#include <mercury/kernel/fs/tarfs.hpp>

//in fs::tarfs_instance, storage::node_id_t refers to the number
//of bytes into the block device that the info sector is located

namespace mercury::kernel::fs {

  storage::io_result tarfs_mounter(
    storage::block_device *bd, storage::file_system_instance *&fs_out
  ) {
    fs_out = new tarfs_instance(bd);
    return storage::io_result::success;
  }

  tarfs_instance::tarfs_instance(storage::block_device *bd) : bd(bd) {}

  storage::io_result tarfs_instance::next_node(storage::node_id_t &node) {
    uint64_t file_length;
    storage::io_result result = read_num(node + 124, 12, file_length);
    if (result != storage::io_result::success)
      return result;
    node += ((file_length - 1) / 512 + 2) * 512;
    uint8_t sector[512];
    result = bd->read_bytes(node, 512, sector);
    if (result != storage::io_result::success)
      return result;
    for (unsigned i = 0; i < 512; ++i)
      if (sector[i] != 0)
        return storage::io_result::success;
    return storage::io_result::out_of_bounds;
  }

  storage::io_result tarfs_instance::read_name(
    storage::node_id_t node, char *name_buf, unsigned &name_len_out
  ) {
    name_len_out = 0;
    storage::io_result result = bd->read_bytes(node + 345, 155, name_buf);
    if (result != storage::io_result::success)
      return result;
    while (name_buf[name_len_out] && name_len_out < 155)
      ++name_len_out;
    result = bd->read_bytes(node, 100, name_buf + name_len_out);
    if (result != storage::io_result::success)
      return result;
    unsigned new_limit = name_len_out + 100;
    while (name_buf[name_len_out] && name_len_out < new_limit)
      ++name_len_out;
    return storage::io_result::success;
  }

  storage::io_result tarfs_instance::read_num(
    uint64_t offset, unsigned len, uint64_t &out
  ) {

    //len <= 12
    char buffer[12];
    storage::io_result result = bd->read_bytes(offset, len, buffer);
    if (result != storage::io_result::success)
      return result;
    out = 0;

    for (unsigned i = 0; i < len; ++i) {
      if (!buffer[i])
        return i == 0 ? storage::io_result::fs_corrupt
                      : storage::io_result::success;
      if (buffer[i] < '0' || buffer[i] > '7')
        return storage::io_result::fs_corrupt;
      out = out * 8 + buffer[i] - '0';
    }

    return storage::io_result::success;

  }

#define RETURN_MAYBE_NOT_FOUND(expr) \
  { \
    storage::io_result _result = expr; \
    if (_result == storage::io_result::out_of_bounds) \
      return storage::io_result::not_found; \
    if (_result != storage::io_result::success) \
      return _result; \
  }

#define RETURN_NOT_SUCCESS(expr) \
  { \
    storage::io_result _result = expr; \
    if (_result != storage::io_result::success) \
      return _result; \
  }

  storage::io_result tarfs_instance::get_root_node(storage::node_id_t &out) {
    out = 0;
    while (true) {
      char name_buf[255];
      unsigned name_len;
      RETURN_MAYBE_NOT_FOUND(read_name(out, name_buf, name_len))
      if (name_len == 2 && name_buf[0] == '.' && name_buf[1] == '/')
        return storage::io_result::success;
      RETURN_MAYBE_NOT_FOUND(next_node(out))
    }
  }

  storage::io_result tarfs_instance::get_first_child(storage::node_id_t node,
    storage::node_id_t &out, storage::directory_iter_t &iter_out
  ) {

    char name_buf[255];
    unsigned name_len;
    RETURN_NOT_SUCCESS(read_name(node, name_buf, name_len))

    out = 0;
    while (true) {

      char cand_name_buf[255];
      unsigned cand_name_len;
      RETURN_MAYBE_NOT_FOUND(read_name(out, cand_name_buf, cand_name_len))

      if (cand_name_len > name_len && utility::starts_with(
        cand_name_buf, cand_name_len, name_buf, name_len
      )) {
        const char *rem = cand_name_buf + name_len;
        unsigned rem_len = cand_name_len - name_len;
        unsigned slash = utility::find(rem, rem_len, '/');
        if (slash == rem_len - 1 || slash == rem_len) {
          iter_out = out;
          return storage::io_result::success;
        }
      }

      RETURN_MAYBE_NOT_FOUND(next_node(out))

    }

  }

  storage::io_result tarfs_instance::get_next_child(storage::node_id_t node,
    storage::node_id_t &out, storage::directory_iter_t &iter
  ) {

    char name_buf[255];
    unsigned name_len;
    RETURN_NOT_SUCCESS(read_name(node, name_buf, name_len))

    out = iter;

    RETURN_MAYBE_NOT_FOUND(next_node(out))

    while (true) {

      char cand_name_buf[255];
      unsigned cand_name_len;
      RETURN_MAYBE_NOT_FOUND(read_name(out, cand_name_buf, cand_name_len))

      if (cand_name_len > name_len && utility::starts_with(
        cand_name_buf, cand_name_len, name_buf, name_len
      )) {
        const char *rem = cand_name_buf + name_len;
        unsigned rem_len = cand_name_len - name_len;
        unsigned slash = utility::find(rem, rem_len, '/');
        if (slash == rem_len - 1 || slash == rem_len) {
          iter = out;
          return storage::io_result::success;
        }
      }

      RETURN_MAYBE_NOT_FOUND(next_node(out))

    }

  }

  storage::io_result tarfs_instance::get_child(storage::node_id_t node,
    storage::node_id_t &out, const char *name, unsigned name_len
  ) {

    char full_name[255];
    unsigned full_name_len;
    RETURN_MAYBE_NOT_FOUND(read_name(node, full_name, full_name_len))

    if (full_name_len + name_len > 255)
      return storage::io_result::not_supported;

    for (unsigned i = 0; i < name_len; ++i)
      full_name[full_name_len + i] = name[i];
    full_name_len += name_len;

    out = 0;
    while (true) {

      char cand_name[255];
      unsigned cand_name_len;
      RETURN_MAYBE_NOT_FOUND(read_name(out, cand_name, cand_name_len))

      if (cand_name_len != full_name_len && cand_name_len != full_name_len + 1)
        goto next_iter;
      for (unsigned i = 0; i < full_name_len; ++i)
        if (cand_name[i] != full_name[i])
          goto next_iter;
      if (cand_name_len == full_name_len + 1 &&
          cand_name[full_name_len] != '/')
        goto next_iter;

      return storage::io_result::success;

    next_iter:
      RETURN_MAYBE_NOT_FOUND(next_node(out))

    }

  }

  storage::io_result tarfs_instance::get_name_length(
    storage::node_id_t node, unsigned &length_out
  ) {

    char name_buf[255];
    return get_name(node, name_buf, length_out);

  }

  storage::io_result tarfs_instance::get_name(
    storage::node_id_t node, char *buffer, unsigned &length_out
  ) {

    unsigned full_length;
    char full_buffer[255];
    RETURN_NOT_SUCCESS(read_name(node, full_buffer, full_length))
    if (full_length == 2) {
      //full buffer must be ./
      length_out = 0;
      return storage::io_result::success;
    }
    if (full_buffer[full_length - 1] == '/')
      --full_length;
    unsigned start = utility::find_last(full_buffer, full_length, '/') + 1;
    length_out = full_length - start;
    for (unsigned i = 0; i < length_out; ++i)
      buffer[i] = full_buffer[start + i];
    return storage::io_result::success;

  }

  storage::io_result tarfs_instance::get_file_length(
    storage::node_id_t node, uint64_t &length_out
  ) {

    return read_num(node + 124, 12, length_out);

  }

  storage::io_result tarfs_instance::get_file_type(
    storage::node_id_t node, storage::file_type &out
  ) {

    uint64_t ft;
    storage::io_result result = read_num(node + 156, 1, ft);
    if (result != storage::io_result::success)
      return result;

    switch (ft) {
    case 0:
      out = storage::file_type::regular_file;
      return storage::io_result::success;
    case 2:
      out = storage::file_type::symlink;
      return storage::io_result::success;
    case 5:
      out = storage::file_type::directory;
      return storage::io_result::success;
    default:
      return storage::io_result::not_supported;
    }

  }

  storage::io_result tarfs_instance::resize_file(
    storage::node_id_t, uint64_t
  ) {
    //TODO: support resize if sector count isn't changed?
    return storage::io_result::not_supported;
  }

  storage::io_result tarfs_instance::read_bytes_from_file(
    storage::node_id_t node, uint64_t start, uint64_t count, void *into
  ) {
    return bd->read_bytes(node + 512 + start, count, into);
  }

  storage::io_result tarfs_instance::write_bytes_into_file(
    storage::node_id_t, uint64_t, uint64_t, const void *
  ) {
    //TODO: support this.
    return storage::io_result::not_supported;
  }

}