// Lattice-based cryptographic parameter sets.
package hamcrypto

import "git.smesh.lol/gnarl-hamadryad/moxie/ratio"

// SecurityLevel specifies cryptographic strength.
type SecurityLevel uint8

const (
	Security128 SecurityLevel = iota
	Security192
	Security256
)

// Params holds the parameters for a lattice-based cryptographic instance.
type Params struct {
	N                 int32
	Q                 ratio.Ratio
	SmoothingParam    ratio.Ratio
	NoiseWidth        ratio.Ratio
	MaxWalkSteps      int32
	DissolutionPasses int32
}

// DefaultParams returns parameters for a given security level.
func DefaultParams(level SecurityLevel) (p Params) {
	switch level {
	case Security192:
		return Params{
			N:                 384,
			Q:                 ratio.FromInt(251),
			SmoothingParam:    ratio.New(2, 10),
			NoiseWidth:        ratio.New(3, 10),
			MaxWalkSteps:      1600,
			DissolutionPasses: 3,
		}
	case Security256:
		return Params{
			N:                 512,
			Q:                 ratio.FromInt(509),
			SmoothingParam:    ratio.New(2, 10),
			NoiseWidth:        ratio.New(3, 10),
			MaxWalkSteps:      2000,
			DissolutionPasses: 4,
		}
	default:
		return Params{
			N:                 256,
			Q:                 ratio.FromInt(127),
			SmoothingParam:    ratio.New(2, 10),
			NoiseWidth:        ratio.New(3, 10),
			MaxWalkSteps:      1024,
			DissolutionPasses: 2,
		}
	}
}

// Valid reports whether the parameters are internally consistent.
func (p *Params) Valid() (ok bool) {
	if p.N <= 0 {
		return false
	}
	if !p.Q.IsPositive() || p.Q.Denom != 1 {
		return false
	}
	if !p.SmoothingParam.IsPositive() {
		return false
	}
	if !p.NoiseWidth.IsPositive() {
		return false
	}
	if !p.SmoothingParam.Less(&p.NoiseWidth) {
		return false
	}
	if !p.NoiseWidth.Less(&ratio.One) {
		return false
	}
	if p.MaxWalkSteps <= 0 {
		return false
	}
	if p.DissolutionPasses <= 0 {
		return false
	}
	return true
}