import math
import sys

const (
	range_limit = 40
	value_count = 1000
	seeds       = [u32(42), 256]
)

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

fn get_n_randoms(n int, r sys.SysRNG) []int {
	mut ints := []int{cap: n}
	for _ in 0 .. n {
		ints << r.int()
	}
	return ints
}

fn test_sys_rng_reproducibility() {
	// Note that C.srand() sets the seed globally.
	// So the order of seeding matters. It is recommended
	// to obtain all necessary data first, then set the
	// seed for another batch of data.
	for seed in seeds {
		seed_data := [seed]
		mut r1 := sys.SysRNG{}
		mut r2 := sys.SysRNG{}
		r1.seed(seed_data)
		ints1 := get_n_randoms(value_count, r1)
		r2.seed(seed_data)
		ints2 := get_n_randoms(value_count, r2)
		assert ints1 == ints2
	}
}

// TODO: use the `in` syntax and remove this function
// after generics has been completely implemented
fn found(value u64, arr []u64) bool {
	for item in arr {
		if value == item {
			return true
		}
	}
	return false
}

fn test_sys_rng_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 {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		mut values := []u64{cap: value_count}
		for i in 0 .. value_count {
			value := rng.u64()
			assert !found(value, values)
			assert values.len == i
			values << value
		}
	}
}

fn check_uniformity_u64(rng sys.SysRNG, 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)) - 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_sys_rng_uniformity_u64() {
	// This assumes that C.rand() produces uniform results to begin with.
	// If the failure persists, report an issue on GitHub
	ranges := [14019545, 80240, 130]
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for range in ranges {
			check_uniformity_u64(rng, u64(range))
		}
	}
}

fn check_uniformity_f64(rng sys.SysRNG) {
	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_sys_rng_uniformity_f64() {
	// The f64 version
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		check_uniformity_f64(rng)
	}
}

fn test_sys_rng_u32n() {
	max := u32(16384)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.u32n(max)
			assert value >= 0
			assert value < max
		}
	}
}

fn test_sys_rng_u64n() {
	max := u64(379091181005)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.u64n(max)
			assert value >= 0
			assert value < max
		}
	}
}

fn test_sys_rng_u32_in_range() {
	max := u32(484468466)
	min := u32(316846)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.u32_in_range(min, max)
			assert value >= min
			assert value < max
		}
	}
}

fn test_sys_rng_u64_in_range() {
	max := u64(216468454685163)
	min := u64(6848646868)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.u64_in_range(min, max)
			assert value >= min
			assert value < max
		}
	}
}

fn test_sys_rng_intn() {
	max := 2525642
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.intn(max)
			assert value >= 0
			assert value < max
		}
	}
}

fn test_sys_rng_i64n() {
	max := i64(3246727724653636)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.i64n(max)
			assert value >= 0
			assert value < max
		}
	}
}

fn test_sys_rng_int_in_range() {
	min := -4252
	max := 23054962
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.int_in_range(min, max)
			assert value >= min
			assert value < max
		}
	}
}

fn test_sys_rng_i64_in_range() {
	min := i64(-24095)
	max := i64(324058)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.i64_in_range(min, max)
			assert value >= min
			assert value < max
		}
	}
}

fn test_sys_rng_int31() {
	max_u31 := 0x7FFFFFFF
	sign_mask := 0x80000000
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		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_sys_rng_int63() {
	max_u63 := i64(0x7FFFFFFFFFFFFFFF)
	sign_mask := i64(0x8000000000000000)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.int63()
			assert value >= 0
			assert value <= max_u63
			assert (value & sign_mask) == 0
		}
	}
}

fn test_sys_rng_f32() {
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.f32()
			assert value >= 0.0
			assert value < 1.0
		}
	}
}

fn test_sys_rng_f64() {
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.f64()
			assert value >= 0.0
			assert value < 1.0
		}
	}
}

fn test_sys_rng_f32n() {
	max := f32(357.0)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.f32n(max)
			assert value >= 0.0
			assert value < max
		}
	}
}

fn test_sys_rng_f64n() {
	max := 1.52e6
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.f64n(max)
			assert value >= 0.0
			assert value < max
		}
	}
}

fn test_sys_rng_f32_in_range() {
	min := f32(-24.0)
	max := f32(125.0)
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.f32_in_range(min, max)
			assert value >= min
			assert value < max
		}
	}
}

fn test_sys_rng_f64_in_range() {
	min := -548.7
	max := 5015.2
	for seed in seeds {
		seed_data := [seed]
		mut rng := sys.SysRNG{}
		rng.seed(seed_data)
		for _ in 0 .. range_limit {
			value := rng.f64_in_range(min, max)
			assert value >= min
			assert value < max
		}
	}
}