Can read consumption from a file

central_backend/src/app_config.rs

@@ -6,7 +6,7 @@ use std::path::{Path, PathBuf};
 pub enum ConsumptionBackend {
     /// Constant consumption value
     Constant {
-        #[clap(long, default_value_t = 500)]
+        #[clap(short, long, default_value_t = 500)]
         value: i32,
     },
 
@@ -17,6 +17,12 @@ pub enum ConsumptionBackend {
         #[clap(long, default_value_t = 20000)]
         max: i32,
     },
+
+    /// Read consumption value in a file, on the filesystem
+    File {
+        #[clap(short, long, default_value = "/dev/shm/consumption.txt")]
+        path: String,
+    },
 }
 
 /// Solar system central backend

central_backend/src/energy/consumption.rs

@@ -1,5 +1,15 @@
 use crate::app_config::{AppConfig, ConsumptionBackend};
 use rand::{thread_rng, Rng};
+use std::num::ParseIntError;
+use std::path::Path;
+
+#[derive(thiserror::Error, Debug)]
+pub enum ConsumptionError {
+    #[error("The file that should contain the consumption does not exists!")]
+    NonExistentFile,
+    #[error("The file that should contain the consumption has an invalid content!")]
+    FileInvalidContent(#[source] ParseIntError),
+}
 
 pub type EnergyConsumption = i32;
 
@@ -14,5 +24,19 @@ pub async fn get_curr_consumption() -> anyhow::Result<EnergyConsumption> {
         ConsumptionBackend::Constant { value } => Ok(*value),
 
         ConsumptionBackend::Random { min, max } => Ok(thread_rng().gen_range(*min..*max)),
+
+        ConsumptionBackend::File { path } => {
+            let path = Path::new(path);
+            if !path.is_file() {
+                return Err(ConsumptionError::NonExistentFile.into());
+            }
+
+            let content = std::fs::read_to_string(path)?;
+
+            Ok(content
+                .trim()
+                .parse()
+                .map_err(ConsumptionError::FileInvalidContent)?)
+        }
     }
 }