use std::fmt::{Debug, Formatter, Result as FormatResult};
use std::{any::type_name, path::PathBuf};
use tokens::{ChangeToken, NeverChangeToken};

use crate::Value;

/// Defines the possible load errors.
#[derive(PartialEq, Clone)]
pub enum LoadError {
    /// Indicates a generic load error with an error message.
    Generic(String),

    /// Indicates a file load error.
    File {
        /// Gets the error message.
        message: String,

        /// Gets the path of the file being loaded.
        path: PathBuf,
    },
}

impl LoadError {
    /// Gets the load error message.
    pub fn message(&self) -> &str {
        match self {
            Self::Generic(message) => message,
            Self::File { message, .. } => message,
        }
    }
}

impl Debug for LoadError {
    fn fmt(&self, f: &mut Formatter<'_>) -> FormatResult {
        match self {
            Self::Generic(message) => f.write_str(message),
            Self::File { message, .. } => f.write_str(message),
        }
    }
}

/// Represents a configuration load result.
pub type LoadResult = std::result::Result<(), LoadError>;

/// Defines the behavior of an object that provides configuration key/values for an application.
pub trait ConfigurationProvider {
    /// Gets the name of the provider.
    fn name(&self) -> &str {
        type_name::<Self>()
    }

    /// Attempts to get a configuration value with the specified key.
    ///
    /// # Arguments
    ///
    /// * `key` - The key of the value to retrieve
    fn get(&self, key: &str) -> Option<Value>;

    /// Returns a [`ChangeToken`](tokens::ChangeToken) if this provider supports change tracking.
    fn reload_token(&self) -> Box<dyn ChangeToken> {
        Box::new(NeverChangeToken::new())
    }

    /// Loads the configuration values from the implemented source.
    fn load(&mut self) -> LoadResult {
        Ok(())
    }

    /// Gets the immediate descendent configuration keys for a given parent path based
    /// on this [`ConfigurationProvider`] and the set of keys returned by all of the
    /// preceding [`ConfigurationProvider`].
    ///
    /// # Arguments
    ///
    /// * `earlier_keys` - The sequence of keys returned by preceding provider for the same parent path
    /// * `parent_path` - The optional parent path to evaluate
    fn child_keys(&self, earlier_keys: &mut Vec<String>, parent_path: Option<&str>);
}