feat: implement receiving file link

src/telega/api.gleam

@@ -15,7 +15,7 @@ import gleam/string
 import telega/log
 import telega/model.{
   type AnswerCallbackQueryParameters, type BotCommand, type BotCommandParameters,
-  type EditMessageTextParameters, type EditMessageTextResult,
+  type EditMessageTextParameters, type EditMessageTextResult, type File,
   type ForwardMessageParameters, type Message as ModelMessage,
   type SendDiceParameters, type SendMessageParameters, type User,
   type WebhookInfo,
@@ -325,6 +325,15 @@ fn build_url(config: TelegramApiConfig, path: String) -> String {
   config.tg_api_url <> config.token <> "/" <> path
 }
 
+pub fn get_file(
+  config config: TelegramApiConfig,
+  file_id file_id: String,
+) -> Result(File, String) {
+  new_get_request(config, path: "getFile", query: Some([#("file_id", file_id)]))
+  |> fetch(config)
+  |> map_resonse(model.decode_file)
+}
+
 fn new_post_request(
   config config: TelegramApiConfig,
   path path: String,

src/telega/model.gleam

@@ -2146,6 +2146,36 @@ pub fn encode_set_webhook_parameters(params: SetWebhookParameters) -> Json {
   ])
 }
 
+// File --------------------------------------------------------------------------------------------------------------
+
+/// https://core.telegram.org/bots/api#file
+pub type File {
+  /// This object represents a file ready to be downloaded. The file can be downloaded via the link `https://api.telegram.org/file/bot<token>/<file_path>`. It is guaranteed that the link will be valid for at least 1 hour. When the link expires, a new one can be requested by calling [getFile](https://core.telegram.org/bots/api#getfile).
+  ///
+  /// **Official reference:** [File](https://core.telegram.org/bots/api#file)
+  File(
+    /// Unique identifier for this file
+    file_id: String,
+    /// _Optional_. Unique identifier for this file, which is supposed to be the same over time and for different bots. Can't be used to download or reuse the file
+    file_unique_id: Option(String),
+    /// _Optional_. File size, if known
+    file_size: Option(Int),
+    /// _Optional_. File path. Use `https://api.telegram.org/file/bot<token>/<file_path>` to get the file
+    file_path: Option(String),
+  )
+}
+
+pub fn decode_file(json: Dynamic) -> Result(File, dynamic.DecodeErrors) {
+  json
+  |> dynamic.decode4(
+    File,
+    dynamic.field("file_id", dynamic.string),
+    dynamic.optional_field("file_unique_id", dynamic.string),
+    dynamic.optional_field("file_size", dynamic.int),
+    dynamic.optional_field("file_path", dynamic.string),
+  )
+}
+
 // Common ------------------------------------------------------------------------------------------------------------
 
 pub type IntOrString {

src/telega/reply.gleam

@@ -1,4 +1,5 @@
 import gleam/option.{type Option}
+import gleam/result
 import telega/api
 import telega/bot.{type Context}
 import telega/model.{
@@ -90,3 +91,23 @@ pub fn answer_callback_query(
 ) -> Result(Bool, String) {
   api.answer_callback_query(ctx.config.api, parameters)
 }
+
+/// Get download link for the file.
+pub fn with_file_link(
+  ctx ctx: Context(session),
+  file_id file_id: String,
+) -> Result(String, String) {
+  use file <- result.try(api.get_file(ctx.config.api, file_id))
+  use file_path <- result.try(option.to_result(
+    file.file_path,
+    "File path is missing",
+  ))
+
+  Ok(
+    ctx.config.api.tg_api_url
+    <> "/file/bot"
+    <> ctx.config.secret_token
+    <> "/"
+    <> file_path,
+  )
+}