/**
 * fix-duplicate-imports.mjs
 *
 * Merges duplicate import statements from the same module across all TypeScript
 * source files in the project. Run this whenever `npm run lint` reports
 * `no-duplicate-imports` errors.
 *
 * Usage:
 *   node scripts/fix-duplicate-imports.mjs
 *
 * Handles:
 *   import type { A, B } from 'module'   — type-only imports
 *   import Default from 'module'         — default imports
 *   import Default, { A, B } from 'mod' — mixed default + named
 *   import { A, B } from 'module'        — named imports
 *   import {\n  A,\n  B\n} from 'mod'   — multi-line named imports
 *
 * When merging a `import type` with a value import from the same module,
 * type-only specifiers are inlined as `type Name` in the merged statement.
 */

import { readFileSync, readdirSync, statSync, writeFileSync } from "fs";
import { extname, join, resolve } from "path";

// ---------------------------------------------------------------------------
// Config
// ---------------------------------------------------------------------------

const projectRoot = resolve(new URL(".", import.meta.url).pathname, "..");
const srcDir = join(projectRoot, "src");
const extensions = new Set([".ts", ".tsx"]);

// ---------------------------------------------------------------------------
// File discovery — recursively find all TS/TSX files under src/
// ---------------------------------------------------------------------------

function findFiles(dir) {
  const results = [];
  for (const entry of readdirSync(dir)) {
    const full = join(dir, entry);
    if (statSync(full).isDirectory()) {
      results.push(...findFiles(full));
    } else if (extensions.has(extname(entry))) {
      results.push(full);
    }
  }
  return results;
}

// ---------------------------------------------------------------------------
// Import extraction
// ---------------------------------------------------------------------------

/**
 * Extracts all top-level import statements from file content.
 * Returns array of { start, end, raw, module, isType, defaultImport, namedImports }
 * where start/end are character positions in the content.
 */
function extractImports(content) {
  const results = [];
  const importRe = /^import\s+([\s\S]*?)from\s+['"]([^'"]+)['"]\s*;?/gm;

  let match;
  while ((match = importRe.exec(content)) !== null) {
    const raw = match[0];
    const specifierPart = match[1];
    const moduleName = match[2];

    const isType = /^type\s+/.test(specifierPart.trimStart());
    const cleanSpec = specifierPart.replace(/^type\s+/, "").trim();

    let defaultImport = null;
    let namedStr = null;

    const namespaceMatch = cleanSpec.match(/^\*\s+as\s+(\w+)/);
    if (namespaceMatch) {
      defaultImport = `* as ${namespaceMatch[1]}`;
    } else {
      const braceIdx = cleanSpec.indexOf("{");
      if (braceIdx === -1) {
        const def = cleanSpec.replace(/,$/, "").trim();
        if (def) defaultImport = def;
      } else {
        const beforeBrace = cleanSpec.slice(0, braceIdx).replace(/,$/, "").trim();
        if (beforeBrace) defaultImport = beforeBrace;
        const closeBrace = cleanSpec.lastIndexOf("}");
        namedStr = cleanSpec.slice(braceIdx + 1, closeBrace);
      }
    }

    const namedImports = namedStr
      ? namedStr.split(",").map((s) => s.trim()).filter(Boolean)
      : [];

    results.push({
      start: match.index,
      end: match.index + raw.length,
      raw,
      module: moduleName,
      isType,
      defaultImport,
      namedImports,
    });
  }

  return results;
}

// ---------------------------------------------------------------------------
// Import merging
// ---------------------------------------------------------------------------

/**
 * Build a single merged import statement from multiple imports of the same module.
 *
 * - All type imports → merged `import type { ... }`
 * - Mixed type + value → merged value import with inline `type Name` specifiers
 */
function buildMergedImport(moduleName, importList) {
  const allType = importList.every((i) => i.isType);

  if (allType) {
    const allNamed = new Set(importList.flatMap((i) => i.namedImports));
    const defaultImport = importList.map((i) => i.defaultImport).find(Boolean) ?? null;
    const parts = [];
    if (defaultImport) parts.push(defaultImport);
    if (allNamed.size > 0) parts.push(`{ ${[...allNamed].join(", ")} }`);
    if (parts.length === 0) return `import type "${moduleName}";`;
    return `import type ${parts.join(", ")} from "${moduleName}";`;
  }

  // Mixed: collect value default, type-only named, value named separately
  let valueDefault = null;
  const typeNamed = new Set();
  const valueNamed = new Set();

  for (const imp of importList) {
    if (imp.defaultImport && !imp.isType) valueDefault = imp.defaultImport;
    for (const n of imp.namedImports) {
      (imp.isType ? typeNamed : valueNamed).add(n);
    }
  }

  // Build named specifiers: `type X` for type-only, plain for value
  const typeSpecifiers = [...typeNamed].filter((n) => !valueNamed.has(n)).map((n) => `type ${n}`);
  const valueSpecifiers = [...valueNamed];
  const namedParts = [...typeSpecifiers, ...valueSpecifiers];

  const parts = [];
  if (valueDefault) parts.push(valueDefault);
  if (namedParts.length > 0) parts.push(`{ ${namedParts.join(", ")} }`);
  if (parts.length === 0) return `import "${moduleName}";`;
  return `import ${parts.join(", ")} from "${moduleName}";`;
}

// ---------------------------------------------------------------------------
// File fixer
// ---------------------------------------------------------------------------

function fixFile(filePath) {
  let content = readFileSync(filePath, "utf-8");
  const imports = extractImports(content);
  if (imports.length === 0) return null;

  // Group by module
  const byModule = new Map();
  for (const imp of imports) {
    if (!byModule.has(imp.module)) byModule.set(imp.module, []);
    byModule.get(imp.module).push(imp);
  }

  if (![...byModule.values()].some((v) => v.length > 1)) return null;

  // Build merged text for each module
  const mergedMap = new Map();
  for (const [mod, imps] of byModule) {
    mergedMap.set(mod, imps.length === 1 ? imps[0].raw : buildMergedImport(mod, imps));
  }

  // Build replacement list (process in reverse order to preserve character positions)
  imports.sort((a, b) => a.start - b.start);
  const placedModules = new Set();
  const replacements = [];

  for (const imp of imports) {
    if (!placedModules.has(imp.module)) {
      replacements.push({ start: imp.start, end: imp.end, replacement: mergedMap.get(imp.module) });
      placedModules.add(imp.module);
    } else {
      // Remove duplicate, including its trailing newline
      const end = content[imp.end] === "\n" ? imp.end + 1 : imp.end;
      replacements.push({ start: imp.start, end, replacement: "" });
    }
  }

  replacements.sort((a, b) => b.start - a.start);
  for (const { start, end, replacement } of replacements) {
    content = content.slice(0, start) + replacement + content.slice(end);
  }

  return content;
}

// ---------------------------------------------------------------------------
// Main
// ---------------------------------------------------------------------------

const files = findFiles(srcDir);
let fixedCount = 0;

for (const filePath of files) {
  try {
    const original = readFileSync(filePath, "utf-8");
    const fixed = fixFile(filePath);
    if (fixed && fixed !== original) {
      writeFileSync(filePath, fixed, "utf-8");
      const rel = filePath.replace(projectRoot + "/", "");
      console.log(`Fixed: ${rel}`);
      fixedCount++;
    }
  } catch (err) {
    const rel = filePath.replace(projectRoot + "/", "");
    console.error(`Error: ${rel} — ${err.message}`);
  }
}

console.log(`\nDone. Fixed ${fixedCount} file${fixedCount !== 1 ? "s" : ""}.`);