/**
 * Source-of-truth game state and the derived render state.
 *
 * The store holds the enabled surfaces and a per-part placement map
 * (`bgm-tabletop.md` §2). Each part on the board is keyed by its id
 * (`package:type#id`) and records which path it's on, its index in that path's
 * stack, and which face is up. A path's ordered children (for stacking) are
 * derived from this map. The derived render state is computed from the game
 * state plus a package's surface routes: a stable list of placements, one per
 * (surface, piece) pair, keyed for rendering.
 */
import { useMemo } from 'react';
import { create } from 'zustand';
import type { Candidate, Facing, Package, Route, Surface } from '@tts/bgm';

/** The placement state of a single part on the board. */
export interface PartState {
  /** The path key this part is on. */
  path: string;
  /** The part's position in its path's stack. */
  index: number;
  /** How the part is oriented on the board. */
  facing: Facing;
}

/** Source-of-truth game state. */
export interface GameState {
  /** Enabled per surface id (`type#id`). */
  surfaces: Record<string, boolean>;
  /** Part id (`package:type#id`) -> placement state. */
  parts: Record<string, PartState>;
}

/** A single placed piece on a surface, ready for rendering. */
export interface Placement {
  /** Surface id (`type#id`). */
  surface: string;
  /** The path key this placement came from. */
  path: string;
  /** The matched route. */
  route: Route;
  /** The matched candidate, when the route has `:param`s. */
  candidate?: Candidate;
  /** The piece id (`package:type#id`). */
  piece: string;
  /** The piece's position in its path's stack. */
  index: number;
  /** The number of pieces on the path. */
  stackSize: number;
  /** How the piece is oriented on the board. */
  facing: Facing;
}

interface TabletopState extends GameState {
  setSurfaces: (surfaces: Record<string, boolean>) => void;
  setParts: (parts: Record<string, PartState>) => void;
  seed: (state: GameState) => void;
  enableSurface: (id: string) => void;
  disableSurface: (id: string) => void;
  setPart: (id: string, patch: Partial<PartState>) => void;
  movePart: (id: string, path: string, index: number) => void;
}

export const useTabletopStore = create<TabletopState>((set) => ({
  surfaces: {},
  parts: {},
  setSurfaces: (surfaces) => set({ surfaces }),
  setParts: (parts) => set({ parts }),
  seed: (state) => set(state),
  enableSurface: (id) => set((s) => ({ surfaces: { ...s.surfaces, [id]: true } })),
  disableSurface: (id) => set((s) => ({ surfaces: { ...s.surfaces, [id]: false } })),
  setPart: (id, patch) =>
    set((s) => {
      const cur = s.parts[id];
      if (!cur) return s;
      return { parts: { ...s.parts, [id]: { ...cur, ...patch } } };
    }),
  movePart: (id, path, index) =>
    set((s) => {
      const cur = s.parts[id];
      if (!cur) return s;
      const parts = { ...s.parts };
      // Siblings on the source path, in order, excluding the moved part.
      const srcIds = Object.keys(parts)
        .filter((pid) => pid !== id && parts[pid]!.path === cur.path)
        .sort((a, b) => parts[a]!.index - parts[b]!.index);
      // Siblings on the destination path, in order, excluding the moved part.
      const dstIds = Object.keys(parts)
        .filter((pid) => pid !== id && parts[pid]!.path === path)
        .sort((a, b) => parts[a]!.index - parts[b]!.index);
      // Reindex the source path so the gap closes.
      srcIds.forEach((pid, i) => {
        parts[pid] = { ...parts[pid]!, index: i };
      });
      // Reindex the destination path with the moved part inserted at `index`.
      const clamped = Math.max(0, Math.min(index, dstIds.length));
      dstIds.forEach((pid, i) => {
        parts[pid] = { ...parts[pid]!, index: i >= clamped ? i + 1 : i };
      });
      parts[id] = { ...cur, path, index: clamped };
      return { parts };
    }),
}));

// --- Route matching ---

/**
 * Match a route pattern against a path key. Returns the matched candidate (or
 * undefined when the route has no `:param`s), or null when the route doesn't
 * match. A route with candidates matches only when a candidate's props match
 * every `:param`; the first such candidate wins.
 */
export function matchRoute(route: Route, path: string): { candidate?: Candidate } | null {
  const routeSegs = route.route.split('/').filter(Boolean);
  const pathSegs = path.split('/').filter(Boolean);
  if (routeSegs.length !== pathSegs.length) return null;

  const params: Record<string, string> = {};
  for (let i = 0; i < routeSegs.length; i++) {
    const rs = routeSegs[i]!;
    const ps = pathSegs[i]!;
    if (rs.startsWith(':')) params[rs.slice(1)] = ps;
    else if (rs !== ps) return null;
  }

  if (route.candidates) {
    for (const cand of route.candidates) {
      const allMatch = Object.entries(params).every(([k, v]) => cand[k] === v);
      if (allMatch) return { candidate: cand };
    }
    return null;
  }
  return { candidate: undefined };
}

/**
 * Derive each path's ordered children from the parts map. A path's children are
 * its part ids sorted by `index`, used for stacking (`stackSize` and per-piece
 * `index`).
 */
export function childrenByPath(parts: Record<string, PartState>): Record<string, string[]> {
  const children: Record<string, string[]> = {};
  for (const [id, ps] of Object.entries(parts)) {
    (children[ps.path] ??= []).push(id);
  }
  for (const list of Object.values(children)) {
    list.sort((a, b) => parts[a]!.index - parts[b]!.index);
  }
  return children;
}

/** Compute the placements for a single surface from the game state's parts. */
export function computeSurfacePlacements(surface: Surface, parts: Record<string, PartState>): Placement[] {
  const placements: Placement[] = [];
  const surfaceId = `${surface.type}#${surface.id}`;
  const children = childrenByPath(parts);
  for (const [path, ids] of Object.entries(children)) {
    const route = surface.layout.find((r) => matchRoute(r, path));
    if (!route) continue;
    const match = matchRoute(route, path)!;
    const stackSize = ids.length;
    for (const piece of ids) {
      const ps = parts[piece]!;
      placements.push({
        surface: surfaceId,
        path,
        route,
        candidate: match.candidate,
        piece,
        index: ps.index,
        stackSize,
        facing: ps.facing,
      });
    }
  }
  return placements;
}

/** Compute the full render state across all enabled surfaces. */
export function computeRenderState(pkg: Package, state: GameState): Placement[] {
  const out: Placement[] = [];
  for (const [surfaceId, enabled] of Object.entries(state.surfaces)) {
    if (!enabled) continue;
    const surface = pkg.surfaces.get(surfaceId);
    if (!surface) continue;
    out.push(...computeSurfacePlacements(surface, state.parts));
  }
  return out;
}

/**
 * A stable key for a placement, unique across surfaces and pieces. A piece is
 * on exactly one path, so `path` is implied; it may still render on more than
 * one enabled surface, so the surface is part of the key.
 */
export function placementKey(p: Placement): string {
  return `${p.surface}:${p.piece}`;
}

/** The derived render state for a package, from the current game state. */
export function useRenderState(pkg: Package): Placement[] {
  const surfaces = useTabletopStore((s) => s.surfaces);
  const parts = useTabletopStore((s) => s.parts);
  return useMemo(() => computeRenderState(pkg, { surfaces, parts }), [pkg, surfaces, parts]);
}