import { randomUUID } from 'node:crypto';
import fsp from 'node:fs/promises';
import type { FileHandle } from 'node:fs/promises';
import os from 'node:os';
import path from 'node:path';
import {
  AGENT_KEY,
  CONFIG_FILE,
  type CopilotDocument,
  type CopilotSources,
  type JsonObject,
  type RenderedDocument,
  type RuntimeContract,
  createDocument,
  isObject,
  parseDocument,
} from './copilot-contract.js';

interface FileChange {
  readonly filePath: string;
  readonly label: string;
  readonly original?: string;
  readonly next?: string;
}

interface StagedChange {
  readonly change: FileChange;
  readonly tempPath?: string;
  readonly rollbackPath?: string;
  committed: boolean;
}

function errorMessage(error: unknown): string {
  return error instanceof Error ? error.message : String(error);
}

function asError(error: unknown): Error {
  return error instanceof Error ? error : new Error(String(error));
}

function hasErrorCode(error: unknown, code: string): boolean {
  return isObject(error) && error.code === code;
}

function paths(): { readonly user: string; readonly legacy: string } {
  const override = process.env.COPILOT_HOME?.trim();
  const copilotHome = override || path.join(os.homedir(), '.copilot');
  return {
    user: path.join(copilotHome, 'hooks', CONFIG_FILE),
    legacy: path.join(process.cwd(), '.github', 'hooks', 'hooks.json'),
  };
}

async function readOptional(filePath: string, label: string): Promise<string | undefined> {
  try {
    return await fsp.readFile(filePath, 'utf-8');
  } catch (error) {
    if (hasErrorCode(error, 'ENOENT')) return undefined;
    throw new Error(`Read ${label} at ${filePath}: ${errorMessage(error)}`, {
      cause: asError(error),
    });
  }
}

async function readDocument(filePath: string, label: string): Promise<CopilotDocument | undefined> {
  const raw = await readOptional(filePath, label);
  return raw === undefined ? undefined : parseDocument(filePath, raw, label);
}

export async function readSources(): Promise<CopilotSources> {
  const configPaths = paths();
  const [user, legacy] = await Promise.all([
    readDocument(configPaths.user, 'GitHub Copilot user hooks'),
    readDocument(configPaths.legacy, 'GitHub Copilot legacy project hooks'),
  ]);
  return {
    user: user ?? createDocument(configPaths.user),
    legacy,
  };
}

function changeFor(rendered: RenderedDocument): FileChange | undefined {
  if (!rendered.changed) return undefined;
  return {
    filePath: rendered.document.filePath,
    label: 'GitHub Copilot hook source',
    original: rendered.document.raw,
    next: rendered.next,
  };
}

async function unlinkOptional(filePath: string): Promise<void> {
  try {
    await fsp.unlink(filePath);
  } catch (error) {
    if (!hasErrorCode(error, 'ENOENT')) throw error;
  }
}

async function writeExclusive(filePath: string, contents: string, label: string): Promise<void> {
  let handle: FileHandle | undefined;
  try {
    handle = await fsp.open(filePath, 'wx', 0o600);
    await handle.writeFile(contents, 'utf-8');
    await handle.sync();
    await handle.close();
    handle = undefined;
  } catch (error) {
    const failures = [asError(error)];
    if (handle) {
      try {
        await handle.close();
      } catch (closeError) {
        failures.push(asError(closeError));
      }
    }
    try {
      await unlinkOptional(filePath);
    } catch (cleanupError) {
      failures.push(asError(cleanupError));
    }
    if (failures.length > 1) throw new AggregateError(failures, `Stage ${label}`);
    throw new Error(`Stage ${label}: ${errorMessage(error)}`, { cause: failures[0] });
  }
}

async function assertUnchanged(change: FileChange): Promise<void> {
  const current = await readOptional(change.filePath, change.label);
  if (current !== change.original) {
    throw new Error(`${change.label} changed during Copilot hook update: ${change.filePath}`);
  }
}

async function stage(change: FileChange): Promise<StagedChange> {
  await assertUnchanged(change);
  const directory = path.dirname(change.filePath);
  await fsp.mkdir(directory, { recursive: true, mode: 0o700 });
  const token = randomUUID();
  const tempPath = change.next === undefined
    ? undefined
    : path.join(directory, `.${path.basename(change.filePath)}.${token}.tmp`);
  const rollbackPath = change.original === undefined
    ? undefined
    : path.join(directory, `.${path.basename(change.filePath)}.${token}.rollback`);
  try {
    if (tempPath) await writeExclusive(tempPath, change.next!, change.label);
    if (rollbackPath && change.next !== undefined) {
      await writeExclusive(rollbackPath, change.original!, `${change.label} rollback`);
    }
  } catch (error) {
    const failures = [asError(error)];
    for (const stagedPath of [tempPath, rollbackPath]) {
      if (!stagedPath) continue;
      try {
        await unlinkOptional(stagedPath);
      } catch (cleanupError) {
        failures.push(asError(cleanupError));
      }
    }
    if (failures.length > 1) throw new AggregateError(failures, `Stage ${change.label}`);
    throw error;
  }
  return { change, tempPath, rollbackPath, committed: false };
}

async function commit(staged: StagedChange): Promise<void> {
  await assertUnchanged(staged.change);
  if (staged.change.next === undefined) {
    if (!staged.rollbackPath) throw new Error(`Missing rollback path for ${staged.change.label}`);
    await fsp.rename(staged.change.filePath, staged.rollbackPath);
  } else {
    if (!staged.tempPath) throw new Error(`Missing staged file for ${staged.change.label}`);
    await fsp.rename(staged.tempPath, staged.change.filePath);
  }
  staged.committed = true;
}

async function rollback(staged: StagedChange): Promise<void> {
  if (!staged.committed) return;
  if (staged.change.original === undefined) {
    await unlinkOptional(staged.change.filePath);
    return;
  }
  if (!staged.rollbackPath) throw new Error(`Missing rollback data for ${staged.change.label}`);
  await fsp.rename(staged.rollbackPath, staged.change.filePath);
}

async function cleanup(staged: StagedChange): Promise<void> {
  const files = [staged.tempPath, staged.rollbackPath].filter(
    (filePath): filePath is string => filePath !== undefined,
  );
  await Promise.all(files.map(unlinkOptional));
}

export async function writeDocuments(rendered: RenderedDocument[]): Promise<void> {
  const changes = rendered.flatMap((document) => {
    const change = changeFor(document);
    return change ? [change] : [];
  });
  const staged: StagedChange[] = [];
  try {
    for (const change of changes) staged.push(await stage(change));
    for (const item of staged) await commit(item);
  } catch (error) {
    const failures = [asError(error)];
    for (const item of [...staged].reverse()) {
      try {
        await rollback(item);
      } catch (rollbackError) {
        failures.push(asError(rollbackError));
      }
    }
    for (const item of staged) {
      try {
        await cleanup(item);
      } catch (cleanupError) {
        failures.push(asError(cleanupError));
      }
    }
    throw new AggregateError(failures, `Write GitHub Copilot hook sources: ${errorMessage(error)}`);
  }
  const cleanupErrors: Error[] = [];
  for (const item of staged) {
    try {
      await cleanup(item);
    } catch (error) {
      cleanupErrors.push(asError(error));
    }
  }
  if (cleanupErrors.length > 0) {
    throw new AggregateError(cleanupErrors, 'Clean GitHub Copilot hook transaction files');
  }
}

export async function regularFileExists(filePath: string, label: string): Promise<boolean> {
  try {
    return (await fsp.stat(filePath)).isFile();
  } catch (error) {
    if (hasErrorCode(error, 'ENOENT') || hasErrorCode(error, 'ENOTDIR')) return false;
    throw new Error(`Read ${label} at ${filePath}: ${errorMessage(error)}`, {
      cause: asError(error),
    });
  }
}

export async function requireRuntime(filePath: string, label: string): Promise<void> {
  if (!filePath) throw new Error(`${label} path is required`);
  if (!await regularFileExists(filePath, label)) throw new Error(`${label} is missing: ${filePath}`);
}

async function readRuntimeConfig(filePath: string): Promise<JsonObject | undefined> {
  const raw = await readOptional(filePath, 'Elydora runtime config');
  if (raw === undefined) return undefined;
  let value: unknown;
  try {
    value = JSON.parse(raw);
  } catch (error) {
    throw new Error(`Failed to parse Elydora runtime config at ${filePath}: ${errorMessage(error)}`, {
      cause: asError(error),
    });
  }
  if (!isObject(value)) throw new Error(`Elydora runtime config at ${filePath} must contain a JSON object`);
  return value;
}

export async function runtimeFilesExist(contracts: RuntimeContract[]): Promise<boolean> {
  for (const contract of contracts) {
    const runtimeConfig = await readRuntimeConfig(
      path.join(path.dirname(contract.guardPath), 'config.json'),
    );
    if (!runtimeConfig
      || runtimeConfig.agent_name !== AGENT_KEY
      || runtimeConfig.agent_id !== contract.agentId) continue;
    const files = await Promise.all([
      regularFileExists(contract.guardPath, 'Elydora guard runtime'),
      regularFileExists(contract.auditPath, 'Elydora audit runtime'),
    ]);
    if (files.every(Boolean)) return true;
  }
  return false;
}