1 files changed, 121 insertions, 0 deletions
diff --git a/users/sterni/nix/string/default.nix b/users/sterni/nix/string/default.nix
new file mode 100644
index 000000000000..381c8ddff748
--- /dev/null
+++ b/users/sterni/nix/string/default.nix
@@ -0,0 +1,121 @@
+{ depot, lib, ... }:
+
+let
+
+  inherit (depot.users.sterni.nix.char)
+    chr
+    ord
+    ;
+
+  inherit (depot.users.sterni.nix)
+    int
+    flow
+    ;
+
+  take = n: s:
+    builtins.substring 0 n s;
+
+  drop = n: s:
+    builtins.substring n int.maxBound s;
+
+  charAt = i: s:
+    let
+      r = builtins.substring i 1 s;
+    in
+    if r == "" then null else r;
+
+  charIndex = char: s:
+    let
+      len = builtins.stringLength s;
+      go = i:
+        flow.cond [
+          [ (i >= len) null ]
+          [ (charAt i s == char) i ]
+          [ true (go (i + 1)) ]
+        ];
+    in
+    go 0;
+
+  toChars = lib.stringToCharacters;
+  fromChars = lib.concatStrings;
+
+  toBytes = str:
+    builtins.map ord (toChars str);
+
+  fromBytes = is: lib.concatMapStrings chr is;
+
+  pad = { left ? 0, right ? 0, char ? " " }: s:
+    let
+      leftS = fromChars (builtins.genList (_: char) left);
+      rightS = fromChars (builtins.genList (_: char) right);
+    in
+    "${leftS}${s}${rightS}";
+
+  fit = { char ? " ", width, side ? "left" }: s:
+    let
+      diff = width - builtins.stringLength s;
+    in
+    if diff <= 0
+    then s
+    else pad { inherit char; "${side}" = diff; } s;
+
+  # pattern matching for strings only
+  match = val: matcher: matcher."${val}";
+
+  /* Bare-bones printf implementation. Supported format specifiers:
+
+     * `%%` escapes `%`
+     * `%s` is substituted by a string
+
+     As expected, the first argument is a format string and the values
+     for its format specifiers need to provided as the next arguments
+     in order.
+
+     Type: string -> (printfVal : either string (a -> printfVal))
+  */
+  printf = formatString:
+    let
+      specifierWithArg = token: builtins.elem token [
+        "%s"
+      ];
+      isSpecifier = lib.hasPrefix "%";
+
+      tokens = lib.flatten (builtins.split "(%.)" formatString);
+      argsNeeded = builtins.length (builtins.filter specifierWithArg tokens);
+
+      format = args: (builtins.foldl'
+        ({ out ? "", argIndex ? 0 }: token: {
+          argIndex = argIndex + (if specifierWithArg token then 1 else 0);
+          out =
+            if token == "%s" then out + builtins.elemAt args argIndex
+            else if token == "%%" then out + "%"
+            else if isSpecifier token then throw "Unsupported format specifier ${token}"
+            else out + token;
+        })
+        { }
+        tokens).out;
+
+      accumulateArgs = argCount: args:
+        if argCount > 0
+        then arg: accumulateArgs (argCount - 1) (args ++ [ arg ])
+        else format args;
+    in
+    accumulateArgs argsNeeded [ ];
+
+in
+{
+  inherit
+    take
+    drop
+    charAt
+    charIndex
+    toBytes
+    fromBytes
+    toChars
+    fromChars
+    pad
+    fit
+    match
+    printf
+    ;
+}