use std::panic::Location;

use serde::de::Deserialize;

use crate::{Profile, Provider, Metadata};
use crate::error::{Kind, Result};
use crate::value::{Value, Map, Dict, Id, Tag, ConfiguredValueDe};
use crate::coalesce::{Coalescible, Order};

/// Combiner of [`Provider`]s for configuration value extraction.
///
/// # Overview
///
/// A `Figment` combines providers by merging or joining their provided data.
/// The combined value or a subset of the combined value can be extracted into
/// any type that implements [`Deserialize`]. Additionally, values can be nested
/// in _profiles_, and a profile can be selected via [`Figment::select()`] for
/// extraction; the profile to be extracted can be retrieved with
/// [`Figment::profile()`] and defaults to [`Profile::Default`]. The [top-level
/// docs](crate) contain a broad overview of these topics.
///
/// ## Merging vs. Joining
///
/// _Merging_ and _joining_ control whether duplicate values are replaced or
/// discarded. A _merged_ value replaces an existing value with the same key,
/// while a _joined_ value is discarded if a value with the same key exists:
///
/// ```rust
/// use figment::{Figment};
///
/// let figment = Figment::from(("key", "original"));
///
/// let original: String = figment.extract_inner("key").unwrap();
/// assert_eq!(original, "original");
///
/// let figment = figment.merge(("key", "replaced"));
/// let replaced: String = figment.extract_inner("key").unwrap();
/// assert_eq!(replaced, "replaced");
///
/// let figment = figment.join(("key", "joined"));
/// let joined: String = figment.extract_inner("key").unwrap();
/// assert_eq!(joined, "replaced");
/// ```
///
/// ## Extraction
///
/// The configuration or a subset thereof can be extracted from a `Figment` in
/// one of several ways:
///
///   * [`Figment::extract()`], which extracts the complete value into any `T:
///     Deserialize`.
///   * [`Figment::extract_inner()`], which extracts a subset of the value for a
///     given key path.
///   * [`Figment::find_value()`], which returns the raw, serialized [`Value`]
///     for a given key path.
///
/// A "key path" is a string of the form `a.b.c` (e.g, `item`, `item.fruits`,
/// etc.) where each component delimited by a `.` is a key for the dictionary of
/// the preceding key in the path, or the root dictionary if it is the first key
/// in the path. See [`Value::find()`] for examples.
///
/// ## Metadata
///
/// Every value collected by a `Figment` is accompanied by metadata. If the
/// metadata has no `source`, the `merge` or `join` `Location` is added as a
/// source. `Metadata` can be retrieved in one of several ways:
///
///   * [`Figment::metadata()`], which returns an iterator over all of the
///     metadata for all values.
///   * [`Figment::find_metadata()`], which returns the metadata for a value at
///     a given key path.
///   * [`Figment::get_metadata()`], which returns the metadata for a given
///     metadata [`Id`].
#[derive(Clone, Debug, PartialEq)]
pub struct Figment {
    pub(crate) profile: Profile,
    pub(crate) metadata: Map<Id, Metadata>,
    pub(crate) value: Result<Map<Profile, Dict>>,
}

impl Figment {
    /// Creates a new `Figment` with the default profile selected and no
    /// providers.
    ///
    /// ```rust
    /// use figment::Figment;
    ///
    /// let figment = Figment::new();
    /// # assert_eq!(figment.profile(), "default");
    /// assert_eq!(figment.metadata().count(), 0);
    /// ```
    pub fn new() -> Self {
        Figment {
            metadata: Map::new(),
            profile: Profile::Default,
            value: Ok(Map::new()),
        }
    }

    /// Creates a new `Figment` with the default profile selected and an initial
    /// `provider`.
    ///
    /// ```rust
    /// use figment::Figment;
    /// use figment::providers::Env;
    ///
    /// let figment = Figment::from(Env::raw());
    /// # assert_eq!(figment.profile(), "default");
    /// assert_eq!(figment.metadata().count(), 1);
    /// ```
    pub fn from<T: Provider>(provider: T) -> Self {
        Figment::new().merge(provider)
    }

    #[track_caller]
    fn provide<T: Provider>(mut self, provider: T, order: Order) -> Self {
        if let Some(map) = provider.__metadata_map() {
            self.metadata.extend(map);
        }

        if let Some(profile) = provider.profile() {
            self.profile = self.profile.coalesce(profile, order);
        }

        let mut metadata = provider.metadata();
        if metadata.source.is_none() {
            metadata = metadata.source(Location::caller());
        }

        let id = Id::next();
        self.metadata.insert(id, metadata);

        let tag = Tag::Id(id);
        match (provider.data(), self.value) {
            (Ok(_), e@Err(_)) => self.value = e,
            (Err(e), Ok(_)) => self.value = Err(e.retagged(tag)),
            (Err(e), Err(prev)) => self.value = Err(e.retagged(tag).chain(prev)),
            (Ok(mut new), Ok(old)) => {
                new.iter_mut()
                    .map(|(_, v)| v.iter_mut())
                    .flatten()
                    .for_each(|(_, v)| v.map_tag(|t| *t = tag));

                self.value = Ok(old.coalesce(new, order));
            }
        }

        self
    }

    /// Joins `provider` into the current figment. See [merging vs.
    /// joining](#merging-vs-joining) for details.
    ///
    /// ```rust
    /// use figment::Figment;
    /// use figment::providers::Env;
    ///
    /// let figment = Figment::new().join(Env::raw());
    /// assert_eq!(figment.metadata().count(), 1);
    /// ```
    #[track_caller]
    pub fn join<T: Provider>(self, provider: T) -> Self {
        self.provide(provider, Order::Join)
    }

    /// Merges `provider` into the current figment. See [merging vs.
    /// joining](#merging-vs-joining) for details.
    ///
    /// ```rust
    /// use figment::Figment;
    /// use figment::providers::Env;
    ///
    /// let figment = Figment::new().merge(Env::raw());
    /// assert_eq!(figment.metadata().count(), 1);
    /// ```
    #[track_caller]
    pub fn merge<T: Provider>(self, provider: T) -> Self {
        self.provide(provider, Order::Merge)
    }

    /// Sets the profile to extract from to `profile`.
    ///
    /// # Example
    ///
    /// ```
    /// use figment::Figment;
    ///
    /// let figment = Figment::new().select("staging");
    /// assert_eq!(figment.profile(), "staging");
    /// ```
    pub fn select<P: Into<Profile>>(mut self, profile: P) -> Self {
        self.profile = profile.into();
        self
    }

    fn merged(&self) -> Result<Value> {
        let mut map = self.value.clone()?;
        let def = map.remove(&Profile::Default).unwrap_or(Dict::new());
        let global = map.remove(&Profile::Global).unwrap_or(Dict::new());

        let map = match map.remove(&self.profile) {
            Some(v) if self.profile.is_custom() => def.merge(v).merge(global),
            _ => def.merge(global)
        };

        Ok(Value::Dict(Tag::Default, map))
    }

    /// Deserializes the collected value into `T`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use serde::Deserialize;
    ///
    /// use figment::{Figment, providers::{Format, Toml, Json, Env}};
    ///
    /// #[derive(Debug, PartialEq, Deserialize)]
    /// struct Config {
    ///     name: String,
    ///     numbers: Option<Vec<usize>>,
    ///     debug: bool,
    /// }
    ///
    /// figment::Jail::expect_with(|jail| {
    ///     jail.create_file("Config.toml", r#"
    ///         name = "test"
    ///         numbers = [1, 2, 3, 10]
    ///     "#)?;
    ///
    ///     jail.set_env("config_name", "env-test");
    ///
    ///     jail.create_file("Config.json", r#"
    ///         {
    ///             "name": "json-test",
    ///             "debug": true
    ///         }
    ///     "#)?;
    ///
    ///     let config: Config = Figment::new()
    ///         .merge(Toml::file("Config.toml"))
    ///         .merge(Env::prefixed("CONFIG_"))
    ///         .join(Json::file("Config.json"))
    ///         .extract()?;
    ///
    ///     assert_eq!(config, Config {
    ///         name: "env-test".into(),
    ///         numbers: vec![1, 2, 3, 10].into(),
    ///         debug: true
    ///     });
    ///
    ///     Ok(())
    /// });
    /// ```
    pub fn extract<'a, T: Deserialize<'a>>(&self) -> Result<T> {
        // println!("figment = {:?}", self);
        let merged = self.merged().map_err(|e| e.resolved(self))?;
        // println!("merged = {:?}", self);
        // FIXME: We need to know the profile, if any, a key came from when
        // deserializing to tag it appropriately. (for global/default)
        T::deserialize(ConfiguredValueDe::from(self, &merged))
    }

    /// Deserializes the value at the `key` path in the collected value into
    /// `T`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use figment::{Figment, providers::{Format, Toml, Json}};
    ///
    /// figment::Jail::expect_with(|jail| {
    ///     jail.create_file("Config.toml", r#"
    ///         numbers = [1, 2, 3, 10]
    ///     "#)?;
    ///
    ///     jail.create_file("Config.json", r#"{ "debug": true } "#)?;
    ///
    ///     let numbers: Vec<usize> = Figment::new()
    ///         .merge(Toml::file("Config.toml"))
    ///         .join(Json::file("Config.json"))
    ///         .extract_inner("numbers")?;
    ///
    ///     assert_eq!(numbers, vec![1, 2, 3, 10]);
    ///
    ///     Ok(())
    /// });
    /// ```
    pub fn extract_inner<'a, T: Deserialize<'a>>(&self, key: &str) -> Result<T> {
        let merged = self.merged().map_err(|e| e.resolved(self))?;
        let inner = merged.find(key).ok_or(Kind::MissingField(key.to_string().into()))?;

        // FIXME: We need to know the profile, if any, a key came from when
        // deserializing to tag it appropriately. (for global/default)
        T::deserialize(ConfiguredValueDe::from(self, &inner))
    }

    /// Returns an iterator over the metadata for all of the collected values in
    /// the order in which they were added to `self`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use figment::{Figment, providers::{Format, Toml, Json}};
    ///
    /// let figment = Figment::new()
    ///     .merge(Toml::file("Config.toml"))
    ///     .join(Json::file("Config.json"));
    ///
    /// assert_eq!(figment.metadata().count(), 2);
    /// for (i, md) in figment.metadata().enumerate() {
    ///     match i {
    ///         0 => assert!(md.name.starts_with("TOML")),
    ///         1 => assert!(md.name.starts_with("JSON")),
    ///         _ => unreachable!(),
    ///     }
    /// }
    /// ```
    //
    // In fact, the order in which they were added globally. Why? Because
    // `BTreeMap` returns values in order of keys, and we generate a new ID,
    // monotonically greater than the previous, each time a new item is
    // provided. It's important that the IDs are unique globally since we can
    // allow combining `Figment`s.
    pub fn metadata(&self) -> impl Iterator<Item = &Metadata> {
        self.metadata.values()
    }

    /// Returns the selected profile.
    ///
    /// # Example
    ///
    /// ```
    /// use figment::Figment;
    ///
    /// let figment = Figment::new();
    /// assert_eq!(figment.profile(), "default");
    ///
    /// let figment = figment.select("staging");
    /// assert_eq!(figment.profile(), "staging");
    /// ```
    pub fn profile(&self) -> &Profile {
        &self.profile
    }

    /// Finds the value at `key` path in the combined value. See
    /// [`Value::find()`] for details on the syntax for `key`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use serde::Deserialize;
    ///
    /// use figment::{Figment, providers::{Format, Toml, Json, Env}};
    ///
    /// figment::Jail::expect_with(|jail| {
    ///     jail.create_file("Config.toml", r#"
    ///         name = "test"
    ///
    ///         [package]
    ///         name = "my-package"
    ///     "#)?;
    ///
    ///     jail.create_file("Config.json", r#"
    ///         {
    ///             "author": { "name": "Bob" }
    ///         }
    ///     "#)?;
    ///
    ///     let figment = Figment::new()
    ///         .merge(Toml::file("Config.toml"))
    ///         .join(Json::file("Config.json"));
    ///
    ///     let name = figment.find_value("name")?;
    ///     assert_eq!(name.as_str(), Some("test"));
    ///
    ///     let package_name = figment.find_value("package.name")?;
    ///     assert_eq!(package_name.as_str(), Some("my-package"));
    ///
    ///     let author_name = figment.find_value("author.name")?;
    ///     assert_eq!(author_name.as_str(), Some("Bob"));
    ///
    ///     Ok(())
    /// });
    /// ```
    pub fn find_value(&self, key: &str) -> Result<Value> {
        self.merged()?
            .find(key)
            .ok_or_else(|| Kind::MissingField(key.to_string().into()).into())
    }

    /// Finds the metadata for the value at `key` path. See [`Value::find()`]
    /// for details on the syntax for `key`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use serde::Deserialize;
    ///
    /// use figment::{Figment, providers::{Format, Toml, Json, Env}};
    ///
    /// figment::Jail::expect_with(|jail| {
    ///     jail.create_file("Config.toml", r#" name = "test" "#)?;
    ///     jail.create_file("Config.json", r#" { "author": "Bob" } "#)?;
    ///
    ///     let figment = Figment::new()
    ///         .merge(Toml::file("Config.toml"))
    ///         .join(Json::file("Config.json"));
    ///
    ///     let name_md = figment.find_metadata("name").unwrap();
    ///     assert!(name_md.name.starts_with("TOML"));
    ///
    ///     let author_md = figment.find_metadata("author").unwrap();
    ///     assert!(author_md.name.starts_with("JSON"));
    ///
    ///     Ok(())
    /// });
    /// ```
    pub fn find_metadata(&self, key: &str) -> Option<&Metadata> {
        self.metadata.get(&self.find_value(key).ok()?.metadata_id()?)
    }

    /// Returns the metadata with the given `id` if this figment contains a
    /// value with said metadata.
    ///
    /// # Example
    ///
    /// ```rust
    /// use serde::Deserialize;
    ///
    /// use figment::{Figment, providers::{Format, Toml, Json, Env}};
    ///
    /// figment::Jail::expect_with(|jail| {
    ///     jail.create_file("Config.toml", r#" name = "test" "#)?;
    ///     jail.create_file("Config.json", r#" { "author": "Bob" } "#)?;
    ///
    ///     let figment = Figment::new()
    ///         .merge(Toml::file("Config.toml"))
    ///         .join(Json::file("Config.json"));
    ///
    ///     let name = figment.find_value("name").unwrap();
    ///     let id = name.metadata_id().unwrap();
    ///     let metadata = figment.get_metadata(id).unwrap();
    ///     assert!(metadata.name.starts_with("TOML"));
    ///
    ///     let author = figment.find_value("author").unwrap();
    ///     let id = author.metadata_id().unwrap();
    ///     let metadata = figment.get_metadata(id).unwrap();
    ///     assert!(metadata.name.starts_with("JSON"));
    ///
    ///     Ok(())
    /// });
    /// ```
    pub fn get_metadata(&self, id: Id) -> Option<&Metadata> {
        self.metadata.get(&id)
    }
}

impl Provider for Figment {
    fn metadata(&self) -> Metadata { Metadata::default() }

    fn data(&self) -> Result<Map<Profile, Dict>> { self.value.clone() }

    fn profile(&self) -> Option<Profile> {
        Some(self.profile.clone())
    }

    fn __metadata_map(&self) -> Option<Map<Id, Metadata>> {
        Some(self.metadata.clone())
    }
}

impl Default for Figment {
    fn default() -> Self {
        Figment::new()
    }
}