Save plots in folder and fix opening them on Windows

plotly/plotly.rs#132 (comment)

.gitignore

@@ -10,3 +10,6 @@
 
 # mock files with unique endsong data?
 ex*.txt
+
+# folder with plots generated at runtime
+/plots/

src/plot/absolute.rs

@@ -31,8 +31,58 @@ pub fn artist(entries: &SongEntries, art: &Artist) {
     let layout = Layout::new().title(format!("<b>{art}</b>").as_str().into());
     plot.set_layout(layout);
 
+    // creates plots/ folder
+    std::fs::create_dir_all("plots").unwrap();
+
     // opens the plot in the browser
-    plot.show();
+    match std::env::consts::OS {
+        // see https://github.com/igiagkiozis/plotly/issues/132#issuecomment-1488920563
+        "windows" => {
+            let path = format!(
+                "{}\\plots\\{}.html",
+                std::env::current_dir().unwrap().display(),
+                &art.name
+            );
+            plot.write_html(path.as_str());
+            std::process::Command::new("explorer")
+                .arg(&path)
+                .output()
+                .unwrap();
+        }
+        "macos" => {
+            let path = format!(
+                "{}/plots/{}.html",
+                std::env::current_dir().unwrap().display(),
+                &art.name
+            );
+            plot.write_html(path.as_str());
+            std::process::Command::new("open")
+                .arg(&path)
+                .output()
+                .unwrap();
+        }
+        _ => {
+            let path = format!(
+                "{}/plots/{}.html",
+                std::env::current_dir().unwrap().display(),
+                &art.name
+            );
+            plot.write_html(path.as_str());
+
+            // https://doc.rust-lang.org/book/ch12-05-working-with-environment-variables.html
+            match std::env::var("BROWSER") {
+                Ok(browser) => {
+                    std::process::Command::new(&browser)
+                        .arg(&path)
+                        .output()
+                        .unwrap();
+                }
+                Err(_) => {
+                    eprintln!("Your BROWSER environmental variable is not set!");
+                }
+            }
+        }
+    };
 }
 
 /// Used by [`artist()`] to get the dates of all of its occurrence