#!/bin/bash
set -e

####################### Configuration ######################

ENABLE_NETWORK_STATS="yes" ## Enable or disable network statistics generation using vnStat
INTERFACE="eth0" ## Network interface to monitor (e.g., eth0, wlan0)

PAGE_TITLE="$HOSTNAME - Chrony Statistics"
OUTPUT_DIR="/var/www/html/" ## Output directory for HTML and images
HTML_FILENAME="index.html" ## Output HTML file name

RRD_DIR="/var/lib/chrony-rrd"
RRD_FILE="$RRD_DIR/chrony.rrd" ## RRD file for storing chrony statistics

ENABLE_LOGGING="yes"
LOG_FILE="/var/log/chrony-network-stats.log"
# In-script log truncation (prevents logfile from growing indefinitely)
# - LOG_MAX_SIZE_BYTES: when >0 use byte-based truncation (default 10MB)
# - LOG_MAX_LINES: when >0 use line-based truncation instead of bytes
# - LOG_TRIM_TO_BYTES / LOG_TRIM_TO_LINES: amount to keep when trimming (defaults to half)
LOG_MAX_SIZE_BYTES=0 # $((10 * 1024 * 1024))  # 10 MB
LOG_MAX_LINES=10000
LOG_TRIM_TO_BYTES=0 # $((LOG_MAX_SIZE_BYTES / 2))
LOG_TRIM_TO_LINES=9000

AUTO_REFRESH_SECONDS=300 ## Auto-refresh interval in seconds (0 = disabled, e.g., 300 for 5 minutes)
GITHUB_REPO_LINK_SHOW="yes" ## You can display the link to the repo 'chrony-stats' in the HTML footer | Not required | Default: no


###### Advanced Configuration ######

CHRONY_ALLOW_DNS_LOOKUP="no" ##  Yes allow DNS reverse lookups. No to prevent slow DNS reverse lookups
DISPLAY_PRESET="default" # Preset for large screens. Options: default | 2k | 4k

TIMEOUT_SECONDS=5
SERVER_STATS_UPPER_LIMIT=250000 ## When chrony restarts, it generate abnormally high values (e.g., 12M) | This filters out values above the threshold
##############################################################

WIDTH=800   ## These graph sizes are changing with DISPLAY_PRESET
HEIGHT=300  ## 

log_message() {
    local level="$1"
    local message="$2"
    if [[ "$ENABLE_LOGGING" == "yes" ]]; then
        # ensure logfile stays within configured limits before writing
        rotate_logfile_if_needed
        printf '[%s] [%s] %s\n' "$(date '+%Y-%m-%d %H:%M:%S')" "$level" "$message" >> "$LOG_FILE"
    fi
    echo "[$level] $message"
}

rotate_logfile_if_needed() {
    # no-op when logging disabled or logfile missing
    [ "$ENABLE_LOGGING" != "yes" ] && return 0
    [ -f "$LOG_FILE" ] || return 0

    # Line-based truncation (preferred when configured)
    if [[ "${LOG_MAX_LINES:-0}" -gt 0 ]]; then
        local total_lines
        total_lines=$(wc -l < "$LOG_FILE" 2>/dev/null || echo 0)
        if [[ "$total_lines" -gt "$LOG_MAX_LINES" ]]; then
            local keep_lines=${LOG_TRIM_TO_LINES:-$(( LOG_MAX_LINES / 2 ))}
            (( keep_lines <= 0 )) && keep_lines=$(( LOG_MAX_LINES / 2 ))
            tail -n "$keep_lines" "$LOG_FILE" > "${LOG_FILE}.tmp" && mv "${LOG_FILE}.tmp" "$LOG_FILE"
            printf '[%s] [INFO] Log truncated to last %d lines (was %d lines)\n' "$(date '+%Y-%m-%d %H:%M:%S')" "$keep_lines" "$total_lines" >> "$LOG_FILE"
        fi
        return 0
    fi

    # Size-based truncation (bytes)
    local max_bytes=${LOG_MAX_SIZE_BYTES:-10485760}
    local filesize
    if ! filesize=$(stat -c%s "$LOG_FILE" 2>/dev/null); then
        filesize=$(wc -c < "$LOG_FILE" 2>/dev/null || echo 0)
    fi
    if [[ "$filesize" -ge "$max_bytes" ]]; then
        local keep_bytes=${LOG_TRIM_TO_BYTES:-$(( max_bytes / 2 ))}
        (( keep_bytes <= 0 )) && keep_bytes=$(( max_bytes / 2 ))
        tail -c "$keep_bytes" "$LOG_FILE" > "${LOG_FILE}.tmp" && mv "${LOG_FILE}.tmp" "$LOG_FILE"
        printf '[%s] [INFO] Log truncated to last %d bytes (was %d bytes)\n' "$(date '+%Y-%m-%d %H:%M:%S')" "$keep_bytes" "$filesize" >> "$LOG_FILE"
    fi
}

configure_display_preset() {
    local preset="${DISPLAY_PRESET,,}"
    local scale_pct=100
    local container_px=1400
    local font_px=16

    case "$preset" in
        1080p|1080|default)
            scale_pct=100; container_px=1400; font_px=16 ;;
        2k|1440p|qhd)
            scale_pct=135; container_px=2000; font_px=18 ;;
        4k|2160p|uhd)
            scale_pct=170; container_px=2600; font_px=20 ;;
        *)
            scale_pct=100; container_px=1400; font_px=16 ;;
    esac

    WIDTH=$(( WIDTH * scale_pct / 100 ))
    HEIGHT=$(( HEIGHT * scale_pct / 100 ))

    CSS_CUSTOM_ROOT=$(cat <<EOF
:root {
    --container-max: ${container_px}px;
    --font-size-base: ${font_px}px;
}
EOF
)

    log_message "INFO" "Preset '${DISPLAY_PRESET}' -> graph ${WIDTH}x${HEIGHT}, container ${container_px}px, font ${font_px}px"
}

validate_numeric() {
    local value="$1"
    local name="$2"
    if ! [[ "$value" =~ ^[0-9]+$ ]]; then
        log_message "ERROR" "Invalid $name: $value. Must be numeric."
        exit 1
    fi
}

check_commands() {
    local commands=("rrdtool" "chronyc" "sudo" "timeout")
    
    if [[ "$ENABLE_NETWORK_STATS" == "yes" ]]; then
        commands+=("vnstati")
    fi
    
    for cmd in "${commands[@]}"; do
        if ! command -v "$cmd" &>/dev/null; then
            log_message "ERROR" "Command '$cmd' not found in PATH."
            exit 1
        fi
    done
}

setup_directories() {
    log_message "INFO" "Checking and preparing directories..."
    for dir in "$OUTPUT_DIR" "$RRD_DIR" "$OUTPUT_DIR/img"; do
        mkdir -p "$dir" || {
            log_message "ERROR" "Failed to create directory: $dir"
            exit 1
        }
        if [ ! -w "$dir" ]; then
            log_message "ERROR" "Directory '$dir' is not writable."
            exit 1
        fi
    done
}

generate_vnstat_images() {
    if [[ "$ENABLE_NETWORK_STATS" != "yes" ]]; then
        log_message "INFO" "Network stats disabled, skipping vnStat image generation..."
        return 0
    fi
    
    log_message "INFO" "Generating vnStat images for interface '$INTERFACE'..."
    local modes=("s" "d" "t" "h" "m" "y")
    for mode in "${modes[@]}"; do
        vnstati -"$mode" -i "$INTERFACE" -o "$OUTPUT_DIR/img/vnstat_${mode}.png" || {
            log_message "ERROR" "Failed to generate vnstat image for mode $mode Check configuaration section : INTERFACE=\"here\""
            exit 1
        }
    done
}

collect_chrony_data() {
    log_message "INFO" "Collecting Chrony data..."
    
    local CHRONYC_OPTS=""
    if [[ "$CHRONY_ALLOW_DNS_LOOKUP" == "no" ]]; then
        CHRONYC_OPTS="-n"
        log_message "INFO" "Using chronyc -n option to prevent DNS lookups"
    fi
    
    get_html() {
        timeout "$TIMEOUT_SECONDS"s sudo chronyc $CHRONYC_OPTS "$1" -v 2>&1 | sed 's/&/\&amp;/g;s/</\&lt;/g;s/>/\&gt;/g' || {
            log_message "ERROR" "Failed to collect chronyc $1 data"
            return 1
        }
    }

    RAW_TRACKING=$(timeout "$TIMEOUT_SECONDS"s sudo chronyc $CHRONYC_OPTS tracking) || {
        log_message "ERROR" "Failed to collect chronyc tracking data"
        exit 1
    }
    CHRONYC_TRACKING_HTML=$(echo "$RAW_TRACKING" | sed 's/&/\&amp;/g;s/</\&lt;/g;s/>/\&gt;/g')
    CHRONYC_SOURCES=$(get_html sources) || exit 1
    CHRONYC_SOURCESTATS=$(get_html sourcestats) || exit 1
    CHRONYC_SELECTDATA=$(get_html selectdata) || exit 1
}

extract_chronyc_values() {
    extract_val() {
        echo "$RAW_TRACKING" | awk "/$1/ {print \$($2)}" | grep -E '^[-+]?[0-9.]+$' || echo "U"
    }

    OFFSET=$(extract_val "Last offset" "NF-1")

    local systime_line
    systime_line=$(echo "$RAW_TRACKING" | grep "System time")
    if [[ -n "$systime_line" ]]; then
        local value
        value=$(echo "$systime_line" | awk '{print $4}')
        if [[ "$systime_line" == *"slow"* ]]; then
            SYSTIME="-$value"
        else
            SYSTIME="$value"
        fi
    else
        SYSTIME="U"
    fi

    FREQ=$(extract_val "Frequency" "NF-2")
    RESID_FREQ=$(extract_val "Residual freq" "NF-1")
    SKEW=$(extract_val "Skew" "NF-1")
    DELAY=$(extract_val "Root delay" "NF-1")
    DISPERSION=$(extract_val "Root dispersion" "NF-1")
    STRATUM=$(extract_val "Stratum" "3")

    local CHRONYC_OPTS=""
    if [[ "$CHRONY_ALLOW_DNS_LOOKUP" == "no" ]]; then
        CHRONYC_OPTS="-n"
    fi

    RAW_STATS=$(LC_ALL=C sudo chronyc $CHRONYC_OPTS serverstats) || {
        log_message "ERROR" "Failed to collect chronyc serverstats"
        exit 1
    }
    get_stat() {
        echo "$RAW_STATS" | awk -F'[[:space:]]*:[[:space:]]*' "/$1/ {print \$2}" | grep -E '^[0-9]+$' || echo "U"
    }
    PKTS_RECV=$(get_stat "NTP packets received")
    PKTS_DROP=$(get_stat "NTP packets dropped")
    CMD_RECV=$(get_stat "Command packets received")
    CMD_DROP=$(get_stat "Command packets dropped")
    LOG_DROP=$(get_stat "Client log records dropped")
    INTERLEAVED=$(get_stat "Interleaved NTP packets")
    TS_HELD=$(get_stat "NTP timestamps held")
}

create_rrd_database() {
    if [ ! -f "$RRD_FILE" ]; then
        log_message "INFO" "Creating new RRD file: $RRD_FILE"
        LC_ALL=C rrdtool create "$RRD_FILE" --step 300 \
            DS:offset:GAUGE:600:U:U DS:frequency:GAUGE:600:U:U DS:resid_freq:GAUGE:600:U:U DS:skew:GAUGE:600:U:U \
            DS:delay:GAUGE:600:U:U DS:dispersion:GAUGE:600:U:U DS:stratum:GAUGE:600:0:16 \
	    DS:systime:GAUGE:600:U:U \
            DS:pkts_recv:COUNTER:600:0:U DS:pkts_drop:COUNTER:600:0:U DS:cmd_recv:COUNTER:600:0:U \
            DS:cmd_drop:COUNTER:600:0:U DS:log_drop:COUNTER:600:0:U DS:interleaved:COUNTER:600:0:U \
            DS:ts_held:GAUGE:600:0:U \
            RRA:AVERAGE:0.5:1:576 RRA:AVERAGE:0.5:6:672 RRA:AVERAGE:0.5:24:732 RRA:AVERAGE:0.5:288:730 \
            RRA:MAX:0.5:1:576 RRA:MAX:0.5:6:672 RRA:MAX:0.5:24:732 RRA:MAX:0.5:288:730 \
            RRA:MIN:0.5:1:576 RRA:MIN:0.5:6:672 RRA:MIN:0.5:24:732 RRA:MIN:0.5:288:730 || {
                log_message "ERROR" "Failed to create RRD database"
                exit 1
            }
    fi
}

update_rrd_database() {
    log_message "INFO" "Updating RRD database..."
    UPDATE_STRING="N:$OFFSET:$FREQ:$RESID_FREQ:$SKEW:$DELAY:$DISPERSION:$STRATUM:$SYSTIME:$PKTS_RECV:$PKTS_DROP:$CMD_RECV:$CMD_DROP:$LOG_DROP:$INTERLEAVED:$TS_HELD"
    LC_ALL=C rrdtool update "$RRD_FILE" "$UPDATE_STRING" || {
        log_message "ERROR" "Failed to update RRD database"
        exit 1
    }
}

generate_graphs() {
    log_message "INFO" "Generating graphs..."
    local END_TIME=$(date +%s)
    
    declare -A time_periods=(
        ["day"]="end-1d"
        ["week"]="end-1w" 
        ["month"]="end-1m"
    )
    
    declare -A period_titles=(
        ["day"]="by day"
        ["week"]="by week"
        ["month"]="by month"
    )
    
    declare -A graphs=(
        ["chrony_serverstats"]="--title 'Chrony Server Statistics - PERIOD_TITLE' --vertical-label 'Packets/second' \
            --lower-limit 0 --rigid --units-exponent 0 \
            DEF:pkts_recv_raw='$RRD_FILE':pkts_recv:AVERAGE \
            DEF:pkts_drop_raw='$RRD_FILE':pkts_drop:AVERAGE \
            DEF:cmd_recv_raw='$RRD_FILE':cmd_recv:AVERAGE \
            DEF:cmd_drop_raw='$RRD_FILE':cmd_drop:AVERAGE \
            DEF:log_drop_raw='$RRD_FILE':log_drop:AVERAGE \
            CDEF:pkts_recv=pkts_recv_raw,$SERVER_STATS_UPPER_LIMIT,GT,UNKN,pkts_recv_raw,IF \
            CDEF:pkts_drop=pkts_drop_raw,$SERVER_STATS_UPPER_LIMIT,GT,UNKN,pkts_drop_raw,IF \
            CDEF:cmd_recv=cmd_recv_raw,$SERVER_STATS_UPPER_LIMIT,GT,UNKN,cmd_recv_raw,IF \
            CDEF:cmd_drop=cmd_drop_raw,$SERVER_STATS_UPPER_LIMIT,GT,UNKN,cmd_drop_raw,IF \
            CDEF:log_drop=log_drop_raw,$SERVER_STATS_UPPER_LIMIT,GT,UNKN,log_drop_raw,IF \
            'COMMENT: \l' \
            'AREA:pkts_recv#C4FFC4:Packets received            ' \
            'LINE1:pkts_recv#00E000:' \
            'GPRINT:pkts_recv:LAST:Cur\: %5.2lf%s' \
            'GPRINT:pkts_recv:MIN:Min\: %5.2lf%s' \
            'GPRINT:pkts_recv:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:pkts_recv:MAX:Max\: %5.2lf%s\l' \
            'LINE1:pkts_drop#FF8C00:Packets dropped             ' \
            'GPRINT:pkts_drop:LAST:Cur\: %5.2lf%s' \
            'GPRINT:pkts_drop:MIN:Min\: %5.2lf%s' \
            'GPRINT:pkts_drop:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:pkts_drop:MAX:Max\: %5.2lf%s\l' \
            'LINE1:cmd_recv#4169E1:Command packets received    ' \
            'GPRINT:cmd_recv:LAST:Cur\: %5.2lf%s' \
            'GPRINT:cmd_recv:MIN:Min\: %5.2lf%s' \
            'GPRINT:cmd_recv:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:cmd_recv:MAX:Max\: %5.2lf%s\l' \
            'LINE1:cmd_drop#FFD700:Command packets dropped     ' \
            'GPRINT:cmd_drop:LAST:Cur\: %5.2lf%s' \
            'GPRINT:cmd_drop:MIN:Min\: %5.2lf%s' \
            'GPRINT:cmd_drop:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:cmd_drop:MAX:Max\: %5.2lf%s\l' \
            'LINE1:log_drop#9400D3:Client log records dropped  ' \
            'GPRINT:log_drop:LAST:Cur\: %5.2lf%s' \
            'GPRINT:log_drop:MIN:Min\: %5.2lf%s' \
            'GPRINT:log_drop:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:log_drop:MAX:Max\: %5.2lf%s\l'"
        ["chrony_tracking"]="--title 'Chrony Dispersion + Stratum - PERIOD_TITLE' --vertical-label 'milliseconds' --alt-autoscale \
            --units-exponent 0 \
            DEF:stratum='$RRD_FILE':stratum:AVERAGE \
            DEF:freq='$RRD_FILE':frequency:AVERAGE \
            DEF:skew='$RRD_FILE':skew:AVERAGE \
            DEF:delay='$RRD_FILE':delay:AVERAGE \
            DEF:dispersion='$RRD_FILE':dispersion:AVERAGE \
            CDEF:skew_scaled=skew,100,* \
            CDEF:delay_scaled=delay,1000,* \
            CDEF:disp_scaled=dispersion,1000,* \
            'COMMENT: \l' \
            'LINE1:stratum#00ff00:Stratum                                    ' \
            'GPRINT:stratum:LAST:  Cur\: %5.2lf%s' \
            'GPRINT:stratum:MIN:Min\: %5.2lf%s' \
            'GPRINT:stratum:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:stratum:MAX:Max\: %5.2lf%s\l' \
            'LINE1:disp_scaled#9400D3:Root dispersion    [Root dispersion]       ' \
            'GPRINT:disp_scaled:LAST:  Cur\: %5.2lf%s' \
            'GPRINT:disp_scaled:MIN:Min\: %5.2lf%s' \
            'GPRINT:disp_scaled:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:disp_scaled:MAX:Max\: %5.2lf%s\l'"
        ["chrony_offset"]="--title 'Chrony System Time Offset - PERIOD_TITLE' --vertical-label 'milliseconds' \
            DEF:offset='$RRD_FILE':offset:AVERAGE \
	    DEF:systime='$RRD_FILE':systime:AVERAGE \
	    CDEF:systime_scaled=systime,1000,* \
	    CDEF:offset_ms=offset,1000,* \
            'LINE2:offset_ms#00ff00:Actual Offset from NTP Source [Last Offset] ' \
            'GPRINT:offset_ms:LAST:  Cur\: %5.2lf%s' \
	    'GPRINT:offset_ms:MIN:Min\: %5.2lf%s' \
            'GPRINT:offset_ms:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:offset_ms:MAX:Max\: %5.2lf%s\l' \
            'LINE1:systime_scaled#4169E1:System Clock Adjustment       [System Time] ' \
            'GPRINT:systime_scaled:LAST:  Cur\: %5.2lf%s' \
            'GPRINT:systime_scaled:MIN:Min\: %5.2lf%s' \
            'GPRINT:systime_scaled:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:systime_scaled:MAX:Max\: %5.2lf%s\l'"
        ["chrony_delay"]="--title 'Chrony Root Delay - PERIOD_TITLE' --vertical-label 'milliseconds' --units-exponent 0 \
            DEF:delay='$RRD_FILE':delay:AVERAGE \
            CDEF:delay_ms=delay,1000,* \
            LINE2:delay_ms#00ff00:'Network Delay to Root Source   [Root Delay]  ' \
            'GPRINT:delay_ms:LAST:Cur\: %5.2lf%s' \
            'GPRINT:delay_ms:MIN:Min\: %5.2lf%s' \
            'GPRINT:delay_ms:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:delay_ms:MAX:Max\: %5.2lf%s\l'"
        ["chrony_frequency"]="--title 'Chrony Clock Frequency Error - PERIOD_TITLE' --vertical-label 'ppm'\
            DEF:freq='$RRD_FILE':frequency:AVERAGE \
            DEF:resid_freq='$RRD_FILE':resid_freq:AVERAGE \
            CDEF:resfreq_scaled=resid_freq,100,* \
            CDEF:freq_scaled=freq,1,* \
            'LINE2:freq_scaled#00ff00:Natural Clock Drift      [Frequency]         ' \
            'GPRINT:freq_scaled:LAST:Cur\: %5.2lf%s' \
            'GPRINT:freq_scaled:MIN:Min\: %5.2lf%s' \
            'GPRINT:freq_scaled:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:freq_scaled:MAX:Max\: %5.2lf%s\n' \
            'LINE1:resfreq_scaled#4169E1:Residual Drift (x100)    [Residual freq]     ' \
            'GPRINT:resfreq_scaled:LAST:Cur\: %5.2lf%s' \
            'GPRINT:resfreq_scaled:MIN:Min\: %5.2lf%s' \
            'GPRINT:resfreq_scaled:AVERAGE:Avg\: %5.2lf%s' \
            'GPRINT:resfreq_scaled:MAX:Max\: %5.2lf%s\l'"
	["chrony_drift"]="--title 'Chrony Drift Margin Error - PERIOD_TITLE' --vertical-label 'ppm' \
            --units-exponent 0 \
            DEF:resid_freq='$RRD_FILE':resid_freq:AVERAGE \
            DEF:skew_raw='$RRD_FILE':skew:AVERAGE \
            CDEF:resfreq_scaled=resid_freq,100,* \
	    CDEF:skew_scaled=skew_raw,100,* \
            'COMMENT: \l' \
            'LINE1:skew_scaled#00ff00:Estimate Drift Error Margin (x100)  [Skew]   ' \
            'GPRINT:skew_scaled:LAST:Cur\: %5.2lf' \
            'GPRINT:skew_scaled:MIN:Min\: %5.2lf' \
            'GPRINT:skew_scaled:AVERAGE:Avg\: %5.2lf' \
            'GPRINT:skew_scaled:MAX:Max\: %5.2lf\l'"
    )

    for period in "${!time_periods[@]}"; do
        for graph in "${!graphs[@]}"; do
            local graph_title="${graphs[$graph]//PERIOD_TITLE/${period_titles[$period]}}"
            local output_file="$OUTPUT_DIR/img/${graph}_${period}.png"
            local time_range="${time_periods[$period]}"
            
            local cmd="LC_ALL=C rrdtool graph '$output_file' --width '$WIDTH' --height '$HEIGHT' --start $time_range --end now-180s $graph_title"
            eval "$cmd" || {
                log_message "ERROR" "Failed to generate graph: ${graph}_${period}"
                exit 1
            }
        done
    done
}

generate_html() {
    log_message "INFO" "Generating HTML report..."
    local GENERATED_TIMESTAMP=$(date)
    
    local CHRONYC_DISPLAY_OPTS=""
    if [[ "$CHRONY_ALLOW_DNS_LOOKUP" == "no" ]]; then
        CHRONYC_DISPLAY_OPTS=" -n"
    fi
    
    local AUTO_REFRESH_META=""
    if [[ "$AUTO_REFRESH_SECONDS" -gt 0 ]]; then
        AUTO_REFRESH_META="    <meta http-equiv=\"refresh\" content=\"$AUTO_REFRESH_SECONDS\">"
    fi
    
    cat >"$OUTPUT_DIR/$HTML_FILENAME" <<EOF
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
$AUTO_REFRESH_META
    <title>${PAGE_TITLE} - Server Status</title>
    <style>
        :root {
            --primary-text: #212529;
            --secondary-text: #6c757d;
            --background-color: #f8f9fa;
            --content-background: #ffffff;
            --border-color: #787879;
            --code-background: #e1e1e1;
            --code-text: #000000;
            --container-max: 1400px;
            --font-size-base: 16px;
        }
$CSS_CUSTOM_ROOT
        body {
            font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
            margin: 0;
            padding: 20px;
            background-color: var(--background-color);
            color: var(--primary-text);
            line-height: 1.6;
            font-size: var(--font-size-base);
        }
        .container {
            max-width: var(--container-max);
            margin: 0 auto;
            background-color: var(--content-background);
            padding: 20px 20px;
            border-radius: 8px;
            box-shadow: 0 4px 8px rgba(0,0,0,0.05);
        }
        header {
            text-align: center;
            border-bottom: 1px solid var(--border-color);
            padding-bottom: 20px;
            margin-bottom: 30px;
        }
        header h1 {
            margin: 0;
            font-size: 2.5em;
            color: var(--primary-text);
        }
        section {
            margin-bottom: 40px;
        }
        h2 {
            font-size: 1.8em;
            color: var(--primary-text);
            border-bottom: 1px solid var(--border-color);
            padding-bottom: 10px;
            margin-top: 0;
            margin-bottom: 20px;
        }
        h2 a {
            font-size: 0.8em;
            font-weight: normal;
            vertical-align: middle;
            margin-left: 10px;
        }
        h3 {
            font-size: 1.3em;
            color: var(--primary-text);
            margin-top: 25px;
        }
	@media (max-width: 767px) {
            #vnstat-graphs table,
            #vnstat-graphs tbody,
            #vnstat-graphs tr,
            #vnstat-graphs td {
                display: block;
                width: 100%;
            }

            #vnstat-graphs td {
                padding-left: 0;
                padding-right: 0;
                text-align: center;
            }
        }
        .graph-grid {
            display: grid;
            grid-template-columns: 1fr;
            gap: 10px;
            text-align: center;
        }
        @media (min-width: 768px) {
            .graph-grid {
                grid-template-columns: repeat(2, 1fr);
            }
        }
        figure {
            margin: 0;
            padding: 0;
        }
        img {
            max-width: 100%;
            height: auto;
            border: 1px solid var(--border-color);
            border-radius: 4px;
            box-shadow: 0 2px 4px rgba(0,0,0,0.05);
            cursor: zoom-in;
        }
        .lightbox-overlay {
            position: fixed;
            inset: 0;
            background: rgba(0, 0, 0, 0.85);
            display: none;
            align-items: center;
            justify-content: center;
            z-index: 9999;
            cursor: zoom-out;
        }
        .lightbox-overlay.open {
            display: flex;
        }
        .lightbox-img {
            width: 96vw;
            height: 94vh; 
            object-fit: contain;
            border: 0;
            cursor: zoom-out;
        }
        pre {
            background-color: var(--code-background);
            color: var(--code-text);
            padding: 10px;
            border: 1px solid #c3bebe;
            border-radius: 4px;
            overflow-x: auto;
            white-space: pre-wrap;
            word-wrap: break-word;
            font-size: 0.8em;
        }
        footer {
            text-align: center;
            margin-top: 40px;
            padding-top: 20px;
            border-top: 1px solid var(--border-color);
            font-size: 0.9em;
            color: var(--secondary-text);
        }
        
        .tabs {
            display: flex;
            border-bottom: 1px solid var(--border-color);
            margin-bottom: 20px;
        }
        .tab {
            padding: 10px 20px;
            cursor: pointer;
            background-color: var(--background-color);
            border: 1px solid var(--border-color);
            border-bottom: none;
            margin-right: 2px;
            transition: background-color 0.3s;
        }
        .tab:hover {
            background-color: #e9ecef;
        }
        .tab.active {
            background-color: var(--content-background);
            border-bottom: 1px solid var(--content-background);
            margin-bottom: -1px;
        }
        .tab-content {
            display: none;
        }
        .tab-content.active {
            display: block;
        }
    </style>
</head>
<body>
    <div class="container">
	<main>
            <section id="chrony-graphs">
                <h2>Chrony Graphs <a target="_blank" href="https://chrony-project.org/doc/4.3/chronyc.html#:~:text=System%20clock-,tracking,-The%20tracking%20command">[Data Legend]</a></h2>
                
                <div class="tabs">
                    <div class="tab active" onclick="showTab('day')">Day</div>
                    <div class="tab" onclick="showTab('week')">Week</div>
                    <div class="tab" onclick="showTab('month')">Month</div>
                </div>
                
                <div id="day-content" class="tab-content active">
                    <div class="graph-grid">
                        <figure>
                            <img src="img/chrony_serverstats_day.png" alt="Chrony server statistics graph - day">
                        </figure>
                        <figure>
                            <img src="img/chrony_offset_day.png" alt="Chrony system clock offset graph - day">
                        </figure>
                        <figure>
                            <img src="img/chrony_tracking_day.png" alt="Chrony system clock tracking graph - day">
                        </figure>
                        <figure>
                            <img src="img/chrony_delay_day.png" alt="Chrony sync delay graph - day">
                        </figure>
                        <figure>
                            <img src="img/chrony_frequency_day.png" alt="Chrony clock frequency graph - day">
                        </figure>
                        <figure>
                            <img src="img/chrony_drift_day.png" alt="Chrony clock frequency drift graph - day">
                        </figure>
                    </div>
                </div>
                
                <div id="week-content" class="tab-content">
                    <div class="graph-grid">
                        <figure>
                            <img src="img/chrony_serverstats_week.png" alt="Chrony server statistics graph - week">
                        </figure>
                        <figure>
                            <img src="img/chrony_offset_week.png" alt="Chrony system clock offset graph - week">
                        </figure>
                        <figure>
                            <img src="img/chrony_tracking_week.png" alt="Chrony system clock tracking graph - week">
                        </figure>
                        <figure>
                            <img src="img/chrony_delay_week.png" alt="Chrony sync delay graph - week">
                        </figure>
                        <figure>
                            <img src="img/chrony_frequency_week.png" alt="Chrony clock frequency graph - week">
                        </figure>
                        <figure>
                            <img src="img/chrony_drift_week.png" alt="Chrony clock frequency drift graph - week">
                        </figure>
                    </div>
                </div>
                
                <div id="month-content" class="tab-content">
                    <div class="graph-grid">
                        <figure>
                            <img src="img/chrony_serverstats_month.png" alt="Chrony server statistics graph - month">
                        </figure>
                        <figure>
                            <img src="img/chrony_offset_month.png" alt="Chrony system clock offset graph - month">
                        </figure>
                        <figure>
                            <img src="img/chrony_tracking_month.png" alt="Chrony system clock tracking graph - month">
                        </figure>
                        <figure>
                            <img src="img/chrony_delay_month.png" alt="Chrony sync delay graph - month">
                        </figure>
                        <figure>
                            <img src="img/chrony_frequency_month.png" alt="Chrony clock frequency graph - month">
                        </figure>
                        <figure>
                            <img src="img/chrony_drift_month.png" alt="Chrony clock frequency drift graph - month">
                        </figure>
                    </div>
                </div>
            </section>
EOF

    if [[ "$ENABLE_NETWORK_STATS" == "yes" ]]; then
        cat >>"$OUTPUT_DIR/$HTML_FILENAME" <<EOF

            <section id="vnstat-graphs">
                <h2>vnStati Graphs</h2>
                <table border="0" style="margin-left: auto; margin-right: auto;">
                    <tbody>
                        <tr>
                            <td valign="top" style="padding: 0 10px;">
                                <img src="img/vnstat_s.png" alt="vnStat summary"><br>
                                <img src="img/vnstat_d.png" alt="vnStat daily" style="margin-top: 4px;"><br>
                                <img src="img/vnstat_t.png" alt="vnStat top 10" style="margin-top: 4px;"><br>
                            </td>
                            <td valign="top" style="padding: 0 10px;">
                                <img src="img/vnstat_h.png" alt="vnStat hourly"><br>
                                <img src="img/vnstat_m.png" alt="vnStat monthly" style="margin-top: 4px;"><br>
                                <img src="img/vnstat_y.png" alt="vnStat yearly" style="margin-top: 4px;"><br>
                            </td>
                        </tr>
                    </tbody>
                </table>
            </section>
EOF
    fi

    cat >>"$OUTPUT_DIR/$HTML_FILENAME" <<EOF

            <section id="chrony-stats">
                <h2>Chrony - NTP Statistics</h2>

                <h3>Command: <code>chronyc${CHRONYC_DISPLAY_OPTS} sources -v</code></h3>
                <pre><code>${CHRONYC_SOURCES}</code></pre>

                <h3>Command: <code>chronyc${CHRONYC_DISPLAY_OPTS} selectdata -v</code></h3>
                <pre><code>${CHRONYC_SELECTDATA}</code></pre>

                <h3>Command: <code>chronyc${CHRONYC_DISPLAY_OPTS} sourcestats -v</code></h3>
                <pre><code>${CHRONYC_SOURCESTATS}</code></pre>

                <h3>Command: <code>chronyc${CHRONYC_DISPLAY_OPTS} tracking</code></h3>
                <pre><code>${CHRONYC_TRACKING_HTML}</code></pre>
            </section>
        </main>

        <footer>
            <p>Page generated on: ${GENERATED_TIMESTAMP}</p>
EOF
    if [[ "$GITHUB_REPO_LINK_SHOW" == "yes" ]]; then
        cat >>"$OUTPUT_DIR/$HTML_FILENAME" <<EOF
            <p>Made with ❤️ by TheHuman00 | <a href="https://github.com/TheHuman00/chrony-stats" target="_blank">View on GitHub</a></p>
            <p>Modified from original script by Medowar<a href="https://www.medowar.de>" target="_blank"> (https://www.medowar.de)</a></p>
EOF
    fi
    cat >>"$OUTPUT_DIR/$HTML_FILENAME" <<EOF
        </footer>
    </div>

    <div id="lightbox" class="lightbox-overlay" aria-hidden="true" role="dialog">
        <img id="lightbox-img" class="lightbox-img" alt="Expanded graph">
    </div>

    <script>
        function showTab(period) {
            const contents = document.querySelectorAll('.tab-content');
            contents.forEach(content => content.classList.remove('active'));
            const tabs = document.querySelectorAll('.tab');
            tabs.forEach(tab => tab.classList.remove('active'));
            document.getElementById(period + '-content').classList.add('active');
            const evt = event || window.event; // works with inline onclick
            if (evt && evt.target) {
            }
                evt.target.classList.add('active');
        }

        (function enableImageLightbox() {
            const overlay = document.getElementById('lightbox');
            const overlayImg = document.getElementById('lightbox-img');
            if (!overlay || !overlayImg) return;

            const open = (src, alt) => {
                overlayImg.src = src;
                overlayImg.alt = alt || 'Expanded image';
                overlay.classList.add('open');
                overlay.setAttribute('aria-hidden', 'false');
                // Prevent background scroll
                document.body.style.overflow = 'hidden';
            };
            const close = () => {
                overlay.classList.remove('open');
                overlay.setAttribute('aria-hidden', 'true');
                overlayImg.src = '';
                document.body.style.overflow = '';
            };

            document.querySelectorAll('.container img').forEach(img => {
                img.addEventListener('click', () => open(img.src, img.alt));
            });
            overlay.addEventListener('click', close);
            overlayImg.addEventListener('click', close);
            document.addEventListener('keydown', (e) => {
                if (e.key === 'Escape' && overlay.classList.contains('open')) close();
            });
        })();
    </script>
</body>
</html>
EOF
}

main() {
    log_message "INFO" "Starting chrony-network-stats script..."
    validate_numeric "$WIDTH" "WIDTH"
    validate_numeric "$HEIGHT" "HEIGHT"
    validate_numeric "$TIMEOUT_SECONDS" "TIMEOUT_SECONDS"
    validate_numeric "$SERVER_STATS_UPPER_LIMIT" "SERVER_STATS_UPPER_LIMIT"
    validate_numeric "$AUTO_REFRESH_SECONDS" "AUTO_REFRESH_SECONDS"
    configure_display_preset
    check_commands
    setup_directories
    generate_vnstat_images
    collect_chrony_data
    extract_chronyc_values
    create_rrd_database
    update_rrd_database
    generate_graphs
    generate_html
    log_message "INFO" "HTML page and graphs generated in: $OUTPUT_DIR/$HTML_FILENAME"
    echo "✅ Successfully generated report"
}

main