chore: add release installer script

Author: owainlewis

install.sh

@@ -0,0 +1,131 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+repo="owainlewis/cortex"
+install_dir="${CORTEX_INSTALL_DIR:-$HOME/.local/bin}"
+version=""
+install_tmp=""
+
+usage() {
+  cat <<'USAGE'
+Install or update Cortex from GitHub Releases.
+
+Usage:
+  install.sh [--version vX.Y.Z]
+
+Environment:
+  CORTEX_INSTALL_DIR  Install directory. Defaults to ~/.local/bin.
+USAGE
+}
+
+error() {
+  printf 'cortex install: %s\n' "$*" >&2
+  exit 1
+}
+
+need() {
+  command -v "$1" >/dev/null 2>&1 || error "missing required command: $1"
+}
+
+while [ "$#" -gt 0 ]; do
+  case "$1" in
+    --version)
+      [ "$#" -ge 2 ] || error "--version requires a tag such as v0.2.0"
+      version="$2"
+      shift 2
+      ;;
+    -h | --help)
+      usage
+      exit 0
+      ;;
+    *)
+      error "unknown argument: $1"
+      ;;
+  esac
+done
+
+need curl
+need head
+need install
+need mkdir
+need mktemp
+need mv
+need rm
+need sed
+need shasum
+need tar
+need uname
+
+os="$(uname -s)"
+arch="$(uname -m)"
+
+if [ "$os" != "Darwin" ]; then
+  error "unsupported platform: $os. Cortex currently ships macOS binaries only."
+fi
+
+case "$arch" in
+  arm64)
+    target_triple="aarch64-apple-darwin"
+    ;;
+  *)
+    error "unsupported macOS architecture: $arch. Cortex currently ships arm64 binaries only."
+    ;;
+esac
+
+latest_version() {
+  response="$(curl -fsSL "https://api.github.com/repos/${repo}/releases/latest")" \
+    || error "failed to fetch latest release metadata"
+  tag="$(printf '%s\n' "$response" | sed -n 's/.*"tag_name"[[:space:]]*:[[:space:]]*"\([^"]*\)".*/\1/p' | head -n 1)"
+  [ -n "$tag" ] || error "could not find a latest release tag"
+  printf '%s\n' "$tag"
+}
+
+if [ -z "$version" ]; then
+  version="$(latest_version)"
+fi
+
+archive="cortex-${version}-${target_triple}.tar.gz"
+checksum="${archive}.sha256"
+base_url="https://github.com/${repo}/releases/download/${version}"
+tmp_dir="$(mktemp -d)"
+
+cleanup() {
+  rm -rf "$tmp_dir"
+  if [ -n "$install_tmp" ]; then
+    rm -f "$install_tmp"
+  fi
+}
+trap cleanup EXIT
+
+printf 'Installing Cortex %s for %s\n' "$version" "$target_triple"
+
+curl -fsSL "${base_url}/${archive}" -o "${tmp_dir}/${archive}" \
+  || error "failed to download ${archive}"
+curl -fsSL "${base_url}/${checksum}" -o "${tmp_dir}/${checksum}" \
+  || error "failed to download ${checksum}"
+
+(
+  cd "$tmp_dir"
+  shasum -a 256 -c "$checksum" >/dev/null
+) || error "checksum verification failed"
+
+tar -xzf "${tmp_dir}/${archive}" -C "$tmp_dir" cortex \
+  || error "failed to extract cortex binary"
+
+mkdir -p "$install_dir"
+install_tmp="$(mktemp "${install_dir}/.cortex.XXXXXX")" \
+  || error "failed to create temporary install file in ${install_dir}"
+install -m 0755 "${tmp_dir}/cortex" "$install_tmp" \
+  || error "failed to stage cortex binary in ${install_dir}"
+mv -f "$install_tmp" "${install_dir}/cortex" \
+  || error "failed to replace ${install_dir}/cortex"
+install_tmp=""
+
+printf 'Installed cortex to %s/cortex\n' "$install_dir"
+
+case ":$PATH:" in
+  *":$install_dir:"*) ;;
+  *)
+    printf 'Add %s to PATH to run cortex from any shell.\n' "$install_dir"
+    ;;
+esac