import { readdir, readFile, stat } from "node:fs/promises";
import path from "node:path";
import { pathToFileURL } from "node:url";

type Layer = "app" | "builder" | "core" | "module" | "neutral" | "shared" | "surface";

interface Location {
  layer: Layer;
  owner: string;
  relativePath: string;
  role?: string;
}

interface PackageManifest {
  dependencies?: Record<string, string>;
  devDependencies?: Record<string, string>;
  ekklesia?: { layer?: string };
  exports?: unknown;
  name?: string;
  optionalDependencies?: Record<string, string>;
  peerDependencies?: Record<string, string>;
}

interface WorkspacePackage {
  directory: string;
  location: Location;
  manifest: PackageManifest;
  name: string;
}

export interface BoundaryViolation {
  from: string;
  message: string;
  rule: string;
  to?: string;
}

export interface BoundaryResult {
  filesChecked: number;
  packagesChecked: number;
  violations: BoundaryViolation[];
}

const CODE_EXTENSIONS = new Set([".cjs", ".cts", ".js", ".jsx", ".mjs", ".mts", ".ts", ".tsx"]);
const MODULE_UI_EXTENSIONS = new Set([".css", ".jsx", ".less", ".scss", ".svelte", ".tsx", ".vue"]);
const MODULE_UI_PACKAGES = new Set([
  "@angular/core",
  "expo",
  "next",
  "react",
  "react-dom",
  "react-native",
  "solid-js",
  "svelte",
  "tailwindcss",
  "vue",
]);
const IGNORED_DIRECTORIES = new Set([
  ".git",
  ".next",
  ".turbo",
  "coverage",
  "dist",
  "node_modules",
]);
const DEPENDENCY_FIELDS = [
  "dependencies",
  "devDependencies",
  "optionalDependencies",
  "peerDependencies",
] as const;

function normalizePath(value: string): string {
  return value.split(path.sep).join("/").replace(/^\.\//, "");
}

export function describeRepositoryPath(relativePath: string): Location {
  const normalized = normalizePath(relativePath);
  const [area, owner = area] = normalized.split("/");

  if (area === "core") {
    return { layer: "core", owner: "core", relativePath: normalized };
  }

  if (area === "modules" && owner) {
    return { layer: "module", owner, relativePath: normalized };
  }

  if (area === "surfaces" && owner) {
    return { layer: "surface", owner, relativePath: normalized };
  }

  if ((area === "builders" || area === "surface-builder") && owner) {
    return { layer: "builder", owner, relativePath: normalized };
  }

  if (area === "apps" && owner) {
    return { layer: "app", owner, relativePath: normalized };
  }

  if (area === "packages" && owner) {
    return { layer: "shared", owner, relativePath: normalized, role: owner };
  }

  if (area === "templates" && owner === "module") {
    return { layer: "module", owner: "template-module", relativePath: normalized };
  }

  return { layer: "neutral", owner: area ?? "root", relativePath: normalized };
}

function boundaryRule(from: Location, to: Location): string | undefined {
  if (from.layer === "neutral" || to.layer === "neutral") {
    return undefined;
  }

  if (from.layer === to.layer && from.owner === to.owner) {
    return undefined;
  }

  if (from.layer === "core" && ["app", "builder", "module", "surface"].includes(to.layer)) {
    return "core-is-feature-agnostic";
  }

  if (from.layer === "module") {
    if (["app", "builder", "core", "surface"].includes(to.layer)) {
      return "modules-use-public-platform-contracts";
    }
    if (to.layer === "module" && from.owner !== to.owner) {
      return "modules-do-not-import-other-modules";
    }
  }

  if (from.layer === "surface") {
    if (["app", "builder", "core", "module"].includes(to.layer)) {
      return "surfaces-use-public-contracts";
    }
    if (to.layer === "surface" && from.owner !== to.owner) {
      return "surfaces-are-independent";
    }
  }

  if (from.layer === "builder" && ["app", "core", "module", "surface"].includes(to.layer)) {
    return "builder-composes-contracts";
  }

  if (
    from.layer === "shared" &&
    from.role === "contracts" &&
    ["app", "builder", "core", "module", "surface"].includes(to.layer)
  ) {
    return "contracts-do-not-depend-upward";
  }

  if (
    from.layer === "shared" &&
    ["module-sdk", "surface-sdk"].includes(from.role ?? "") &&
    ["app", "builder", "core", "module", "surface"].includes(to.layer)
  ) {
    return "sdks-do-not-depend-on-implementations";
  }

  return undefined;
}

function packageNameFromSpecifier(specifier: string): string {
  if (specifier.startsWith("@")) {
    return specifier.split("/").slice(0, 2).join("/");
  }
  return specifier.split("/")[0] ?? specifier;
}

function isModuleUiPackage(packageName: string): boolean {
  return MODULE_UI_PACKAGES.has(packageName) || packageName.startsWith("@angular/");
}

async function isFile(filePath: string): Promise<boolean> {
  try {
    return (await stat(filePath)).isFile();
  } catch {
    return false;
  }
}

async function walkFiles(root: string, current = root): Promise<string[]> {
  const entries = await readdir(current, { withFileTypes: true });
  const files: string[] = [];

  for (const entry of entries) {
    if (entry.isDirectory() && IGNORED_DIRECTORIES.has(entry.name)) {
      continue;
    }

    const absolutePath = path.join(current, entry.name);
    const relativePath = normalizePath(path.relative(root, absolutePath));

    if (entry.isDirectory()) {
      if (relativePath === "tests/fixtures" || relativePath.startsWith("tests/fixtures/")) {
        continue;
      }
      files.push(...(await walkFiles(root, absolutePath)));
      continue;
    }

    if (entry.isFile()) {
      files.push(absolutePath);
    }
  }

  return files;
}

function collectImportSpecifiers(sourceText: string): string[] {
  const specifiers = new Set<string>();
  const staticImport =
    /\b(?:import|export)\s+(?:type\s+)?(?:[^"'\n;]*?\s+from\s+)?["']([^"'\n]+)["']/gu;
  const dynamicImport = /\b(?:import|require)\s*\(\s*["']([^"'\n]+)["']\s*\)/gu;

  for (const pattern of [staticImport, dynamicImport]) {
    for (const match of sourceText.matchAll(pattern)) {
      const specifier = match[1];
      if (specifier) {
        specifiers.add(specifier);
      }
    }
  }

  return [...specifiers];
}

async function resolveSourceImport(
  fromFile: string,
  specifier: string,
): Promise<string | undefined> {
  if (!specifier.startsWith(".")) {
    return undefined;
  }

  const candidate = path.resolve(path.dirname(fromFile), specifier);
  const extension = path.extname(candidate);
  const withoutExtension = extension ? candidate.slice(0, -extension.length) : candidate;
  const candidates = [candidate];

  if ([".js", ".jsx", ".mjs", ".cjs"].includes(extension)) {
    candidates.push(
      `${withoutExtension}.ts`,
      `${withoutExtension}.tsx`,
      `${withoutExtension}.mts`,
      `${withoutExtension}.cts`,
    );
  } else if (!extension) {
    for (const codeExtension of CODE_EXTENSIONS) {
      candidates.push(
        `${candidate}${codeExtension}`,
        path.join(candidate, `index${codeExtension}`),
      );
    }
  }

  for (const possibleFile of candidates) {
    if (await isFile(possibleFile)) {
      return possibleFile;
    }
  }

  return candidate;
}

function findCycles(graph: Map<string, Set<string>>): string[][] {
  const visited = new Set<string>();
  const active = new Set<string>();
  const stack: string[] = [];
  const cycles: string[][] = [];
  const seenCycles = new Set<string>();

  function visit(node: string): void {
    if (active.has(node)) {
      const start = stack.indexOf(node);
      const cycle = [...stack.slice(start), node];
      const key = [...new Set(cycle)].sort().join("|");
      if (!seenCycles.has(key)) {
        seenCycles.add(key);
        cycles.push(cycle);
      }
      return;
    }

    if (visited.has(node)) {
      return;
    }

    visited.add(node);
    active.add(node);
    stack.push(node);
    for (const target of graph.get(node) ?? []) {
      if (graph.has(target)) {
        visit(target);
      }
    }
    stack.pop();
    active.delete(node);
  }

  for (const node of graph.keys()) {
    visit(node);
  }

  return cycles;
}

function exportedSubpath(
  manifest: PackageManifest,
  specifier: string,
  packageName: string,
): boolean {
  const suffix = specifier.slice(packageName.length);
  if (!suffix) {
    return true;
  }

  if (!manifest.exports || typeof manifest.exports !== "object") {
    return false;
  }

  const requested = `.${suffix}`;
  return Object.hasOwn(manifest.exports, requested);
}

export async function checkBoundaries(rootDirectory: string): Promise<BoundaryResult> {
  const root = path.resolve(rootDirectory);
  const allFiles = await walkFiles(root);
  const manifestFiles = allFiles.filter((file) => path.basename(file) === "package.json");
  const codeFiles = allFiles.filter((file) => CODE_EXTENSIONS.has(path.extname(file)));
  const workspacePackages = new Map<string, WorkspacePackage>();
  const packageByDirectory = new Map<string, WorkspacePackage>();
  const violations: BoundaryViolation[] = [];

  for (const manifestFile of manifestFiles) {
    const manifest = JSON.parse(await readFile(manifestFile, "utf8")) as PackageManifest;
    if (!manifest.name || manifestFile === path.join(root, "package.json")) {
      continue;
    }
    const directory = path.dirname(manifestFile);
    const relativeDirectory = normalizePath(path.relative(root, directory));
    const location = describeRepositoryPath(relativeDirectory);
    if (manifest.ekklesia?.layer) {
      location.role = manifest.ekklesia.layer;
    }
    const workspacePackage = { directory, location, manifest, name: manifest.name };
    workspacePackages.set(manifest.name, workspacePackage);
    packageByDirectory.set(directory, workspacePackage);
  }

  const packageGraph = new Map<string, Set<string>>();
  for (const workspacePackage of workspacePackages.values()) {
    packageGraph.set(workspacePackage.name, new Set());
    for (const dependencyField of DEPENDENCY_FIELDS) {
      for (const dependencyName of Object.keys(workspacePackage.manifest[dependencyField] ?? {})) {
        if (workspacePackage.location.layer === "module" && isModuleUiPackage(dependencyName)) {
          violations.push({
            from: workspacePackage.location.relativePath,
            message: `Module package depends on UI framework ${dependencyName}.`,
            rule: "modules-do-not-own-ui",
          });
        }

        const targetPackage = workspacePackages.get(dependencyName);
        if (!targetPackage) {
          continue;
        }
        packageGraph.get(workspacePackage.name)?.add(targetPackage.name);
        const rule = boundaryRule(workspacePackage.location, targetPackage.location);
        if (rule) {
          violations.push({
            from: workspacePackage.location.relativePath,
            message: `${workspacePackage.name} may not depend on ${targetPackage.name}.`,
            rule,
            to: targetPackage.location.relativePath,
          });
        }
      }
    }
  }

  for (const cycle of findCycles(packageGraph)) {
    violations.push({
      from: cycle[0] ?? "unknown-package",
      message: `Workspace package cycle: ${cycle.join(" -> ")}`,
      rule: "no-circular-package-dependencies",
    });
  }

  for (const repositoryFile of allFiles) {
    const relativeFile = normalizePath(path.relative(root, repositoryFile));
    const location = describeRepositoryPath(relativeFile);
    if (location.layer === "module" && MODULE_UI_EXTENSIONS.has(path.extname(repositoryFile))) {
      violations.push({
        from: relativeFile,
        message: "UI source files belong in a surface, not a module.",
        rule: "modules-do-not-own-ui",
      });
    }
  }

  const sourceGraph = new Map<string, Set<string>>();
  for (const codeFile of codeFiles) {
    const relativeFile = normalizePath(path.relative(root, codeFile));
    const from = describeRepositoryPath(relativeFile);
    sourceGraph.set(relativeFile, new Set());

    const sourceText = await readFile(codeFile, "utf8");
    for (const specifier of collectImportSpecifiers(sourceText)) {
      const dependencyName = packageNameFromSpecifier(specifier);
      if (from.layer === "module" && isModuleUiPackage(dependencyName)) {
        violations.push({
          from: relativeFile,
          message: `Module source imports UI framework ${dependencyName}.`,
          rule: "modules-do-not-own-ui",
          to: specifier,
        });
      }

      let targetFile: string | undefined;
      let to: Location | undefined;
      if (specifier.startsWith(".")) {
        targetFile = await resolveSourceImport(codeFile, specifier);
        if (targetFile) {
          to = describeRepositoryPath(normalizePath(path.relative(root, targetFile)));
          if (await isFile(targetFile)) {
            sourceGraph.get(relativeFile)?.add(normalizePath(path.relative(root, targetFile)));
          }
        }
      } else {
        const targetPackage = workspacePackages.get(dependencyName);
        if (targetPackage) {
          to = targetPackage.location;
          if (!exportedSubpath(targetPackage.manifest, specifier, dependencyName)) {
            violations.push({
              from: relativeFile,
              message: `${specifier} is not a public package export.`,
              rule: "workspace-imports-use-public-exports",
              to: targetPackage.location.relativePath,
            });
          }
        }
      }

      if (to) {
        const rule = boundaryRule(from, to);
        if (rule) {
          violations.push({
            from: relativeFile,
            message: `${from.layer} code may not import ${to.layer} code directly.`,
            rule,
            to: to.relativePath,
          });
        }
      }
    }
  }

  for (const cycle of findCycles(sourceGraph)) {
    violations.push({
      from: cycle[0] ?? "unknown-source",
      message: `Source dependency cycle: ${cycle.join(" -> ")}`,
      rule: "no-circular-source-dependencies",
    });
  }

  return {
    filesChecked: codeFiles.length,
    packagesChecked: packageByDirectory.size,
    violations,
  };
}

async function main(): Promise<void> {
  const root = process.argv[2] ? path.resolve(process.argv[2]) : process.cwd();
  const result = await checkBoundaries(root);
  if (result.violations.length > 0) {
    console.error(`Boundary validation failed with ${result.violations.length} violation(s):`);
    for (const violation of result.violations) {
      const target = violation.to ? ` -> ${violation.to}` : "";
      console.error(`- [${violation.rule}] ${violation.from}${target}: ${violation.message}`);
    }
    process.exitCode = 1;
    return;
  }

  console.log(
    `Boundary validation passed (${result.packagesChecked} packages, ${result.filesChecked} source files).`,
  );
}

const entryPoint = process.argv[1];
if (entryPoint && import.meta.url === pathToFileURL(path.resolve(entryPoint)).href) {
  await main();
}