/**
 * Fixture loader for codec parser tests.
 *
 * Each fixture is a pair of files:
 *   <name>.hex          — hex-encoded AVL body (CodecID + N1 + records + N2)
 *   <name>.expected.json — parsed expected output as { positions, ack_record_count }
 *
 * Special JSON sentinel values:
 *   "__bigint:<decimal>"   → BigInt(decimal)
 *   "__buffer_b64:<base64>" → Buffer.from(base64, 'base64')
 *
 * The loader returns typed fixture objects; the auto-discovery helper
 * `loadFixturesFromDir` reads all pairs in a directory so adding a new
 * fixture file automatically produces a new test.
 */

import fs from 'node:fs';
import path from 'node:path';
import type { Position } from '../../src/core/types.js';

// ---------------------------------------------------------------------------
// JSON representation types (what lives on disk)
// ---------------------------------------------------------------------------

type JsonAttributeValue = number | string; // "__bigint:..." | "__buffer_b64:..." | number

type JsonPosition = {
  readonly device_id: string;
  readonly timestamp: string; // ISO 8601
  readonly latitude: number;
  readonly longitude: number;
  readonly altitude: number;
  readonly angle: number;
  readonly speed: number;
  readonly satellites: number;
  readonly priority: 0 | 1 | 2;
  readonly attributes: Record<string, JsonAttributeValue>;
};

type FixtureJson = {
  readonly positions: readonly JsonPosition[];
  readonly ack_record_count: number;
};

// ---------------------------------------------------------------------------
// Sentinel decoders
// ---------------------------------------------------------------------------

function decodeAttributeValue(raw: JsonAttributeValue): number | bigint | Buffer {
  if (typeof raw === 'number') {
    return raw;
  }
  if (raw.startsWith('__bigint:')) {
    return BigInt(raw.slice('__bigint:'.length));
  }
  if (raw.startsWith('__buffer_b64:')) {
    const b64 = raw.slice('__buffer_b64:'.length);
    return Buffer.from(b64, 'base64');
  }
  throw new Error(`Unknown fixture sentinel value: ${JSON.stringify(raw)}`);
}

function decodePosition(json: JsonPosition): Position {
  const attributes: Record<string, number | bigint | Buffer> = {};
  for (const [key, value] of Object.entries(json.attributes)) {
    attributes[key] = decodeAttributeValue(value);
  }
  return {
    device_id: json.device_id,
    timestamp: new Date(json.timestamp),
    latitude: json.latitude,
    longitude: json.longitude,
    altitude: json.altitude,
    angle: json.angle,
    speed: json.speed,
    satellites: json.satellites,
    priority: json.priority,
    attributes,
  };
}

// ---------------------------------------------------------------------------
// Public types
// ---------------------------------------------------------------------------

export type LoadedFixture = {
  readonly name: string;
  readonly body: Buffer;
  readonly expected: {
    readonly positions: readonly Position[];
    readonly ack_record_count: number;
  };
};

// ---------------------------------------------------------------------------
// Loader
// ---------------------------------------------------------------------------

/**
 * Loads a single fixture pair by base path (without extension).
 */
export function loadFixture(basePath: string): LoadedFixture {
  const hexPath = `${basePath}.hex`;
  const jsonPath = `${basePath}.expected.json`;

  const rawHex = fs.readFileSync(hexPath, 'utf8');
  // Strip all non-hex characters (whitespace, newlines)
  const cleanHex = rawHex.replace(/[^0-9a-fA-F]/g, '');
  const body = Buffer.from(cleanHex, 'hex');

  const rawJson = fs.readFileSync(jsonPath, 'utf8');
  const parsed = JSON.parse(rawJson) as FixtureJson;

  const positions = parsed.positions.map(decodePosition);

  return {
    name: path.basename(basePath),
    body,
    expected: {
      positions,
      ack_record_count: parsed.ack_record_count,
    },
  };
}

/**
 * Discovers all fixture pairs in a directory.
 * A "fixture pair" is a `.hex` file that also has a corresponding
 * `.expected.json` file with the same base name.
 *
 * Returns fixtures sorted by filename so test order is deterministic.
 */
export function loadFixturesFromDir(dirPath: string): readonly LoadedFixture[] {
  const entries = fs.readdirSync(dirPath);
  const hexFiles = entries
    .filter((f) => f.endsWith('.hex'))
    .sort();

  return hexFiles.map((hexFile) => {
    const baseName = hexFile.slice(0, -'.hex'.length);
    return loadFixture(path.join(dirPath, baseName));
  });
}

// ---------------------------------------------------------------------------
// Deep-equality comparator (bigint + Buffer aware)
// ---------------------------------------------------------------------------

/**
 * Compares two attribute values for equality. Handles number, bigint, and
 * Buffer types correctly (vitest's expect().toEqual does not handle Buffer
 * and bigint mixed comparisons out of the box in all edge cases).
 */
function attributeValuesEqual(
  actual: number | bigint | Buffer,
  expected: number | bigint | Buffer,
): boolean {
  if (Buffer.isBuffer(actual) && Buffer.isBuffer(expected)) {
    return actual.equals(expected);
  }
  if (typeof actual === 'bigint' && typeof expected === 'bigint') {
    return actual === expected;
  }
  if (typeof actual === 'number' && typeof expected === 'number') {
    return actual === expected;
  }
  return false;
}

/**
 * Deep-equality check between actual parsed positions and expected positions.
 * Returns a descriptive mismatch string on failure, or null on success.
 */
export function compareToExpected(
  actual: readonly Position[],
  expected: readonly Position[],
): string | null {
  if (actual.length !== expected.length) {
    return `Position count mismatch: got ${actual.length}, expected ${expected.length}`;
  }

  for (let i = 0; i < actual.length; i++) {
    const a = actual[i];
    const e = expected[i];

    if (a === undefined || e === undefined) {
      return `Undefined position at index ${i}`;
    }

    if (a.device_id !== e.device_id) {
      return `[${i}] device_id: got "${a.device_id}", expected "${e.device_id}"`;
    }
    if (a.timestamp.getTime() !== e.timestamp.getTime()) {
      return `[${i}] timestamp: got "${a.timestamp.toISOString()}", expected "${e.timestamp.toISOString()}"`;
    }
    if (a.latitude !== e.latitude) {
      return `[${i}] latitude: got ${a.latitude}, expected ${e.latitude}`;
    }
    if (a.longitude !== e.longitude) {
      return `[${i}] longitude: got ${a.longitude}, expected ${e.longitude}`;
    }
    if (a.altitude !== e.altitude) {
      return `[${i}] altitude: got ${a.altitude}, expected ${e.altitude}`;
    }
    if (a.angle !== e.angle) {
      return `[${i}] angle: got ${a.angle}, expected ${e.angle}`;
    }
    if (a.speed !== e.speed) {
      return `[${i}] speed: got ${a.speed}, expected ${e.speed}`;
    }
    if (a.satellites !== e.satellites) {
      return `[${i}] satellites: got ${a.satellites}, expected ${e.satellites}`;
    }
    if (a.priority !== e.priority) {
      return `[${i}] priority: got ${a.priority}, expected ${e.priority}`;
    }

    const actualKeys = Object.keys(a.attributes).sort();
    const expectedKeys = Object.keys(e.attributes).sort();

    if (JSON.stringify(actualKeys) !== JSON.stringify(expectedKeys)) {
      return `[${i}] attribute keys mismatch: got [${actualKeys.join(', ')}], expected [${expectedKeys.join(', ')}]`;
    }

    for (const key of actualKeys) {
      const av = a.attributes[key];
      const ev = e.attributes[key];
      if (av === undefined || ev === undefined) {
        return `[${i}] attribute "${key}" undefined`;
      }
      if (!attributeValuesEqual(av, ev)) {
        return (
          `[${i}] attribute "${key}": ` +
          `got ${Buffer.isBuffer(av) ? `Buffer<${av.toString('hex')}>` : String(av)}, ` +
          `expected ${Buffer.isBuffer(ev) ? `Buffer<${ev.toString('hex')}>` : String(ev)}`
        );
      }
    }
  }

  return null;
}