// Copyright 2025 Google LLC. All Rights Reserved. This file and proprietary
// source code may only be used and distributed under the Widevine License
// Agreement.
#ifndef WVCDM_UTIL_WV_TIMESTAMP_H_
#define WVCDM_UTIL_WV_TIMESTAMP_H_

#include <inttypes.h>

#include <chrono>

#include "wv_class_utils.h"
#include "wv_duration.h"

namespace wvutil {
// The Timestamp class is a light-weight representation of a
// time point.
//
// Internally, the time is measured in Unix Time (milliseconds
// since January 1st, 1970 UTC (epoch)).
//
// For this library, we are not concerned about time points before
// January 1st, 1970; this class does not support negative epoch
// seconds.  In addition, zero is treated as a special value
// which indicates an uninitialized time point.
//
// Min Timestamp: 1970-01-01 00:00:00.001 (epoch ms = 1)
// Max Timestamp: 9999-12-31 23:59:59.999 (epoch ms = 253402300799999)
class Timestamp {
 public:
  constexpr Timestamp() = default;  // Defaults to "unset".
  WVCDM_CONSTEXPR_DEFAULT_COPY_AND_MOVE(Timestamp);

  // Create a Timestamp instance from Unix Time in epoch seconds.
  // Optionally allowed to include |millisecond| (0 to 999).
  // If |epoch_seconds| or |millisecond| are invalid values, then an
  // uninitlaized Timestamp instance is returned.
  static constexpr Timestamp FromUnixSeconds(uint64_t epoch_seconds,
                                             uint32_t milliseconds = 0) {
    if (milliseconds > 999u) return Timestamp();
    return Timestamp(Seconds(epoch_seconds) + Milliseconds(milliseconds));
  }
  static constexpr Timestamp FromUnixSeconds(const Seconds& epoch_seconds,
                                             uint32_t milliseconds = 0) {
    if (milliseconds > 999u) return Timestamp();
    return Timestamp(epoch_seconds + Milliseconds(milliseconds));
  }

  // Create a Timestamp instance from Unix Time in epoch milliseconds.
  // If |epoch_milliseconds| is an invalid value (zero), then an
  // uninitlaized Timestamp instance is returned.
  static constexpr Timestamp FromUnixMilliseconds(uint64_t epoch_milliseconds) {
    return Timestamp(Milliseconds(epoch_milliseconds));
  }
  static constexpr Timestamp FromUnixMilliseconds(
      const Milliseconds& epoch_milliseconds) {
    return Timestamp(epoch_milliseconds);
  }

  // Obtain the minimum and maximum representable Timestamp.
  static constexpr Timestamp Min() { return Timestamp(kMinMsDuration); }
  static constexpr Timestamp Max() { return Timestamp(kMaxMsDuration); }

  // == General Accessors ==

  // Get the epoch seconds duration (rounding down milliseconds).
  constexpr Seconds epoch_seconds() const {
    return std::chrono::floor<Seconds>(epoch_milliseconds_);
  }
  // Get the milliseconds fraction of the epoch time (0-999).
  constexpr uint32_t milliseconds() const {
    return static_cast<uint32_t>(
        (epoch_milliseconds_ - epoch_seconds()).count());
  }

  constexpr Milliseconds epoch_milliseconds() const {
    return epoch_milliseconds_;
  }

  // As noted, the timestamp is considered "unset" if zero.
  constexpr bool IsSet() const {
    return epoch_milliseconds_ > Milliseconds::zero();
  }
  explicit constexpr operator bool() const { return IsSet(); }

  constexpr void Clear() { epoch_milliseconds_ = kUnsetMsDuration; }

  // == Comparisons ==

  constexpr bool IsEqualTo(const Timestamp& other) const {
    return epoch_milliseconds_ == other.epoch_milliseconds_;
  }
  constexpr int64_t CompareTo(const Timestamp& other) const {
    return static_cast<int64_t>(epoch_milliseconds_.count() -
                                other.epoch_milliseconds_.count());
  }
  WVCDM_DEFINE_CONSTEXPR_EQ_AND_CMP_OPERATORS(Timestamp);

  // == Arithmetic Operations ==

  // Duration-based addition/subtraction operations.
  // Returns a new Timestamp instance with time point adjusted by
  // the provided Duration.
  // If current Timestamp instance is unset, or if result value
  // is outside the range of valid Timestamp values, then an unset
  // Timestamp is returned.
  constexpr Timestamp operator+(const Duration& duration) const {
    if (!IsSet()) return Timestamp();
    return Timestamp(epoch_milliseconds_ + duration.total_milliseconds());
  }
  constexpr Timestamp operator-(const Duration& duration) const {
    if (!IsSet()) return Timestamp();
    return Timestamp(epoch_milliseconds_ - duration.total_milliseconds());
  }

  // Duration-based increment/decrement operators.
  // Increment or decrement the Timestamp by the provided Duration
  // amount.
  // If current Timestamp instance is unset, then no action will
  // occur.  If result value is outside the range of valid Timestamp
  // values, then Timestamp will be unset.
  constexpr Timestamp& operator+=(const Duration& duration) {
    if (!IsSet()) return *this;
    epoch_milliseconds_ =
        Normalize(epoch_milliseconds_ + duration.total_milliseconds());
    return *this;
  }
  constexpr Timestamp& operator-=(const Duration& duration) {
    if (!IsSet()) return *this;
    epoch_milliseconds_ =
        Normalize(epoch_milliseconds_ - duration.total_milliseconds());
    return *this;
  }

  // Timestamp difference.
  // Returns the duration between the two provided Timestamp
  // instances.
  // If either Timestamp instance is unset, then the resulting
  // Duration is zero.
  constexpr Duration operator-(const Timestamp& other) const {
    if (!IsSet() || !other.IsSet()) return Duration();
    return Duration(epoch_milliseconds_ - other.epoch_milliseconds_);
  }

 private:
  static constexpr const uint64_t kMinMs = 1;
  static constexpr const uint64_t kMaxMs = 253402300799999;
  static constexpr const Milliseconds kMinMsDuration = Milliseconds(kMinMs);
  static constexpr const Milliseconds kMaxMsDuration = Milliseconds(kMaxMs);
  static constexpr const Milliseconds kUnsetMsDuration = Milliseconds::zero();

  static constexpr bool IsInRange(const Milliseconds& epoch_milliseconds) {
    return epoch_milliseconds >= kMinMsDuration &&
           epoch_milliseconds <= kMaxMsDuration;
  }

  // Ensures the provided |epoch_milliseconds| is in range of the
  // Timestamp class; otherwise returns an unset duration value.
  static constexpr Milliseconds Normalize(
      const Milliseconds& epoch_milliseconds) {
    return IsInRange(epoch_milliseconds) ? epoch_milliseconds
                                         : kUnsetMsDuration;
  }

  constexpr Timestamp(const Milliseconds& epoch_milliseconds)
      : epoch_milliseconds_(Normalize(epoch_milliseconds)) {}

  Milliseconds epoch_milliseconds_ = kUnsetMsDuration;
};  // class Timestamp
}  // namespace wvutil
#endif  // WVCDM_UTIL_WV_TIMESTAMP_H_