//-
// Copyright 2017 Jason Lingle
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Strategies for working with bit sets.
//!
//! Besides `BitSet` itself, this also defines strategies for all the primitive
//! integer types. These strategies are appropriate for integers which are used
//! as bit flags, etc; e.g., where the most reasonable simplification of `64`
//! is `0` (clearing one bit) and not `63` (clearing one bit but setting 6
//! others). For integers treated as numeric values, see the corresponding
//! modules of the `num` module instead.

use std::fmt;
use std::marker::PhantomData;
use std::mem;

use bit_set::BitSet;
use rand::Rng;

use strategy::*;
use test_runner::*;

/// Trait for types which can be handled with `BitSetStrategy`.
pub trait BitSetLike : Clone + fmt::Debug {
    /// Create a new value of `Self` with space for up to `max` bits, all
    /// initialised to zero.
    fn new_bitset(max: usize) -> Self;
    /// Return an upper bound on the greatest bit set.
    fn max(&self) -> usize;
    /// Test whether the given bit is set.
    fn test(&self, ix: usize) -> bool;
    /// Set the given bit.
    fn set(&mut self, ix: usize);
    /// Clear the given bit.
    fn clear(&mut self, ix: usize);
}

macro_rules! int_bitset {
    ($typ:ty) => {
        impl BitSetLike for $typ {
            fn new_bitset(_: usize) -> Self { 0 }
            fn max(&self) -> usize { mem::size_of::<$typ>()*8 }
            fn test(&self, ix: usize) -> bool {
                0 != (*self & ((1 as $typ) << ix))
            }
            fn set(&mut self, ix: usize) {
                *self |= (1 as $typ) << ix;
            }
            fn clear(&mut self, ix: usize) {
                *self &= !((1 as $typ) << ix);
            }
        }
    }
}
int_bitset!(u8);
int_bitset!(u16);
int_bitset!(u32);
int_bitset!(u64);
int_bitset!(usize);
int_bitset!(i8);
int_bitset!(i16);
int_bitset!(i32);
int_bitset!(i64);
int_bitset!(isize);

impl BitSetLike for BitSet {
    fn new_bitset(max: usize) -> Self {
        BitSet::with_capacity(max)
    }

    fn max(&self) -> usize {
        self.capacity()
    }

    fn test(&self, bit: usize) -> bool {
        self.contains(bit)
    }

    fn set(&mut self, bit: usize) {
        self.insert(bit);
    }

    fn clear(&mut self, bit: usize) {
        self.remove(bit);
    }
}

/// Generates values as a set of bits between the two bounds.
///
/// Values are generated by uniformly setting individual bits to 0
/// or 1 between the bounds. Shrinking iteratively clears bits.
pub struct BitSetStrategy<T : BitSetLike> {
    min: usize,
    max: usize,
    _marker: PhantomData<T>,
}

impl<T : BitSetLike> Clone for BitSetStrategy<T> {
    fn clone(&self) -> Self {
        *self
    }
}
impl<T : BitSetLike> Copy for BitSetStrategy<T> { }
impl<T : BitSetLike> fmt::Debug for BitSetStrategy<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("BitSetStrategy")
            .field("min", &self.min)
            .field("max", &self.max)
            .finish()
    }
}

impl<T : BitSetLike> BitSetStrategy<T> {
    /// Create a strategy which generates values where bits between `min`
    /// (inclusive) and `max` (exclusive) may be set.
    ///
    /// Due to the generics, the functions in the typed submodules are usually
    /// preferable to calling this directly.
    pub fn new(min: usize, max: usize) -> Self {
        BitSetStrategy {
            min, max, _marker: PhantomData
        }
    }
}

impl<T : BitSetLike> Strategy for BitSetStrategy<T> {
    type Value = BitSetValueTree<T>;

    fn new_value(&self, runner: &mut TestRunner)
                 -> Result<Self::Value, String> {
        let mut inner = T::new_bitset(self.max);
        for bit in self.min..self.max {
            if runner.rng().gen() {
                inner.set(bit);
            }
        }

        Ok(BitSetValueTree { inner, shrink: self.min, prev_shrink: None })
    }
}

/// Value tree produced by `BitSetStrategy`.
#[derive(Clone, Copy, Debug)]
pub struct BitSetValueTree<T : BitSetLike> {
    inner: T,
    shrink: usize,
    prev_shrink: Option<usize>,
}

impl<T : BitSetLike> ValueTree for BitSetValueTree<T> {
    type Value = T;

    fn current(&self) -> T {
        self.inner.clone()
    }

    fn simplify(&mut self) -> bool {
        while self.shrink < self.inner.max() &&
            !self.inner.test(self.shrink)
        { self.shrink += 1; }

        if self.shrink >= self.inner.max() {
            self.prev_shrink = None;
            false
        } else {
            self.prev_shrink = Some(self.shrink);
            self.inner.clear(self.shrink);
            self.shrink += 1;
            true
        }
    }

    fn complicate(&mut self) -> bool {
        if let Some(bit) = self.prev_shrink.take() {
            self.inner.set(bit);
            true
        } else {
            false
        }
    }
}

macro_rules! int_api {
    ($typ:ident, $max:expr) => {
        #[allow(missing_docs)]
        pub mod $typ {
            use super::*;

            /// Generates integers where all bits may be set.
            pub const ANY: BitSetStrategy<$typ> = BitSetStrategy {
                min: 0,
                max: $max,
                _marker: PhantomData
            };

            /// Generates values where bits between the given bounds may be
            /// set.
            pub fn between(min: usize, max: usize) -> BitSetStrategy<$typ> {
                BitSetStrategy::new(min, max)
            }
        }
    }
}

int_api!(u8, 8);
int_api!(u16, 16);
int_api!(u32, 32);
int_api!(u64, 64);
int_api!(i8, 8);
int_api!(i16, 16);
int_api!(i32, 32);
int_api!(i64, 64);

macro_rules! minimal_api {
    ($md:ident, $typ:ty) => {
        #[allow(missing_docs)]
        pub mod $md {
            use super::*;

            /// Generates values where bits between the given bounds may be
            /// set.
            pub fn between(min: usize, max: usize) -> BitSetStrategy<$typ> {
                BitSetStrategy::new(min, max)
            }
        }
    }
}
minimal_api!(usize, usize);
minimal_api!(isize, isize);
minimal_api!(bitset, BitSet);

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

    #[test]
    fn generates_values_in_range() {
        let input = u32::between(4, 8);

        let mut runner = TestRunner::new(Config::default());
        for _ in 0..256 {
            let value = input.new_value(&mut runner).unwrap().current();
            assert!(0 == value & !0xF0u32,
                    "Generate value {}", value);
        }
    }

    #[test]
    fn shrinks_to_zero() {
        let input = u32::between(4, 24);

        let mut runner = TestRunner::new(Config::default());
        for _ in 0..256 {
            let mut value = input.new_value(&mut runner).unwrap();
            let mut prev = value.current();
            while value.simplify() {
                let v = value.current();
                assert!(1 == (prev & !v).count_ones(),
                        "Shrank from {} to {}", prev, v);
                prev = v;
            }

            assert_eq!(0, value.current());
        }
    }

    #[test]
    fn complicates_to_previous() {
        let input = u32::between(4, 24);

        let mut runner = TestRunner::new(Config::default());
        for _ in 0..256 {
            let mut value = input.new_value(&mut runner).unwrap();
            let orig = value.current();
            if value.simplify() {
                assert!(value.complicate());
                assert_eq!(orig, value.current());
            }
        }
    }
}