/*
 * Copyright (c) 2021, Jan de Visser <jan@de-visser.net>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Format.h>
#include <AK/QuickSort.h>
#include <AK/String.h>
#include <LibCore/IODevice.h>
#include <LibSQL/Heap.h>
#include <LibSQL/Serialize.h>
#include <sys/stat.h>
#include <sys/types.h>

namespace SQL {

Heap::Heap(String file_name)
{
    set_name(move(file_name));
    size_t file_size = 0;
    struct stat stat_buffer;
    if (stat(name().characters(), &stat_buffer) != 0) {
        if (errno != ENOENT) {
            perror("stat");
            VERIFY_NOT_REACHED();
        }
    } else {
        file_size = stat_buffer.st_size;
    }
    if (file_size > 0)
        m_next_block = m_end_of_file = file_size / BLOCKSIZE;

    auto file_or_error = Core::File::open(name(), Core::OpenMode::ReadWrite);
    if (file_or_error.is_error()) {
        warnln("Couldn't open '{}': {}", name(), file_or_error.error());
        VERIFY_NOT_REACHED();
    }
    m_file = file_or_error.value();
    if (file_size > 0)
        read_zero_block();
    else
        initialize_zero_block();
}

Result<ByteBuffer, String> Heap::read_block(u32 block)
{
    auto buffer_or_empty = m_write_ahead_log.get(block);
    if (buffer_or_empty.has_value())
        return buffer_or_empty.value();

    VERIFY(block < m_next_block);
    dbgln_if(SQL_DEBUG, "Read heap block {}", block);
    if (!seek_block(block))
        VERIFY_NOT_REACHED();
    auto ret = m_file->read(BLOCKSIZE);
    if (ret.is_empty())
        return String("Could not read block");
    return ret;
}

bool Heap::write_block(u32 block, ByteBuffer& buffer)
{
    VERIFY(block < m_next_block);
    if (!seek_block(block))
        VERIFY_NOT_REACHED();
    dbgln_if(SQL_DEBUG, "Write heap block {} size {}", block, buffer.size());
    VERIFY(buffer.size() <= BLOCKSIZE);
    auto sz = buffer.size();
    if (sz < BLOCKSIZE) {
        buffer.resize(BLOCKSIZE);
        memset(buffer.offset_pointer((int)sz), 0, BLOCKSIZE - sz);
    }
    if (m_file->write(buffer.data(), (int)buffer.size())) {
        if (block == m_end_of_file)
            m_end_of_file++;
        return true;
    }
    return false;
}

bool Heap::seek_block(u32 block)
{
    if (block == m_end_of_file) {
        off_t pos;
        if (!m_file->seek(0, Core::SeekMode::FromEndPosition, &pos)) {
            warnln("Could not seek block {} from file {}, which is at the end of the file", block, name());
            warnln("FD: {} Position: {} error: {}", m_file->fd(), pos, m_file->error_string());
            return false;
        }
    } else if (block > m_end_of_file) {
        warnln("Seeking block {} of file {} which is beyond the end of the file", block, name());
        return false;
    } else {
        if (!m_file->seek(block * BLOCKSIZE)) {
            warnln("Could not seek block {} of file {}. The current size is {} blocks",
                block, name(), m_end_of_file);
            return false;
        }
    }
    return true;
}

u32 Heap::new_record_pointer()
{
    if (m_free_list) {
        auto block_or_error = read_block(m_free_list);
        if (block_or_error.is_error()) {
            warnln("FREE LIST CORRUPTION");
            VERIFY_NOT_REACHED();
        }
        auto new_pointer = m_free_list;
        size_t offset = 0;
        deserialize_from<u32>(block_or_error.value(), offset, m_free_list);
        update_zero_block();
        return new_pointer;
    }
    return m_next_block++;
}

void Heap::flush()
{
    Vector<u32> blocks;
    for (auto& wal_entry : m_write_ahead_log) {
        blocks.append(wal_entry.key);
    }
    quick_sort(blocks);
    for (auto& block : blocks) {
        auto buffer_or_empty = m_write_ahead_log.get(block);
        if (buffer_or_empty->is_empty()) {
            VERIFY_NOT_REACHED();
        }
        dbgln_if(SQL_DEBUG, "Flushing block {} to {}", block, name());
        write_block(block, buffer_or_empty.value());
    }
    m_write_ahead_log.clear();
}

constexpr static const char* FILE_ID = "SerenitySQL ";
constexpr static int VERSION_OFFSET = 12;
constexpr static int SCHEMAS_ROOT_OFFSET = 16;
constexpr static int TABLES_ROOT_OFFSET = 20;
constexpr static int TABLE_COLUMNS_ROOT_OFFSET = 24;
constexpr static int FREE_LIST_OFFSET = 28;
constexpr static int USER_VALUES_OFFSET = 32;

void Heap::read_zero_block()
{
    char file_id[256];
    auto bytes_or_error = read_block(0);
    if (bytes_or_error.is_error())
        VERIFY_NOT_REACHED();
    auto buffer = bytes_or_error.value();
    memcpy(file_id, buffer.offset_pointer(0), strlen(FILE_ID));
    file_id[strlen(FILE_ID)] = 0;
    if (strncmp(file_id, FILE_ID, strlen(FILE_ID)) != 0) {
        warnln("Corrupt zero page in {}", name());
        VERIFY_NOT_REACHED();
    }
    dbgln_if(SQL_DEBUG, "Read zero block from {}", name());
    memcpy(&m_version, buffer.offset_pointer(VERSION_OFFSET), sizeof(u32));
    dbgln_if(SQL_DEBUG, "Version: {}.{}", (m_version & 0xFFFF0000) >> 16, (m_version & 0x0000FFFF));
    memcpy(&m_schemas_root, buffer.offset_pointer(SCHEMAS_ROOT_OFFSET), sizeof(u32));
    dbgln_if(SQL_DEBUG, "Schemas root node: {}", m_tables_root);
    memcpy(&m_tables_root, buffer.offset_pointer(TABLES_ROOT_OFFSET), sizeof(u32));
    dbgln_if(SQL_DEBUG, "Tables root node: {}", m_tables_root);
    memcpy(&m_table_columns_root, buffer.offset_pointer(TABLE_COLUMNS_ROOT_OFFSET), sizeof(u32));
    dbgln_if(SQL_DEBUG, "Table columns root node: {}", m_table_columns_root);
    memcpy(&m_free_list, buffer.offset_pointer(FREE_LIST_OFFSET), sizeof(u32));
    dbgln_if(SQL_DEBUG, "Free list: {}", m_free_list);
    memcpy(m_user_values.data(), buffer.offset_pointer(USER_VALUES_OFFSET), m_user_values.size() * sizeof(u32));
    for (auto ix = 0u; ix < m_user_values.size(); ix++) {
        if (m_user_values[ix]) {
            dbgln_if(SQL_DEBUG, "User value {}: {}", ix, m_user_values[ix]);
        }
    }
}

void Heap::update_zero_block()
{
    dbgln_if(SQL_DEBUG, "Write zero block to {}", name());
    dbgln_if(SQL_DEBUG, "Version: {}.{}", (m_version & 0xFFFF0000) >> 16, (m_version & 0x0000FFFF));
    dbgln_if(SQL_DEBUG, "Schemas root node: {}", m_schemas_root);
    dbgln_if(SQL_DEBUG, "Tables root node: {}", m_tables_root);
    dbgln_if(SQL_DEBUG, "Table Columns root node: {}", m_table_columns_root);
    dbgln_if(SQL_DEBUG, "Free list: {}", m_free_list);
    for (auto ix = 0u; ix < m_user_values.size(); ix++) {
        if (m_user_values[ix]) {
            dbgln_if(SQL_DEBUG, "User value {}: {}", ix, m_user_values[ix]);
        }
    }

    auto buffer = ByteBuffer::create_zeroed(BLOCKSIZE);
    buffer.overwrite(0, FILE_ID, strlen(FILE_ID));
    buffer.overwrite(VERSION_OFFSET, &m_version, sizeof(u32));
    buffer.overwrite(SCHEMAS_ROOT_OFFSET, &m_schemas_root, sizeof(u32));
    buffer.overwrite(TABLES_ROOT_OFFSET, &m_tables_root, sizeof(u32));
    buffer.overwrite(TABLE_COLUMNS_ROOT_OFFSET, &m_table_columns_root, sizeof(u32));
    buffer.overwrite(FREE_LIST_OFFSET, &m_free_list, sizeof(u32));
    buffer.overwrite(USER_VALUES_OFFSET, m_user_values.data(), m_user_values.size() * sizeof(u32));

    add_to_wal(0, buffer);
}

void Heap::initialize_zero_block()
{
    m_version = 0x00000001;
    m_schemas_root = 0;
    m_tables_root = 0;
    m_table_columns_root = 0;
    m_next_block = 1;
    m_free_list = 0;
    for (auto& user : m_user_values) {
        user = 0u;
    }
    update_zero_block();
}

}