#!/usr/bin/env node

/**
 * Generates a combined bundle stats comment for GitHub Actions.
 * Heavily inspired by https://github.com/twk3/rollup-size-compare-action (MIT).
 */

import { readFile } from 'node:fs/promises';
import path from 'node:path';
import process from 'node:process';

const REQUIRED_ARGS = new Map([
  ['base', 'Mapping of bundle names to base stats JSON'],
  ['head', 'Mapping of bundle names to head stats JSON'],
]);

function parseRawArgs(argv) {
  const args = new Map();

  for (let index = 2; index < argv.length; index += 1) {
    const key = argv[index];

    if (!key?.startsWith('--')) {
      throw new Error(
        `Unexpected argument "${key ?? ''}". Use --key value pairs.`,
      );
    }

    const values = [];

    while (index + 1 < argv.length && !argv[index + 1].startsWith('--')) {
      values.push(argv[index + 1]);
      index += 1;
    }

    if (values.length === 0) {
      throw new Error(`Missing value for argument "${key}".`);
    }

    const keyName = key.slice(2);
    // Accumulate values if the key already exists
    if (args.has(keyName)) {
      args.set(keyName, [...args.get(keyName), ...values]);
    } else {
      args.set(keyName, values);
    }
  }

  return args;
}

function getSingleValue(args, key) {
  const values = args.get(key);
  if (!values) {
    return undefined;
  }
  if (values.length !== 1) {
    throw new Error(`Argument "--${key}" must have exactly one value.`);
  }
  return values[0];
}

function parseMapping(values, key, description) {
  if (!values || values.length === 0) {
    throw new Error(`Missing required argument "--${key}" (${description}).`);
  }

  if (values.length === 1) {
    const [rawValue] = values;
    const trimmed = rawValue.trim();

    if (trimmed.startsWith('{')) {
      try {
        const parsed = JSON.parse(trimmed);

        if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
          throw new Error('Value must be a JSON object.');
        }

        return new Map(
          Object.entries(parsed).map(([name, pathValue]) => {
            if (typeof pathValue !== 'string') {
              throw new Error(
                `Value for "${name}" in "--${key}" must be a string path.`,
              );
            }
            return [name, pathValue];
          }),
        );
      } catch (error) {
        const message =
          error instanceof Error ? error.message : 'Unknown parsing error';
        throw new Error(
          `Failed to parse "--${key}" value as JSON object: ${message}`,
        );
      }
    }
  }

  const entries = new Map();

  for (const value of values) {
    const [rawName, ...rawPathParts] = value.split('=');

    if (!rawName || rawPathParts.length === 0) {
      throw new Error(
        `Argument "--${key}" must be provided as name=path pairs or a JSON object.`,
      );
    }

    const name = rawName.trim();
    const pathValue = rawPathParts.join('=').trim();

    if (!name) {
      throw new Error(`Argument "--${key}" contains an empty bundle name.`);
    }

    if (!pathValue) {
      throw new Error(
        `Argument "--${key}" for bundle "${name}" must include a non-empty path.`,
      );
    }

    entries.set(name, pathValue);
  }

  if (entries.size === 0) {
    throw new Error(`Argument "--${key}" must define at least one bundle.`);
  }

  return entries;
}

function parseArgs(argv) {
  const args = parseRawArgs(argv);

  const baseMap = parseMapping(
    args.get('base'),
    'base',
    REQUIRED_ARGS.get('base'),
  );
  const headMap = parseMapping(
    args.get('head'),
    'head',
    REQUIRED_ARGS.get('head'),
  );

  const sections = [];

  for (const [name, basePath] of baseMap.entries()) {
    const headPath = headMap.get(name);

    if (!headPath) {
      throw new Error(
        `Bundle "${name}" is missing a corresponding "--head" entry.`,
      );
    }

    sections.push({
      name,
      basePath,
      headPath,
    });
  }

  for (const name of headMap.keys()) {
    if (!baseMap.has(name)) {
      throw new Error(
        `Bundle "${name}" is missing a corresponding "--base" entry.`,
      );
    }
  }

  return {
    sections,
    identifier: getSingleValue(args, 'identifier') ?? 'bundle-stats',
    format: getSingleValue(args, 'format') ?? 'pr-body',
  };
}

async function loadStats(filePath) {
  try {
    const absolutePath = path.resolve(process.cwd(), filePath);
    const fileContents = await readFile(absolutePath, 'utf8');
    const parsed = JSON.parse(fileContents);

    // Validate that we got a meaningful stats object
    if (!parsed || typeof parsed !== 'object') {
      throw new Error('Stats file does not contain a valid JSON object');
    }

    return parsed;
  } catch (error) {
    const message =
      error instanceof Error
        ? error.message
        : 'Unknown error while parsing stats file';
    console.error(`[bundle-stats] Failed to parse "${filePath}": ${message}`);
    throw new Error(`Failed to load stats file "${filePath}": ${message}`);
  }
}

function findAllChildren(node = {}) {
  if (Array.isArray(node.children)) {
    return node.children.flatMap(findAllChildren);
  }
  return [node];
}

function trimPath(input) {
  if (!input) {
    return '';
  }
  return input.replace(/.*node_modules/, '/node_modules');
}

function assetNameToSizeMap(statAssets = {}) {
  const children = statAssets?.tree?.children;

  if (!Array.isArray(children) || children.length === 0) {
    return new Map();
  }

  return new Map(
    children.map(asset => {
      const descendants = findAllChildren(asset);
      let size = 0;
      let gzipSize = statAssets?.options?.gzip ? 0 : null;

      for (const mod of descendants) {
        const nodePart = statAssets?.nodeParts?.[mod.uid];

        if (!nodePart) {
          continue;
        }

        size += nodePart.renderedLength ?? 0;

        if (gzipSize !== null) {
          gzipSize += nodePart.gzipLength ?? 0;
        }
      }

      return [trimPath(asset.name), { size, gzipSize }];
    }),
  );
}

function chunkModuleNameToSizeMap(statChunks = {}) {
  if (!statChunks?.tree) {
    return new Map();
  }

  return new Map(
    findAllChildren(statChunks.tree).map(mod => {
      const modInfo = statChunks?.nodeParts?.[mod.uid] ?? {};
      const meta = statChunks?.nodeMetas?.[modInfo.metaUid] ?? {};
      const id = trimPath(meta.id ?? '');

      return [
        id,
        {
          size: modInfo.renderedLength ?? 0,
          gzipSize: statChunks?.options?.gzip
            ? (modInfo.gzipLength ?? 0)
            : null,
        },
      ];
    }),
  );
}

function sortDiffDescending(items) {
  return items.sort((a, b) => Math.abs(b.diff) - Math.abs(a.diff));
}

function normaliseGzip(value) {
  if (value == null || Number.isNaN(value)) {
    return NaN;
  }
  return value;
}

function getAssetDiff(name, oldSize, newSize) {
  const diff = newSize.size - oldSize.size;

  const percent =
    oldSize.size === 0
      ? newSize.size === 0
        ? 0
        : Infinity
      : +((1 - newSize.size / oldSize.size) * -100).toFixed(5) || 0;

  return {
    name,
    new: {
      size: newSize.size,
      gzipSize: normaliseGzip(newSize.gzipSize),
    },
    old: {
      size: oldSize.size,
      gzipSize: normaliseGzip(oldSize.gzipSize),
    },
    diff,
    diffPercentage: percent,
  };
}

function webpackStatsDiff(oldAssets, newAssets) {
  const added = [];
  const removed = [];
  const bigger = [];
  const smaller = [];
  const unchanged = [];

  let newSizeTotal = 0;
  let oldSizeTotal = 0;
  let newGzipSizeTotal = 0;
  let oldGzipSizeTotal = 0;

  for (const [name, oldAssetSizes] of oldAssets) {
    oldSizeTotal += oldAssetSizes.size;
    oldGzipSizeTotal += oldAssetSizes.gzipSize ?? NaN;

    const newAsset = newAssets.get(name);

    if (!newAsset) {
      removed.push(getAssetDiff(name, oldAssetSizes, { size: 0, gzipSize: 0 }));
      continue;
    }

    const diff = getAssetDiff(name, oldAssetSizes, newAsset);

    if (diff.diffPercentage > 0) {
      bigger.push(diff);
    } else if (diff.diffPercentage < 0) {
      smaller.push(diff);
    } else {
      unchanged.push(diff);
    }
  }

  for (const [name, newAssetSizes] of newAssets) {
    newSizeTotal += newAssetSizes.size;
    newGzipSizeTotal += newAssetSizes.gzipSize ?? NaN;

    if (!oldAssets.has(name)) {
      added.push(getAssetDiff(name, { size: 0, gzipSize: 0 }, newAssetSizes));
    }
  }

  const oldFilesCount = oldAssets.size;
  const newFilesCount = newAssets.size;

  return {
    added: sortDiffDescending(added),
    removed: sortDiffDescending(removed),
    bigger: sortDiffDescending(bigger),
    smaller: sortDiffDescending(smaller),
    unchanged,
    total: getAssetDiff(
      oldFilesCount === newFilesCount
        ? `${newFilesCount}`
        : `${oldFilesCount} → ${newFilesCount}`,
      { size: oldSizeTotal, gzipSize: oldGzipSizeTotal },
      { size: newSizeTotal, gzipSize: newGzipSizeTotal },
    ),
  };
}

function getStatsDiff(oldStats, newStats) {
  return webpackStatsDiff(
    assetNameToSizeMap(oldStats),
    assetNameToSizeMap(newStats),
  );
}

function getChunkModuleDiff(oldStats, newStats) {
  const diff = webpackStatsDiff(
    chunkModuleNameToSizeMap(oldStats),
    chunkModuleNameToSizeMap(newStats),
  );

  if (
    diff.added.length === 0 &&
    diff.removed.length === 0 &&
    diff.bigger.length === 0 &&
    diff.smaller.length === 0
  ) {
    return null;
  }

  return diff;
}

const BYTES_PER_KILOBYTE = 1024;
const FILE_SIZE_DENOMINATIONS = [
  'B',
  'kB',
  'MB',
  'GB',
  'TB',
  'PB',
  'EB',
  'ZB',
  'YB',
  'BB',
];

function formatFileSizeIEC(bytes, precision = 2) {
  if (bytes == null || Number.isNaN(bytes)) {
    return 'N/A';
  }

  if (bytes === 0) {
    return `0 ${FILE_SIZE_DENOMINATIONS[0]}`;
  }

  const absBytes = Math.abs(bytes);
  const denominationIndex = Math.floor(
    Math.log(absBytes) / Math.log(BYTES_PER_KILOBYTE),
  );
  const value = absBytes / Math.pow(BYTES_PER_KILOBYTE, denominationIndex);
  const stripped = parseFloat(value.toFixed(precision));

  return `${stripped} ${FILE_SIZE_DENOMINATIONS[denominationIndex]}`;
}

function conditionalPercentage(number) {
  if (number === Infinity || number === -Infinity) {
    return '-';
  }

  const absValue = Math.abs(number);

  if (absValue === 0 || absValue === 100) {
    return `${number}%`;
  }

  const value = Number.isFinite(absValue) ? absValue.toFixed(2) : absValue;
  return `${signFor(number)}${value}%`;
}

function capitalize(text) {
  if (!text) return '';
  return `${text[0].toUpperCase()}${text.slice(1)}`;
}

function makeHeader(columns) {
  const header = columns.join(' | ');
  const separator = columns
    .map(column =>
      Array.from({ length: column.length })
        .map(() => '-')
        .join(''),
    )
    .join(' | ');

  return `${header}\n${separator}`;
}

const TOTAL_HEADERS = makeHeader([
  'Files count',
  'Total bundle size',
  '% Changed',
]);
const SUMMARY_HEADERS = makeHeader([
  'Bundle',
  'Files count',
  'Total bundle size',
  '% Changed',
]);
const TABLE_HEADERS = makeHeader(['Asset', 'File Size', '% Changed']);
const CHUNK_TABLE_HEADERS = makeHeader(['File', 'Δ', 'Size']);

function signFor(num) {
  if (num === 0) return '';
  return num > 0 ? '+' : '-';
}

function toFileSizeDiff(oldSize, newSize, diff) {
  const diffLine = [
    `${formatFileSizeIEC(oldSize)} → ${formatFileSizeIEC(newSize)}`,
  ];

  if (typeof diff !== 'undefined') {
    diffLine.push(`(${signFor(diff)}${formatFileSizeIEC(diff)})`);
  }

  return diffLine.join(' ');
}

function toFileSizeDiffCell(asset) {
  const lines = [];

  if (asset.diff === 0) {
    lines.push(formatFileSizeIEC(asset.new.size));

    if (asset.new.gzipSize) {
      lines.push(formatFileSizeIEC(asset.new.gzipSize));
    }
  } else {
    lines.push(toFileSizeDiff(asset.old.size, asset.new.size, asset.diff));

    if (asset.old.gzipSize || asset.new.gzipSize) {
      lines.push(
        `${toFileSizeDiff(asset.old.gzipSize, asset.new.gzipSize)} (gzip)`,
      );
    }
  }

  return lines.join('<br />');
}

function printAssetTableRow(asset) {
  return [
    asset.name,
    toFileSizeDiffCell(asset),
    conditionalPercentage(asset.diffPercentage),
  ].join(' | ');
}

function printAssetTablesByGroup(statsDiff) {
  const statsFields = ['added', 'removed', 'bigger', 'smaller', 'unchanged'];

  return statsFields
    .map(field => {
      const assets = statsDiff[field] ?? [];

      if (assets.length === 0) {
        return `**${capitalize(field)}**\nNo assets were ${field}`;
      }

      return `**${capitalize(field)}**\n${TABLE_HEADERS}\n${assets
        .map(asset => printAssetTableRow(asset))
        .join('\n')}`;
    })
    .join('\n\n');
}

function getDiffEmoji(diff) {
  if (diff.diffPercentage === Infinity) return '🆕';
  if (diff.diffPercentage <= -100) return '🔥';
  if (diff.diffPercentage > 0) return '📈';
  if (diff.diffPercentage < 0) return '📉';
  return ' ';
}

function getTrimmedChunkName(chunkModule) {
  const chunkName = chunkModule.name ?? '';
  if (chunkName.startsWith('./')) {
    return chunkName.substring(2);
  }
  if (chunkName.startsWith('/')) {
    return chunkName.substring(1);
  }
  return chunkName;
}

function printChunkModuleRow(chunkModule) {
  const emoji = getDiffEmoji(chunkModule);
  const chunkName = getTrimmedChunkName(chunkModule);
  const diffPart = `${chunkModule.diff >= 0 ? '+' : '-'}${formatFileSizeIEC(chunkModule.diff)}`;
  const percentPart = Number.isFinite(chunkModule.diffPercentage)
    ? ` (${conditionalPercentage(chunkModule.diffPercentage)})`
    : '';

  return [
    `\`${chunkName}\``,
    `${emoji} ${diffPart}${percentPart}`,
    `${formatFileSizeIEC(chunkModule.old.size)} → ${formatFileSizeIEC(chunkModule.new.size)}`,
  ].join(' | ');
}

function printChunkModulesTable(statsDiff) {
  if (!statsDiff) {
    return '';
  }

  const changedModules = [
    ...(statsDiff.added ?? []),
    ...(statsDiff.removed ?? []),
    ...(statsDiff.bigger ?? []),
    ...(statsDiff.smaller ?? []),
  ].sort((a, b) => b.diffPercentage - a.diffPercentage);

  if (changedModules.length === 0) {
    return `<details>\n<summary>Changeset</summary>\nNo files were changed\n</details>`;
  }

  const rows = changedModules
    .slice(0, 100)
    .map(chunkModule => printChunkModuleRow(chunkModule))
    .join('\n');

  const summarySuffix =
    changedModules.length > 100 ? ' (largest 100 files by percent change)' : '';

  return `<details>\n<summary>Changeset${summarySuffix}</summary>\n\n${CHUNK_TABLE_HEADERS}\n${rows}\n</details>`;
}

function printTotalAssetTable(statsDiff) {
  return `**Total**\n${TOTAL_HEADERS}\n${printAssetTableRow(statsDiff.total)}`;
}

function printSummaryTable(sections) {
  if (sections.length === 0) {
    return `${SUMMARY_HEADERS}\nNo bundle stats were generated.`;
  }

  const rows = sections.map(section => {
    const total = section.statsDiff.total;
    return [
      section.name,
      total.name,
      toFileSizeDiffCell(total),
      conditionalPercentage(total.diffPercentage),
    ].join(' | ');
  });

  return `${SUMMARY_HEADERS}\n${rows.join('\n')}`;
}

function renderSection(title, statsDiff, chunkModuleDiff) {
  const { total, ...groups } = statsDiff;
  const parts = [`#### ${title}`, '', printTotalAssetTable({ total })];

  const chunkTable = printChunkModulesTable(chunkModuleDiff);
  if (chunkTable) {
    parts.push('', chunkTable);
  }

  parts.push(
    '',
    `<details>\n<summary>View detailed bundle breakdown</summary>\n<div>\n\n${printAssetTablesByGroup(
      groups,
    )}\n</div>\n</details>`,
  );

  return parts.join('\n');
}

function renderSections(sections) {
  return sections
    .map(section =>
      renderSection(section.name, section.statsDiff, section.chunkDiff),
    )
    .join('\n\n---\n\n');
}

function getIdentifierMarkers(key) {
  const label = 'bundlestats-action-comment';
  return {
    start: `<!--- ${label} key:${key} start --->`,
    end: `<!--- ${label} key:${key} end --->`,
  };
}

async function main() {
  const args = parseArgs(process.argv);
  const allowedFormats = new Set(['comment', 'pr-body']);
  if (!allowedFormats.has(args.format)) {
    throw new Error(
      `Invalid format "${args.format}". Use "comment" or "pr-body".`,
    );
  }

  console.error(
    `[bundle-stats] Found ${args.sections.length} sections to process`,
  );
  args.sections.forEach((section, index) => {
    console.error(
      `[bundle-stats] Section ${index + 1}: ${section.name} (base: ${section.basePath}, head: ${section.headPath})`,
    );
  });

  const sections = [];

  for (const section of args.sections) {
    console.error(`[bundle-stats] Processing section: ${section.name}`);
    console.error(
      `[bundle-stats] Loading base stats from: ${section.basePath}`,
    );
    const baseStats = await loadStats(section.basePath);
    console.error(
      `[bundle-stats] Loading head stats from: ${section.headPath}`,
    );
    const headStats = await loadStats(section.headPath);

    const statsDiff = getStatsDiff(baseStats, headStats);
    const chunkDiff = getChunkModuleDiff(baseStats, headStats);

    console.error(
      `[bundle-stats] Section ${section.name}: ${statsDiff.total.name} files, total size ${statsDiff.total.old.size} → ${statsDiff.total.new.size}`,
    );

    sections.push({
      name: section.name,
      statsDiff,
      chunkDiff,
    });
  }

  const markers = getIdentifierMarkers(args.identifier);
  const sectionsContent = renderSections(sections);
  const summaryTable = printSummaryTable(sections);

  const detailedBody = ['### Bundle Stats', '', sectionsContent].join('\n');

  const commentBody = [markers.start, detailedBody, '', markers.end, ''].join(
    '\n',
  );

  const prBody = [
    markers.start,
    '### Bundle Stats',
    '',
    summaryTable,
    '',
    `<details>\n<summary>View detailed bundle stats</summary>\n\n${sectionsContent}\n</details>`,
    '',
    markers.end,
    '',
  ].join('\n');

  process.stdout.write(args.format === 'comment' ? commentBody : prBody);
}

main().catch(error => {
  console.error(error);
  process.exitCode = 1;
});