import { promises as fs } from "node:fs";
import path from "node:path";
import process from "node:process";
import { pathToFileURL } from "node:url";

const SCAN_ROOTS = ["src", "tests"];
const SCAN_EXTENSIONS = new Set([".vue", ".js", ".ts", ".json"]);
const CP1252_EXTRA_BYTE_BY_CHAR = new Map([
  ["€", 0x80],
  ["‚", 0x82],
  ["ƒ", 0x83],
  ["„", 0x84],
  ["…", 0x85],
  ["†", 0x86],
  ["‡", 0x87],
  ["ˆ", 0x88],
  ["‰", 0x89],
  ["Š", 0x8a],
  ["‹", 0x8b],
  ["Œ", 0x8c],
  ["Ž", 0x8e],
  ["‘", 0x91],
  ["’", 0x92],
  ["“", 0x93],
  ["”", 0x94],
  ["•", 0x95],
  ["–", 0x96],
  ["—", 0x97],
  ["˜", 0x98],
  ["™", 0x99],
  ["š", 0x9a],
  ["›", 0x9b],
  ["œ", 0x9c],
  ["ž", 0x9e],
  ["Ÿ", 0x9f],
]);
const SUSPICIOUS_PATTERNS = [
  /ÃÂ/g,
  /Ã./g,
  /Â(?=\S)/g,
  /â€[™œžŸ"“”‘’•–—…]/g,
  /’/g,
  /“/g,
  /”/g,
  /–/g,
  /—/g,
  /…/g,
  /�/g,
];
const REGIONAL_CHAR_REGEX = /[æøåÆØÅäöÄÖüÜßéÉèÈáÁàÀóÓúÚíÍñÑçÇ]/g;
const LATIN_EXTENDED_CHAR_REGEX = /[\u00C0-\u024F]/g;
// eslint-disable-next-line no-control-regex -- these are precisely the invalid control characters this scanner detects.
const CONTROL_CHAR_REGEX = new RegExp("[\\x00-\\x08\\x0b\\x0c\\x0e-\\x1f\\x7f-\\x9f]", "g");
const utf8Decoder = new TextDecoder("utf-8", { fatal: true });

function countMatches(text, regex) {
  const matches = text.match(regex);
  return matches ? matches.length : 0;
}

export function countSuspiciousMarkers(text) {
  return SUSPICIOUS_PATTERNS.reduce((count, pattern) => count + countMatches(text, pattern), 0);
}

export function countRegionalCharacters(text) {
  return countMatches(text, REGIONAL_CHAR_REGEX);
}

function countLatinExtendedCharacters(text) {
  return countMatches(text, LATIN_EXTENDED_CHAR_REGEX);
}

function countControlCharacters(text) {
  return countMatches(text, CONTROL_CHAR_REGEX);
}

function encodeLatin1(text) {
  const bytes = [];

  for (const character of text) {
    const codePoint = character.codePointAt(0);
    if (codePoint > 0xff) {
      return null;
    }
    bytes.push(codePoint);
  }

  return Uint8Array.from(bytes);
}

function encodeWindows1252(text) {
  const bytes = [];

  for (const character of text) {
    if (CP1252_EXTRA_BYTE_BY_CHAR.has(character)) {
      bytes.push(CP1252_EXTRA_BYTE_BY_CHAR.get(character));
      continue;
    }

    const codePoint = character.codePointAt(0);
    if (codePoint > 0xff) {
      return null;
    }
    bytes.push(codePoint);
  }

  return Uint8Array.from(bytes);
}

function decodeUtf8(bytes) {
  try {
    return utf8Decoder.decode(bytes);
  } catch {
    return null;
  }
}

function buildRepairCandidates(text) {
  const candidateSet = new Set();
  const encoders = [encodeLatin1, encodeWindows1252];

  for (const encoder of encoders) {
    const encoded = encoder(text);
    if (!encoded) {
      continue;
    }

    const decoded = decodeUtf8(encoded);
    if (decoded && decoded !== text) {
      candidateSet.add(decoded);
    }
  }

  return [...candidateSet];
}

function isRepairImprovement(before, after) {
  if (!after || after === before) {
    return false;
  }

  const beforeSuspicious = countSuspiciousMarkers(before);
  const afterSuspicious = countSuspiciousMarkers(after);
  const beforeRegional = countRegionalCharacters(before);
  const afterRegional = countRegionalCharacters(after);
  const beforeLatinExtended = countLatinExtendedCharacters(before);
  const afterLatinExtended = countLatinExtendedCharacters(after);
  const beforeControls = countControlCharacters(before);
  const afterControls = countControlCharacters(after);

  if (afterControls > beforeControls) {
    return false;
  }

  if (afterSuspicious < beforeSuspicious) {
    return afterRegional >= beforeRegional || afterLatinExtended >= beforeLatinExtended || afterSuspicious === 0;
  }

  return (
    afterSuspicious === beforeSuspicious && (afterRegional > beforeRegional || afterLatinExtended > beforeLatinExtended)
  );
}

function scoreCandidate(text) {
  return (
    countSuspiciousMarkers(text) * 20 +
    countControlCharacters(text) * 30 -
    countLatinExtendedCharacters(text) * 2 -
    countRegionalCharacters(text) * 3
  );
}

function repairOnce(text) {
  const candidates = buildRepairCandidates(text).filter((candidate) => isRepairImprovement(text, candidate));
  if (candidates.length === 0) {
    return text;
  }

  return candidates.reduce((bestCandidate, candidate) => {
    return scoreCandidate(candidate) < scoreCandidate(bestCandidate) ? candidate : bestCandidate;
  });
}

function repairSegment(text) {
  let current = text;

  for (let pass = 0; pass < 4; pass += 1) {
    const repaired = repairOnce(current);
    if (repaired === current) {
      break;
    }
    current = repaired;
  }

  return current;
}

export function repairText(text) {
  const wholeTextRepair = repairSegment(text);
  const linewiseRepair = wholeTextRepair
    .split(/(\r?\n)/)
    .map((segment) => (segment.match(/\r?\n/) ? segment : repairSegment(segment)))
    .join("");

  return repairSegment(linewiseRepair);
}

export function containsSuspiciousEncoding(text) {
  return countSuspiciousMarkers(text) > 0;
}

function getPreview(line) {
  return line.replace(/\s+/g, " ").trim().slice(0, 180);
}

export function findSuspiciousLines(text) {
  return text
    .split(/\r?\n/)
    .map((line, index) => ({
      lineNumber: index + 1,
      preview: getPreview(line),
      suspiciousCount: countSuspiciousMarkers(line),
    }))
    .filter((entry) => entry.suspiciousCount > 0);
}

async function collectScanFiles(rootDir) {
  const files = [];

  async function walk(currentDir) {
    let entries;
    try {
      entries = await fs.readdir(currentDir, { withFileTypes: true });
    } catch {
      return;
    }

    for (const entry of entries) {
      const entryPath = path.join(currentDir, entry.name);

      if (entry.isDirectory()) {
        await walk(entryPath);
        continue;
      }

      if (!entry.isFile() || !SCAN_EXTENSIONS.has(path.extname(entry.name))) {
        continue;
      }

      files.push(entryPath);
    }
  }

  for (const scanRoot of SCAN_ROOTS) {
    await walk(path.join(rootDir, scanRoot));
  }

  return files.sort();
}

async function run(mode) {
  const rootDir = process.cwd();
  const files = await collectScanFiles(rootDir);
  const suspiciousReports = [];
  let changedFiles = 0;

  for (const filePath of files) {
    const originalText = await fs.readFile(filePath, "utf8");
    const repairedText = repairText(originalText);

    if (mode === "fix" && repairedText !== originalText) {
      await fs.writeFile(filePath, repairedText, "utf8");
      changedFiles += 1;
    }

    const inspectedText = mode === "fix" ? repairedText : originalText;
    const suspiciousLines = findSuspiciousLines(inspectedText);
    if (suspiciousLines.length > 0) {
      suspiciousReports.push({
        filePath: path.relative(rootDir, filePath),
        lines: suspiciousLines.slice(0, 12),
      });
    }
  }

  if (mode === "fix") {
    console.log(`Updated ${changedFiles} file(s).`);
  }

  if (suspiciousReports.length > 0) {
    console.error(`Detected suspicious encoding markers in ${suspiciousReports.length} file(s):`);
    suspiciousReports.forEach((report) => {
      console.error(`- ${report.filePath}`);
      report.lines.forEach((line) => {
        console.error(`  ${line.lineNumber}: ${line.preview}`);
      });
    });
    process.exitCode = 1;
    return;
  }

  console.log(`No suspicious encoding markers found across ${files.length} file(s).`);
}

const isDirectRun = typeof process.argv[1] === "string" && pathToFileURL(process.argv[1]).href === import.meta.url;

if (isDirectRun) {
  const mode = process.argv[2] || "check";
  if (!["check", "fix"].includes(mode)) {
    console.error("Usage: node scripts/text-encoding.mjs <check|fix>");
    process.exit(1);
  }

  await run(mode);
}