/***
    Copyright (C) 2021 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: AuRandomDevice.cpp
    Date: 2021-9-3
    Author: Reece
***/
#include <AuroraRuntime.hpp>
#include "AuRandomDevice.hpp"

namespace Aurora::RNG
{
    RandomDevice::RandomDevice()
    {

    }

    RandomDevice::RandomDevice(const RandomDef &def)
    {
        this->Init(def);
    }

    void RandomDevice::Init(const RandomDef &def)
    {
        this->def_ = def;

        // Gross...
        if (!def.bSecure)
        {
            if (def.seed)
            {
                this->fast_ = AuMove(WELL_SeedRand(def.seed.value()));
            }
            else if (def.seed64)
            {
                this->fast_ = AuMove(WELL_SeedRand64(def.seed64.value()));
            }
            else if (def.seedMassive)
            {
                this->fast_ = AuMove(WELL_SeedRandBig64(def.seedMassive.value()));
            }
            else
            {
                RNG::RngFillArray<false>(this->fast_.state);
            }
        }
        // secure rng requires no init -> we just passthrough to the global ReadSecureRNG function
    }

    void     RandomDevice::Read(Memory::MemoryViewWrite view)
    {
        if (!view)
        {
            SysPushErrorArg();
            return;
        }

        if (this->def_.bSecure)
        {
            ReadSecureRNG(view);
        }
        else
        {
            WELL_NextBytes(&this->fast_, view.ptr, AuUInt32(view.length));
        }
    }

    AuString RandomDevice::NextString(AuUInt32 uLength, ERngStringCharacters type)
    {
        AuString ret(uLength, '\00');
        NextString(ret.data(), AuUInt32(ret.size()), type);
        return ret;
    }

    static AuUInt64 RngConvertBounds(AuUInt32 i)
    {
        AuUInt8 ret;
        AuBitScanReverse(ret, i);
        return 1ull << (ret + 1);
    }

    void     RandomDevice::NextString(char *pString, AuUInt32 uLength, ERngStringCharacters type)
    {
        static AuPair<const char *, int> rngSequence[static_cast<int>(ERngStringCharacters::eEnumCount)] =
        {
            {"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", 52},
            {"abcdefghijklmnopqrstuvwxyz", 26},
            {"ABCDEFGHIJKLMNOPQRSTUVWXYZ", 26},
            {"1234567890", 10},
            {"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890", 62},
            {"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890=-+!$%^*.[];:", 75}
        };

        if (!pString)
        {
            SysPushErrorArg();
            return;
        }

        Read(AuMemoryViewWrite { pString, uLength });

        if (!ERngStringCharactersIsValid(type))
        {
            SysPushErrorArg("NextString was called with an invalid ERngStringCharacters {}", (AuUInt)type);
            type = ERngStringCharacters::eAlphaNumericCharacters; // guess we cant just return false
        }

        const auto &pair = rngSequence[static_cast<int>(type)];

        for (auto i = 0u; i < uLength; i++)
        {
            auto uUpperBound = RngConvertBounds(pair.second);
            AuUInt8 uNext {};
            auto uWord = reinterpret_cast<const AuUInt8 *>(pString)[i];
            while ((uNext = (uWord & (uUpperBound - 1))) >= pair.second)
            {
                uWord = AuFnv1a32Runtime(&uWord, sizeof(uWord));
            }
            pString[i] = pair.first[uNext];
        }
    }

    AuUInt8  RandomDevice::NextByte()
    {
        if (this->def_.bSecure)
        {
            AuUInt8 uRet {};
            ReadSecureRNG({ &uRet, 1 });
            return uRet;
        }
        else
        {
            return AuUInt8(WELL_NextLong(&this->fast_) & 0xFF);
        }
    }

    bool     RandomDevice::NextBoolean()
    {
        if (this->def_.bSecure)
        {
            AuUInt8 uRet {};
            ReadSecureRNG({ &uRet, 1 });
            return bool(uRet & 0x1);
        }
        else
        {
            return bool(WELL_NextLong(&this->fast_) & 0x1);
        }
    }
    
    AuUInt32 RandomDevice::NextU32()
    {
        if (this->def_.bSecure)
        {
            AuUInt32 uRet {};
            ReadSecureRNG({ &uRet, 4 });
            return uRet;
        }
        else
        {
            return WELL_NextLong(&this->fast_);
        }
    }
    
    AuUInt64 RandomDevice::NextU64()
    {
        if (this->def_.bSecure)
        {
            AuUInt64 uRet {};
            ReadSecureRNG({ &uRet, 8 });
            return uRet;
        }
        else
        {
            return NextFillTmpl<AuUInt64>();
        }
    }
    
    AuInt32 RandomDevice::NextInt(AuInt32 uMin, AuInt32 uMax)
    {
        auto uRange = uMax - uMin;
        auto uMassiveWord = NextU32();
        auto uUpperBound = RngConvertBounds(uRange + 1);
        AuUInt32 uNext {};
        while ((uNext = (uMassiveWord & (uUpperBound - 1))) > uRange)
        {
            uMassiveWord = AuFnv1a32Runtime(&uMassiveWord, sizeof(uMassiveWord));
        }
        return uMin + uNext;
    }

    AuUInt32 RandomDevice::NextU32(AuUInt32 uMin, AuUInt32 uMax)
    {
        auto uRange = uMax - uMin;
        auto uMassiveWord = NextU32();
        auto uUpperBound = RngConvertBounds(uRange + 1);
        AuUInt32 uNext {};
        while ((uNext = (uMassiveWord & (uUpperBound - 1))) > uRange)
        {
            uMassiveWord = AuFnv1a32Runtime(&uMassiveWord, sizeof(uMassiveWord));
        }
        return uMin + uNext;
    }

    // Source: https://stackoverflow.com/a/5016867
    bool RandomDevice::DecGeometric(int x)
    {
        if (x <= 0)
        {
            return true;
        }

        while (true)
        {
            auto r = this->NextByte();

            if (x < 8)
            {
                return (r & ((1 << x) - 1)) == 0;
            }
            else if (r != 0)
            {
                return false;
            }

            x -= 8;
        }
    }

    // Source: https://stackoverflow.com/a/5016867
    double RandomDevice::UniformFloatInRange(double udMin, double udMax)
    {
    #if defined(AURNG_USE_GARBAGE_DECIMALS)
        return (double(this->NextU32()) * (double(1.0) / double(AuNumericLimits<AuUInt32>::max()))) * udMax;
    #else
        union
        {
            double f;
            AuUInt64 u;
        } convert;

        convert.f = udMin;
        auto uABits = convert.u;
        convert.f = udMax;
        auto uBBits = convert.u;
        
        auto uMask = uBBits - uABits;
        uMask |= uMask >> 1;
        uMask |= uMask >> 2;
        uMask |= uMask >> 4;
        uMask |= uMask >> 8;
        uMask |= uMask >> 16;
        uMask |= uMask >> 32;

        int bExp {};
        frexp(udMax, &bExp);

        while (true)
        {
            int iXExp {};
            double x;

            auto uXBits = this->NextU64();
            uXBits &= uMask;
            uXBits += uABits;
            if (uXBits >= uBBits)
            {
                continue;
            }

            convert.u = uXBits;
            x         = convert.f;
            frexp(x, &iXExp);

            if (DecGeometric(bExp - iXExp))
            {
                return x;
            }
        }
    #endif
    }

    double   RandomDevice::NextDecimal() 
    {
        return this->UniformFloatInRange(0.0, 1.0);
    }

    AuUInt32 RandomDevice::NextIndex(AuUInt32 uCount /* = max + 1*/)
    {
        auto uMassiveWord = NextU32();
        auto uUpperBound = RngConvertBounds(uCount);
        AuUInt32 uNext {};
        while ((uNext = (uMassiveWord & (uUpperBound - 1))) >= uCount)
        {
            uMassiveWord = AuFnv1a32Runtime(&uMassiveWord, sizeof(uMassiveWord));
        }
        return uNext;
    }

    double   RandomDevice::NextNumber(double dMin, double dMax)
    {
        auto dRange = dMin - dMin;
        return this->UniformFloatInRange(0.0, dRange) + dMin;
    }

    AuMemoryViewRead RandomDevice::ToSeed()
    {
        if (this->def_.bSecure)
        {
            return {};
        }

        return this->fast_.state;
    }

    AUKN_SYM IRandomDevice *RandomNew(const Aurora::RNG::RandomDef &def)
    {
        auto pDevice = _new RandomDevice();
        if (!pDevice)
        {
            return nullptr;
        }

        pDevice->Init(def);
        
        return pDevice;
    }

    AUKN_SYM void RandomRelease(IRandomDevice *pDevice)
    {
        AuSafeDelete<RandomDevice *>(pDevice);
    }

    AUROXTL_INTERFACE_SOO_SRC(Random, RandomDevice, (const RandomDef &, def))
}