From-date option for graphing

src/graphing.rs

@@ -3,6 +3,7 @@ use crate::datafile;
 use crate::datafile::DiaryData;
 use anyhow::{bail, Result};
 use chrono::NaiveDate;
+use std::fmt::Write;
 use yansi::{Color, Paint};
 
 const COLORS: &[Color] = &[
@@ -51,8 +52,9 @@ pub fn pretty_print_diary_rows(
         if let Some(row) = current_row {
             ret += &pretty_print_row(&current_date, row);
         } else {
-            ret += &format!(
-                "{} !date missing from diary!\n",
+            _ = writeln!(
+                ret,
+                "{} !date missing from diary!",
                 current_date.format(datafile::DATE_FORMAT)
             );
         }
@@ -130,7 +132,7 @@ fn generate_rows(
                 }
                 ret += " ";
             }
-            ret += &format!("{}\n", Paint::new(current_count).bold());
+            _ = writeln!(ret, "{}", Paint::new(current_count).bold());
         }
     }
     Ok(ret)

src/main.rs

@@ -58,7 +58,11 @@ enum Command {
     },
 
     /// Displays the habit data according to the specified options to the terminal.
-    Graph,
+    Graph {
+        /// Start the graphing from this date. Must be in format YYYY-MM-DD.
+        #[structopt(long)]
+        from_date: Option<String>,
+    },
 
     /// Queries for habit information on the specified date.
     Insert {
@@ -97,9 +101,11 @@ fn main() -> Result<()> {
                 plot_datafile(&opt, &to_date, &data)?;
             }
         }
-        Command::Graph => {
+        Command::Graph { ref from_date } => {
             let data = datafile::parse_csv_to_diary_data(datafile_path)?;
-            plot_datafile(&opt, &Local::today().naive_local(), &data)?;
+            let from_date = parse_from_date(from_date)?;
+            let from_date = from_date.unwrap_or_else(|| Local::today().naive_local());
+            plot_datafile(&opt, &from_date, &data)?;
         }
         Command::Insert { ref date, no_graph } => {
             let date = parse_from_date(&Some(date.clone()))?.unwrap();