2 files changed, 124 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..782f86b7f79b
--- /dev/null
+++ b/users/sterni/nix/string/default.nix
@@ -0,0 +1,71 @@
+{ depot, lib, ... }:
+
+let
+
+  inherit (depot.users.sterni.nix.char)
+    chr
+    ord
+    ;
+
+  inherit (depot.users.sterni.nix.flow)
+    cond
+    ;
+
+  take = n: s:
+    builtins.substring 0 n s;
+
+  drop = n: s:
+    builtins.substring n (builtins.stringLength s - n) 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:
+        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;
+
+in {
+  inherit
+    take
+    drop
+    charAt
+    charIndex
+    toBytes
+    fromBytes
+    toChars
+    fromChars
+    pad
+    fit
+    ;
+}
diff --git a/users/sterni/nix/string/tests/default.nix b/users/sterni/nix/string/tests/default.nix
new file mode 100644
index 000000000000..576952673471
--- /dev/null
+++ b/users/sterni/nix/string/tests/default.nix
@@ -0,0 +1,53 @@
+{ depot, ... }:
+
+let
+
+  inherit (depot.users.sterni.nix)
+    string
+    ;
+
+  inherit (depot.nix.runTestsuite)
+    it
+    assertEq
+    runTestsuite
+    ;
+
+  testTakeDrop = it "tests take and drop" [
+    (assertEq "take"
+      (string.take 5 "five and more")
+      "five ")
+    (assertEq "drop"
+      (string.drop 2 "coin")
+      "in")
+    (assertEq "take out of bounds"
+      (string.take 100 "foo")
+      "foo")
+    (assertEq "drop out of bounds"
+      (string.drop 42 "lol")
+      "")
+  ];
+
+  testIndexing = it "tests string indexing" [
+    (assertEq "normal charAt"
+      (string.charAt 3 "helo")
+      "o")
+    (assertEq "out of bounds charAt"
+      (string.charAt 5 "helo")
+      null)
+  ];
+
+  testFinding = it "tests finding in strings" [
+    (assertEq "normal charIndex"
+      (string.charIndex "d" "abcdefghijkl")
+      3)
+    (assertEq "charIndex no match"
+      (string.charIndex "w" "zZzZzzzZZZ")
+      null)
+  ];
+
+in
+  runTestsuite "nix.string" [
+    testTakeDrop
+    testIndexing
+    testFinding
+  ]