if result.kind == nnkPostfix: result = result[1]

when defined(nimscript):
  func scriptNameParamIdx: int =
    for i in 1 ..< paramCount():
      var param = paramStr(i)
      if param.len > 0 and param[0] != '-':
        return i

  proc appInvocation: string =
    let scriptNameIdx = scriptNameParamIdx()
    "nim " & (if paramCount() > scriptNameIdx: paramStr(scriptNameIdx) else: "<nims-script>")

  type stderr = object

  template writeLine(T: type stderr, msg: string) =
    echo msg

  proc commandLineParams(): seq[string] =
    for i in scriptNameParamIdx() + 1 .. paramCount():
      result.add paramStr(i)

  # TODO: Why isn't this available in NimScript?
  proc getCurrentExceptionMsg(): string =
    ""

  template terminalWidth: int =
    100000

else:
  template appInvocation: string =
    getAppFilename().splitFile.name

when noColors:
  const
    styleBright = ""
    fgYellow = ""
    fgWhite = ""
    fgGreen = ""
    fgCyan = ""
    fgBlue = ""
    resetStyle = ""

when useBufferedOutput:
  template helpOutput(args: varargs[string]) =
    for arg in args:
      help.add arg

  template errorOutput(args: varargs[string]) =
    helpOutput(args)

  template flushOutput =
    echo help

else:
  template errorOutput(args: varargs[untyped]) =
    styledWrite stderr, args

  template helpOutput(args: varargs[untyped]) =
    styledWrite stdout, args

  template flushOutput =
    discard

const
  fgSection = fgYellow
  fgDefault = fgWhite
  fgCommand = fgCyan
  fgOption = fgBlue
  fgArg = fgBlue

  # TODO: Start using these:
  # fgValue = fgGreen
  # fgType = fgYellow

template flushOutputAndQuit(exitCode: int) =
  flushOutput
  quit exitCode

func isCliSwitch(opt: OptInfo): bool =
  opt.kind == CliSwitch or
  (opt.kind == Discriminator and opt.isCommand == false)

func hasOpts(cmd: CmdInfo): bool =
  for opt in cmd.opts:
    if opt.isCliSwitch and not opt.isHidden:
      return true

  return false

func hasArgs(cmd: CmdInfo): bool =
  cmd.opts.len > 0 and cmd.opts[^1].kind == Arg

func firstArgIdx(cmd: CmdInfo): int =
  # This will work correctly only if the command has arguments.
  result = cmd.opts.len - 1
  while result > 0:
    if cmd.opts[result - 1].kind != Arg:
      return
    dec result

iterator args(cmd: CmdInfo): OptInfo =
  if cmd.hasArgs:
    for i in cmd.firstArgIdx ..< cmd.opts.len:
      yield cmd.opts[i]

func getSubCmdDiscriminator(cmd: CmdInfo): OptInfo =
  for i in countdown(cmd.opts.len - 1, 0):
    let opt = cmd.opts[i]
    if opt.kind != Arg:
      if opt.kind == Discriminator and opt.isCommand:
        return opt
      else:
        return nil

template hasSubCommands(cmd: CmdInfo): bool =
  getSubCmdDiscriminator(cmd) != nil

iterator subCmds(cmd: CmdInfo): CmdInfo =
  let subCmdDiscriminator = cmd.getSubCmdDiscriminator
  if subCmdDiscriminator != nil:
    for cmd in subCmdDiscriminator.subCmds:
      yield cmd

template isSubCommand(cmd: CmdInfo): bool =
  cmd.name.len > 0

func maxNameLen(cmd: CmdInfo): int =
  result = 0
  for opt in cmd.opts:
    if opt.kind == Arg or opt.kind == Discriminator and opt.isCommand:
      continue
    result = max(result, opt.name.len)
    if opt.kind == Discriminator:
      for subCmd in opt.subCmds:
        result = max(result, subCmd.maxNameLen)

func hasAbbrs(cmd: CmdInfo): bool =
  for opt in cmd.opts:
    if opt.kind == Arg or opt.kind == Discriminator and opt.isCommand:
      continue
    if opt.abbr.len > 0:
      return true
    if opt.kind == Discriminator:
      for subCmd in opt.subCmds:
        if hasAbbrs(subCmd):
          return true

template hasDefault(opt: OptInfo): bool =
  opt.defaultValue.len > 0

func humaneName(opt: OptInfo): string =
  if opt.name.len > 0: opt.name
  else: opt.abbr

template padding(output: string, desiredWidth: int): string =
  spaces(max(desiredWidth - output.len, 0))

proc writeDesc(help: var string,
               appInfo: HelpAppInfo,
               desc, defaultValue: string) =
  const descSpacing = "  "
  let
    descIndent = (5 + appInfo.namesWidth + descSpacing.len)
    remainingColumns = appInfo.terminalWidth - descIndent
    defaultValSuffix = if defaultValue.len == 0: ""
                       else: " [=" & defaultValue & "]"
    fullDesc = desc & defaultValSuffix & "."

  if remainingColumns < confutils_narrow_terminal_width:
    helpOutput "\p ", wrapWords(fullDesc, appInfo.terminalWidth - 2,
                                newLine = "\p ")
  else:
    let wrappingWidth = min(remainingColumns, confutils_description_width)
    helpOutput descSpacing, wrapWords(fullDesc, wrappingWidth,
                                      newLine = "\p" & spaces(descIndent))

proc describeInvocation(help: var string,
                        cmd: CmdInfo, cmdInvocation: string,
                        appInfo: HelpAppInfo) =
  helpOutput styleBright, "\p", fgCommand, cmdInvocation
  var longestArg = 0

  if cmd.opts.len > 0:
    if cmd.hasOpts: helpOutput " [OPTIONS]..."

    let subCmdDiscriminator = cmd.getSubCmdDiscriminator
    if subCmdDiscriminator != nil: helpOutput " command"

    for arg in cmd.args:
      helpOutput " <", arg.name, ">"
      longestArg = max(longestArg, arg.name.len)

  helpOutput "\p"

  if cmd.desc.len > 0:
    helpOutput "\p", cmd.desc, ".\p"

  var argsSectionStarted = false

  for arg in cmd.args:
    if arg.desc.len > 0:
      if not argsSectionStarted:
        helpOutput "\p"
        argsSectionStarted = true

      let cliArg = " <" & arg.humaneName & ">"
      helpOutput fgArg, styleBright, cliArg
      helpOutput padding(cliArg, 6 + appInfo.namesWidth)
      help.writeDesc appInfo, arg.desc, arg.defaultValue
      helpOutput "\p"

type
  OptionsType = enum
    normalOpts
    defaultCmdOpts
    conditionalOpts

proc describeOptions(help: var string,
                     cmd: CmdInfo, cmdInvocation: string,
                     appInfo: HelpAppInfo, optionsType = normalOpts) =
  if cmd.hasOpts:
    case optionsType
    of normalOpts:
      helpOutput "\pThe following options are available:\p\p"
    of conditionalOpts:
      helpOutput ", the following additional options are available:\p\p"
    of defaultCmdOpts:
      discard

    for opt in cmd.opts:
      if opt.kind == Arg or
         opt.kind == Discriminator or
         opt.isHidden: continue

      # Indent all command-line switches
      helpOutput " "

      if opt.abbr.len > 0:
        helpOutput fgOption, styleBright, "-", opt.abbr, ", "
      elif appInfo.hasAbbrs:
        # Add additional indentatition, so all names are aligned
        helpOutput "    "

      if opt.name.len > 0:
        let switch = "--" & opt.name
        helpOutput fgOption, styleBright,
                   switch, padding(switch, appInfo.namesWidth)
      else:
        helpOutput spaces(2 + appInfo.namesWidth)

      if opt.desc.len > 0:
        help.writeDesc appInfo,
                       opt.desc.replace("%t", opt.typename),
                       opt.defaultValue

      helpOutput "\p"

      if opt.kind == Discriminator:
        for i, subCmd in opt.subCmds:
          if not subCmd.hasOpts: continue

          helpOutput "\pWhen ", styleBright, fgBlue, opt.humaneName, resetStyle, " = ", fgGreen, subCmd.name

          if i == opt.defaultSubCmd: helpOutput " (default)"
          help.describeOptions subCmd, cmdInvocation, appInfo, conditionalOpts

  let subCmdDiscriminator = cmd.getSubCmdDiscriminator
  if subCmdDiscriminator != nil:
    let defaultCmdIdx = subCmdDiscriminator.defaultSubCmd
    if defaultCmdIdx != -1:
      let defaultCmd = subCmdDiscriminator.subCmds[defaultCmdIdx]
      help.describeOptions defaultCmd, cmdInvocation, appInfo, defaultCmdOpts

    helpOutput fgSection, "\pAvailable sub-commands:\p"

    for i, subCmd in subCmdDiscriminator.subCmds:
      if i != subCmdDiscriminator.defaultSubCmd:
        let subCmdInvocation = cmdInvocation & " " & subCmd.name
        help.describeInvocation subCmd, subCmdInvocation, appInfo
        help.describeOptions subCmd, subCmdInvocation, appInfo

proc showHelp(help: var string,
              appInfo: HelpAppInfo,
              activeCmds: openarray[CmdInfo]) =
  if appInfo.copyrightBanner.len > 0:
    helpOutput appInfo.copyrightBanner, "\p\p"

  let cmd = activeCmds[^1]

  appInfo.maxNameLen = cmd.maxNameLen
  appInfo.hasAbbrs = cmd.hasAbbrs
  appInfo.terminalWidth = terminalWidth()
  appInfo.namesWidth = min(minNameWidth, appInfo.maxNameLen) + descPadding

  var cmdInvocation = appInfo.appInvocation
  for i in 1 ..< activeCmds.len:
    cmdInvocation.add " "
    cmdInvocation.add activeCmds[i].name

  # Write out the app or script name
  helpOutput fgSection, "Usage: \p"
  help.describeInvocation cmd, cmdInvocation, appInfo
  help.describeOptions cmd, cmdInvocation, appInfo
  helpOutput "\p"

  flushOutputAndQuit QuitSuccess

func getNextArgIdx(cmd: CmdInfo, consumedArgIdx: int): int =
  for i in consumedArgIdx + 1 ..< cmd.opts.len:
    if cmd.opts[i].kind == Arg:
      return cmd.opts[i].idx

  return -1

proc noMoreArgsError(cmd: CmdInfo): string =
  result = if cmd.isSubCommand: "The command '$1'" % [cmd.name]
           else: appInvocation()
  result.add " does not accept"
  if cmd.hasArgs: result.add " additional"
  result.add " arguments"

proc findOpt(opts: openarray[OptInfo], name: string): OptInfo =
  for opt in opts:
    if cmpIgnoreStyle(opt.name, name) == 0 or
       cmpIgnoreStyle(opt.abbr, name) == 0:
      return opt

proc findOpt(activeCmds: openarray[CmdInfo], name: string): OptInfo =
  for i in countdown(activeCmds.len - 1, 0):
    let found = findOpt(activeCmds[i].opts, name)
    if found != nil: return found

proc findCmd(cmds: openarray[CmdInfo], name: string): CmdInfo =
  for cmd in cmds:
    if cmpIgnoreStyle(cmd.name, name) == 0:
      return cmd

proc findSubCmd(cmd: CmdInfo, name: string): CmdInfo =
  let subCmdDiscriminator = cmd.getSubCmdDiscriminator
  if subCmdDiscriminator != nil:
    let cmd = findCmd(subCmdDiscriminator.subCmds, name)
    if cmd != nil: return cmd

  return nil

proc startsWithIgnoreStyle(s: string, prefix: string): bool =
  # Similar in spirit to cmpIgnoreStyle, but compare only the prefix.
  var i = 0
  var j = 0

  while true:
    # Skip any underscore
    while i < s.len and s[i] == '_': inc i
    while j < prefix.len and prefix[j] == '_': inc j

    if j == prefix.len:
      # The whole prefix matches
      return true
    elif i == s.len:
      # We've reached the end of `s` without matching the prefix
      return false
    elif toLowerAscii(s[i]) != toLowerAscii(prefix[j]):
      return false

    inc i
    inc j

when defined(debugCmdTree):
  proc printCmdTree(cmd: CmdInfo, indent = 0) =
    let blanks = spaces(indent)
    echo blanks, "> ", cmd.name

    for opt in cmd.opts:
      if opt.kind == Discriminator:
        for subcmd in opt.subCmds:
          printCmdTree(subcmd, indent + 2)
      else:
        echo blanks, "  - ", opt.name, ": ", opt.typename

else:
  template printCmdTree(cmd: CmdInfo) = discard

# TODO remove the overloads here to get better "missing overload" error message
proc parseCmdArg*(T: type InputDir, p: TaintedString): T =
  if not dirExists(p.string):
    raise newException(ValueError, "Directory doesn't exist")

  result = T(p)

proc parseCmdArg*(T: type InputFile, p: TaintedString): T =
  # TODO this is needed only because InputFile cannot be made
  # an alias of TypedInputFile at the moment, because of a generics
  # caching issue
  if not fileExists(p.string):
    raise newException(ValueError, "File doesn't exist")

  when not defined(nimscript):
    try:
      let f = system.open(p.string, fmRead)
      close f
    except IOError:
      raise newException(ValueError, "File not accessible")

  result = T(p.string)

proc parseCmdArg*(T: type TypedInputFile, p: TaintedString): T =
  var path = p.string
  when T.defaultExt.len > 0:
    path = path.addFileExt(T.defaultExt)

  if not fileExists(path):
    raise newException(ValueError, "File doesn't exist")

  when not defined(nimscript):
    try:
      let f = system.open(path, fmRead)
      close f
    except IOError:
      raise newException(ValueError, "File not accessible")

  result = T(path)

proc parseCmdArg*(T: type[OutDir|OutFile|OutPath], p: TaintedString): T =
  result = T(p)

proc parseCmdArg*[T](_: type Option[T], s: TaintedString): Option[T] =
  return some(parseCmdArg(T, s))

template parseCmdArg*(T: type string, s: TaintedString): string =
  string s

proc parseCmdArg*(T: type SomeSignedInt, s: TaintedString): T =
  T parseInt(string s)

proc parseCmdArg*(T: type SomeUnsignedInt, s: TaintedString): T =
  T parseUInt(string s)

proc parseCmdArg*(T: type SomeFloat, p: TaintedString): T =
  result = parseFloat(p)

proc parseCmdArg*(T: type bool, p: TaintedString): T =
  try:
    result = p.len == 0 or parseBool(p)
  except CatchableError:
    raise newException(ValueError, "'" & p.string & "' is not a valid boolean value. Supported values are on/off, yes/no, true/false or 1/0")

proc parseCmdArg*(T: type enum, s: TaintedString): T =
  parseEnum[T](string(s))

proc parseCmdArgAux(T: type, s: TaintedString): T = # {.raises: [ValueError].} =
  # The parseCmdArg procs are allowed to raise only `ValueError`.
  # If you have provided your own specializations, please handle
  # all other exception types.
  mixin parseCmdArg
  parseCmdArg(T, s)

proc completeCmdArg*(T: type enum, val: TaintedString): seq[string] =
  for e in low(T)..high(T):
    let as_str = $e
    if startsWithIgnoreStyle(as_str, val):
      result.add($e)

proc completeCmdArg*(T: type SomeNumber, val: TaintedString): seq[string] =
  return @[]

proc completeCmdArg*(T: type bool, val: TaintedString): seq[string] =
  return @[]

proc completeCmdArg*(T: type string, val: TaintedString): seq[string] =
  return @[]

proc completeCmdArg*(T: type[InputFile|TypedInputFile|InputDir|OutFile|OutDir|OutPath],
                     val: TaintedString): seq[string] =
  when not defined(nimscript):
    let (dir, name, ext) = splitFile(val)
    let tail = name & ext
    # Expand the directory component for the directory walker routine
    let dir_path = if dir == "": "." else: expandTilde(dir)
    # Dotfiles are hidden unless the user entered a dot as prefix
    let show_dotfiles = len(name) > 0 and name[0] == '.'

    try:
      for kind, path in walkDir(dir_path, relative=true):
        if not show_dotfiles and path[0] == '.':
          continue

        # Do not show files if asked for directories, on the other hand we must show
        # directories even if a file is requested to allow the user to select a file
        # inside those
        if type(T) is (InputDir or OutDir) and kind notin {pcDir, pcLinkToDir}:
          continue

        # Note, no normalization is needed here
        if path.startsWith(tail):
          var match = dir_path / path
          # Add a trailing slash so that completions can be chained
          if kind in {pcDir, pcLinkToDir}:
            match &= DirSep

          result.add(shellPathEscape(match))
    except OSError:
      discard

proc completeCmdArg*[T](_: type seq[T], val: TaintedString): seq[string] =
  return @[]

proc completeCmdArg*[T](_: type Option[T], val: TaintedString): seq[string] =
  mixin completeCmdArg
  return completeCmdArg(type(T), val)

proc completeCmdArgAux(T: type, val: TaintedString): seq[string] =
  mixin completeCmdArg
  return completeCmdArg(T, val)

template setField[T](loc: var T, val: Option[TaintedString], defaultVal: untyped) =
  type FieldType = type(loc)
  loc = if isSome(val): parseCmdArgAux(FieldType, val.get)
        else: FieldType(defaultVal)

template setField[T](loc: var seq[T], val: Option[TaintedString], defaultVal: untyped) =
  if val.isSome:
    loc.add parseCmdArgAux(type(loc[0]), val.get)
  else:
    type FieldType = type(loc)
    loc = FieldType(defaultVal)

proc makeDefaultValue*(T: type): T =
  discard

proc requiresInput*(T: type): bool =
  not ((T is seq) or (T is Option) or (T is bool))

proc acceptsMultipleValues*(T: type): bool =
  T is seq

template debugMacroResult(macroName: string) {.dirty.} =
  when defined(debugMacros) or defined(debugConfutils):
    echo "\n-------- ", macroName, " ----------------------"
    echo result.repr

proc generateFieldSetters(RecordType: NimNode): NimNode =
  var recordDef = getImpl(RecordType)
  let makeDefaultValue = bindSym"makeDefaultValue"

  result = newTree(nnkStmtListExpr)
  var settersArray = newTree(nnkBracket)

  for field in recordFields(recordDef):
    var
      setterName = ident($field.name & "Setter")
      fieldName = field.name
      namePragma = field.readPragma"name"
      paramName = if namePragma != nil: namePragma
                  else: fieldName
      configVar = ident "config"
      configField = newTree(nnkDotExpr, configVar, fieldName)
      defaultValue = field.readPragma"defaultValue"
      completerName = ident($field.name & "Complete")

    if defaultValue == nil:
      defaultValue = newCall(makeDefaultValue, newTree(nnkTypeOfExpr, configField))

    # TODO: This shouldn't be necessary. The type symbol returned from Nim should
    # be typed as a tyTypeDesc[tyString] instead of just `tyString`. To be filed.
    var fixedFieldType = newTree(nnkTypeOfExpr, field.typ)

    settersArray.add newTree(nnkTupleConstr,
                             newLit($paramName),
                             setterName, completerName,
                             newCall(bindSym"requiresInput", fixedFieldType),
                             newCall(bindSym"acceptsMultipleValues", fixedFieldType))

    result.add quote do:
      proc `completerName`(val: TaintedString): seq[string] {.
        nimcall
        gcsafe
        sideEffect
        raises: [Defect]
      .} =
        return completeCmdArgAux(`fixedFieldType`, val)

      proc `setterName`(`configVar`: var `RecordType`, val: Option[TaintedString]) {.
        nimcall
        gcsafe
        sideEffect
        raises: [Defect, CatchableError]
      .} =
        when `configField` is enum:
          # TODO: For some reason, the normal `setField` rejects enum fields
          # when they are used as case discriminators. File this as a bug.
          if isSome(val):
            `configField` = parseEnum[type(`configField`)](string(val.get))
          else:
            `configField` = `defaultValue`
        else:
          setField(`configField`, val, `defaultValue`)

  result.add settersArray
  debugMacroResult "Field Setters"

proc cmdInfoFromType(T: NimNode): CmdInfo =
  result = CmdInfo()

  var
    recordDef = getImpl(T)
    discriminatorFields = newSeq[OptInfo]()
    fieldIdx = 0

  for field in recordFields(recordDef):
    let
      isImplicitlySelectable = field.readPragma"implicitlySelectable" != nil
      defaultValue = field.readPragma"defaultValue"
      defaultValueDesc = field.readPragma"defaultValueDesc"
      defaultValueOnScreen = if defaultValueDesc != nil: defaultValueDesc
                             else: defaultValue
      isHidden = field.readPragma("hidden") != nil
      abbr = field.readPragma"abbr"
      name = field.readPragma"name"
      desc = field.readPragma"desc"
      optKind = if field.isDiscriminator: Discriminator
                elif field.readPragma("argument") != nil: Arg
                else: CliSwitch

    var opt = OptInfo(kind: optKind,
                      idx: fieldIdx,
                      name: $field.name,
                      isHidden: isHidden,
                      defaultValue: if defaultValueOnScreen == nil: ""
                                    elif defaultValueOnScreen.kind in {nnkStrLit..nnkTripleStrLit}: defaultValueOnScreen.strVal
                                    else: repr(defaultValueOnScreen),
                      typename: field.typ.repr)

    if desc != nil: opt.desc = desc.strVal
    if name != nil: opt.name = name.strVal
    if abbr != nil: opt.abbr = abbr.strVal

    inc fieldIdx

    if field.isDiscriminator:
      discriminatorFields.add opt
      let cmdType = field.typ.getImpl[^1]
      if cmdType.kind != nnkEnumTy:
        error "Only enums are supported as case object discriminators", field.name

      opt.isImplicitlySelectable = isImplicitlySelectable
      opt.isCommand = field.readPragma"command" != nil

      for i in 1 ..< cmdType.len:
        let enumVal = cmdType[i]
        var name, desc: string
        if enumVal.kind == nnkEnumFieldDef:
          name = $enumVal[0]
          desc = $enumVal[1]
        else:
          name = $enumVal
        if defaultValue != nil and eqIdent(name, defaultValue):
          opt.defaultSubCmd = i - 1
        opt.subCmds.add CmdInfo(name: name, desc: desc)

      if defaultValue == nil:
        opt.defaultSubCmd = -1
      else:
        if opt.defaultSubCmd == -1:
          error "The default value is not a valid enum value", defaultValue

    if field.caseField != nil and field.caseBranch != nil:
      let fieldName = field.caseField.getFieldName
      var discriminator = findOpt(discriminatorFields, $fieldName)

      if discriminator == nil:
        error "Unable to find " & $fieldName

      if field.caseBranch.kind == nnkElse:
        error "Sub-command parameters cannot appear in an else branch. " &
              "Please specify the sub-command branch precisely", field.caseBranch[0]

      var branchEnumVal = field.caseBranch[0]
      if branchEnumVal.kind == nnkDotExpr:
        branchEnumVal = branchEnumVal[1]
      var cmd = findCmd(discriminator.subCmds, $branchEnumVal)
      cmd.opts.add opt

    else:
      result.opts.add opt

macro configurationRtti(RecordType: type): untyped =
  let
    T = RecordType.getType[1]
    cmdInfo = cmdInfoFromType T
    fieldSetters = generateFieldSetters T

  result = newTree(nnkPar, newLitFixed cmdInfo, fieldSetters)

proc load*(Configuration: type,
           cmdLine = commandLineParams(),
           version = "",
           copyrightBanner = "",
           printUsage = true,
           quitOnFailure = true): Configuration =
  ## Loads a program configuration by parsing command-line arguments
  ## and a standard set of config files that can specify:
  ##
  ##  - working directory settings
  ##  - user settings
  ##  - system-wide setttings
  ##
  ##  Supports multiple config files format (INI/TOML, YAML, JSON).

  # This is an initial naive implementation that will be improved
  # over time.

  # users can override default `appendConfigFileFormats`
  # `appName`, and `vendorName`
  mixin appendConfigFileFormats
  mixin appName, vendorName
  appendConfigFileFormats(Configuration)

  let (rootCmd, fieldSetters) = configurationRtti(Configuration)
  var fieldCounters: array[fieldSetters.len, int]
  let configFile = configFile(Configuration)

  printCmdTree rootCmd

  let confAddr = addr result
  var activeCmds = @[rootCmd]
  template lastCmd: auto = activeCmds[^1]
  var nextArgIdx = lastCmd.getNextArgIdx(-1)

  var help = ""

  proc suggestCallingHelp =
    errorOutput "Try ", fgCommand, ("$1 --help" % appInvocation())
    errorOutput " for more information.\p"
    flushOutputAndQuit QuitFailure

  template fail(args: varargs[untyped]) =
    if quitOnFailure:
      errorOutput args
      errorOutput "\p"
      suggestCallingHelp()
    else:
      # TODO: populate this string
      raise newException(ConfigurationError, "")

  template applySetter(setterIdx: int, cmdLineVal: TaintedString) =
    try:
      fieldSetters[setterIdx][1](confAddr[], some(cmdLineVal))
      inc fieldCounters[setterIdx]
    except:
      fail("Error while processing the ",
           fgOption, fieldSetters[setterIdx][0],
           "=", cmdLineVal.string, resetStyle, " parameter: ",
           getCurrentExceptionMsg())

  when hasCompletions:
    template getArgCompletions(opt: OptInfo, prefix: TaintedString): seq[string] =
      fieldSetters[opt.idx][2](prefix)

  template required(opt: OptInfo): bool =
    fieldSetters[opt.idx][3] and not opt.hasDefault

  proc processMissingOpts(conf: var Configuration, cmd: CmdInfo) =
    for opt in cmd.opts:
      if fieldCounters[opt.idx] == 0:
        if opt.required:
          fail "The required option '$1' was not specified" % [opt.name]
        elif configFile.setters[opt.idx](conf, configFile):
          # all work is done in the config file setter,
          # there is nothing left to do here.
          discard
        elif opt.hasDefault:
          fieldSetters[opt.idx][1](conf, none[TaintedString]())

  template activateCmd(discriminator: OptInfo, activatedCmd: CmdInfo) =
    let cmd = activatedCmd
    applySetter(discriminator.idx, if cmd.desc.len > 0: TaintedString(cmd.desc)
                                   else: TaintedString(cmd.name))
    activeCmds.add cmd
    nextArgIdx = cmd.getNextArgIdx(-1)

  when hasCompletions:
    type
      ArgKindFilter = enum
        argName
        argAbbr

    proc showMatchingOptions(cmd: CmdInfo, prefix: string, filterKind: set[ArgKindFilter]) =
      var matchingOptions: seq[OptInfo]

      if len(prefix) > 0:
        # Filter the options according to the input prefix
        for opt in cmd.opts:
          if argName in filterKind and len(opt.name) > 0:
            if startsWithIgnoreStyle(opt.name, prefix):
              matchingOptions.add(opt)
          if argAbbr in filterKind and len(opt.abbr) > 0:
            if startsWithIgnoreStyle(opt.abbr, prefix):
              matchingOptions.add(opt)
      else:
        matchingOptions = cmd.opts

      for opt in matchingOptions:
        # The trailing '=' means the switch accepts an argument
        let trailing = if opt.typename != "bool": "=" else: ""

        if argName in filterKind and len(opt.name) > 0:
          stdout.writeLine("--", opt.name, trailing)
        if argAbbr in filterKind and len(opt.abbr) > 0:
          stdout.writeLine('-', opt.abbr, trailing)

    let completion = splitCompletionLine()
    # If we're not asked to complete a command line the result is an empty list
    if len(completion) != 0:
      var cmdStack = @[rootCmd]
      # Try to understand what the active chain of commands is without parsing the
      # whole command line
      for tok in completion[1..^1]:
        if not tok.startsWith('-'):
          let subCmd = findSubCmd(cmdStack[^1], tok)
          if subCmd != nil: cmdStack.add(subCmd)

      let cur_word = completion[^1]
      let prev_word = if len(completion) > 2: completion[^2] else: ""
      let prev_prev_word = if len(completion) > 3: completion[^3] else: ""

      if cur_word.startsWith('-'):
        # Show all the options matching the prefix input by the user
        let isFullName = cur_word.startsWith("--")
        var option_word = cur_word
        option_word.removePrefix('-')

        for i in countdown(cmdStack.len - 1, 0):
          let argFilter =
            if isFullName:
              {argName}
            elif len(cur_word) > 1:
              # If the user entered a single hypen then we show both long & short
              # variants
              {argAbbr}
            else:
              {argName, argAbbr}

          showMatchingOptions(cmdStack[i], option_word, argFilter)
      elif (prev_word.startsWith('-') or
          (prev_word == "=" and prev_prev_word.startsWith('-'))):
        # Handle cases where we want to complete a switch choice
        # -switch
        # -switch=
        var option_word = if len(prev_word) == 1: prev_prev_word else: prev_word
        option_word.removePrefix('-')

        let opt = findOpt(cmdStack, option_word)
        if opt != nil:
          for arg in getArgCompletions(opt, cur_word):
            stdout.writeLine(arg)
      elif cmdStack[^1].hasSubCommands:
        # Show all the available subcommands
        for subCmd in subCmds(cmdStack[^1]):
          if startsWithIgnoreStyle(subCmd.name, cur_word):
            stdout.writeLine(subCmd.name)
      else:
        # Full options listing
        for i in countdown(cmdStack.len - 1, 0):
          showMatchingOptions(cmdStack[i], "", {argName, argAbbr})

      stdout.flushFile()

      return

  proc lazyHelpAppInfo: HelpAppInfo =
    HelpAppInfo(
      copyrightBanner: copyrightBanner,
      appInvocation: appInvocation())

  template processHelpAndVersionOptions(optKey: string) =
    let key = optKey
    if cmpIgnoreStyle(key, "help") == 0:
      help.showHelp lazyHelpAppInfo(), activeCmds
    elif version.len > 0 and cmpIgnoreStyle(key, "version") == 0:
      help.helpOutput version, "\p"
      flushOutputAndQuit QuitSuccess

  for kind, key, val in getopt(cmdLine):
    let key = string(key)
    case kind
    of cmdLongOption, cmdShortOption:
      processHelpAndVersionOptions key

      var opt = findOpt(activeCmds, key)
      if opt == nil:
        # We didn't find the option.
        # Check if it's from the default command and activate it if necessary:
        let subCmdDiscriminator = lastCmd.getSubCmdDiscriminator
        if subCmdDiscriminator != nil:
          if subCmdDiscriminator.defaultSubCmd != -1:
            let defaultCmd = subCmdDiscriminator.subCmds[subCmdDiscriminator.defaultSubCmd]
            opt = findOpt(defaultCmd.opts, key)
            if opt != nil:
              activateCmd(subCmdDiscriminator, defaultCmd)
          else:
            discard

      if opt != nil:
        applySetter(opt.idx, val)
      else:
        fail "Unrecognized option '$1'" % [key]

    of cmdArgument:
      if lastCmd.hasSubCommands:
        processHelpAndVersionOptions key

      block processArg:
        let subCmdDiscriminator = lastCmd.getSubCmdDiscriminator
        if subCmdDiscriminator != nil:
          let subCmd = findCmd(subCmdDiscriminator.subCmds, key)
          if subCmd != nil:
            activateCmd(subCmdDiscriminator, subCmd)
            break processArg

        if nextArgIdx == -1:
          fail lastCmd.noMoreArgsError

        applySetter(nextArgIdx, key)

        if not fieldSetters[nextArgIdx][4]:
          nextArgIdx = lastCmd.getNextArgIdx(nextArgIdx)

    else:
      discard

  let subCmdDiscriminator = lastCmd.getSubCmdDiscriminator
  if subCmdDiscriminator != nil and
     subCmdDiscriminator.defaultSubCmd != -1 and
     fieldCounters[subCmdDiscriminator.idx] == 0:
    let defaultCmd = subCmdDiscriminator.subCmds[subCmdDiscriminator.defaultSubCmd]
    activateCmd(subCmdDiscriminator, defaultCmd)

  for cmd in activeCmds:
    result.processMissingOpts(cmd)

proc defaults*(Configuration: type): Configuration =
  load(Configuration, cmdLine = @[], printUsage = false, quitOnFailure = false)

proc dispatchImpl(cliProcSym, cliArgs, loadArgs: NimNode): NimNode =
  # Here, we'll create a configuration object with fields matching
  # the CLI proc params. We'll also generate a call to the designated proc
  let configType = genSym(nskType, "CliConfig")
  let configFields = newTree(nnkRecList)
  let configVar = genSym(nskLet, "config")
  var dispatchCall = newCall(cliProcSym)

  # The return type of the proc is skipped over
  for i in 1 ..< cliArgs.len:
    var arg = copy cliArgs[i]

    # If an argument doesn't specify a type, we infer it from the default value
    if arg[1].kind == nnkEmpty:
      if arg[2].kind == nnkEmpty:
        error "Please provide either a default value or type of the parameter", arg
      arg[1] = newCall(bindSym"typeof", arg[2])

    # Turn any default parameters into the confutils's `defaultValue` pragma
    if arg[2].kind != nnkEmpty:
      if arg[0].kind != nnkPragmaExpr:
        arg[0] = newTree(nnkPragmaExpr, arg[0], newTree(nnkPragma))
      arg[0][1].add newColonExpr(bindSym"defaultValue", arg[2])
      arg[2] = newEmptyNode()

    configFields.add arg
    dispatchCall.add newTree(nnkDotExpr, configVar, skipPragma arg[0])

  let cliConfigType = nnkTypeSection.newTree(
    nnkTypeDef.newTree(
      configType,
      newEmptyNode(),
      nnkObjectTy.newTree(
        newEmptyNode(),
        newEmptyNode(),
        configFields)))

  var loadConfigCall = newCall(bindSym"load", configType)
  for p in loadArgs: loadConfigCall.add p

  result = quote do:
    `cliConfigType`
    let `configVar` = `loadConfigCall`
    `dispatchCall`

macro dispatch*(fn: typed, args: varargs[untyped]): untyped =
  if fn.kind != nnkSym or
     fn.symKind notin {nskProc, nskFunc, nskMacro, nskTemplate}:
    error "The first argument to `confutils.dispatch` should be a callable symbol"

  let fnImpl = fn.getImpl
  result = dispatchImpl(fnImpl.name, fnImpl.params, args)
  debugMacroResult "Dispatch Code"

macro cli*(args: varargs[untyped]): untyped =
  if args.len == 0:
    error "The cli macro expects a do block", args

  let doBlock = args[^1]
  if doBlock.kind notin {nnkDo, nnkLambda}:
    error "The last argument to `confutils.cli` should be a do block", doBlock

  args.del(args.len - 1)

  # Create a new anonymous proc we'll dispatch to
  let cliProcName = genSym(nskProc, "CLI")
  var cliProc = newTree(nnkProcDef, cliProcName)
  # Copy everything but the name from the do block:
  for i in 1 ..< doBlock.len: cliProc.add doBlock[i]

  # Generate the final code
  result = newStmtList(cliProc, dispatchImpl(cliProcName, cliProc.params, args))

  # TODO: remove this once Nim supports custom pragmas on proc params
  for p in cliProc.params:
    if p.kind == nnkEmpty: continue
    p[0] = skipPragma p[0]

  debugMacroResult "CLI Code"

proc load*(f: TypedInputFile): f.ContentType =
  when f.Format is Unspecified or f.ContentType is Unspecified:
    {.fatal: "To use `InputFile.load`, please specify the Format and ContentType of the file".}

  when f.Format is Txt:
    # TODO: implement a proper Txt serialization format
    mixin init
    f.ContentType.init readFile(f.string).string
  else:
    mixin loadFile
    loadFile(f.Format, f.string, f.ContentType)