Fix/data writer improvements (#8)

* Remove unused imports

* Improve DataWriter

.gitignore

@@ -3,3 +3,4 @@
 Cargo.lock
 .idea/*
 .DS_Store
+/data

src/geometry/types.rs

@@ -1,7 +1,5 @@
 use std::ops::{Add, AddAssign, Div, Mul};
 use std::cmp::PartialEq;
-use std::fs::File;
-use std::io::prelude::*;
 
 // Point /////////////////////////////////////////////////////////////////////
 //

src/util/mod.rs

@@ -1,9 +1,80 @@
-use geometry::types::Point;
-use std::fs::File;
+use std::fs;
 use std::io::Write;
+use std::path::Path;
+
+use geometry::types::Point;
+
+// DataWriter ////////////////////////////////////////////////////////////////
+//
+// A utility object to simplify persistence of point data. Each call to
+// write will generate a new file in the specified directory. Files are
+// sequentially numbered.
+
+pub struct DataWriter {
+    directory: String,
+    counter: u32,
+}
+
+impl DataWriter {
+    /// Creates a new directory in the current working path.
+    pub fn new(directory: &str) -> DataWriter {
+        if !Path::new(directory).exists() {
+            fs::create_dir(directory)
+                .expect("Couldn't create dir.");
+        }
+        DataWriter {
+            directory: directory.to_owned(),
+            counter: 0
+        }
+    }
+
+    /// Creates a new file in the writers directory with each point written
+    /// on a separate line.
+    pub fn write(&mut self, points: Vec<Point>) {
+        let path = format!("{}/frame-{}.txt", self.directory, self.counter);
+        match self.write_points(points, path) {
+            Err(e) => panic!("Error writing data. {}", e),
+            Ok(_) => (),
+        }
+        self.counter += 1;
+    }
+
+    fn write_points(&self, points: Vec<Point>, path: String) -> std::io::Result<()> {
+        let mut file = fs::File::create(path)?;
+        for point in points { write!(file, "{},{}\n", point.x, point.y)?; }
+        Ok(())
+    }
+}
+
+// Tests /////////////////////////////////////////////////////////////////////
+
+#[cfg(test)]
+mod tests {
+    use std::io::Read;
+
+    use super::*;
+
+    #[test]
+    fn data_writer_writes() {
+        // given
+        let mut writer = DataWriter::new("temp");
+
+        // when
+        writer.write(vec![Point::new(3.4, 6.7)]);
+        writer.write(vec![Point::new(6.4, 6.785)]);
+
+        // then
+        let mut file = fs::File::open("temp/frame-0.txt").expect("Error opening file.");
+        let mut contents = String::new();
+        file.read_to_string(&mut contents);
+        assert_eq!(contents, "3.4,6.7\n".to_owned());
+
+        let mut file = fs::File::open("temp/frame-1.txt").expect("Error opening file.");
+        let mut contents = String::new();
+        file.read_to_string(&mut contents);
+        assert_eq!(contents, "6.4,6.785\n".to_owned());
 
-pub fn write_points(points: Vec<Point>, file_name: &str) -> std::io::Result<()> {
-    let mut file = File::create(file_name)?;
-    for point in points { write!(file, "{},{}\n", point.x, point.y)?; }
-    Ok(())
+        // after
+        fs::remove_dir_all("temp").expect("Error cleaning up test.");
+    }
 }