#!/bin/bash
set -euo pipefail

CONFIG_DIR="${CONFIG_DIR:-/opt/monok8s/config}"
NODE_ENV="${NODE_ENV:-$CONFIG_DIR/node.env}"

log() {
    echo "[monok8s-node] $*"
}

fail() {
    echo "[monok8s-node] ERROR: $*" >&2
    exit 1
}

need_cmd() {
    command -v "$1" >/dev/null 2>&1 || fail "missing required command: $1"
}

require_file() {
    [ -f "$1" ] || fail "required file not found: $1"
}

load_config() {
    require_file "$NODE_ENV"

    # shellcheck disable=SC1090
    . "$NODE_ENV"

    HOSTNAME="${HOSTNAME:-}"
    MGMT_IFACE="${MGMT_IFACE:-}"
    MGMT_ADDRESS="${MGMT_ADDRESS:-}"
    MGMT_GATEWAY="${MGMT_GATEWAY:-}"
    DNS_NAMESERVERS="${DNS_NAMESERVERS:-}"
    DNS_SEARCH_DOMAINS="${DNS_SEARCH_DOMAINS:-}"
}

validate_config() {
    [ -n "$HOSTNAME" ] || fail "HOSTNAME is required"
    [ -n "$MGMT_IFACE" ] || fail "MGMT_IFACE is required"
    [ -n "$MGMT_ADDRESS" ] || fail "MGMT_ADDRESS is required"

    case "$MGMT_ADDRESS" in
        */*)
            ;;
        *)
            fail "MGMT_ADDRESS must include a CIDR prefix, example: 10.0.0.13/24"
            ;;
    esac

    if [ -n "$DNS_NAMESERVERS" ]; then
        for ns in $DNS_NAMESERVERS; do
            case "$ns" in
                10.96.0.10)
                    fail "DNS_NAMESERVERS must not contain cluster DNS service IP (10.96.0.10)"
                    ;;
            esac
        done
    fi
}

check_prereqs() {
	# only the special one, coreutils should not be checked
    need_cmd ip
    need_cmd hostname
    need_cmd grep
}

configure_mgmt_interface() {
    local addr_ip

    ip link show "$MGMT_IFACE" >/dev/null 2>&1 || fail "interface not found: $MGMT_IFACE"

    log "bringing up interface: $MGMT_IFACE"
    ip link set "$MGMT_IFACE" up

    addr_ip="${MGMT_ADDRESS%/*}"

    if ip -o addr show dev "$MGMT_IFACE" | awk '{print $4}' | cut -d/ -f1 | grep -Fx "$addr_ip" >/dev/null 2>&1; then
        log "address already present on $MGMT_IFACE: $MGMT_ADDRESS"
    else
        log "assigning $MGMT_ADDRESS to $MGMT_IFACE"
        ip addr add "$MGMT_ADDRESS" dev "$MGMT_IFACE"
    fi

    if [ -n "${MGMT_GATEWAY:-}" ]; then
        log "ensuring default route via $MGMT_GATEWAY"
        ip route replace default via "$MGMT_GATEWAY" dev "$MGMT_IFACE"
    fi
}

set_hostname_if_needed() {
    local current_hostname

    current_hostname="$(hostname 2>/dev/null || true)"

    if [ "$current_hostname" != "$HOSTNAME" ]; then
        log "setting hostname to $HOSTNAME"

        hostname "$HOSTNAME"

        mkdir -p /etc
        printf '%s\n' "$HOSTNAME" > /etc/hostname

        if [ -f /etc/hosts ]; then
            if ! grep -Eq "[[:space:]]$HOSTNAME([[:space:]]|$)" /etc/hosts; then
                printf '127.0.0.1\tlocalhost %s\n' "$HOSTNAME" >> /etc/hosts
            fi
        else
            cat > /etc/hosts <<EOF
127.0.0.1 localhost $HOSTNAME
EOF
        fi
    else
        log "hostname already set: $HOSTNAME"
    fi
}

ensure_ip_forward() {
    local current

    current="$(cat /proc/sys/net/ipv4/ip_forward 2>/dev/null || echo 0)"
    if [ "$current" != "1" ]; then
        log "enabling IPv4 forwarding"
        echo 1 > /proc/sys/net/ipv4/ip_forward
    fi

    mkdir -p /etc/sysctl.d
    cat > /etc/sysctl.d/99-monok8s.conf <<'EOF'
net.ipv4.ip_forward = 1
EOF
}

configure_dns() {
    local tmpfile
    local ns_count=0

    if [ -z "$DNS_NAMESERVERS" ]; then
        log "DNS_NAMESERVERS not set; leaving /etc/resolv.conf unchanged"
        return
    fi

    mkdir -p /etc
    tmpfile="/etc/resolv.conf.monok8s.tmp"
    : > "$tmpfile"

    if [ -n "$DNS_SEARCH_DOMAINS" ]; then
        printf 'search %s\n' "$DNS_SEARCH_DOMAINS" >> "$tmpfile"
    fi

    for ns in $DNS_NAMESERVERS; do
        printf 'nameserver %s\n' "$ns" >> "$tmpfile"
        ns_count=$((ns_count + 1))
    done

    [ "$ns_count" -gt 0 ] || fail "DNS_NAMESERVERS is set but no valid nameservers were parsed"

    printf 'options timeout:2 attempts:3\n' >> "$tmpfile"

    mv "$tmpfile" /etc/resolv.conf
    log "configured /etc/resolv.conf from DNS_NAMESERVERS"
}

print_summary() {
    log "node configuration applied"
    log "hostname: $HOSTNAME"
    log "interface: $MGMT_IFACE"
    log "address: $MGMT_ADDRESS"

    if [ -n "${MGMT_GATEWAY:-}" ]; then
        log "gateway: $MGMT_GATEWAY"
    else
        log "gateway: <not set>"
    fi

    if [ -n "${DNS_NAMESERVERS:-}" ]; then
        log "dns nameservers: $DNS_NAMESERVERS"
    else
        log "dns nameservers: <unchanged>"
    fi

    if [ -n "${DNS_SEARCH_DOMAINS:-}" ]; then
        log "dns search: $DNS_SEARCH_DOMAINS"
    else
        log "dns search: <not set>"
    fi
}

main() {
    load_config
    validate_config
    check_prereqs

    ensure_ip_forward
    configure_mgmt_interface
    configure_dns
    set_hostname_if_needed
    print_summary
}

main "$@"