/*
 * Copyright (c) 2023, Matthew Olsson <mattco@serenityos.org>.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibWeb/Animations/Animation.h>
#include <LibWeb/Animations/AnimationEffect.h>
#include <LibWeb/Animations/DocumentTimeline.h>
#include <LibWeb/Bindings/Intrinsics.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/HTML/Window.h>
#include <LibWeb/WebIDL/ExceptionOr.h>
#include <LibWeb/WebIDL/Promise.h>

namespace Web::Animations {

// https://www.w3.org/TR/web-animations-1/#dom-animation-animation
JS::NonnullGCPtr<Animation> Animation::create(JS::Realm& realm, JS::GCPtr<AnimationEffect> effect, JS::GCPtr<AnimationTimeline> timeline)
{
    // 1. Let animation be a new Animation object.
    auto animation = realm.heap().allocate<Animation>(realm, realm);

    // 2. Run the procedure to set the timeline of an animation on animation passing timeline as the new timeline or, if
    //    a timeline argument is missing, passing the default document timeline of the Document associated with the
    //    Window that is the current global object.
    if (!timeline) {
        auto& window = verify_cast<HTML::Window>(HTML::current_global_object());
        timeline = window.associated_document().timeline();
    }
    animation->set_timeline(timeline);

    // 3. Run the procedure to set the associated effect of an animation on animation passing source as the new effect.
    animation->set_effect(effect);

    return animation;
}

WebIDL::ExceptionOr<JS::NonnullGCPtr<Animation>> Animation::construct_impl(JS::Realm& realm, JS::GCPtr<AnimationEffect> effect, JS::GCPtr<AnimationTimeline> timeline)
{
    return create(realm, effect, timeline);
}

// https://www.w3.org/TR/web-animations-1/#animation-set-the-associated-effect-of-an-animation
void Animation::set_effect(JS::GCPtr<AnimationEffect> new_effect)
{
    // Setting this attribute updates the object’s associated effect using the procedure to set the associated effect of
    // an animation.

    // 1. Let old effect be the current associated effect of animation, if any.
    auto old_effect = m_effect;

    // 2. If new effect is the same object as old effect, abort this procedure.
    if (new_effect == old_effect)
        return;

    // 3. If animation has a pending pause task, reschedule that task to run as soon as animation is ready.
    if (m_pending_pause_task == TaskState::Pending)
        m_pending_pause_task = TaskState::RunAsSoonAsReady;

    // 4. If animation has a pending play task, reschedule that task to run as soon as animation is ready to play ne
    //    effect.
    if (m_pending_play_task == TaskState::Pending)
        m_pending_play_task = TaskState::RunAsSoonAsReady;

    // 5. If new effect is not null and if new effect is the associated effect of another animation, previous animation,
    //    run the procedure to set the associated effect of an animation (this procedure) on previous animation passing
    //    null as new effect.
    if (new_effect && new_effect->associated_animation() != this) {
        if (auto animation = new_effect->associated_animation())
            animation->set_effect({});
    }

    // 6. Let the associated effect of animation be new effect.
    if (new_effect)
        new_effect->set_associated_animation(this);
    if (m_effect)
        m_effect->set_associated_animation({});
    m_effect = new_effect;

    // FIXME: 7. Run the procedure to update an animation’s finished state for animation with the did seek flag set to
    //           false, and the synchronously notify flag set to false.
}

// https://www.w3.org/TR/web-animations-1/#animation-set-the-timeline-of-an-animation
void Animation::set_timeline(JS::GCPtr<AnimationTimeline> new_timeline)
{
    // Setting this attribute updates the object’s timeline using the procedure to set the timeline of an animation.

    // 1. Let old timeline be the current timeline of animation, if any.
    auto old_timeline = m_timeline;

    // 2. If new timeline is the same object as old timeline, abort this procedure.
    if (new_timeline == old_timeline)
        return;

    // 3. Let the timeline of animation be new timeline.
    if (m_timeline)
        m_timeline->disassociate_with_animation(*this);
    m_timeline = new_timeline;
    m_timeline->associate_with_animation(*this);

    // 4. If the start time of animation is resolved, make animation’s hold time unresolved.
    if (m_start_time.has_value())
        m_hold_time = {};

    // FIXME: 5. Run the procedure to update an animation’s finished state for animation with the did seek flag set to
    //           false, and the synchronously notify flag set to false.
}

// https://www.w3.org/TR/web-animations-1/#dom-animation-starttime
// https://www.w3.org/TR/web-animations-1/#set-the-start-time
void Animation::set_start_time(Optional<double> const& new_start_time)
{
    // Setting this attribute updates the start time using the procedure to set the start time of this object to the new
    // value.

    // 1. Let timeline time be the current time value of the timeline that animation is associated with. If there is no
    //    timeline associated with animation or the associated timeline is inactive, let the timeline time be
    //    unresolved.
    auto timeline_time = m_timeline && !m_timeline->is_inactive() ? m_timeline->current_time() : Optional<double> {};

    // 2. If timeline time is unresolved and new start time is resolved, make animation’s hold time unresolved.
    if (!timeline_time.has_value() && new_start_time.has_value())
        m_hold_time = {};

    // 3. Let previous current time be animation’s current time.
    auto previous_current_time = current_time();

    // 4. Apply any pending playback rate on animation.
    apply_any_pending_playback_rate();

    // 5. Set animation’s start time to new start time.
    m_start_time = new_start_time;

    // 6. Update animation’s hold time based on the first matching condition from the following,

    // -> If new start time is resolved,
    if (new_start_time.has_value()) {
        // If animation’s playback rate is not zero, make animation’s hold time unresolved.
        if (m_playback_rate != 0.0)
            m_hold_time = {};
    }
    // -> Otherwise (new start time is unresolved),
    else {
        // Set animation’s hold time to previous current time even if previous current time is unresolved.
        m_hold_time = previous_current_time;
    }

    // 7. If animation has a pending play task or a pending pause task, cancel that task and resolve animation’s current
    //    ready promise with animation.
    if (m_pending_play_task == TaskState::Pending || m_pending_pause_task == TaskState::Pending) {
        m_pending_play_task = TaskState::None;
        m_pending_pause_task = TaskState::None;
        WebIDL::resolve_promise(realm(), current_ready_promise(), this);
    }

    // FIXME: 8. Run the procedure to update an animation’s finished state for animation with the did seek flag set to
    //           true, and the synchronously notify flag set to false.
}

// https://www.w3.org/TR/web-animations-1/#animation-current-time
Optional<double> Animation::current_time() const
{
    // The current time is calculated from the first matching condition from below:

    // -> If the animation’s hold time is resolved,
    if (m_hold_time.has_value()) {
        // The current time is the animation’s hold time.
        return m_hold_time.value();
    }

    // -> If any of the following are true:
    //    - the animation has no associated timeline, or
    //    - the associated timeline is inactive, or
    //    - the animation’s start time is unresolved.
    if (!m_timeline || m_timeline->is_inactive() || !m_start_time.has_value()) {
        // The current time is an unresolved time value.
        return {};
    }

    // -> Otherwise,
    //    current time = (timeline time - start time) × playback rate
    //    Where timeline time is the current time value of the associated timeline. The playback rate value is defined
    //    in §4.4.15 Speed control.
    return (m_timeline->current_time().value() - m_start_time.value()) * playback_rate();
}

// https://www.w3.org/TR/web-animations-1/#animation-set-the-current-time
WebIDL::ExceptionOr<void> Animation::set_current_time(Optional<double> const& seek_time)
{
    // 1. Run the steps to silently set the current time of animation to seek time.
    TRY(silently_set_current_time(seek_time));

    // 2. If animation has a pending pause task, synchronously complete the pause operation by performing the following
    //    steps:
    if (m_pending_pause_task == TaskState::Pending) {
        // 1. Set animation’s hold time to seek time.
        m_hold_time = seek_time;

        // 2. Apply any pending playback rate to animation.
        apply_any_pending_playback_rate();

        // 3. Make animation’s start time unresolved.
        m_start_time = {};

        // 4. Cancel the pending pause task.
        m_pending_pause_task = TaskState::None;

        // 5 Resolve animation’s current ready promise with animation.
        WebIDL::resolve_promise(realm(), current_ready_promise(), this);
    }

    // FIXME: 3. Run the procedure to update an animation’s finished state for animation with the did seek flag set to
    //           true, and the synchronously notify flag set to false.

    return {};
}

// https://www.w3.org/TR/web-animations-1/#dom-animation-playbackrate
// https://www.w3.org/TR/web-animations-1/#set-the-playback-rate
WebIDL::ExceptionOr<void> Animation::set_playback_rate(double new_playback_rate)
{
    // Setting this attribute follows the procedure to set the playback rate of this object to the new value.

    // 1. Clear any pending playback rate on animation.
    m_pending_playback_rate = {};

    // 2. Let previous time be the value of the current time of animation before changing the playback rate.
    auto previous_time = current_time();

    // 3. Let previous playback rate be the current effective playback rate of animation.
    auto previous_playback_rate = playback_rate();

    // 4. Set the playback rate to new playback rate.
    m_playback_rate = new_playback_rate;

    // 5. Perform the steps corresponding to the first matching condition from the following, if any:

    // -> If animation is associated with a monotonically increasing timeline and the previous time is resolved,
    if (m_timeline && m_timeline->is_monotonically_increasing() && previous_time.has_value()) {
        // set the current time of animation to previous time.
        TRY(set_current_time(previous_time));
    }
    // -> If animation is associated with a non-null timeline that is not monotonically increasing, the start time of
    //    animation is resolved, associated effect end is not infinity, and either:
    //    - the previous playback rate < 0 and the new playback rate ≥ 0, or
    //    - the previous playback rate ≥ 0 and the new playback rate < 0,
    else if (m_timeline && !m_timeline->is_monotonically_increasing() && m_start_time.has_value() && !isinf(associated_effect_end()) && ((previous_playback_rate < 0.0 && new_playback_rate >= 0.0) || (previous_playback_rate >= 0 && new_playback_rate < 0))) {
        // Set animation’s start time to the result of evaluating associated effect end - start time for animation.
        m_start_time = associated_effect_end() - m_start_time.value();
    }

    return {};
}

// https://www.w3.org/TR/web-animations-1/#animation-play-state
Bindings::AnimationPlayState Animation::play_state() const
{
    // The play state of animation, animation, at a given moment is the state corresponding to the first matching
    // condition from the following:

    // -> All of the following conditions are true:
    //    - The current time of animation is unresolved, and
    //    - the start time of animation is unresolved, and
    //    - animation does not have either a pending play task or a pending pause task,
    auto current_time = this->current_time();
    if (!current_time.has_value() && !m_start_time.has_value() && !pending()) {
        // → idle
        return Bindings::AnimationPlayState::Idle;
    }

    // -> Either of the following conditions are true:
    //    - animation has a pending pause task, or
    //    - both the start time of animation is unresolved and it does not have a pending play task,
    if (m_pending_pause_task == TaskState::Pending || (!m_start_time.has_value() && m_pending_play_task == TaskState::None)) {
        // → paused
        return Bindings::AnimationPlayState::Paused;
    }

    // -> For animation, current time is resolved and either of the following conditions are true:
    //    - animation’s effective playback rate > 0 and current time ≥ associated effect end; or
    //    - animation’s effective playback rate < 0 and current time ≤ 0,
    auto effective_playback_rate = this->effective_playback_rate();
    if (current_time.has_value() && ((effective_playback_rate > 0.0 && current_time.value() >= associated_effect_end()) || (effective_playback_rate < 0.0 && current_time.value() <= 0.0))) {
        // → finished
        return Bindings::AnimationPlayState::Finished;
    }

    // -> Otherwise,
    //    → running
    return Bindings::AnimationPlayState::Running;
}

// https://www.w3.org/TR/web-animations-1/#associated-effect-end
double Animation::associated_effect_end() const
{
    // The associated effect end of an animation is equal to the end time of the animation’s associated effect. If the
    // animation has no associated effect, the associated effect end is zero.
    return m_effect ? m_effect->end_time() : 0.0;
}

// https://www.w3.org/TR/web-animations-1/#effective-playback-rate
double Animation::effective_playback_rate() const
{
    // The effective playback rate of an animation is its pending playback rate, if set, otherwise it is the animation’s
    // playback rate.
    return m_pending_playback_rate.has_value() ? m_pending_playback_rate.value() : m_playback_rate;
}

// https://www.w3.org/TR/web-animations-1/#apply-any-pending-playback-rate
void Animation::apply_any_pending_playback_rate()
{
    // 1. If animation does not have a pending playback rate, abort these steps.
    if (!m_pending_playback_rate.has_value())
        return;

    // 2. Set animation’s playback rate to its pending playback rate.
    m_playback_rate = m_pending_playback_rate.value();

    // 3. Clear animation’s pending playback rate.
    m_pending_playback_rate = {};
}

// https://www.w3.org/TR/web-animations-1/#animation-silently-set-the-current-time
WebIDL::ExceptionOr<void> Animation::silently_set_current_time(Optional<double> seek_time)
{
    // 1. If seek time is an unresolved time value, then perform the following steps.
    if (!seek_time.has_value()) {
        // 1. If the current time is resolved, then throw a TypeError.
        if (current_time().has_value()) {
            return WebIDL::SimpleException {
                WebIDL::SimpleExceptionType::TypeError,
                "Cannot change an animation's current time from a resolve value to an unresolved value"sv
            };
        }

        // 2. Abort these steps.
        return {};
    }

    // 2. Update either animation’s hold time or start time as follows:

    // -> If any of the following conditions are true:
    //    - animation’s hold time is resolved, or
    //    - animation’s start time is unresolved, or
    //    - animation has no associated timeline or the associated timeline is inactive, or
    //    - animation’s playback rate is 0,
    if (m_hold_time.has_value() || !m_start_time.has_value() || !m_timeline || m_timeline->is_inactive() || m_playback_rate == 0.0) {
        // Set animation’s hold time to seek time.
        m_hold_time = seek_time;
    }
    // -> Otherwise,
    else {
        // Set animation’s start time to the result of evaluating timeline time - (seek time / playback rate) where
        // timeline time is the current time value of timeline associated with animation.
        m_start_time = m_timeline->current_time().value() - (seek_time.value() / m_playback_rate);
    }

    // 3. If animation has no associated timeline or the associated timeline is inactive, make animation’s start time
    //    unresolved.
    if (!m_timeline || m_timeline->is_inactive())
        m_start_time = {};

    // 4. Make animation’s previous current time unresolved.
    m_previous_current_time = {};

    return {};
}

JS::NonnullGCPtr<WebIDL::Promise> Animation::current_ready_promise() const
{
    if (!m_current_ready_promise) {
        // The current ready promise is initially a resolved Promise created using the procedure to create a new
        // resolved Promise with the animation itself as its value and created in the relevant Realm of the animation.
        m_current_ready_promise = WebIDL::create_resolved_promise(realm(), this);
    }

    return *m_current_ready_promise;
}

JS::NonnullGCPtr<WebIDL::Promise> Animation::current_finished_promise() const
{
    if (!m_current_finished_promise) {
        // The current finished promise is initially a pending Promise object.
        m_current_finished_promise = WebIDL::create_promise(realm());
    }

    return *m_current_finished_promise;
}

Animation::Animation(JS::Realm& realm)
    : DOM::EventTarget(realm)
{
}

void Animation::initialize(JS::Realm& realm)
{
    Base::initialize(realm);
    set_prototype(&Bindings::ensure_web_prototype<Bindings::AnimationPrototype>(realm, "Animation"));
}

void Animation::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_effect);
    visitor.visit(m_timeline);
    visitor.visit(m_current_ready_promise);
    visitor.visit(m_current_finished_promise);
}

}