From 4573e911816ecba90565d33d219e6f04ee7e2f05 Mon Sep 17 00:00:00 2001
From: Ryan Leckey <ryan@launchbadge.com>
Date: Tue, 13 Jun 2017 18:34:28 -0700
Subject: Add Environment

---
 src/env.rs | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs |  2 ++
 2 files changed, 90 insertions(+)
 create mode 100644 src/env.rs

diff --git a/src/env.rs b/src/env.rs
new file mode 100644
index 0000000..c49bb0e
--- /dev/null
+++ b/src/env.rs
@@ -0,0 +1,88 @@
+use std::env;
+use std::collections::HashMap;
+use error::*;
+use source::Source;
+use value::{Value, ValueKind};
+
+pub struct Environment {
+    /// Optional prefix that will limit access to the environment to only keys that
+    /// begin with the defined prefix.
+    ///
+    /// A prefix, followed by `_` (the seperator),
+    /// is tested to be present on each key before its considered
+    /// to be part of the source environment.
+    ///
+    /// For example, the key `CONFIG_DEBUG` would become `DEBUG` with a prefix of `config`.
+    prefix: Option<String>,
+
+    /// The character sequence that separates each key segment in an environment key pattern.
+    /// Consider a nested configuration such as `redis.password`, a separator of `_` would allow
+    /// an environment key of `REDIS_PASSWORD` to match.
+    ///
+    /// The default separator is `_`.
+    separator: String,
+}
+
+impl Environment {
+    pub fn new() -> Self {
+        Environment::default()
+    }
+
+    pub fn with_prefix(s: String) -> Self {
+        Environment { separator: s, ..Environment::default() }
+    }
+
+    pub fn prefix(&mut self, s: String) -> &mut Self {
+        self.prefix = s.into();
+        self
+    }
+
+    pub fn separator(&mut self, s: String) -> &mut Self {
+        self.separator = s;
+        self
+    }
+}
+
+impl Default for Environment {
+    fn default() -> Environment {
+        Environment {
+            prefix: None,
+            separator: "_".into(),
+        }
+    }
+}
+
+impl Source for Environment {
+    fn collect(&self) -> Result<HashMap<String, Value>> {
+        let mut m = HashMap::new();
+        let uri: String = "the environment".into();
+
+        // Define a prefiux pattern to test and exclude from keys
+        let prefix_pattern = match self.prefix {
+            Some(ref prefix) => Some(prefix.clone() + &self.separator),
+            _ => None,
+        };
+
+        for (key, value) in env::vars() {
+            let mut key = key.to_string();
+
+            // Check for prefix
+            if let Some(ref prefix_pattern) = prefix_pattern {
+                if key.starts_with(prefix_pattern) {
+                    // Remove this prefix from the key
+                    key = key[prefix_pattern.len()..].to_string();
+                } else {
+                    // Skip this key
+                    continue;
+                }
+            }
+
+            // Replace `separator` with `.`
+            key = key.replace(&self.separator, ".");
+
+            m.insert(key, Value::new(Some(&uri), ValueKind::String(value)));
+        }
+
+        Ok(m)
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 534533d..fe02a93 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -43,9 +43,11 @@ mod path;
 mod source;
 mod config;
 mod file;
+mod env;
 
 pub use config::Config;
 pub use error::ConfigError;
 pub use value::Value;
 pub use source::Source;
 pub use file::{File, FileFormat};
+pub use env::Environment;
-- 
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