/*
    Copyright© 2021 John Sennesael

    UsenetSearch is Free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    UsenetSearch is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with UsenetSearch.  If not, see <https://www.gnu.org/licenses/>.
*/

#include <iomanip>
#include <iostream>
#include <chrono>
#include <filesystem>
#include <fstream>
#include <string>
#include <thread>
#include <vector>

#include "usenetsearch/Application.h"
#include "usenetsearch/StringUtils.h"
#include "usenetsearch/UsenetClient.h"
#include "usenetsearch/ScopeExit.h"
#include "usenetsearch/Serialize.h"

#include "usenetsearch/Database.h"

namespace usenetsearch {

// Database class --------------------------------------------------------------

Database::Database(Application& app): m_app(app)
{
}

Database::~Database()
{
    m_newsGroupFileIO.Close();
}

std::unique_ptr<NntpListEntry> Database::FindNntpEntry(
    const std::string& subject)
{
    OpenNewsGroupFile();
    ScopeExit closeNewsGroupFile([&](){ m_newsGroupFileIO.Close(); });
    const std::uint64_t numGroups = m_newsGroupFileIO.ReadInt64();
    std::unique_ptr<NntpListEntry> result = nullptr;
    for (std::uint64_t n = 0; n != numGroups; ++n)
    {
        NntpListEntry entry;
        m_newsGroupFileIO >> entry;
        if (entry.name == subject)
        {
            result = std::make_unique<NntpListEntry>(entry);
            break;
        }
    }
    return result;
}

std::uint32_t Database::GetLastIndexedArticle(std::uint64_t newsgroupID)
{
    OpenNewsGroupFile();
    ScopeExit closeNewsGroupFile([&](){ m_newsGroupFileIO.Close(); });
    const std::uint64_t numGroups = m_newsGroupFileIO.ReadInt64();
    for (std::uint64_t n = 0; n != numGroups; ++n)
    {
        NntpListEntry entry;
        m_newsGroupFileIO >> entry;
        if (entry.id == newsgroupID)
        {
            return entry.lastIndexedArticle;
        }
    }
    return 0;
}

std::filesystem::path Database::GetTokenFilePath(
    const std::string& token,
    bool mkdirs
)
{
    const std::string md5 = StringHash(token);
    const std::string tok1 = md5.substr(0, 2);
    const std::string tok2 = md5.substr(2, 1);
    const std::string tok3 = md5.substr(3, 2);
    const std::filesystem::path groupPath = m_databasePath / "tokens" / tok1
        / tok2;
    if (mkdirs)
    {
        if (!std::filesystem::exists(groupPath))
        {
            std::filesystem::create_directories(groupPath);
        }
    }
    const auto groupFile = tok3 + ".db";
    return groupPath / groupFile;
}

std::uint64_t Database::GetUniqueNntpEntryId(
        const std::vector<NntpListEntry>& list) const
{
    std::uint64_t result{0};
    for (auto& entry: list)
    {
        if (result <= entry.id)
        {
            result = entry.id + 1;
        }
    }
    return result;
}

void Database::MaxTreeDepth(std::uint8_t depth)
{
    m_maxTreeDepth = depth;
}

std::unique_ptr<std::vector<NntpListEntry>> Database::LoadNewsgroupList()
{
    OpenNewsGroupFile();
    ScopeExit closeNewsGroupFile([&](){ m_newsGroupFileIO.Close(); });
    const size_t newsGroupCount = m_newsGroupFileIO.ReadInt64();

    auto result = std::make_unique<std::vector<NntpListEntry>>();
    for (size_t numLoaded = 0; numLoaded != newsGroupCount; ++numLoaded)
    {
        NntpListEntry entry;
        m_newsGroupFileIO >> entry;
        result->emplace_back(entry);
    }
    return result;
}

void Database::Open(std::filesystem::path dbPath)
{
    m_databasePath = dbPath;
    if (!std::filesystem::exists(dbPath))
    {
        std::filesystem::create_directory(dbPath);
    }
}

void Database::OpenNewsGroupFile()
{
    if (m_newsGroupFileIO.IsOpen())
    {
        m_newsGroupFileIO.Seek(sizeof(m_databaseVersion), std::ios_base::beg);
        return;
    }
    const std::filesystem::path newsGroupFilePath =
        m_databasePath / "newsgroups.db";
    const bool exists = std::filesystem::exists(newsGroupFilePath);
    m_newsGroupFileIO.Open(newsGroupFilePath);
    if (exists)
    {
        const std::uint64_t ver = m_newsGroupFileIO.ReadInt64();
        if (ver != m_databaseVersion)
        {
            throw DatabaseException(EBADF,
                std::string{"Mismatching newgroup file database version:"}
                + " have: " + std::to_string(ver) + " - want: "
                + std::to_string(m_databaseVersion)
            );
        }
    }
    else
    {
        m_newsGroupFileIO << m_databaseVersion;
        m_newsGroupFileIO << std::uint64_t{0}; // newsgroup count.
        m_newsGroupFileIO.Seek(sizeof(m_databaseVersion), std::ios_base::beg);
    }
}

void Database::ParseTokenFile(
    const std::filesystem::path& dbFile,
    std::function<void(const ArticleEntry& entry)> onParse)
{
    if (!std::filesystem::exists(dbFile))
    {
        throw DatabaseException(
            ENOTFOUND,
            "File does not exist: " + dbFile.string()
        );
    }
    SerializableFile io;
    io.Open(dbFile);
    const std::uint64_t tokenCount = io.ReadInt64();
    for (std::uint64_t i = 0; i != tokenCount; ++i)
    {
        ArticleEntry token;
        io >> token;
        onParse(token);
    }
}

void Database::SetLastIndexedArticle(
    std::uint64_t newsgroupID,
    std::int32_t articleID)
{
    auto outItems = LoadNewsgroupList();
    bool found{false};
    if (outItems)
    {
        for (auto& entry: *outItems)
        {
            if (entry.id == newsgroupID)
            {
                entry.lastIndexedArticle = articleID;
                found = true;
            }
        }
    }
    if (!found)
    {
        throw DatabaseException(EINVAL,
            "Attempt to update newsgroup not found in database - id: "
            + std::to_string(newsgroupID));
    }
    UpdateNewsgroupList(*outItems);
}

void Database::SaveSearchTokens(
    std::uint64_t newsgroupID,
    std::uint64_t articleID,
    const std::string& searchString)
{
    const std::string sstr(searchString);
    StringTreeOperation(
        sstr,
        " ",
        m_maxTreeDepth,
        [&](const std::string& subToken, const std::string& str){
            const std::string tok = m_app.GetFilter().ProcessToken(
                subToken,
                str
            );
            if (tok.empty()) return;
            SaveToken(tok, newsgroupID, articleID);
        }
    );
}

bool Database::HasToken(
    const std::string& subtoken,
    std::uint64_t newsgroupID,
    std::uint32_t articleID)
{
    if (subtoken.empty()) return false;
    const std::filesystem::path path = GetTokenFilePath(subtoken, true);
    if (!std::filesystem::exists(path)) return false;
    SerializableFile io;
    io.Open(path);
    const std::uint64_t tokenCount = io.ReadInt64();
    for (std::uint64_t i = 0; i != tokenCount; ++i)
    {
        ArticleEntry token;
        io >> token;
        if (token.newsgroupID == newsgroupID)
        {
            if (token.articleID == articleID) return true;
        }
    }
    return false;
}

std::unique_ptr<std::vector<ArticleEntry>> Database::LoadTokens(
    const std::filesystem::path dbFile,
    const std::string& subtoken)
{
    auto result = std::make_unique<std::vector<ArticleEntry>>();
    if (!std::filesystem::exists(dbFile)) return result;
    SerializableFile io;
    io.Open(dbFile);
    const std::uint64_t tokenCount = io.ReadInt64();
    const auto tokenHash = StringHashBytes(subtoken);
    for (std::uint64_t ntok = 0; ntok != tokenCount; ++ntok)
    {
        ArticleEntry entry{};
        io >> entry;
        if (entry.hash != tokenHash) continue;
        result->emplace_back(entry);
    }
    return result;
}

void Database::SaveToken(
    const std::string& subtoken,
    std::uint64_t newsgroupID,
    std::uint32_t articleID)
{
    if (subtoken.empty()) return;
    const std::filesystem::path path = GetTokenFilePath(subtoken, true);
    const bool exists = std::filesystem::exists(path);

    SerializableFile io;
    io.Open(path);
    ArticleEntry token{};
    token.articleID = articleID;
    token.newsgroupID = newsgroupID;
    token.hash = StringHashBytes(subtoken);
    if (exists)
    {
        // Read token count and increment it by one, and write it back.
        const std::uint64_t tokenCount = io.ReadInt64() + 1;
        io.Seek(0, std::ios_base::beg);
        io << tokenCount;
        // Now seek back to the end of the file to append our token entry.
        io.Seek(0, std::ios_base::end);
    }
    else
    {
        // A new file just has a token count of 1 - should already be at pos=0.
        io << std::uint64_t{1};
    }
    // write out token.
#if 0
    std::cout << "Token: " << subtoken << std::endl;
    std::cout << "Saving into file: " << path << std::endl;
    std::cout << "Token hash: " << HashBytesToString(token.hash) << std::endl << std::endl;
#endif
    io << token;
}

std::unique_ptr<std::vector<ArticleEntry>> Database::Search(
    const std::string& searchString)
{
    auto result = std::make_unique<std::vector<ArticleEntry>>();
    // Tokenize the search string.
    std::vector<std::string> searchTokens;
    StringTreeOperation(
        searchString,
        " ",
        m_maxTreeDepth,
        [&searchTokens](const std::string& subToken, const std::string&){
            searchTokens.emplace_back(subToken);
        }
    );
    for (const auto& searchToken: searchTokens)
    {
        const auto path = GetTokenFilePath(searchToken, false);
        const bool exists = std::filesystem::exists(path);
        if (!exists) continue;
        const auto foundTokens = LoadTokens(path, searchToken);
        if (foundTokens->empty()) continue;
        result->insert(result->end(), foundTokens->begin(), foundTokens->end());
        std::cout << std::left << std::setw(searchString.length() + 7)
                  << "token: " + searchToken
                  << std::setw(3) << " | "
                  << std::setw(10)
                  << "db file: " << path.string()
                  << std::setw(3) << " | "
                  << std::setw(9)
                  << "#results: " + std::to_string(foundTokens->size())
                  << std::endl; 
    }
    return result;
}

void Database::UpdateNewsgroupList(std::vector<NntpListEntry>& list)
{
    if (list.size() == 0) return;

    auto outList = LoadNewsgroupList();
    for (auto& entry: list)
    {
        NntpListEntry newEntry(entry);
        bool found{false};
        if (outList)
        {
            std::for_each(
                outList->begin(),
                outList->end(),
                [&entry, &found](NntpListEntry& oldEntry)
                {
                    if (oldEntry.name == entry.name)
                    {
                        // update existing (copy everything but ID & name)
                        found = true;
                        oldEntry.count = entry.count;
                        oldEntry.high = entry.high;
                        oldEntry.lastIndexedArticle = entry.lastIndexedArticle;
                        oldEntry.low = entry.low;
                        oldEntry.status = entry.status;
                    }
                }
            );
        }
        if (found) continue;
        // add new.
        newEntry.id = GetUniqueNntpEntryId(*outList);
        outList->emplace_back(newEntry);
        entry.id = newEntry.id;
    }
    OpenNewsGroupFile();
    ScopeExit closeNewsGroupFile([&](){ m_newsGroupFileIO.Close(); });
    m_newsGroupFileIO << std::uint64_t{outList->size()};
    std::for_each(
        outList->begin(),
        outList->end(),
        [&](const NntpListEntry& e)
        {
            m_newsGroupFileIO << e;
        }
    );
}

} // namespace usenetsearch