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    use std::fmt::Debug;

    use crate::builder::{ConfigBuilder, DefaultState};
    use serde::de::Deserialize;
    use serde::ser::Serialize;

    use crate::error::{ConfigError, Result};
    use crate::map::Map;
    use crate::path;
    use crate::ser::ConfigSerializer;
    use crate::source::Source;
    use crate::value::{Table, Value};

    /// A prioritized configuration repository. It maintains a set of
    /// configuration sources, fetches values to populate those, and provides
    /// them according to the source's priority.
    #[derive(Clone, Debug)]
    pub struct Config {
        defaults: Map<path::Expression, Value>,
        overrides: Map<path::Expression, Value>,
        sources: Vec<Box<dyn Source + Send + Sync>>,

        /// Root of the cached configuration.
        pub cache: Value,
    }

    impl Default for Config {
        fn default() -> Self {
            Self {
                defaults: Default::default(),
                overrides: Default::default(),
                sources: Default::default(),
                cache: Value::new(None, Table::new()),
            }
        }
    }

    impl Config {
        pub(crate) fn new(value: Value) -> Self {
            Self {
                cache: value,
                ..Self::default()
            }
        }

        /// Creates new [`ConfigBuilder`] instance
        pub fn builder() -> ConfigBuilder<DefaultState> {
            ConfigBuilder::<DefaultState>::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 Self>
        where
            T: 'static,
            T: Source + Send + Sync,
        {
            self.sources.push(Box::new(source));

            #[allow(deprecated)]
            self.refresh()
        }

        /// 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,
            T: Source + Send + Sync,
        {
            self.sources.push(Box::new(source));

            #[allow(deprecated)]
            self.refresh()?;
            Ok(self)
        }

        /// Refresh the configuration cache with fresh
        /// data from added sources.
        ///
        /// 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 Self> {
            self.cache = {
                let mut cache: Value = Map::<String, Value>::new().into();

                // Add defaults
                for (key, val) in &self.defaults {
                    key.set(&mut cache, val.clone());
                }

                // Add sources
                self.sources.collect_to(&mut cache)?;

                // Add overrides
                for (key, val) in &self.overrides {
                    key.set(&mut cache, val.clone());
                }

                cache
            };

            Ok(self)
        }

        /// 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 Self>
        where
            T: Into<Value>,
        {
            self.defaults.insert(key.parse()?, value.into());

            #[allow(deprecated)]
            self.refresh()
        }

        /// Set an overwrite
        ///
        /// This function sets an overwrite value.
        /// The overwrite `value` is written to the `key` location on every `refresh()`
        ///
        /// # 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 Self>
        where
            T: Into<Value>,
        {
            self.overrides.insert(key.parse()?, value.into());

            #[allow(deprecated)]
            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()?;

            // Traverse the cache using the path to (possibly) retrieve a value
            if let Some(ref mut val) = expr.get_mut(&mut self.cache) {
                **val = value;
            } else {
                expr.set(&mut self.cache, value);
            }
            Ok(())
        }

        pub fn get<'de, T: Deserialize<'de>>(&self, key: &str) -> Result<T> {
            // Parse the key into a path expression
            let expr: path::Expression = key.parse()?;

            // Traverse the cache using the path to (possibly) retrieve a value
            let value = expr.get(&self.cache).cloned();

            match value {
                Some(value) => {
                    // Deserialize the received value into the requested type
                    T::deserialize(value).map_err(|e| e.extend_with_key(key))
                }

                None => Err(ConfigError::NotFound(key.into())),
            }
        }

        pub fn get_string(&self, key: &str) -> Result<String> {
            self.get(key).and_then(Value::into_string)
        }

        pub fn get_int(&self, key: &str) -> Result<i64> {
            self.get(key).and_then(Value::into_int)
        }

        pub fn get_float(&self, key: &str) -> Result<f64> {
            self.get(key).and_then(Value::into_float)
        }

        pub fn get_bool(&self, key: &str) -> Result<bool> {
            self.get(key).and_then(Value::into_bool)
        }

        pub fn get_table(&self, key: &str) -> Result<Map<String, Value>> {
            self.get(key).and_then(Value::into_table)
        }

        pub fn get_array(&self, key: &str) -> Result<Vec<Value>> {
            self.get(key).and_then(Value::into_array)
        }

        /// Attempt to deserialize the entire configuration into the requested type.
        pub fn try_deserialize<'de, T: Deserialize<'de>>(self) -> Result<T> {
            T::deserialize(self)
        }

        /// Attempt to serialize the entire configuration from the given type.
        pub fn try_from<T: Serialize>(from: &T) -> Result<Self> {
            let mut serializer = ConfigSerializer::default();
            from.serialize(&mut serializer)?;
            Ok(serializer.output)
        }

        #[deprecated(since = "0.7.0", note = "please use 'try_deserialize' instead")]
        pub fn deserialize<'de, T: Deserialize<'de>>(self) -> Result<T> {
            self.try_deserialize()
        }
    }

    impl Source for Config {
        fn clone_into_box(&self) -> Box<dyn Source + Send + Sync> {
            Box::new((*self).clone())
        }

        fn collect(&self) -> Result<Map<String, Value>> {
            self.cache.clone().into_table()
        }
    }