// ----------------------------------------------------------------------------
// -                        Open3D: www.open3d.org                            -
// ----------------------------------------------------------------------------
// Copyright (c) 2018-2023 www.open3d.org
// SPDX-License-Identifier: MIT
// ----------------------------------------------------------------------------

#pragma once

#include <string>
#include <unordered_map>
#include <unordered_set>

#include "open3d/core/Tensor.h"

namespace open3d {
namespace t {
namespace geometry {

/// TensorMap is a unordered_map<string, Tensor> with a primary key. It is
/// typically used as a container for geometry attributes.
///
/// e.g.
/// tensor_map.primary_key: "positions"
/// tensor_map["positions"]  : Tensor of shape {100, 3}.
/// tensor_map["colors"]  : Tensor of shape {100, 3}.
/// tensor_map["normals"] : Tensor of shape {100, 3}.
///
/// Typically, tensors in the TensorMap should have the same length (the first
/// dimension of shape) and device as the primary tensor.
class TensorMap : public std::unordered_map<std::string, core::Tensor> {
public:
    /// Create empty TensorMap and set primary key.
    explicit TensorMap(const std::string& primary_key)
        : std::unordered_map<std::string, core::Tensor>(),
          primary_key_(primary_key) {
        AssertPrimaryKeyInMapOrEmpty();
        AssertNoReservedKeys();
    }

    /// A primary key is always required. This constructor can be marked as
    /// delete in C++, but it is needed for pybind to bind as a generic python
    /// map interface.
    explicit TensorMap() : TensorMap("Undefined") {
        utility::LogError("Please construct TensorMap with a primary key.");
    }

    template <class InputIt>
    TensorMap(const std::string& primary_key, InputIt first, InputIt last)
        : std::unordered_map<std::string, core::Tensor>(first, last),
          primary_key_(primary_key) {
        AssertPrimaryKeyInMapOrEmpty();
        AssertNoReservedKeys();
    }

    TensorMap(const std::string& primary_key,
              const std::unordered_map<std::string, core::Tensor>& tensor_map)
        : TensorMap(primary_key, tensor_map.begin(), tensor_map.end()) {
        AssertPrimaryKeyInMapOrEmpty();
        AssertNoReservedKeys();
    }

    TensorMap(const std::string& primary_key,
              std::initializer_list<value_type> init)
        : std::unordered_map<std::string, core::Tensor>(init),
          primary_key_(primary_key) {
        AssertPrimaryKeyInMapOrEmpty();
        AssertNoReservedKeys();
    }

    /// Copy constructor performs a "shallow" copy of the Tensors.
    TensorMap(const TensorMap& other)
        : std::unordered_map<std::string, core::Tensor>(other),
          primary_key_(other.primary_key_) {
        AssertPrimaryKeyInMapOrEmpty();
        AssertNoReservedKeys();
    }

    /// Move constructor performs a "shallow" copy of the Tensors.
    TensorMap(TensorMap&& other)
        : std::unordered_map<std::string, core::Tensor>(other),
          primary_key_(other.primary_key_) {
        AssertPrimaryKeyInMapOrEmpty();
        AssertNoReservedKeys();
    }

    /// \brief Erase elements for the TensorMap by key value, if the key
    /// exists. If the key does not exists, a warning is thrown.
    /// Also `primary_key` cannot be deleted. It is based on
    /// `size_type unordered_map::erase(const key_type& k);`.
    /// \return The number of elements deleted. [0 if key was not present].
    std::size_t Erase(const std::string key) {
        if (key == primary_key_) {
            utility::LogError("Primary key \"{}\" cannot be deleted.",
                              primary_key_);
        } else if (!Contains(key)) {
            utility::LogWarning("Key \"{}\" is not present.", key);
        }
        return this->erase(key);
    }

    std::pair<iterator, bool> insert(const value_type& value) {
        if (GetReservedKeys().count(value.first)) {
            utility::LogError("Key \"{}\" is reserved.", value.first);
        }
        return std::unordered_map<std::string, core::Tensor>::insert(value);
    }

    template <class P>
    std::pair<iterator, bool> insert(P&& value) {
        if (GetReservedKeys().count(value.first)) {
            utility::LogError("Key \"{}\" is reserved.", value.first);
        }
        return std::unordered_map<std::string, core::Tensor>::insert(
                std::forward<P>(value));
    }

    iterator insert(const_iterator hint, const value_type& value) {
        if (GetReservedKeys().count(value.first)) {
            utility::LogError("Key \"{}\" is reserved.", value.first);
        }
        return std::unordered_map<std::string, core::Tensor>::insert(hint,
                                                                     value);
    }

    template <class P>
    iterator insert(const_iterator hint, P&& value) {
        if (GetReservedKeys().count(value.first)) {
            utility::LogError("Key \"{}\" is reserved.", value.first);
        }
        return std::unordered_map<std::string, core::Tensor>::insert(
                hint, std::forward<P>(value));
    }

    template <class InputIt>
    void insert(InputIt first, InputIt last) {
        for (auto it = first; it != last; ++it) {
            if (GetReservedKeys().count(it->first)) {
                utility::LogError("Key \"{}\" is reserved.", it->first);
            }
        }
        std::unordered_map<std::string, core::Tensor>::insert(first, last);
    }

    void insert(std::initializer_list<value_type> ilist) {
        for (auto it = ilist.begin(); it != ilist.end(); ++it) {
            if (GetReservedKeys().count(it->first)) {
                utility::LogError("Key \"{}\" is reserved.", it->first);
            }
        }
        std::unordered_map<std::string, core::Tensor>::insert(ilist);
    }

    TensorMap& operator=(const TensorMap&) = default;

    TensorMap& operator=(TensorMap&&) = default;

    /// Returns the primary key of the TensorMap.
    std::string GetPrimaryKey() const { return primary_key_; }

    /// Returns a set with all keys.
    std::unordered_set<std::string> GetKeySet() const {
        std::unordered_set<std::string> keys;
        for (const auto& item : *this) {
            keys.insert(item.first);
        }
        return keys;
    }

    /// Returns true if all tensors in the map have the same size.
    bool IsSizeSynchronized() const;

    /// Assert IsSizeSynchronized().
    void AssertSizeSynchronized() const;

    /// Returns True if the underlying memory buffers of all the Tensors in the
    /// TensorMap is contiguous.
    bool IsContiguous() const;

    /// Returns a new contiguous TensorMap containing the same data in the same
    /// device. For the contiguous tensors in the TensorMap, the same underlying
    /// memory will be used.
    TensorMap Contiguous() const;

    /// Returns true if the key exists in the map.
    /// Same as C++20's std::unordered_map::contains().
    bool Contains(const std::string& key) const { return count(key) != 0; }

    /// Get reserved keys for the map. A map cannot contain any of these keys.
    static std::unordered_set<std::string> GetReservedKeys();

    /// Print the TensorMap to string.
    std::string ToString() const;

private:
    /// Asserts that the map indeed contains the primary_key. This is typically
    /// called in constructors.
    void AssertPrimaryKeyInMapOrEmpty() const;

    /// Asserts that there are no reserved keys in the map. This is typically
    /// called in constructors or in modifying functions.
    void AssertNoReservedKeys() const;

    /// Returns the size (length) of the primary key's tensor.
    int64_t GetPrimarySize() const { return at(primary_key_).GetLength(); }

    /// Returns the device of the primary key's tensor.
    core::Device GetPrimaryDevice() const {
        return at(primary_key_).GetDevice();
    }

    /// Primary key of the TensorMap.
    std::string primary_key_;
};

}  // namespace geometry
}  // namespace t
}  // namespace open3d