// This file Copyright © 2007-2022 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.

#include <algorithm>
#include <cerrno>
#include <optional>
#include <vector>

#include <fmt/core.h>

#include "transmission.h"

#include "cache.h" /* tr_cacheReadBlock() */
#include "crypto-utils.h"
#include "error.h"
#include "file.h"
#include "inout.h"
#include "log.h"
#include "stats.h" /* tr_statsFileCreated() */
#include "torrent.h"
#include "tr-assert.h"
#include "utils.h"

using namespace std::literals;

namespace
{

bool readEntireBuf(tr_sys_file_t fd, uint64_t file_offset, uint8_t* buf, uint64_t buflen, tr_error** error)
{
    while (buflen > 0)
    {
        auto n_read = uint64_t{};

        if (!tr_sys_file_read_at(fd, buf, buflen, file_offset, &n_read, error))
        {
            return false;
        }

        buf += n_read;
        buflen -= n_read;
        file_offset += n_read;
    }

    return true;
}

bool writeEntireBuf(tr_sys_file_t fd, uint64_t file_offset, uint8_t const* buf, uint64_t buflen, tr_error** error)
{
    while (buflen > 0)
    {
        auto n_written = uint64_t{};

        if (!tr_sys_file_write_at(fd, buf, buflen, file_offset, &n_written, error))
        {
            return false;
        }

        buf += n_written;
        buflen -= n_written;
        file_offset += n_written;
    }

    return true;
}

enum class IoMode
{
    Read,
    Prefetch,
    Write
};

/* returns 0 on success, or an errno on failure */
int readOrWriteBytes(
    tr_session* session,
    tr_torrent* tor,
    IoMode io_mode,
    tr_file_index_t file_index,
    uint64_t file_offset,
    uint8_t* buf,
    size_t buflen)
{
    TR_ASSERT(file_index < tor->fileCount());

    int err = 0;
    bool const do_write = io_mode == IoMode::Write;
    auto const file_size = tor->fileSize(file_index);
    TR_ASSERT(file_size == 0 || file_offset < file_size);
    TR_ASSERT(file_offset + buflen <= file_size);

    if (file_size == 0)
    {
        return 0;
    }

    /***
    ****  Find the fd
    ***/

    auto fd = session->openFiles().get(tor->uniqueId, file_index, do_write);
    if (!fd) // it's not cached, so open/create it now
    {
        auto found = tor->findFile(file_index); // see if the file exists...
        if (!found)
        {
            if (!do_write)
            {
                err = ENOENT;
            }

            // We didn't find the file that we want to write to.
            // Let's figure out where it goes so that we can create it.
            auto const base = tor->currentDir();
            auto const suffix = tor->session->isIncompleteFileNamingEnabled ? tr_torrent_files::PartialFileSuffix : ""sv;
            found = { {}, tr_pathbuf{ base, "/"sv, tor->fileSubpath(file_index), suffix }, std::size(base) };
        }

        if (err == 0)
        {
            // open (and maybe create) the file
            auto const prealloc = (!do_write || !tor->fileIsWanted(file_index)) ? TR_PREALLOCATE_NONE :
                                                                                  tor->session->preallocationMode;

            fd = session->openFiles().get(tor->uniqueId, file_index, do_write, found->filename(), prealloc, file_size);
            if (!fd)
            {
                err = errno;
                tr_logAddErrorTor(
                    tor,
                    fmt::format(
                        _("Couldn't get '{path}': {error} ({error_code})"),
                        fmt::arg("path", found->filename()),
                        fmt::arg("error", tr_strerror(err)),
                        fmt::arg("error_code", err)));
            }
            else if (do_write)
            {
                /* make a note that we just created a file */
                tr_statsFileCreated(tor->session);
            }
        }
    }

    if (err != 0)
    {
        return err;
    }

    /***
    ****  Use the fd
    ***/

    tr_error* error = nullptr;

    switch (io_mode)
    {
    case IoMode::Read:
        if (!readEntireBuf(*fd, file_offset, buf, buflen, &error))
        {
            err = error->code;
            tr_logAddErrorTor(
                tor,
                fmt::format(
                    _("Couldn't read '{path}': {error} ({error_code})"),
                    fmt::arg("path", tor->fileSubpath(file_index)),
                    fmt::arg("error", error->message),
                    fmt::arg("error_code", error->code)));
            tr_error_free(error);
        }
        break;

    case IoMode::Write:
        if (!writeEntireBuf(*fd, file_offset, buf, buflen, &error))
        {
            err = error->code;
            tr_logAddErrorTor(
                tor,
                fmt::format(
                    _("Couldn't save '{path}': {error} ({error_code})"),
                    fmt::arg("path", tor->fileSubpath(file_index)),
                    fmt::arg("error", error->message),
                    fmt::arg("error_code", error->code)));
            tr_error_free(error);
        }
        break;

    case IoMode::Prefetch:
        tr_sys_file_advise(*fd, file_offset, buflen, TR_SYS_FILE_ADVICE_WILL_NEED);
        break;
    }

    return err;
}

/* returns 0 on success, or an errno on failure */
int readOrWritePiece(tr_torrent* tor, IoMode io_mode, tr_block_info::Location loc, uint8_t* buf, size_t buflen)
{
    int err = 0;

    if (loc.piece >= tor->pieceCount())
    {
        return EINVAL;
    }

    auto [file_index, file_offset] = tor->fileOffset(loc);

    while (buflen != 0 && err == 0)
    {
        uint64_t const bytes_this_pass = std::min(uint64_t{ buflen }, uint64_t{ tor->fileSize(file_index) - file_offset });

        err = readOrWriteBytes(tor->session, tor, io_mode, file_index, file_offset, buf, bytes_this_pass);
        buf += bytes_this_pass;
        buflen -= bytes_this_pass;

        if (err != 0 && io_mode == IoMode::Write && tor->error != TR_STAT_LOCAL_ERROR)
        {
            auto const path = tr_pathbuf{ tor->downloadDir(), '/', tor->fileSubpath(file_index) };
            tor->setLocalError(fmt::format(FMT_STRING("{:s} ({:s})"), tr_strerror(err), path));
        }

        ++file_index;
        file_offset = 0;
    }

    return err;
}

std::optional<tr_sha1_digest_t> recalculateHash(tr_torrent* tor, tr_piece_index_t piece)
{
    TR_ASSERT(tor != nullptr);
    TR_ASSERT(piece < tor->pieceCount());

    auto bytes_left = size_t(tor->pieceSize(piece));
    auto loc = tor->pieceLoc(piece);
    tr_ioPrefetch(tor, loc, bytes_left);

    auto sha = tr_sha1_init();
    auto buffer = std::vector<uint8_t>(tr_block_info::BlockSize);
    while (bytes_left != 0)
    {
        size_t const len = std::min(bytes_left, std::size(buffer));
        if (auto const success = tr_cacheReadBlock(tor->session->cache, tor, loc, len, std::data(buffer)) == 0; !success)
        {
            tr_sha1_final(sha);
            return {};
        }

        tr_sha1_update(sha, std::data(buffer), len);
        loc = tor->byteLoc(loc.byte + len);
        bytes_left -= len;
    }

    return tr_sha1_final(sha);
}

} // namespace

int tr_ioRead(tr_torrent* tor, tr_block_info::Location loc, uint32_t len, uint8_t* buf)
{
    return readOrWritePiece(tor, IoMode::Read, loc, buf, len);
}

int tr_ioPrefetch(tr_torrent* tor, tr_block_info::Location loc, uint32_t len)
{
    return readOrWritePiece(tor, IoMode::Prefetch, loc, nullptr, len);
}

int tr_ioWrite(tr_torrent* tor, tr_block_info::Location loc, uint32_t len, uint8_t const* buf)
{
    return readOrWritePiece(tor, IoMode::Write, loc, (uint8_t*)buf, len);
}

bool tr_ioTestPiece(tr_torrent* tor, tr_piece_index_t piece)
{
    auto const hash = recalculateHash(tor, piece);
    return hash && *hash == tor->pieceHash(piece);
}