// © 2017 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html

// edits.cpp
// created: 2017feb08 Markus W. Scherer

#include "unicode/utypes.h"
#include "unicode/edits.h"
#include "cmemory.h"
#include "uassert.h"

U_NAMESPACE_BEGIN

namespace {

// 0000uuuuuuuuuuuu records u+1 unchanged text units.
const int32_t MAX_UNCHANGED_LENGTH = 0x1000;
const int32_t MAX_UNCHANGED = MAX_UNCHANGED_LENGTH - 1;

// 0wwwcccccccccccc with w=1..6 records ccc+1 replacements of w:w text units.
// No length change.
const int32_t MAX_SHORT_WIDTH = 6;
const int32_t MAX_SHORT_CHANGE_LENGTH = 0xfff;
const int32_t MAX_SHORT_CHANGE = 0x6fff;

// 0111mmmmmmnnnnnn records a replacement of m text units with n.
// m or n = 61: actual length follows in the next edits array unit.
// m or n = 62..63: actual length follows in the next two edits array units.
// Bit 30 of the actual length is in the head unit.
// Trailing units have bit 15 set.
const int32_t LENGTH_IN_1TRAIL = 61;
const int32_t LENGTH_IN_2TRAIL = 62;

}  // namespace

Edits::~Edits() {
    if(array != stackArray) {
        uprv_free(array);
    }
}

void Edits::reset() {
    length = delta = 0;
}

void Edits::addUnchanged(int32_t unchangedLength) {
    if(U_FAILURE(errorCode) || unchangedLength == 0) { return; }
    if(unchangedLength < 0) {
        errorCode = U_ILLEGAL_ARGUMENT_ERROR;
        return;
    }
    // Merge into previous unchanged-text record, if any.
    int32_t last = lastUnit();
    if(last < MAX_UNCHANGED) {
        int32_t remaining = MAX_UNCHANGED - last;
        if (remaining >= unchangedLength) {
            setLastUnit(last + unchangedLength);
            return;
        }
        setLastUnit(MAX_UNCHANGED);
        unchangedLength -= remaining;
    }
    // Split large lengths into multiple units.
    while(unchangedLength >= MAX_UNCHANGED_LENGTH) {
        append(MAX_UNCHANGED);
        unchangedLength -= MAX_UNCHANGED_LENGTH;
    }
    // Write a small (remaining) length.
    if(unchangedLength > 0) {
        append(unchangedLength - 1);
    }
}

void Edits::addReplace(int32_t oldLength, int32_t newLength) {
    if(U_FAILURE(errorCode)) { return; }
    if(oldLength == newLength && 0 < oldLength && oldLength <= MAX_SHORT_WIDTH) {
        // Replacement of short oldLength text units by same-length new text.
        // Merge into previous short-replacement record, if any.
        int32_t last = lastUnit();
        if(MAX_UNCHANGED < last && last < MAX_SHORT_CHANGE &&
                (last >> 12) == oldLength && (last & 0xfff) < MAX_SHORT_CHANGE_LENGTH) {
            setLastUnit(last + 1);
            return;
        }
        append(oldLength << 12);
        return;
    }

    if(oldLength < 0 || newLength < 0) {
        errorCode = U_ILLEGAL_ARGUMENT_ERROR;
        return;
    }
    if (oldLength == 0 && newLength == 0) {
        return;
    }
    int32_t newDelta = newLength - oldLength;
    if (newDelta != 0) {
        if ((newDelta > 0 && delta >= 0 && newDelta > (INT32_MAX - delta)) ||
                (newDelta < 0 && delta < 0 && newDelta < (INT32_MIN - delta))) {
            // Integer overflow or underflow.
            errorCode = U_INDEX_OUTOFBOUNDS_ERROR;
            return;
        }
        delta += newDelta;
    }

    int32_t head = 0x7000;
    if (oldLength < LENGTH_IN_1TRAIL && newLength < LENGTH_IN_1TRAIL) {
        head |= oldLength << 6;
        head |= newLength;
        append(head);
    } else if ((capacity - length) >= 5 || growArray()) {
        int32_t limit = length + 1;
        if(oldLength < LENGTH_IN_1TRAIL) {
            head |= oldLength << 6;
        } else if(oldLength <= 0x7fff) {
            head |= LENGTH_IN_1TRAIL << 6;
            array[limit++] = (uint16_t)(0x8000 | oldLength);
        } else {
            head |= (LENGTH_IN_2TRAIL + (oldLength >> 30)) << 6;
            array[limit++] = (uint16_t)(0x8000 | (oldLength >> 15));
            array[limit++] = (uint16_t)(0x8000 | oldLength);
        }
        if(newLength < LENGTH_IN_1TRAIL) {
            head |= newLength;
        } else if(newLength <= 0x7fff) {
            head |= LENGTH_IN_1TRAIL;
            array[limit++] = (uint16_t)(0x8000 | newLength);
        } else {
            head |= LENGTH_IN_2TRAIL + (newLength >> 30);
            array[limit++] = (uint16_t)(0x8000 | (newLength >> 15));
            array[limit++] = (uint16_t)(0x8000 | newLength);
        }
        array[length] = (uint16_t)head;
        length = limit;
    }
}

void Edits::append(int32_t r) {
    if(length < capacity || growArray()) {
        array[length++] = (uint16_t)r;
    }
}

UBool Edits::growArray() {
    int32_t newCapacity;
    if (array == stackArray) {
        newCapacity = 2000;
    } else if (capacity == INT32_MAX) {
        // Not U_BUFFER_OVERFLOW_ERROR because that could be confused on a string transform API
        // with a result-string-buffer overflow.
        errorCode = U_INDEX_OUTOFBOUNDS_ERROR;
        return FALSE;
    } else if (capacity >= (INT32_MAX / 2)) {
        newCapacity = INT32_MAX;
    } else {
        newCapacity = 2 * capacity;
    }
    // Grow by at least 5 units so that a maximal change record will fit.
    if ((newCapacity - capacity) < 5) {
        errorCode = U_INDEX_OUTOFBOUNDS_ERROR;
        return FALSE;
    }
    uint16_t *newArray = (uint16_t *)uprv_malloc((size_t)newCapacity * 2);
    if (newArray == NULL) {
        errorCode = U_MEMORY_ALLOCATION_ERROR;
        return FALSE;
    }
    uprv_memcpy(newArray, array, (size_t)length * 2);
    if (array != stackArray) {
        uprv_free(array);
    }
    array = newArray;
    capacity = newCapacity;
    return TRUE;
}

UBool Edits::copyErrorTo(UErrorCode &outErrorCode) {
    if (U_FAILURE(outErrorCode)) { return TRUE; }
    if (U_SUCCESS(errorCode)) { return FALSE; }
    outErrorCode = errorCode;
    return TRUE;
}

UBool Edits::hasChanges() const {
    if (delta != 0) {
        return TRUE;
    }
    for (int32_t i = 0; i < length; ++i) {
        if (array[i] > MAX_UNCHANGED) {
            return TRUE;
        }
    }
    return FALSE;
}

Edits::Iterator::Iterator(const uint16_t *a, int32_t len, UBool oc, UBool crs) :
        array(a), index(0), length(len), remaining(0),
        onlyChanges_(oc), coarse(crs),
        changed(FALSE), oldLength_(0), newLength_(0),
        srcIndex(0), replIndex(0), destIndex(0) {}

int32_t Edits::Iterator::readLength(int32_t head) {
    if (head < LENGTH_IN_1TRAIL) {
        return head;
    } else if (head < LENGTH_IN_2TRAIL) {
        U_ASSERT(index < length);
        U_ASSERT(array[index] >= 0x8000);
        return array[index++] & 0x7fff;
    } else {
        U_ASSERT((index + 2) <= length);
        U_ASSERT(array[index] >= 0x8000);
        U_ASSERT(array[index + 1] >= 0x8000);
        int32_t len = ((head & 1) << 30) |
                ((int32_t)(array[index] & 0x7fff) << 15) |
                (array[index + 1] & 0x7fff);
        index += 2;
        return len;
    }
}

void Edits::Iterator::updateIndexes() {
    srcIndex += oldLength_;
    if (changed) {
        replIndex += newLength_;
    }
    destIndex += newLength_;
}

UBool Edits::Iterator::noNext() {
    // No change beyond the string.
    changed = FALSE;
    oldLength_ = newLength_ = 0;
    return FALSE;
}

UBool Edits::Iterator::next(UBool onlyChanges, UErrorCode &errorCode) {
    if (U_FAILURE(errorCode)) { return FALSE; }
    // We have an errorCode in case we need to start guarding against integer overflows.
    // It is also convenient for caller loops if we bail out when an error was set elsewhere.
    updateIndexes();
    if (remaining > 0) {
        // Fine-grained iterator: Continue a sequence of equal-length changes.
        --remaining;
        return TRUE;
    }
    if (index >= length) {
        return noNext();
    }
    int32_t u = array[index++];
    if (u <= MAX_UNCHANGED) {
        // Combine adjacent unchanged ranges.
        changed = FALSE;
        oldLength_ = u + 1;
        while (index < length && (u = array[index]) <= MAX_UNCHANGED) {
            ++index;
            oldLength_ += u + 1;
        }
        newLength_ = oldLength_;
        if (onlyChanges) {
            updateIndexes();
            if (index >= length) {
                return noNext();
            }
            // already fetched u > MAX_UNCHANGED at index
            ++index;
        } else {
            return TRUE;
        }
    }
    changed = TRUE;
    if (u <= MAX_SHORT_CHANGE) {
        if (coarse) {
            int32_t w = u >> 12;
            int32_t len = (u & 0xfff) + 1;
            oldLength_ = newLength_ = len * w;
        } else {
            // Split a sequence of equal-length changes that was compressed into one unit.
            oldLength_ = newLength_ = u >> 12;
            remaining = u & 0xfff;
            return TRUE;
        }
    } else {
        U_ASSERT(u <= 0x7fff);
        oldLength_ = readLength((u >> 6) & 0x3f);
        newLength_ = readLength(u & 0x3f);
        if (!coarse) {
            return TRUE;
        }
    }
    // Combine adjacent changes.
    while (index < length && (u = array[index]) > MAX_UNCHANGED) {
        ++index;
        if (u <= MAX_SHORT_CHANGE) {
            int32_t w = u >> 12;
            int32_t len = (u & 0xfff) + 1;
            len = len * w;
            oldLength_ += len;
            newLength_ += len;
        } else {
            U_ASSERT(u <= 0x7fff);
            int32_t oldLen = readLength((u >> 6) & 0x3f);
            int32_t newLen = readLength(u & 0x3f);
            oldLength_ += oldLen;
            newLength_ += newLen;
        }
    }
    return TRUE;
}

UBool Edits::Iterator::findSourceIndex(int32_t i, UErrorCode &errorCode) {
    if (U_FAILURE(errorCode) || i < 0) { return FALSE; }
    if (i < srcIndex) {
        // Reset the iterator to the start.
        index = remaining = oldLength_ = newLength_ = srcIndex = replIndex = destIndex = 0;
    } else if (i < (srcIndex + oldLength_)) {
        // The index is in the current span.
        return TRUE;
    }
    while (next(FALSE, errorCode)) {
        if (i < (srcIndex + oldLength_)) {
            // The index is in the current span.
            return TRUE;
        }
        if (remaining > 0) {
            // Is the index in one of the remaining compressed edits?
            // srcIndex is the start of the current span, before the remaining ones.
            int32_t len = (remaining + 1) * oldLength_;
            if (i < (srcIndex + len)) {
                int32_t n = (i - srcIndex) / oldLength_;  // 1 <= n <= remaining
                len = n * oldLength_;
                srcIndex += len;
                replIndex += len;
                destIndex += len;
                remaining -= n;
                return TRUE;
            }
            // Make next() skip all of these edits at once.
            oldLength_ = newLength_ = len;
            remaining = 0;
        }
    }
    return FALSE;
}

U_NAMESPACE_END