import type { Vec2, Segment } from '../types';
import { flattenArc } from '../geometry/arc';

export interface ParseResult {
  segments: Segment[];
  warnings: string[];
}

interface State {
  x: number;
  y: number;
  z: number;
  absolute: boolean;
  scale: number; // 1 for mm, 25.4 for inch
  motion: number; // 0,1,2,3
}

const WORD_RE = /([A-Za-z])\s*([-+]?[0-9]*\.?[0-9]+)/g;

function stripComments(line: string): string {
  return line.replace(/\(.*?\)/g, '').replace(/;.*$/, '').trim();
}

export function parseGcode(text: string): ParseResult {
  const segments: Segment[] = [];
  const warnings: string[] = [];
  const st: State = { x: 0, y: 0, z: 0, absolute: true, scale: 1, motion: 0 };

  const lines = text.split(/\r?\n/);
  for (let lineNo = 0; lineNo < lines.length; lineNo++) {
    const clean = stripComments(lines[lineNo]!);
    if (!clean) continue;

    const words: Array<[string, number]> = [];
    let m: RegExpExecArray | null;
    WORD_RE.lastIndex = 0;
    while ((m = WORD_RE.exec(clean)) !== null) {
      words.push([m[1]!.toUpperCase(), parseFloat(m[2]!)]);
    }

    const axis: Record<string, number> = {};
    let motionThisLine: number | null = null;
    for (const [letter, value] of words) {
      switch (letter) {
        case 'G':
          if (value === 0 || value === 1 || value === 2 || value === 3) {
            st.motion = value;
            motionThisLine = value;
          } else if (value === 20) st.scale = 25.4;
          else if (value === 21) st.scale = 1;
          else if (value === 90) st.absolute = true;
          else if (value === 91) st.absolute = false;
          // G17/G18/G19 plane select and others: ignored (G17/XY assumed)
          break;
        case 'X': case 'Y': case 'Z': case 'I': case 'J': case 'R':
          axis[letter] = value * st.scale;
          break;
        // F, S, T, M, N etc. ignored
        default:
          break;
      }
    }

    const hasCoord = 'X' in axis || 'Y' in axis || 'Z' in axis;
    if (motionThisLine === null && !hasCoord) continue; // no movement on this line

    const start: Vec2 = [st.x, st.y];
    const target = resolveTarget(st, axis);

    switch (st.motion) {
      case 0:
        segments.push({ kind: 'rapid', points: [start, target] });
        break;
      case 1:
        segments.push({ kind: 'cut', points: [start, target] });
        break;
      case 2:
      case 3: {
        const center = arcCenter(start, target, axis, st.motion === 2);
        if (!center) {
          warnings.push(`Line ${lineNo + 1}: could not resolve arc centre`);
          segments.push({ kind: 'cut', points: [start, target] });
        } else {
          segments.push({ kind: 'cut', points: flattenArc(start, target, center, st.motion === 2) });
        }
        break;
      }
    }
    st.x = target[0];
    st.y = target[1];
    if ('Z' in axis) st.z = axis['Z']!;
  }

  return { segments, warnings };
}

function resolveTarget(st: State, axis: Record<string, number>): Vec2 {
  if (st.absolute) {
    return ['X' in axis ? axis['X']! : st.x, 'Y' in axis ? axis['Y']! : st.y] as Vec2;
  }
  return [st.x + (axis['X'] ?? 0), st.y + (axis['Y'] ?? 0)] as Vec2;
}

function arcCenter(start: Vec2, end: Vec2, axis: Record<string, number>, clockwise: boolean): Vec2 | null {
  if ('I' in axis || 'J' in axis) {
    // I/J are offsets from the start point (already unit-scaled).
    return [start[0] + (axis['I'] ?? 0), start[1] + (axis['J'] ?? 0)];
  }
  if ('R' in axis) {
    return centerFromRadius(start, end, axis['R']!, clockwise);
  }
  return null;
}

/** GRBL-style centre-from-radius. R>0 selects the minor arc, R<0 the major arc. */
function centerFromRadius(start: Vec2, end: Vec2, r: number, clockwise: boolean): Vec2 | null {
  const x = end[0] - start[0];
  const y = end[1] - start[1];
  const d2 = x * x + y * y;
  const disc = 4 * r * r - d2;
  if (disc < 0 || d2 === 0) return null;
  let h = Math.sqrt(disc) / Math.sqrt(d2);
  if (clockwise) h = -h;
  if (r < 0) h = -h;
  return [start[0] + 0.5 * (x - y * h), start[1] + 0.5 * (y + x * h)];
}