#include "WaveSystem.h"

#include <algorithm>

#include "ShipSystem.h"

WaveSystem::WaveSystem(const GameConfig& config, std::mt19937& rng)
    : m_config(config)
    , m_rng(rng)
{
    // Draw the initial inter-wave gap (REQ-WAV-GAP, REQ-WAV-GRACE-PERIOD).
    m_nextEventTick = drawGapTicks();
}

void WaveSystem::tickWaveScheduler(Tick currentTick, ShipSystem& ships,
                                    int worldHeightTiles)
{
    if (!m_waveActive)
    {
        if (currentTick < m_nextEventTick)
        {
            return;
        }
        // Gap expired: compose the next wave.
        m_pendingSpawns = composeWave(currentTick, worldHeightTiles);
        m_waveActive    = true;
    }

    // Spawn any ships whose scheduled tick has arrived.
    std::vector<SpawnEntry> remaining;
    remaining.reserve(m_pendingSpawns.size());
    for (const SpawnEntry& entry : m_pendingSpawns)
    {
        if (currentTick >= entry.spawnAt)
        {
            ships.spawn(entry.schematicId, entry.level, entry.position,
                        /*isEnemy=*/true);
        }
        else
        {
            remaining.push_back(entry);
        }
    }
    m_pendingSpawns = std::move(remaining);

    if (m_pendingSpawns.empty())
    {
        m_waveActive    = false;
        m_nextEventTick = currentTick + drawGapTicks();
    }
}

void WaveSystem::tickThreatAccumulation(Tick currentTick)
{
    const double elapsedSeconds = static_cast<double>(currentTick) * kTickDurationSeconds;
    const double rate = m_config.world.waves.threatRateFormula.evaluate(elapsedSeconds);
    if (rate > 0.0)
    {
        m_threatLevel += rate * m_pushScalingMultiplier * kTickDurationSeconds;
    }
}

void WaveSystem::applyPush()
{
    m_pushScalingMultiplier *= m_config.world.push.scalingFactor;
    ++m_generation;
}

double WaveSystem::threatLevel() const
{
    return m_threatLevel;
}

int WaveSystem::generation() const
{
    return m_generation;
}

// ---------------------------------------------------------------------------
// Private helpers
// ---------------------------------------------------------------------------

std::vector<WaveSystem::SpawnEntry> WaveSystem::composeWave(Tick currentTick,
                                                             int worldHeightTiles)
{
    const double elapsedSeconds = static_cast<double>(currentTick) * kTickDurationSeconds;
    const int shipLevel = std::max(1, static_cast<int>(
        m_config.world.waves.shipLevelFormula.evaluate(elapsedSeconds)));

    // Build eligible ship list with their costs at the current level.
    struct EligibleShip
    {
        std::string schematicId;
        double      cost;
    };
    std::vector<EligibleShip> eligible;
    for (const ShipDef& def : m_config.ships.ships)
    {
        const double cost = def.threat.costFormula.evaluate(static_cast<double>(shipLevel));
        if (cost > 0.0)
        {
            EligibleShip es;
            es.schematicId = def.id;
            es.cost        = cost;
            eligible.push_back(es);
        }
    }

    if (eligible.empty())
    {
        return {};
    }

    // Take the current threat level as the wave budget and reset it.
    // Unspent budget is re-added after composition (carry-over).
    double budget = m_threatLevel;
    m_threatLevel = 0.0;

    // Enemy spawn buffer X range for the current generation.
    const float leftX = static_cast<float>(
        m_config.world.regions.playerBufferWidth
        + m_config.world.regions.contestZoneWidth
        + m_generation * m_config.world.push.pushExpandColumns);
    const float rightX = leftX + static_cast<float>(m_config.world.regions.enemyBufferWidth) - 1.0f;

    std::uniform_real_distribution<float> xDist(leftX, rightX);
    std::uniform_int_distribution<int>    yDist(0, worldHeightTiles - 1);

    std::vector<SpawnEntry> picked;

    while (true)
    {
        // Collect indices of ships whose cost fits the remaining budget.
        std::vector<std::size_t> fitting;
        for (std::size_t i = 0; i < eligible.size(); ++i)
        {
            if (eligible[i].cost <= budget)
            {
                fitting.push_back(i);
            }
        }
        if (fitting.empty())
        {
            break;
        }

        std::uniform_int_distribution<int> pick(0, static_cast<int>(fitting.size()) - 1);
        const std::size_t chosenIdx = fitting[static_cast<std::size_t>(pick(m_rng))];
        const EligibleShip& chosen  = eligible[chosenIdx];

        budget -= chosen.cost;

        SpawnEntry entry;
        entry.schematicId = chosen.schematicId;
        entry.level       = shipLevel;
        entry.spawnAt     = 0;  // set below after all picks are done
        entry.position    = QVector2D(xDist(m_rng),
                                      static_cast<float>(yDist(m_rng)) + 0.5f);
        picked.push_back(entry);
    }

    // Carry leftover budget forward to the next wave.
    m_threatLevel += budget;

    // Spread spawn times evenly across spawnDurationSeconds.
    const int count = static_cast<int>(picked.size());
    if (count == 1)
    {
        picked[0].spawnAt = currentTick;
    }
    else if (count > 1)
    {
        const Tick spawnDurationTicks =
            secondsToTicks(m_config.world.waves.spawnDurationSeconds);
        for (int i = 0; i < count; ++i)
        {
            picked[static_cast<std::size_t>(i)].spawnAt =
                currentTick + static_cast<Tick>(i) * spawnDurationTicks / (count - 1);
        }
    }

    return picked;
}

Tick WaveSystem::drawGapTicks()
{
    const Tick minTicks = secondsToTicks(m_config.world.waves.gapMinSeconds);
    const Tick maxTicks = secondsToTicks(m_config.world.waves.gapMaxSeconds);
    std::uniform_int_distribution<Tick> dist(minTicks, maxTicks);
    return dist(m_rng);
}