path: root/lib/strings.nix

/* String manipulation functions. */

let lib = import ./default.nix;

inherit (builtins) length;

in

rec {

  inherit (builtins) stringLength substring head tail isString replaceStrings;


  # Concatenate a list of strings.
  concatStrings =
    if builtins ? concatStringsSep then
      builtins.concatStringsSep ""
    else
      lib.foldl' (x: y: x + y) "";


  # Map a function over a list and concatenate the resulting strings.
  concatMapStrings = f: list: concatStrings (map f list);
  concatImapStrings = f: list: concatStrings (lib.imap f list);


  # Place an element between each element of a list, e.g.,
  # `intersperse "," ["a" "b" "c"]' returns ["a" "," "b" "," "c"].
  intersperse = separator: list:
    if list == [] || length list == 1
    then list
    else tail (lib.concatMap (x: [separator x]) list);


  # Concatenate a list of strings with a separator between each element, e.g.
  # concatStringsSep " " ["foo" "bar" "xyzzy"] == "foo bar xyzzy"
  concatStringsSep = builtins.concatStringsSep or (separator: list:
    concatStrings (intersperse separator list));

  concatMapStringsSep = sep: f: list: concatStringsSep sep (map f list);
  concatImapStringsSep = sep: f: list: concatStringsSep sep (lib.imap f list);


  # Construct a Unix-style search path consisting of each `subDir"
  # directory of the given list of packages.  For example,
  # `makeSearchPath "bin" ["x" "y" "z"]' returns "x/bin:y/bin:z/bin".
  makeSearchPath = subDir: packages:
    concatStringsSep ":" (map (path: path + "/" + subDir) packages);


  # Construct a library search path (such as RPATH) containing the
  # libraries for a set of packages, e.g. "${pkg1}/lib:${pkg2}/lib:...".
  makeLibraryPath = makeSearchPath "lib";

  # Construct a binary search path (such as $PATH) containing the
  # binaries for a set of packages, e.g. "${pkg1}/bin:${pkg2}/bin:...".
  makeBinPath = makeSearchPath "bin";


  # Idem for Perl search paths.
  makePerlPath = makeSearchPath "lib/perl5/site_perl";


  # Dependening on the boolean `cond', return either the given string
  # or the empty string.
  optionalString = cond: string: if cond then string else "";


  # Determine whether a string has given prefix/suffix.
  hasPrefix = pref: str:
    substring 0 (stringLength pref) str == pref;
  hasSuffix = suff: str:
    let
      lenStr = stringLength str;
      lenSuff = stringLength suff;
    in lenStr >= lenSuff &&
       substring (lenStr - lenSuff) lenStr str == suff;


  # Convert a string to a list of characters (i.e. singleton strings).
  # For instance, "abc" becomes ["a" "b" "c"].  This allows you to,
  # e.g., map a function over each character.  However, note that this
  # will likely be horribly inefficient; Nix is not a general purpose
  # programming language.  Complex string manipulations should, if
  # appropriate, be done in a derivation.
  stringToCharacters = s:
    map (p: substring p 1 s) (lib.range 0 (stringLength s - 1));


  # Manipulate a string charactter by character and replace them by
  # strings before concatenating the results.
  stringAsChars = f: s:
    concatStrings (
      map f (stringToCharacters s)
    );


  # Escape occurrence of the elements of ‘list’ in ‘string’ by
  # prefixing it with a backslash. For example, ‘escape ["(" ")"]
  # "(foo)"’ returns the string ‘\(foo\)’.
  escape = list: replaceChars list (map (c: "\\${c}") list);


  # Escape all characters that have special meaning in the Bourne shell.
  escapeShellArg = lib.escape (stringToCharacters "\\ ';$`()|<>\t*[]");


  # Obsolete - use replaceStrings instead.
  replaceChars = builtins.replaceStrings or (
    del: new: s:
    let
      substList = lib.zipLists del new;
      subst = c:
        let found = lib.findFirst (sub: sub.fst == c) null substList; in
        if found == null then
          c
        else
          found.snd;
    in
      stringAsChars subst s);


  # Case conversion utilities.
  lowerChars = stringToCharacters "abcdefghijklmnopqrstuvwxyz";
  upperChars = stringToCharacters "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  toLower = replaceChars upperChars lowerChars;
  toUpper = replaceChars lowerChars upperChars;


  # Appends string context from another string.
  addContextFrom = a: b: substring 0 0 a + b;


  # Cut a string with a separator and produces a list of strings which
  # were separated by this separator; e.g., `splitString "."
  # "foo.bar.baz"' returns ["foo" "bar" "baz"].
  splitString = _sep: _s:
    let
      sep = addContextFrom _s _sep;
      s = addContextFrom _sep _s;
      sepLen = stringLength sep;
      sLen = stringLength s;
      lastSearch = sLen - sepLen;
      startWithSep = startAt:
        substring startAt sepLen s == sep;

      recurse = index: startAt:
        let cutUntil = i: [(substring startAt (i - startAt) s)]; in
        if index < lastSearch then
          if startWithSep index then
            let restartAt = index + sepLen; in
            cutUntil index ++ recurse restartAt restartAt
          else
            recurse (index + 1) startAt
        else
          cutUntil sLen;
    in
      recurse 0 0;


  # return the suffix of the second argument if the first argument match its
  # prefix. e.g.,
  # `removePrefix "foo." "foo.bar.baz"' returns "bar.baz".
  removePrefix = pre: s:
    let
      preLen = stringLength pre;
      sLen = stringLength s;
    in
      if hasPrefix pre s then
        substring preLen (sLen - preLen) s
      else
        s;

  removeSuffix = suf: s:
    let
      sufLen = stringLength suf;
      sLen = stringLength s;
    in
      if sufLen <= sLen && suf == substring (sLen - sufLen) sufLen s then
        substring 0 (sLen - sufLen) s
      else
        s;

  # Return true iff string v1 denotes a version older than v2.
  versionOlder = v1: v2: builtins.compareVersions v2 v1 == 1;


  # Return true iff string v1 denotes a version equal to or newer than v2.
  versionAtLeast = v1: v2: !versionOlder v1 v2;


  # This function takes an argument that's either a derivation or a
  # derivation's "name" attribute and extracts the version part from that
  # argument. For example:
  #
  #    lib.getVersion "youtube-dl-2016.01.01" ==> "2016.01.01"
  #    lib.getVersion pkgs.youtube-dl         ==> "2016.01.01"
  getVersion = x: (builtins.parseDrvName (x.name or x)).version;


  # Extract name with version from URL. Ask for separator which is
  # supposed to start extension.
  nameFromURL = url: sep:
    let
      components = splitString "/" url;
      filename = lib.last components;
      name = builtins.head (splitString sep filename);
    in assert name !=  filename; name;


  # Create an --{enable,disable}-<feat> string that can be passed to
  # standard GNU Autoconf scripts.
  enableFeature = enable: feat: "--${if enable then "enable" else "disable"}-${feat}";


  # Create a fixed width string with additional prefix to match
  # required width.
  fixedWidthString = width: filler: str:
    let
      strw = lib.stringLength str;
      reqWidth = width - (lib.stringLength filler);
    in
      assert strw <= width;
      if strw == width then str else filler + fixedWidthString reqWidth filler str;


  # Format a number adding leading zeroes up to fixed width.
  fixedWidthNumber = width: n: fixedWidthString width "0" (toString n);


  # Check whether a value is a store path.
  isStorePath = x: builtins.substring 0 1 (toString x) == "/" && dirOf (builtins.toPath x) == builtins.storeDir;

  # Convert string to int
  # Obviously, it is a bit hacky to use fromJSON that way.
  toInt = str:
    let may_be_int = builtins.fromJSON str; in
    if builtins.isInt may_be_int
    then may_be_int
    else throw "Could not convert ${str} to int.";

  # Read a list of paths from `file', relative to the `rootPath'. Lines
  # beginning with `#' are treated as comments and ignored. Whitespace
  # is significant.
  readPathsFromFile = rootPath: file:
    let
      root = toString rootPath;
      lines =
        builtins.map (lib.removeSuffix "\n")
        (lib.splitString "\n" (builtins.readFile file));
      removeComments = lib.filter (line: !(lib.hasPrefix "#" line));
      relativePaths = removeComments lines;
      absolutePaths = builtins.map (path: builtins.toPath (root + "/" + path)) relativePaths;
    in
      absolutePaths;

}