start project

.gitignore

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+# Created by https://www.toptal.com/developers/gitignore/api/zig,vim
+# Edit at https://www.toptal.com/developers/gitignore?templates=zig,vim
+
+### Vim ###
+# Swap
+[._]*.s[a-v][a-z]
+!*.svg  # comment out if you don't need vector files
+[._]*.sw[a-p]
+[._]s[a-rt-v][a-z]
+[._]ss[a-gi-z]
+[._]sw[a-p]
+
+# Session
+Session.vim
+Sessionx.vim
+
+# Temporary
+.netrwhist
+*~
+# Auto-generated tag files
+tags
+# Persistent undo
+[._]*.un~
+
+### zig ###
+# Zig programming language
+
+zig-cache/
+zig-out/
+build/
+build-*/
+docgen_tmp/
+
+### meta ###
+run.sh
+result
+
+# End of https://www.toptal.com/developers/gitignore/api/zig,vim

build.zig

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+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    var exe = b.addExecutable(.{
+        .name = "zremap",
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+    exe.linkLibC();
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    run_cmd.step.dependOn(b.getInstallStep());
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
+    const unit_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const run_unit_tests = b.addRunArtifact(unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_unit_tests.step);
+}

flake.lock

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+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1693060755,
+        "narHash": "sha256-KNsbfqewEziFJEpPR0qvVz4rx0x6QXxw1CcunRhlFdk=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c66ccfa00c643751da2fd9290e096ceaa30493fc",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "zremap nix flake";
+
+  outputs = { self, nixpkgs }: {
+
+    defaultPackage.x86_64-linux =
+      with import nixpkgs { system = "x86_64-linux"; };
+      stdenv.mkDerivation {
+        pname = "zremap";
+        version = "0.1";
+        src = self;
+        nativeBuildInputs = [ zig.hook ];
+      };
+  };
+}

src/main.zig

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+const std = @import("std");
+const print = std.debug.print;
+const input = @cImport(@cInclude("linux/input.h"));
+
+const CapsLockDown = input.input_event{ .type = input.EV_KEY, .code = input.KEY_CAPSLOCK, .value = 1, .time = undefined };
+const CapsLockUp = input.input_event{ .type = input.EV_KEY, .code = input.KEY_CAPSLOCK, .value = 0, .time = undefined };
+const EscDown = input.input_event{ .type = input.EV_KEY, .code = input.KEY_ESC, .value = 1, .time = undefined };
+const EscUp = input.input_event{ .type = input.EV_KEY, .code = input.KEY_ESC, .value = 0, .time = undefined };
+const LShiftDown = input.input_event{ .type = input.EV_KEY, .code = input.KEY_LEFTSHIFT, .value = 1, .time = undefined };
+const LShiftUp = input.input_event{ .type = input.EV_KEY, .code = input.KEY_LEFTSHIFT, .value = 0, .time = undefined };
+const RShiftDown = input.input_event{ .type = input.EV_KEY, .code = input.KEY_RIGHTSHIFT, .value = 1, .time = undefined };
+const RShiftUp = input.input_event{ .type = input.EV_KEY, .code = input.KEY_RIGHTSHIFT, .value = 0, .time = undefined };
+const Syn = input.input_event{ .type = input.EV_SYN, .code = input.SYN_REPORT, .value = 0, .time = undefined };
+
+fn event_equal(e1: *const input.input_event, e2: *const input.input_event) bool {
+    return (e1.*.type == e2.*.type) and (e1.*.code == e2.*.code) and (e1.*.value == e2.*.value);
+}
+
+fn event_read(event: *input.input_event) !void {
+    event.* = try std.io.getStdIn().reader().readStruct(@TypeOf(event.*));
+}
+
+fn event_write(event: *const input.input_event) !void {
+    try std.io.getStdOut().writer().writeStruct(event.*);
+}
+
+fn write_esc() !void {
+    std.time.sleep(20000);
+    try event_write(&EscDown);
+    try event_write(&Syn);
+    std.time.sleep(20000);
+    try event_write(&EscUp);
+}
+
+pub fn main() !void {
+    var event: input.input_event = undefined;
+    var write_esc_lshift: bool = undefined;
+    var write_esc_rshift: bool = undefined;
+    var is_lshift_down: bool = false;
+    var is_rshift_down: bool = false;
+
+    while (true) {
+        try event_read(&event);
+        if (event.type == input.EV_MSC and event.type == input.MSC_SCAN) {
+            continue;
+        }
+
+        if (event.type != input.EV_KEY) {
+            try event_write(&event);
+            continue;
+        }
+
+        write_esc_lshift = event_equal(&event, &LShiftUp) and is_lshift_down;
+        write_esc_rshift = event_equal(&event, &RShiftUp) and is_rshift_down;
+        is_lshift_down = event_equal(&event, &LShiftDown);
+        is_rshift_down = event_equal(&event, &RShiftDown);
+
+        if (event_equal(&event, &CapsLockUp) or event_equal(&event, &CapsLockDown)) {
+            event.code = input.KEY_LEFTMETA;
+        }
+
+        try event_write(&event);
+
+        if (write_esc_lshift) {
+            write_esc_lshift = false;
+            try write_esc();
+        }
+
+        if (write_esc_rshift) {
+            write_esc_rshift = false;
+            try write_esc();
+        }
+    }
+}