#include "calculation_store.h"
#include "../shared/poincare_helpers.h"
#include "../global_preferences.h"
#include <poincare/rational.h>
#include <poincare/symbol.h>
#include <poincare/undefined.h>
#include "../exam_mode_configuration.h"
#include <assert.h>

using namespace Poincare;
using namespace Shared;

namespace Calculation {

CalculationStore::CalculationStore(char * buffer, int size) :
  m_buffer(buffer),
  m_bufferSize(size),
  m_calculationAreaEnd(m_buffer),
  m_numberOfCalculations(0)
{
  assert(m_buffer != nullptr);
  assert(m_bufferSize > 0);
}

// Returns an expiring pointer to the calculation of index i
ExpiringPointer<Calculation> CalculationStore::calculationAtIndex(int i) {
  assert(i >= 0 && i < m_numberOfCalculations);
  // m_buffer is the adress of the oldest calculation in calculation store
  Calculation * c = (Calculation *) m_buffer;
  if (i != m_numberOfCalculations-1) {
    // The calculation we want is not the oldest one so we get its pointer
    c = *reinterpret_cast<Calculation**>(addressOfPointerToCalculationOfIndex(i+1));
  }
  return ExpiringPointer<Calculation>(c);
}

// Pushes an expression in the store
ExpiringPointer<Calculation> CalculationStore::push(const char * text, Context * context, HeightComputer heightComputer) {
  /* Compute ans now, before the buffer is updated and before the calculation
   * might be deleted */
  Expression ans = ansExpression(context);

  /* Prepare the buffer for the new calculation
   *The minimal size to store the new calculation is the minimal size of a calculation plus the pointer to its end */
  int minSize = Calculation::MinimalSize() + sizeof(Calculation *);
  assert(m_bufferSize > minSize);
  while (remainingBufferSize() < minSize) {
    // If there is no more space to store a calculation, we delete the oldest one
    deleteOldestCalculation();
  }

  // Getting the adresses of the limits of the free space
  char * beginingOfFreeSpace = (char *)m_calculationAreaEnd;
  char * endOfFreeSpace = beginingOfMemoizationArea();
  char * previousCalc = beginingOfFreeSpace;

  // Add the beginning of the calculation
  {
    /* Copy the begining of the calculation. The calculation minimal size is
     * available, so this memmove will not overide anything. */
    Calculation newCalc = Calculation();
    size_t calcSize = sizeof(newCalc);
    memcpy(beginingOfFreeSpace, &newCalc, calcSize);
    beginingOfFreeSpace += calcSize;
  }

  /* Add the input expression.
   * We do not store directly the text entered by the user because we do not
   * want to keep Ans symbol in the calculation store. */
  const char * inputSerialization = beginingOfFreeSpace;
  {
    Expression input = Expression::Parse(text, context).replaceSymbolWithExpression(Symbol::Ans(), ans);
    if (!pushSerializeExpression(input, beginingOfFreeSpace, &endOfFreeSpace)) {
      /* If the input does not fit in the store (event if the current
       * calculation is the only calculation), just replace the calculation with
       * undef. */
      return emptyStoreAndPushUndef(context, heightComputer);
    }
    beginingOfFreeSpace += strlen(beginingOfFreeSpace) + 1;
  }

  // Compute and serialize the outputs
  /* The serialized outputs are:
   * - the exact ouput
   * - the approximate output with the maximal number of significant digits
   * - the approximate output with the displayed number of significant digits */
  {
    // Outputs hold exact output, approximate output and its duplicate
    constexpr static int numberOfOutputs = Calculation::k_numberOfExpressions - 1;
    Expression outputs[numberOfOutputs] = {Expression(), Expression(), Expression()};
    PoincareHelpers::ParseAndSimplifyAndApproximate(inputSerialization, &(outputs[0]), &(outputs[1]), context, GlobalPreferences::sharedGlobalPreferences()->isInExamModeSymbolic() ? Poincare::ExpressionNode::SymbolicComputation::ReplaceAllDefinedSymbolsWithDefinition : Poincare::ExpressionNode::SymbolicComputation::ReplaceAllSymbolsWithDefinitionsOrUndefined);
    if (ExamModeConfiguration::exactExpressionsAreForbidden(GlobalPreferences::sharedGlobalPreferences()->examMode()) && outputs[1].hasUnit()) {
      // Hide results with units on units if required by the exam mode configuration
      outputs[1] = Undefined::Builder();
    }
    outputs[2] = outputs[1];
    int numberOfSignificantDigits = Poincare::PrintFloat::k_numberOfStoredSignificantDigits;
    for (int i = 0; i < numberOfOutputs; i++) {
      if (i == numberOfOutputs - 1) {
        numberOfSignificantDigits = Poincare::Preferences::sharedPreferences()->numberOfSignificantDigits();
      }
      if (!pushSerializeExpression(outputs[i], beginingOfFreeSpace, &endOfFreeSpace, numberOfSignificantDigits)) {
        /* If the exat/approximate output does not fit in the store (event if the
         * current calculation is the only calculation), replace the output with
         * undef if it fits, else replace the whole calcualtion with undef. */
        Expression undef = Undefined::Builder();
        if (!pushSerializeExpression(undef, beginingOfFreeSpace, &endOfFreeSpace)) {
          return emptyStoreAndPushUndef(context, heightComputer);
        }
      }
      beginingOfFreeSpace += strlen(beginingOfFreeSpace) + 1;
    }
  }
  // Storing the pointer of the end of the new calculation
  memcpy(endOfFreeSpace-sizeof(Calculation*),&beginingOfFreeSpace,sizeof(beginingOfFreeSpace));

  // The new calculation is now stored
  m_numberOfCalculations++;

  // The end of the calculation storage area is updated
  m_calculationAreaEnd += beginingOfFreeSpace - previousCalc;
  ExpiringPointer<Calculation> calculation = ExpiringPointer<Calculation>(reinterpret_cast<Calculation *>(previousCalc));
  /* Heights are computed now to make sure that the display output is decided
   * accordingly to the remaining size in the Poincare pool. Once it is, it
   * can't change anymore: the calculation heights are fixed which ensures that
   * scrolling computation is right. */
  calculation->setHeights(
      heightComputer(calculation.pointer(), false),
      heightComputer(calculation.pointer(), true));
  return calculation;
}

// Delete the calculation of index i
void CalculationStore::deleteCalculationAtIndex(int i) {
  assert(i >= 0 && i < m_numberOfCalculations);
  if (i == 0) {
    ExpiringPointer<Calculation> lastCalculationPointer = calculationAtIndex(0);
    m_calculationAreaEnd = (char *)(lastCalculationPointer.pointer());
    m_numberOfCalculations--;
    return;
  }
  char * calcI = (char *)calculationAtIndex(i).pointer();
  char * nextCalc = (char *) calculationAtIndex(i-1).pointer();
  assert(m_calculationAreaEnd >= nextCalc);
  size_t slidingSize = m_calculationAreaEnd - nextCalc;
  // Slide the i-1 most recent calculations right after the i+1'th
  memmove(calcI, nextCalc, slidingSize);
  m_calculationAreaEnd -= nextCalc - calcI;
  // Recompute pointer to calculations after the i'th
  recomputeMemoizedPointersAfterCalculationIndex(i);
  m_numberOfCalculations--;
}

// Delete the oldest calculation in the store and returns the amount of space freed by the operation
size_t CalculationStore::deleteOldestCalculation() {
  char * oldBufferEnd = (char *) m_calculationAreaEnd;
  deleteCalculationAtIndex(numberOfCalculations()-1);
  char * newBufferEnd = (char *) m_calculationAreaEnd;
  return oldBufferEnd - newBufferEnd;
}

// Delete all calculations
void CalculationStore::deleteAll() {
  m_calculationAreaEnd = m_buffer;
  m_numberOfCalculations = 0;
}

// Replace "Ans" by its expression
Expression CalculationStore::ansExpression(Context * context) {
  if (numberOfCalculations() == 0) {
    return Rational::Builder(0);
  }
  ExpiringPointer<Calculation> mostRecentCalculation = calculationAtIndex(0);
  /* Special case: the exact output is a Store/Equal expression.
   * Store/Equal expression can only be at the root of an expression.
   * To avoid turning 'ans->A' in '2->A->A' or '2=A->A' (which cannot be
   * parsed), ans is replaced by the approximation output when any Store or
   * Equal expression appears. */
  Expression e = mostRecentCalculation->exactOutput();
  bool exactOuptutInvolvesStoreEqual = e.type() == ExpressionNode::Type::Store || e.type() == ExpressionNode::Type::Equal;
  if (mostRecentCalculation->input().recursivelyMatches(Expression::IsApproximate, context) || exactOuptutInvolvesStoreEqual) {
    return mostRecentCalculation->approximateOutput(context, Calculation::NumberOfSignificantDigits::Maximal);
  }
  return mostRecentCalculation->exactOutput();
}

// Push converted expression in the buffer
bool CalculationStore::pushSerializeExpression(Expression e, char * location, char * * newCalculationsLocation, int numberOfSignificantDigits) {
  assert(*newCalculationsLocation <= m_buffer + m_bufferSize);
  bool expressionIsPushed = false;
  while (true) {
    size_t locationSize = *newCalculationsLocation - location;
    expressionIsPushed = (PoincareHelpers::Serialize(e, location, locationSize, numberOfSignificantDigits) < (int)locationSize-1);
    if (expressionIsPushed || *newCalculationsLocation >= m_buffer + m_bufferSize) {
      break;
    }
    *newCalculationsLocation = *newCalculationsLocation + deleteOldestCalculation();
    assert(*newCalculationsLocation <= m_buffer + m_bufferSize);
  }
  return expressionIsPushed;
}



Shared::ExpiringPointer<Calculation> CalculationStore::emptyStoreAndPushUndef(Context * context, HeightComputer heightComputer) {
  /* We end up here as a result of a failed calculation push. The store
   * attributes are not necessarily clean, so we need to reset them. */
  deleteAll();
  return push(Undefined::Name(), context, heightComputer);
}

// Recompute memoized pointers to the calculations after index i
void CalculationStore::recomputeMemoizedPointersAfterCalculationIndex(int index) {
  assert(index < m_numberOfCalculations);
  // Clear pointer and recompute new ones
  Calculation * c = calculationAtIndex(index).pointer();
  Calculation * nextCalc;
  while (index != 0) {
    nextCalc = c->next();
    memcpy(addressOfPointerToCalculationOfIndex(index), &nextCalc, sizeof(Calculation *));
    c = nextCalc;
    index--;
  }
}

}