path: root/src/bahnhofname.gleam

import gleam/http/response.{Response}
import gleam/http/request.{Request}
import gleam/http.{Get}
import gleam/bit_builder.{BitBuilder}
import gleam/erlang/process
import gleam/erlang/atom
import gleam/io
import gleam/int
import gleam/string
import gleam/bit_string
import gleam/list
import gleam/map.{Map}
import gleam/uri
import gleam/hackney
import mist

external type Index
external type Field

external fn index_new(atom.Atom) -> Index =
  "Elixir.Haystack.Index" "new"

external fn index_ref(Index, Field) -> Index =
  "Elixir.Haystack.Index" "ref"

external fn index_field(Index, Field) -> Index =
  "Elixir.Haystack.Index" "field"

external fn field_term(String) -> Field =
  "Elixir.Haystack.Index.Field" "term"

external fn field_new(String) -> Field =
  "Elixir.Haystack.Index.Field" "new"

external fn index_add(Index, List(a)) -> Index =
  "Elixir.Haystack.Index" "add"

external fn index_search(Index, String) -> List(Map(atom.Atom, String)) =
  "Elixir.Haystack.Index" "search"

pub external fn inspect(a) -> a =
  "Elixir.IO" "inspect"

external type Query
external type Clause
external type Expression
external fn query_new() -> Query =
  "Elixir.Haystack.Query" "new"
external fn query_clause(Query, Clause) -> Query =
  "Elixir.Haystack.Query" "clause"
external fn query_run(Query, Index) -> List(Map(atom.Atom, String)) =
  "Elixir.Haystack.Query" "run"
external fn clause_new(atom.Atom) -> Clause =
  "Elixir.Haystack.Query.Clause" "new"
external fn query_expressions(Clause, List(Expression)) -> Clause =
  "Elixir.Haystack.Query.Clause" "expressions"
external fn query_expression_new(atom.Atom, List(#(atom.Atom, String))) -> Expression =
  "Elixir.Haystack.Query.Expression" "new"

external fn tokenize(String) -> List(Map(atom.Atom, String)) =
  "Elixir.Haystack.Tokenizer" "tokenize"

fn unpercent(encoded: String) -> String {
  let #([head], chunks) =
    encoded
    |> string.split(on: "%")
    |> list.split(at: 1)

  let assert Ok(res) =
    chunks
    |> list.map(fn(str) {
      case string.length(str) < 2 {
        True -> bit_string.from_string(str)
        False -> {
          let assert Ok(codepoint) =
            str
            |> string.slice(at_index: 0, length: 2)
            |> int.base_parse(16)
          <<codepoint:8, string.drop_left(str, 2):utf8>>
        }
      }
    })
    |> list.prepend(bit_string.from_string(head))
    |> bit_string.concat
    |> bit_string.to_string
  res
}

/// Looks up a query in a Map by exact value, no fuzzy matching.
fn lookup_exact(query: String, lookup: Map(String, String)) -> #(Int, String) {
  case map.get(lookup, query) {
    Ok(result) -> #(200, result)
    _ -> #(404, "??")
  }
}

/// Looks up a station by its name, with fuzzy matching.
fn lookup_by_name(
  query: String,
  stations: Map(String, String),
  ds100s: Map(String, String),
  fuzzy: fn(String) -> List(String)
) -> #(Int, String) {
  io.println(query)

  case map.get(stations, query) {
    Ok(ds100) -> #(200, ds100)
    _ -> {
      let results = fuzzy(query)
        |> list.filter_map(fn (res) { map.get(ds100s, string.uppercase(res)) })
      case results {
        // results -> {
        //   let names = results
        //     |> list.map (fn (res) {
        //     map.get(ds100s, string.uppercase(res))
        //     |> result.map(fn(a) { "/" <> a })
        //     |> result.unwrap("/")})
        //   #(200, string.join(names, "\n"))
        // }
        [res] -> #(302, res)
        [res, ..] -> #(302, res)
        _ -> #(404, "??")
      }
    }
  }
}

fn lookup_station(
  request: Request(t),
  stations: Map(String, String),
  ds100s: Map(String, String),
  baseurl: String,
  fuzzy: fn (String) -> List(String)
) -> Response(BitBuilder) {
  let #(code, text) = case request {
    // blackhole favicon.ico requests instead of using the index
    Request(method: Get, path: "/favicon.ico", ..) -> #(404, "")
    Request(method: Get, path: "/help", ..)
    | Request(method: Get, path: "/", ..) -> #(
      200,
      "ds100 → Name: " <> baseurl <> "/NN\n" <> "Name → ds100: " <> baseurl <> "/Nürnberg Hbf",
    )
    Request(method: Get, path: "/" <> path, ..) -> {
      let path = unpercent(path)

      let by_ds100 = lookup_exact(path, ds100s)

      case by_ds100.0 {
        200 -> by_ds100
        _ -> lookup_by_name(path, stations, ds100s, fuzzy)
      }
    }
    _ -> #(404, "intended usage is e.g. curl " <> baseurl <> "/FF")
  }
  let body = bit_builder.from_string(text)

  response.new(code)
  |> response.prepend_header(
    "x-data-source",
    "https://data.deutschebahn.com/dataset/data-betriebsstellen.html",
  )
  |> response.prepend_header(
    "x-sources-at",
    "https://stuebinm.eu/git/bahnhof.name",
  )
  |> response.prepend_header("content-type", "text/plain; charset=utf8")
  |> fn (a) { case code == 302 {
        True -> response.prepend_header(a, "location", text)
        _ -> a
     } }
  |> response.set_body(body)
}

fn fetch_data() -> Result(String, hackney.Error) {
  let assert Ok(uri) =
    uri.parse(
      "https://download-data.deutschebahn.com/static/datasets/betriebsstellen/DBNetz-Betriebsstellenverzeichnis-Stand2021-10.csv",
    )
  let assert Ok(request) = request.from_uri(uri)
  let assert Ok(response) = hackney.send(request)

  // some ü are corrupted for some reason
  Ok(string.replace(response.body, "�", "ü"))
}

fn read_csv() -> List(#(String, String)) {
  // let assert Ok(contents) = file.read(path)
  let assert Ok(contents) = fetch_data()
  contents
  // the file doesn't use quotes, so this is fine
  |> string.split(on: "\n")
  // drop CSV header
  |> list.drop(1)
  |> list.map(fn(a) { string.split(a, on: ";") })
  |> list.filter_map(fn(fields) {
    case fields {
      [_, ds100, name, ..] -> Ok(#(name, ds100))
      _ -> Error(fields)
    }
  })
}

pub fn main() {
  let baseurl = "https://bahnhof.name"
  let stations = read_csv()
  let stationmap =
    stations
    |> map.from_list
  let ds100map =
    stations
    |> list.map(fn(a) { #(a.1, a.0) })
    |> map.from_list
  let ref = atom.create_from_string("ref")
  let index =  index_new(atom.create_from_string("stations"))
    |> index_ref(field_term("id"))
    |> index_field(field_new("name"))
    |> index_add(stations
        |> list.map(fn(tuple) {case tuple {
          #(name, ds100)
          -> map.from_list([#("id", ds100), #("name", name)]
    )}}))


  let fuzzy = fn(searchterm: String) -> List(String) {
    let query = query_new()
    let match = atom.create_from_string("match")
    let field = atom.create_from_string("field")
    let term = atom.create_from_string("term")
    let expressions = tokenize(inspect(searchterm))
      |> list.filter_map(fn (a) { map.get(a, atom.create_from_string("v")) })
      |> list.map(fn (token) { query_expression_new(match, [#(field, "name"), #(term, token)]) })
    let clause = query_expressions(clause_new(atom.create_from_string("all")), expressions)
    let query = query_clause(query, clause)

    let matches = query_run(query, index)
      |> list.filter_map(fn (a) { map.get(a, ref) })

    inspect(matches)
    case list.length(matches) > 5 {
      True -> {
        let query = query_new()
        let clause = query_expressions(
          clause_new(atom.create_from_string("all")),
          [query_expression_new(match, [#(field, "name"), #(term, "hbf")]) , ..expressions]
        )
        let query = query_clause(query, clause)
        let narrow = query_run(query, index)
          |> list.filter_map(fn (a) { map.get(a, ref) })
        case narrow {
          [] -> matches
          _ -> narrow
        }
      }
      _ -> matches
    }
  }

  io.println("compiled index, starting server …")

  let _ = mist.run_service(
    2345,
    fn(req) { lookup_station(req, stationmap, ds100map, baseurl, fuzzy) },
    max_body_limit: 100,
  )
  process.sleep_forever()
}