module xoroshiro128pp

import math
import rand
import rand.seed

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

const (
	sample_size   = 1000
	stats_epsilon = 0.05
	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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		mut values := []u64{cap: xoroshiro128pp.value_count}
		for i in 0 .. xoroshiro128pp.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 .. xoroshiro128pp.sample_size {
		diff := f64(rng.u64n(range) or { panic("Couldn't obtain u64") }) - expected_mean
		variance += diff * diff
	}
	variance /= xoroshiro128pp.sample_size - 1
	sigma := math.sqrt(variance)
	expected_sigma := range_f64 * xoroshiro128pp.inv_sqrt_12
	error := (sigma - expected_sigma) / expected_sigma
	assert math.abs(error) < xoroshiro128pp.stats_epsilon
}

fn test_xoroshiro128pp_uniformity_u64() {
	ranges := [14019545, 80240, 130]
	for seed in xoroshiro128pp.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 .. xoroshiro128pp.sample_size {
		diff := rng.f64() - expected_mean
		variance += diff * diff
	}
	variance /= xoroshiro128pp.sample_size - 1
	sigma := math.sqrt(variance)
	expected_sigma := xoroshiro128pp.inv_sqrt_12
	error := (sigma - expected_sigma) / expected_sigma
	assert math.abs(error) < xoroshiro128pp.stats_epsilon
}

fn test_xoroshiro128pp_uniformity_f64() {
	// The f64 version
	for seed in xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		check_uniformity_f64(mut rng)
	}
}

fn test_xoroshiro128pp_u32n() {
	max := u32(16384)
	for seed in xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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(0x80000000)
	for seed in xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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(0x8000000000000000)
	for seed in xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.range_limit {
			value := rng.f32()
			assert value >= 0.0
			assert value < 1.0
		}
	}
}

fn test_xoroshiro128pp_f64() {
	for seed in xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.range_limit {
			value := rng.f64()
			assert value >= 0.0
			assert value < 1.0
		}
	}
}

fn test_xoroshiro128pp_f32n() {
	max := f32(357.0)
	for seed in xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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 xoroshiro128pp.seeds {
		mut rng := &rand.PRNG(&XOROS128PPRNG{})
		rng.seed(seed)
		for _ in 0 .. xoroshiro128pp.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{}))
}