Add ConfigBuilder

3 files changed, 185 insertions, 0 deletions

diff --git a/src/builder.rs b/src/builder.rs
new file mode 100644
index 0000000..8f3081c
--- /dev/null
+++ b/src/builder.rs
@@ -0,0 +1,164 @@
+use std::str::FromStr;
+use std::{collections::HashMap, iter::IntoIterator};
+
+use crate::{
+    config::Config, error, error::ConfigError, path::Expression, source::Source, value::Value,
+};
+
+/// A configuration builder
+///
+/// It registers ordered sources of configuration to later build consistent [`Config`] from them.
+/// Configuration sources it defines are defaults, [`Source`]s and overrides.
+///
+/// Defaults are alaways loaded first and can be overwritten by any of two other sources.
+/// Overrides are always loaded last, thus cannot be overridden.
+/// Both can be only set explicitly key by key in code
+/// using [`set_default`](Self::set_default) or [`set_override`](Self::set_override).
+///
+/// An intermediate category, [`Source`], set groups of keys at once implicitly using data coming from external sources
+/// like files, environment variables or others that one implements. Defining a [`Source`] is as simple as implementing
+/// a trait for a struct.
+///
+/// Adding sources, setting defaults and overrides does not invoke any I/O nor builds a config.
+/// It happens on demand when [`build`](Self::build) (or its alternative) is called.
+/// Therefore all errors, related to any of the [`Source`] will only show up then.
+///
+/// # Examples
+///
+/// ```rust
+/// # use config::*;
+/// # use std::error::Error;
+/// # fn main() -> Result<(), Box<dyn Error>> {
+/// let mut builder = ConfigBuilder::default();
+///
+/// builder.set_default("default", "1")?;
+/// builder.add_source(File::new("config/settings", FileFormat::Json));
+/// builder.set_override("override", "1")?;
+///
+/// match builder.build() {
+///     Ok(config) => {
+///         // use your config
+///     },
+///     Err(e) => {
+///         // something went wrong
+///     }
+/// }
+/// # Ok(())
+/// # }
+/// ```
+///
+/// Calls can be chained as well
+/// ```rust
+/// # use std::error::Error;
+/// # use config::*;
+/// # fn main() -> Result<(), Box<dyn Error>> {
+/// let mut builder = ConfigBuilder::default();
+///
+/// builder
+///     .set_default("default", "1")?
+///     .add_source(File::new("config/settings", FileFormat::Json))
+///     .add_source(File::new("config/settings.prod", FileFormat::Json))
+///     .set_override("override", "1")?;
+/// # Ok(())
+/// # }
+/// ```
+#[derive(Debug, Clone, Default)]
+pub struct ConfigBuilder {
+    defaults: HashMap<Expression, Value>,
+    overrides: HashMap<Expression, Value>,
+    sources: Vec<Box<dyn Source + Send + Sync>>,
+}
+
+impl ConfigBuilder {
+    /// Set a default `value` at `key`
+    ///
+    /// This value can be overwritten by any [`Source`] or override.
+    ///
+    /// # Errors
+    ///
+    /// Fails if `Expression::from_str(key)` fails.
+    pub fn set_default<S, T>(&mut self, key: S, value: T) -> error::Result<&mut ConfigBuilder>
+    where
+        S: AsRef<str>,
+        T: Into<Value>,
+    {
+        self.defaults
+            .insert(Expression::from_str(key.as_ref())?, value.into());
+        Ok(self)
+    }
+
+    /// Registers new [`Source`] in this builder.
+    ///
+    /// Calling this method does not invoke any I/O. [`Source`] is only saved in internal register for later use.
+    pub fn add_source<T>(&mut self, source: T) -> &mut Self
+    where
+        T: Source + Send + Sync + 'static,
+    {
+        self.sources.push(Box::new(source));
+        self
+    }
+
+    /// Set an override
+    ///
+    /// This function sets an overwrite value. It will not be altered by any default or [`Source`]
+    ///
+    /// # Errors
+    ///
+    /// Fails if `Expression::from_str(key)` fails.
+    pub fn set_override<S, T>(&mut self, key: S, value: T) -> error::Result<&mut ConfigBuilder>
+    where
+        S: AsRef<str>,
+        T: Into<Value>,
+    {
+        self.overrides
+            .insert(Expression::from_str(key.as_ref())?, value.into());
+        Ok(self)
+    }
+
+    /// Reads all registered [`Source`]s.
+    ///
+    /// This is the method that invokes all I/O operations.
+    /// For a non consuming alternative see [`build_cloned`](Self::build_cloned)
+    ///
+    /// # Errors
+    /// If source collection fails, be it technical reasons or related to inability to read data as `Config` for different reasons,
+    /// this method returns error.
+    pub fn build(self) -> error::Result<Config> {
+        Self::build_internal(self.defaults, self.overrides, &self.sources)
+    }
+
+    /// Reads all registered [`Source`]s.
+    ///
+    /// Similar to [`build`](Self::build), but it does not take ownership of `ConfigBuilder` to allow later reuse.
+    /// Internally it clones data to achieve it.
+    ///
+    /// # Errors
+    /// If source collection fails, be it technical reasons or related to inability to read data as `Config` for different reasons,
+    /// this method returns error.
+    pub fn build_cloned(&self) -> error::Result<Config> {
+        Self::build_internal(self.defaults.clone(), self.overrides.clone(), &self.sources)
+    }
+
+    fn build_internal(
+        defaults: HashMap<Expression, Value>,
+        overrides: HashMap<Expression, Value>,
+        sources: &Vec<Box<dyn Source + Send + Sync>>,
+    ) -> error::Result<Config> {
+        let mut cache: Value = HashMap::<String, Value>::new().into();
+
+        // Add defaults
+        for (key, val) in defaults.into_iter() {
+            key.set(&mut cache, val);
+        }
+
+        // Add sources
+        sources.collect_to(&mut cache)?;
+
+        // Add overrides
+        for (key, val) in overrides.into_iter() {
+            key.set(&mut cache, val);
+        }
+
+        Ok(Config::new(cache))
+    }
+}
diff --git a/src/config.rs b/src/config.rs
index 2b6c5b6..5b4d40e 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 use std::fmt::Debug;
 
+use builder::ConfigBuilder;
 use serde::de::Deserialize;
 use serde::ser::Serialize;
 
@@ -35,7 +36,20 @@ impl Default for Config {
 }
 
 impl Config {
+    pub(crate) fn new(value: Value) -> Self {
+        Config {
+            cache: value,
+            ..Default::default()
+        }
+    }
+
+    /// Creates new [`ConfigBuilder`] instance
+    pub fn builder() -> ConfigBuilder {
+        ConfigBuilder::default()
+    }
+
     /// Merge in a configuration property source.
+    #[deprecated(since = "0.12.0", note = "please use 'ConfigBuilder' instead")]
     pub fn merge<T>(&mut self, source: T) -> Result<&mut Config>
     where
         T: 'static,
@@ -46,6 +60,7 @@ impl Config {
     }
 
     /// Merge in a configuration property source.
+    #[deprecated(since = "0.12.0", note = "please use 'ConfigBuilder' instead")]
     pub fn with_merged<T>(mut self, source: T) -> Result<Self>
     where
         T: 'static,
@@ -61,6 +76,7 @@ impl Config {
     ///
     /// Configuration is automatically refreshed after a mutation
     /// operation (`set`, `merge`, `set_default`, etc.).
+    #[deprecated(since = "0.12.0", note = "please use 'ConfigBuilder' instead")]
     pub fn refresh(&mut self) -> Result<&mut Config> {
         self.cache = {
             let mut cache: Value = HashMap::<String, Value>::new().into();
@@ -85,6 +101,7 @@ impl Config {
     }
 
     /// Set a default `value` at `key`
+    #[deprecated(since = "0.12.0", note = "please use 'ConfigBuilder' instead")]
     pub fn set_default<T>(&mut self, key: &str, value: T) -> Result<&mut Config>
     where
         T: Into<Value>,
@@ -101,6 +118,7 @@ impl Config {
     /// # Warning
     ///
     /// Errors if config is frozen
+    #[deprecated(since = "0.12.0", note = "please use 'ConfigBuilder' instead")]
     pub fn set<T>(&mut self, key: &str, value: T) -> Result<&mut Config>
     where
         T: Into<Value>,
@@ -109,6 +127,7 @@ impl Config {
         self.refresh()
     }
 
+    #[deprecated(since = "0.12.0", note = "please use 'ConfigBuilder' instead")]
     pub fn set_once(&mut self, key: &str, value: Value) -> Result<()> {
         let expr: path::Expression = key.parse()?;
 
diff --git a/src/lib.rs b/src/lib.rs
index 2dbd7b8..ae02c36 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -51,6 +51,7 @@ extern crate ini;
 #[cfg(feature = "ron")]
 extern crate ron;
 
+mod builder;
 mod config;
 mod de;
 mod env;
@@ -61,6 +62,7 @@ mod ser;
 mod source;
 mod value;
 
+pub use crate::builder::ConfigBuilder;
 pub use crate::config::Config;
 pub use crate::env::Environment;
 pub use crate::error::ConfigError;