#!/usr/bin/env bash
set -Eeuo pipefail
IFS=$'\n\t'

readonly TABLE_FAMILY="inet"
readonly TABLE_NAME="ochenstarik_smm"
readonly CHAIN_NAME="links"

fail() { printf '%s\n' "policy helper: $*" >&2; exit 78; }

testing="${SMM_POLICY_TESTING:-0}"
if [[ "$testing" != "1" ]]; then
    [[ ${EUID:-$(id -u)} -eq 0 ]] || fail "root is required"
    readonly STATE_FILE="/var/lib/ochenstarik-server-monitor-manager/mesh/nodes.tsv"
else
    readonly STATE_FILE="${SMM_POLICY_STATE_FILE:?SMM_POLICY_STATE_FILE is required in testing mode}"
fi

node_pattern='^[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?$'
ipv4_pattern='^([0-9]{1,3}\.){3}[0-9]{1,3}$'

validate_node_id() {
    [[ "$1" =~ $node_pattern ]] || fail "invalid node id"
}

lookup_node_ip() {
    local node_id="$1" ip
    [[ -r "$STATE_FILE" ]] || fail "mesh node state is unavailable"
    ip="$(awk -F '\t' -v node="$node_id" '$1 == node { print $2; exit }' "$STATE_FILE")"
    [[ "$ip" =~ $ipv4_pattern ]] || fail "node has no valid mesh address: $node_id"
    printf '%s\n' "$ip"
}

validate_rule() {
    local action="$1"
    case "$action" in
        link-connect) [[ $# -eq 6 ]] || fail "invalid link-connect argument count" ;;
        link-disconnect) [[ $# -eq 5 ]] || fail "invalid link-disconnect argument count" ;;
        link-status) [[ $# -eq 5 ]] || fail "invalid link-status argument count" ;;
        *) fail "unsupported action" ;;
    esac
    validate_node_id "$2"
    validate_node_id "$3"
    [[ "$2" != "$3" ]] || fail "source and destination must differ"
    [[ "$4" == "tcp" || "$4" == "udp" ]] || fail "invalid protocol"
    [[ "$5" =~ ^[0-9]+$ ]] && (( 10#$5 >= 1 && 10#$5 <= 65535 )) || fail "invalid port"
    if [[ "$action" == "link-connect" ]]; then
        [[ "$6" =~ ^[0-9]+$ ]] && (( 10#$6 >= 0 && 10#$6 <= 525600 )) || fail "invalid TTL"
    fi
}

run_nft() {
    if [[ "$testing" == "1" ]]; then
        printf 'nft'
        printf ' %q' "$@"
        printf '\n'
    else
        /usr/sbin/nft "$@"
    fi
}

rule_exists() {
    local comment="$1" listing
    if [[ "$testing" == "1" ]]; then
        return 1
    fi
    if ! listing="$(/usr/sbin/nft -a list chain "$TABLE_FAMILY" "$TABLE_NAME" "$CHAIN_NAME")"; then
        fail "could not inspect nftables Link policy"
    fi
    grep -Fq "comment \"$comment\"" <<<"$listing"
}

connect_rule() {
    local source_id="$1" target_id="$2" protocol="$3" port="$4"
    local source_ip target_ip comment
    source_ip="$(lookup_node_ip "$source_id")"
    target_ip="$(lookup_node_ip "$target_id")"
    comment="smm:${source_id}:${target_id}:${protocol}:${port}"
    rule_exists "$comment" && return 0
    run_nft add rule "$TABLE_FAMILY" "$TABLE_NAME" "$CHAIN_NAME" \
        ip saddr "$source_ip" ip daddr "$target_ip" "$protocol" dport "$port" \
        counter accept comment "$comment"
}

disconnect_rule() {
    local source_id="$1" target_id="$2" protocol="$3" port="$4" comment handle
    # Resolve both identities before touching firewall state.
    lookup_node_ip "$source_id" >/dev/null
    lookup_node_ip "$target_id" >/dev/null
    comment="smm:${source_id}:${target_id}:${protocol}:${port}"
    if [[ "$testing" == "1" ]]; then
        printf 'nft-delete-comment %q\n' "$comment"
        return
    fi
    while IFS= read -r handle; do
        [[ "$handle" =~ ^[0-9]+$ ]] || continue
        run_nft delete rule "$TABLE_FAMILY" "$TABLE_NAME" "$CHAIN_NAME" handle "$handle"
    done < <(
        /usr/sbin/nft -a list chain "$TABLE_FAMILY" "$TABLE_NAME" "$CHAIN_NAME" \
            | grep -F "comment \"$comment\"" \
            | sed -n 's/.* # handle \([0-9][0-9]*\)$/\1/p'
    )
}

status_rule() {
    local source_id="$1" target_id="$2" protocol="$3" port="$4" comment
    # A status is meaningful only for identities currently known to the mesh.
    lookup_node_ip "$source_id" >/dev/null
    lookup_node_ip "$target_id" >/dev/null
    comment="smm:${source_id}:${target_id}:${protocol}:${port}"
    if rule_exists "$comment"; then
        printf '%s\n' active
    else
        printf '%s\n' disabled
    fi
}

action="${1:-}"
validate_rule "$@"
case "$action" in
    link-connect) connect_rule "$2" "$3" "$4" "$5" ;;
    link-disconnect) disconnect_rule "$2" "$3" "$4" "$5" ;;
    link-status) status_rule "$2" "$3" "$4" "$5" ;;
esac