(* (c) 2017, 2018 Hannes Mehnert, all rights reserved *)

open Astring
open Rresult.R.Infix

open Vmm_core

external sysctl_rusage : int -> rusage = "vmmanage_sysctl_rusage"
external sysctl_ifcount : unit -> int = "vmmanage_sysctl_ifcount"
external sysctl_ifdata : int -> ifdata = "vmmanage_sysctl_ifdata"

type vmctx

external vmmapi_open : string -> vmctx = "vmmanage_vmmapi_open"
external vmmapi_close : vmctx -> unit = "vmmanage_vmmapi_close"
external vmmapi_statnames : vmctx -> string list = "vmmanage_vmmapi_statnames"
external vmmapi_stats : vmctx -> int64 list = "vmmanage_vmmapi_stats"

let my_version = `WV1

let descr = ref []

type t = {
  pid_nic : ((vmctx, int) result * (int * string) list) IM.t ;
  pid_rusage : rusage IM.t ;
  pid_vmmapi : (string * int64) list IM.t ;
  nic_ifdata : ifdata String.Map.t ;
  vmid_pid : int String.Map.t ;
}

let pp_strings pp taps = Fmt.(list ~sep:(unit ",@ ") string) pp taps

let empty () =
  { pid_nic = IM.empty ; pid_rusage = IM.empty ; pid_vmmapi = IM.empty ; nic_ifdata = String.Map.empty ; vmid_pid = String.Map.empty }

let rec wrap f arg =
  try Some (f arg) with
  | Unix.Unix_error (Unix.EINTR, _, _) -> wrap f arg
  | e ->
    Logs.err (fun m -> m "exception %s" (Printexc.to_string e)) ;
    None

let fill_descr ctx =
  match !descr with
  | [] ->
    begin match wrap vmmapi_statnames ctx with
      | None ->
        Logs.err (fun m -> m "vmmapi_statnames failed, shouldn't happen") ;
        ()
      | Some d ->
        Logs.info (fun m -> m "descr are %a" pp_strings d) ;
        descr := d
    end
  | ds -> Logs.info (fun m -> m "%d descr are already present" (List.length ds))

let open_vmmapi ?(retries = 4) pid =
  let name = "ukvm" ^ string_of_int pid in
  if retries = 0 then begin
    Logs.debug (fun m -> m "(ignored 0) vmmapi_open failed for %d" pid) ;
    Error 0
  end else
    match wrap vmmapi_open name with
    | None ->
      let left = max 0 (pred retries) in
      Logs.warn (fun m -> m "(ignored, %d attempts left) vmmapi_open failed for %d" left pid) ;
      Error left
    | Some vmctx ->
      Logs.info (fun m -> m "vmmapi_open succeeded for %d" pid) ;
      fill_descr vmctx ;
      Ok vmctx

let try_open_vmmapi pid_nic =
  IM.fold (fun pid (vmctx, nics) fresh ->
      let vmctx =
        match vmctx with
        | Ok vmctx -> Ok vmctx
        | Error retries -> open_vmmapi ~retries pid
      in
      IM.add pid (vmctx, nics) fresh)
    pid_nic IM.empty

let gather pid vmctx nics =
  wrap sysctl_rusage pid,
  (match vmctx with
   | Error _ -> None
   | Ok vmctx -> wrap vmmapi_stats vmctx),
  List.fold_left (fun ifd (nic, nname) ->
      match wrap sysctl_ifdata nic with
      | None ->
        Logs.warn (fun m -> m "failed to get ifdata for %s" nname) ;
        ifd
      | Some data ->
        Logs.debug (fun m -> m "adding ifdata for %s" nname) ;
        String.Map.add data.name data ifd)
    String.Map.empty nics

let tick t =
  Logs.debug (fun m -> m "tick with %d vms" (IM.cardinal t.pid_nic)) ;
  let pid_rusage, pid_vmmapi, nic_ifdata =
    IM.fold (fun pid (vmctx, nics) (rus, vmms, ifds) ->
        let ru, vmm, ifd = gather pid vmctx nics in
        (match ru with
         | None ->
           Logs.warn (fun m -> m "failed to get rusage for %d" pid) ;
           rus
         | Some ru ->
           Logs.debug (fun m -> m "adding resource usage for %d" pid) ;
           IM.add pid ru rus),
        (match vmm with
         | None ->
           Logs.warn (fun m -> m "failed to get vmmapi_stats for %d" pid) ;
           vmms
         | Some vmm ->
           Logs.debug (fun m -> m "adding vmmapi_stats for %d" pid) ;
           IM.add pid (List.combine !descr vmm) vmms),
        String.Map.union (fun _k a _b -> Some a) ifd ifds)
      t.pid_nic (IM.empty, IM.empty, String.Map.empty)
  in
  let pid_nic = try_open_vmmapi t.pid_nic in
  { t with pid_rusage ; pid_vmmapi ; nic_ifdata ; pid_nic }

let add_pid t vmid pid nics =
  match wrap sysctl_ifcount () with
  | None ->
    Logs.err (fun m -> m "sysctl ifcount failed for %d %a" pid pp_strings nics) ;
    Error (`Msg "sysctl ifcount failed")
  | Some max_nic ->
    let rec go cnt acc id =
      if id > 0 && cnt > 0 then
        match wrap sysctl_ifdata id with
        | Some ifd when List.mem ifd.name nics ->
          go (pred cnt) ((id, ifd.name) :: acc) (pred id)
        | _ -> go cnt acc (pred id)
      else
        List.rev acc
    in
    Ok (go (List.length nics) [] max_nic) >>= fun nic_ids ->
    let vmctx = open_vmmapi pid in
    Logs.info (fun m -> m "adding %d %a with vmctx %b" pid pp_strings nics
                  (match vmctx with Error _ -> false | Ok _ -> true)) ;
    let pid_nic = IM.add pid (vmctx, nic_ids) t.pid_nic
    and vmid_pid = String.Map.add vmid pid t.vmid_pid
    in
    Ok { t with pid_nic ; vmid_pid }


let stats t vmid =
  Logs.debug (fun m -> m "querying statistics for vmid %s" vmid) ;
  match String.Map.find vmid t.vmid_pid with
  | None -> Error (`Msg ("unknown vm " ^ vmid))
  | Some pid ->
    Logs.debug (fun m -> m "querying statistics for %d" pid) ;
    try
      let _, nics = IM.find pid t.pid_nic
      and ru = IM.find pid t.pid_rusage
      and vmm =
        try IM.find pid t.pid_vmmapi with
        | Not_found ->
          Logs.err (fun m -> m "failed to find vmm stats for %d" pid);
          []
      in
      match
        List.fold_left (fun acc nic ->
            match String.Map.find nic t.nic_ifdata, acc with
            | None, _ -> None
            | _, None -> None
            | Some ifd, Some acc -> Some (ifd :: acc))
          (Some []) (snd (List.split nics))
      with
      | None -> Error (`Msg "failed to find interface statistics")
      | Some ifd -> Ok (ru, vmm, ifd)
    with
    | _ -> Error (`Msg "failed to find resource usage")

let remove_vmid t vmid =
  Logs.info (fun m -> m "removing vmid %s" vmid) ;
  match String.Map.find vmid t.vmid_pid with
  | None -> Logs.warn (fun m -> m "no pid found for %s" vmid) ; t
  | Some pid ->
    Logs.info (fun m -> m "removing pid %d" pid) ;
    (try
       match IM.find pid t.pid_nic with
       | Ok vmctx, _ -> ignore (wrap vmmapi_close vmctx)
       | Error _, _ -> ()
     with
       _ -> ()) ;
    let pid_nic = IM.remove pid t.pid_nic
    and vmid_pid = String.Map.remove vmid t.vmid_pid
    in
    { t with pid_nic ; vmid_pid }

let remove_vmids t vmids =
  List.fold_left remove_vmid t vmids

let handle t hdr buf =
  let open Vmm_wire in
  let open Vmm_wire.Stats in
  let cs = Cstruct.of_string buf in
  let r =
    if not (version_eq my_version hdr.version) then
      Error (`Msg "cannot handle version")
    else
      decode_string cs >>= fun (name, off) ->
      match int_to_op hdr.tag with
      | Some Add ->
        decode_pid_taps (Cstruct.shift cs off) >>= fun (pid, taps) ->
        add_pid t name pid taps >>= fun t ->
        Ok (t, `Add name, success ~msg:"added" hdr.id my_version)
      | Some Remove ->
        let t = remove_vmid t name in
        Ok (t, `Remove name, success ~msg:"removed" hdr.id my_version)
      | Some Stat_request ->
        stats t name >>= fun s ->
        Ok (t, `None, stat_reply hdr.id my_version (encode_stats s))
      | _ -> Error (`Msg "unknown command")
  in
  match r with
  | Ok (t, action, out) -> t, action, out
  | Error (`Msg msg) ->
    Logs.err (fun m -> m "error while processing %s" msg) ;
    t, `None, fail ~msg hdr.id my_version