/**
 * Bounded weight-paint operation contract shared by validation and tests.
 * Native Blender remains authoritative for Main writes; these helpers make
 * the ordering and symmetry rules explicit before a command crosses the
 * Worker boundary.
 */

export const WEIGHT_PAINT_SCHEMA_VERSION = 1 as const;
export const WEIGHT_PAINT_BUDGET = {
  maxVertices: 1_000_000,
  maxInfluencesPerVertex: 32,
  maxMirrorTolerance: 1,
} as const;

export interface WeightPaintOptionsIR {
  schemaVersion: typeof WEIGHT_PAINT_SCHEMA_VERSION;
  normalize: boolean;
  limit?: number;
  mirror: boolean;
  mirrorAxis: 0 | 1 | 2;
  mirrorTolerance: number;
}

export interface WeightPaintVertexIR {
  index: number;
  position: [number, number, number];
  influences: Array<{ group: string; weight: number }>;
}

export interface WeightPaintPatchIR {
  vertexGroup: string;
  indices: number[];
  values: number[];
  options: WeightPaintOptionsIR;
}

function fail(message: string): never {
  throw new Error(`PAINT_SCHEMA_INVALID: ${message}`);
}

function finite(value: unknown, label: string): number {
  if (typeof value !== "number" || !Number.isFinite(value)) fail(`${label} must be finite`);
  return value;
}

function integer(value: unknown, label: string): number {
  const result = finite(value, label);
  if (!Number.isSafeInteger(result) || result < 0) fail(`${label} must be a non-negative safe integer`);
  return result;
}

function string(value: unknown, label: string): string {
  if (typeof value !== "string" || value.length === 0 || value.length > 63) fail(`${label} is outside the bounded range`);
  return value;
}

function boolean(value: unknown, label: string): boolean {
  if (typeof value !== "boolean") fail(`${label} must be boolean`);
  return value;
}

export function parseWeightPaintOptions(value: unknown = {}): WeightPaintOptionsIR {
  if (typeof value !== "object" || value === null || Array.isArray(value)) fail("options must be an object");
  const source = value as Record<string, unknown>;
  const allowed = new Set(["schemaVersion", "normalize", "limit", "mirror", "mirrorAxis", "mirrorTolerance"]);
  if (Object.keys(source).some((key) => !allowed.has(key))) fail("options contains undeclared fields");
  if (source.schemaVersion !== undefined && source.schemaVersion !== WEIGHT_PAINT_SCHEMA_VERSION) fail("options.schemaVersion is unsupported");
  const normalize = source.normalize === undefined ? false : boolean(source.normalize, "options.normalize");
  const mirror = source.mirror === undefined ? false : boolean(source.mirror, "options.mirror");
  const mirrorAxisValue = source.mirrorAxis === undefined ? 0 : integer(source.mirrorAxis, "options.mirrorAxis");
  if (mirrorAxisValue > 2) fail("options.mirrorAxis must be 0, 1 or 2");
  const mirrorTolerance = source.mirrorTolerance === undefined ? 1e-4 : finite(source.mirrorTolerance, "options.mirrorTolerance");
  if (mirrorTolerance <= 0 || mirrorTolerance > WEIGHT_PAINT_BUDGET.maxMirrorTolerance) fail("options.mirrorTolerance is outside the bounded range");
  let limit: number | undefined;
  if (source.limit !== undefined) {
    limit = integer(source.limit, "options.limit");
    if (limit < 1 || limit > WEIGHT_PAINT_BUDGET.maxInfluencesPerVertex) fail("options.limit is outside the bounded range");
  }
  if (!mirror && (source.mirrorAxis !== undefined || source.mirrorTolerance !== undefined)) fail("mirrorAxis/mirrorTolerance require mirror=true");
  return {
    schemaVersion: WEIGHT_PAINT_SCHEMA_VERSION,
    normalize,
    ...(limit === undefined ? {} : { limit }),
    mirror,
    mirrorAxis: mirrorAxisValue as 0 | 1 | 2,
    mirrorTolerance,
  };
}

export function parseWeightPaintPatch(value: unknown): WeightPaintPatchIR {
  if (typeof value !== "object" || value === null || Array.isArray(value)) fail("patch must be an object");
  const source = value as Record<string, unknown>;
  const vertexGroup = string(source.vertexGroup, "patch.vertexGroup");
  if (!Array.isArray(source.indices) || !Array.isArray(source.values) || source.indices.length === 0 || source.indices.length !== source.values.length) fail("patch indices and values must have equal non-empty lengths");
  if (source.indices.length > WEIGHT_PAINT_BUDGET.maxVertices) throw new Error("PAINT_BUDGET_EXCEEDED: patch exceeds the vertex budget");
  const seen = new Set<number>();
  const indices = source.indices.map((value, offset) => {
    const index = integer(value, `patch.indices[${offset}]`);
    if (seen.has(index)) fail(`patch.indices[${offset}] contains a duplicate vertex`);
    seen.add(index);
    return index;
  });
  const values = source.values.map((value, offset) => {
    const weight = finite(value, `patch.values[${offset}]`);
    if (weight < 0 || weight > 1) fail(`patch.values[${offset}] must be in [0,1]`);
    return weight;
  });
  return {
    vertexGroup,
    indices,
    values,
    options: parseWeightPaintOptions({
      schemaVersion: source.schemaVersion,
      normalize: source.normalize,
      limit: source.limit,
      mirror: source.mirror,
      mirrorAxis: source.mirrorAxis,
      mirrorTolerance: source.mirrorTolerance,
    }),
  };
}

function mirrorMap(vertices: readonly WeightPaintVertexIR[], axis: 0 | 1 | 2, tolerance: number): Map<number, number> {
  const result = new Map<number, number>();
  for (const vertex of vertices) {
    let best: WeightPaintVertexIR | undefined;
    let bestDistance = Number.POSITIVE_INFINITY;
    for (const candidate of vertices) {
      const reflected = [...vertex.position] as [number, number, number];
      reflected[axis] = -reflected[axis];
      const distance = Math.hypot(...reflected.map((value, component) => value - candidate.position[component]));
      if (distance < bestDistance || (distance === bestDistance && (best === undefined || candidate.index < best.index))) {
        best = candidate;
        bestDistance = distance;
      }
    }
    if (!best || bestDistance > tolerance) throw new Error("CAPABILITY_MISSING: WEIGHT_MIRROR_SYMMETRY_UNVERIFIED");
    result.set(vertex.index, best.index);
  }
  for (const [source, target] of result) if (result.get(target) !== source) throw new Error("CAPABILITY_MISSING: WEIGHT_MIRROR_SYMMETRY_UNVERIFIED");
  return result;
}

function normalize(influences: Array<{ group: string; weight: number }>): void {
  const total = influences.reduce((sum, influence) => sum + influence.weight, 0);
  if (total > 0) for (const influence of influences) influence.weight /= total;
}

function limit(influences: Array<{ group: string; weight: number }>, count: number): void {
  influences.sort((left, right) => right.weight - left.weight || left.group.localeCompare(right.group));
  influences.splice(count);
}

/** Apply the deterministic bounded operation used by the desktop comparison. */
export function applyWeightPaintPatch(verticesValue: unknown, patchValue: unknown): WeightPaintVertexIR[] {
  if (!Array.isArray(verticesValue) || verticesValue.length === 0 || verticesValue.length > WEIGHT_PAINT_BUDGET.maxVertices) fail("vertices exceeds the weight paint budget");
  const vertices = verticesValue.map((value, offset) => {
    if (typeof value !== "object" || value === null || Array.isArray(value)) fail(`vertices[${offset}] must be an object`);
    const source = value as Record<string, unknown>;
    const index = integer(source.index, `vertices[${offset}].index`);
    const positionValue = source.position;
    if (!Array.isArray(positionValue) || positionValue.length !== 3) fail(`vertices[${offset}].position must contain three numbers`);
    const position = positionValue.map((component, axis) => finite(component, `vertices[${offset}].position[${axis}]`)) as [number, number, number];
    if (!Array.isArray(source.influences)) fail(`vertices[${offset}].influences must be an array`);
    const influences = source.influences.map((item, influenceIndex) => {
      if (typeof item !== "object" || item === null || Array.isArray(item)) fail(`vertices[${offset}].influences[${influenceIndex}] must be an object`);
      const entry = item as Record<string, unknown>;
      const weight = finite(entry.weight, `vertices[${offset}].influences[${influenceIndex}].weight`);
      if (weight < 0 || weight > 1) fail("influence weight must be in [0,1]");
      return { group: string(entry.group, `vertices[${offset}].influences[${influenceIndex}].group`), weight };
    });
    return { index, position, influences };
  });
  const patch = parseWeightPaintPatch(patchValue);
  const byIndex = new Map(vertices.map((vertex) => [vertex.index, vertex]));
  const targets = new Map<number, number>();
  patch.indices.forEach((index, offset) => {
    if (!byIndex.has(index)) fail(`patch.indices[${offset}] references an unknown vertex`);
    targets.set(index, patch.values[offset]);
  });
  if (patch.options.mirror) {
    const mirrored = mirrorMap(vertices, patch.options.mirrorAxis, patch.options.mirrorTolerance);
    for (const [index, value] of [...targets]) targets.set(mirrored.get(index)!, value);
  }
  for (const [index, value] of targets) {
    const vertex = byIndex.get(index)!;
    const influence = vertex.influences.find((item) => item.group === patch.vertexGroup);
    if (value === 0) vertex.influences.splice(vertex.influences.indexOf(influence!), influence ? 1 : 0);
    else if (influence) influence.weight = value;
    else vertex.influences.push({ group: patch.vertexGroup, weight: value });
    if (patch.options.limit !== undefined) limit(vertex.influences, patch.options.limit);
    if (patch.options.normalize) normalize(vertex.influences);
  }
  return vertices.map((vertex) => ({ ...vertex, position: [...vertex.position] as [number, number, number], influences: vertex.influences.map((influence) => ({ ...influence })) }));
}