#!/bin/bash

### === VALIDATE ARGUMENTS ===

if [[ $# -eq 0 ]]; then
    echo "Usage: $0 <node_numbers...>"
    echo "Example: $0 0 1 2 3 4"
    exit 1
fi

NODES=("$@")

### === CONFIGURATION ===
# NODES=(0 1 2 3 4 9 14 19 24)    # List of all participating node numbers, in order
SUBNET_BASE="10.0"

### === GET SELF ID ===
HOSTNAME=$(hostname)
# NODE_ID="${HOSTNAME//[!0-9]/}"   # Extract numeric part of "apuXX"
NODE_ID=$(echo "$HOSTNAME" | grep -o '[0-9]\+' | sed 's/^0*//') # Extract numeric part of "apuXX"
NODE_IP=$((NODE_ID + 10))
NODE_INDEX=-1

# Find our index in the node list
for idx in "${!NODES[@]}"; do
  if [[ "${NODES[$idx]}" -eq "$NODE_ID" ]]; then
    NODE_INDEX=$idx
    break
  fi
done

if [[ "$NODE_INDEX" -lt 0 ]]; then
  echo "Skip [ETH line topology]: Node ID $NODE_ID not found in node list."
  exit 1
fi

### === IP ASSIGNMENT ===
CONFIG_CMDS=""

# Configure eth1 (to previous node)
if (( NODE_INDEX > 0 )); then # Not the first node (has a left neighbor)
    # Get the previous node ID
    LEFT_SUBNET=${NODES[$NODE_INDEX]} # Previous node ID
    SELF_IP="${SUBNET_BASE}.${LEFT_SUBNET}.${NODE_IP}"
    CONFIG_CMDS+="ip addr flush dev eth1; "
    CONFIG_CMDS+="ip addr add ${SELF_IP}/24 dev eth1; ip link set eth1 up; "
fi

# Configure eth2 (to next node)
if (( NODE_INDEX < ${#NODES[@]} - 1 )); then
    # Get the next node ID
    RIGHT_SUBNET=${NODES[$NODE_INDEX +1]} # Next node ID
    SELF_IP="${SUBNET_BASE}.${RIGHT_SUBNET}.${NODE_IP}"
    CONFIG_CMDS+="ip addr flush dev eth2; "
    CONFIG_CMDS+="ip addr add ${SELF_IP}/24 dev eth2; ip link set eth2 up; "
fi

# Enable forwarding if not endpoint
if (( NODE_INDEX > 0 && NODE_INDEX < ${#NODES[@]} - 1 )); then
  CONFIG_CMDS+="sysctl -w net.ipv4.ip_forward=1; "
fi

### === ROUTING TO OTHER NODES ===
for target_idx in "${!NODES[@]}"; do
    if [[ "${NODES[$target_idx]}" -eq "$NODE_ID" ]]; then continue; fi

    SUBNET_TARGET_0=-1
    SUBNET_TARGET_1=-1
    
    IP_TARGET=$((${NODES[$target_idx]} +10))

    if (( target_idx < NODE_INDEX )); then # left hand
        SUBNET_TARGET_0=$((${NODES[$target_idx]}))
        SUBNET_TARGET_1=$((${NODES[$target_idx +1]}))
        SUBNET_NEXT=$((${NODES[$NODE_INDEX]}))
        IP_NEXT=$((${NODES[$NODE_INDEX -1]} + 10))
        IFACE="eth1"
    else # right hand
        SUBNET_TARGET_0=$((${NODES[$target_idx]}))
        if (( target_idx < ${#NODES[@]} -1 )); then # last node?
            SUBNET_TARGET_1=$((${NODES[$target_idx +1]}))
        fi
        SUBNET_NEXT=$((${NODES[$NODE_INDEX +1]}))
        IP_NEXT=$((${NODES[$NODE_INDEX +1]} + 10))
        IFACE="eth2"
    fi

    if (( SUBNET_TARGET_0 != SUBNET_NEXT && SUBNET_TARGET_0 != -1 )); then
        TARGET_IP="${SUBNET_BASE}.${SUBNET_TARGET_0}.${IP_TARGET}"
        NEXT_IP="${SUBNET_BASE}.${SUBNET_NEXT}.${IP_NEXT}"

        CONFIG_CMDS+="ip route add ${TARGET_IP}/32 via ${NEXT_IP} dev ${IFACE} || true; "
    fi

    if (( SUBNET_TARGET_1 != SUBNET_NEXT && SUBNET_TARGET_1 != -1 )); then
        TARGET_IP="${SUBNET_BASE}.${SUBNET_TARGET_1}.${IP_TARGET}"
        NEXT_IP="${SUBNET_BASE}.${SUBNET_NEXT}.${IP_NEXT}"

        CONFIG_CMDS+="ip route add ${TARGET_IP}/32 via ${NEXT_IP} dev ${IFACE} || true; "
    fi
done

### === EXECUTE CONFIGURATION ===
echo "line configuration:"
echo "NODES: ${NODES[*]}"

IFS=';' read -ra COMMANDS <<< "$CONFIG_CMDS"
for cmd in "${COMMANDS[@]}"; do
    cmd=$(echo "$cmd" | xargs)  # Trim whitespace
    if [[ -n "$cmd" ]]; then
        echo "[Running] $cmd"
        eval "$cmd"
    fi
done
# eval "$CONFIG_CMDS"
echo "[$HOSTNAME] Configuration complete."