library MultiPartRLEToSVG {
    struct SVGParams {
        bytes[] parts;
        string background;
    }

    struct ContentBounds {
        uint8 top;
        uint8 right;
        uint8 bottom;
        uint8 left;
    }

    struct Rect {
        uint8 length;
        uint8 colorIndex;
    }

    struct DecodedImage {
        uint8 paletteIndex;
        ContentBounds bounds;
        Rect[] rects;
    }

    /**
     * @notice Given RLE image parts and color palettes, merge to generate a single SVG image.
     */
    function generateSVG(SVGParams memory params, mapping(uint8 => string[]) storage palettes)
        internal
        view
        returns (string memory svg)
    {
        // prettier-ignore
        return string(
            abi.encodePacked(
                '<svg width="190" height="190" viewBox="0 0 190 190" xmlns="http://www.w3.org/2000/svg" shape-rendering="crispEdges">',
                '<rect width="100%" height="100%" fill="#', params.background, '" />',
                _generateSVGRects(params, palettes),
                '</svg>'
            )
        );
    }

    /**
     * @notice Given RLE image parts and color palettes, generate SVG rects.
     * This is a lookup table that enables very cheap int to string
     * conversions when operating on a set of predefined integers.
     * This is used below to convert the integer length of each rectangle
     * in a 19x19 pixel grid to the string representation of the length
     * in a 190x190 pixel grid, which is the chosen dimension for all Wizards.
     * For example: A length of 3 gets mapped to '30'.
     */    
    // prettier-ignore
    function _generateSVGRects(SVGParams memory params, mapping(uint8 => string[]) storage palettes)
        private
        view
        returns (string memory svg)
    {
        string[20] memory lookup = [
            '0', '10', '20', '30', '40', '50', '60', '70', 
            '80', '90', '100', '110', '120', '130', '140', '150', 
            '160', '170', '180', '190'
        ];
        string memory rects;
        for (uint8 p = 0; p < params.parts.length; p++) {
            DecodedImage memory image = _decodeRLEImage(params.parts[p]);
            string[] storage palette = palettes[image.paletteIndex];
            uint256 currentX = image.bounds.left;
            uint256 currentY = image.bounds.top;
            uint256 cursor;
            string[16] memory buffer;

            string memory part;
            for (uint256 i = 0; i < image.rects.length; i++) {
                Rect memory rect = image.rects[i];
                if (rect.colorIndex != 0) {
                    buffer[cursor] = lookup[rect.length];          // width
                    buffer[cursor + 1] = lookup[currentX];         // x
                    buffer[cursor + 2] = lookup[currentY];         // y
                    buffer[cursor + 3] = palette[rect.colorIndex]; // color

                    cursor += 4;

                    if (cursor >= 16) {
                        part = string(abi.encodePacked(part, _getChunk(cursor, buffer)));
                        cursor = 0;
                    }
                }

                currentX += rect.length;
                if (currentX == image.bounds.right) {
                    currentX = image.bounds.left;
                    currentY++;
                }
            }

            if (cursor != 0) {
                part = string(abi.encodePacked(part, _getChunk(cursor, buffer)));
            }
            rects = string(abi.encodePacked(rects, part));
        }
        return rects;
    }

    /**
     * @notice Return a string that consists of all rects in the provided `buffer`.
     */
    // prettier-ignore
    function _getChunk(uint256 cursor, string[16] memory buffer) private pure returns (string memory) {
        string memory chunk;
        for (uint256 i = 0; i < cursor; i += 4) {
            chunk = string(
                abi.encodePacked(
                    chunk,
                    '<rect width="', buffer[i], '" height="10" x="', buffer[i + 1], '" y="', buffer[i + 2], '" fill="#', buffer[i + 3], '" />'
                )
            );
        }
        return chunk;
    }

    /**
     * @notice Decode a single RLE compressed image into a `DecodedImage`.
     */
    function _decodeRLEImage(bytes memory image) private pure returns (DecodedImage memory) {
        uint8 paletteIndex = uint8(image[0]);
        ContentBounds memory bounds = ContentBounds({
            top: uint8(image[1]),
            right: uint8(image[2]),
            bottom: uint8(image[3]),
            left: uint8(image[4])
        });

        uint256 cursor;
        Rect[] memory rects = new Rect[]((image.length - 5) / 2);
        for (uint256 i = 5; i < image.length; i += 2) {
            rects[cursor] = Rect({ length: uint8(image[i]), colorIndex: uint8(image[i + 1]) });
            cursor++;
        }
        return DecodedImage({ paletteIndex: paletteIndex, bounds: bounds, rects: rects });
    }
}
function _decodeRLEImage(bytes memory image) private pure returns (DecodedImage memory) {
    uint8 paletteIndex = uint8(image[0]);
    ContentBounds memory bounds = ContentBounds({
        top: uint8(image[1]),
        right: uint8(image[2]),
        bottom: uint8(image[3]),
        left: uint8(image[4])
    });

    uint256 cursor;
    Rect[] memory rects = new Rect[]((image.length - 5) / 2);
    for (uint256 i = 5; i < image.length; i += 2) {
        rects[cursor] = Rect({ length: uint8(image[i]), colorIndex: uint8(image[i + 1]) });
        cursor++;
    }
    return DecodedImage({ paletteIndex: paletteIndex, bounds: bounds, rects: rects });
}

/**
 * @notice Decode a single RLE compressed image into a `DecodedImage`.
 */