#include "effects/tileswap.hpp"

#include <algorithm>
#include <cmath>
#include <vector>

#include "effects/source_fill.hpp"
#include "effects/tile_plan.hpp"

namespace effector {

const std::vector<ParamSpec>& TileSwapEffect::params() const {
    static const std::vector<ParamSpec> specs = {
        ParamSpec::makeChoice("tileswap_layout", "Layout", "grid", {"grid", "brick", "scatter"},
                              "grid lines the tiles up in rows and columns; brick packs every row "
                              "on its own so the seams do not meet; scatter drops loose tiles over "
                              "a filled background, overlapping."),
        ParamSpec::makeInt("tileswap_width", "Tile width", 96, 1, 2048,
                           "Width in pixels of each cut-out tile."),
        ParamSpec::makeInt("tileswap_height", "Tile height", 96, 1, 2048,
                           "Height in pixels of each cut-out tile."),
        ParamSpec::makeInt("tileswap_jitter", "Size jitter", 0, 0, 512,
                           "Random +/- variation added to both tile sizes (0 = uniform)."),
        ParamSpec::makeInt("tileswap_count", "Tile count", 64, 1, 4096,
                           "How many tiles are dropped on the canvas; scattered layout only."),
        ParamSpec::makeBool("tileswap_keep_order", "Cycle images in order", false,
                            "Take tiles from the images in order instead of picking randomly."),
        ParamSpec::makeDouble("tileswap_rate", "Swap rate", 1.0, 0.0, 5.0,
                              "Swaps per second of each tile, on average; 0 for none. Below two "
                              "swaps in the clip only some of the tiles swap, fewer the lower it "
                              "goes, so that the clip still loops without a jump.",
                              0.01, 2)
            .slider(3.0),
    };
    return specs;
}

namespace {

struct Settings {
    std::string layout;
    int tileWidth;
    int tileHeight;
    int jitter;
    long count;
    bool keepOrder;
    double rate;

    explicit Settings(const ParamValues& values)
        : layout(paramChoice(values, "tileswap_layout", "grid")),
          tileWidth(static_cast<int>(std::max(1L, paramInt(values, "tileswap_width", 96)))),
          tileHeight(static_cast<int>(std::max(1L, paramInt(values, "tileswap_height", 96)))),
          jitter(static_cast<int>(std::max(0L, paramInt(values, "tileswap_jitter", 0)))),
          count(std::max(1L, paramInt(values, "tileswap_count", 64))),
          keepOrder(paramBool(values, "tileswap_keep_order", false)),
          rate(std::max(0.0, paramDouble(values, "tileswap_rate", 1.0))) {}
};

double unit(Rng& rng) { return static_cast<double>(rng.next() >> 11) * 0x1.0p-53; }

// Where a tile sits for the whole clip, when in its swaps it turns over, the
// seed its cuts come from, and the draw that settles how often it swaps.
struct Cell {
    int x;
    int y;
    int w;
    int h;
    double phase;
    std::uint64_t seed;
    double share;
};

}  // namespace

Image TileSwapEffect::compose(const std::vector<Image>& sources, int width, int height,
                              const ParamValues& values, const Moment& at) const {
    const Settings settings(values);
    const bool scatter = settings.layout == "scatter";
    Image canvas(width, height);

    // What stays put for the whole clip: the cells, and for loose tiles the
    // backdrop they lie on.
    Rng steady = at.steady();
    std::vector<Cell> cells;
    auto addCell = [&](int x, int y, int w, int h) {
        cells.push_back(Cell{x, y, w, h, 0.0, 0, 0.0});
    };
    if (scatter) {
        const Image& src = sources[steady.below(sources.size() - 1)];
        const int sx = static_cast<int>(steady.inRange(0, std::max(0, src.width() - width)));
        const int sy = static_cast<int>(steady.inRange(0, std::max(0, src.height() - height)));
        fillFromSource(canvas, src, sx, sy);

        cells.reserve(static_cast<std::size_t>(settings.count));
        for (long i = 0; i < settings.count; ++i) {
            int w = settings.tileWidth;
            int h = settings.tileHeight;
            if (settings.jitter > 0) {
                w += static_cast<int>(steady.inRange(-settings.jitter, settings.jitter));
                h += static_cast<int>(steady.inRange(-settings.jitter, settings.jitter));
            }
            const int x = static_cast<int>(steady.inRange(0, width - 1));
            const int y = static_cast<int>(steady.inRange(0, height - 1));
            addCell(x, y, std::max(1, std::min(w, width - x)), std::max(1, std::min(h, height - y)));
        }
    } else {
        const bool brick = settings.layout == "brick";
        const std::vector<int> rows = planSpans(steady, settings.tileHeight, settings.jitter, height);
        std::vector<int> columns;
        if (!brick) columns = planSpans(steady, settings.tileWidth, settings.jitter, width);
        int y = 0;
        for (const int rowHeight : rows) {
            if (brick) columns = planSpans(steady, settings.tileWidth, settings.jitter, width);
            int x = 0;
            for (const int cellWidth : columns) {
                addCell(x, y, cellWidth, rowHeight);
                x += cellWidth;
            }
            y += rowHeight;
        }
    }
    for (Cell& cell : cells) {
        cell.phase = unit(steady);
        cell.seed = steady.next();
        cell.share = unit(steady);
    }

    // How often each tile swaps in one pass of the clip, `each` on average. A
    // tile has to come back to the cut it started with, so one that swaps at
    // all swaps at least twice; below that a share of the tiles swap twice and
    // the rest hold still, so a low rate thins out the tiles that move instead
    // of moving every one of them. Above it, each tile rounds `each` up or
    // down by its own draw.
    const double length = at.length();
    const double each = settings.rate * length;
    auto swapsOf = [&](const Cell& cell) -> long {
        if (each <= 0.0) return 0;
        if (each < 2.0) return cell.share < each / 2.0 ? 2 : 0;
        const double whole = std::floor(each);
        return static_cast<long>(whole) + (cell.share < each - whole ? 1 : 0);
    };

    // What a tile shows depends only on the tile and how many times it has
    // swapped, counted round the clip so that the frame after the last shows
    // what the first does; so it holds still between swaps and any frame can
    // be drawn on its own.
    std::vector<Tile> plan;
    plan.reserve(cells.size());
    for (std::size_t i = 0; i < cells.size(); ++i) {
        const Cell& cell = cells[i];
        const long swaps = swapsOf(cell);
        std::uint64_t turn = 0;
        if (swaps > 0) {
            const auto passed =
                static_cast<long>(std::floor(at.seconds() * swaps / length + cell.phase));
            turn = static_cast<std::uint64_t>(passed % swaps);
        }
        Rng cut(cell.seed + turn * 0x9e3779b97f4a7c15ULL);
        const std::size_t sourceIndex =
            settings.keepOrder ? (i + turn) % sources.size() : cut.below(sources.size() - 1);
        const Image& src = sources[sourceIndex];
        const int sx = static_cast<int>(cut.inRange(0, std::max(0, src.width() - cell.w)));
        const int sy = static_cast<int>(cut.inRange(0, std::max(0, src.height() - cell.h)));
        plan.push_back(Tile{cell.x, cell.y, cell.w, cell.h, static_cast<int>(sourceIndex), sx, sy});
    }

    paintTiles(canvas, sources, plan, scatter);
    return canvas;
}

}  // namespace effector