//! Error values produces when extracting configurations.

use std::fmt::{self, Display};
use std::borrow::Cow;

use serde::{ser, de};

use crate::{Figment, Profile, Metadata};
use crate::value::Tag;

/// A simple alias to `Result` with an error type of [`Error`].
pub type Result<T> = std::result::Result<T, Error>;

/// An error that occured while producing data or extracting a configuration.
///
/// # Constructing Errors
///
/// An `Error` will generally be constructed indirectly via its implementations
/// of serde's [`de::Error`] and [`ser::Error`], that is, as a result of
/// serialization or deserialization errors. When implementing [`Provider`],
/// however, it may be necessary to construct an `Error` directly.
///
/// [`Provider`]: crate::Provider
///
/// Broadly, there are two ways to construct an `Error`:
///
///   * Via an error message, since `Error` impls `From<String>`:
///
///     ```
///     use figment::Error;
///
///     Error::from("whoops, something went wrong!".to_string());
///     ```
///
///   * Via a [`Kind`], since `Error` impls `From<Kind>`:
///
///     ```
///     use figment::{error::{Error, Kind}, value::Value};
///
///     let value = Value::serialize(&100).unwrap();
///     if !value.as_str().is_some() {
///         let kind = Kind::InvalidType(value.to_actual(), "string".into());
///         let error = Error::from(kind);
///     }
///     ```
///
/// As always, `?` can be used to automatically convert into an `Error` using
/// the available `From` implementations:
///
/// ```
/// use std::fs::File;
///
/// fn try_read() -> Result<(), figment::Error> {
///     let x = File::open("/tmp/foo.boo").map_err(|e| e.to_string())?;
///     Ok(())
/// }
/// ```
///
/// # Display
///
/// By default, `Error` uses all of the available information about the error,
/// including the `Metadata`, `path`, and `profile` to display a message that
/// resembles the following, where `$` is `error.` for some `error: Error`:
///
/// ```text
/// $kind: `$metadata.interpolate($path)` in $($metadata.sources())*
/// ```
///
/// Concretely, such an error may look like:
///
/// ```text
/// invalid type: found sequence, expected u16: `staging.port` in TOML file Config.toml
/// ```
///
/// # Iterator
///
/// An `Error` may contain more than one error. To process all errors, iterator
/// over an `Error`:
///
/// ```rust
/// fn with_error(error: figment::Error) {
///     for error in error {
///         println!("error: {}", error);
///     }
/// }
/// ```
#[derive(Clone, Debug, PartialEq)]
pub struct Error {
    tag: Tag,
    /// The profile that was selected when the error occured, if any.
    pub profile: Option<Profile>,
    /// The metadata for the provider of the value that errored, if known.
    pub metadata: Option<Metadata>,
    /// The path to the configuration key that errored, if known.
    pub path: Vec<String>,
    /// The error kind.
    pub kind: Kind,
    prev: Option<Box<Error>>,
}

/// An error kind, encapsulating serde's [`serde::de::Error`].
#[derive(Clone, Debug, PartialEq)]
pub enum Kind {
    /// A custom error message.
    Message(String),

    /// An invalid type: (actual, expected). See
    /// [`serde::de::Error::invalid_type()`].
    InvalidType(Actual, String),
    /// An invalid value: (actual, expected). See
    /// [`serde::de::Error::invalid_value()`].
    InvalidValue(Actual, String),
    /// Too many or too few items: (actual, expected). See
    /// [`serde::de::Error::invalid_length()`].
    InvalidLength(usize, String),

    /// A variant with an unrecognized name: (actual, expected). See
    /// [`serde::de::Error::unknown_variant()`].
    UnknownVariant(String, &'static [&'static str]),
    /// A field with an unrecognized name: (actual, expected). See
    /// [`serde::de::Error::unknown_field()`].
    UnknownField(String, &'static [&'static str]),
    /// A field was missing: (name). See [`serde::de::Error::missing_field()`].
    MissingField(Cow<'static, str>),
    /// A field appeared more than once: (name). See
    /// [`serde::de::Error::duplicate_field()`].
    DuplicateField(&'static str),

    /// The `isize` was not in range of any known sized signed integer.
    ISizeOutOfRange(isize),
    /// The `usize` was not in range of any known sized unsigned integer.
    USizeOutOfRange(usize),

    /// The serializer or deserializer does not support the `Actual` type.
    Unsupported(Actual),

    /// The type `.0` cannot be used for keys, need a `.1`.
    UnsupportedKey(Actual, Cow<'static, str>),
}

impl Error {
    pub(crate) fn prefixed(mut self, path: &str) -> Self {
        self.path.insert(0, path.into());
        self
    }

    pub(crate) fn chain(self, mut error: Error) -> Self {
        error.prev = Some(Box::new(self));
        error
    }

    pub(crate) fn retagged(mut self, tag: Tag) -> Self {
        match self.tag {
            Tag::Default => { self.tag = tag; self }
            _ => self
        }
    }

    pub(crate) fn resolved(mut self, config: &Figment) -> Self {
        let mut error = Some(&mut self);
        while let Some(e) = error {
            e.profile = Some(config.profile().clone());
            e.metadata = e.tag.id().and_then(|i| config.metadata.get(&i)).cloned();
            error = e.prev.as_mut().map(|v| &mut **v);
        }

        self
    }
}

impl Error {
    /// Returns `true` if the error's kind is `MissingField`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use figment::error::{Error, Kind};
    ///
    /// let error = Error::from(Kind::MissingField("path".into()));
    /// assert!(error.missing());
    /// ```
    pub fn missing(&self) -> bool {
        match self.kind {
            Kind::MissingField(..) => true,
            _ => false
        }
    }

    /// Append the string `path` to the error's path.
    ///
    /// # Example
    ///
    /// ```rust
    /// use figment::Error;
    ///
    /// let error = Error::from("an error message".to_string())
    ///     .with_path("some_path");
    /// ```
    pub fn with_path(mut self, path: &str) -> Self {
        self.path.push(path.into());
        self
    }
}

/// An iterator over all errors in an [`Error`].
pub struct IntoIter(Option<Error>);

impl Iterator for IntoIter {
    type Item = Error;

    fn next(&mut self) -> Option<Self::Item> {
        if let Some(mut error) = self.0.take() {
            self.0 = error.prev.take().map(|e| *e);
            Some(error)
        } else {
            None
        }
    }
}

impl IntoIterator for Error {
    type Item = Error;
    type IntoIter = IntoIter;

    fn into_iter(self) -> Self::IntoIter {
        IntoIter(Some(self))
    }
}

/// A type that enumerates all of serde's types, used to indicate that a value
/// of the given type was received.
#[derive(Clone, Debug, PartialEq)]
pub enum Actual {
    Bool(bool),
    Unsigned(u64),
    Signed(i64),
    Float(f64),
    Char(char),
    Str(String),
    Bytes(Vec<u8>),
    Unit,
    Option,
    NewtypeStruct,
    Seq,
    Map,
    Enum,
    UnitVariant,
    NewtypeVariant,
    TupleVariant,
    StructVariant,
    Other(String),
}

impl fmt::Display for Actual {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Actual::Bool(v) => write!(f, "bool {}", v),
            Actual::Unsigned(v) => write!(f, "unsigned int `{}`", v),
            Actual::Signed(v) => write!(f, "signed int `{}`", v),
            Actual::Float(v) => write!(f, "float `{}`", v),
            Actual::Char(v) => write!(f, "char {:?}", v),
            Actual::Str(v) => write!(f, "string {:?}", v),
            Actual::Bytes(v) => write!(f, "bytes {:?}", v),
            Actual::Unit => write!(f, "unit"),
            Actual::Option => write!(f, "option"),
            Actual::NewtypeStruct => write!(f, "new-type struct"),
            Actual::Seq => write!(f, "sequence"),
            Actual::Map => write!(f, "map"),
            Actual::Enum => write!(f, "enum"),
            Actual::UnitVariant => write!(f, "unit variant"),
            Actual::NewtypeVariant => write!(f, "new-type variant"),
            Actual::TupleVariant => write!(f, "tuple variant"),
            Actual::StructVariant => write!(f, "struct variant"),
            Actual::Other(v) => v.fmt(f),
        }
    }
}

impl From<de::Unexpected<'_>> for Actual {
    fn from(value: de::Unexpected<'_>) -> Actual {
        match value {
            de::Unexpected::Bool(v) => Actual::Bool(v),
            de::Unexpected::Unsigned(v) => Actual::Unsigned(v),
            de::Unexpected::Signed(v) => Actual::Signed(v),
            de::Unexpected::Float(v) => Actual::Float(v),
            de::Unexpected::Char(v) => Actual::Char(v),
            de::Unexpected::Str(v) => Actual::Str(v.into()),
            de::Unexpected::Bytes(v) => Actual::Bytes(v.into()),
            de::Unexpected::Unit => Actual::Unit,
            de::Unexpected::Option => Actual::Option,
            de::Unexpected::NewtypeStruct => Actual::NewtypeStruct,
            de::Unexpected::Seq => Actual::Seq,
            de::Unexpected::Map => Actual::Map,
            de::Unexpected::Enum => Actual::Enum,
            de::Unexpected::UnitVariant => Actual::UnitVariant,
            de::Unexpected::NewtypeVariant => Actual::NewtypeVariant,
            de::Unexpected::TupleVariant => Actual::TupleVariant,
            de::Unexpected::StructVariant => Actual::StructVariant,
            de::Unexpected::Other(v) => Actual::Other(v.into())
        }
    }
}

impl de::Error for Error {
    fn custom<T: Display>(msg: T) -> Self {
        Kind::Message(msg.to_string()).into()
    }

    fn invalid_type(unexp: de::Unexpected, exp: &dyn de::Expected) -> Self {
        Kind::InvalidType(unexp.into(), exp.to_string()).into()
    }

    fn invalid_value(unexp: de::Unexpected, exp: &dyn de::Expected) -> Self {
        Kind::InvalidValue(unexp.into(), exp.to_string()).into()
    }

    fn invalid_length(len: usize, exp: &dyn de::Expected) -> Self {
        Kind::InvalidLength(len, exp.to_string()).into()
    }

    fn unknown_variant(variant: &str, expected: &'static [&'static str]) -> Self {
        Kind::UnknownVariant(variant.into(), expected).into()
    }

    fn unknown_field(field: &str, expected: &'static [&'static str]) -> Self {
        Kind::UnknownField(field.into(), expected).into()
    }

    fn missing_field(field: &'static str) -> Self {
        Kind::MissingField(field.into()).into()
    }

    fn duplicate_field(field: &'static str) -> Self {
        Kind::DuplicateField(field).into()
    }
}

impl ser::Error for Error {
    fn custom<T: Display>(msg: T) -> Self {
        Kind::Message(msg.to_string()).into()
    }
}

impl From<Kind> for Error {
    fn from(kind: Kind) -> Error {
        Error {
            tag: Tag::Default,
            path: vec![],
            profile: None,
            metadata: None,
            prev: None,
            kind,
        }
    }
}

impl From<String> for Error {
    fn from(string: String) -> Error {
        Kind::Message(string).into()
    }
}

impl Display for Kind {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Kind::Message(msg) => f.write_str(&msg),
            Kind::InvalidType(v, exp) => {
                write!(f, "invalid type: found {}, expected {}", v, exp)
            }
            Kind::InvalidValue(v, exp) => {
                write!(f, "invalid value {}, expected {}", v, exp)
            },
            Kind::InvalidLength(v, exp) => {
                write!(f, "invalid length {}, expected {}", v, exp)
            },
            Kind::UnknownVariant(v, exp) => {
                write!(f, "unknown variant: found `{}`, expected `{}`", v, OneOf(exp))
            }
            Kind::UnknownField(v, exp) => {
                write!(f, "unknown field: found `{}`, expected `{}`", v, OneOf(exp))
            }
            Kind::MissingField(v) => {
                write!(f, "missing field `{}`", v)
            }
            Kind::DuplicateField(v) => {
                write!(f, "duplicate field `{}`", v)
            }
            Kind::ISizeOutOfRange(v) => {
                write!(f, "signed integer `{}` is out of range", v)
            }
            Kind::USizeOutOfRange(v) => {
                write!(f, "unsigned integer `{}` is out of range", v)
            }
            Kind::Unsupported(v) => {
                write!(f, "unsupported type `{}`", v)
            }
            Kind::UnsupportedKey(a, e) => {
                write!(f, "unsupported type `{}` for key: must be `{}`", a, e)
            }
        }
    }
}

impl Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.kind.fmt(f)?;

        if let (Some(ref profile), Some(ref md)) = (&self.profile, &self.metadata) {
            write!(f, ":")?;
            if !self.path.is_empty() {
                write!(f, " `{}`", md.interpolate(profile, &self.path))?;
            }
        }

        if let Some(source) = self.metadata.as_ref().and_then(|m| m.source.as_ref()) {
            write!(f, " in {}", source)?;
        }

        if let Some(prev) = &self.prev {
            write!(f, "\n{}", prev)?;
        }

        Ok(())
    }
}

impl std::error::Error for Error {}

/// A structure that implements [`de::Expected`] signaling that one of the types
/// in the slice was expected.
pub struct OneOf(pub &'static [&'static str]);

impl fmt::Display for OneOf {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.0.len() {
            0 => write!(f, "none"),
            1 => write!(f, "`{}`", self.0[0]),
            2 => write!(f, "`{}` or `{}`", self.0[0], self.0[1]),
            _ => {
                write!(f, "one of ")?;
                for (i, alt) in self.0.iter().enumerate() {
                    if i > 0 { write!(f, ", ")?; }
                    write!(f, "`{}`", alt)?;
                }

                Ok(())
            }
        }
    }
}

impl de::Expected for OneOf {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        Display::fmt(self, f)
    }
}