module xoroshiro128pp

import math
import rand
import rand.seed

const range_limit = 40
const value_count = 1000
const seeds = [[u32(42), 242, 267, 14195], [u32(256), 340, 1451, 1505]]

const sample_size = 1000
const stats_epsilon = 0.05
const inv_sqrt_12 = 1.0 / math.sqrt(12)

fn gen_randoms(seed_data []u32, bound int) []u32 {
    mut randoms := []u32{len: 20}
    mut rng := &rand.PRNG(&XOROS128PPRNG{})
    rng.seed(seed_data)
    for i in 0 .. 20 {
        randoms[i] = rng.u32n(u32(bound)) or { panic("Couldn't obtain u32") }
    }
    return randoms
}

fn test_xoroshiro128pp_reproducibility() {
    seed_data := seed.time_seed_array(4)
    randoms1 := gen_randoms(seed_data, 1000)
    randoms2 := gen_randoms(seed_data, 1000)
    assert randoms1.len == randoms2.len
    len := randoms1.len
    for i in 0 .. len {
        r1 := randoms1[i]
        r2 := randoms2[i]
        assert r1 == r2
    }
}

fn test_xoroshiro128pp_variability() {
    // If this test fails and if it is certainly not the implementation
    // at fault, try changing the seed values. Repeated values are
    // improbable but not impossible.
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        mut values := []u64{cap: value_count}
        for i in 0 .. value_count {
            value := rng.u64()
            assert value !in values
            assert values.len == i
            values << value
        }
    }
}

fn check_uniformity_u64(mut rng rand.PRNG, range u64) {
    range_f64 := f64(range)
    expected_mean := range_f64 / 2.0
    mut variance := 0.0
    for _ in 0 .. sample_size {
        diff := f64(rng.u64n(range) or { panic("Couldn't obtain u64") }) - expected_mean
        variance += diff * diff
    }
    variance /= sample_size - 1
    sigma := math.sqrt(variance)
    expected_sigma := range_f64 * inv_sqrt_12
    error := (sigma - expected_sigma) / expected_sigma
    assert math.abs(error) < stats_epsilon
}

fn test_xoroshiro128pp_uniformity_u64() {
    ranges := [14019545, 80240, 130]
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for range in ranges {
            check_uniformity_u64(mut rng, u64(range))
        }
    }
}

fn check_uniformity_f64(mut rng rand.PRNG) {
    expected_mean := 0.5
    mut variance := 0.0
    for _ in 0 .. sample_size {
        diff := rng.f64() - expected_mean
        variance += diff * diff
    }
    variance /= sample_size - 1
    sigma := math.sqrt(variance)
    expected_sigma := inv_sqrt_12
    error := (sigma - expected_sigma) / expected_sigma
    assert math.abs(error) < stats_epsilon
}

fn test_xoroshiro128pp_uniformity_f64() {
    // The f64 version
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        check_uniformity_f64(mut rng)
    }
}

fn test_xoroshiro128pp_u32n() {
    max := u32(16384)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.u32n(max) or { panic("Couldn't obtain u32") }
            assert value >= 0
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_u64n() {
    max := u64(379091181005)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.u64n(max) or { panic("Couldn't obtain u64") }
            assert value >= 0
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_u32_in_range() {
    max := u32(484468466)
    min := u32(316846)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.u32_in_range(u32(min), u32(max)) or {
                panic("Couldn't obtain u32 in range")
            }
            assert value >= min
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_u64_in_range() {
    max := u64(216468454685163)
    min := u64(6848646868)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.u64_in_range(min, max) or { panic("Couldn't obtain u64 in range") }
            assert value >= min
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_int31() {
    max_u31 := int(0x7FFFFFFF)
    sign_mask := int(u32(0x80000000))
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.int31()
            assert value >= 0
            assert value <= max_u31
            // This statement ensures that the sign bit is zero
            assert (value & sign_mask) == 0
        }
    }
}

fn test_xoroshiro128pp_int63() {
    max_u63 := i64(0x7FFFFFFFFFFFFFFF)
    sign_mask := i64(u64(0x8000000000000000))
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.int63()
            assert value >= 0
            assert value <= max_u63
            assert (value & sign_mask) == 0
        }
    }
}

fn test_xoroshiro128pp_intn() {
    max := 2525642
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.intn(max) or { panic("Couldn't obtain int") }
            assert value >= 0
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_i64n() {
    max := i64(3246727724653636)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.i64n(max) or { panic("Couldn't obtain i64") }
            assert value >= 0
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_int_in_range() {
    min := -4252
    max := 1034
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.int_in_range(min, max) or { panic("Couldn't obtain int in range") }
            assert value >= min
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_i64_in_range() {
    min := i64(-24095)
    max := i64(324058)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.i64_in_range(min, max) or { panic("Couldn't obtain i64 in range") }
            assert value >= min
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_f32() {
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.f32()
            assert value >= 0.0
            assert value < 1.0
        }
    }
}

fn test_xoroshiro128pp_f64() {
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.f64()
            assert value >= 0.0
            assert value < 1.0
        }
    }
}

fn test_xoroshiro128pp_f32n() {
    max := f32(357.0)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.f32n(max) or { panic("Couldn't obtain f32") }
            assert value >= 0.0
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_f64n() {
    max := 1.52e6
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.f64n(max) or { panic("Couldn't obtain f64") }
            assert value >= 0.0
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_f32_in_range() {
    min := f32(-24.0)
    max := f32(125.0)
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.f32_in_range(min, max) or { panic("Couldn't obtain f32 in range") }
            assert value >= min
            assert value < max
        }
    }
}

fn test_xoroshiro128pp_f64_in_range() {
    min := -548.7
    max := 5015.2
    for seed in seeds {
        mut rng := &rand.PRNG(&XOROS128PPRNG{})
        rng.seed(seed)
        for _ in 0 .. range_limit {
            value := rng.f64_in_range(min, max) or { panic("Couldn't obtain f64 in range") }
            assert value >= min
            assert value < max
        }
    }
}

fn test_change_default_random_generator() {
    rand.set_rng(&rand.PRNG(&XOROS128PPRNG{}))
}