import type { VideoFrame } from "./frame-buffer.ts";

const RESET = "\x1b[0m";
const UPPER_HALF_BLOCK = "▀";

export function renderHalfBlock(frame: VideoFrame, targetCols: number, targetRows: number): string[] {
  if (!Number.isInteger(targetCols) || !Number.isInteger(targetRows) || targetCols < 1 || targetRows < 1) {
    throw new RangeError("Half-block target dimensions must be positive integers");
  }

  const targetPixelHeight = targetRows * 2;
  const lines = new Array<string>(targetRows);

  for (let row = 0; row < targetRows; row++) {
    const topY = sampleCoordinate(row * 2, targetPixelHeight, frame.height);
    const bottomY = sampleCoordinate(row * 2 + 1, targetPixelHeight, frame.height);
    const cells = new Array<string>(targetCols + 1);

    for (let col = 0; col < targetCols; col++) {
      const sourceX = sampleCoordinate(col, targetCols, frame.width);
      const topOffset = topY * frame.stride + sourceX * 4;
      const bottomOffset = bottomY * frame.stride + sourceX * 4;

      cells[col] =
        `\x1b[38;2;${frame.pixels[topOffset]};${frame.pixels[topOffset + 1]};${frame.pixels[topOffset + 2]}m` +
        `\x1b[48;2;${frame.pixels[bottomOffset]};${frame.pixels[bottomOffset + 1]};${frame.pixels[bottomOffset + 2]}m` +
        UPPER_HALF_BLOCK;
    }

    cells[targetCols] = RESET;
    lines[row] = cells.join("");
  }

  return lines;
}

function sampleCoordinate(target: number, targetSize: number, sourceSize: number): number {
  return Math.min(sourceSize - 1, Math.floor((target * sourceSize) / targetSize));
}