import type OlMap from 'ol/Map';
import type { Extent } from 'ol/extent';
import { getWidth } from 'ol/extent';
import ImageLayer from 'ol/layer/Image';
import ImageCanvas from 'ol/source/ImageCanvas';
import { transform, transformExtent } from 'ol/proj';
import { obtainViewer2D } from '@/gis/ol/map';
import type {
  ContourWorkerRequest,
  ContourWorkerResponse,
  FlexpartContourLayerOptions,
  FlexpartContourLayerResult,
  FlexpartGridFrame,
  SerializedContour,
} from './flexpartContourTypes';
import { PYTHON_CONTOUR_COLORS } from './flexpartContourTypes';

const WEB_MERCATOR_MAX_LATITUDE = 85.0511287798066;

interface ProjectedContour {
  color: string;
  path: Path2D;
}

interface PendingRequest {
  resolve: (value: SerializedContour[]) => void;
  reject: (reason?: unknown) => void;
}

interface PreparedContourGrid {
  longitudes: readonly number[];
  values: Float64Array;
}

export function createLogLevels(
  colorMin: number,
  colorMax: number,
  bandCount = 10,
): number[] {
  if (!Number.isFinite(colorMin)
      || !Number.isFinite(colorMax)
      || colorMin <= 0
      || colorMax <= colorMin
      || bandCount < 1) {
    throw new Error('Invalid logarithmic color range.');
  }

  const minExponent = Math.log10(colorMin);
  const maxExponent = Math.log10(colorMax);

  return Array.from({ length: bandCount + 1 }, (_, index) => (
    10 ** (
      minExponent
      + (maxExponent - minExponent) * index / bandCount
    )
  ));
}

export class FlexpartContourRenderer {
  private readonly map: OlMap;

  private readonly source: ImageCanvas;

  private readonly layer: ImageLayer<ImageCanvas>;

  private readonly worker: Worker;

  private readonly pending = new Map<number, PendingRequest>();

  private requestId = 0;

  private frameVersion = 0;

  private projectedContours: ProjectedContour[] = [];

  private layerExtent?: Extent;

  private readonly colors: readonly string[];

  private readonly wrapX: boolean;

  private readonly worldWidth?: number;

  constructor(
    map: OlMap,
    options: FlexpartContourLayerOptions = {},
  ) {
    this.map = map;
    this.colors = options.colors ?? PYTHON_CONTOUR_COLORS;
    this.wrapX = options.wrapX ?? true;

    const projection = map.getView().getProjection();
    const projectionCode = projection.getCode();
    const projectionExtent = projection.getExtent();
    this.worldWidth = this.wrapX
      && projection.canWrapX()
      && projectionExtent
      ? getWidth(projectionExtent)
      : undefined;

    this.source = new ImageCanvas({
      projection: projectionCode,
      ratio: 1,
      canvasFunction: (
        extent,
        _resolution,
        _pixelRatio,
        size,
      ) => this.drawCanvas(extent, size),
    });

    this.layer = new ImageLayer({
      source: this.source,
      opacity: options.opacity ?? 0.78,
      zIndex: options.zIndex ?? 1000,
    });

    if (options.layerName) {
      this.layer.set('name', options.layerName);
    }

    this.worker = new Worker(
      new URL('./flexpartContour.worker.ts', import.meta.url),
      { type: 'module' },
    );

    this.worker.onmessage = (
      event: MessageEvent<ContourWorkerResponse>,
    ) => {
      const request = this.pending.get(event.data.id);
      if (!request) {
        return;
      }

      this.pending.delete(event.data.id);

      if (event.data.error) {
        request.reject(new Error(event.data.error));
      }
      else {
        request.resolve(event.data.contours ?? []);
      }
    };

    this.worker.onerror = (event) => {
      const error = new Error(
        event.message || 'Contour worker failed.',
      );
      this.pending.forEach((request) => request.reject(error));
      this.pending.clear();
    };

    map.addLayer(this.layer);
  }

  async setFrame(
    frame: FlexpartGridFrame,
  ): Promise<FlexpartContourLayerResult> {
    this.validateFrame(frame);

    const version = ++this.frameVersion;
    const levels = this.resolveLevels(frame);
    const normalizedValues = this.prepareValues(frame);
    const contourGrid = this.prepareCyclicLongitudeGrid(
      frame.longitudes,
      frame.latitudes.length,
      normalizedValues,
    );
    const rawContours = await this.calculateContours(
      contourGrid.longitudes.length,
      frame.latitudes.length,
      contourGrid.values,
      levels.slice(0, -1),
    );

    if (version !== this.frameVersion) {
      throw new Error('A newer FLEXPART frame superseded this frame.');
    }

    const projection = this.map.getView().getProjection();
    this.projectedContours = rawContours.map((contour, index) => ({
      color: this.colors[index],
      path: this.createProjectedPath(
        contour,
        contourGrid.longitudes,
        frame.latitudes,
        projection.getCode(),
      ),
    }));

    this.layerExtent = this.createLayerExtent(
      frame.longitudes,
      frame.latitudes,
      projection.getCode(),
    );
    // A wrapped global layer must not be clipped to the canonical world.
    this.layer.setExtent(this.worldWidth ? undefined : this.layerExtent);
    this.layer.setVisible(true);
    this.source.changed();
    this.map.render();

    return {
      layerExtent: this.layerExtent,
      levels,
      validTime: frame.validTime,
    };
  }

  getLayer(): ImageLayer<ImageCanvas> {
    return this.layer;
  }

  setVisible(visible: boolean): void {
    this.layer.setVisible(visible);
  }

  setOpacity(opacity: number): void {
    this.layer.setOpacity(Math.max(0, Math.min(1, opacity)));
  }

  clear(): void {
    this.projectedContours = [];
    this.source.changed();
  }

  destroy(): void {
    this.worker.terminate();
    this.map.removeLayer(this.layer);
  }

  private validateFrame(frame: FlexpartGridFrame): void {
    const width = frame.longitudes.length;
    const height = frame.latitudes.length;

    if (width < 2 || height < 2) {
      throw new Error('Longitude and latitude need at least two points.');
    }

    if (isNestedValues(frame.values)) {
      if (frame.values.length !== height
          || frame.values.some((row) => row.length !== width)) {
        throw new Error(
          `values must be a ${height}x${width} two-dimensional array.`,
        );
      }
    }
    else if (frame.values.length !== width * height) {
      throw new Error(
        `values length must be ${width * height}, got ${frame.values.length}.`,
      );
    }

    this.validateAxis(frame.longitudes, 'longitudes');
    this.validateAxis(frame.latitudes, 'latitudes');

    if (!Number.isFinite(frame.colorMin)
        || !Number.isFinite(frame.colorMax)
        || frame.colorMin <= 0
        || frame.colorMax <= frame.colorMin) {
      throw new Error('Invalid colorMin/colorMax.');
    }
  }

  private validateAxis(axis: readonly number[], name: string): void {
    let direction = 0;

    for (let index = 0; index < axis.length; index++) {
      if (!Number.isFinite(axis[index])) {
        throw new Error(`${name} contains a non-finite coordinate.`);
      }

      if (index === 0) {
        continue;
      }

      const difference = axis[index] - axis[index - 1];
      const currentDirection = Math.sign(difference);

      if (currentDirection === 0
          || (direction !== 0 && currentDirection !== direction)) {
        throw new Error(`${name} must be strictly monotonic.`);
      }

      direction = currentDirection;
    }
  }

  private resolveLevels(frame: FlexpartGridFrame): number[] {
    const levels = frame.levels
      ? Array.from(frame.levels)
      : createLogLevels(frame.colorMin, frame.colorMax);

    if (levels.length !== this.colors.length + 1) {
      throw new Error(
        `levels must contain ${this.colors.length + 1} values.`,
      );
    }

    for (let index = 0; index < levels.length; index++) {
      if (!Number.isFinite(levels[index])
          || levels[index] <= 0
          || (index > 0 && levels[index] <= levels[index - 1])) {
        throw new Error('levels must be positive and strictly increasing.');
      }
    }

    return levels;
  }

  private prepareValues(frame: FlexpartGridFrame): Float64Array {
    const width = frame.longitudes.length;
    const height = frame.latitudes.length;
    const values = new Float64Array(width * height);

    for (let row = 0; row < height; row++) {
      for (let column = 0; column < width; column++) {
        const sourceValue = isNestedValues(frame.values)
          ? frame.values[row][column]
          : frame.values[row * width + column];
        const value = Number(sourceValue);

        // Positive values below colorMin still influence contour interpolation.
        // The first threshold keeps those cells transparent without log10 data.
        values[row * width + column] = Number.isFinite(value) && value > 0
          ? value
          : Number.NaN;
      }
    }

    return values;
  }

  private prepareCyclicLongitudeGrid(
    longitudes: readonly number[],
    height: number,
    values: Float64Array,
  ): PreparedContourGrid {
    if (!this.wrapX || !isGlobalCyclicAxis(longitudes)) {
      return { longitudes, values };
    }

    const sourceWidth = longitudes.length;
    const targetWidth = sourceWidth + 1;
    const direction = Math.sign(
      longitudes[sourceWidth - 1] - longitudes[0],
    );
    const cyclicLongitudes = [
      ...longitudes,
      longitudes[0] + direction * 360,
    ];
    const cyclicValues = new Float64Array(targetWidth * height);

    for (let row = 0; row < height; row++) {
      const sourceOffset = row * sourceWidth;
      const targetOffset = row * targetWidth;
      cyclicValues.set(
        values.subarray(sourceOffset, sourceOffset + sourceWidth),
        targetOffset,
      );
      cyclicValues[targetOffset + sourceWidth] = values[sourceOffset];
    }

    return {
      longitudes: cyclicLongitudes,
      values: cyclicValues,
    };
  }

  private calculateContours(
    width: number,
    height: number,
    values: Float64Array,
    thresholds: number[],
  ): Promise<SerializedContour[]> {
    const id = ++this.requestId;

    return new Promise((resolve, reject) => {
      this.pending.set(id, { resolve, reject });

      const request: ContourWorkerRequest = {
        id,
        width,
        height,
        values,
        thresholds,
      };

      this.worker.postMessage(request, [
        values.buffer,
      ]);
    });
  }

  private createProjectedPath(
    contour: SerializedContour,
    longitudes: readonly number[],
    latitudes: readonly number[],
    projectionCode: string,
  ): Path2D {
    const path = new Path2D();

    contour.coordinates.forEach((polygon) => {
      polygon.forEach((ring) => {
        ring.forEach(([gridX, gridY], pointIndex) => {
          const lon = interpolateGridCoordinate(longitudes, gridX);
          const lat = interpolateGridCoordinate(latitudes, gridY);
          const projected = transform(
            [lon, clampLatitude(lat)],
            'EPSG:4326',
            projectionCode,
          );

          if (pointIndex === 0) {
            path.moveTo(projected[0], projected[1]);
          }
          else {
            path.lineTo(projected[0], projected[1]);
          }
        });

        path.closePath();
      });
    });

    return path;
  }

  private createLayerExtent(
    longitudes: readonly number[],
    latitudes: readonly number[],
    projectionCode: string,
  ): Extent {
    const lonMin = interpolateGridCoordinate(longitudes, 0);
    const lonMax = interpolateGridCoordinate(longitudes, longitudes.length);
    const latMin = interpolateGridCoordinate(latitudes, 0);
    const latMax = interpolateGridCoordinate(latitudes, latitudes.length);

    return transformExtent(
      [
        Math.min(lonMin, lonMax),
        clampLatitude(Math.min(latMin, latMax)),
        Math.max(lonMin, lonMax),
        clampLatitude(Math.max(latMin, latMax)),
      ],
      'EPSG:4326',
      projectionCode,
    );
  }

  private drawCanvas(
    extent: Extent,
    size: readonly number[],
  ): HTMLCanvasElement {
    const canvas = document.createElement('canvas');
    canvas.width = Math.max(1, Math.round(size[0]));
    canvas.height = Math.max(1, Math.round(size[1]));

    const context = canvas.getContext('2d');
    if (!context || extent[2] <= extent[0] || extent[3] <= extent[1]) {
      return canvas;
    }

    context.clearRect(0, 0, canvas.width, canvas.height);

    const scaleX = canvas.width / (extent[2] - extent[0]);
    const scaleY = canvas.height / (extent[3] - extent[1]);

    context.setTransform(
      scaleX,
      0,
      0,
      -scaleY,
      -extent[0] * scaleX,
      extent[3] * scaleY,
    );

    const worldOffsets = this.worldWidth
      ? [-this.worldWidth, 0, this.worldWidth]
      : [0];

    // Lower thresholds are drawn first; higher thresholds cover them.
    this.projectedContours.forEach((contour) => {
      context.fillStyle = contour.color;
      worldOffsets.forEach((offset) => {
        context.save();
        context.translate(offset, 0);
        context.fill(contour.path, 'evenodd');
        context.restore();
      });
    });

    context.setTransform(1, 0, 0, 1, 0, 0);
    return canvas;
  }
}

let defaultRenderer: FlexpartContourRenderer | undefined;

/** Direct adapter for the existing olContainer map. */
export async function addFlexpartContourLayer(
  frame: FlexpartGridFrame,
  options: FlexpartContourLayerOptions = {},
): Promise<FlexpartContourLayerResult> {
  const map = obtainViewer2D('olContainer') as OlMap | undefined;

  if (!map) {
    throw new Error('OpenLayers map olContainer is not initialized.');
  }

  if (!defaultRenderer) {
    defaultRenderer = new FlexpartContourRenderer(map, options);
  }

  return defaultRenderer.setFrame(frame);
}

export function clearFlexpartContourLayer(): void {
  defaultRenderer?.clear();
}

export function destroyFlexpartContourLayer(): void {
  defaultRenderer?.destroy();
  defaultRenderer = undefined;
}

/** Move the existing olContainer view to a Pacific-centered longitude. */
// export function centerFlexpartMap(
//   longitude = 180,
//   latitude = 0,
//   duration = 0,
// ): void {
//   const map = obtainViewer2D('olContainer') as OlMap | undefined;

//   if (!map) {
//     throw new Error('OpenLayers map olContainer is not initialized.');
//   }

//   if (!Number.isFinite(longitude)
//       || !Number.isFinite(latitude)
//       || !Number.isFinite(duration)
//       || duration < 0) {
//     throw new Error('Invalid map center or animation duration.');
//   }

//   const center = transform(
//     [longitude, clampLatitude(latitude)],
//     'EPSG:4326',
//     map.getView().getProjection(),
//   );

//   if (duration > 0) {
//     map.getView().animate({ center, duration });
//   }
//   else {
//     map.getView().setCenter(center);
//   }
// }

function interpolateGridCoordinate(
  coordinates: readonly number[],
  gridPosition: number,
): number {
  const centerPosition = gridPosition - 0.5;
  const lastIndex = coordinates.length - 1;

  if (centerPosition <= 0) {
    return coordinates[0]
      + centerPosition * (coordinates[1] - coordinates[0]);
  }

  if (centerPosition >= lastIndex) {
    return coordinates[lastIndex]
      + (centerPosition - lastIndex)
      * (coordinates[lastIndex] - coordinates[lastIndex - 1]);
  }

  const lowerIndex = Math.floor(centerPosition);
  const ratio = centerPosition - lowerIndex;

  return coordinates[lowerIndex]
    + (coordinates[lowerIndex + 1] - coordinates[lowerIndex]) * ratio;
}

function clampLatitude(latitude: number): number {
  return Math.max(
    -WEB_MERCATOR_MAX_LATITUDE,
    Math.min(WEB_MERCATOR_MAX_LATITUDE, latitude),
  );
}

function isNestedValues(
  values: FlexpartGridFrame['values'],
): values is readonly (readonly number[])[] {
  return Array.isArray(values)
    && values.length > 0
    && Array.isArray(values[0]);
}

function isGlobalCyclicAxis(longitudes: readonly number[]): boolean {
  if (longitudes.length < 3) {
    return false;
  }

  const span = Math.abs(
    longitudes[longitudes.length - 1] - longitudes[0],
  );
  const averageStep = span / (longitudes.length - 1);
  const coverage = span + averageStep;
  const tolerance = Math.max(1e-6, averageStep * 0.1);

  return Math.abs(coverage - 360) <= tolerance;
}