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use crate::raw;
use core::mem::MaybeUninit;
use core::{slice, str};
#[cfg(feature = "no-panic")]
use no_panic::no_panic;

const NAN: &str = "NaN";
const INFINITY: &str = "Infinity";
const NEG_INFINITY: &str = "-Infinity";

/// Safe API for formatting floating point numbers to text.
///
/// ## Example
///
/// ```
/// let mut buffer = ryu_js::Buffer::new();
/// let printed = buffer.format_finite(1.234);
/// assert_eq!(printed, "1.234");
/// ```
pub struct Buffer {
    bytes: [MaybeUninit<u8>; 25],
}

impl Buffer {
    /// This is a cheap operation; you don't need to worry about reusing buffers
    /// for efficiency.
    #[inline]
    #[cfg_attr(feature = "no-panic", no_panic)]
    pub fn new() -> Self {
        let bytes = [MaybeUninit::<u8>::uninit(); 25];

        Buffer { bytes }
    }

    /// Print a floating point number into this buffer and return a reference to
    /// its string representation within the buffer.
    ///
    /// # Special cases
    ///
    /// This function formats NaN as the string "NaN", positive infinity as
    /// "Infinity", and negative infinity as "-Infinity" to match the [ECMAScript specification][spec].
    ///
    /// If your input is known to be finite, you may get better performance by
    /// calling the `format_finite` method instead of `format` to avoid the
    /// checks for special cases.
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-numeric-types-number-tostring
    #[cfg_attr(feature = "no-panic", inline)]
    #[cfg_attr(feature = "no-panic", no_panic)]
    pub fn format<F: Float>(&mut self, f: F) -> &str {
        if f.is_nonfinite() {
            f.format_nonfinite()
        } else {
            self.format_finite(f)
        }
    }

    /// Print a floating point number into this buffer and return a reference to
    /// its string representation within the buffer.
    ///
    /// # Special cases
    ///
    /// This function **does not** check for NaN or infinity. If the input
    /// number is not a finite float, the printed representation will be some
    /// correctly formatted but unspecified numerical value.
    ///
    /// Please check [`is_finite`] yourself before calling this function, or
    /// check [`is_nan`] and [`is_infinite`] and handle those cases yourself.
    ///
    /// [`is_finite`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_finite
    /// [`is_nan`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_nan
    /// [`is_infinite`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_infinite
    #[inline]
    #[cfg_attr(feature = "no-panic", no_panic)]
    pub fn format_finite<F: Float>(&mut self, f: F) -> &str {
        unsafe {
            let n = f.write_to_ryu_buffer(self.bytes.as_mut_ptr() as *mut u8);
            debug_assert!(n <= self.bytes.len());
            let slice = slice::from_raw_parts(self.bytes.as_ptr() as *const u8, n);
            str::from_utf8_unchecked(slice)
        }
    }
}

impl Copy for Buffer {}

impl Clone for Buffer {
    #[inline]
    fn clone(&self) -> Self {
        Buffer::new()
    }
}

impl Default for Buffer {
    #[inline]
    #[cfg_attr(feature = "no-panic", no_panic)]
    fn default() -> Self {
        Buffer::new()
    }
}

/// A floating point number, f32 or f64, that can be written into a
/// [`ryu_js::Buffer`][Buffer].
///
/// This trait is sealed and cannot be implemented for types outside of the
/// `ryu_js` crate.
pub trait Float: Sealed {}
impl Float for f32 {}
impl Float for f64 {}

pub trait Sealed: Copy {
    fn is_nonfinite(self) -> bool;
    fn format_nonfinite(self) -> &'static str;
    unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize;
}

impl Sealed for f32 {
    #[inline]
    fn is_nonfinite(self) -> bool {
        const EXP_MASK: u32 = 0x7f800000;
        let bits = self.to_bits();
        bits & EXP_MASK == EXP_MASK
    }

    #[cold]
    #[cfg_attr(feature = "no-panic", inline)]
    fn format_nonfinite(self) -> &'static str {
        const MANTISSA_MASK: u32 = 0x007fffff;
        const SIGN_MASK: u32 = 0x80000000;
        let bits = self.to_bits();
        if bits & MANTISSA_MASK != 0 {
            NAN
        } else if bits & SIGN_MASK != 0 {
            NEG_INFINITY
        } else {
            INFINITY
        }
    }

    #[inline]
    unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize {
        raw::format32(self, result)
    }
}

impl Sealed for f64 {
    #[inline]
    fn is_nonfinite(self) -> bool {
        const EXP_MASK: u64 = 0x7ff0000000000000;
        let bits = self.to_bits();
        bits & EXP_MASK == EXP_MASK
    }

    #[cold]
    #[cfg_attr(feature = "no-panic", inline)]
    fn format_nonfinite(self) -> &'static str {
        const MANTISSA_MASK: u64 = 0x000fffffffffffff;
        const SIGN_MASK: u64 = 0x8000000000000000;
        let bits = self.to_bits();
        if bits & MANTISSA_MASK != 0 {
            NAN
        } else if bits & SIGN_MASK != 0 {
            NEG_INFINITY
        } else {
            INFINITY
        }
    }

    #[inline]
    unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize {
        raw::format64(self, result)
    }
}