use std::{
    fmt,
    ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign},
    os::raw::c_long,
};

use rb_sys::{
    rb_big_cmp, rb_big_div, rb_big_eq, rb_big_minus, rb_big_mul, rb_big_norm, rb_big_plus,
    rb_int2big, rb_ll2inum, rb_to_int, rb_ull2inum, ruby_special_consts, ruby_value_type, Qtrue,
    VALUE,
};

use crate::{
    error::{protect, Error},
    into_value::IntoValue,
    numeric::Numeric,
    r_bignum::RBignum,
    try_convert::TryConvert,
    value::{
        private::{self, ReprValue as _},
        Fixnum, NonZeroValue, ReprValue, Value,
    },
    Ruby,
};

pub(crate) enum IntegerType {
    Fixnum(Fixnum),
    Bignum(RBignum),
}

/// # `Integer`
///
/// Functions that can be used to create instances of [`Integer`].
///
/// See also the [`Integer`] type.
impl Ruby {
    /// Create a new `Integer` from an `i64.`
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{rb_assert, Error, Ruby};
    ///
    /// fn example(ruby: &Ruby) -> Result<(), Error> {
    ///     rb_assert!(ruby, "i == 0", i = ruby.integer_from_i64(0));
    ///     rb_assert!(
    ///         ruby,
    ///         "i == 4611686018427387904",
    ///         i = ruby.integer_from_i64(4611686018427387904),
    ///     );
    ///     rb_assert!(
    ///         ruby,
    ///         "i == -4611686018427387905",
    ///         i = ruby.integer_from_i64(-4611686018427387905),
    ///     );
    ///
    ///     Ok(())
    /// }
    /// # Ruby::init(example).unwrap()
    /// ```
    #[inline]
    pub fn integer_from_i64(&self, n: i64) -> Integer {
        unsafe {
            Integer::from_rb_value_unchecked(
                Fixnum::from_i64_impl(n)
                    .map(|f| f.as_rb_value())
                    .unwrap_or_else(|| rb_ll2inum(n)),
            )
        }
    }

    /// Create a new `Integer` from a `u64.`
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{rb_assert, Error, Ruby};
    ///
    /// fn example(ruby: &Ruby) -> Result<(), Error> {
    ///     rb_assert!("i == 0", i = ruby.integer_from_u64(0));
    ///     rb_assert!(
    ///         "i == 4611686018427387904",
    ///         i = ruby.integer_from_u64(4611686018427387904),
    ///     );
    ///
    ///     Ok(())
    /// }
    /// # Ruby::init(example).unwrap()
    /// ```
    #[inline]
    pub fn integer_from_u64(&self, n: u64) -> Integer {
        unsafe {
            Integer::from_rb_value_unchecked(
                Fixnum::from_i64_impl(i64::try_from(n).unwrap_or(i64::MAX))
                    .map(|f| f.as_rb_value())
                    .unwrap_or_else(|| rb_ull2inum(n)),
            )
        }
    }
}

/// A type wrapping either a [`Fixnum`] or a [`RBignum`].
///
/// See the [`ReprValue`] trait for additional methods available on this type.
/// See [`Ruby`](Ruby#integer) for methods to create an `Integer`.
#[derive(Clone, Copy)]
#[repr(transparent)]
pub struct Integer(NonZeroValue);

impl Integer {
    /// Return `Some(Integer)` if `val` is an `Integer`, `None` otherwise.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert!(Integer::from_value(eval("0").unwrap()).is_some());
    /// assert!(Integer::from_value(eval("9223372036854775807").unwrap()).is_some());
    /// // not an int
    /// assert!(Integer::from_value(eval("1.23").unwrap()).is_none());
    /// ```
    #[inline]
    pub fn from_value(val: Value) -> Option<Self> {
        unsafe {
            if val.as_rb_value() & ruby_special_consts::RUBY_FIXNUM_FLAG as VALUE != 0 {
                return Some(Self(NonZeroValue::new_unchecked(val)));
            }
            debug_assert_value!(val);
            (val.rb_type() == ruby_value_type::RUBY_T_BIGNUM)
                .then(|| Self(NonZeroValue::new_unchecked(val)))
        }
    }

    #[inline]
    pub(crate) unsafe fn from_rb_value_unchecked(val: VALUE) -> Self {
        Self(NonZeroValue::new_unchecked(Value::new(val)))
    }

    pub(crate) fn integer_type(self) -> IntegerType {
        unsafe {
            if self.as_rb_value() & ruby_special_consts::RUBY_FIXNUM_FLAG as VALUE != 0 {
                IntegerType::Fixnum(Fixnum::from_rb_value_unchecked(self.as_rb_value()))
            } else {
                IntegerType::Bignum(RBignum::from_rb_value_unchecked(self.as_rb_value()))
            }
        }
    }

    /// Create a new `Integer` from an `i64.`
    ///
    /// # Panics
    ///
    /// Panics if called from a non-Ruby thread. See [`Ruby::integer_from_i64`]
    /// for the non-panicking version.
    ///
    /// # Examples
    ///
    /// ```
    /// # #![allow(deprecated)]
    /// use magnus::{rb_assert, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// rb_assert!("i == 0", i = Integer::from_i64(0));
    /// rb_assert!(
    ///     "i == 4611686018427387904",
    ///     i = Integer::from_i64(4611686018427387904),
    /// );
    /// rb_assert!(
    ///     "i == -4611686018427387905",
    ///     i = Integer::from_i64(-4611686018427387905),
    /// );
    /// ```
    #[cfg_attr(
        not(feature = "old-api"),
        deprecated(note = "please use `Ruby::integer_from_i64` instead")
    )]
    #[cfg_attr(docsrs, doc(cfg(feature = "old-api")))]
    #[inline]
    pub fn from_i64(n: i64) -> Self {
        get_ruby!().integer_from_i64(n)
    }

    /// Create a new `Integer` from a `u64.`
    ///
    /// # Panics
    ///
    /// Panics if called from a non-Ruby thread. See [`Ruby::integer_from_u64`]
    /// for the non-panicking version.
    ///
    /// # Examples
    ///
    /// ```
    /// # #![allow(deprecated)]
    /// use magnus::{rb_assert, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// rb_assert!("i == 0", i = Integer::from_u64(0));
    /// rb_assert!(
    ///     "i == 4611686018427387904",
    ///     i = Integer::from_u64(4611686018427387904),
    /// );
    /// ```
    #[cfg_attr(
        not(feature = "old-api"),
        deprecated(note = "please use `Ruby::integer_from_u64` instead")
    )]
    #[cfg_attr(docsrs, doc(cfg(feature = "old-api")))]
    #[inline]
    pub fn from_u64(n: u64) -> Self {
        get_ruby!().integer_from_u64(n)
    }

    /// Convert `self` to an `i8`. Returns `Err` if `self` is out of range for
    /// `i8`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(eval::<Integer>("127").unwrap().to_i8().unwrap(), 127);
    /// assert!(eval::<Integer>("128").unwrap().to_i8().is_err());
    /// assert_eq!(eval::<Integer>("-128").unwrap().to_i8().unwrap(), -128);
    /// assert!(eval::<Integer>("-129").unwrap().to_i8().is_err());
    /// ```
    #[inline]
    pub fn to_i8(self) -> Result<i8, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_i8(),
            IntegerType::Bignum(_) => Err(Error::new(
                Ruby::get_with(self).exception_range_error(),
                "bignum too big to convert into `i8`",
            )),
        }
    }

    /// Convert `self` to an `i16`. Returns `Err` if `self` is out of range for
    /// `i16`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(eval::<Integer>("32767").unwrap().to_i16().unwrap(), 32767);
    /// assert!(eval::<Integer>("32768").unwrap().to_i16().is_err());
    /// assert_eq!(eval::<Integer>("-32768").unwrap().to_i16().unwrap(), -32768);
    /// assert!(eval::<Integer>("-32769").unwrap().to_i16().is_err());
    /// ```
    #[inline]
    pub fn to_i16(self) -> Result<i16, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_i16(),
            IntegerType::Bignum(_) => Err(Error::new(
                Ruby::get_with(self).exception_range_error(),
                "bignum too big to convert into `i16`",
            )),
        }
    }

    /// Convert `self` to an `i32`. Returns `Err` if `self` is out of range for
    /// `i32`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(
    ///     eval::<Integer>("2147483647").unwrap().to_i32().unwrap(),
    ///     2147483647
    /// );
    /// assert!(eval::<Integer>("2147483648").unwrap().to_i32().is_err());
    /// assert_eq!(
    ///     eval::<Integer>("-2147483648").unwrap().to_i32().unwrap(),
    ///     -2147483648
    /// );
    /// assert!(eval::<Integer>("-2147483649").unwrap().to_i32().is_err());
    /// ```
    #[inline]
    pub fn to_i32(self) -> Result<i32, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_i32(),
            IntegerType::Bignum(big) => big.to_i32(),
        }
    }

    /// Convert `self` to an `i64`. Returns `Err` if `self` is out of range for
    /// `i64`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(
    ///     eval::<Integer>("4611686018427387903")
    ///         .unwrap()
    ///         .to_i64()
    ///         .unwrap(),
    ///     4611686018427387903
    /// );
    /// assert_eq!(
    ///     eval::<Integer>("-4611686018427387904")
    ///         .unwrap()
    ///         .to_i64()
    ///         .unwrap(),
    ///     -4611686018427387904
    /// );
    /// assert!(eval::<Integer>("9223372036854775808")
    ///     .unwrap()
    ///     .to_i64()
    ///     .is_err());
    /// assert!(eval::<Integer>("-9223372036854775809")
    ///     .unwrap()
    ///     .to_i64()
    ///     .is_err());
    /// ```
    #[inline]
    pub fn to_i64(self) -> Result<i64, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => Ok(fix.to_i64()),
            IntegerType::Bignum(big) => big.to_i64(),
        }
    }

    /// Convert `self` to an `isize`. Returns `Err` if `self` is out of range
    /// for `isize`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(
    ///     eval::<Integer>("4611686018427387903")
    ///         .unwrap()
    ///         .to_isize()
    ///         .unwrap(),
    ///     4611686018427387903
    /// );
    /// assert_eq!(
    ///     eval::<Integer>("-4611686018427387904")
    ///         .unwrap()
    ///         .to_isize()
    ///         .unwrap(),
    ///     -4611686018427387904
    /// );
    /// ```
    #[inline]
    pub fn to_isize(self) -> Result<isize, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => Ok(fix.to_isize()),
            IntegerType::Bignum(big) => big.to_isize(),
        }
    }

    /// Convert `self` to a `u8`. Returns `Err` if `self` is negative or out of
    /// range for `u8`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(eval::<Integer>("255").unwrap().to_u8().unwrap(), 255);
    /// assert!(eval::<Integer>("256").unwrap().to_u8().is_err());
    /// assert!(eval::<Integer>("-1").unwrap().to_u8().is_err());
    /// ```
    #[inline]
    pub fn to_u8(self) -> Result<u8, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_u8(),
            IntegerType::Bignum(_) => Err(Error::new(
                Ruby::get_with(self).exception_range_error(),
                "bignum too big to convert into `u8`",
            )),
        }
    }

    /// Convert `self` to a `u16`. Returns `Err` if `self` is negative or out
    /// of range for `u16`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(eval::<Integer>("65535").unwrap().to_u16().unwrap(), 65535);
    /// assert!(eval::<Integer>("65536").unwrap().to_u16().is_err());
    /// assert!(eval::<Integer>("-1").unwrap().to_u16().is_err());
    /// ```
    #[inline]
    pub fn to_u16(self) -> Result<u16, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_u16(),
            IntegerType::Bignum(_) => Err(Error::new(
                Ruby::get_with(self).exception_range_error(),
                "bignum too big to convert into `u16`",
            )),
        }
    }

    /// Convert `self` to a `u32`. Returns `Err` if `self` is negative or out
    /// of range for `u32`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(
    ///     eval::<Integer>("4294967295").unwrap().to_u32().unwrap(),
    ///     4294967295
    /// );
    /// assert!(eval::<Integer>("4294967296").unwrap().to_u32().is_err());
    /// assert!(eval::<Integer>("-1").unwrap().to_u32().is_err());
    /// ```
    #[inline]
    pub fn to_u32(self) -> Result<u32, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_u32(),
            IntegerType::Bignum(big) => big.to_u32(),
        }
    }

    /// Convert `self` to a `u64`. Returns `Err` if `self` is negative or out
    /// of range for `u64`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(
    ///     eval::<Integer>("4611686018427387903")
    ///         .unwrap()
    ///         .to_u64()
    ///         .unwrap(),
    ///     4611686018427387903
    /// );
    /// assert!(eval::<Integer>("-1").unwrap().to_u64().is_err());
    /// assert!(eval::<Integer>("18446744073709551616")
    ///     .unwrap()
    ///     .to_u64()
    ///     .is_err());
    /// ```
    #[inline]
    pub fn to_u64(self) -> Result<u64, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_u64(),
            IntegerType::Bignum(big) => big.to_u64(),
        }
    }

    /// Convert `self` to a `usize`. Returns `Err` if `self` is negative or out
    /// of range for `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// use magnus::{eval, Integer};
    /// # let _cleanup = unsafe { magnus::embed::init() };
    ///
    /// assert_eq!(
    ///     eval::<Integer>("4611686018427387903")
    ///         .unwrap()
    ///         .to_usize()
    ///         .unwrap(),
    ///     4611686018427387903
    /// );
    /// assert!(eval::<Integer>("-1").unwrap().to_usize().is_err());
    /// ```
    #[inline]
    pub fn to_usize(self) -> Result<usize, Error> {
        match self.integer_type() {
            IntegerType::Fixnum(fix) => fix.to_usize(),
            IntegerType::Bignum(big) => big.to_usize(),
        }
    }

    /// Normalize `self`. If `self` is a `Fixnum`, returns `self`. If `self` is
    /// a `Bignum`, if it is small enough to fit in a `Fixnum`, returns a
    /// `Fixnum` with the same value. Otherwise, returns `self`.
    pub fn norm(&self) -> Self {
        match self.integer_type() {
            IntegerType::Fixnum(_) => *self,
            IntegerType::Bignum(big) => unsafe {
                Integer::from_rb_value_unchecked(rb_big_norm(big.as_rb_value()))
            },
        }
    }

    fn binary_operation_visit<T>(
        &self,
        other: &Self,
        rust_op: fn(Fixnum, Fixnum) -> T,
        ruby_op: fn(VALUE, VALUE) -> T,
    ) -> T {
        match self.integer_type() {
            IntegerType::Bignum(a) => ruby_op(a.as_rb_value(), other.as_rb_value()),
            IntegerType::Fixnum(a) => match other.integer_type() {
                IntegerType::Bignum(b) => {
                    let a = unsafe { rb_int2big(a.to_isize()) };
                    ruby_op(a, b.as_rb_value())
                }
                IntegerType::Fixnum(b) => rust_op(a, b),
            },
        }
    }
}

impl fmt::Display for Integer {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", unsafe { self.to_s_infallible() })
    }
}

impl fmt::Debug for Integer {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.inspect())
    }
}

impl IntoValue for Integer {
    #[inline]
    fn into_value_with(self, _: &Ruby) -> Value {
        self.0.get()
    }
}

impl Numeric for Integer {}

unsafe impl private::ReprValue for Integer {}

impl ReprValue for Integer {}

impl TryConvert for Integer {
    fn try_convert(val: Value) -> Result<Self, Error> {
        match Self::from_value(val) {
            Some(i) => Ok(i),
            None => protect(|| {
                debug_assert_value!(val);
                unsafe { Self::from_rb_value_unchecked(rb_to_int(val.as_rb_value())) }
            }),
        }
    }
}

impl PartialEq for Integer {
    fn eq(&self, other: &Self) -> bool {
        match self.integer_type() {
            IntegerType::Bignum(a) => unsafe {
                rb_big_eq(a.as_rb_value(), other.as_rb_value()) == Qtrue.into()
            },
            IntegerType::Fixnum(a) => a.as_rb_value() == other.norm().as_rb_value(),
        }
    }
}

impl PartialOrd for Integer {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        self.binary_operation_visit(
            other,
            |a, b| (a.as_rb_value() as c_long).partial_cmp(&(b.as_rb_value() as c_long)),
            |a, b| unsafe {
                let result = rb_big_cmp(a, b);
                Integer::from_rb_value_unchecked(result)
                    .to_i64()
                    .unwrap()
                    .partial_cmp(&0)
            },
        )
    }
}

impl Add for Integer {
    type Output = Self;

    fn add(self, other: Self) -> Self {
        self.binary_operation_visit(
            &other,
            |a, b| {
                let raw_a = a.as_rb_value() as c_long;
                let raw_b = b.as_rb_value() as c_long;
                let result = raw_a.checked_add(raw_b).and_then(|i| i.checked_sub(1));
                if let Some(result) = result {
                    unsafe { Integer::from_rb_value_unchecked(result as VALUE) }
                } else {
                    let a = unsafe { rb_int2big(a.to_isize()) };
                    let result = unsafe { rb_big_plus(a, b.as_rb_value()) };
                    unsafe { Integer::from_rb_value_unchecked(result) }
                }
            },
            |a, b| {
                let result = unsafe { rb_big_plus(a, b) };
                unsafe { Integer::from_rb_value_unchecked(result) }
            },
        )
    }
}

impl AddAssign for Integer {
    fn add_assign(&mut self, other: Self) {
        *self = *self + other;
    }
}

impl Sub for Integer {
    type Output = Self;

    fn sub(self, other: Self) -> Self {
        self.binary_operation_visit(
            &other,
            |a, b| {
                let raw_a = a.as_rb_value() as c_long;
                let raw_b = b.as_rb_value() as c_long;
                let result = raw_a.checked_sub(raw_b).and_then(|i| i.checked_add(1));
                if let Some(result) = result {
                    unsafe { Integer::from_rb_value_unchecked(result as VALUE) }
                } else {
                    let a = unsafe { rb_int2big(a.to_isize()) };
                    let result = unsafe { rb_big_minus(a, b.as_rb_value()) };
                    unsafe { Integer::from_rb_value_unchecked(result) }
                }
            },
            |a, b| {
                let result = unsafe { rb_big_minus(a, b) };
                unsafe { Integer::from_rb_value_unchecked(result) }
            },
        )
    }
}

impl SubAssign for Integer {
    fn sub_assign(&mut self, other: Self) {
        *self = *self - other;
    }
}

impl Mul for Integer {
    type Output = Self;

    fn mul(self, other: Self) -> Self {
        self.binary_operation_visit(
            &other,
            |a, b| {
                let raw_a = a.to_i64();
                let raw_b = b.to_i64();
                let result = raw_a.checked_mul(raw_b);
                if let Some(result) = result {
                    Ruby::get_with(a).integer_from_i64(result)
                } else {
                    let a = unsafe { rb_int2big(a.to_isize()) };
                    let result = unsafe { rb_big_mul(a, b.as_rb_value()) };
                    unsafe { Integer::from_rb_value_unchecked(result) }
                }
            },
            |a, b| {
                let result = unsafe { rb_big_mul(a, b) };
                unsafe { Integer::from_rb_value_unchecked(result) }
            },
        )
    }
}

impl MulAssign for Integer {
    fn mul_assign(&mut self, other: Self) {
        *self = *self * other;
    }
}

impl Div for Integer {
    type Output = Self;

    fn div(self, other: Self) -> Self {
        self.binary_operation_visit(
            &other,
            |a, b| {
                let raw_a = a.to_i64();
                let raw_b = b.to_i64();
                // the only case when division can overflow is when dividing
                // i64::MIN by -1, but Fixnum can't represent that I64::MIN
                // so we can safely not use checked_div here
                Ruby::get_with(a).integer_from_i64(raw_a / raw_b)
            },
            |a, b| {
                let result = unsafe { rb_big_div(a, b) };
                unsafe { Integer::from_rb_value_unchecked(result) }
            },
        )
    }
}

impl DivAssign for Integer {
    fn div_assign(&mut self, other: Self) {
        *self = *self / other;
    }
}