#include "PatternEngine.h"

#include <limits>

namespace timbre_core {

void PatternEngine::initializeDefaults() noexcept {
    for (std::size_t i = 0; i < kMaxPatterns; ++i) {
        patterns_[i].id = patternIdFromIndex(i);
    }
    configuredPatternMask_ =
        static_cast<std::uint8_t>((1u << kMaxPatterns) - 1u);
}

std::uint64_t PatternEngine::readClock() const {
    if (clockInterface_ != nullptr) {
        return clockInterface_->nowMs();
    }
    if (clock_) {
        return clock_();
    }
    return 0;
}

bool PatternEngine::validPattern(const Pattern& pattern) const noexcept {
    return isPatternId(pattern.id) && ScheduleValidator::validatePattern(pattern).valid;
}

void PatternEngine::setPattern(const Pattern& pattern) noexcept {
    if (!validPattern(pattern)) {
        return;
    }
    const std::size_t index = patternIndex(pattern.id);
    if (index < patterns_.size()) {
        patterns_[index] = pattern;
        configuredPatternMask_ = static_cast<std::uint8_t>(
            configuredPatternMask_ | (1u << index));
    }
}

void PatternEngine::setPatterns(const AppState& state) noexcept {
    bool allValid = true;
    for (std::size_t i = 0; i < kMaxPatterns; ++i) {
        if (!validPattern(state.patterns[i])) {
            allValid = false;
            break;
        }
    }
    if (!allValid) {
        return;
    }
    patterns_ = state.patterns;
    configuredPatternMask_ = static_cast<std::uint8_t>((1u << kMaxPatterns) - 1u);
}

bool PatternEngine::enqueueSnapshot(const Pattern& pattern, std::uint64_t startAtMs) {
    if (!validPattern(pattern) || queueSize_ >= kQueueCapacity) {
        return false;
    }
    const std::size_t tail = (queueHead_ + queueSize_) % kQueueCapacity;
    queue_[tail].pattern = pattern;
    queue_[tail].startAtMs = startAtMs;
    ++queueSize_;
    return true;
}

bool PatternEngine::enqueue(PatternId id) {
    return enqueue(id, readClock());
}

bool PatternEngine::enqueue(PatternId id, std::uint64_t startAtMs) {
    const std::size_t index = patternIndex(id);
    if (index >= patterns_.size() ||
        (configuredPatternMask_ & (1u << index)) == 0) {
        return false;
    }
    return enqueueSnapshot(patterns_[index], startAtMs);
}

bool PatternEngine::enqueue(const Pattern& pattern) {
    return enqueue(pattern, readClock());
}

bool PatternEngine::enqueue(const Pattern& pattern, std::uint64_t startAtMs) {
    return enqueueSnapshot(pattern, startAtMs);
}

bool PatternEngine::enqueue(PatternId id, const AppState& state, std::uint64_t startAtMs) {
    const Pattern* pattern = state.pattern(id);
    return pattern != nullptr && enqueueSnapshot(*pattern, startAtMs);
}

bool PatternEngine::enqueue(PatternId id, const AppState& state) {
    return enqueue(id, state, readClock());
}

bool PatternEngine::start(PatternId id, std::uint64_t nowMs) {
    const std::size_t index = patternIndex(id);
    if (index >= patterns_.size() ||
        (configuredPatternMask_ & (1u << index)) == 0) {
        return false;
    }
    return startSnapshot(patterns_[index], nowMs);
}

bool PatternEngine::start(const Pattern& pattern, std::uint64_t nowMs) {
    return startSnapshot(pattern, nowMs);
}

bool PatternEngine::start(PatternId id, const AppState& state, std::uint64_t nowMs) {
    const Pattern* pattern = state.pattern(id);
    return pattern != nullptr && startSnapshot(*pattern, nowMs);
}

bool PatternEngine::start(PatternId id, const AppState& state) {
    return start(id, state, readClock());
}

std::uint64_t PatternEngine::addDuration(std::uint64_t deadline,
                                          std::uint8_t seconds) noexcept {
    const std::uint64_t duration = static_cast<std::uint64_t>(seconds) * kMillisecondsPerSecond;
    if (deadline > std::numeric_limits<std::uint64_t>::max() - duration) {
        return std::numeric_limits<std::uint64_t>::max();
    }
    return deadline + duration;
}

bool PatternEngine::startSnapshot(const Pattern& pattern, std::uint64_t nowMs) {
    if (!validPattern(pattern)) {
        return false;
    }
    if (active_) {
        finishActive();
    }
    activePattern_ = pattern;
    active_ = true;
    phase_ = 0;
    deadlineMs_ = 0;
    outputOn_ = false;
    hasUpdateTime_ = true;
    lastUpdateMs_ = nowMs;

    std::size_t firstActivePhase = 0;
    while (firstActivePhase < pattern.phaseCount &&
           pattern.phases[firstActivePhase] == 0) {
        ++firstActivePhase;
    }
    if (firstActivePhase == pattern.phaseCount) {
        finishActive();
        return true;
    }

    phase_ = static_cast<std::uint8_t>(firstActivePhase);
    emit(pattern.phaseIsOn(firstActivePhase));
    deadlineMs_ = addDuration(nowMs, pattern.phases[firstActivePhase]);
    return true;
}

void PatternEngine::emit(bool on) noexcept {
    // The engine has one physical output by design.  Reserved GPIO23 is never
    // passed to an output sink, even if a caller supplies an arbitrary ID.
    outputOn_ = on;
    lastOutputRelay_ = RelayId::Main;
    if (output_) {
        output_(RelayId::Main, on);
    } else if (simpleOutput_) {
        simpleOutput_(on);
    }
}

void PatternEngine::finishActive() noexcept {
    if (active_ && outputOn_) {
        emit(false);
    }
    active_ = false;
    phase_ = kNoPhase;
    deadlineMs_ = 0;
    outputOn_ = false;
}

void PatternEngine::pump(std::uint64_t nowMs) {
    // FIFO order is intentional.  A future head blocks later requests rather
    // than reordering a user's schedule.
    while (!active_ && queueSize_ != 0 && queue_[queueHead_].startAtMs <= nowMs) {
        const Request request = queue_[queueHead_];
        queueHead_ = (queueHead_ + 1) % kQueueCapacity;
        --queueSize_;
        (void)startSnapshot(request.pattern, nowMs);
    }
}

bool PatternEngine::update(std::uint64_t nowMs) {
    if (hasUpdateTime_ && nowMs < lastUpdateMs_) {
        // A clock regression is unsafe for an active relay.  Stop the sequence
        // instead of leaving the last output energized indefinitely.
        const bool changed = active_ || outputOn_;
        finishActive();
        return changed;
    }
    hasUpdateTime_ = true;
    lastUpdateMs_ = nowMs;
    bool changed = false;

    if (active_) {
        // Deadlines are absolute.  A delayed poll walks the finite phase list
        // and cannot accumulate delay or schedule a phase in the past.
        while (active_ && nowMs >= deadlineMs_) {
            if (phase_ + 1u >= activePattern_.phaseCount) {
                finishActive();
                changed = true;
                break;
            }
            ++phase_;
            emit(activePattern_.phaseIsOn(phase_));
            deadlineMs_ = addDuration(deadlineMs_, activePattern_.phases[phase_]);
            changed = true;
        }
    }

    if (!active_ && queueSize_ != 0) {
        const std::size_t before = queueSize_;
        pump(nowMs);
        changed = changed || before != queueSize_ || active_;
    }
    return changed;
}

bool PatternEngine::update() {
    if (clockInterface_ == nullptr && !clock_) {
        return false;
    }
    return update(readClock());
}

void PatternEngine::stop(std::uint64_t nowMs) {
    if (hasUpdateTime_ && nowMs < lastUpdateMs_) {
        // A bad sample must not prevent the safety turn-off.
        finishActive();
        return;
    }
    hasUpdateTime_ = true;
    lastUpdateMs_ = nowMs;
    finishActive();
}

void PatternEngine::stop() {
    if (clockInterface_ != nullptr || clock_) {
        stop(readClock());
    } else {
        stop(lastUpdateMs_);
    }
}

void PatternEngine::cancelAll() noexcept {
    queueHead_ = 0;
    queueSize_ = 0;
}

} // namespace timbre_core