// © 2020 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html

#ifndef __MEASUNIT_IMPL_H__
#define __MEASUNIT_IMPL_H__

#include "unicode/utypes.h"

#if !UCONFIG_NO_FORMATTING

#include "unicode/measunit.h"
#include "cmemory.h"
#include "charstr.h"
#include "fixedstring.h"

U_NAMESPACE_BEGIN

namespace number::impl {
class LongNameHandler;
}

static const char16_t kDefaultCurrency[] = u"XXX";
static const char kDefaultCurrency8[] = "XXX";

/**
 * Looks up the "unitQuantity" (aka "type" or "category") of a base unit
 * identifier. The category is returned via `result`, which must initially be
 * empty.
 *
 * This only supports base units: other units must be resolved to base units
 * before passing to this function, otherwise U_UNSUPPORTED_ERROR status may be
 * returned.
 *
 * Categories are found in `unitQuantities` in the `units` resource (see
 * `units.txt`).
 */
// TODO: make this function accepts any `MeasureUnit` as Java and move it to the `UnitsData` class.
CharString U_I18N_API getUnitQuantity(const MeasureUnitImpl &baseMeasureUnitImpl, UErrorCode &status);

/**
 * A struct representing a single unit (optional SI or binary prefix, and dimensionality).
 */
struct U_I18N_API_CLASS SingleUnitImpl : public UMemory {
    /**
     * Gets a single unit from the MeasureUnit. If there are multiple single units, sets an error
     * code and returns the base dimensionless unit. Parses if necessary.
     */
    U_I18N_API static SingleUnitImpl forMeasureUnit(const MeasureUnit& measureUnit, UErrorCode& status);

    /** Transform this SingleUnitImpl into a MeasureUnit, simplifying if possible. */
    MeasureUnit build(UErrorCode& status) const;

    /**
     * Returns the "simple unit ID", without SI or dimensionality prefix: this
     * instance may represent a square-kilometer, but only "meter" will be
     * returned.
     *
     * The returned pointer points at memory that exists for the duration of the
     * program's running.
     */
    U_I18N_API const char* getSimpleUnitID() const;

    /**
     * Generates and append a neutral identifier string for a single unit which means we do not include
     * the dimension signal.
     */
    void appendNeutralIdentifier(CharString &result, UErrorCode &status) const;

    /**
     * Returns the index of this unit's "quantity" in unitQuantities (in
     * measunit_extra.cpp). The value of this index determines sort order for
     * normalization of unit identifiers.
     */
    int32_t getUnitCategoryIndex() const;

    /**
     * Compare this SingleUnitImpl to another SingleUnitImpl for the sake of
     * sorting and coalescing.
     *
     * Sort order of units is specified by UTS #35
     * (https://unicode.org/reports/tr35/tr35-info.html#Unit_Identifier_Normalization).
     *
     * Takes the sign of dimensionality into account, but not the absolute
     * value: per-meter is not considered the same as meter, but meter is
     * considered the same as square-meter.
     *
     * The dimensionless unit generally does not get compared, but if it did, it
     * would sort before other units by virtue of index being < 0 and
     * dimensionality not being negative.
     */
    int32_t compareTo(const SingleUnitImpl& other) const {
        if (dimensionality < 0 && other.dimensionality > 0) {
            // Positive dimensions first
            return 1;
        }
        if (dimensionality > 0 && other.dimensionality < 0) {
            return -1;
        }

        // Sort by official quantity order
        int32_t thisQuantity = this->getUnitCategoryIndex();
        int32_t otherQuantity = other.getUnitCategoryIndex();
        if (thisQuantity < otherQuantity) {
            return -1;
        }
        if (thisQuantity > otherQuantity) {
            return 1;
        }

        // If quantity order didn't help, then we go by index.
        if (index < other.index) {
            return -1;
        }
        if (index > other.index) {
            return 1;
        }

        // When comparing binary prefixes vs SI prefixes, instead of comparing the actual values, we can
        // multiply the binary prefix power by 3 and compare the powers. if they are equal, we can can
        // compare the bases.
        // NOTE: this methodology will fail if the binary prefix more than or equal 98.
        int32_t unitBase = umeas_getPrefixBase(unitPrefix);
        int32_t otherUnitBase = umeas_getPrefixBase(other.unitPrefix);

        // Values for comparison purposes only.
        int32_t unitPower = unitBase == 1024 /* Binary Prefix */ ? umeas_getPrefixPower(unitPrefix) * 3
                                                                 : umeas_getPrefixPower(unitPrefix);
        int32_t otherUnitPower =
            otherUnitBase == 1024 /* Binary Prefix */ ? umeas_getPrefixPower(other.unitPrefix) * 3
                                                      : umeas_getPrefixPower(other.unitPrefix);

        // NOTE: if the unitPower is less than the other,
        // we return 1 not -1. Thus because we want th sorting order
        // for the bigger prefix to be before the smaller.
        // Example: megabyte should come before kilobyte.
        if (unitPower < otherUnitPower) {
            return 1;
        }
        if (unitPower > otherUnitPower) {
            return -1;
        }

        if (unitBase < otherUnitBase) {
            return 1;
        }
        if (unitBase > otherUnitBase) {
            return -1;
        }

        return 0;
    }

    /**
     * Return whether this SingleUnitImpl is compatible with another for the purpose of coalescing.
     *
     * Units with the same base unit and SI or binary prefix should match, except that they must also
     * have the same dimensionality sign, such that we don't merge numerator and denominator.
     */
    bool isCompatibleWith(const SingleUnitImpl& other) const {
        return (compareTo(other) == 0);
    }

    /**
     * Returns true if this unit is the "dimensionless base unit", as produced
     * by the MeasureUnit() default constructor. (This does not include the
     * likes of concentrations or angles.)
     */
    bool isDimensionless() const {
        return index == -1;
    }

    /**
     * Simple unit index, unique for every simple unit, -1 for the dimensionless
     * unit. This is an index into a string list in measunit_extra.cpp, as
     * loaded by SimpleUnitIdentifiersSink.
     *
     * The default value is -1, meaning the dimensionless unit:
     * isDimensionless() will return true, until index is changed.
     */
    int32_t index = -1;

    /**
     * SI or binary prefix.
     *
     * This is ignored for the dimensionless unit.
     */
    UMeasurePrefix unitPrefix = UMEASURE_PREFIX_ONE;

    /**
     * Dimensionality.
     *
     * This is meaningless for the dimensionless unit.
     */
    int32_t dimensionality = 1;
};

// Forward declaration
struct MeasureUnitImplWithIndex;

/**
 * Internal representation of measurement units. Capable of representing all complexities of units,
 * including mixed and compound units.
 */
class U_I18N_API_CLASS MeasureUnitImpl : public UMemory {
  public:
    MeasureUnitImpl() = default;
    MeasureUnitImpl(MeasureUnitImpl &&other) = default;
    // No copy constructor, use MeasureUnitImpl::copy() to make it explicit.
    MeasureUnitImpl(const MeasureUnitImpl &other, UErrorCode &status) = delete;
    MeasureUnitImpl(const SingleUnitImpl &singleUnit, UErrorCode &status);

    MeasureUnitImpl &operator=(MeasureUnitImpl &&other) noexcept = default;

    /** Extract the MeasureUnitImpl from a MeasureUnit. */
    static inline const MeasureUnitImpl *get(const MeasureUnit &measureUnit) {
        return measureUnit.fImpl;
    }

    /**
     * Parse a unit identifier into a MeasureUnitImpl.
     *
     * @param identifier The unit identifier string.
     * @param status Set if the identifier string is not valid.
     * @return A newly parsed value object. Behaviour of this unit is
     * unspecified if an error is returned via status.
     */
    U_I18N_API static MeasureUnitImpl forIdentifier(StringPiece identifier, UErrorCode& status);

    /**
     * Extract the MeasureUnitImpl from a MeasureUnit, or parse if it is not present.
     * 
     * @param measureUnit The source MeasureUnit.
     * @param memory A place to write the new MeasureUnitImpl if parsing is required.
     * @param status Set if an error occurs.
     * @return A reference to either measureUnit.fImpl or memory.
     */
    U_I18N_API static const MeasureUnitImpl& forMeasureUnit(
        const MeasureUnit& measureUnit, MeasureUnitImpl& memory, UErrorCode& status);

    /**
     * Extract the MeasureUnitImpl from a MeasureUnit, or parse if it is not present.
     *
     * @param measureUnit The source MeasureUnit.
     * @param status Set if an error occurs.
     * @return A value object, either newly parsed or copied from measureUnit.
     */
    static MeasureUnitImpl forMeasureUnitMaybeCopy(
        const MeasureUnit& measureUnit, UErrorCode& status);

    /**
     * Used for currency units.
     */
    static inline MeasureUnitImpl forCurrencyCode(StringPiece currencyCode, UErrorCode& status) {
        MeasureUnitImpl result;
        if (U_SUCCESS(status)) {
            result.identifier = currencyCode;
            if (result.identifier.isEmpty() != currencyCode.empty()) {
                status = U_MEMORY_ALLOCATION_ERROR;
            }
        }
        return result;
    }

    /** Transform this MeasureUnitImpl into a MeasureUnit, simplifying if possible. */
    U_I18N_API MeasureUnit build(UErrorCode& status) &&;

    /**
     * Create a copy of this MeasureUnitImpl. Don't use copy constructor to make this explicit.
     */
    MeasureUnitImpl copy(UErrorCode& status) const;

    /**
     * Extracts the list of all the individual units inside the `MeasureUnitImpl` with their indices.
     *      For example:    
     *          -   if the `MeasureUnitImpl` is `foot-per-hour`
     *                  it will return a list of 1 {(0, `foot-per-hour`)} 
     *          -   if the `MeasureUnitImpl` is `foot-and-inch` 
     *                  it will return a list of 2 {(0, `foot`), (1, `inch`)}
     */
    MaybeStackVector<MeasureUnitImplWithIndex>
    extractIndividualUnitsWithIndices(UErrorCode &status) const;

    /** Mutates this MeasureUnitImpl to take the reciprocal. */
    void takeReciprocal(UErrorCode& status);

    /**
     * Returns a simplified version of the unit.
     * NOTE: the simplification happen when there are two units equals in their base unit and their
     * prefixes.
     *
     * Example 1: "square-meter-per-meter" --> "meter"
     * Example 2: "square-millimeter-per-meter" --> "square-millimeter-per-meter"
     */
    MeasureUnitImpl copyAndSimplify(UErrorCode &status) const;

    /**
     * Mutates this MeasureUnitImpl to append a single unit.
     *
     * @return true if a new item was added. If unit is the dimensionless unit,
     * it is never added: the return value will always be false.
     */
    U_I18N_API bool appendSingleUnit(const SingleUnitImpl& singleUnit, UErrorCode& status);

    /**
     * Normalizes a MeasureUnitImpl and generate the identifier string in place.
     */
    void serialize(UErrorCode &status);

    /** The complexity, either SINGLE, COMPOUND, or MIXED. */
    UMeasureUnitComplexity complexity = UMEASURE_UNIT_SINGLE;

    /**
     * The list of single units. These may be summed or multiplied, based on the
     * value of the complexity field.
     *
     * The "dimensionless" unit (SingleUnitImpl default constructor) must not be
     * added to this list.
     */
    MaybeStackVector<SingleUnitImpl> singleUnits;

    /**
     * The full unit identifier.  Owned by the MeasureUnitImpl.  Empty if not computed.
     */
    FixedString identifier;

    /**
     * Represents the unit constant denominator.
     *
     * NOTE:
     *   if set to 0, it means that the constant is not set.
     */
    uint64_t constantDenominator = 0;

    // For calling serialize
    // TODO(icu-units#147): revisit serialization
    friend class number::impl::LongNameHandler;
};

struct MeasureUnitImplWithIndex : public UMemory {
    const int32_t index;
    MeasureUnitImpl unitImpl;
    // Makes a copy of unitImpl.
    MeasureUnitImplWithIndex(int32_t index, const MeasureUnitImpl &unitImpl, UErrorCode &status)
        : index(index), unitImpl(unitImpl.copy(status)) {
    }
    MeasureUnitImplWithIndex(int32_t index, const SingleUnitImpl &singleUnitImpl, UErrorCode &status)
        : index(index), unitImpl(MeasureUnitImpl(singleUnitImpl, status)) {
    }
};

U_NAMESPACE_END

#endif /* #if !UCONFIG_NO_FORMATTING */
#endif //__MEASUNIT_IMPL_H__
