feat(downloader): download schedule from different source

providers/provider-engels-polytechnic/src/xls_downloader/mod.rs

@@ -0,0 +1,99 @@
+use chrono::{DateTime, Utc};
+use derive_more::{Display, Error};
+use std::mem::discriminant;
+use std::sync::Arc;
+
+mod yandex_disk;
+
+/// XLS data retrieval errors.
+#[derive(Clone, Debug, Display, Error)]
+pub enum FetchError {
+    /// Unknown error.
+    #[display("An unknown error occurred while downloading the file.")]
+    Reqwest(Arc<reqwest::Error>),
+
+    /// Server returned a status code different from 200.
+    #[display("Server returned a status code {status_code}.")]
+    BadStatusCode { status_code: u16 },
+
+    /// The folder contains no file matching the schedule name pattern.
+    #[display("No schedule file was found in the shared folder.")]
+    NoScheduleFile,
+}
+
+impl FetchError {
+    pub fn unknown(error: Arc<reqwest::Error>) -> Self {
+        Self::Reqwest(error)
+    }
+
+    pub fn bad_status_code(status_code: u16) -> Self {
+        Self::BadStatusCode { status_code }
+    }
+}
+
+impl PartialEq for FetchError {
+    fn eq(&self, other: &Self) -> bool {
+        discriminant(self) == discriminant(other)
+    }
+}
+
+pub type FetchResult<T> = Result<T, FetchError>;
+
+/// Description of the remote schedule file, obtained without downloading its content.
+#[derive(Clone, Debug, PartialEq)]
+pub struct RemoteFile {
+    /// Permanent link to the file, shown to API clients.
+    pub url: String,
+
+    /// Link the content is actually downloaded from.
+    pub download_url: String,
+
+    /// Content hash, changing whenever the file content changes.
+    pub version: String,
+
+    /// Time of the last file modification reported by the remote side.
+    pub modified_at: DateTime<Utc>,
+}
+
+/// Public Yandex Disk folder the schedule is downloaded from.
+#[derive(Clone, Debug)]
+pub struct Source {
+    pub public_url: String,
+}
+
+impl Source {
+    pub fn new(public_url: String) -> Self {
+        Self { public_url }
+    }
+
+    /// Looks up the current schedule file without downloading its content.
+    pub async fn probe(&self) -> FetchResult<RemoteFile> {
+        yandex_disk::probe(&self.public_url).await
+    }
+
+    /// Downloads the content of a previously probed file.
+    pub async fn download(&self, file: &RemoteFile) -> FetchResult<Vec<u8>> {
+        get(&file.download_url)
+            .await?
+            .bytes()
+            .await
+            .map(|bytes| bytes.to_vec())
+            .map_err(|error| FetchError::unknown(Arc::new(error)))
+    }
+}
+
+/// Performs a GET request with a spoofed browser User-Agent and checks the status code.
+async fn get(url: &str) -> FetchResult<reqwest::Response> {
+    let response = reqwest::Client::new()
+        .get(url)
+        .header("User-Agent", ua_generator::ua::spoof_chrome_ua())
+        .send()
+        .await
+        .map_err(|error| FetchError::unknown(Arc::new(error)))?;
+
+    if response.status().as_u16() != 200 {
+        return Err(FetchError::bad_status_code(response.status().as_u16()));
+    }
+
+    Ok(response)
+}