import { INode, parseSync } from 'svgson';
import toPath from 'element-to-path';
import { SVGPathData, encodeSVGPath } from 'svg-pathdata';
import { Path, Point } from './types';
import { memoize } from 'lodash-es';

function assertNever(x: never): never {
  throw new Error('Unknown type: ' + x['type']);
}
export function assert(value: unknown): asserts value {
  if (value === undefined) {
    throw new Error('value must be defined');
  }
}

const convertToPathNode = (node: INode): { d: string; name: typeof node.name } => {
  if (node.name === 'path') {
    return { d: node.attributes.d, name: node.name };
  }
  if (node.name === 'circle') {
    const cx = parseFloat(node.attributes.cx);
    const cy = parseFloat(node.attributes.cy);
    const r = parseFloat(node.attributes.r);
    return {
      d: [
        `M ${cx} ${cy - r}`,
        `a ${r} ${r} 0 0 1 ${r} ${r}`,
        `a ${r} ${r} 0 0 1 ${0 - r} ${r}`,
        `a ${r} ${r} 0 0 1 ${0 - r} ${0 - r}`,
        `a ${r} ${r} 0 0 1 ${r} ${0 - r}`,
      ].join(''),
      name: node.name,
    };
  }
  return { d: toPath(node).replace(/z$/i, ''), name: node.name };
};

const extractNodes = (node: INode): INode[] => {
  if (['rect', 'circle', 'ellipse', 'polygon', 'polyline', 'line', 'path'].includes(node.name)) {
    return [node];
  } else if (node.children && Array.isArray(node.children)) {
    return node.children.flatMap(extractNodes);
  }

  return [];
};

export const getNodes = memoize((src: string) =>
  extractNodes(parseSync(src.includes('<svg') ? src : `<svg>${src}</svg>`)),
);

export const getCommands = (src: string) =>
  getNodes(src)
    .map(convertToPathNode)
    .flatMap(({ d, name }, idx) =>
      new SVGPathData(d)
        .toAbs()
        // @ts-expect-error `commands` is typed as a union of command types svgson does not narrow
        .commands.map((c, cIdx) => ({ ...c, id: idx, idx: cIdx, name })),
    );

const getPaths = (src: string) => {
  const commands = getCommands(src.includes('<svg') ? src : `<svg>${src}</svg>`);
  const paths: Path[] = [];
  let prev: Point | undefined = undefined;
  let start: Point | undefined = undefined;
  const addPath = (
    c: (typeof commands)[number],
    next: Point,
    d?: string,
    extras?: { circle?: Path['circle']; cp1?: Path['cp1']; cp2?: Path['cp2'] },
  ) => {
    assert(prev);
    paths.push({
      c,
      d: d || `M ${prev.x} ${prev.y} L ${next.x} ${next.y}`,
      prev,
      next,
      ...extras,
      isStart: start === prev,
    });
    prev = next;
  };
  let prevCP: Point | undefined = undefined;
  for (let i = 0; i < commands.length; i++) {
    const previousCommand = commands[i - 1];
    const c = commands[i];
    switch (c.type) {
      case SVGPathData.MOVE_TO: {
        prev = c;
        start = c;
        break;
      }
      case SVGPathData.LINE_TO: {
        assert(prev);
        addPath(c, c);
        break;
      }
      case SVGPathData.HORIZ_LINE_TO: {
        assert(prev);
        addPath(c, { x: c.x, y: prev.y });
        break;
      }
      case SVGPathData.VERT_LINE_TO: {
        assert(prev);
        addPath(c, { x: prev.x, y: c.y });
        break;
      }
      case SVGPathData.CLOSE_PATH: {
        assert(prev);
        assert(start);
        addPath(c, start);
        start = undefined;
        break;
      }
      case SVGPathData.CURVE_TO: {
        assert(prev);
        addPath(c, c, `M ${prev.x} ${prev.y} ${encodeSVGPath(c)}`, {
          cp1: { x: c.x1, y: c.y1 },
          cp2: { x: c.x2, y: c.y2 },
        });
        break;
      }
      case SVGPathData.SMOOTH_CURVE_TO: {
        assert(prev);
        assert(previousCommand);
        const reflectedCp1 = {
          x:
            previousCommand &&
            (previousCommand.type === SVGPathData.SMOOTH_CURVE_TO ||
              previousCommand.type === SVGPathData.CURVE_TO)
              ? previousCommand.relative
                ? previousCommand.x2 - previousCommand.x
                : previousCommand.x2 - prev.x
              : 0,
          y:
            previousCommand &&
            (previousCommand.type === SVGPathData.SMOOTH_CURVE_TO ||
              previousCommand.type === SVGPathData.CURVE_TO)
              ? previousCommand.relative
                ? previousCommand.y2 - previousCommand.y
                : previousCommand.y2 - prev.y
              : 0,
        };
        addPath(
          c,
          c,
          `M ${prev.x} ${prev.y} ${encodeSVGPath({
            type: SVGPathData.CURVE_TO,
            relative: false,
            x: c.x,
            y: c.y,
            x1: prev.x - reflectedCp1.x,
            y1: prev.y - reflectedCp1.y,
            x2: c.x2,
            y2: c.y2,
          })}`,
          {
            cp1: { x: prev.x - reflectedCp1.x, y: prev.y - reflectedCp1.y },
            cp2: { x: c.x2, y: c.y2 },
          },
        );
        break;
      }
      case SVGPathData.QUAD_TO: {
        assert(prev);
        addPath(c, c, `M ${prev.x} ${prev.y} ${encodeSVGPath(c)}`, {
          cp1: { x: c.x1, y: c.y1 },
          cp2: { x: c.x1, y: c.y1 },
        });
        break;
      }
      case SVGPathData.SMOOTH_QUAD_TO: {
        assert(prev);
        const backTrackCP = (
          index: number,
          currentPoint: { x: number; y: number },
        ): { x: number; y: number } => {
          const previousCommand = commands[index - 1];
          if (!previousCommand) {
            return currentPoint;
          }
          if (previousCommand.type === SVGPathData.QUAD_TO) {
            return {
              x: previousCommand.relative
                ? currentPoint.x - (previousCommand.x1 - previousCommand.x)
                : currentPoint.x - (previousCommand.x1 - currentPoint.x),
              y: previousCommand.relative
                ? currentPoint.y - (previousCommand.y1 - previousCommand.y)
                : currentPoint.y - (previousCommand.y1 - currentPoint.y),
            };
          }
          if (previousCommand.type === SVGPathData.SMOOTH_QUAD_TO) {
            if (!prevCP) {
              return currentPoint;
            }
            return {
              x: currentPoint.x - (prevCP.x - currentPoint.x),
              y: currentPoint.y - (prevCP.y - currentPoint.y),
            };
          }
          return currentPoint;
        };
        prevCP = backTrackCP(i, prev);
        addPath(
          c,
          c,
          `M ${prev.x} ${prev.y} ${encodeSVGPath({
            type: SVGPathData.QUAD_TO,
            relative: false,
            x: c.x,
            y: c.y,
            x1: prevCP.x,
            y1: prevCP.y,
          })}`,
          {
            cp1: { x: prevCP.x, y: prevCP.y },
            cp2: { x: prevCP.x, y: prevCP.y },
          },
        );
        break;
      }
      case SVGPathData.ARC: {
        assert(prev);
        const center = arcEllipseCenter(
          prev.x,
          prev.y,
          c.rX,
          c.rY,
          c.xRot,
          c.lArcFlag,
          c.sweepFlag,
          c.x,
          c.y,
        );
        addPath(
          c,
          c,
          `M ${prev.x} ${prev.y} A${c.rX} ${c.rY} ${c.xRot} ${c.lArcFlag} ${c.sweepFlag} ${c.x} ${c.y}`,
          { circle: c.rX === c.rY ? { ...center, r: c.rX } : undefined },
        );
        break;
      }
      default: {
        // @ts-expect-error every command type is handled above, so `c` is not `never` here
        assertNever(c);
      }
    }
  }
  return paths;
};

const arcEllipseCenter = (
  x1: number,
  y1: number,
  rx: number,
  ry: number,
  a: number,
  fa: number,
  fs: number,
  x2: number,
  y2: number,
) => {
  const phi = (a * Math.PI) / 180;

  const M = [
    [Math.cos(phi), Math.sin(phi)],
    [-Math.sin(phi), Math.cos(phi)],
  ];
  const V = [(x1 - x2) / 2, (y1 - y2) / 2];

  const [x1p, y1p] = [M[0][0] * V[0] + M[0][1] * V[1], M[1][0] * V[0] + M[1][1] * V[1]];

  rx = Math.abs(rx);
  ry = Math.abs(ry);

  const lambda = (x1p * x1p) / (rx * rx) + (y1p * y1p) / (ry * ry);
  if (lambda > 1) {
    rx = Math.sqrt(lambda) * rx;
    ry = Math.sqrt(lambda) * ry;
  }

  const sign = fa === fs ? -1 : 1;

  const co =
    sign *
    Math.sqrt(
      Math.max(rx * rx * ry * ry - rx * rx * y1p * y1p - ry * ry * x1p * x1p, 0) /
        (rx * rx * y1p * y1p + ry * ry * x1p * x1p),
    );

  const V2 = [(rx * y1p) / ry, (-ry * x1p) / rx];
  const Cp = [V2[0] * co, V2[1] * co];

  const M2 = [
    [Math.cos(phi), -Math.sin(phi)],
    [Math.sin(phi), Math.cos(phi)],
  ];
  const V3 = [(x1 + x2) / 2, (y1 + y2) / 2];
  const C = [
    M2[0][0] * Cp[0] + M2[0][1] * Cp[1] + V3[0],
    M2[1][0] * Cp[0] + M2[1][1] * Cp[1] + V3[1],
  ];

  return {
    x: C[0],
    y: C[1],
    tangentIntersection: intersectTangents(
      { x: x1, y: y1 },
      { x: x2, y: y2 },
      { x: C[0], y: C[1] },
    ),
  };
};

function getTangentDirection(p: Point, center: Point): Point {
  // Tangent is perpendicular to the radius vector (rotate radius 90°)
  const dx = p.x - center.x;
  const dy = p.y - center.y;
  return { x: -dy, y: dx }; // 90° rotation
}

function intersectTangents(start: Point, end: Point, center: Point): Point | null {
  const t1 = getTangentDirection(start, center);
  const t2 = getTangentDirection(end, center);

  // Solve: start + λ * t1 = end + μ * t2
  const A = [
    [t1.x, -t2.x],
    [t1.y, -t2.y],
  ];
  const b = [end.x - start.x, end.y - start.y];

  // Compute determinant
  const det = A[0][0] * A[1][1] - A[0][1] * A[1][0];

  if (Math.abs(det) < 1e-10) {
    // Lines are parallel, no intersection
    return null;
  }

  const invDet = 1 / det;

  const lambda = (b[0] * A[1][1] - b[1] * A[0][1]) * invDet;

  // Intersection point = start + lambda * t1
  return {
    x: start.x + lambda * t1.x,
    y: start.y + lambda * t1.y,
  };
}

export default memoize(getPaths);