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use crate::mir::interpret::truncate;
use rustc_target::abi::Size;

#[derive(Copy, Clone)]
/// A type for representing any integer. Only used for printing.
// FIXME: Use this for the integer-tree representation needed for type level ints and
// const generics?
pub struct ConstInt {
    /// Number of bytes of the integer. Only 1, 2, 4, 8, 16 are legal values.
    size: u8,
    /// Whether the value is of a signed integer type.
    signed: bool,
    /// Whether the value is a `usize` or `isize` type.
    is_ptr_sized_integral: bool,
    /// Raw memory of the integer. All bytes beyond the `size` are unused and must be zero.
    raw: u128,
}

impl ConstInt {
    pub fn new(raw: u128, size: Size, signed: bool, is_ptr_sized_integral: bool) -> Self {
        assert!(raw <= truncate(u128::MAX, size));
        Self { raw, size: size.bytes() as u8, signed, is_ptr_sized_integral }
    }
}

impl std::fmt::Debug for ConstInt {
    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let Self { size, signed, raw, is_ptr_sized_integral } = *self;
        if signed {
            let bit_size = size * 8;
            let min = 1u128 << (bit_size - 1);
            let max = min - 1;
            if raw == min {
                match (size, is_ptr_sized_integral) {
                    (_, true) => write!(fmt, "isize::MIN"),
                    (1, _) => write!(fmt, "i8::MIN"),
                    (2, _) => write!(fmt, "i16::MIN"),
                    (4, _) => write!(fmt, "i32::MIN"),
                    (8, _) => write!(fmt, "i64::MIN"),
                    (16, _) => write!(fmt, "i128::MIN"),
                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
                }
            } else if raw == max {
                match (size, is_ptr_sized_integral) {
                    (_, true) => write!(fmt, "isize::MAX"),
                    (1, _) => write!(fmt, "i8::MAX"),
                    (2, _) => write!(fmt, "i16::MAX"),
                    (4, _) => write!(fmt, "i32::MAX"),
                    (8, _) => write!(fmt, "i64::MAX"),
                    (16, _) => write!(fmt, "i128::MAX"),
                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
                }
            } else {
                match size {
                    1 => write!(fmt, "{}", raw as i8)?,
                    2 => write!(fmt, "{}", raw as i16)?,
                    4 => write!(fmt, "{}", raw as i32)?,
                    8 => write!(fmt, "{}", raw as i64)?,
                    16 => write!(fmt, "{}", raw as i128)?,
                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
                }
                if fmt.alternate() {
                    match (size, is_ptr_sized_integral) {
                        (_, true) => write!(fmt, "_isize")?,
                        (1, _) => write!(fmt, "_i8")?,
                        (2, _) => write!(fmt, "_i16")?,
                        (4, _) => write!(fmt, "_i32")?,
                        (8, _) => write!(fmt, "_i64")?,
                        (16, _) => write!(fmt, "_i128")?,
                        _ => bug!(),
                    }
                }
                Ok(())
            }
        } else {
            let max = truncate(u128::MAX, Size::from_bytes(size));
            if raw == max {
                match (size, is_ptr_sized_integral) {
                    (_, true) => write!(fmt, "usize::MAX"),
                    (1, _) => write!(fmt, "u8::MAX"),
                    (2, _) => write!(fmt, "u16::MAX"),
                    (4, _) => write!(fmt, "u32::MAX"),
                    (8, _) => write!(fmt, "u64::MAX"),
                    (16, _) => write!(fmt, "u128::MAX"),
                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
                }
            } else {
                match size {
                    1 => write!(fmt, "{}", raw as u8)?,
                    2 => write!(fmt, "{}", raw as u16)?,
                    4 => write!(fmt, "{}", raw as u32)?,
                    8 => write!(fmt, "{}", raw as u64)?,
                    16 => write!(fmt, "{}", raw as u128)?,
                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
                }
                if fmt.alternate() {
                    match (size, is_ptr_sized_integral) {
                        (_, true) => write!(fmt, "_usize")?,
                        (1, _) => write!(fmt, "_u8")?,
                        (2, _) => write!(fmt, "_u16")?,
                        (4, _) => write!(fmt, "_u32")?,
                        (8, _) => write!(fmt, "_u64")?,
                        (16, _) => write!(fmt, "_u128")?,
                        _ => bug!(),
                    }
                }
                Ok(())
            }
        }
    }
}