const axios = require('axios');
const crypto = require('crypto');
const fs = require('fs');
const { getOS, getArch } = require('../utils/platformUtils');

// Patches CDN via auth server redirect gateway (allows instant CDN switching)
const AUTH_DOMAIN = process.env.HYTALE_AUTH_DOMAIN || 'auth.sanasol.ws';
const MIRROR_BASE_URL = `https://${AUTH_DOMAIN}/patches`;
const MIRROR_MANIFEST_URL = `${MIRROR_BASE_URL}/manifest.json`;

// Fallback: latest known build number if manifest is unreachable
const FALLBACK_LATEST_BUILD = 11;

let manifestCache = null;
let manifestCacheTime = 0;
const MANIFEST_CACHE_DURATION = 60000; // 1 minute

/**
 * Fetch the mirror manifest from MEGA S4
 */
async function fetchMirrorManifest() {
  const now = Date.now();

  if (manifestCache && (now - manifestCacheTime) < MANIFEST_CACHE_DURATION) {
    console.log('[Mirror] Using cached manifest');
    return manifestCache;
  }

  try {
    console.log('[Mirror] Fetching manifest from:', MIRROR_MANIFEST_URL);
    const response = await axios.get(MIRROR_MANIFEST_URL, {
      timeout: 15000,
      headers: { 'User-Agent': 'Hytale-F2P-Launcher' }
    });

    if (response.data && response.data.files) {
      manifestCache = response.data;
      manifestCacheTime = now;
      console.log('[Mirror] Manifest fetched successfully');
      return response.data;
    }
    throw new Error('Invalid manifest structure');
  } catch (error) {
    console.error('[Mirror] Error fetching manifest:', error.message);
    if (manifestCache) {
      console.log('[Mirror] Using expired cache');
      return manifestCache;
    }
    throw error;
  }
}

/**
 * Parse manifest to get available patches for current platform
 * Returns array of { from, to, key, size }
 */
function getPlatformPatches(manifest, branch = 'release') {
  const os = getOS();
  const arch = getArch();
  const prefix = `${os}/${arch}/${branch}/`;
  const patches = [];

  for (const [key, info] of Object.entries(manifest.files)) {
    if (key.startsWith(prefix) && key.endsWith('.pwr')) {
      const filename = key.slice(prefix.length, -4); // e.g., "0_to_11"
      const match = filename.match(/^(\d+)_to_(\d+)$/);
      if (match) {
        patches.push({
          from: parseInt(match[1]),
          to: parseInt(match[2]),
          key,
          size: info.size
        });
      }
    }
  }

  return patches;
}

/**
 * Find optimal patch path using BFS with download size minimization
 * Returns array of { from, to, url, size, key } steps, or null if no path found
 */
function findOptimalPatchPath(currentBuild, targetBuild, patches) {
  if (currentBuild >= targetBuild) return [];

  const edges = {};
  for (const patch of patches) {
    if (!edges[patch.from]) edges[patch.from] = [];
    edges[patch.from].push(patch);
  }

  const queue = [{ build: currentBuild, path: [], totalSize: 0 }];
  let bestPath = null;
  let bestSize = Infinity;

  while (queue.length > 0) {
    const { build, path, totalSize } = queue.shift();

    if (build === targetBuild) {
      if (totalSize < bestSize) {
        bestPath = path;
        bestSize = totalSize;
      }
      continue;
    }

    if (totalSize >= bestSize) continue;

    const nextEdges = edges[build] || [];
    for (const edge of nextEdges) {
      if (edge.to <= build || edge.to > targetBuild) continue;
      if (path.some(p => p.to === edge.to)) continue;

      queue.push({
        build: edge.to,
        path: [...path, {
          from: edge.from,
          to: edge.to,
          url: `${MIRROR_BASE_URL}/${edge.key}`,
          size: edge.size,
          key: edge.key
        }],
        totalSize: totalSize + edge.size
      });
    }
  }

  return bestPath;
}

/**
 * Get the optimal update plan from currentBuild to targetBuild
 * Returns { steps: [{from, to, url, size}], totalSize, isFullInstall }
 */
async function getUpdatePlan(currentBuild, targetBuild, branch = 'release') {
  const manifest = await fetchMirrorManifest();
  const patches = getPlatformPatches(manifest, branch);

  // Try optimal path
  const steps = findOptimalPatchPath(currentBuild, targetBuild, patches);

  if (steps && steps.length > 0) {
    const totalSize = steps.reduce((sum, s) => sum + s.size, 0);
    console.log(`[Mirror] Update plan: ${steps.map(s => `${s.from}\u2192${s.to}`).join(' + ')} (${(totalSize / 1024 / 1024).toFixed(0)} MB)`);
    return { steps, totalSize, isFullInstall: steps.length === 1 && steps[0].from === 0 };
  }

  // Fallback: full install 0 -> target
  const fullPatch = patches.find(p => p.from === 0 && p.to === targetBuild);
  if (fullPatch) {
    const step = {
      from: 0,
      to: targetBuild,
      url: `${MIRROR_BASE_URL}/${fullPatch.key}`,
      size: fullPatch.size,
      key: fullPatch.key
    };
    console.log(`[Mirror] Full install: 0\u2192${targetBuild} (${(fullPatch.size / 1024 / 1024).toFixed(0)} MB)`);
    return { steps: [step], totalSize: fullPatch.size, isFullInstall: true };
  }

  throw new Error(`No patch path found from build ${currentBuild} to ${targetBuild} for ${getOS()}/${getArch()}`);
}

async function getLatestClientVersion(branch = 'release') {
  try {
    console.log(`[Mirror] Fetching latest client version (branch: ${branch})...`);
    const manifest = await fetchMirrorManifest();
    const patches = getPlatformPatches(manifest, branch);

    if (patches.length === 0) {
      console.log(`[Mirror] No patches for branch '${branch}', using fallback`);
      return `v${FALLBACK_LATEST_BUILD}`;
    }

    const latestBuild = Math.max(...patches.map(p => p.to));
    console.log(`[Mirror] Latest client version: v${latestBuild}`);
    return `v${latestBuild}`;
  } catch (error) {
    console.error('[Mirror] Error:', error.message);
    return `v${FALLBACK_LATEST_BUILD}`;
  }
}

/**
 * Get PWR download URL for fresh install (0 -> target)
 * Backward-compatible with old getPWRUrlFromNewAPI signature
 * Checks mirror first, then constructs URL for the branch
 */
async function getPWRUrl(branch = 'release', version = 'v11') {
  const targetBuild = extractVersionNumber(version);
  const os = getOS();
  const arch = getArch();

  try {
    const manifest = await fetchMirrorManifest();
    const patches = getPlatformPatches(manifest, branch);
    const fullPatch = patches.find(p => p.from === 0 && p.to === targetBuild);

    if (fullPatch) {
      const url = `${MIRROR_BASE_URL}/${fullPatch.key}`;
      console.log(`[Mirror] PWR URL: ${url}`);
      return url;
    }

    if (patches.length > 0) {
      // Branch exists in mirror but no full patch for this target - construct URL
      console.log(`[Mirror] No 0->${targetBuild} patch found, constructing URL`);
    } else {
      console.log(`[Mirror] Branch '${branch}' not in mirror, constructing URL`);
    }
  } catch (error) {
    console.error('[Mirror] Error getting PWR URL:', error.message);
  }

  // Construct mirror URL (will work if patch was uploaded but manifest is stale)
  return `${MIRROR_BASE_URL}/${os}/${arch}/${branch}/0_to_${targetBuild}.pwr`;
}

// Backward-compatible alias
const getPWRUrlFromNewAPI = getPWRUrl;

// Utility function to extract version number
// Supports: "7.pwr", "v8", "v8-windows-amd64.pwr", "5_to_10", etc.
function extractVersionNumber(version) {
  if (!version) return 0;

  // New format: "v8" or "v8-xxx.pwr"
  const vMatch = version.match(/v(\d+)/);
  if (vMatch) return parseInt(vMatch[1]);

  // Old format: "7.pwr"
  const pwrMatch = version.match(/(\d+)\.pwr/);
  if (pwrMatch) return parseInt(pwrMatch[1]);

  // Fallback
  const num = parseInt(version);
  return isNaN(num) ? 0 : num;
}

function buildArchiveUrl(buildNumber, branch = 'release') {
  const os = getOS();
  const arch = getArch();
  return `${MIRROR_BASE_URL}/${os}/${arch}/${branch}/0_to_${buildNumber}.pwr`;
}

async function checkArchiveExists(buildNumber, branch = 'release') {
  const url = buildArchiveUrl(buildNumber, branch);
  try {
    const response = await axios.head(url, { timeout: 10000 });
    return response.status === 200;
  } catch {
    return false;
  }
}

async function discoverAvailableVersions(latestKnown, branch = 'release') {
  try {
    const manifest = await fetchMirrorManifest();
    const patches = getPlatformPatches(manifest, branch);
    const versions = [...new Set(patches.map(p => p.to))].sort((a, b) => b - a);
    return versions.map(v => `${v}.pwr`);
  } catch {
    return [];
  }
}

async function extractVersionDetails(targetVersion, branch = 'release') {
  const buildNumber = extractVersionNumber(targetVersion);
  const fullUrl = buildArchiveUrl(buildNumber, branch);

  return {
    version: targetVersion,
    buildNumber,
    buildName: `HYTALE-Build-${buildNumber}`,
    fullUrl,
    differentialUrl: null,
    checksum: null,
    sourceVersion: null,
    isDifferential: false,
    releaseNotes: null
  };
}

function canUseDifferentialUpdate() {
  // Differential updates are now handled via getUpdatePlan()
  return false;
}

function needsIntermediatePatches(currentVersion, targetVersion) {
  if (!currentVersion) return [];
  const current = extractVersionNumber(currentVersion);
  const target = extractVersionNumber(targetVersion);
  if (current >= target) return [];
  return [targetVersion];
}

async function computeFileChecksum(filePath) {
  return new Promise((resolve, reject) => {
    const hash = crypto.createHash('sha256');
    const stream = fs.createReadStream(filePath);
    stream.on('data', data => hash.update(data));
    stream.on('end', () => resolve(hash.digest('hex')));
    stream.on('error', reject);
  });
}

async function validateChecksum(filePath, expectedChecksum) {
  if (!expectedChecksum) return true;
  const actualChecksum = await computeFileChecksum(filePath);
  return actualChecksum === expectedChecksum;
}

function getInstalledClientVersion() {
  try {
    const { loadVersionClient } = require('../core/config');
    return loadVersionClient();
  } catch {
    return null;
  }
}

module.exports = {
  getLatestClientVersion,
  buildArchiveUrl,
  checkArchiveExists,
  discoverAvailableVersions,
  extractVersionDetails,
  canUseDifferentialUpdate,
  needsIntermediatePatches,
  computeFileChecksum,
  validateChecksum,
  getInstalledClientVersion,
  fetchMirrorManifest,
  getPWRUrl,
  getPWRUrlFromNewAPI,
  getUpdatePlan,
  extractVersionNumber,
  getPlatformPatches,
  findOptimalPatchPath,
  MIRROR_BASE_URL
};