Specify alias file as a command line argument

* Add a dependency on 'getopts'
* Remove the hard-coded "testaliases" file used previously.
* write_alias: Update to include a `file` attribute that can reference
  an arbitrary file
* find_alias_in_file: Change the `file` parameter to be a Path reference
  instead of a string so that it can be called correctly from
  `write_alias`. Also because it matches the File module's signature.

Originally I planned to make the file argument available under a `-f`
command-line option. Later I decided instead to make it a required
argument, so it made more sense not to prefix it with an option flag.
Since I no longer need command line options—just the first argument—I
realised that I could get rid of the `getopts` dependency and use
`std::env::args`. Will do this in a later commit.

3 files changed, 38 insertions, 5 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 81030eb..8db7560 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,4 +1,12 @@
 [root]
 name = "alias-auto-add"
 version = "0.0.1"
+dependencies = [
+ "getopts 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "getopts"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
 
diff --git a/Cargo.toml b/Cargo.toml
index 4fa9b0b..582992c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,3 +3,4 @@ name = "alias-auto-add"
 version = "0.0.1"
 
 [dependencies]
+getopts = "0.2"
diff --git a/src/main.rs b/src/main.rs
index ae7bf17..6b9d79e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,7 @@
+extern crate getopts;
+
+use getopts::Options;
+use std::env;
 use std::error::{self, Error};
 use std::io::{self, BufRead, BufReader, Write};
 use std::fmt;
@@ -65,11 +69,11 @@ impl Alias {
     }
 }
 
-fn write_alias(from: String) -> Result<(), AliasSearchError> {
+fn write_alias<P: AsRef<Path>>(from: String, file: P) -> Result<(), AliasSearchError> {
     let mut alias = Alias::new(&from);
-    let similar_aliases = try!(find_alias_in_file(&alias, "./testaliases"));
+    let similar_aliases = try!(find_alias_in_file(&alias, &file));
     alias.update_alias_id(similar_aliases);
-    try!(alias.write_to_file("./testaliases"));
+    try!(alias.write_to_file(&file));
     Ok(())
 }
 
@@ -133,7 +137,7 @@ impl PartialEq<AliasSearchError> for AliasSearchError {
     }
 }
 
-fn find_alias_in_file(alias: &Alias, file: &str) -> Result<Vec<String>, AliasSearchError> {
+fn find_alias_in_file<P: AsRef<Path>>(alias: &Alias, file: P) -> Result<Vec<String>, AliasSearchError> {
     let mut matches = Vec::new();
     let f = try!(File::open(file));
     let file = BufReader::new(&f);
@@ -157,7 +161,27 @@ fn find_alias_in_file(alias: &Alias, file: &str) -> Result<Vec<String>, AliasSea
     }
 }
 
+fn print_usage(program: &str) {
+    println!("Usage: {} FILE", program);
+}
+
 fn main() {
+    let args: Vec<String> = env::args().collect();
+    let program = args[0].clone();
+    let opts = Options::new();
+
+    let opt_matches = match opts.parse(&args[1..]) {
+        Ok(m) => m,
+        Err(f) => panic!(f.to_string()),
+    };
+
+    let file = if !opt_matches.free.is_empty() {
+        opt_matches.free[0].clone()
+    } else {
+        print_usage(&program);
+        return;
+    };
+
     let stdin = io::stdin();
 
     for line in stdin.lock().lines() {
@@ -167,7 +191,7 @@ fn main() {
         println!("{}", line);
 
         if line.starts_with("From: ") {
-            match write_alias(line) {
+            match write_alias(line, &file) {
                 Ok(_)  => continue,
                 Err(e @ AliasSearchError::NotFound) | Err(e @ AliasSearchError::EmailExists) =>
                     io::stderr().write(e.to_string().as_bytes()).ok(),