{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.numbus-server.services.disk-space-checker;

  disk_space_notifier = pkgs.writeScript "disk-space-notifier.sh" ''
    #!${pkgs.bash}/bin/bash

    ALERT_FILE="/var/lib/numbus-server/disk_alert.env"
    if [ ! -f "$ALERT_FILE" ]; then
      exit 0
    fi

    source "$ALERT_FILE"
    rm "$ALERT_FILE"

    # Update the timestamp for this specific path to prevent spamming
    SAFE_PATH=$(echo "$DISK_ALERT_PATH" | tr '/' '_')
    date +%s > "/var/lib/numbus-server/last_alert_$SAFE_PATH.ts"

    ADMIN_EMAIL="${config.numbus-server.mail.adminAddress}"
    USER_EMAIL="${config.numbus-server.mail.userAddress}"
    OWNER_NAME="${config.numbus-server.owner}"

    SUBJECT="Numbus Server Alert: Low Disk Space Detected"

    TECH_BODY="
    Disk Space Alert:
    Server owner: $OWNER_NAME

    The following mount point has exceeded the safety threshold:
    Mount: $DISK_ALERT_PATH
    Usage: $DISK_ALERT_USAGE%

    Full partition details:
    $(df -h "$DISK_ALERT_PATH")

    Action required: Please investigate and clear space or expand the storage capacity.
    "

    FRIENDLY_BODY="Cher/Chère $OWNER_NAME,

    L'espace de stockage de votre serveur Numbus est presque saturé.
    Disque concerné : $DISK_ALERT_PATH ($DISK_ALERT_USAGE% utilisé)

    Votre administrateur a été notifié avec les détails techniques.
    Nous vous conseillons d'éviter d'ajouter des fichiers volumineux pour garantir le bon fonctionnement de vos services.
    Contactez votre administrateur afin d'évoquer les possibilités d'expansion du stockage.
    "

    printf "Subject: [ADMIN] %s\n\n%s" "$SUBJECT" "$TECH_BODY" | /run/wrappers/bin/sendmail -t "$ADMIN_EMAIL"
    printf "Subject: [Alerte] Espace disque presque saturé sur votre serveur Numbus\n\n%s\n\nMerci de votre confiance,\nL'équipe de support,\nNumbus-Server." "$FRIENDLY_BODY" | /run/wrappers/bin/sendmail -t "$USER_EMAIL"
  '';

  disk_space_checker = pkgs.writeScript "disk-space-checker.sh" ''
    #!${pkgs.bash}/bin/bash
    
    # Safety threshold in percentage
    THRESHOLD=90
    # Paths to monitor (Root and MergerFS data pool)
    PATHS=("/" "/mnt/data")
    ALERT_FILE="/var/lib/numbus-server/disk_alert.env"

    for path in "''${PATHS[@]}"; do
      # Skip if path does not exist (e.g. if mergerfs is not mounted yet)
      if [ ! -d "$path" ]; then
        continue
      fi
      
      # Anti-spam logic: Check if we alerted on this path recently (7 days = 604800 seconds)
      SAFE_PATH=$(echo "$path" | tr '/' '_')
      TS_FILE="/var/lib/numbus-server/last_alert_$SAFE_PATH.ts"
      NOW=$(date +%s)

      if [ -f "$TS_FILE" ]; then
        LAST_SENT=$(cat "$TS_FILE")
        DIFF=$((NOW - LAST_SENT))
        if [ "$DIFF" -lt 604800 ]; then
          echo "Alert for $path was sent recently. Skipping notification to avoid spam."
          continue
        fi
      fi

      # Extract usage percentage using df
      USAGE=$(df -h "$path" | awk 'NR==2 {print $5}' | sed 's/%//')
      
      if [ "$USAGE" -ge "$THRESHOLD" ]; then
        echo "DISK_ALERT_PATH=$path" > "$ALERT_FILE"
        echo "DISK_ALERT_USAGE=$USAGE" >> "$ALERT_FILE"
        
        echo "Threshold exceeded for $path ($USAGE%). Triggering notification."
        
        # Trigger the notification service
        /run/current-system/sw/bin/systemctl start disk-space-notifier.service
        
        # We exit after the first alert to avoid multiple overlapping emails in one run
        exit 0
      fi
    done
  '';
in

{ 
  config = mkIf cfg.enable {
    systemd.services.disk-space-notifier = {
      description = "Email notification for low disk space";
      serviceConfig = {
        Type = "oneshot";
        ExecStart = "${disk_space_notifier}";
      };
    };
    systemd.services.disk-space-checker = {
      description = "Check for low disk space";
      serviceConfig = {
        Type = "oneshot";
        ExecStart = "${disk_space_checker}";
      };
    };
    systemd.timers.disk-space-checker = {
      description = "Run disk space check every day";
      timerConfig = {
        OnCalendar = "daily";
        Persistent = true;
      };
      wantedBy = [ "timers.target" ];
    };
  };
}