Add Nix installation script

Author: andrejusk

script/install.d/13-nix.sh

@@ -0,0 +1,109 @@
+#!/usr/bin/env bash
+
+# -----------------------------------------------------------------------------
+# Description:
+#   Install the Nix package manager on supported platforms.
+#
+
+ensure_prereqs() {
+    local missing=()
+    for dep in curl xz; do
+        if ! command -v "$dep" >/dev/null 2>&1; then
+            missing+=("$dep")
+        fi
+    done
+
+    if [[ ${#missing[@]} -eq 0 ]]; then
+        return 0
+    fi
+
+    if command -v brew >/dev/null 2>&1; then
+        log_info "Installing ${missing[*]} via Homebrew"
+        brew install "${missing[@]}" >/dev/null 2>&1 || return 1
+        return 0
+    fi
+
+    if command -v pacman >/dev/null 2>&1; then
+        log_info "Installing ${missing[*]} via pacman"
+        sudo pacman -S --noconfirm --needed "${missing[@]}" >/dev/null 2>&1 || return 1
+        return 0
+    fi
+
+    if command -v apt-get >/dev/null 2>&1; then
+        log_info "Installing ${missing[*]} via apt"
+        sudo apt-get update -qq >/dev/null 2>&1 || return 1
+        sudo apt-get install -y curl xz-utils >/dev/null 2>&1 || return 1
+        return 0
+    fi
+
+    log_warn "Unable to install prerequisites automatically (${missing[*]} missing)"
+    return 1
+}
+
+run_nix_installer() {
+    local platform="$1"
+    local -a args=()
+
+    case "$platform" in
+        linux)
+            args+=("--daemon")
+            ;;
+        darwin)
+            args+=("--daemon")
+            ;;
+        *)
+            log_warn "Unsupported platform for Nix installer"
+            return 1
+            ;;
+    esac
+
+    if ! ensure_prereqs; then
+        log_warn "Skipping Nix install: prerequisites not satisfied"
+        return 1
+    fi
+
+    local installer
+    installer=$(mktemp)
+    if ! curl -fsSL https://nixos.org/nix/install -o "$installer"; then
+        log_error "Failed to download Nix installer"
+        rm -f "$installer"
+        return 1
+    fi
+
+    chmod +x "$installer"
+    if yes | sh "$installer" "${args[@]}"; then
+        log_pass "Nix installation complete"
+        rm -f "$installer"
+        return 0
+    else
+        log_error "Nix installer exited with an error"
+        rm -f "$installer"
+        return 1
+    fi
+}
+
+main() {
+    if command -v nix-env >/dev/null 2>&1 || command -v nix >/dev/null 2>&1; then
+        log_info "Nix already installed; skipping"
+        return
+    fi
+
+    case "${OSTYPE:-}" in
+        linux-gnu*)
+            log_info "Installing Nix (Linux daemon mode)"
+            run_nix_installer "linux"
+            ;;
+        darwin*)
+            log_info "Installing Nix (macOS daemon mode)"
+            run_nix_installer "darwin"
+            ;;
+        *)
+            log_warn "Skipping Nix install: unsupported platform (${OSTYPE:-unknown})"
+            ;;
+    esac
+}
+
+main "$@"
+unset -f main
+unset -f ensure_prereqs
+unset -f run_nix_installer