#!/usr/bin/env bash
set -Eeuo pipefail

usage() {
    cat <<'EOF'
Quicksh ubuntu 0.1.0 — Ubuntu developer essentials
Usage: bash ubuntu.sh [--help|-h|--version|--packages|--install]

Default: report OS, kernel, architecture, apt, and basic developer tools.
--packages  List the recommended packages without making changes.
--install   Preview apt-get update and install, then require a terminal and yes.

Packages: build-essential git bash curl ca-certificates
Only genuine Ubuntu (ID=ubuntu) is supported, not derivatives.
Installation refreshes package indexes and installs essentials/dependencies;
requested packages may be updated. apt-get also confirms its transaction.
No -y, automatic full upgrade, or automatic package removal is used.
EOF
}

install_packages() {
    local -a packages=(build-essential git bash curl ca-certificates)
    local -a elevate=()
    if (( EUID != 0 )); then
        if ! command -v sudo >/dev/null 2>&1; then
            printf 'quicksh ubuntu: sudo is required for --install as a non-root user.\n' >&2
            return 1
        fi
        elevate=(sudo --)
    fi
    printf '\nProposed commands:\n  '
    printf '%s ' "${elevate[@]}" apt-get update
    printf '\n  '
    printf '%s ' "${elevate[@]}" apt-get install "${packages[@]}"
    printf '\nThis refreshes package indexes, then installs essentials and dependencies.\n'
    printf 'Requested packages may be updated; there is no full system upgrade.\n'
    if [[ ! -t 0 || ! -t 1 ]]; then
        printf 'quicksh ubuntu: --install requires interactive stdin and stdout; no changes made.\n' >&2
        return 1
    fi
    local answer
    printf 'Proceed to the apt-get commands? Type yes to continue: '
    if ! IFS= read -r answer; then
        printf '\nquicksh ubuntu: confirmation could not be read; no changes made.\n' >&2
        return 1
    fi
    if [[ "$answer" != yes ]]; then
        printf 'Cancelled; no changes made.\n'
        return 0
    fi
    if ! "${elevate[@]}" apt-get update; then
        printf 'quicksh ubuntu: package index update failed; installation was not attempted.\n' >&2
        return 1
    fi
    if ! "${elevate[@]}" apt-get install "${packages[@]}"; then
        printf 'quicksh ubuntu: installation failed or was cancelled. Indexes may already be updated.\n' >&2
        return 1
    fi
    printf 'Package commands completed.\n'
}

main() {
    if (( $# > 1 )); then
        printf 'quicksh ubuntu: expected at most one option. Use --help.\n' >&2
        return 2
    fi
    case "${1:-}" in
        --help|-h) usage; return ;;
        --version) printf 'Quicksh ubuntu 0.1.0\n'; return ;;
        ''|--packages|--install) ;;
        *) printf 'quicksh ubuntu: unsupported option: %s. Use --help.\n' "$1" >&2; return 2 ;;
    esac
    local ID=unknown PRETTY_NAME='Unknown system'
    if [[ ! -r /etc/os-release ]]; then
        printf 'quicksh ubuntu: cannot identify the OS; expected /etc/os-release.\n' >&2
        return 1
    fi
    # shellcheck disable=SC1091
    if ! . /etc/os-release; then
        printf 'quicksh ubuntu: could not read OS identification.\n' >&2
        return 1
    fi
    if [[ "$ID" != ubuntu ]]; then
        printf 'quicksh ubuntu: unsupported OS: %s. Requires ID=ubuntu; no changes made.\n' "$ID" >&2
        return 1
    fi
    printf 'Quicksh ubuntu 0.1.0\nOS: %s\n' "$PRETTY_NAME"
    if [[ "${1:-}" == --packages ]]; then
        printf 'Recommended: build-essential git bash curl ca-certificates\n'
        printf 'Compiler/build tools, Git, Bash, HTTPS downloads, and trusted CA certificates.\n'
        printf 'Review --install to opt in; listing packages makes no changes.\n'
        return 0
    fi
    if ! command -v apt >/dev/null 2>&1 || ! command -v apt-get >/dev/null 2>&1; then
        printf 'quicksh ubuntu: apt and apt-get must be available in PATH.\n' >&2
        return 1
    fi
    if [[ "${1:-}" == --install ]]; then
        install_packages
        return
    fi
    local system tool
    if ! system=$(uname -srmo); then
        printf 'quicksh ubuntu: could not read kernel and architecture information.\n' >&2
        return 1
    fi
    printf 'System: %s\n\nTool availability:\n' "$system"
    for tool in apt apt-get git bash curl make cc; do
        if command -v "$tool" >/dev/null 2>&1; then
            printf '  [ok]      %s\n' "$tool"
        else
            printf '  [missing] %s\n' "$tool"
        fi
    done
    printf '\nUse --packages for recommendations or --install for an interactive opt-in.\n'
}

main "$@"