Göran Krampe / Lapp for Nim

  import strutils
  from os import paramCount, paramStr
  import tables
  export tables.`[]`
  
  #### Simple string lexer ###
  type
    PLexer = ref TLexer
    TLexer = object
      str: string
      idx: int
    TLexType = enum
      tend
      tword
      tint
      tfloat
      trange
      telipsis
      tchar
  
  proc thisChar(L: PLexer):char = L.str[L.idx]
  proc next(L: PLexer) = L.idx += 1
  
  proc skipws(L: PLexer) =
    while thisChar(L) in Whitespace: next(L)
      
  proc get(L: PLexer; t: var TLexType): string =
    skipws(L)
    let c = thisChar(L)
    t = tend
    if c == '\0': return nil
    result = ""
    result.add(c)
    next(L) 
    t = tchar
    case c
    of '-':  # '-", "--"
      if thisChar(L) == '-':
        result.add('-')
        next(L)
    of Letters: # word
      t = tword
      while thisChar(L) in Letters:
        result.add(thisChar(L))
        next(L)
    of Digits: # number
      t = tint
      while thisChar(L) in Digits:
        result.add(thisChar(L))
        next(L)
      if thisChar(L) == '.':
        t = tfloat

        result.add(thisChar(L))

        next(L)
        while thisChar(L) in Digits:

          result.add(thisChar(L))

          next(L)
    of '.': # ".", "..", "..."
      if thisChar(L) == '.':
        t = trange
        result.add('.')
        next(L)
        if thisChar(L) == '.':
          t = telipsis
          result.add('.')
          next(L)
    else: discard
      
  proc get(L: PLexer): string = 
    var t: TLexType
    get(L,t)
      
  proc reset(L: PLexer, s: string) =
    L.str  = s
    L.idx = 0
  
  proc newLexer(s: string): PLexer =
    new(result)
    result.reset(s)
      
  ### a container for values ###
      
  type
    TValueKind = enum
      vInt,
      vFloat,
      vString,
      vBool,
      vFile,
      vSeq
  

    PValue* = ref TValue
    TValue* = object
      case kind*: TValueKind
        of vInt: asInt*: int
        of vFloat: asFloat*: float
        of vString: asString*: string
        of vBool: asBool*: bool

        of vFile:

          asFile*: File
          fileName*: string
        of vSeq: asSeq*: seq[PValue]

  
  proc boolValue(c: bool): PValue =  PValue(kind: vBool, asBool: c)
      
  proc fileValue(f: File, name: string): PValue =  PValue(kind: vFile, asFile: f, fileName: name)
      
  proc strValue(s: string): PValue =  PValue(kind: vString, asString: s) 
      
  proc intValue(v: int): PValue =   PValue(kind: vInt, asInt: v)
      
  proc floatValue(v: float): PValue = PValue(kind: vFloat, asFloat: v)
      
  proc seqValue(v: seq[PValue]): PValue = PValue(kind: vSeq, asSeq: v)
  
  const MAX_FILES = 30
      
  type
    PSpec = ref TSpec
    TSpec = object
      defVal: string
      ptype: string
      needsValue, multiple, used: bool
  var
    progname, usage: string
    aliases: array[char,string]
    parm_spec =  initTable[string,PSpec]()
      
  proc fail(msg: string)  =
    stderr.writeln(progname & ": " & msg)
    quit(usage)
  

  proc parseSpec(u: string) =    

    var
      L: PLexer
      tok: string
      k = 1
        
    let lines = u.splitLines
    L = newLexer(lines[0])
    progname = L.get
    usage = u
    for line in lines[1..(-1)]:
      var
        isarg = false
        multiple = false
        getnext = true
        name: string
        alias: char
      L.reset(line)
      tok = L.get
      if tok == "-" or tok == "--":  # flag
        if tok == "-": #short flag
          let flag = L.get

          if len(flag) != 1: fail("short option has one character!")

          tok = L.get
          if tok == ",": # which is alias for long flag
            tok = L.get
            if tok != "--": fail("expecting long --flag")
            name = L.get
            alias = flag[0]
          else: # only short flag
            name = flag
            alias = flag[0]
            getnext = false
        else: # only long flag
          name = L.get
          alias = '\0'
      elif tok == "<":  # argument
        isarg = true
        name = L.get
        alias = chr(k)
        k += 1
        tok = L.get
        if tok != ">": fail("argument must be enclosed in <...>")
          
      if getnext:  tok = L.get
      if tok == ":": # allowed to have colon after flags
        tok = L.get
      if tok == nil: continue
      # default types for flags and arguments
      var 
        ftype = if isarg: "string" else: "bool"
        defValue = ""
      if tok == "(": # typed flag/argument
        var t = tchar
        tok = L.get(t)
        if tok == "default":  # type from default value
          defValue = L.get(t)
          if t == tint: ftype = "int"
          elif t == tfloat: ftype = "float"
          elif t == tword:
            if defValue == "stdin": ftype = "infile"
            elif defValue == "stdout": ftype = "outfile"
            else: ftype = "string"
          else: fail("unknown default value " & tok)
        else: # explicit type
          if t == tword:
            ftype = tok
            if tok == "bool": defValue = "false"
          else: fail("unknown type " & tok)
        discard L.get(t)
        multiple = t == telipsis
      elif ftype == "bool": # no type or default
        defValue = "false"
              
      if name != nil:

        # echo("Param: " & name & " type: " & $ftype & " needsvalue: " & $(ftype != "bool") & " default: " & $defValue & " multiple: " & $multiple)

        let spec = PSpec(defVal:defValue, ptype: ftype, needsValue: ftype != "bool",multiple:multiple)
        aliases[alias] = name        
        parm_spec[name] = spec
  
  proc tail(s: string): string = s[1..(-1)]
  
  var 
    files: array[1..MAX_FILES,File]
    nfiles = 0 
  
  proc closeFiles() {.noconv.} =
    if nfiles == 0: return
    for i in 1..nfiles: files[i].close()
  

  proc parseArguments*(usage: string, args: seq[string]): Table[string,PValue] =

    var
      vars = initTable[string,PValue]()
      n = len(args) - 1
      i = 1
      k = 1
      flag,value, arg: string        
      info: PSpec
      short: bool
      flagvalues: seq[seq[string]]
        
    proc next(): string =

      if i > n: fail("an option required a value!")

      result = args[i]
      i += 1
        
    proc get_alias(c: char): string =
      result = aliases[c]
      if result == nil:
        n = ord(c)
        if n < 20:
          fail("no such argument: " & $n)
        else:

          fail("no such option: " & c)

        
    proc get_spec(name: string): PSpec =
      result = parm_spec[name]
      if result == nil:

        fail("no such option: " & name)

  
    newSeq(flagvalues, 0)
    parseSpec(usage)
    addQuitProc(closeFiles)
  
    # parse the flags and arguments
    while i <= n:
      arg = next()
      if arg[0] == '-':  #flag
        short = arg[1] != '-'
        arg = arg.tail
        if short: # all short args are aliases, even if only to themselves
          flag = get_alias(arg[0])
        else:

          flag = arg[1..high(arg)]

        info = get_spec(flag)
        if info.needsValue:
          if short and len(arg) > 1: # value can follow short flag
            value = arg.tail
          else:  # grab next argument
            value = next()
        else:
          value = "true"
          if short and len(arg) > 0: # short flags can be combined
            for c in arg.tail:
              let f = get_alias(c)
              let i = get_spec(f)
              if i.needsValue: fail("needs value! " & f)
              flagvalues.add(@[f,"true"])
              i.used = true
      else: # argument (stored as \001, \002, etc
        flag = get_alias(chr(k))
        value = arg
        info = get_spec(flag)
        # don't move on if this is a varags last param
        if not info.multiple:  k += 1
      flagvalues.add(@[flag,value])
      info.used = true
        
    # any flags not mentioned?
    for flag,info in parm_spec:
      if not info.used:
        if info.defVal == "": # no default!

          fail("required option or argument missing: " & flag)

        flagvalues.add(@[flag,info.defVal])
            
    # cool, we have the info, can convert known flags
    for item in flagvalues:
      var pval: PValue;
      let
        flag = item[0]
        value = item[1]
        info = get_spec(flag)
      case info.ptype
      of "int":
        var v: int
        try:
          v = value.parseInt
        except:
          fail("bad integer")
        pval = intValue(v)
      of "float":
        var v: float
        try:
          v = value.parseFloat
        except:

          fail("bad float")

        pval = floatValue(v)
      of "bool":
        pval = boolValue(value.parseBool)
      of "string":
        pval = strValue(value)
      of "infile","outfile": # we open files for the app...
        var f: File
        try:
          if info.ptype == "infile":
            f = if value=="stdin": stdin else: open(value,fmRead)
          else:
            f = if value=="stdout": stdout else: open(value,fmWrite)
          # they will be closed automatically on program exit
          nfiles += 1
          if nfiles <= MAX_FILES:  files[nfiles] = f
        except:
          fail("cannot open " & value)
        pval = fileValue(f,value)
      else: discard
      
      var oval = vars[flag]
      if info.multiple: # multiple flags are sequence values
        if oval == nil: # first value!
          pval = seqValue(@[pval])
        else: # just add to existing sequence
          oval.asSeq.add(pval)
          pval = oval
      elif oval != nil: # cannot repeat a single flag!
        fail("cannot use '" & flag & "' more than once")
      vars[flag] = pval
  
    return vars
  

  proc parse*(usage: string): Table[string,PValue] =

    var 
      args: seq[string]
      n = paramCount()
    newSeq(args,n+1)
    for i in 0..n:
      args[i] = paramStr(i)
    return parseArguments(usage,args)    
  
  when isMainModule:
    var args = parse"""

    head [flags] file [out]

      -n: (default 10) number of lines
      -v,--verbose: (bool...) verbosity level 
      -a,--alpha  useless parm

      <file>: (default stdin...)

      <out>: (default stdout)

    """
  
    echo args["n"].asInt
    echo args["alpha"].asBool
    
    for v in args["verbose"].asSeq:
      echo "got ",v.asBool
    
    let myfiles = args["files"].asSeq
    for f in myfiles:
      echo f.asFile.readLine()