import gleam/list
import gleam/io
import gleam/int
import gleam/iterator
import gleam/result
import gleam/string
import snag.{Result, Snag}
import ffi/file
import parse.{Day}
import gleam/erlang/charlist
import gleam/erlang/file as efile
import cmd.{days_dir, input_dir}
import glint.{CommandInput}

fn input_path(day: Day) -> String {
  string.concat([input_dir, "day_", int.to_string(day), ".txt"])
}

fn gleam_src_path(day: Day) -> String {
  string.concat([days_dir, "day_", int.to_string(day), ".gleam"])
}

fn do(day: Day) -> Result(Nil) {
  try _ = case efile.make_directory(input_dir) {
    Ok(_) | Error(efile.Eexist) -> Ok(Nil)
    _ -> Error(failed_to_create_dir_err(input_dir))
  }

  try _ = case efile.make_directory(days_dir) {
    Ok(_) | Error(efile.Eexist) -> Ok(Nil)
    _ -> Error(failed_to_create_dir_err(days_dir))
  }

  let gleam_src_path = gleam_src_path(day)

  let create_src_res =
    file.open_file_exclusive(gleam_src_path)
    |> result.then(file.write(_, gleam_starter))
    |> result.map_error(handle_file_open_failure(_, gleam_src_path))

  let input_path = input_path(day)

  let create_input_res =
    file.open_file_exclusive(input_path)
    |> result.map_error(handle_file_open_failure(_, input_path))
  case create_src_res, create_input_res {
    Ok(_), Ok(_) -> Ok(Nil)
    Error(Snag(s1, errs1)), Error(Snag(s2, errs2)) ->
      [string.join([s1, ..errs1], ": "), string.join([s2, ..errs2], ": ")]
      |> string.join(" && ")
      |> snag.error()
    _, Error(err) -> Error(err)
    Error(err), _ -> Error(err)
  }
}

const gleam_starter = "pub fn run(input) {
  #(pt_1(input), pt_2(input))
}

fn pt_1(input: String) -> Int {
  0
}

fn pt_2(input: String) -> Int {
  0
}
"

fn handle_file_open_failure(reason: efile.Reason, filename: String) -> Snag {
  case reason {
    efile.Eexist -> file_already_exists_err(filename)
    _ -> failed_to_create_file_err(filename)
  }
}

fn file_already_exists_err(filename: String) -> Snag {
  filename
  |> snag.new()
  |> snag.layer("file already exists")
}

fn failed_to_create_file_err(filename: String) -> Snag {
  filename
  |> snag.new()
  |> snag.layer("failed to create file")
}

fn failed_to_create_dir_err(dir: String) -> Snag {
  dir
  |> snag.new()
  |> snag.layer("failed to create dir")
}

fn collect(x: #(Result(Nil), Day)) -> String {
  let day = int.to_string(x.1)
  case x.0
  |> snag.context(string.append("error occurred when initializing day ", day))
  |> result.map_error(snag.pretty_print) {
    Ok(_) -> string.append("initialized day: ", day)
    Error(reason) -> reason
  }
}

pub fn register_command(
  glint: glint.Command(Result(List(String))),
) -> glint.Command(Result(List(String))) {
  glint.add_command(
    to: glint,
    at: ["new"],
    do: run,
    with: [],
    described: "Create .gleam and input files",
    used: "gleam run new <dayX> <dayY> <...> ",
  )
}

pub fn run(input: CommandInput) -> Result(List(String)) {
  input.args
  |> parse.days
  |> result.map(cmd.exec(_, cmd.Endless, do, collect))
}