#!/bin/bash
################################################################################
# Script Name: game-server-exporter.sh
# Version: 1.0
# Description: Prometheus exporter for game servers providing operational
#              metrics — Minecraft, Valheim, and Palworld player counts,
#              server status, TPS, query response times, and server version info
#
# Author: Phil Connor
# Contact: contact@mylinux.work
# Website: https://mylinux.work
# License: MIT
#
# Prerequisites:
#   - nmap-ncat (nc) for network queries
#   - curl for REST API queries (Palworld)
#   - python3 with mcstatus (optional, enhanced Minecraft metrics)
#   - netcat (nc) for HTTP mode
#
# Usage:
#   # Output to stdout
#   ./game-server-exporter.sh
#
#   # HTTP server mode
#   ./game-server-exporter.sh --http -p 9195
#
#   # Textfile collector mode
#   ./game-server-exporter.sh --textfile
#
#   # Custom server addresses
#   ./game-server-exporter.sh --minecraft-host mc.example.com
#
# Metrics Exported:
#   - game_server_up{game,server} - Server reachability (1=up, 0=down)
#   - game_server_players_online{game,server} - Online player count
#   - game_server_players_max{game,server} - Maximum player slots
#   - game_server_info{game,server,version,motd} - Server version info
#   - game_server_tps{game="minecraft",server} - Ticks per second (Minecraft)
#   - game_server_query_duration_seconds{game,server} - Query time per server
#   - game_server_exporter_duration_seconds - Total script execution time
#   - game_server_exporter_last_run_timestamp - Last run timestamp
#
# Configuration:
#   Default HTTP port: 9195
#   Textfile directory: /var/lib/node_exporter
#
################################################################################

set -euo pipefail

# ============================================================================
# CONFIGURATION VARIABLES
# ============================================================================

TEXTFILE_DIR="/var/lib/node_exporter"
OUTPUT_FILE=""
HTTP_MODE=false
HTTP_PORT=9195

# Server configuration
MINECRAFT_HOST=""
MINECRAFT_QUERY_PORT=25565
MINECRAFT_RCON_PORT=25575
MINECRAFT_RCON_PASS=""
VALHEIM_HOST=""
VALHEIM_QUERY_PORT=2457
PALWORLD_HOST=""
PALWORLD_QUERY_PORT=8212

# ============================================================================
# HELPER FUNCTIONS
# ============================================================================

show_usage() {
    cat <<EOF
Usage: $0 [OPTIONS]

Export game server statistics as Prometheus metrics.

MODES:
    --textfile      Write to node_exporter textfile collector
    --http          Run HTTP server on port $HTTP_PORT

OPTIONS:
    -p, --port                  HTTP port (default: 9195)
    -o, --output                Output file path
    --minecraft-host            Minecraft server hostname/IP
    --minecraft-query-port      Minecraft query port (default: 25565)
    --minecraft-rcon-port       Minecraft RCON port (default: 25575)
    --minecraft-rcon-pass       Minecraft RCON password
    --valheim-host              Valheim server hostname/IP
    --valheim-query-port        Valheim query port (default: 2457)
    --palworld-host             Palworld server hostname/IP
    --palworld-query-port       Palworld REST API port (default: 8212)

EXAMPLES:
    $0 --textfile                                        # Write to textfile collector
    $0 --http --port 9195                                # Run HTTP server
    $0 --minecraft-host mc.local --valheim-host vh.local # Multiple servers
    $0 -o /tmp/game-servers.prom                         # Write to custom file

EOF
    exit 0
}

parse_args() {
    while [[ $# -gt 0 ]]; do
        case $1 in
            -h|--help) show_usage ;;
            --textfile) OUTPUT_FILE="$TEXTFILE_DIR/game_server.prom"; shift ;;
            --http) HTTP_MODE=true; shift ;;
            -p|--port) HTTP_PORT="$2"; shift 2 ;;
            -o|--output) OUTPUT_FILE="$2"; shift 2 ;;
            --minecraft-host) MINECRAFT_HOST="$2"; shift 2 ;;
            --minecraft-query-port) MINECRAFT_QUERY_PORT="$2"; shift 2 ;;
            --minecraft-rcon-port) MINECRAFT_RCON_PORT="$2"; shift 2 ;;
            --minecraft-rcon-pass) MINECRAFT_RCON_PASS="$2"; shift 2 ;;
            --valheim-host) VALHEIM_HOST="$2"; shift 2 ;;
            --valheim-query-port) VALHEIM_QUERY_PORT="$2"; shift 2 ;;
            --palworld-host) PALWORLD_HOST="$2"; shift 2 ;;
            --palworld-query-port) PALWORLD_QUERY_PORT="$2"; shift 2 ;;
            *) echo "Unknown option: $1" >&2; exit 1 ;;
        esac
    done
}

# Check prerequisites
# Returns: 0 if OK, 1 if error
check_prerequisites() {
    if ! command -v nc >/dev/null 2>&1; then
        echo "ERROR: nc (nmap-ncat) not found" >&2
        return 1
    fi

    if [ -n "$PALWORLD_HOST" ] && ! command -v curl >/dev/null 2>&1; then
        echo "ERROR: curl not found (required for Palworld REST API)" >&2
        return 1
    fi

    return 0
}

# Escape special characters in Prometheus label values
# Args: $1 - string to escape
# Returns: escaped string safe for Prometheus labels
prom_escape() {
    local val="$1"
    val="${val//\\/\\\\}"
    val="${val//\"/\\\"}"
    val="${val//$'\n'/}"
    echo "$val"
}

# ============================================================================
# GAME SERVER QUERY FUNCTIONS
# ============================================================================

# Query Minecraft server using python3 mcstatus or basic TCP check
# Args: $1 - host, $2 - port
# Sets global variables: mc_up, mc_players_online, mc_players_max, mc_version, mc_motd, mc_tps, mc_query_duration
query_minecraft() {
    local host="$1"
    local port="$2"
    local query_start query_end

    mc_up=0
    mc_players_online=0
    mc_players_max=0
    mc_version="unknown"
    mc_motd="unknown"
    mc_tps=""
    mc_query_duration=0

    query_start=$(date +%s%N)

    # Try python3 mcstatus first (most reliable)
    if command -v python3 >/dev/null 2>&1; then
        local py_result
        py_result=$(python3 -c "
import sys
try:
    from mcstatus import JavaServer
    server = JavaServer.lookup('${host}:${port}', timeout=5)
    status = server.status()
    print('UP')
    print(status.players.online)
    print(status.players.max)
    print(status.version.name)
    desc = status.description
    if isinstance(desc, dict):
        desc = desc.get('text', 'unknown')
    print(str(desc).replace(chr(10), ' '))
except ImportError:
    print('NO_MCSTATUS')
except Exception as e:
    print('DOWN')
" 2>/dev/null) || true

        local first_line
        first_line=$(echo "$py_result" | head -1)

        if [ "$first_line" = "UP" ]; then
            mc_up=1
            mc_players_online=$(echo "$py_result" | sed -n '2p')
            mc_players_max=$(echo "$py_result" | sed -n '3p')
            mc_version=$(echo "$py_result" | sed -n '4p')
            mc_motd=$(echo "$py_result" | sed -n '5p')
        elif [ "$first_line" != "NO_MCSTATUS" ]; then
            # mcstatus available but server is down
            query_end=$(date +%s%N)
            mc_query_duration=$(( (query_end - query_start) / 1000000000 ))
            return
        fi
    fi

    # Fallback: basic TCP check if mcstatus not available or not tried yet
    if [ "$mc_up" -eq 0 ] && [ -z "${py_result:-}" ] || { [ -n "${first_line:-}" ] && [ "$first_line" = "NO_MCSTATUS" ]; }; then
        if nc -z -w 3 "$host" "$port" 2>/dev/null; then
            mc_up=1
            # Try to read SLP response for basic info
            local slp_response
            slp_response=$(printf '\xfe\x01' | nc -w 3 "$host" "$port" 2>/dev/null | strings 2>/dev/null) || true
            if [ -n "$slp_response" ]; then
                # Legacy SLP response: §1\0<protocol>\0<version>\0<motd>\0<online>\0<max>
                mc_version=$(echo "$slp_response" | tr '\0' '\n' | sed -n '4p' 2>/dev/null) || mc_version="unknown"
                mc_motd=$(echo "$slp_response" | tr '\0' '\n' | sed -n '5p' 2>/dev/null) || mc_motd="unknown"
                mc_players_online=$(echo "$slp_response" | tr '\0' '\n' | sed -n '6p' 2>/dev/null) || mc_players_online=0
                mc_players_max=$(echo "$slp_response" | tr '\0' '\n' | sed -n '7p' 2>/dev/null) || mc_players_max=0
                # Sanitize numeric values
                [[ "$mc_players_online" =~ ^[0-9]+$ ]] || mc_players_online=0
                [[ "$mc_players_max" =~ ^[0-9]+$ ]] || mc_players_max=0
            fi
        fi
    fi

    # Try RCON for TPS if credentials are provided and server is up
    if [ "$mc_up" -eq 1 ] && [ -n "$MINECRAFT_RCON_PASS" ]; then
        local tps_result
        tps_result=$(python3 -c "
import sys
try:
    from mcrcon import MCRcon
    with MCRcon('${host}', '${MINECRAFT_RCON_PASS}', port=${MINECRAFT_RCON_PORT}) as mcr:
        resp = mcr.command('tps')
        # Parse TPS from response (e.g., '§6TPS from last 1m, 5m, 15m: §a20.0, §a20.0, §a20.0')
        import re
        nums = re.findall(r'[\d.]+', resp)
        if nums:
            print(nums[-1])  # Last TPS value (15m average)
except Exception:
    pass
" 2>/dev/null) || true
        if [ -n "$tps_result" ]; then
            mc_tps="$tps_result"
        fi
    fi

    query_end=$(date +%s%N)
    mc_query_duration=$(( (query_end - query_start) / 1000000000 ))
}

# Query Valheim server using Steam A2S protocol or TCP fallback
# Args: $1 - host, $2 - port
# Sets global variables: vh_up, vh_players_online, vh_players_max, vh_version, vh_motd, vh_query_duration
query_valheim() {
    local host="$1"
    local port="$2"
    local query_start query_end

    vh_up=0
    vh_players_online=0
    vh_players_max=0
    vh_version="unknown"
    vh_motd="unknown"
    vh_query_duration=0

    query_start=$(date +%s%N)

    # Try python3 A2S query first (Steam query protocol)
    if command -v python3 >/dev/null 2>&1; then
        local py_result
        py_result=$(python3 -c "
import sys
try:
    import a2s
    address = ('${host}', ${port})
    info = a2s.info(address, timeout=5)
    print('UP')
    print(info.player_count)
    print(info.max_players)
    print(info.version)
    print(info.server_name.replace(chr(10), ' '))
except ImportError:
    print('NO_A2S')
except Exception:
    print('DOWN')
" 2>/dev/null) || true

        local first_line
        first_line=$(echo "$py_result" | head -1)

        if [ "$first_line" = "UP" ]; then
            vh_up=1
            vh_players_online=$(echo "$py_result" | sed -n '2p')
            vh_players_max=$(echo "$py_result" | sed -n '3p')
            vh_version=$(echo "$py_result" | sed -n '4p')
            vh_motd=$(echo "$py_result" | sed -n '5p')
        elif [ "$first_line" != "NO_A2S" ]; then
            query_end=$(date +%s%N)
            vh_query_duration=$(( (query_end - query_start) / 1000000000 ))
            return
        fi
    fi

    # Fallback: TCP port check on game port (query port - 1 is typically the game port)
    if [ "$vh_up" -eq 0 ]; then
        local game_port=$((port - 1))
        if nc -z -w 3 "$host" "$game_port" 2>/dev/null || nc -z -w 3 "$host" "$port" 2>/dev/null; then
            vh_up=1
        fi
    fi

    query_end=$(date +%s%N)
    vh_query_duration=$(( (query_end - query_start) / 1000000000 ))
}

# Query Palworld server using REST API or TCP fallback
# Args: $1 - host, $2 - port
# Sets global variables: pw_up, pw_players_online, pw_players_max, pw_version, pw_motd, pw_query_duration
query_palworld() {
    local host="$1"
    local port="$2"
    local query_start query_end

    pw_up=0
    pw_players_online=0
    pw_players_max=0
    pw_version="unknown"
    pw_motd="unknown"
    pw_query_duration=0

    query_start=$(date +%s%N)

    # Try REST API query first
    if command -v curl >/dev/null 2>&1; then
        local api_response
        api_response=$(curl -s -m 5 "http://${host}:${port}/v1/api/info" 2>/dev/null) || true

        if [ -n "$api_response" ] && command -v python3 >/dev/null 2>&1; then
            local parse_result
            parse_result=$(python3 -c "
import json, sys
try:
    data = json.loads('''${api_response}''')
    print('UP')
    print(data.get('currentPlayerNum', 0))
    print(data.get('maxPlayerNum', 0))
    print(data.get('version', 'unknown'))
    print(data.get('serverName', 'unknown').replace(chr(10), ' '))
except Exception:
    print('PARSE_FAIL')
" 2>/dev/null) || true

            local first_line
            first_line=$(echo "$parse_result" | head -1)

            if [ "$first_line" = "UP" ]; then
                pw_up=1
                pw_players_online=$(echo "$parse_result" | sed -n '2p')
                pw_players_max=$(echo "$parse_result" | sed -n '3p')
                pw_version=$(echo "$parse_result" | sed -n '4p')
                pw_motd=$(echo "$parse_result" | sed -n '5p')
            fi
        elif [ -n "$api_response" ]; then
            # curl got a response but no python3 to parse JSON
            pw_up=1
        fi
    fi

    # Fallback: TCP port check
    if [ "$pw_up" -eq 0 ]; then
        if nc -z -w 3 "$host" "$port" 2>/dev/null; then
            pw_up=1
        fi
    fi

    query_end=$(date +%s%N)
    pw_query_duration=$(( (query_end - query_start) / 1000000000 ))
}

# ============================================================================
# METRIC GENERATION
# ============================================================================

# Generate all Prometheus metrics
# Returns: Prometheus text format metrics on stdout
generate_metrics() {
    local script_start
    script_start=$(date +%s)

    # Check prerequisites
    if ! check_prerequisites; then
        return
    fi

    # Check that at least one server is configured
    if [ -z "$MINECRAFT_HOST" ] && [ -z "$VALHEIM_HOST" ] && [ -z "$PALWORLD_HOST" ]; then
        echo "# No game servers configured. Use --minecraft-host, --valheim-host, or --palworld-host" >&2
        return
    fi

    cat <<EOF
# HELP game_server_up Server reachability (1=up, 0=down)
# TYPE game_server_up gauge
EOF

    cat <<EOF
# HELP game_server_players_online Current online player count
# TYPE game_server_players_online gauge
EOF

    cat <<EOF
# HELP game_server_players_max Maximum player slots
# TYPE game_server_players_max gauge
EOF

    cat <<EOF
# HELP game_server_info Server version and MOTD information
# TYPE game_server_info gauge
EOF

    cat <<EOF
# HELP game_server_tps Server ticks per second
# TYPE game_server_tps gauge
EOF

    cat <<EOF
# HELP game_server_query_duration_seconds Time to query individual server
# TYPE game_server_query_duration_seconds gauge
EOF

    echo ""

    # ========================================================================
    # MINECRAFT METRICS
    # ========================================================================

    if [ -n "$MINECRAFT_HOST" ]; then
        local mc_server="${MINECRAFT_HOST}:${MINECRAFT_QUERY_PORT}"

        query_minecraft "$MINECRAFT_HOST" "$MINECRAFT_QUERY_PORT"

        echo "game_server_up{game=\"minecraft\",server=\"$(prom_escape "$mc_server")\"} $mc_up"

        if [ "$mc_up" -eq 1 ]; then
            echo "game_server_players_online{game=\"minecraft\",server=\"$(prom_escape "$mc_server")\"} $mc_players_online"
            echo "game_server_players_max{game=\"minecraft\",server=\"$(prom_escape "$mc_server")\"} $mc_players_max"
            echo "game_server_info{game=\"minecraft\",server=\"$(prom_escape "$mc_server")\",version=\"$(prom_escape "$mc_version")\",motd=\"$(prom_escape "$mc_motd")\"} 1"

            if [ -n "$mc_tps" ]; then
                echo "game_server_tps{game=\"minecraft\",server=\"$(prom_escape "$mc_server")\"} $mc_tps"
            fi
        fi

        echo "game_server_query_duration_seconds{game=\"minecraft\",server=\"$(prom_escape "$mc_server")\"} $mc_query_duration"
        echo ""
    fi

    # ========================================================================
    # VALHEIM METRICS
    # ========================================================================

    if [ -n "$VALHEIM_HOST" ]; then
        local vh_server="${VALHEIM_HOST}:${VALHEIM_QUERY_PORT}"

        query_valheim "$VALHEIM_HOST" "$VALHEIM_QUERY_PORT"

        echo "game_server_up{game=\"valheim\",server=\"$(prom_escape "$vh_server")\"} $vh_up"

        if [ "$vh_up" -eq 1 ]; then
            echo "game_server_players_online{game=\"valheim\",server=\"$(prom_escape "$vh_server")\"} $vh_players_online"
            echo "game_server_players_max{game=\"valheim\",server=\"$(prom_escape "$vh_server")\"} $vh_players_max"
            echo "game_server_info{game=\"valheim\",server=\"$(prom_escape "$vh_server")\",version=\"$(prom_escape "$vh_version")\",motd=\"$(prom_escape "$vh_motd")\"} 1"
        fi

        echo "game_server_query_duration_seconds{game=\"valheim\",server=\"$(prom_escape "$vh_server")\"} $vh_query_duration"
        echo ""
    fi

    # ========================================================================
    # PALWORLD METRICS
    # ========================================================================

    if [ -n "$PALWORLD_HOST" ]; then
        local pw_server="${PALWORLD_HOST}:${PALWORLD_QUERY_PORT}"

        query_palworld "$PALWORLD_HOST" "$PALWORLD_QUERY_PORT"

        echo "game_server_up{game=\"palworld\",server=\"$(prom_escape "$pw_server")\"} $pw_up"

        if [ "$pw_up" -eq 1 ]; then
            echo "game_server_players_online{game=\"palworld\",server=\"$(prom_escape "$pw_server")\"} $pw_players_online"
            echo "game_server_players_max{game=\"palworld\",server=\"$(prom_escape "$pw_server")\"} $pw_players_max"
            echo "game_server_info{game=\"palworld\",server=\"$(prom_escape "$pw_server")\",version=\"$(prom_escape "$pw_version")\",motd=\"$(prom_escape "$pw_motd")\"} 1"
        fi

        echo "game_server_query_duration_seconds{game=\"palworld\",server=\"$(prom_escape "$pw_server")\"} $pw_query_duration"
        echo ""
    fi

    # ========================================================================
    # EXPORTER RUNTIME
    # ========================================================================

    local script_end script_duration
    script_end=$(date +%s)
    script_duration=$((script_end - script_start))

    cat <<EOF
# HELP game_server_exporter_duration_seconds Time to generate all metrics
# TYPE game_server_exporter_duration_seconds gauge
game_server_exporter_duration_seconds $script_duration

# HELP game_server_exporter_last_run_timestamp Unix timestamp of last successful run
# TYPE game_server_exporter_last_run_timestamp gauge
game_server_exporter_last_run_timestamp $script_end
EOF

    echo ""
}

# ============================================================================
# HTTP SERVER MODE
# ============================================================================

# Run simple HTTP server using netcat
# Serves metrics on /metrics endpoint
run_http_server() {
    echo "Starting game server exporter on port $HTTP_PORT..." >&2

    if ! command -v nc >/dev/null 2>&1; then
        echo "ERROR: netcat (nc) required for HTTP mode" >&2
        exit 1
    fi

    # Infinite loop accepting HTTP requests
    while true; do
        {
            read -r request
            # Check if request is for /metrics endpoint
            if [[ "$request" =~ ^GET\ /metrics ]]; then
                echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/plain; version=0.0.4\r\n\r"
                generate_metrics
            else  # Serve HTML landing page for other requests
                echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r"
                cat <<EOF
<!DOCTYPE html>
<html>
<head><title>Game Server Exporter v1.0</title></head>
<body>
<h1>Game Server Prometheus Exporter v1.0</h1>
<p><a href="/metrics">Metrics</a></p>
<p>Operational metrics from Minecraft, Valheim, and Palworld servers.</p>
</body>
</html>
EOF
            fi
        } | nc -l -p "$HTTP_PORT" -q 1 2>/dev/null
    done
}

# ============================================================================
# MAIN EXECUTION
# ============================================================================

# Main entry point - routes to appropriate output mode
main() {
    parse_args "$@"

    if [ "$HTTP_MODE" = true ]; then
        # Run HTTP server (blocks until killed)
        run_http_server
    elif [ -n "$OUTPUT_FILE" ]; then
        # Textfile collector mode: write atomically using temp file
        local output_dir
        output_dir="$(dirname "$OUTPUT_FILE")"
        mkdir -p "$output_dir"

        # Create temp file in SAME directory for atomic rename (same filesystem)
        local temp_file
        temp_file=$(mktemp "${output_dir}/.game_server_metrics.XXXXXX")

        # Generate metrics to temp file
        if ! generate_metrics > "$temp_file" 2>/dev/null; then
            rm -f "$temp_file"
            echo "ERROR: Failed to generate metrics" >&2
            exit 1
        fi

        # Validate: file must exist, have content
        local file_lines
        file_lines=$(wc -l < "$temp_file" 2>/dev/null || echo 0)

        if [ "$file_lines" -lt 10 ]; then
            rm -f "$temp_file"
            echo "ERROR: Metrics file too small ($file_lines lines), keeping previous" >&2
            exit 1
        fi

        # Set permissions before move
        chmod 644 "$temp_file"

        # Atomic rename - no gap where file is missing
        mv -f "$temp_file" "$OUTPUT_FILE"

        echo "Metrics written to $OUTPUT_FILE ($file_lines lines)" >&2
    else
        # Default: output to stdout
        generate_metrics
    fi
}

# Execute main function with all script arguments
main "$@"