// fpv.js — first-person (Eye-of-the-Beholder / Daggerfall style) depth exporter.
//
// A renderer concern, like depth.js: it reads the same envelope and produces an
// 8-bit depth map for the AI-render pipeline — but viewed from *inside* the
// dungeon rather than top-down. A grid dungeon is a 2D map extruded: walls are
// full-height blocks, floor and ceiling are flat planes, the eye sits at mid
// height, and you face one of four cardinal directions. So we don't need any 3D
// data from the core — a classic Wolfenstein-style raycaster turns the grid into
// a perspective depth map directly.
//
// Per screen column we cast one ray, march the grid (DDA) to the first blocking
// cell, and fill the column: a wall slice at that distance, floor ramping toward
// the camera below it, ceiling above. Distance → gray with NEAR=white/FAR=black
// (the same convention comfy.py expects). Doorways are non-blocking, so they
// read as dark recesses leading deeper — which is exactly what we want.

import { getStage, distanceToWall } from './render.js';
import { depthToCanvas } from './depth.js';

const WALL = 0, PILLAR = 3;

// Cardinal facings as (dx, dy) on the grid (y grows downward / "south").
export const DIRS = { N: [0, -1], E: [1, 0], S: [0, 1], W: [-1, 0] };

const clamp = (v, lo, hi) => v < lo ? lo : v > hi ? hi : v;
const blocks = (t) => t === WALL || t === PILLAR; // line-of-sight blockers

// Centroid of a cell list as [cx, cy].
export function centroidOf(cells) {
  let cx = 0, cy = 0;
  for (const [x, y] of cells) { cx += x; cy += y; }
  return [cx / cells.length, cy / cells.length];
}

// The *most open* cell (max distance-to-wall) among `cells`, so a camera stands
// in open space rather than against a wall (a room centroid can land near a wall
// when the room is non-convex). Ties break toward the cell nearest the centroid,
// keeping it visually centred. `dist` is a precomputed distanceToWall field.
export function mostOpenCell(dist, w, cells) {
  const [cx, cy] = centroidOf(cells);
  let pick = cells[0], pmax = -1, pcen = Infinity;
  for (const [x, y] of cells) {
    const d = dist[y * w + x];
    const cen = (x - cx) ** 2 + (y - cy) ** 2;
    if (d > pmax || (d === pmax && cen < pcen)) { pmax = d; pcen = cen; pick = [x, y]; }
  }
  return pick;
}

// Vantage cell for one room region (its most-open cell).
export function roomVantage(env, region, opts = {}) {
  const { tiles } = getStage(env, opts.stage);
  return mostOpenCell(distanceToWall(tiles, env.width, env.height), env.width, region.cells);
}

// Default demo vantage: the most-open cell of the largest room (or, failing that,
// the most open floor cell anywhere).
export function vantage(env, opts = {}) {
  const { tiles, regions } = getStage(env, opts.stage);
  const w = env.width, h = env.height;
  const dist = distanceToWall(tiles, w, h);
  let best = null, bestArea = 0;
  for (const r of regions) {
    if (r.kind !== 'Room' || !r.cells || r.cells.length === 0) continue;
    if (r.cells.length > bestArea) { bestArea = r.cells.length; best = r; }
  }
  if (best) return mostOpenCell(dist, w, best.cells);
  const all = [];
  for (let y = 0; y < h; y++) for (let x = 0; x < w; x++) if (!blocks(tiles[y][x])) all.push([x, y]);
  return all.length ? mostOpenCell(dist, w, all) : [w >> 1, h >> 1];
}

// Build a first-person depth field. Returns { width, height, gray, at, dir }.
// opts: { stage?, at?[x,y], dir?'N'|'E'|'S'|'W', width?, height?, fov?deg, maxView?, gamma? }
export function computeFPVDepth(env, opts = {}) {
  const { tiles } = getStage(env, opts.stage);
  const w = env.width, h = env.height;
  const W = opts.width ?? 1280, H = opts.height ?? 720;   // 16:9 — integer-scales to 1080p/1440p
  const fov = (opts.fov ?? 80) * Math.PI / 180;            // wider horizontal FOV to fill the widescreen frame
  const planeLen = Math.tan(fov / 2);
  const maxView = opts.maxView ?? 12;     // how far the eye sees (cells) before it's pure dark
  const gamma = opts.gamma ?? 2.0;        // >1 deepens the falloff to black (matches the proven corridor look)

  const at = opts.at ?? vantage(env, opts);
  const dirName = opts.dir ?? 'N';
  const [dirX, dirY] = DIRS[dirName];
  const posX = at[0] + 0.5, posY = at[1] + 0.5;
  // Camera plane ⟂ to the view direction (rotate dir 90°), scaled to the FOV.
  const planeX = -dirY * planeLen, planeY = dirX * planeLen;

  const gray = new Uint8ClampedArray(W * H);
  const half = H / 2;
  const centerX = W >> 1;
  let ahead = maxView; // straight-ahead wall distance (cells) — big = an opening leads onward

  for (let x = 0; x < W; x++) {
    const camX = 2 * x / W - 1;            // −1 … 1 across the screen
    const rayX = dirX + planeX * camX;
    const rayY = dirY + planeY * camX;

    // DDA grid march.
    let mapX = posX | 0, mapY = posY | 0;
    const deltaX = Math.abs(1 / rayX), deltaY = Math.abs(1 / rayY); // Infinity when axis-aligned — fine
    let stepX, stepY, sideX, sideY;
    if (rayX < 0) { stepX = -1; sideX = (posX - mapX) * deltaX; } else { stepX = 1; sideX = (mapX + 1 - posX) * deltaX; }
    if (rayY < 0) { stepY = -1; sideY = (posY - mapY) * deltaY; } else { stepY = 1; sideY = (mapY + 1 - posY) * deltaY; }

    let hit = false, side = 0;
    const maxSteps = maxView * 2 + 4;
    for (let s = 0; s < maxSteps; s++) {
      if (sideX < sideY) { sideX += deltaX; mapX += stepX; side = 0; }
      else { sideY += deltaY; mapY += stepY; side = 1; }
      if (mapX < 0 || mapY < 0 || mapX >= w || mapY >= h) break; // off-map → open/far
      if (blocks(tiles[mapY][mapX])) { hit = true; break; }
    }
    const perp = side === 0 ? sideX - deltaX : sideY - deltaY;
    const dist = hit ? clamp(perp, 0.02, maxView) : maxView;
    if (x === centerX) ahead = dist;

    // Project the 1-cell-tall wall: lineH = H/dist (fills the screen at dist 1).
    const lineH = H / dist;
    const ds = clamp(Math.floor(half - lineH / 2), 0, H);
    const de = clamp(Math.floor(half + lineH / 2), 0, H);

    for (let y = 0; y < H; y++) {
      let dpix;
      if (y >= ds && y < de) {
        dpix = dist;                       // wall slice
      } else {
        // Floor (below) / ceiling (above). (0.5·H)/p is continuous with the
        // wall distance exactly at the slice edge, so the column has no seam.
        const p = y < half ? (half - y) : (y - half + 1);
        dpix = Math.min((0.5 * H) / p, maxView);
      }
      const t = clamp(dpix / maxView, 0, 1);
      gray[y * W + x] = Math.round(255 * Math.pow(1 - t, gamma));
    }
  }

  return { width: W, height: H, gray, at, dir: dirName, ahead };
}

// --- export glue (mirrors depth.js) --------------------------------------

export function exportFPVDataURL(env, opts = {}) {
  const field = computeFPVDepth(env, opts);
  return { url: depthToCanvas(field).toDataURL('image/png'), width: field.width, height: field.height, at: field.at, dir: field.dir, ahead: field.ahead };
}

export async function exportFPVToServer(env, name, opts = {}) {
  const field = computeFPVDepth(env, opts);
  const blob = await new Promise((res) => depthToCanvas(field).toBlob(res, 'image/png'));
  const resp = await fetch('/save/' + encodeURIComponent(name), { method: 'POST', body: blob });
  if (!resp.ok) throw new Error('save failed: ' + resp.status);
  const info = await resp.json();
  return { ...info, width: field.width, height: field.height, at: field.at, dir: field.dir, ahead: field.ahead };
}