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use std::fmt;
use std::fmt::{Display, Formatter};
use ty::*;
use result::Result;

#[derive(Debug, PartialEq)]
pub enum Error {
    TypeMismatch(&'static str, Ty),
    MissingField(&'static str),
    IndexOutOfBounds(usize, usize),
    WrongArrayLength(usize, usize),
    IllegalString(&'static str, String)
}

impl Display for Error {
    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
        match self {
            &Error::TypeMismatch(ref expected, ref ty) => {
                fmt.write_fmt(format_args!("expected {}, got {}", expected, ty))
            }
            &Error::MissingField(ref name) => {
                fmt.write_fmt(format_args!("missing object field '{}'", name))
            }
            &Error::IndexOutOfBounds(ref len, ref index) => {
                fmt.write_fmt(format_args!("array index {} out of bounds (length {})", index, len))
            }
            &Error::WrongArrayLength(ref expected, ref actual) => {
                fmt.write_fmt(format_args!("expected array of length {}, got array of length {}", expected, actual))
            }
            &Error::IllegalString(ref expected, ref actual) => {
                fmt.write_fmt(format_args!("expected {}, got {:?}", expected, actual))
            }
        }
    }
}

pub fn type_error<T>(expected: &'static str, actual: Ty) -> Result<T> {
    Err(Error::TypeMismatch(expected, actual))
}

pub fn field_error<T>(name: &'static str) -> Result<T> {
    Err(Error::MissingField(name))
}

pub fn array_error<T>(expected: usize, actual: usize) -> Result<T> {
    Err(Error::WrongArrayLength(expected, actual))
}

pub fn index_error<T>(len: usize, index: usize) -> Result<T> {
    Err(Error::IndexOutOfBounds(len, index))
}

pub fn string_error<T>(expected: &'static str, actual: String) -> Result<T> {
    Err(Error::IllegalString(expected, actual))
}