IColumn.h

#pragma once

#include <memory>

#include <Common/PODArray.h>
#include <Common/typeid_cast.h>

#include <Core/Field.h>
#include <Common/Exception.h>
#include <Core/StringRef.h>


class SipHash;


namespace DB
{

namespace ErrorCodes
{
    extern const int CANNOT_GET_SIZE_OF_FIELD;
    extern const int NOT_IMPLEMENTED;
    extern const int SIZES_OF_COLUMNS_DOESNT_MATCH;
}

class IColumn;

using ColumnPtr = std::shared_ptr<IColumn>;
using Columns = std::vector<ColumnPtr>;
using ColumnPlainPtrs = std::vector<IColumn *>;
using ConstColumnPlainPtrs = std::vector<const IColumn *>;

class Arena;


/// Declares interface to store columns in memory.
class IColumn : private boost::noncopyable
{
public:
    /// Name of a Column. It is used in info messages.
    virtual std::string getName() const = 0;

    /// Column is vector of numbers or numeric constant.
    virtual bool isNumeric() const { return false; }

    /// Is this column numeric and not nullable?
    virtual bool isNumericNotNullable() const { return isNumeric(); }

    /// Column stores a constant value.
    virtual bool isConst() const { return false; }

    /// Is this column a container for nullable values?
    virtual bool isNullable() const { return false; }

    /// Is this a null column?
    virtual bool isNull() const { return false; }

    /** If column isn't constant, returns nullptr (or itself).
      * If column is constant, transforms constant to full column (if column type allows such tranform) and return it.
      * Special case:
      * If column is composed from several other columns (tuple for example), and contains both constant and full columns,
      *  then each constant column is transformed, and final result is returned.
      */
    virtual ColumnPtr convertToFullColumnIfConst() const { return {}; }

    /// Values in column have equal size in memory.
    virtual bool isFixed() const { return false; }

    /// If column isFixed(), returns size of value.
    virtual size_t sizeOfField() const { throw Exception("Cannot get sizeOfField() for column " + getName(), ErrorCodes::CANNOT_GET_SIZE_OF_FIELD); }

    /// Creates the same column with the same data.
    virtual ColumnPtr clone() const { return cut(0, size()); }

    /// Creates empty column with the same type.
    virtual ColumnPtr cloneEmpty() const { return cloneResized(0); }

    /// Creates column with the same type and specified size.
    /// If size is less current size, then data is cut.
    /// If size is greater, than default values are appended.
    virtual ColumnPtr cloneResized(size_t size) const { throw Exception("Cannot cloneResized() column " + getName(), ErrorCodes::NOT_IMPLEMENTED); }

    /// Returns number of values in column.
    virtual size_t size() const = 0;

    /// There are no values in columns.
    bool empty() const { return size() == 0; }

    /// Returns value of n-th element in universal Field representation.
    /// Is used in rare cases, since creation of Field instance is expensive usually.
    virtual Field operator[](size_t n) const = 0;

    /// Like the previous one, but avoids extra copying if Field is in a container, for example.
    virtual void get(size_t n, Field & res) const = 0;

    /// If possible, returns pointer to memory chunk which contains n-th element (if it isn't possible, throws an exception)
    /// Is used to optimize some computations (in aggregation, for example).
    virtual StringRef getDataAt(size_t n) const = 0;

    /// Like getData, but has special behavior for columns that contain variable-length strings.
    /// Returns zero-ending memory chunk (i.e. its size is 1 byte longer).
    virtual StringRef getDataAtWithTerminatingZero(size_t n) const
    {
        return getDataAt(n);
    }

    /// If column stores integers, it returns n-th element transformed to UInt64 using static_cast.
    /// If column stores floting point numbers, bits of n-th elements are copied to lower bits of UInt64, the remaining bits are zeros.
    /// Is used to optimize some computations (in aggregation, for example).
    virtual UInt64 get64(size_t n) const
    {
        throw Exception("Method get64 is not supported for " + getName(), ErrorCodes::NOT_IMPLEMENTED);
    }

    /// Removes all elements outside of specified range.
    /// Is used in LIMIT operation, for example.
    virtual ColumnPtr cut(size_t start, size_t length) const
    {
        ColumnPtr res = cloneEmpty();
        res.get()->insertRangeFrom(*this, start, length);
        return res;
    }

    /// Appends new value at the end of column (column's size is increased by 1).
    /// Is used to transform raw strings to Blocks (for example, inside input format parsers)
    virtual void insert(const Field & x) = 0;

    /// Appends n-th element from other column with the same type.
    /// Is used in merge-sort and merges. It could be implemented in inherited classes more optimally than default implementation.
    virtual void insertFrom(const IColumn & src, size_t n) { insert(src[n]); }

    /// Appends range of elements from other column.
    /// Could be used to concatenate columns.
    virtual void insertRangeFrom(const IColumn & src, size_t start, size_t length) = 0;

    /// Appends data located in specified memory chunk if it is possible (throws an exception if it cannot be implemented).
    /// Is used to optimize some computations (in aggregation, for example).
    /// Parameter length could be ignored if column isFixed().
    virtual void insertData(const char * pos, size_t length) = 0;

    /// Like getData, but has special behavior for columns that contain variable-length strings.
    /// In this special case inserting data should be zero-ending (i.e. length is 1 byte greater than real string size).
    virtual void insertDataWithTerminatingZero(const char * pos, size_t length)
    {
        insertData(pos, length);
    }

    /// Appends "default value".
    /// Is used when there are need to increase column size, but inserting value doesn't make sense.
    /// For example, ColumnNullable(Nested) absolutely ignores values of nested column if it is marked as NULL.
    virtual void insertDefault() = 0;

    /** Removes last n elements.
      * Is used to support exeption-safety of several operations.
      *  For example, sometimes insertion should be reverted if we catch an exception during operation processing.
      * If column has less than n elements or n == 0 - undefined behavior.
      */
    virtual void popBack(size_t n) = 0;

    /** Serializes n-th element. Serialized element should be placed continuously inside Arena's memory.
      * Serialized value can be deserialized to reconstruct original object. Is used in aggregation.
      * The method is similar to getDataAt(), but can work when element's value cannot be mapped to existing continuous memory chunk,
      *  For example, to obtain unambiguous representation of Array of strings, strings data should be interleaved with their sizes.
      * Parameter begin should be used with Arena::allocContinue.
      */
    virtual StringRef serializeValueIntoArena(size_t n, Arena & arena, char const *& begin) const = 0;

    /// Deserializes a value that was serialized using IColumn::serializeValueIntoArena method.
    /// Returns pointer to the position after the read data.
    virtual const char * deserializeAndInsertFromArena(const char * pos) = 0;

    /// Update state of hash function with value of n-th element.
    /// On subsequent calls of this method for sequence of column values of arbitary types,
    ///  passed bytes to hash must identify sequence of values unambiguously.
    virtual void updateHashWithValue(size_t n, SipHash & hash) const = 0;

    /** Removes elements that don't match the filter.
      * Is used in WHERE and HAVING operations.
      * If result_size_hint > 0, then makes advance reserve(result_size_hint) for the result column;
      *  if 0, then don't makes reserve(),
      *  otherwise (i.e. < 0), makes reserve() using size of source column.
      */
    using Filter = PaddedPODArray<UInt8>;
    virtual ColumnPtr filter(const Filter & filt, ssize_t result_size_hint) const = 0;

    /// Permutes elements using specified permutation. Is used in sortings.
    /// limit - if it isn't 0, puts only first limit elements in the result.
    using Permutation = PaddedPODArray<size_t>;
    virtual ColumnPtr permute(const Permutation & perm, size_t limit) const = 0;

    /** Compares (*this)[n] and rhs[m].
      * Returns negative number, 0, or positive number (*this)[n] is less, equal, greater than rhs[m] respectively.
      * Is used in sortings.
      *
      * If one of element's value is NaN or NULLs, then:
      * - if nan_direction_hint == -1, NaN and NULLs are considered as least than everything other;
      * - if nan_direction_hint ==  1, NaN and NULLs are considered as greatest than everything other.
      * For example, if nan_direction_hint == -1 is used by descending sorting, NaNs will be at the end.
      *
      * For non Nullable and non floating point types, nan_direction_hint is ignored.
      */
    virtual int compareAt(size_t n, size_t m, const IColumn & rhs, int nan_direction_hint) const = 0;

    /** Returns a permutation that sorts elements of this column,
      *  i.e. perm[i]-th element of source column should be i-th element of sorted column.
      * reverse - reverse ordering (acsending).
      * limit - if isn't 0, then only first limit elements of the result column could be sorted.
      * nan_direction_hint - see above.
      */
    virtual void getPermutation(bool reverse, size_t limit, int nan_direction_hint, Permutation & res) const = 0;

    /** Copies each element according offsets parameter.
      * (i-th element should be copied offsets[i] - offsets[i - 1] times.)
      * It is necessary in ARRAY JOIN operation.
      */
    using Offset_t = UInt64;
    using Offsets_t = PaddedPODArray<Offset_t>;
    virtual ColumnPtr replicate(const Offsets_t & offsets) const = 0;

    /** Split column to smaller columns. Each value goes to column index, selected by corresponding element of 'selector'.
      * Selector must contain values from 0 to num_columns - 1.
      * For default implementation, see scatterImpl.
      */
    using ColumnIndex = UInt64;
    using Selector = PaddedPODArray<ColumnIndex>;
    virtual Columns scatter(ColumnIndex num_columns, const Selector & selector) const = 0;

    /** Computes minimum and maximum element of the column.
      * In addition to numeric types, the funtion is completely implemented for Date and DateTime.
      * For strings and arrays function should retrurn default value.
      *  (except for constant columns; they should return value of the constant).
      * If column is empty function should return default value.
      */
    virtual void getExtremes(Field & min, Field & max) const = 0;

    /// Reserves memory for specified amount of elements. If reservation isn't possible, does nothing.
    /// It affects performance only (not correctness).
    virtual void reserve(size_t n) {};

    /// Size of column data in memory (may be approximate) - for profiling. Zero, if could not be determined.
    virtual size_t byteSize() const = 0;

    /// Size of memory, allocated for column.
    /// This is greater or equals to byteSize due to memory reservation in containers.
    /// Zero, if could be determined.
    virtual size_t allocatedSize() const = 0;

    virtual ~IColumn() {}

protected:

    /// Template is to devirtualize calls to insertFrom method.
    /// In derived classes (that use final keyword), implement scatter method as call to scatterImpl.
    template <typename Derived>
    Columns scatterImpl(ColumnIndex num_columns, const Selector & selector) const
    {
        size_t num_rows = size();

        if (num_rows != selector.size())
            throw Exception("Size of selector doesn't match size of column.", ErrorCodes::SIZES_OF_COLUMNS_DOESNT_MATCH);

        Columns columns(num_columns);
        for (auto & column : columns)
            column = cloneEmpty();

        {
            size_t reserve_size = num_rows / num_columns * 1.1;    /// 1.1 is just a guess. Better to use n-sigma rule.

            if (reserve_size > 1)
                for (auto & column : columns)
                    column->reserve(reserve_size);
        }

        for (size_t i = 0; i < num_rows; ++i)
            static_cast<Derived &>(*columns[selector[i]]).insertFrom(*this, i);

        return columns;
    }
};


}