// EndBASIC
// Copyright 2022 Julio Merino
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License.  You may obtain a copy
// of the License at:
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
// License for the specific language governing permissions and limitations
// under the License.

//! Operations on EndBASIC values.

use crate::ast::*;
use std::convert::TryFrom;

/// Evaluation errors.
#[derive(Debug, thiserror::Error)]
#[error("{message}")]
pub struct Error {
    pub(crate) message: String,
}

impl Error {
    /// Constructs a new evaluation error from a textual `message`.
    pub(crate) fn new<S: Into<String>>(message: S) -> Self {
        Self { message: message.into() }
    }
}

/// Result for value computation return values.
pub type Result<T> = std::result::Result<T, Error>;

impl Value {
    /// Given a `target` variable type, tries to convert the value to that type if they are
    /// compatible or otherwise returns self.
    ///
    /// Can return an error when the conversion is feasible but it is not possible, such as trying
    /// to cast a NaN to an integer.
    pub(crate) fn maybe_cast(self, target: Option<ExprType>) -> Result<Value> {
        match (target, self) {
            (Some(ExprType::Integer), Value::Double(d)) => {
                Ok(Value::Integer(double_to_integer(d)?))
            }
            (Some(ExprType::Double), Value::Integer(i)) => Ok(Value::Double(integer_to_double(i))),
            (_, v) => Ok(v),
        }
    }
}

/// Converts the double `d` to an integer and fails if the conversion is not possible.
pub fn double_to_integer(d: f64) -> Result<i32> {
    let d = d.round();
    if d.is_finite() && d >= (i32::MIN as f64) && (d <= i32::MAX as f64) {
        Ok(d as i32)
    } else {
        Err(Error::new(format!("Cannot cast {} to integer due to overflow", d)))
    }
}

/// Converts the integer `i` to a double.
pub(crate) fn integer_to_double(i: i32) -> f64 {
    i as f64
}

/// Performs a left shift.
pub(crate) fn bitwise_shl(lhs: i32, rhs: i32) -> Result<i32> {
    let bits = match u32::try_from(rhs) {
        Ok(n) => n,
        Err(_) => {
            return Err(Error::new(format!("Number of bits to << ({}) must be positive", rhs)))
        }
    };

    match lhs.checked_shl(bits) {
        Some(i) => Ok(i),
        None => Ok(0),
    }
}

/// Performs a right shift.
pub(crate) fn bitwise_shr(lhs: i32, rhs: i32) -> Result<i32> {
    let bits = match u32::try_from(rhs) {
        Ok(n) => n,
        Err(_) => {
            return Err(Error::new(format!("Number of bits to >> ({}) must be positive", rhs)))
        }
    };

    match lhs.checked_shr(bits) {
        Some(i) => Ok(i),
        None if lhs < 0 => Ok(-1),
        None => Ok(0),
    }
}

/// Performs an arithmetic addition of integers.
pub fn add_integer(lhs: i32, rhs: i32) -> Result<i32> {
    match lhs.checked_add(rhs) {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer overflow".to_owned())),
    }
}

/// Performs an arithmetic subtraction of integers.
pub fn sub_integer(lhs: i32, rhs: i32) -> Result<i32> {
    match lhs.checked_sub(rhs) {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer underflow".to_owned())),
    }
}

/// Performs a multiplication of integers.
pub fn mul_integer(lhs: i32, rhs: i32) -> Result<i32> {
    match lhs.checked_mul(rhs) {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer overflow".to_owned())),
    }
}

/// Performs an arithmetic division of integers.
pub fn div_integer(lhs: i32, rhs: i32) -> Result<i32> {
    if rhs == 0 {
        return Err(Error::new("Division by zero"));
    }
    match lhs.checked_div(rhs) {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer underflow".to_owned())),
    }
}

/// Performs a modulo operation of integers.
pub fn modulo_integer(lhs: i32, rhs: i32) -> Result<i32> {
    if rhs == 0 {
        return Err(Error::new("Modulo by zero"));
    }
    match lhs.checked_rem(rhs) {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer underflow".to_owned())),
    }
}

/// Performs a power operation of integers.
pub fn pow_integer(lhs: i32, rhs: i32) -> Result<i32> {
    let exp = match u32::try_from(rhs) {
        Ok(exp) => exp,
        Err(_) => {
            return Err(Error::new(format!("Exponent {} cannot be negative", rhs)));
        }
    };
    match lhs.checked_pow(exp) {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer overflow".to_owned())),
    }
}

/// Performs an arithmetic negation of an integer.
pub fn neg_integer(i: i32) -> Result<i32> {
    match i.checked_neg() {
        Some(i) => Ok(i),
        None => Err(Error::new("Integer underflow".to_owned())),
    }
}

#[cfg(test)]
mod tests {
    use super::Value::*;
    use super::*;

    #[test]
    fn test_double_to_integer() {
        assert_eq!(8, double_to_integer(8.4).unwrap());
        assert_eq!(9, double_to_integer(8.5).unwrap());
        assert_eq!(9, double_to_integer(8.6).unwrap());

        double_to_integer(f64::NAN).unwrap_err();
        double_to_integer(i32::MAX as f64 + 1.0).unwrap_err();
        double_to_integer(i32::MIN as f64 - 1.0).unwrap_err();
    }

    #[test]
    fn test_integer_to_double() {
        assert_eq!(7.0, integer_to_double(7));
    }

    #[test]
    fn test_value_maybe_cast() {
        let all_types = [ExprType::Boolean, ExprType::Double, ExprType::Integer, ExprType::Text];
        for target in all_types {
            assert_eq!(Boolean(true), Boolean(true).maybe_cast(Some(target)).unwrap());
            if target != ExprType::Integer {
                assert_eq!(Double(3.8), Double(3.8).maybe_cast(Some(target)).unwrap());
                match Double(f64::NAN).maybe_cast(Some(target)).unwrap() {
                    Double(d) => assert!(d.is_nan()),
                    _ => panic!(),
                }
            }
            if target != ExprType::Double {
                assert_eq!(Integer(3), Integer(3).maybe_cast(Some(target)).unwrap());
            }
            assert_eq!(
                Text("a".to_owned()),
                Text("a".to_owned()).maybe_cast(Some(target)).unwrap()
            );
        }

        assert_eq!(Integer(8), Double(8.4).maybe_cast(Some(ExprType::Integer)).unwrap());
        assert_eq!(Integer(9), Double(8.5).maybe_cast(Some(ExprType::Integer)).unwrap());
        assert_eq!(Integer(9), Double(8.6).maybe_cast(Some(ExprType::Integer)).unwrap());
        assert_eq!(Double(7.0), Integer(7).maybe_cast(Some(ExprType::Double)).unwrap());

        Double(f64::NAN).maybe_cast(Some(ExprType::Integer)).unwrap_err();
        assert_eq!(
            Double(i32::MAX as f64),
            Integer(i32::MAX).maybe_cast(Some(ExprType::Double)).unwrap()
        );
        Double(i32::MAX as f64 + 1.0).maybe_cast(Some(ExprType::Integer)).unwrap_err();
        assert_eq!(
            Double(i32::MIN as f64),
            Integer(i32::MIN).maybe_cast(Some(ExprType::Double)).unwrap()
        );
        Double(i32::MIN as f64 - 1.0).maybe_cast(Some(ExprType::Integer)).unwrap_err();
    }

    #[test]
    fn test_value_shl() {
        assert_eq!(12, bitwise_shl(3, 2).unwrap());
        assert_eq!(0xf0000000u32 as i32, bitwise_shl(0xf0000000u32 as i32, 0).unwrap());
        assert_eq!(0x80000000u32 as i32, bitwise_shl(1, 31).unwrap());
        assert_eq!(0, bitwise_shl(0xf0000000u32 as i32, 31).unwrap());

        assert_eq!(0xe0000000u32 as i32, bitwise_shl(0xf0000000u32 as i32, 1).unwrap());
        assert_eq!(0, bitwise_shl(0x80000000u32 as i32, 1).unwrap());
        assert_eq!(0, bitwise_shl(1, 32).unwrap());
        assert_eq!(0, bitwise_shl(1, 64).unwrap());

        assert_eq!(
            "Number of bits to << (-1) must be positive",
            format!("{}", bitwise_shl(3, -1).unwrap_err())
        );
    }

    #[test]
    fn test_value_shr() {
        assert_eq!(3, bitwise_shr(12, 2).unwrap());
        assert_eq!(0xf0000000u32 as i32, bitwise_shr(0xf0000000u32 as i32, 0).unwrap());
        assert_eq!(-1, bitwise_shr(0xf0000000u32 as i32, 31).unwrap());
        assert_eq!(1, bitwise_shr(0x70000000u32 as i32, 30).unwrap());
        assert_eq!(-2, bitwise_shr(-8, 2).unwrap());

        assert_eq!(0xf0000000u32 as i32, bitwise_shr(0xe0000000u32 as i32, 1).unwrap());
        assert_eq!(0xc0000000u32 as i32, bitwise_shr(0x80000000u32 as i32, 1).unwrap());
        assert_eq!(0x38000000, bitwise_shr(0x70000000, 1).unwrap());
        assert_eq!(0, bitwise_shr(0x70000000u32 as i32, 32).unwrap());
        assert_eq!(0, bitwise_shr(0x70000000u32 as i32, 32).unwrap());
        assert_eq!(-1, bitwise_shr(0x80000000u32 as i32, 32).unwrap());
        assert_eq!(-1, bitwise_shr(0x80000000u32 as i32, 64).unwrap());

        assert_eq!(
            "Number of bits to >> (-1) must be positive",
            format!("{}", bitwise_shr(3, -1).unwrap_err())
        );
    }

    #[test]
    fn test_value_add_integer() {
        assert_eq!(5, add_integer(2, 3).unwrap());
        assert_eq!(i32::MAX, add_integer(i32::MAX, 0).unwrap());
        assert_eq!("Integer overflow", format!("{}", add_integer(i32::MAX, 1).unwrap_err()));
    }

    #[test]
    fn test_value_sub_integer() {
        assert_eq!(-1, sub_integer(2, 3).unwrap());
        assert_eq!(i32::MIN, sub_integer(i32::MIN, 0).unwrap());
        assert_eq!("Integer underflow", format!("{}", sub_integer(i32::MIN, 1).unwrap_err()));
    }

    #[test]
    fn test_value_mul_integer() {
        assert_eq!(6, mul_integer(2, 3).unwrap());
        assert_eq!(i32::MAX, mul_integer(i32::MAX, 1).unwrap());
        assert_eq!("Integer overflow", format!("{}", mul_integer(i32::MAX, 2).unwrap_err()));
    }

    #[test]
    fn test_value_div_integer() {
        assert_eq!(2, div_integer(10, 5).unwrap());
        assert_eq!(6, div_integer(20, 3).unwrap());
        assert_eq!(i32::MIN, div_integer(i32::MIN, 1).unwrap());
        assert_eq!("Division by zero", format!("{}", div_integer(4, 0).unwrap_err()));
        assert_eq!("Integer underflow", format!("{}", div_integer(i32::MIN, -1).unwrap_err()));
    }

    #[test]
    fn test_value_modulo_integer() {
        assert_eq!(0, modulo_integer(10, 5).unwrap());
        assert_eq!(2, modulo_integer(20, 3).unwrap());
        assert_eq!("Modulo by zero", format!("{}", modulo_integer(4, 0).unwrap_err()));
        assert_eq!("Integer underflow", format!("{}", modulo_integer(i32::MIN, -1).unwrap_err()));
    }

    #[test]
    fn test_value_pow_integer() {
        assert_eq!(1, pow_integer(0, 0).unwrap());
        assert_eq!(9, pow_integer(3, 2).unwrap());
        assert_eq!(i32::MAX, pow_integer(i32::MAX, 1).unwrap());
        assert_eq!("Integer overflow", format!("{}", pow_integer(i32::MAX, 2).unwrap_err()));
        assert_eq!(
            "Exponent -3 cannot be negative",
            format!("{}", pow_integer(1, -3).unwrap_err())
        );
    }

    #[test]
    fn test_value_neg_integer() {
        assert_eq!(-6, neg_integer(6).unwrap());
        assert_eq!(5, neg_integer(-5).unwrap());
    }
}