#!/bin/bash
################################################################################
# Script Name: syncthing-exporter.sh
# Version: 1.0
# Description: Prometheus exporter for Syncthing — scrapes the built-in
#              /metrics endpoint and writes to a textfile collector .prom file,
#              adding connection status and completion metrics from the REST API
#
# Author: Phil Connor
# Contact: contact@mylinux.work
# Website: https://mylinux.work
# License: MIT
#
# Prerequisites:
#   - Syncthing running with GUI/API enabled
#   - curl and jq for API access
#   - netcat (nc) for HTTP mode
#
# Usage:
#   ./syncthing-exporter.sh --textfile
#   ./syncthing-exporter.sh --http -p 9599
#   ./syncthing-exporter.sh -o /tmp/syncthing.prom
#
# Configuration:
#   Set SYNCTHING_API_KEY via environment variable, --api-key flag,
#   or the script reads it from ~/.local/state/syncthing/config.xml
#
# Metrics exported (from /metrics):
#   syncthing_model_folder_summary        - File/byte counts per folder
#   syncthing_model_folder_state          - Current folder state
#   syncthing_model_folder_pull_seconds   - Time in pull iterations
#   syncthing_model_folder_scan_seconds   - Time in scan iterations
#   syncthing_protocol_recv_bytes_total   - Bytes received per device
#   syncthing_protocol_sent_bytes_total   - Bytes sent per device
#   syncthing_fs_operation_bytes_total    - Filesystem bytes per operation
#   syncthing_fs_operations_total         - Filesystem operation count
#   syncthing_scanner_hashed_bytes_total  - Data hashed per folder
#   syncthing_events_total                - Events created/forwarded/dropped
#
# Extra metrics (from REST API):
#   syncthing_device_connected            - Per-device connection status (1/0)
#   syncthing_device_paused               - Per-device paused status (1/0)
#   syncthing_device_last_seen_timestamp  - Last seen Unix timestamp
#   syncthing_connected_devices           - Total connected device count
#   syncthing_folder_completion_pct       - Per-device folder completion %
#
################################################################################

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

SYNCTHING_URL="${SYNCTHING_URL:-http://127.0.0.1:8384}"
SYNCTHING_API_KEY="${SYNCTHING_API_KEY:-}"
TEXTFILE_DIR="/var/lib/node_exporter"
OUTPUT_FILE=""
HTTP_MODE=false
HTTP_PORT=9599

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

Export Syncthing statistics as Prometheus metrics.

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

OPTIONS:
    -u, --url       Syncthing URL (default: $SYNCTHING_URL)
    -k, --api-key   Syncthing API key (or set SYNCTHING_API_KEY)
    -p, --port      HTTP port (default: $HTTP_PORT)
    -o, --output    Output file path

EXAMPLES:
    $0 --textfile
    $0 --textfile --api-key abc123
    $0 --http --port 9599
    SYNCTHING_API_KEY=abc123 $0 --textfile

EOF
    exit 0
}

parse_args() {
    while [[ $# -gt 0 ]]; do
        case $1 in
            -h|--help) show_usage ;;
            --textfile) OUTPUT_FILE="$TEXTFILE_DIR/syncthing.prom"; shift ;;
            --http) HTTP_MODE=true; shift ;;
            -u|--url) SYNCTHING_URL="$2"; shift 2 ;;
            -k|--api-key) SYNCTHING_API_KEY="$2"; shift 2 ;;
            -p|--port) HTTP_PORT="$2"; shift 2 ;;
            -o|--output) OUTPUT_FILE="$2"; shift 2 ;;
            *) echo "Unknown option: $1" >&2; exit 1 ;;
        esac
    done
}

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

detect_api_key() {
    if [ -n "$SYNCTHING_API_KEY" ]; then
        return 0
    fi

    local config_paths=(
        "$HOME/.local/state/syncthing/config.xml"
        "$HOME/.config/syncthing/config.xml"
        "/var/lib/syncthing/.config/syncthing/config.xml"
        "/root/.local/state/syncthing/config.xml"
        "/root/.config/syncthing/config.xml"
    )

    for cfg in "${config_paths[@]}"; do
        if [ -f "$cfg" ]; then
            SYNCTHING_API_KEY=$(grep -oP '<apikey>\K[^<]+' "$cfg" 2>/dev/null)
            if [ -n "$SYNCTHING_API_KEY" ]; then
                return 0
            fi
        fi
    done

    echo "ERROR: No API key found. Set SYNCTHING_API_KEY or use --api-key" >&2
    return 1
}

api_call() {
    local endpoint="$1"
    curl -sf --max-time 10 \
        -H "X-API-Key: $SYNCTHING_API_KEY" \
        "${SYNCTHING_URL}${endpoint}"
}

prom_escape() {
    local val="$1"
    val="${val//\\/\\\\}"
    val="${val//\"/\\\"}"
    val="${val//$'\n'/\\n}"
    echo "$val"
}

iso_to_unix() {
    local ts="$1"
    if [ -z "$ts" ] || [ "$ts" = "null" ] || [ "$ts" = "0001-01-01T00:00:00Z" ]; then
        echo "0"
        return
    fi
    local unix_ts
    unix_ts=$(date -d "$ts" +%s 2>/dev/null)
    echo "${unix_ts:-0}"
}

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

generate_metrics() {
    local script_start
    script_start=$(date +%s%N)

    if ! command -v curl >/dev/null 2>&1; then
        echo "ERROR: curl not found" >&2
        return 1
    fi
    if ! command -v jq >/dev/null 2>&1; then
        echo "ERROR: jq not found" >&2
        return 1
    fi

    if ! detect_api_key; then
        echo "# HELP syncthing_up Syncthing reachable (1/0)"
        echo "# TYPE syncthing_up gauge"
        echo "syncthing_up 0"
        return
    fi

    # ------------------------------------------------------------------
    # Scrape built-in /metrics endpoint
    # ------------------------------------------------------------------
    local builtin_metrics
    builtin_metrics=$(curl -sf --max-time 10 \
        -H "X-API-Key: $SYNCTHING_API_KEY" \
        "${SYNCTHING_URL}/metrics" 2>/dev/null)

    if [ -z "$builtin_metrics" ]; then
        echo "# HELP syncthing_up Syncthing reachable (1/0)"
        echo "# TYPE syncthing_up gauge"
        echo "syncthing_up 0"
        return
    fi

    echo "# HELP syncthing_up Syncthing reachable (1/0)"
    echo "# TYPE syncthing_up gauge"
    echo "syncthing_up 1"
    echo ""

    # Output built-in metrics (strip Go runtime metrics to keep it focused)
    echo "$builtin_metrics" | grep -E '^(syncthing_|# (HELP|TYPE) syncthing_)' | awk '/^# HELP/ && NR>1 {print ""} {print}'
    echo ""

    # ------------------------------------------------------------------
    # REST API: system version info
    # ------------------------------------------------------------------
    local version_json
    version_json=$(api_call "/rest/system/version")
    if [ -n "$version_json" ]; then
        local version os arch
        version=$(echo "$version_json" | jq -r '.version // ""')
        os=$(echo "$version_json" | jq -r '.os // ""')
        arch=$(echo "$version_json" | jq -r '.arch // ""')

        echo "# HELP syncthing_version_info Syncthing version information"
        echo "# TYPE syncthing_version_info gauge"
        echo "syncthing_version_info{version=\"$(prom_escape "$version")\",os=\"$(prom_escape "$os")\",arch=\"$(prom_escape "$arch")\"} 1"
        echo ""
    fi

    # ------------------------------------------------------------------
    # REST API: system status (uptime, RAM)
    # ------------------------------------------------------------------
    local status_json
    status_json=$(api_call "/rest/system/status")
    if [ -n "$status_json" ]; then
        local uptime alloc sys goroutines my_id
        uptime=$(echo "$status_json" | jq -r '.uptime // 0')
        alloc=$(echo "$status_json" | jq -r '.alloc // 0')
        sys=$(echo "$status_json" | jq -r '.sys // 0')
        goroutines=$(echo "$status_json" | jq -r '.goroutines // 0')
        my_id=$(echo "$status_json" | jq -r '.myID // ""')

        echo "# HELP syncthing_system_uptime_seconds Syncthing process uptime in seconds"
        echo "# TYPE syncthing_system_uptime_seconds gauge"
        echo "syncthing_system_uptime_seconds $uptime"
        echo ""

        echo "# HELP syncthing_system_alloc_bytes Memory allocated by Syncthing"
        echo "# TYPE syncthing_system_alloc_bytes gauge"
        echo "syncthing_system_alloc_bytes $alloc"
        echo ""

        echo "# HELP syncthing_system_sys_bytes Total system memory obtained"
        echo "# TYPE syncthing_system_sys_bytes gauge"
        echo "syncthing_system_sys_bytes $sys"
        echo ""

        echo "# HELP syncthing_system_goroutines Number of active goroutines"
        echo "# TYPE syncthing_system_goroutines gauge"
        echo "syncthing_system_goroutines $goroutines"
        echo ""
    fi

    # ------------------------------------------------------------------
    # REST API: device connections
    # ------------------------------------------------------------------
    local connections_json
    connections_json=$(api_call "/rest/system/connections")
    if [ -n "$connections_json" ]; then
        local connected_count=0
        local connected_lines=""
        local paused_lines=""
        local conn_type_lines=""

        local device_data
        device_data=$(echo "$connections_json" | jq -r '
            .connections // {} | to_entries[] |
            select(.key != "total") |
            [
                .key,
                (.value.connected // false | tostring),
                (.value.paused // false | tostring),
                (.value.type // ""),
                (.value.address // ""),
                (.value.clientVersion // "")
            ] | @tsv
        ')

        while IFS=$'\t' read -r device_id connected paused conn_type address client_version; do
            [ -z "$device_id" ] && continue
            local short_id="${device_id:0:7}"

            local conn_val=0
            if [ "$connected" = "true" ]; then
                conn_val=1
                connected_count=$((connected_count + 1))
            fi
            connected_lines+="syncthing_device_connected{device_id=\"$(prom_escape "$short_id")\",address=\"$(prom_escape "$address")\",client_version=\"$(prom_escape "$client_version")\"} $conn_val"$'\n'

            local paused_val=0
            if [ "$paused" = "true" ]; then
                paused_val=1
            fi
            paused_lines+="syncthing_device_paused{device_id=\"$(prom_escape "$short_id")\"} $paused_val"$'\n'

            if [ -n "$conn_type" ]; then
                conn_type_lines+="syncthing_device_connection_type{device_id=\"$(prom_escape "$short_id")\",type=\"$(prom_escape "$conn_type")\"} 1"$'\n'
            fi
        done <<< "$device_data"

        echo "# HELP syncthing_device_connected Per-device connection status (1=connected, 0=disconnected)"
        echo "# TYPE syncthing_device_connected gauge"
        printf '%s' "$connected_lines"
        echo ""
        echo "# HELP syncthing_device_paused Per-device paused status (1=paused, 0=active)"
        echo "# TYPE syncthing_device_paused gauge"
        printf '%s' "$paused_lines"
        echo ""
        echo "# HELP syncthing_device_connection_type Per-device connection type"
        echo "# TYPE syncthing_device_connection_type gauge"
        printf '%s' "$conn_type_lines"
        echo ""
        echo "# HELP syncthing_connected_devices Total number of connected devices"
        echo "# TYPE syncthing_connected_devices gauge"
        echo "syncthing_connected_devices $connected_count"
        echo ""
    fi

    # ------------------------------------------------------------------
    # REST API: device stats (last seen)
    # ------------------------------------------------------------------
    local stats_json
    stats_json=$(api_call "/rest/stats/device")
    if [ -n "$stats_json" ]; then
        echo "# HELP syncthing_device_last_seen_timestamp Unix timestamp when device was last seen"
        echo "# TYPE syncthing_device_last_seen_timestamp gauge"

        local stats_data
        stats_data=$(echo "$stats_json" | jq -r '
            to_entries[] |
            [.key, (.value.lastSeen // "")] | @tsv
        ')

        while IFS=$'\t' read -r device_id last_seen; do
            [ -z "$device_id" ] && continue
            local short_id="${device_id:0:7}"
            local last_seen_unix
            last_seen_unix=$(iso_to_unix "$last_seen")
            echo "syncthing_device_last_seen_timestamp{device_id=\"$(prom_escape "$short_id")\"} $last_seen_unix"
        done <<< "$stats_data"
        echo ""
    fi

    # ------------------------------------------------------------------
    # REST API: folder completion per device
    # ------------------------------------------------------------------
    local config_json
    config_json=$(api_call "/rest/config")
    if [ -n "$config_json" ]; then
        local folder_ids device_ids
        folder_ids=$(echo "$config_json" | jq -r '.folders[]?.id // empty')
        device_ids=$(echo "$config_json" | jq -r '.devices[]?.deviceID // empty')

        if [ -n "$folder_ids" ] && [ -n "$device_ids" ]; then
            echo "# HELP syncthing_folder_completion_pct Folder sync completion percentage per device"
            echo "# TYPE syncthing_folder_completion_pct gauge"

            while IFS= read -r folder_id; do
                [ -z "$folder_id" ] && continue
                while IFS= read -r device_id; do
                    [ -z "$device_id" ] && continue
                    local completion_json
                    completion_json=$(api_call "/rest/db/completion?folder=$(printf '%s' "$folder_id" | jq -sRr @uri)&device=$(printf '%s' "$device_id" | jq -sRr @uri)")
                    if [ -n "$completion_json" ]; then
                        local pct
                        pct=$(echo "$completion_json" | jq -r '.completion // 0')
                        local short_id="${device_id:0:7}"
                        echo "syncthing_folder_completion_pct{folder=\"$(prom_escape "$folder_id")\",device_id=\"$(prom_escape "$short_id")\"} $pct"
                    fi
                done <<< "$device_ids"
            done <<< "$folder_ids"
            echo ""
        fi
    fi

    # ------------------------------------------------------------------
    # Exporter metadata
    # ------------------------------------------------------------------
    local script_end script_duration
    script_end=$(date +%s)
    local script_start_s=$((${script_start} / 1000000000))
    script_duration=$((script_end - script_start_s))

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

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

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

run_http_server() {
    echo "Starting Syncthing exporter on port $HTTP_PORT..." >&2
    if ! command -v nc >/dev/null 2>&1; then
        echo "ERROR: netcat (nc) required for HTTP mode" >&2
        exit 1
    fi
    while true; do
        {
            read -r request
            if [[ "$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
                echo -e "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r"
                echo "<html><head><title>Syncthing Exporter</title></head><body><h1>Syncthing Prometheus Exporter</h1><p><a href=\"/metrics\">Metrics</a></p></body></html>"
            fi
        } | nc -l -p "$HTTP_PORT" -q 1 2>/dev/null
    done
}

# ==============================================================================
# MAIN
# ==============================================================================

main() {
    parse_args "$@"
    if [ "$HTTP_MODE" = true ]; then
        run_http_server
    elif [ -n "$OUTPUT_FILE" ]; then
        local output_dir
        output_dir="$(dirname "$OUTPUT_FILE")"
        mkdir -p "$output_dir"
        local temp_file
        temp_file=$(mktemp "${output_dir}/.syncthing_metrics.XXXXXX")
        if ! generate_metrics > "$temp_file" 2>/dev/null; then
            rm -f "$temp_file"
            echo "ERROR: Failed to generate metrics" >&2
            exit 1
        fi
        chmod 644 "$temp_file"
        mv -f "$temp_file" "$OUTPUT_FILE"
        echo "Metrics written to $OUTPUT_FILE" >&2
    else
        generate_metrics
    fi
}

main "$@"