// SPDX-License-Identifier: LGPL-3.0-only
// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

module Crafter.Debug:Registry_impl;
import std;
import Crafter.Debug.Core;
import :Registry;

using namespace Crafter::Debug;
using namespace Crafter::Debug::Detail;

namespace {
    std::atomic<std::uint64_t> frame{ 0 };

    // Points kept per sample path, enough for `trace` over a few seconds of
    // frames without an app logging every frame growing without bound.
    constexpr std::size_t sampleHistory = 512;

    bool ValidName(std::string_view name) {
        return !name.empty() && std::ranges::none_of(name, [](char c) { return c == ' ' || c == '\t' || c == '\n' || c == '\r'; });
    }

    // The registered name that `path` starts with, longest first, ending at a
    // step boundary: "bodies" for "bodies[3].pos", not "bod".
    template<class Map>
    auto LongestPrefix(const Map& map, std::string_view path) -> decltype(map.end()) {
        auto best = map.end();
        std::size_t bestLength = 0;
        for (auto it = map.begin(); it != map.end(); ++it) {
            const std::string_view name = it->first;
            if (!path.starts_with(name)) continue;
            if (path.size() > name.size() && path[name.size()] != '.' && path[name.size()] != '[') continue;
            if (name.size() >= bestLength) {
                best = it;
                bestLength = name.size();
            }
        }
        return best;
    }

    std::vector<std::string_view> MemberNames(const Value& object) {
        std::vector<std::string_view> names;
        for (const auto& [key, member] : object.Members()) names.push_back(key);
        return names;
    }

    std::string JoinNames(std::span<const std::string_view> names) {
        std::string joined;
        for (const std::string_view name : names) {
            if (!joined.empty()) joined += ", ";
            joined += name;
        }
        return joined;
    }

    // Follows `rest` (".name" and "[index]" steps) from `root`. `where` names
    // the root in errors. Returns nullptr and sets `error` when a step fails.
    template<class V>
    V* Walk(V& root, std::string_view rest, std::string where, std::string& error) {
        V* current = &root;
        while (!rest.empty()) {
            if (rest.front() == '.') {
                rest.remove_prefix(1);
                const std::size_t end = std::min(rest.find('.'), rest.find('['));
                const std::string_view name = rest.substr(0, end);
                rest.remove_prefix(name.size());
                if (!current->IsObject()) {
                    error = std::format("'{}' is {}, so it has no member '{}'", where, KindName(current->Kind()), name);
                    return nullptr;
                }
                V* next = current->Find(name);
                if (next == nullptr) {
                    const std::vector<std::string_view> names = MemberNames(*current);
                    const auto suggestion = Suggest(name, names);
                    error = suggestion ? std::format("'{}' has no member '{}'; did you mean '{}'?", where, name, *suggestion)
                                       : std::format("'{}' has no member '{}' (members: {})", where, name, JoinNames(names));
                    return nullptr;
                }
                where += '.';
                where += name;
                current = next;
            } else if (rest.front() == '[') {
                const std::size_t close = rest.find(']');
                std::size_t index = 0;
                const std::string_view digits = rest.substr(1, close == std::string_view::npos ? std::string_view::npos : close - 1);
                const auto [end, failure] = std::from_chars(digits.data(), digits.data() + digits.size(), index);
                if (close == std::string_view::npos || failure != std::errc() || end != digits.data() + digits.size()) {
                    error = std::format("'{}' is followed by a malformed index: '{}'", where, rest);
                    return nullptr;
                }
                rest.remove_prefix(close + 1);
                if (!current->IsArray()) {
                    error = std::format("'{}' is {}, not an array", where, KindName(current->Kind()));
                    return nullptr;
                }
                if (index >= current->Size()) {
                    error = std::format("'{}' has {} items, so [{}] is out of range", where, current->Size(), index);
                    return nullptr;
                }
                where += std::format("[{}]", index);
                current = &current->Items()[index];
            } else {
                error = std::format("cannot read '{}' after '{}'", rest, where);
                return nullptr;
            }
        }
        return current;
    }
}

std::uint64_t Crafter::Debug::Detail::CurrentFrame() {
    return frame.load(std::memory_order_relaxed);
}

void Crafter::Debug::Detail::SetFrame(std::uint64_t value) {
    frame.store(value, std::memory_order_relaxed);
}

bool Crafter::Debug::Detail::GlobMatch(std::string_view glob, std::string_view text) {
    std::size_t g = 0;
    std::size_t t = 0;
    std::size_t star = std::string_view::npos;
    std::size_t mark = 0;
    while (t < text.size()) {
        if (g < glob.size() && (glob[g] == '?' || glob[g] == text[t])) {
            ++g;
            ++t;
        } else if (g < glob.size() && glob[g] == '*') {
            star = g++;
            mark = t;
        } else if (star != std::string_view::npos) {
            g = star + 1;
            t = ++mark;
        } else {
            return false;
        }
    }
    while (g < glob.size() && glob[g] == '*') ++g;
    return g == glob.size();
}

std::string Crafter::Debug::Detail::Joined(std::string_view prefix, std::string_view name) {
    if (prefix.empty()) return std::string(name);
    if (name.empty()) return std::string(prefix);
    return std::format("{}.{}", prefix, name);
}

Registry& Registry::Instance() {
    static Registry registry;
    return registry;
}

std::uint64_t Registry::NewOwner() {
    return nextOwner.fetch_add(1, std::memory_order_relaxed);
}

void Registry::AddCommand(CommandEntry entry) {
    if (!ValidName(entry.name)) throw std::invalid_argument(std::format("Crafter.Debug: '{}' is not a command name: it must be non-empty, without whitespace", entry.name));
    std::string name = entry.name;
    std::lock_guard lock(mutex);
    commands.insert_or_assign(std::move(name), std::make_shared<const CommandEntry>(std::move(entry)));
}

void Registry::AddWatch(WatchEntry entry) {
    if (!ValidName(entry.path)) throw std::invalid_argument(std::format("Crafter.Debug: '{}' is not a watch path: it must be non-empty, without whitespace", entry.path));
    std::string path = entry.path;
    std::lock_guard lock(mutex);
    watches.insert_or_assign(std::move(path), std::make_shared<const WatchEntry>(std::move(entry)));
}

void Registry::AddSample(std::string_view path, Value value, std::uint64_t sampleFrame, std::uint64_t owner) {
    std::lock_guard lock(mutex);
    auto found = samples.find(path);
    if (found == samples.end()) found = samples.emplace(std::string(path), Series{}).first;
    Series& series = found->second;
    series.owner = owner;
    series.points.push_back({ sampleFrame, std::move(value) });
    if (series.points.size() > sampleHistory) series.points.pop_front();
}

void Registry::RemoveOwner(std::uint64_t owner) {
    std::lock_guard lock(mutex);
    std::erase_if(commands, [&](const auto& item) { return item.second->owner == owner; });
    std::erase_if(watches, [&](const auto& item) { return item.second->owner == owner; });
    std::erase_if(samples, [&](const auto& item) { return item.second.owner == owner; });
}

std::shared_ptr<const CommandEntry> Registry::FindCommand(std::string_view name) const {
    std::lock_guard lock(mutex);
    const auto found = commands.find(name);
    return found == commands.end() ? nullptr : found->second;
}

std::vector<std::shared_ptr<const CommandEntry>> Registry::Commands(std::string_view glob) const {
    std::lock_guard lock(mutex);
    std::vector<std::shared_ptr<const CommandEntry>> matched;
    for (const auto& [name, entry] : commands) {
        if (GlobMatch(glob, name)) matched.push_back(entry);
    }
    return matched;
}

std::vector<std::shared_ptr<const WatchEntry>> Registry::Watches(std::string_view glob) const {
    std::lock_guard lock(mutex);
    std::vector<std::shared_ptr<const WatchEntry>> matched;
    for (const auto& [path, entry] : watches) {
        if (GlobMatch(glob, path)) matched.push_back(entry);
    }
    return matched;
}

std::vector<std::string> Registry::SamplePaths(std::string_view glob) const {
    std::lock_guard lock(mutex);
    std::vector<std::string> matched;
    for (const auto& [path, series] : samples) {
        if (GlobMatch(glob, path)) matched.push_back(path);
    }
    return matched;
}

std::vector<SamplePoint> Registry::SampleHistory(std::string_view path) const {
    std::lock_guard lock(mutex);
    const auto found = samples.find(path);
    if (found == samples.end()) return {};
    return std::vector<SamplePoint>(found->second.points.begin(), found->second.points.end());
}

Resolved Registry::Resolve(std::string_view path) const {
    std::shared_ptr<const WatchEntry> watch;
    std::optional<SamplePoint> latest;
    std::string base;
    {
        std::lock_guard lock(mutex);
        const auto foundWatch = LongestPrefix(watches, path);
        const auto foundSample = LongestPrefix(samples, path);
        const std::size_t watchLength = foundWatch == watches.end() ? 0 : foundWatch->first.size();
        const std::size_t sampleLength = foundSample == samples.end() ? 0 : foundSample->first.size();
        if (foundWatch != watches.end() && watchLength >= sampleLength) {
            watch = foundWatch->second;
            base = foundWatch->first;
        } else if (foundSample != samples.end() && !foundSample->second.points.empty()) {
            latest = foundSample->second.points.back();
            base = foundSample->first;
        }
    }
    if (!watch && !latest) {
        const auto suggestion = SuggestPath(path);
        return { Value(), suggestion ? std::format("no watch or sample '{}'; did you mean '{}'?", path, *suggestion)
                                     : std::format("no watch or sample '{}'; list them with: crafter-debug get '*'", path) };
    }
    Value root = watch ? watch->get() : std::move(latest->value);
    std::string error;
    const Value* reached = Walk(std::as_const(root), path.substr(base.size()), base, error);
    if (reached == nullptr) return { Value(), error };
    return { *reached, {} };
}

std::optional<std::string> Registry::Set(std::string_view path, const Value& value) const {
    std::shared_ptr<const WatchEntry> watch;
    {
        std::lock_guard lock(mutex);
        const auto found = LongestPrefix(watches, path);
        if (found != watches.end()) watch = found->second;
    }
    if (!watch) {
        const auto suggestion = SuggestPath(path);
        return suggestion ? std::format("no watch '{}'; did you mean '{}'?", path, *suggestion) : std::format("no watch '{}'", path);
    }
    if (!watch->set) return std::format("'{}' is read-only", watch->path);
    const std::string_view rest = path.substr(watch->path.size());
    if (rest.empty()) return watch->set(value);
    Value whole = watch->get();
    std::string error;
    Value* part = Walk(whole, rest, watch->path, error);
    if (part == nullptr) return error;
    *part = value;
    return watch->set(whole);
}

std::optional<std::string> Registry::SuggestCommand(std::string_view name) const {
    std::lock_guard lock(mutex);
    std::vector<std::string_view> names;
    for (const auto& [command, entry] : commands) names.push_back(command);
    if (const auto suggestion = Suggest(name, names)) return std::string(*suggestion);
    return std::nullopt;
}

std::optional<std::string> Registry::SuggestPath(std::string_view path) const {
    std::lock_guard lock(mutex);
    std::vector<std::string_view> names;
    for (const auto& [watch, entry] : watches) names.push_back(watch);
    for (const auto& [sample, series] : samples) names.push_back(sample);
    if (const auto suggestion = Suggest(path, names)) return std::string(*suggestion);
    return std::nullopt;
}

Group::Group(std::string prefix) : prefix(std::move(prefix)), owner(Registry::Instance().NewOwner()) {}

Group::~Group() {
    Registry::Instance().RemoveOwner(owner);
}