import * as os from 'os';
import * as path from 'path';

/**
 * Utility functions for encoding/decoding Claude Code project directory names.
 *
 * Directory naming pattern:
 * - Path: /Users/username/projectname
 * - Encoded: -Users-username-projectname
 *
 * IMPORTANT: This encoding is LOSSY for paths containing dashes.
 * For accurate path resolution, use extractCwd() from jsonl.ts to read
 * the actual cwd from session files.
 */

// =============================================================================
// Core Encoding/Decoding
// =============================================================================

/**
 * Encodes an absolute path into Claude Code's directory naming format.
 * Replaces all path separators (/ and \) with dashes.
 *
 * @param absolutePath - The absolute path to encode (e.g., "/Users/username/projectname")
 * @returns The encoded directory name (e.g., "-Users-username-projectname")
 */
export function encodePath(absolutePath: string): string {
  if (!absolutePath) {
    return '';
  }

  const encoded = absolutePath.replace(/[/\\]/g, '-');

  // Ensure leading dash for absolute paths
  return encoded.startsWith('-') ? encoded : `-${encoded}`;
}

/**
 * Decodes a project directory name to its original path.
 * Note: This is a best-effort decode. Paths with dashes cannot be decoded accurately.
 *
 * @param encodedName - The encoded directory name (e.g., "-Users-username-projectname")
 * @returns The decoded path (e.g., "/Users/username/projectname")
 */
export function decodePath(encodedName: string): string {
  if (!encodedName) {
    return '';
  }

  // Remove leading dash if present (indicates absolute path)
  const withoutLeadingDash = encodedName.startsWith('-') ? encodedName.slice(1) : encodedName;

  // Replace dashes with slashes
  const decodedPath = withoutLeadingDash.replace(/-/g, '/');

  // Windows paths may decode to "C:/..."
  if (/^[a-zA-Z]:\//.test(decodedPath)) {
    return decodedPath;
  }

  // Ensure leading slash for POSIX-style absolute paths
  return decodedPath.startsWith('/') ? decodedPath : `/${decodedPath}`;
}

/**
 * Extract the project name (last path segment) from an encoded directory name.
 *
 * @param encodedName - The encoded directory name
 * @returns The project name
 */
export function extractProjectName(encodedName: string): string {
  const decoded = decodePath(encodedName);
  const segments = decoded.split('/').filter(Boolean);
  return segments[segments.length - 1] || encodedName;
}

// =============================================================================
// Validation
// =============================================================================

/**
 * Validates if a directory name follows the Claude Code encoding pattern.
 *
 * @param encodedName - The directory name to validate
 * @returns true if valid, false otherwise
 */
export function isValidEncodedPath(encodedName: string): boolean {
  if (!encodedName) {
    return false;
  }

  // Must start with a dash (indicates absolute path)
  if (!encodedName.startsWith('-')) {
    return false;
  }

  // Allow only expected encoded characters:
  // - alphanumeric, underscores, dots, spaces, dashes
  // - optional ":" for Windows drive notation (e.g., -C:-Users-name-project)
  const validPattern = /^-[a-zA-Z0-9_.\s:-]+$/;
  if (!validPattern.test(encodedName)) {
    return false;
  }

  // Windows-style drive syntax is allowed only at the beginning after "-"
  // e.g. "-C:-Users-name-project". Reject stray ":" elsewhere.
  const firstColon = encodedName.indexOf(':');
  if (firstColon === -1) {
    return true;
  }

  if (!/^-[a-zA-Z]:/.test(encodedName)) {
    return false;
  }

  return !encodedName.includes(':', firstColon + 1);
}

/**
 * Validates a project ID that may be either a plain encoded path or
 * a composite subproject ID (`{encodedPath}::{8-char-hex}`).
 *
 * @param projectId - The project ID to validate
 * @returns true if valid
 */
export function isValidProjectId(projectId: string): boolean {
  if (!projectId) {
    return false;
  }

  const sep = projectId.indexOf('::');
  if (sep === -1) {
    // Plain encoded path
    return isValidEncodedPath(projectId);
  }

  // Composite ID: validate base part and hash suffix
  const basePart = projectId.slice(0, sep);
  const hashPart = projectId.slice(sep + 2);

  return isValidEncodedPath(basePart) && /^[a-f0-9]{8}$/.test(hashPart);
}

/**
 * Extract the base directory (encoded path) from a project ID.
 * For composite IDs (`{encoded}::{hash}`), returns the encoded part.
 * For plain IDs, returns the ID as-is.
 */
export function extractBaseDir(projectId: string): string {
  const sep = projectId.indexOf('::');
  if (sep !== -1) {
    return projectId.slice(0, sep);
  }
  return projectId;
}

// =============================================================================
// Session ID Extraction
// =============================================================================

/**
 * Extract session ID from a JSONL filename.
 *
 * @param filename - The filename (e.g., "abc123.jsonl")
 * @returns The session ID (e.g., "abc123")
 */
export function extractSessionId(filename: string): string {
  return filename.replace(/\.jsonl$/, '');
}

// =============================================================================
// Path Construction
// =============================================================================

/**
 * Construct the path to a session JSONL file.
 * Handles composite project IDs by extracting the base directory.
 */
export function buildSessionPath(basePath: string, projectId: string, sessionId: string): string {
  return path.join(basePath, extractBaseDir(projectId), `${sessionId}.jsonl`);
}

/**
 * Construct the path to a session's subagents directory.
 * Handles composite project IDs by extracting the base directory.
 */
export function buildSubagentsPath(basePath: string, projectId: string, sessionId: string): string {
  return path.join(basePath, extractBaseDir(projectId), sessionId, 'subagents');
}

/**
 * Construct the path to a task list file (stored in todos directory).
 */
export function buildTodoPath(claudeBasePath: string, sessionId: string): string {
  return path.join(claudeBasePath, 'todos', `${sessionId}.json`);
}

// =============================================================================
// Home Directory
// =============================================================================

/**
 * Get the user's home directory.
 */
function getHomeDir(): string {
  return process.env.HOME || process.env.USERPROFILE || os.homedir() || '/';
}

/**
 * Get the Claude config base path (~/.claude).
 */
function getClaudeBasePath(): string {
  return path.join(getHomeDir(), '.claude');
}

/**
 * Get the projects directory path (~/.claude/projects).
 */
export function getProjectsBasePath(): string {
  return path.join(getClaudeBasePath(), 'projects');
}

/**
 * Get the todos directory path (~/.claude/todos).
 */
export function getTodosBasePath(): string {
  return path.join(getClaudeBasePath(), 'todos');
}