#include "vde/brep/incremental_update.h"
#include <algorithm>
#include <queue>
#include <set>

namespace vde::brep {

void IncrementalUpdateEngine::register_node(int node_id, const std::vector<int>& deps) {
    if (caches_.find(node_id) == caches_.end()) {
        caches_[node_id] = NodeCache{};
    }
    deps_[node_id] = deps;
}

void IncrementalUpdateEngine::mark_dirty(int node_id) {
    if (caches_.find(node_id) == caches_.end()) return;
    
    // BFS propagation: mark node and all dependents
    std::queue<int> q;
    q.push(node_id);
    
    while (!q.empty()) {
        int nid = q.front(); q.pop();
        if (caches_[nid].dirty) continue; // already marked
        
        caches_[nid].dirty = true;
        dirty_set_.insert(nid);
        
        // Find all nodes that depend on nid
        for (auto& [other, ndeps] : deps_) {
            if (caches_[other].dirty) continue;
            if (std::find(ndeps.begin(), ndeps.end(), nid) != ndeps.end()) {
                q.push(other);
            }
        }
    }
}

const NodeCache* IncrementalUpdateEngine::get_cache(int node_id) const {
    auto it = caches_.find(node_id);
    if (it != caches_.end() && !it->second.dirty) {
        const_cast<IncrementalUpdateEngine*>(this)->cache_hits_++;
        return &it->second;
    }
    const_cast<IncrementalUpdateEngine*>(this)->cache_misses_++;
    return nullptr;
}

void IncrementalUpdateEngine::invalidate_cache(int node_id) {
    auto it = caches_.find(node_id);
    if (it == caches_.end()) return;

    // Clear cached data but keep the entry
    it->second.model.reset();
    it->second.mesh.reset();
    it->second.bounds.reset();

    // Propagate dirty flag to this node and all downstream
    mark_dirty(node_id);
}

void IncrementalUpdateEngine::clear_all() {
    dirty_set_.clear();
    for (auto& [nid, cache] : caches_) {
        cache = NodeCache{};
        cache.dirty = true;
        dirty_set_.insert(nid);
    }
    cache_hits_ = 0;
    cache_misses_ = 0;
}

int IncrementalUpdateEngine::dirty_count() const {
    return static_cast<int>(dirty_set_.size());
}

double IncrementalUpdateEngine::hit_rate() const {
    int total = cache_hits_ + cache_misses_;
    return total > 0 ? static_cast<double>(cache_hits_) / total : 0.0;
}

std::vector<int> IncrementalUpdateEngine::topological_sort_dirty() {
    std::vector<int> result;
    std::unordered_map<int, int> in_degree;

    for (int nid : dirty_set_) {
        in_degree[nid] = 0;
    }
    for (int nid : dirty_set_) {
        for (int dep : deps_[nid]) {
            if (dirty_set_.count(dep)) {
                in_degree[nid]++;
            }
        }
    }

    std::queue<int> q;
    for (auto& [nid, deg] : in_degree) {
        if (deg == 0) q.push(nid);
    }

    while (!q.empty()) {
        int nid = q.front(); q.pop();
        result.push_back(nid);

        for (auto& [other, other_deps] : deps_) {
            if (!dirty_set_.count(other)) continue;
            if (std::find(other_deps.begin(), other_deps.end(), nid) != other_deps.end()) {
                in_degree[other]--;
                if (in_degree[other] == 0) q.push(other);
            }
        }
    }

    return result;
}

int IncrementalUpdateEngine::incremental_rebuild(
    FeatureHistory&, RebuildCallback callback)
{
    int rebuilt = 0;
    auto sorted = topological_sort_dirty();

    for (int nid : sorted) {
        auto& cache = caches_[nid];
        try {
            if (callback) {
                BrepModel dummy;
                callback(nid, dummy);
            }
            cache.dirty = false;
            dirty_set_.erase(nid);
            rebuilt++;
        } catch (...) {}
    }

    return rebuilt;
}

int IncrementalUpdateEngine::full_rebuild(
    FeatureHistory& history, RebuildCallback callback)
{
    clear_all();
    return incremental_rebuild(history, callback);
}

} // namespace vde::brep