(* The Sol language server: JSON-RPC over stdio, hand rolled on
   yojson. One capability, the load-bearing one: diagnostics. Every
   edit runs the same admission the runtime runs, so a rule with no
   decrease witness or a fact violating its schema is an error in
   the editor, at typing time, with the same message the loader
   gives. Parse errors carry positions; admission errors anchor at
   the top of the file until the loader learns locations. *)

let log_json json = Yojson.Safe.to_string json

let send json =
  let body = log_json json in
  Printf.printf "Content-Length: %d\r\n\r\n%s" (String.length body) body;
  flush stdout

let read_message () =
  let rec headers length =
    match In_channel.input_line stdin with
    | None -> None
    | Some line -> (
        let line = String.trim line in
        if line = "" then length
        else
          match String.index_opt line ':' with
          | Some i
            when String.lowercase_ascii (String.sub line 0 i) = "content-length"
            ->
              headers
                (int_of_string_opt
                   (String.trim
                      (String.sub line (i + 1) (String.length line - i - 1))))
          | _ -> headers length)
  in
  match headers None with
  | None -> None
  | Some length -> (
      match really_input_string stdin length with
      | body -> ( try Some (Yojson.Safe.from_string body) with _ -> None)
      | exception End_of_file -> None)

let member name json =
  match json with
  | `Assoc fields -> Option.value ~default:`Null (List.assoc_opt name fields)
  | _ -> `Null

let to_string_opt = function `String s -> Some s | _ -> None

(* Everything the checker can say about a document, as LSP
   diagnostics: (line, column, message), zero-based lines. *)
let diagnostics text =
  match Sol.Front.parse text with
  | Error { Sol.Front.line; column; message } ->
      [ (max 0 (line - 1), max 0 column, message) ]
  | Ok statements -> (
      match Sol.Program.load statements with
      | Error error -> [ (0, 0, Format.asprintf "%a" Sol.Program.pp_error error) ]
      | Ok _ -> [])

let publish uri text =
  let items =
    List.map
      (fun (line, column, message) ->
        `Assoc
          [
            ( "range",
              `Assoc
                [
                  ( "start",
                    `Assoc [ ("line", `Int line); ("character", `Int column) ]
                  );
                  ( "end",
                    `Assoc
                      [ ("line", `Int line); ("character", `Int (column + 1)) ]
                  );
                ] );
            ("severity", `Int 1);
            ("source", `String "sol");
            ("message", `String message);
          ])
      (diagnostics text)
  in
  send
    (`Assoc
      [
        ("jsonrpc", `String "2.0");
        ("method", `String "textDocument/publishDiagnostics");
        ("params", `Assoc [ ("uri", `String uri); ("diagnostics", `List items) ]);
      ])

let respond id result =
  send (`Assoc [ ("jsonrpc", `String "2.0"); ("id", id); ("result", result) ])

let check_notification params =
  let uri =
    to_string_opt (member "uri" (member "textDocument" params))
  in
  let text =
    match to_string_opt (member "text" (member "textDocument" params)) with
    | Some text -> Some text
    | None -> (
        (* didChange, full sync: the last full content change. *)
        match member "contentChanges" params with
        | `List changes -> (
            match List.rev changes with
            | last :: _ -> to_string_opt (member "text" last)
            | [] -> None)
        | _ -> None)
  in
  match (uri, text) with Some uri, Some text -> publish uri text | _ -> ()

let run () =
  set_binary_mode_in stdin true;
  set_binary_mode_out stdout true;
  let running = ref true in
  while !running do
    match read_message () with
    | None -> running := false
    | Some message -> (
        let id = member "id" message in
        let params = member "params" message in
        match to_string_opt (member "method" message) with
        | Some "initialize" ->
            respond id
              (`Assoc
                [
                  ( "capabilities",
                    `Assoc [ ("textDocumentSync", `Int 1) ] );
                  ( "serverInfo",
                    `Assoc
                      [
                        ("name", `String "sol-lsp"); ("version", `String "0.1.0");
                      ] );
                ])
        | Some "shutdown" -> respond id `Null
        | Some "exit" -> running := false
        | Some ("textDocument/didOpen" | "textDocument/didChange") ->
            check_notification params
        | Some "textDocument/didClose" -> (
            match to_string_opt (member "uri" (member "textDocument" params)) with
            | Some uri ->
                send
                  (`Assoc
                    [
                      ("jsonrpc", `String "2.0");
                      ("method", `String "textDocument/publishDiagnostics");
                      ( "params",
                        `Assoc
                          [ ("uri", `String uri); ("diagnostics", `List []) ] );
                    ])
            | None -> ())
        | Some _ when id <> `Null ->
            (* An unsupported request deserves an answer, not silence. *)
            send
              (`Assoc
                [
                  ("jsonrpc", `String "2.0");
                  ("id", id);
                  ( "error",
                    `Assoc
                      [
                        ("code", `Int (-32601));
                        ("message", `String "method not found");
                      ] );
                ])
        | _ -> ())
  done