Add ensure_nix script

ensure_nix.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+
+# Runs the command given in a Nix environment, and create it if it doesn't exist.
+# Useful for environments where nix isn't installed / you do not have root access
+
+# If you need a fresh slate:
+# chmod +w .nix -R
+# rm -rf .nix .nix-defexpr .nix-profile .config/nix .local/state/nix .local/share/nix .cache/nix
+
+set -euo pipefail
+SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
+
+if [ ! -d /nix ]
+then
+    # Doesn't support architectures other than x86_64
+    NIX_USER_CHROOT_URL=https://github.com/nix-community/nix-user-chroot/releases/download/1.2.2/nix-user-chroot-bin-1.2.2-x86_64-unknown-linux-musl
+    NIX_USER_CHROOT_SHA256SUM=e11aff604bb8d3ffd1d9c0c68cd636816d7eb8da540de18ee3a41ccad7ac0972
+
+    nix_user_chroot="$HOME/.local/bin/nix-user-chroot"
+    mkdir -p "$(dirname "$nix_user_chroot")"
+
+    nix_directory="$HOME/.nix"
+    mkdir -p "$nix_directory"
+
+    if [ ! -x "$nix_user_chroot" ] || ! echo "$NIX_USER_CHROOT_SHA256SUM $nix_user_chroot" | sha256sum --check --status
+    then
+        wget "$NIX_USER_CHROOT_URL" -O "$nix_user_chroot"
+        echo "$NIX_USER_CHROOT_SHA256SUM $nix_user_chroot" | sha256sum --check --status
+        chmod +x "$nix_user_chroot"
+    fi
+    exec "$nix_user_chroot" "$nix_directory" "$0" "$@"
+    exit 1
+fi
+
+nix_profile_path="$HOME/.nix-profile/etc/profile.d/nix.sh"
+
+if [ ! -f "$nix_profile_path" ]
+then
+    NIX_INSTALLER_URL=https://releases.nixos.org/nix/nix-2.19.2/install
+    NIX_INSTALLER_SHA256SUM=435f0d7e11f7c7dffeeab0ec9cc55723f6d3c03352379d785633cf4ddb5caf90
+
+    nix_installer="$(mktemp)"
+
+    wget "$NIX_INSTALLER_URL" -O "$nix_installer"
+    echo "$NIX_INSTALLER_SHA256SUM $nix_installer" | sha256sum --check --status
+    chmod +x "$nix_installer"
+
+    "$nix_installer" --no-daemon --yes --no-channel-add --no-modify-profile
+fi
+
+. "$nix_profile_path"
+
+"${SCRIPT_DIR}/add_channels.sh"
+
+exec "$@"