//! A parser for GraphQL. Used in the [`async-graphql`](https://crates.io/crates/async-graphql)
//! crate.
//!
//! It uses the [pest](https://crates.io/crates/pest) crate to parse the input and then transforms
//! it into Rust types.
#![forbid(unsafe_code)]

use crate::types::OperationType;
use async_graphql_value::Name;
use pest::error::LineColLocation;
use pest::RuleType;
use serde::{Serialize, Serializer};
use std::fmt::{self, Display, Formatter};

pub use parse::{parse_query, parse_schema};
pub use pos::{Pos, Positioned};

pub mod types;

mod parse;
mod pos;

/// Parser error.
#[derive(Debug, Clone, PartialEq, Eq)]
#[non_exhaustive]
pub enum Error {
    /// A syntax error occurred.
    Syntax {
        /// The message of the error, nicely formatted with newlines.
        message: String,
        /// The start position of the error.
        start: Pos,
        /// The end position of the error, if present.
        end: Option<Pos>,
    },
    /// The schema contained multiple query, mutation or subscription roots.
    MultipleRoots {
        /// The type of root that was duplicated.
        root: OperationType,
        /// The position of the schema.
        schema: Pos,
        /// The position of the second root.
        pos: Pos,
    },
    /// The schema contained no query root.
    MissingQueryRoot {
        /// The position of the schema.
        pos: Pos,
    },
    /// Multiple operations were found in a document with an anonymous one.
    MultipleOperations {
        /// The position of the anonymous operation.
        anonymous: Pos,
        /// The position of the other operation.
        operation: Pos,
    },
    /// An operation is defined multiple times in a document.
    OperationDuplicated {
        /// The name of the operation.
        operation: Name,
        /// The position of the first definition.
        first: Pos,
        /// The position of the second definition.
        second: Pos,
    },
    /// A fragment is defined multiple times in a document.
    FragmentDuplicated {
        /// The name of the fragment.
        fragment: Name,
        /// The position of the first definition.
        first: Pos,
        /// The position of the second definition.
        second: Pos,
    },
    /// The document does not contain any operation.
    MissingOperation,
}

impl Error {
    /// Get an iterator over the positions of the error.
    ///
    /// The iterator is ordered from most important to least important position.
    #[must_use]
    pub fn positions(&self) -> ErrorPositions {
        match self {
            Self::Syntax {
                start,
                end: Some(end),
                ..
            } => ErrorPositions::new_2(*start, *end),
            Self::Syntax { start, .. } => ErrorPositions::new_1(*start),
            Self::MultipleRoots { schema, pos, .. } => ErrorPositions::new_2(*pos, *schema),
            Self::MissingQueryRoot { pos } => ErrorPositions::new_1(*pos),
            Self::MultipleOperations {
                anonymous,
                operation,
            } => ErrorPositions::new_2(*anonymous, *operation),
            Self::OperationDuplicated { first, second, .. } => {
                ErrorPositions::new_2(*second, *first)
            }
            Self::FragmentDuplicated { first, second, .. } => {
                ErrorPositions::new_2(*second, *first)
            }
            Self::MissingOperation => ErrorPositions::new_0(),
        }
    }
}

impl Display for Error {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        match self {
            Self::Syntax { message, .. } => f.write_str(&message),
            Self::MissingQueryRoot { .. } => f.write_str("schema definition is missing query root"),
            Self::MultipleRoots { root, .. } => {
                write!(f, "multiple {} roots in schema definition", root)
            }
            Self::MultipleOperations { .. } => f.write_str("document contains multiple operations"),
            Self::OperationDuplicated { operation, .. } => {
                write!(f, "operation {} is defined twice", operation)
            }
            Self::FragmentDuplicated { fragment, .. } => {
                write!(f, "fragment {} is defined twice", fragment)
            }
            Self::MissingOperation => f.write_str("document does not contain an operation"),
        }
    }
}

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

impl<R: RuleType> From<pest::error::Error<R>> for Error {
    fn from(err: pest::error::Error<R>) -> Self {
        let (start, end) = match err.line_col {
            LineColLocation::Pos(at) => (at, None),
            LineColLocation::Span(start, end) => (start, Some(end)),
        };

        Error::Syntax {
            message: err.to_string(),
            start: Pos::from(start),
            end: end.map(Pos::from),
        }
    }
}

/// An alias for `Result<T, Error>`.
pub type Result<T> = std::result::Result<T, Error>;

/// An iterator over the positions inside an error.
///
/// Constructed from the `Error::postions` function.
#[derive(Debug, Clone)]
pub struct ErrorPositions(ErrorPositionsInner);

impl ErrorPositions {
    fn new_0() -> Self {
        Self(ErrorPositionsInner::None)
    }
    fn new_1(a: Pos) -> Self {
        Self(ErrorPositionsInner::One(a))
    }
    fn new_2(a: Pos, b: Pos) -> Self {
        Self(ErrorPositionsInner::Two(a, b))
    }
}

impl Iterator for ErrorPositions {
    type Item = Pos;

    fn next(&mut self) -> Option<Self::Item> {
        match self.0 {
            ErrorPositionsInner::Two(a, b) => {
                self.0 = ErrorPositionsInner::One(b);
                Some(a)
            }
            ErrorPositionsInner::One(a) => {
                self.0 = ErrorPositionsInner::None;
                Some(a)
            }
            ErrorPositionsInner::None => None,
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let len = self.len();
        (len, Some(len))
    }
}

impl DoubleEndedIterator for ErrorPositions {
    fn next_back(&mut self) -> Option<Self::Item> {
        match self.0 {
            ErrorPositionsInner::Two(a, b) => {
                self.0 = ErrorPositionsInner::One(a);
                Some(b)
            }
            ErrorPositionsInner::One(a) => {
                self.0 = ErrorPositionsInner::None;
                Some(a)
            }
            ErrorPositionsInner::None => None,
        }
    }
}

impl std::iter::FusedIterator for ErrorPositions {}

impl ExactSizeIterator for ErrorPositions {
    fn len(&self) -> usize {
        match self.0 {
            ErrorPositionsInner::Two(_, _) => 2,
            ErrorPositionsInner::One(_) => 1,
            ErrorPositionsInner::None => 0,
        }
    }
}

impl Serialize for ErrorPositions {
    fn serialize<S: Serializer>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error> {
        serializer.collect_seq(self.clone())
    }
}

#[derive(Debug, Clone, Copy)]
enum ErrorPositionsInner {
    Two(Pos, Pos),
    One(Pos),
    None,
}