// ================================================================================
// ==      This file is a part of Turbo Badger. (C) 2011-2014, Emil Segerås      ==
// ==                     See tb_core.h for more information.                    ==
// ================================================================================

#include "tb_scroller.h"
#include "tb_widgets.h"
#include "tb_system.h"
#include <math.h>

namespace tb {

// == Misc constants ====================================================================

#define PAN_TARGET_FPS 60
#define PAN_MSG_DELAY_MS ((double)(1000.0 / PAN_TARGET_FPS))

#define PAN_START_THRESHOLD_MS 50
#define PAN_POWER_ACC_THRESHOLD_MS 600

#define PAN_POWER_MULTIPLIER 1.3f

#define SCROLL_DECAY 200.0f

#define SF_GATE_THRESHOLD 0.01f

// == TBScrollerFunction ================================================================

// Lab: http://www.madtealab.com/?V=1&C=6&F=5&G=1&O=1&W=774&GW=720&GH=252&GX=13.389616776278201&GY=4.790704772336853&GS=0.13102127484993598&EH=189&a=3.6666666666666665&aMa=20&aN=OrgSpeed&bMa=3&bN=CurPos&c=8&cMa=60&cI=1&cN=FrameRate&d=16&dMa=16&dI=1&dN=numSimulatedSeconds&l=2.388888888888889&lMa=5&lN=Decay&m=0.1&mMa=0.1&mN=GateThreshold&f1=OrgSpeed+%2A+exp%28-x+%2F+Decay%29&f1N=Speed&f2=CurPos+%2B+OrgSpeed+%2A+%281-exp%28-x+%2F+Decay%29%29%2A+Decay&f2N=Pos&f3=marker%28x%2C+predictGatedPoint%29&f3N=GatePoint&f4=aToF%28simulatedPoints%2Cnearest%2C0%2CnumSimulatedSeconds%29%28x%29&f4N=Iterated&f5=OrgSpeed+%2A+x&f5N=Linear1&Expr=%0ApredictGatedPoint+%3D+-log%28GateThreshold+%2F+%28OrgSpeed%29%29+%2A+Decay%0A%0Avar+cur+%3D+OrgSpeed%0AsimulatedPoints+%3D+sample%28function%28%29+%7B%0A+++cur+%3D+cur+%2A+%281+-+0.05%29%3B%0A+++return+cur%0A+%7D%2C+%5BnumSimulatedSeconds+%2A+FrameRate%5D%29%3B%0A%0ApredictGatedPoint

float TBScrollerFunction::GetDurationFromSpeed(float start_speed)
{
    float abs_start_speed = ABS(start_speed);
    if (abs_start_speed <= SF_GATE_THRESHOLD)
        return 0;
    return -log(SF_GATE_THRESHOLD / abs_start_speed) * m_decay;
}

float TBScrollerFunction::GetSpeedFromDistance(float distance)
{
    float speed = distance / m_decay;
    if (distance > SF_GATE_THRESHOLD)
        return speed + SF_GATE_THRESHOLD;
    else if (distance < -SF_GATE_THRESHOLD)
        return speed - SF_GATE_THRESHOLD;
    return speed;
}

float TBScrollerFunction::GetDistanceAtTime(float start_speed, float elapsed_time_ms)
{
    assert(elapsed_time_ms >= 0);
    return start_speed * (1 - exp(-elapsed_time_ms / m_decay)) * m_decay;
}

int TBScrollerFunction::GetDistanceAtTimeInt(float start_speed, float elapsed_time_ms)
{
    float distance = GetDistanceAtTime(start_speed, elapsed_time_ms);
    return (int)(distance < 0 ? distance - 0.5f : distance + 0.5f);
}

// == TBScroller ========================================================================

TBScroller::TBScroller(TBWidget *target)
    : m_target(target)
    , m_snap_listener(nullptr)
    , m_func(SCROLL_DECAY)
    , m_previous_pan_dx(0)
    , m_previous_pan_dy(0)
    , m_scroll_start_ms(0)
    , m_scroll_duration_x_ms(0)
    , m_scroll_duration_y_ms(0)
    , m_pan_power_multiplier_x(1)
    , m_pan_power_multiplier_y(1)
{
    Reset();
}

TBScroller::~TBScroller()
{
}

void TBScroller::Reset()
{
    m_is_started = false;
    m_pan_dx = m_pan_dy = 0;
    m_pan_time_ms = 0;
    m_pan_delta_time_ms = 0;
    m_scroll_start_speed_ppms_x = m_scroll_start_speed_ppms_y = 0;
    m_scroll_start_scroll_x = m_scroll_start_scroll_y = 0;
    // don't reset m_previous_pan_dx and m_previous_pan_dy here.
    // don't reset m_pan_power here. It's done on start since it's needed for next pan!
    m_expected_scroll_x = m_expected_scroll_y = 0;
}

void TBScroller::OnScrollBy(int dx, int dy, bool accumulative)
{
    if (!IsStarted())
        Start();

    float ppms_x = m_func.GetSpeedFromDistance((float)dx);
    float ppms_y = m_func.GetSpeedFromDistance((float)dy);

    if (accumulative && IsScrolling())
    {
        TBWidget::ScrollInfo info = m_target->GetScrollInfo();
        // If new direction is the same as the current direction,
        // calculate the speed needed for the remaining part and
        // add that to the new scroll speed.
        if ((ppms_x < 0) == (m_scroll_start_speed_ppms_x < 0))
        {
            int distance_x = m_func.GetDistanceAtTimeInt(m_scroll_start_speed_ppms_x,
                                                         m_func.GetDurationFromSpeed(m_scroll_start_speed_ppms_x));
            int distance_remaining_x = m_scroll_start_scroll_x + distance_x - info.x;
            distance_remaining_x += m_func.GetDistanceAtTimeInt(ppms_x, m_func.GetDurationFromSpeed(ppms_x));
            ppms_x = m_func.GetSpeedFromDistance((float)distance_remaining_x);
        }
        if ((ppms_y < 0) == (m_scroll_start_speed_ppms_y < 0))
        {
            int distance_y = m_func.GetDistanceAtTimeInt(m_scroll_start_speed_ppms_y,
                                                         m_func.GetDurationFromSpeed(m_scroll_start_speed_ppms_y));
            int distance_remaining_y = m_scroll_start_scroll_y + distance_y - info.y;
            distance_remaining_y += m_func.GetDistanceAtTimeInt(ppms_y, m_func.GetDurationFromSpeed(ppms_y));
            ppms_y = m_func.GetSpeedFromDistance((float)distance_remaining_y);
        }
    }

    AdjustToSnappingAndScroll(ppms_x, ppms_y);
}

bool TBScroller::OnPan(int dx, int dy)
{
    if (!IsStarted())
        Start();

    // Pan the target
    const int in_dx = dx, in_dy = dy;
    m_target->ScrollByRecursive(dx, dy);

    // Calculate the pan speed. Smooth it out with the
    // previous pan speed to reduce fluctuation a little.
    double now_ms = TBSystem::GetTimeMS();
    if (m_pan_time_ms)
    {
        if (m_pan_delta_time_ms)
            m_pan_delta_time_ms = (now_ms - m_pan_time_ms + m_pan_delta_time_ms) / 2.0f;
        else
            m_pan_delta_time_ms = now_ms - m_pan_time_ms;
    }

    m_pan_time_ms = now_ms;
    m_pan_dx = (m_pan_dx + in_dx) / 2.0f;
    m_pan_dy = (m_pan_dy + in_dy) / 2.0f;

    // If we change direction, reset the pan power multiplier in that axis.
    if (m_pan_dx != 0 && (m_previous_pan_dx < 0) != (m_pan_dx < 0))
        m_pan_power_multiplier_x = 1;
    if (m_pan_dy != 0 && (m_previous_pan_dy < 0) != (m_pan_dy < 0))
        m_pan_power_multiplier_y = 1;
    m_previous_pan_dx = m_pan_dx;
    m_previous_pan_dy = m_pan_dy;

    return in_dx != dx || in_dy != dy;
}

void TBScroller::OnPanReleased()
{
    if (TBSystem::GetTimeMS() < m_pan_time_ms + PAN_START_THRESHOLD_MS)
    {
        // Don't start scroll if we have too little speed.
        // This will prevent us from scrolling accidently.
        float pan_start_distance_threshold_px = 2 * TBSystem::GetDPI() / 100.0f;
        if (ABS(m_pan_dx) < pan_start_distance_threshold_px && ABS(m_pan_dy) < pan_start_distance_threshold_px)
        {
            StopOrSnapScroll();
            return;
        }

        if (m_pan_delta_time_ms == 0)
        {
            StopOrSnapScroll();
            return;
        }

        float ppms_x = (float)m_pan_dx / (float)m_pan_delta_time_ms;
        float ppms_y = (float)m_pan_dy / (float)m_pan_delta_time_ms;
        ppms_x *= m_pan_power_multiplier_x;
        ppms_y *= m_pan_power_multiplier_y;

        AdjustToSnappingAndScroll(ppms_x, ppms_y);
    }
    else
        StopOrSnapScroll();
}

void TBScroller::Start()
{
    if (IsStarted())
        return;
    m_is_started = true;
    double now_ms = TBSystem::GetTimeMS();
    if (now_ms < m_scroll_start_ms + PAN_POWER_ACC_THRESHOLD_MS)
    {
        m_pan_power_multiplier_x *= PAN_POWER_MULTIPLIER;
        m_pan_power_multiplier_y *= PAN_POWER_MULTIPLIER;
    }
    else
    {
        m_pan_power_multiplier_x = m_pan_power_multiplier_y = 1;
    }
}

void TBScroller::Stop()
{
    DeleteAllMessages();
    Reset();
}

bool TBScroller::StopIfAlmostStill()
{
    double now_ms = TBSystem::GetTimeMS();
    if (now_ms > m_scroll_start_ms + (double)m_scroll_duration_x_ms &&
            now_ms > m_scroll_start_ms + (double)m_scroll_duration_y_ms)
    {
        Stop();
        return true;
    }
    return false;
}

void TBScroller::StopOrSnapScroll()
{
    AdjustToSnappingAndScroll(0, 0);
    if (!IsScrolling())
        Stop();
}

void TBScroller::AdjustToSnappingAndScroll(float ppms_x, float ppms_y)
{
    if (m_snap_listener)
    {
        // Calculate the distance
        int distance_x = m_func.GetDistanceAtTimeInt(ppms_x, m_func.GetDurationFromSpeed(ppms_x));
        int distance_y = m_func.GetDistanceAtTimeInt(ppms_y, m_func.GetDurationFromSpeed(ppms_y));

        // Let the snap listener modify the distance
        TBWidget::ScrollInfo info = m_target->GetScrollInfo();
        int target_x = distance_x + info.x;
        int target_y = distance_y + info.y;
        m_snap_listener->OnScrollSnap(m_target, target_x, target_y);
        distance_x = target_x - info.x;
        distance_y = target_y - info.y;

        // Get the start speed from the new distance
        ppms_x = m_func.GetSpeedFromDistance((float)distance_x);
        ppms_y = m_func.GetSpeedFromDistance((float)distance_y);
    }

    Scroll(ppms_x, ppms_y);
}

void TBScroller::Scroll(float start_speed_ppms_x, float start_speed_ppms_y)
{
    // Set start values
    m_scroll_start_ms = TBSystem::GetTimeMS();
    GetTargetScrollXY(m_scroll_start_scroll_x, m_scroll_start_scroll_y);
    m_scroll_start_speed_ppms_x = start_speed_ppms_x;
    m_scroll_start_speed_ppms_y = start_speed_ppms_y;

    // Calculate duration for the scroll (each axis independently)
    m_scroll_duration_x_ms = m_func.GetDurationFromSpeed(m_scroll_start_speed_ppms_x);
    m_scroll_duration_y_ms = m_func.GetDurationFromSpeed(m_scroll_start_speed_ppms_y);

    if (StopIfAlmostStill())
        return;

    // Post the pan message if we don't already have one
    if (!GetMessageByID(TBIDC("scroll")))
    {
        // Update expected translation
        GetTargetChildTranslation(m_expected_scroll_x, m_expected_scroll_y);

        PostMessageDelayed(TBIDC("scroll"), nullptr, (uint32)PAN_MSG_DELAY_MS);
    }
}

bool TBScroller::IsScrolling()
{
    return GetMessageByID(TBIDC("scroll")) ? true : false;
}

void TBScroller::GetTargetChildTranslation(int &x, int &y) const
{
    int root_x = 0, root_y = 0;
    int child_translation_x = 0, child_translation_y = 0;
    TBWidget *scroll_root = m_target->GetScrollRoot();
    scroll_root->ConvertToRoot(root_x, root_y);
    scroll_root->GetChildTranslation(child_translation_x, child_translation_y);
    x = root_x + child_translation_x;
    y = root_y + child_translation_y;
}

void TBScroller::GetTargetScrollXY(int &x, int &y) const
{
    x = 0;
    y = 0;
    TBWidget *tmp = m_target->GetScrollRoot();
    while (tmp)
    {
        TBWidget::ScrollInfo info = tmp->GetScrollInfo();
        x += info.x;
        y += info.y;
        tmp = tmp->GetParent();
    }
}

void TBScroller::OnMessageReceived(TBMessage *msg)
{
    if (msg->message == TBIDC("scroll"))
    {
        int actual_scroll_x = 0, actual_scroll_y = 0;
        GetTargetChildTranslation(actual_scroll_x, actual_scroll_y);
        if (actual_scroll_x != m_expected_scroll_x ||
                actual_scroll_y != m_expected_scroll_y)
        {
            // Something else has affected the target child translation.
            // This should abort the scroll.
            // This could happen f.ex if something shrunk the scroll limits,
            // some other action changed scroll position, or if another
            // scroller started operating on a sub child that when reacing
            // its scroll limit, started scrolling its chain of parents.
            Stop();
            return;
        }

        // Calculate the time elapsed from scroll start. Clip within the
        // duration for each axis.
        double now_ms = TBSystem::GetTimeMS();
        float elapsed_time_x = (float)(now_ms - m_scroll_start_ms);
        float elapsed_time_y = elapsed_time_x;
        elapsed_time_x = MIN(elapsed_time_x, m_scroll_duration_x_ms);
        elapsed_time_y = MIN(elapsed_time_y, m_scroll_duration_y_ms);

        // Get the new scroll position from the current distance in each axis.
        int scroll_x = m_func.GetDistanceAtTimeInt(m_scroll_start_speed_ppms_x, elapsed_time_x);
        int scroll_y = m_func.GetDistanceAtTimeInt(m_scroll_start_speed_ppms_y, elapsed_time_y);
        scroll_x += m_scroll_start_scroll_x;
        scroll_y += m_scroll_start_scroll_y;

        // Get the scroll delta and invoke ScrollByRecursive.
        int curr_scroll_x, curr_scroll_y;
        GetTargetScrollXY(curr_scroll_x, curr_scroll_y);
        const int dx = scroll_x - curr_scroll_x;
        const int dy = scroll_y - curr_scroll_y;

        int idx = dx, idy = dy;
        m_target->ScrollByRecursive(idx, idy);

        // Update expected translation
        GetTargetChildTranslation(m_expected_scroll_x, m_expected_scroll_y);

        if ((dx && actual_scroll_x == m_expected_scroll_x) &&
                (dy && actual_scroll_y == m_expected_scroll_y))
        {
            // We didn't get anywhere despite we tried,
            // so we're done (reached the end).
            Stop();
            return;
        }

        if (!StopIfAlmostStill())
        {
            double next_fire_time = msg->GetFireTime() + PAN_MSG_DELAY_MS;
            // avoid timer catch-up if program went sleeping for a while.
            next_fire_time = MAX(next_fire_time, now_ms);
            PostMessageOnTime(TBIDC("scroll"), nullptr, next_fire_time);
        }
    }
}

}; // namespace tb