/*
 * @file session_plugin.cpp
 * @brief Session plugin: conversation message history management with save/load.
 * 会话插件：对话消息历史管理，支持保存/加载。
 * Copyright (c) 2026 dstalk contributors. GPLv3.
 */

// plugin-session: 会话管理服务插件 / Session management service plugin
// 提供 dstalk_session_service_t vtable 实现 / Provides dstalk_session_service_t vtable implementation
// 依赖: file_io (save/load 需要文件操作) / Depends on: file_io (save/load needs file operations)
#include "dstalk/dstalk_host.h"
#include "dstalk/dstalk_types.h"
#include "dstalk/dstalk_services.h"

#include <boost/json.hpp>
#include <boost/json/src.hpp>

#include <algorithm>
#include <atomic>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <exception>
#include <filesystem>
#include <mutex>
#include <string>
#include <utility>
#include <vector>

namespace json = boost::json;

// ============================================================
// 内部 C++ 数据结构 / Internal C++ data structures
// ============================================================

// W14.3: g_host / g_file_io 使用 atomic 指针，写入 acquire/release，读取无锁 / g_host / g_file_io use atomic pointers, write with acquire/release, read lock-free
static std::atomic<const dstalk_host_api_t*> g_host{nullptr};
static std::atomic<const dstalk_file_io_service_t*> g_file_io{nullptr};

// 内部消息结构（C++ 易用，外部暴露 C struct） / Internal message struct (C++ friendly, externally exposed as C struct)
struct InternalMessage {
    std::string role;
    std::string content;
    std::string tool_call_id;
    std::string tool_calls_json;
};

// 会话历史 + 缓存 —— W14.3: mutex 保护读写 / Session history + cache — W14.3: mutex protects read/write
static std::vector<InternalMessage> g_history;
static std::vector<dstalk_message_t> g_cached_history;
static std::mutex g_session_mutex;

// ============================================================
// Token 计数工具（内联，避免硬依赖 context 头文件） / Token counting utilities (inline, avoids hard dep on context headers)
// ============================================================

// 如果字节是 ASCII (0x00–0x7F) 则返回 true / Returns true if the byte is ASCII (0x00–0x7F).
static bool is_ascii(unsigned char c) { return c < 0x80; }

// 启发式判断：如果字节起始一个 UTF-8 CJK 统一表意文字 (0xE4–0xE9) 则返回 true / Heuristic: returns true if the byte starts a CJK Unified Ideograph in UTF-8 (0xE4–0xE9).
static bool starts_cjk(unsigned char c) {
    return c >= 0xE4 && c <= 0xE9;
}

// 使用启发式 UTF-8 字节计数估算单条消息的 token 数 / Estimate token count for a single message using heuristic UTF-8 byte counting.
static size_t count_tokens_one(const std::string& text) {
    size_t ascii_chars   = 0;
    size_t chinese_chars = 0;
    size_t other_chars   = 0;

    size_t i = 0;
    while (i < text.size()) {
        unsigned char c = static_cast<unsigned char>(text[i]);

        if (is_ascii(c)) {
            ascii_chars++;
            i += 1;
        } else if (starts_cjk(c)) {
            chinese_chars++;
            i += 3;
        } else if (c >= 0xC0 && c < 0xE0) {
            other_chars++;
            i += 2;
        } else if (c >= 0xE0 && c < 0xF0) {
            other_chars++;
            i += 3;
        } else if (c >= 0xF0 && c < 0xF8) {
            other_chars++;
            i += 4;
        } else {
            other_chars++;
            i += 1;
        }
    }

    size_t content_tokens = (ascii_chars / 4) + (chinese_chars / 2) + (other_chars / 3);
    return content_tokens + 4; // +4 每条消息开销 / +4 per message overhead
}

// 估算所有消息的总 token 数 / Estimate total token count across all messages.
static size_t count_tokens_all(const std::vector<InternalMessage>& msgs) {
    size_t total = 0;
    for (const auto& m : msgs) {
        total += count_tokens_one(m.content);
    }
    return total;
}

// ============================================================
// 辅助：刷新 C 缓存数组（调用方需持有 g_session_mutex） / Helper: rebuild C cached array (caller must hold g_session_mutex)
// ============================================================

// 从内部消息 vector 重建 C 兼容的缓存历史数组。调用方必须持有 g_session_mutex / Rebuild the C-compatible cached history array from the internal message vector.
// Caller must hold g_session_mutex.
static void rebuild_cached_history_locked() {
    const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);

    // 释放旧的字符串 / Free old strings
    for (auto& m : g_cached_history) {
        if (m.role)           { host->free(const_cast<char*>(m.role)); }
        if (m.content)        { host->free(const_cast<char*>(m.content)); }
        if (m.tool_call_id)   { host->free(const_cast<char*>(m.tool_call_id)); }
        if (m.tool_calls_json){ host->free(const_cast<char*>(m.tool_calls_json)); }
    }
    g_cached_history.clear();

    // 重建 / Rebuild
    g_cached_history.reserve(g_history.size());
    for (const auto& im : g_history) {
        dstalk_message_t cm;
        cm.role            = im.role.empty()            ? nullptr : host->strdup(im.role.c_str());
        cm.content         = im.content.empty()         ? nullptr : host->strdup(im.content.c_str());
        cm.tool_call_id    = im.tool_call_id.empty()    ? nullptr : host->strdup(im.tool_call_id.c_str());
        cm.tool_calls_json = im.tool_calls_json.empty() ? nullptr : host->strdup(im.tool_calls_json.c_str());
        g_cached_history.push_back(cm);
    }
}

// ============================================================
// Session 服务 vtable 实现 (W14.3: try/catch + mutex) / Session service vtable implementation (W14.3: try/catch + mutex)
// ============================================================

// 向对话历史追加一条消息 / Append a message to the conversation history.
static void session_add(const dstalk_message_t* msg) {
    try {
        if (!msg) return;
        InternalMessage im;
        if (msg->role)            im.role            = msg->role;
        if (msg->content)         im.content         = msg->content;
        if (msg->tool_call_id)    im.tool_call_id    = msg->tool_call_id;
        if (msg->tool_calls_json) im.tool_calls_json = msg->tool_calls_json;

        std::lock_guard<std::mutex> lock(g_session_mutex);
        g_history.push_back(std::move(im));
    } catch (const std::exception& e) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_add: %s", e.what());
    } catch (...) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_add: unknown exception");
    }
}

// 清空对话历史中的所有消息 / Clear all messages from the conversation history.
static void session_clear() {
    std::lock_guard<std::mutex> lock(g_session_mutex);
    g_history.clear();
}

// 将当前对话历史序列化为 JSON 行文件并保存到 path / Serialize the current conversation history to a JSON lines file at `path`.
static int session_save(const char* path) {
    try {
        if (!path) return -1;

        const dstalk_file_io_service_t* fio = g_file_io.load(std::memory_order_acquire);
        if (!fio) return -1;

        std::string data;
        {
            std::lock_guard<std::mutex> lock(g_session_mutex);
            for (const auto& m : g_history) {
                json::object entry;
                entry["role"]    = m.role;
                entry["content"] = m.content;
                if (!m.tool_call_id.empty())
                    entry["tool_call_id"] = m.tool_call_id;
                if (!m.tool_calls_json.empty())
                    entry["tool_calls_json"] = m.tool_calls_json;
                data += json::serialize(entry);
                data += '\n';
            }
        }
        return fio->write(path, data.c_str());
    } catch (const std::exception& e) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_save: %s", e.what());
        return -1;
    } catch (...) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_save: unknown exception");
        return -1;
    }
}

// 从 JSON 行文件中加载对话历史，替换当前历史 / Load conversation history from a JSON lines file at `path`, replacing current history.
static int session_load(const char* path) {
    try {
        if (!path) return -1;

        const dstalk_file_io_service_t* fio = g_file_io.load(std::memory_order_acquire);
        if (!fio) return -1;

        char* content = nullptr;
        int ret = fio->read(path, &content);
        if (ret != 0 || !content) return -1;

        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        std::string data(content);
        host->free(content);

        std::vector<InternalMessage> parsed;
        size_t pos = 0;
        while (pos < data.size()) {
            size_t nl = data.find('\n', pos);
            std::string line = (nl != std::string::npos)
                ? data.substr(pos, nl - pos) : data.substr(pos);
            pos = (nl != std::string::npos) ? nl + 1 : data.size();
            if (line.empty()) continue;

            auto obj = json::parse(line).as_object();
            auto* role_j = obj.if_contains("role");
            auto* content_j = obj.if_contains("content");
            if (role_j && content_j && role_j->is_string() && content_j->is_string()) {
                InternalMessage im;
                im.role    = json::value_to<std::string>(*role_j);
                im.content = json::value_to<std::string>(*content_j);
                auto* tci = obj.if_contains("tool_call_id");
                if (tci && tci->is_string())
                    im.tool_call_id = json::value_to<std::string>(*tci);
                auto* tcj = obj.if_contains("tool_calls_json");
                if (tcj && tcj->is_string())
                    im.tool_calls_json = json::value_to<std::string>(*tcj);
                parsed.push_back(std::move(im));
            }
        }

        if (parsed.empty()) return -1;

        {
            std::lock_guard<std::mutex> lock(g_session_mutex);
            g_history = std::move(parsed);
        }
        return 0;
    } catch (const std::exception& e) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_load: %s", e.what());
        return -1;
    } catch (...) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_load: unknown exception");
        return -1;
    }
}

// 返回指向缓存 C 消息数组的指针，并将 *out_count 设置为数组大小 / Return a pointer to the cached C-array of messages and set *out_count to its size.
static const dstalk_message_t* session_history(int* out_count) {
    try {
        std::lock_guard<std::mutex> lock(g_session_mutex);
        rebuild_cached_history_locked();
        if (out_count) *out_count = static_cast<int>(g_cached_history.size());
        return g_cached_history.empty() ? nullptr : g_cached_history.data();
    } catch (const std::exception& e) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_history: %s", e.what());
        if (out_count) *out_count = 0;
        return nullptr;
    } catch (...) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_history: unknown exception");
        if (out_count) *out_count = 0;
        return nullptr;
    }
}

// 返回当前对话历史的估算 token 数 / Return the estimated token count for the current conversation history.
static int session_token_count() {
    try {
        std::lock_guard<std::mutex> lock(g_session_mutex);
        return static_cast<int>(count_tokens_all(g_history));
    } catch (const std::exception& e) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_token_count: %s", e.what());
        return -1;
    } catch (...) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "session_token_count: unknown exception");
        return -1;
    }
}

static dstalk_session_service_t g_session_service = {
    session_add,
    session_clear,
    session_save,
    session_load,
    session_history,
    session_token_count
};

// ============================================================
// W20.6: 默认会话保存路径（平台标准目录） / Default session save path (platform standard directory)
// ============================================================

// 返回平台特定的默认会话保存路径，根据需要创建目录 / Return the platform-specific default session save path, creating directories as needed.
static std::string get_default_session_path() {
    // W22.5: static 缓存 + mkdir 保障 + 失败 fallback 到当前目录 / static cache + mkdir guarantee + fallback to current dir on failure
    static std::string cached_path = []() -> std::string {
#ifdef _WIN32
        char* buf = nullptr;
        size_t len = 0;
        _dupenv_s(&buf, &len, "APPDATA");
        std::string dir = buf ? std::string(buf) + "/dstalk" : "dstalk";
        free(buf);
#else
        const char* home = std::getenv("HOME");
        std::string dir = home ? std::string(home) + "/.dstalk" : "/tmp/dstalk";
#endif

        std::error_code ec;
        std::filesystem::create_directories(dir, ec);
        if (ec) {
            const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
            if (host) host->log(DSTALK_LOG_WARN,
                "get_default_session_path: cannot mkdir '%s' (%s), fallback to .",
                dir.c_str(), ec.message().c_str());
            return std::string("./session.json");
        }

        return dir + "/session.json";
    }();
    return cached_path;
}

// ============================================================
// 插件生命周期 / Plugin lifecycle
// ============================================================

// 插件初始化：保存主机指针，查询 file_io 依赖，注册 session 服务，
// 并从默认路径自动加载已有会话 / Plugin init: store host pointer, query file_io dependency, register session service,
// and auto-load any existing session from the default path.
static int on_init(const dstalk_host_api_t* host) {
    try {
        g_host.store(host, std::memory_order_release);

        // 查询依赖服务: file_io / Query dependency service: file_io
        void* raw = host->query_service("file_io", 1);
        if (!raw) {
            host->log(DSTALK_LOG_ERROR, "[plugin-session] required service 'file_io' not found");
            return -1;
        }
        g_file_io.store(static_cast<const dstalk_file_io_service_t*>(raw), std::memory_order_release);

        // 注册自身服务 / Register own service
        int ret = host->register_service("session", 1, &g_session_service);
        if (ret != 0) return ret;

        // W20.6: 从默认路径恢复会话（文件不存在则静默失败） / Restore session from default path (silent fail if file missing)
        session_load(get_default_session_path().c_str());

        return 0;
    } catch (const std::exception& e) {
        const dstalk_host_api_t* h = g_host.load(std::memory_order_acquire);
        if (h) h->log(DSTALK_LOG_ERROR, "on_init[session]: %s", e.what());
        return -1;
    } catch (...) {
        const dstalk_host_api_t* h = g_host.load(std::memory_order_acquire);
        if (h) h->log(DSTALK_LOG_ERROR, "on_init[session]: unknown exception");
        return -1;
    }
}

// 插件关闭：自动保存会话到默认路径，失败时回退到当前目录，
// 然后释放缓存历史和清空状态 / Plugin shutdown: auto-save session to default path, fallback to current dir on failure,
// then release cached history and clear state.
static void on_shutdown() {
    try {
        // W20.6: 清空前自动保存到默认路径 / Auto-save to default path before clearing
        // W21.4: 失败告警 + 当前目录 fallback / Failure warning + current dir fallback
        int ret = session_save(get_default_session_path().c_str());
        if (ret != 0) {
            const dstalk_host_api_t* h = g_host.load(std::memory_order_acquire);
            if (h) h->log(DSTALK_LOG_WARN, "on_shutdown[session]: auto-save failed (ret=%d), trying fallback", ret);
            int fret = session_save("./dstalk_session_backup.json");
            if (fret != 0) {
                if (h) h->log(DSTALK_LOG_ERROR, "on_shutdown[session]: fallback also failed (ret=%d), data may be lost", fret);
            }
        }

        std::lock_guard<std::mutex> lock(g_session_mutex);
        rebuild_cached_history_locked();
        g_cached_history.clear();
        g_history.clear();
    } catch (const std::exception& e) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "on_shutdown[session]: %s", e.what());
    } catch (...) {
        const dstalk_host_api_t* host = g_host.load(std::memory_order_acquire);
        if (host) host->log(DSTALK_LOG_ERROR, "on_shutdown[session]: unknown exception");
    }
    g_file_io.store(nullptr, std::memory_order_release);
    g_host.store(nullptr, std::memory_order_release);
}

static dstalk_plugin_info_t g_info = {
    "session",
    "1.0.0",
    "Session management plugin with save/load support    / 支持保存/加载的会话管理插件",
    DSTALK_API_VERSION,
    {"file_io", nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr},
    on_init,
    on_shutdown,
    nullptr
};

// 必须入口点：返回插件描述符给主机 / Mandatory entry point: returns the plugin descriptor to the host.
extern "C" DSTALK_PLUGIN_EXPORT dstalk_plugin_info_t* dstalk_plugin_init(void) {
    return &g_info;
}