#include "CgeScanline.h"
#include <stdlib.h>

#define AET_INIT_SIZE 256
#define SPAN_INIT_SIZE 256

#define SWAP(x, y) \
    do { uint32_t t = (x); (x) = (y); (y) = t; } while (0)

#define SETC(x, value) \
    do { if (x) *(x) = (value); } while(0)

typedef size_t (*SpanGeneratorCb)(CgeScanlineEdge *, CgeScanlineEdgeTable *,
                                  size_t, CgeScanlineSpan *, size_t);

static void aetStep(CgeScanlineEdge *edge, CgeScanlineEdgeTable *aet,
                    size_t size) {
    CgeScanlineEdgeTable *current, *end;

    for (current = aet, end = aet + size; current != end; ++current) {
        CgeScanlineEdge *lookupEdge = edge + current->index;
        uint32_t overflow;

        current->x += lookupEdge->step;
        current->error += lookupEdge->error;

        overflow = (current->error >= lookupEdge->threshold) ? 0xFFFFFFFFul : 0;
        current->x += lookupEdge->dir & overflow;
        current->error -= lookupEdge->threshold & overflow;
    }
}

static void aetSort(CgeScanlineEdgeTable *aet, size_t aetSize) {
    CgeScanlineEdgeTable tmp;
    size_t i, j;

    for (i = 1; i < aetSize; ++i) {
        tmp = aet[i];
        for (j = i; j > 0 && aet[j - 1].x > tmp.x; --j)
            aet[j] = aet[j - 1];
        aet[j] = tmp;
    }
}

static size_t aetRemove(CgeScanlineEdge *edge, CgeScanlineEdgeTable *aet,
                        size_t aetSize, uint32_t y) {
    size_t writeIdx, i;

    for (writeIdx = 0, i = 0; i < aetSize; ++i) {
        if (edge[aet[i].index].endY != y)
            aet[writeIdx++] = aet[i];
    }

    return writeIdx;
}

static int aetAdd(CgeScanlineEdge *edge, size_t edgeSize,
                  CgeScanlineEdgeTable *aet, size_t *aetSize,
                  size_t aetCapacity, size_t *edgeCursor, uint32_t y) {
    for (; *edgeCursor < edgeSize && edge[*edgeCursor].startY == y; ++*edgeCursor) {
        if (*aetSize >= aetCapacity)
            return 0;
        aet[*aetSize].index = *edgeCursor;
        aet[*aetSize].x = edge[*edgeCursor].startX;
        aet[*aetSize].error = 0;
        ++*aetSize;
    }
    return 1;
}

static int edgesCmp(const void *lhs, const void *rhs) {
    CgeScanlineEdge *left = (CgeScanlineEdge *)lhs;
    CgeScanlineEdge *right = (CgeScanlineEdge *)rhs;

    return left->startY < right->startY ? -1 : (left->startY == right->startY ? 0 : 1);
}

int CgeScanlineEdgeAdd(CgeScanlineEdge *edge, uint32_t aX, uint32_t aY,
                       uint32_t bX, uint32_t bY) {
    uint32_t dX;

    if (aY == bY)
        return 0;

    edge->winding = 1;
    if (bY < aY) {
        SWAP(aX, bX);
        SWAP(aY, bY);
        edge->winding = -1;
    }

    edge->threshold = bY - aY;
    edge->startY = aY;
    edge->endY = bY;
    edge->startX = aX;
    dX = (aX < bX) ? bX - aX : aX - bX;
    edge->step = dX / edge->threshold;
    edge->error = dX % edge->threshold;
    edge->dir = 1;

    if (bX < aX) {
        edge->dir = -1;
        edge->step *= -1;
    }

    return 1;
}

static size_t spansOddEven(CgeScanlineEdge *edge, CgeScanlineEdgeTable *aet,
                           size_t aetSize, CgeScanlineSpan *span,
                           size_t spanSize) {
    size_t i, size;
    (void)edge;

    for (i = 0, size = 0; i + 1 < aetSize; i += 2) {
        if (aet[i].x < aet[i + 1].x) {
            if (size >= spanSize)
                return SIZE_MAX;
            span[size].start = aet[i].x;
            span[size].end = aet[i + 1].x;
            ++size;
        }
    }

    return size;
}

static size_t spansNonZero(CgeScanlineEdge *edge, CgeScanlineEdgeTable *aet,
                           size_t aetSize, CgeScanlineSpan *span,
                           size_t spanSize) {
    int winding, inSpan;
    uint32_t spanStart;
    size_t i, size;

    winding = 0;
    inSpan = 0;
    spanStart = 0;
    size = 0;

    for (i = 0; i < aetSize; ++i) {
        winding += edge[aet[i].index].winding;

        if (!inSpan && winding != 0) {
            spanStart = aet[i].x;
            inSpan = 1;
        } else if (inSpan && winding == 0) {
            if (spanStart < aet[i].x) {
                if (size >= spanSize)
                    return SIZE_MAX;
                span[size].start = spanStart;
                span[size].end = aet[i].x;
                ++size;
            }
            inSpan = 0;
        }
    }

    return size;
}

int CgeScanlineStateInit(CgeScanlineState *state, CgeScanlineEdge *edge,
                         size_t edgeSize, CgeScanlineEdgeTable *aet,
                         size_t aetCapacity, CgeScanlineSpan *span,
                         size_t spanCapacity, CgeScanlineRowCallback callback,
                         void *userData, int flags) {
    uint32_t yMin, yMax;
    size_t i;

    if (!edgeSize || !aetCapacity || !spanCapacity || !callback)
        return 0;

    state->edge = edge;
    state->edgeSize = edgeSize;
    state->aet = aet;
    state->aetCapacity = aetCapacity;
    state->span = span;
    state->spanCapacity = spanCapacity;
    state->callback = callback;
    state->userData = userData;
    state->flags = flags;

    yMin = state->edge[0].startY;
    yMax = state->edge[0].endY;
    for (i = 1; i < edgeSize; ++i) {
        if (state->edge[i].startY < yMin)
            yMin = state->edge[i].startY;
        if (state->edge[i].endY > yMax)
            yMax = state->edge[i].endY;
    }

    qsort(state->edge, state->edgeSize, sizeof(*state->edge), edgesCmp);
    state->yCurrent = yMin;
    state->yMax = yMax;
    state->edgeCursor = 0;
    state->aetSize = 0;

    return 1;
}

int CgeScanlineStateNext(CgeScanlineState *state, int *result) {
    SpanGeneratorCb generate;
    size_t rowSpans;

    generate = (state->flags & CGE_SCANLINE_NON_ZERO) ? spansNonZero
                                                      : spansOddEven;

    if (state->yCurrent >= state->yMax) {
        SETC(result, CGE_SCANLINE_EDONE);
        return 0;
    }

    state->aetSize = aetRemove(state->edge, state->aet, state->aetSize,
                               state->yCurrent);
    if (!aetAdd(state->edge, state->edgeSize, state->aet, &state->aetSize,
                state->aetCapacity, &state->edgeCursor, state->yCurrent)) {
        SETC(result, CGE_SCANLINE_EAET);
        return 0;
    }

    rowSpans = 0;
    if (state->aetSize != 0) {
        aetSort(state->aet, state->aetSize);

        rowSpans = generate(state->edge, state->aet, state->aetSize,
                            state->span, state->spanCapacity);
        if (rowSpans == SIZE_MAX) {
            SETC(result, CGE_SCANLINE_ESPANS);
            return 0;
        }
        aetStep(state->edge, state->aet, state->aetSize);
    }

    state->callback(state->yCurrent, state->span, rowSpans, state->userData);
    state->yCurrent++;
    return 1;
}

int CgeScanlineSpans(CgeScanlineEdge *edge, size_t edgeSize,
                     CgeScanlineRowCallback callback, void *userData,
                     int flags) {
    CgeScanlineEdgeTable *aet;
    CgeScanlineSpan *spans;
    CgeScanlineState state;
    int result;

    aet = malloc(sizeof(*aet) * AET_INIT_SIZE);
    spans = malloc(sizeof(*spans) * SPAN_INIT_SIZE);
    if (!aet || !spans) {
        free(aet);
        free(spans);
        return 0;
    }

    if (!CgeScanlineStateInit(&state, edge, edgeSize, aet, AET_INIT_SIZE, spans,
                              SPAN_INIT_SIZE, callback, userData, flags)) {
        free(aet);
        free(spans);
        return 0;
    }

    while (1) {
        if (CgeScanlineStateNext(&state, &result))
            continue;

        switch (result) {
        case CGE_SCANLINE_EDONE:
            free(state.aet);
            free(state.span);
            return 1;

        case CGE_SCANLINE_EAET:
            aet = realloc(state.aet, sizeof(*aet) * state.aetCapacity * 2);
            if (aet) {
                state.aetCapacity *= 2;
                state.aet = aet;
            } else {
                free(state.aet);
                free(state.span);
                return 0;
            }
            break;

        case CGE_SCANLINE_ESPANS:
            spans = realloc(state.span, sizeof(*spans) * state.spanCapacity * 2);
            if (spans) {
                state.spanCapacity *= 2;
                state.span = spans;
            } else {
                free(state.aet);
                free(state.span);
                return 0;
            }
            break;
        }
    }
}