(** Email changes operations using core JMAP Changes_args *)

open Jmap.Methods

(** Build Email/changes arguments *)
let build_changes_args ~account_id ~since_state ?max_changes () =
  let account_id_str = Jmap.Id.to_string account_id in
  let max_changes_int = match max_changes with
    | Some uint -> Some (Jmap.UInt.to_int uint)
    | None -> None in
  Changes_args.v
    ~account_id:account_id_str
    ~since_state
    ?max_changes:max_changes_int
    ()

(** Convert Email/changes arguments to JSON *)
let changes_args_to_json args =
  Changes_args.to_json args

(** Track changes since a given state *)
type change_tracker = {
  account_id : Jmap.Id.t;
  current_state : string;
  created : Jmap.Id.t list;
  updated : Jmap.Id.t list;
  destroyed : Jmap.Id.t list;
}

(** Create a new change tracker *)
let create_tracker ~account_id ~initial_state =
  {
    account_id;
    current_state = initial_state;
    created = [];
    updated = [];
    destroyed = [];
  }

(** Update tracker with a Changes_response *)
let update_tracker tracker response =
  {
    tracker with
    current_state = Changes_response.new_state response;
    created = tracker.created @ (List.map (fun s -> match Jmap.Id.of_string s with Ok id -> id | Error e -> failwith e) (Changes_response.created response));
    updated = tracker.updated @ (List.map (fun s -> match Jmap.Id.of_string s with Ok id -> id | Error e -> failwith e) (Changes_response.updated response));
    destroyed = tracker.destroyed @ (List.map (fun s -> match Jmap.Id.of_string s with Ok id -> id | Error e -> failwith e) (Changes_response.destroyed response));
  }

(** Get all changes since tracker was created *)
let get_all_changes tracker =
  (tracker.created, tracker.updated, tracker.destroyed)

(** Get next batch of changes *)
let get_next_changes ~account_id ~since_state ?(max_changes=500) () =
  let max_changes_uint = match Jmap.UInt.of_int max_changes with
    | Ok u -> u
    | Error _ -> failwith ("Invalid max_changes: " ^ string_of_int max_changes) in
  build_changes_args ~account_id ~since_state ~max_changes:max_changes_uint ()

(** Check if there are pending changes *)
let has_pending_changes response =
  Changes_response.has_more_changes response

(** Incremental sync helper *)
module Sync = struct
  type sync_state = {
    account_id : Jmap.Id.t;
    last_state : string;
    pending_created : Jmap.Id.t list;
    pending_updated : Jmap.Id.t list;
    pending_destroyed : Jmap.Id.t list;
  }
  
  let init ~account_id ~initial_state =
    {
      account_id;
      last_state = initial_state;
      pending_created = [];
      pending_updated = [];
      pending_destroyed = [];
    }
  
  let add_response sync response =
    let new_state = Changes_response.new_state response in
    let created = Changes_response.created response in
    let updated = Changes_response.updated response in
    let destroyed = Changes_response.destroyed response in
    {
      sync with
      last_state = new_state;
      pending_created = sync.pending_created @ (List.map (fun s -> match Jmap.Id.of_string s with Ok id -> id | Error e -> failwith e) created);
      pending_updated = sync.pending_updated @ (List.map (fun s -> match Jmap.Id.of_string s with Ok id -> id | Error e -> failwith e) updated);
      pending_destroyed = sync.pending_destroyed @ (List.map (fun s -> match Jmap.Id.of_string s with Ok id -> id | Error e -> failwith e) destroyed);
    }
  
  let clear_pending sync =
    {
      sync with
      pending_created = [];
      pending_updated = [];
      pending_destroyed = [];
    }
  
  let get_pending sync =
    (sync.pending_created, sync.pending_updated, sync.pending_destroyed)
  
  let needs_sync sync response =
    Changes_response.has_more_changes response ||
    sync.pending_created <> [] ||
    sync.pending_updated <> [] ||
    sync.pending_destroyed <> []
end

(** Utility to merge multiple change responses *)
let merge_changes responses =
  List.fold_left (fun (created, updated, destroyed) response ->
    let c = List.map (fun id -> match Jmap.Id.of_string id with | Ok id_t -> id_t | Error _ -> failwith ("Invalid ID: " ^ id)) (Changes_response.created response) in
    let u = List.map (fun id -> match Jmap.Id.of_string id with | Ok id_t -> id_t | Error _ -> failwith ("Invalid ID: " ^ id)) (Changes_response.updated response) in
    let d = List.map (fun id -> match Jmap.Id.of_string id with | Ok id_t -> id_t | Error _ -> failwith ("Invalid ID: " ^ id)) (Changes_response.destroyed response) in
    (created @ c, updated @ u, destroyed @ d)
  ) ([], [], []) responses

(** Get updated properties if available *)
let get_updated_properties response =
  Changes_response.updated_properties response