/**
 * @fileoverview OrdoJS Lexer - Refactored modular implementation
 * @author OrdoJS Framework Team
 */

import {
    LexicalContext,
    LexicalError,
    TokenType,
    type SourcePosition,
    type Token,
    type TokenStream
} from '../types/index.js';

/**
 * Lexer configuration options
 */
export interface LexerOptions {
  /** Enable source map generation */
  generateSourceMaps?: boolean;
  /** Enable error recovery mode */
  enableRecovery?: boolean;
  /** Maximum number of errors before stopping */
  maxErrors?: number;
  /** Enable context-aware tokenization */
  contextAware?: boolean;
  /** Custom token processors */
  tokenProcessors?: TokenProcessor[];
}

/**
 * Token processor interface for plugin-based token processing
 */
export interface TokenProcessor {
  /** Processor name */
  name: string;
  /** Token types this processor handles */
  handles: TokenType[];
  /** Process token and return modified token or null to skip */
  process(token: Token, context: LexicalContext): Token | null;
}

/**
 * Lexer state for error recovery and debugging
 */
export interface LexerState {
  source: string;
  current: number;
  line: number;
  column: number;
  filename: string;
  contextStack: LexicalContext[];
  errors: LexicalError[];
}

/**
 * Character classification utilities
 */
class CharacterUtils {
  static isDigit(char: string): boolean {
    return char >= '0' && char <= '9';
  }

  static isAlpha(char: string): boolean {
    return (char >= 'a' && char <= 'z') ||
           (char >= 'A' && char <= 'Z') ||
           char === '_' || char === '$';
  }

  static isAlphaNumeric(char: string): boolean {
    return this.isAlpha(char) || this.isDigit(char);
  }

  static isWhitespace(char: string): boolean {
    return char === ' ' || char === '\t' || char === '\r';
  }

  static isNewline(char: string): boolean {
    return char === '\n';
  }

  static isQuote(char: string): boolean {
    return char === '"' || char === "'" || char === '`';
  }

  static isHexDigit(char: string): boolean {
    return this.isDigit(char) ||
           (char >= 'a' && char <= 'f') ||
           (char >= 'A' && char <= 'F');
  }
}

/**
 * Keyword registry for efficient keyword lookup
 */
class KeywordRegistry {
  private static readonly keywords = new Map<string, TokenType>([
    ['component', TokenType.COMPONENT],
    ['client', TokenType.CLIENT],
    ['server', TokenType.SERVER],
    ['markup', TokenType.MARKUP],
    ['let', TokenType.LET],
    ['const', TokenType.CONST],
    ['if', TokenType.IF],
    ['else', TokenType.ELSE],
    ['each', TokenType.EACH],
    ['public', TokenType.PUBLIC],
    ['bind', TokenType.BIND],
    ['true', TokenType.BOOLEAN],
    ['false', TokenType.BOOLEAN],
    ['null', TokenType.IDENTIFIER], // null is treated as identifier for now
    ['undefined', TokenType.IDENTIFIER],
    ['function', TokenType.IDENTIFIER],
    ['return', TokenType.IDENTIFIER],
    ['for', TokenType.IDENTIFIER],
    ['while', TokenType.IDENTIFIER],
    ['break', TokenType.IDENTIFIER],
    ['continue', TokenType.IDENTIFIER],
    ['try', TokenType.IDENTIFIER],
    ['catch', TokenType.IDENTIFIER],
    ['finally', TokenType.IDENTIFIER],
    ['throw', TokenType.IDENTIFIER],
    ['async', TokenType.IDENTIFIER],
    ['await', TokenType.IDENTIFIER],
    ['import', TokenType.IDENTIFIER],
    ['export', TokenType.IDENTIFIER],
    ['default', TokenType.IDENTIFIER],
    ['class', TokenType.IDENTIFIER],
    ['extends', TokenType.IDENTIFIER],
    ['interface', TokenType.IDENTIFIER],
    ['type', TokenType.IDENTIFIER],
    ['enum', TokenType.IDENTIFIER],
    ['namespace', TokenType.IDENTIFIER]
  ]);

  static getTokenType(identifier: string): TokenType {
    return this.keywords.get(identifier) || TokenType.IDENTIFIER;
  }

  static isKeyword(identifier: string): boolean {
    return this.keywords.has(identifier);
  }

  static getAllKeywords(): string[] {
    return Array.from(this.keywords.keys());
  }
}

/**
 * Context manager for tracking lexical contexts
 */
class ContextManager {
  private contextStack: LexicalContext[] = [LexicalContext.COMPONENT];

  getCurrentContext(): LexicalContext {
    return this.contextStack[this.contextStack.length - 1] || LexicalContext.COMPONENT;
  }

  pushContext(context: LexicalContext): void {
    this.contextStack.push(context);
  }

  popContext(): LexicalContext | undefined {
    if (this.contextStack.length > 1) {
      return this.contextStack.pop();
    }
    return undefined;
  }

  updateContext(char: string, previousTokens: Token[]): void {
    if (char === '{') {
      const lastToken = previousTokens[previousTokens.length - 1];
      if (lastToken?.value === 'client') {
        this.pushContext(LexicalContext.CLIENT_BLOCK);
      } else if (lastToken?.value === 'server') {
        this.pushContext(LexicalContext.SERVER_BLOCK);
      } else if (lastToken?.value === 'markup') {
        this.pushContext(LexicalContext.MARKUP_BLOCK);
      } else {
        this.pushContext(LexicalContext.JAVASCRIPT);
      }
    } else if (char === '}') {
      this.popContext();
    }
  }

  getContextStack(): LexicalContext[] {
    return [...this.contextStack];
  }

  reset(): void {
    this.contextStack = [LexicalContext.COMPONENT];
  }
}

/**
 * Enhanced OrdoJS Lexer with modular architecture
 */
export class OrdoJSLexer {
  private state: LexerState;
  private options: Required<LexerOptions>;
  private contextManager: ContextManager;
  private tokens: Token[] = [];

  constructor(options: LexerOptions = {}) {
    this.options = {
      generateSourceMaps: true,
      enableRecovery: false,
      maxErrors: 10,
      contextAware: true,
      tokenProcessors: [],
      ...options
    };

    this.contextManager = new ContextManager();
    this.state = this.createInitialState();
  }

  /**
   * Tokenize source code into token stream
   */
  tokenize(source: string, filename: string = 'unknown'): TokenStream {
    this.initializeState(source, filename);

    try {
      while (!this.isAtEnd()) {
        this.scanToken();
      }

      this.addToken(TokenType.EOF, '');

      // Process tokens through registered processors
      this.processTokens();

      return this.createTokenStream();
    } catch (error) {
      if (this.options.enableRecovery && error instanceof LexicalError) {
        this.state.errors.push(error);
        return this.createTokenStream();
      }
      throw error;
    }
  }

  /**
   * Get lexer state for debugging
   */
  getState(): Readonly<LexerState> {
    return { ...this.state };
  }

  /**
   * Get all errors encountered during tokenization
   */
  getErrors(): LexicalError[] {
    return [...this.state.errors];
  }

  /**
   * Add custom token processor
   */
  addTokenProcessor(processor: TokenProcessor): void {
    this.options.tokenProcessors.push(processor);
  }

  /**
   * Remove token processor by name
   */
  removeTokenProcessor(name: string): boolean {
    const index = this.options.tokenProcessors.findIndex(p => p.name === name);
    if (index >= 0) {
      this.options.tokenProcessors.splice(index, 1);
      return true;
    }
    return false;
  }

  private createInitialState(): LexerState {
    return {
      source: '',
      current: 0,
      line: 1,
      column: 1,
      filename: 'unknown',
      contextStack: [LexicalContext.COMPONENT],
      errors: []
    };
  }

  private initializeState(source: string, filename: string): void {
    this.state = {
      ...this.createInitialState(),
      source,
      filename
    };
    this.contextManager.reset();
    this.tokens = [];
  }

  private scanToken(): void {
    const char = this.advance();

    // Skip whitespace but track position
    if (CharacterUtils.isWhitespace(char)) {
      return;
    }

    // Handle newlines
    if (CharacterUtils.isNewline(char)) {
      this.state.line++;
      this.state.column = 1;
      return;
    }

    // Single character tokens
    const singleCharTokens: Record<string, TokenType> = {
      '(': TokenType.LEFT_PAREN,
      ')': TokenType.RIGHT_PAREN,
      '[': TokenType.LEFT_BRACKET,
      ']': TokenType.RIGHT_BRACKET,
      ',': TokenType.COMMA,
      '.': TokenType.DOT,
      ';': TokenType.SEMICOLON,
      ':': TokenType.COLON,
      '?': TokenType.QUESTION
    };

    if (singleCharTokens[char]) {
      this.addToken(singleCharTokens[char], char);
      return;
    }

    // Context-sensitive tokens
    if (char === '{' || char === '}') {
      this.handleBrace(char);
      return;
    }

    // Multi-character operators
    if (this.handleOperators(char)) {
      return;
    }

    // Comments
    if (char === '/' && this.handleComments()) {
      return;
    }

    // Strings
    if (CharacterUtils.isQuote(char)) {
      this.scanString(char);
      return;
    }

    // Numbers
    if (CharacterUtils.isDigit(char)) {
      this.scanNumber();
      return;
    }

    // Identifiers and keywords
    if (CharacterUtils.isAlpha(char)) {
      this.scanIdentifier();
      return;
    }

    // HTML tags (context-sensitive)
    if (char === '<' && this.contextManager.getCurrentContext() === LexicalContext.MARKUP_BLOCK) {
      this.scanHTMLTag();
      return;
    }

    // Handle unexpected characters
    this.handleUnexpectedCharacter(char);
  }

  private handleBrace(char: string): void {
    const tokenType = char === '{' ? TokenType.LEFT_BRACE : TokenType.RIGHT_BRACE;
    this.addToken(tokenType, char);

    if (this.options.contextAware) {
      this.contextManager.updateContext(char, this.tokens);
    }
  }

  private handleOperators(char: string): boolean {
    const operators: Record<string, { single: TokenType; double?: TokenType; doubleChar?: string }> = {
      '+': { single: TokenType.PLUS, double: TokenType.INCREMENT, doubleChar: '+' },
      '-': { single: TokenType.MINUS, double: TokenType.DECREMENT, doubleChar: '-' },
      '*': { single: TokenType.MULTIPLY },
      '%': { single: TokenType.MODULO },
      '=': { single: TokenType.ASSIGN, double: TokenType.EQUALS, doubleChar: '=' },
      '!': { single: TokenType.LOGICAL_NOT, double: TokenType.NOT_EQUALS, doubleChar: '=' },
      '<': { single: TokenType.LESS_THAN, double: TokenType.LESS_EQUAL, doubleChar: '=' },
      '>': { single: TokenType.GREATER_THAN, double: TokenType.GREATER_EQUAL, doubleChar: '=' },
      '&': { single: TokenType.LOGICAL_AND, double: TokenType.LOGICAL_AND, doubleChar: '&' },
      '|': { single: TokenType.LOGICAL_OR, double: TokenType.LOGICAL_OR, doubleChar: '|' }
    };

    const op = operators[char];
    if (!op) return false;

    if (op.double && op.doubleChar && this.match(op.doubleChar)) {
      this.addToken(op.double, char + op.doubleChar);
    } else if (char === '&' || char === '|') {
      // These require double characters
      if (!this.match(char)) {
        this.throwError(`Unexpected character: ${char}. Did you mean '${char}${char}'?`);
      }
      this.addToken(op.single, char + char);
    } else {
      this.addToken(op.single, char);
    }

    return true;
  }

  private handleComments(): boolean {
    if (this.match('/')) {
      // Single-line comment
      this.scanSingleLineComment();
      return true;
    } else if (this.match('*')) {
      // Multi-line comment
      this.scanMultiLineComment();
      return true;
    } else {
      // Division operator
      this.addToken(TokenType.DIVIDE, '/');
      return true;
    }
  }

  private scanSingleLineComment(): void {
    while (this.peek() !== '\n' && !this.isAtEnd()) {
      this.advance();
    }
  }

  private scanMultiLineComment(): void {
    const startLine = this.state.line;

    while (!this.isAtEnd()) {
      if (this.peek() === '*' && this.peekNext() === '/') {
        this.advance(); // consume '*'
        this.advance(); // consume '/'
        return;
      }

      if (this.peek() === '\n') {
        this.state.line++;
        this.state.column = 1;
      }

      this.advance();
    }

    this.throwError(`Unterminated comment starting at line ${startLine}`);
  }

  private scanString(quote: string): void {
    const startPosition = this.getPosition();
    let value = '';
    let isTemplate = quote === '`';

    while (this.peek() !== quote && !this.isAtEnd()) {
      if (this.peek() === '\n') {
        if (quote !== '`') {
          this.throwError('Unterminated string literal');
        }
        this.state.line++;
        this.state.column = 1;
      }

      if (this.peek() === '\\') {
        this.advance(); // consume backslash
        value += this.scanEscapeSequence();
      } else {
        value += this.advance();
      }
    }

    if (this.isAtEnd()) {
      this.throwError(`Unterminated ${isTemplate ? 'template' : 'string'} literal`);
    }

    // Consume closing quote
    this.advance();

    this.addToken(TokenType.STRING, value, startPosition);
  }

  private scanEscapeSequence(): string {
    const char = this.advance();

    switch (char) {
      case 'n': return '\n';
      case 't': return '\t';
      case 'r': return '\r';
      case 'b': return '\b';
      case 'f': return '\f';
      case 'v': return '\v';
      case '0': return '\0';
      case '\\': return '\\';
      case '"': return '"';
      case "'": return "'";
      case '`': return '`';
      case 'x': return this.scanHexEscape();
      case 'u': return this.scanUnicodeEscape();
      default:
        this.throwError(`Invalid escape sequence: \\${char}`);
        return char;
    }
  }

  private scanHexEscape(): string {
    let hex = '';
    for (let i = 0; i < 2; i++) {
      if (!CharacterUtils.isHexDigit(this.peek())) {
        this.throwError('Invalid hex escape sequence');
      }
      hex += this.advance();
    }
    return String.fromCharCode(parseInt(hex, 16));
  }

  private scanUnicodeEscape(): string {
    if (this.peek() === '{') {
      // Unicode code point escape: \u{...}
      this.advance(); // consume '{'
      let hex = '';
      while (this.peek() !== '}' && !this.isAtEnd()) {
        if (!CharacterUtils.isHexDigit(this.peek())) {
          this.throwError('Invalid unicode escape sequence');
        }
        hex += this.advance();
      }
      if (this.peek() !== '}') {
        this.throwError('Unterminated unicode escape sequence');
      }
      this.advance(); // consume '}'
      return String.fromCodePoint(parseInt(hex, 16));
    } else {
      // Fixed-length unicode escape: \uXXXX
      let hex = '';
      for (let i = 0; i < 4; i++) {
        if (!CharacterUtils.isHexDigit(this.peek())) {
          this.throwError('Invalid unicode escape sequence');
        }
        hex += this.advance();
      }
      return String.fromCharCode(parseInt(hex, 16));
    }
  }

  private scanNumber(): void {
    const startPosition = this.getPosition();

    // Handle different number formats
    if (this.state.source.charAt(this.state.current - 1) === '0') {
      if (this.match('x') || this.match('X')) {
        this.scanHexNumber(startPosition);
        return;
      } else if (this.match('b') || this.match('B')) {
        this.scanBinaryNumber(startPosition);
        return;
      } else if (this.match('o') || this.match('O')) {
        this.scanOctalNumber(startPosition);
        return;
      }
    }

    this.scanDecimalNumber(startPosition);
  }

  private scanDecimalNumber(startPosition: SourcePosition): void {
    // Consume integer part
    while (CharacterUtils.isDigit(this.peek())) {
      this.advance();
    }

    // Look for decimal point
    if (this.peek() === '.' && CharacterUtils.isDigit(this.peekNext())) {
      this.advance(); // consume '.'
      while (CharacterUtils.isDigit(this.peek())) {
        this.advance();
      }
    }

    // Look for exponent
    if (this.peek() === 'e' || this.peek() === 'E') {
      this.advance();
      if (this.peek() === '+' || this.peek() === '-') {
        this.advance();
      }
      if (!CharacterUtils.isDigit(this.peek())) {
        this.throwError('Invalid number format: missing exponent digits');
      }
      while (CharacterUtils.isDigit(this.peek())) {
        this.advance();
      }
    }

    const value = this.state.source.substring(startPosition.offset, this.state.current);
    this.addToken(TokenType.NUMBER, value, startPosition);
  }

  private scanHexNumber(startPosition: SourcePosition): void {
    if (!CharacterUtils.isHexDigit(this.peek())) {
      this.throwError('Invalid hex number: missing digits');
    }

    while (CharacterUtils.isHexDigit(this.peek())) {
      this.advance();
    }

    const value = this.state.source.substring(startPosition.offset, this.state.current);
    this.addToken(TokenType.NUMBER, value, startPosition);
  }

  private scanBinaryNumber(startPosition: SourcePosition): void {
    if (this.peek() !== '0' && this.peek() !== '1') {
      this.throwError('Invalid binary number: missing digits');
    }

    while (this.peek() === '0' || this.peek() === '1') {
      this.advance();
    }

    const value = this.state.source.substring(startPosition.offset, this.state.current);
    this.addToken(TokenType.NUMBER, value, startPosition);
  }

  private scanOctalNumber(startPosition: SourcePosition): void {
    if (this.peek() < '0' || this.peek() > '7') {
      this.throwError('Invalid octal number: missing digits');
    }

    while (this.peek() >= '0' && this.peek() <= '7') {
      this.advance();
    }

    const value = this.state.source.substring(startPosition.offset, this.state.current);
    this.addToken(TokenType.NUMBER, value, startPosition);
  }

  private scanIdentifier(): void {
    const startPosition = this.getPosition();

    while (CharacterUtils.isAlphaNumeric(this.peek())) {
      this.advance();
    }

    const value = this.state.source.substring(startPosition.offset, this.state.current);
    const tokenType = KeywordRegistry.getTokenType(value);

    this.addToken(tokenType, value, startPosition);
  }

  private scanHTMLTag(): void {
    const startPosition = this.getPosition();

    if (this.match('/')) {
      this.addToken(TokenType.HTML_TAG_CLOSE, '</', startPosition);
    } else {
      this.addToken(TokenType.HTML_TAG_OPEN, '<', startPosition);
    }
  }

  private handleUnexpectedCharacter(char: string): void {
    this.throwError(`Unexpected character: '${char}' (${char.charCodeAt(0)})`);
  }

  private processTokens(): void {
    if (this.options.tokenProcessors.length === 0) return;

    const processedTokens: Token[] = [];
    const currentContext = this.contextManager.getCurrentContext();

    for (const token of this.tokens) {
      let processedToken: Token | null = token;

      for (const processor of this.options.tokenProcessors) {
        if (processor.handles.includes(token.type)) {
          processedToken = processor.process(processedToken, currentContext);
          if (!processedToken) break;
        }
      }

      if (processedToken) {
        processedTokens.push(processedToken);
      }
    }

    this.tokens = processedTokens;
  }

  private createTokenStream(): TokenStream {
    let currentIndex = 0;
    const eofToken = this.tokens[this.tokens.length - 1] || this.createEOFToken();

    return {
      tokens: this.tokens,
      current: 0,
      peek: () => {
        if (currentIndex >= this.tokens.length) return eofToken;
        return this.tokens[currentIndex];
      },
      advance: () => {
        if (currentIndex >= this.tokens.length) return eofToken;
        const token = this.tokens[currentIndex];
        if (currentIndex < this.tokens.length - 1) {
          currentIndex++;
        }
        return token;
      },
      isAtEnd: () => currentIndex >= this.tokens.length - 1,
      previous: () => {
        const prevIndex = Math.max(0, currentIndex - 1);
        return this.tokens[prevIndex] || eofToken;
      }
    };
  }

  private createEOFToken(): Token {
    return {
      type: TokenType.EOF,
      value: '',
      position: this.getPosition(),
      range: {
        start: this.getPosition(),
        end: this.getPosition()
      }
    };
  }

  // Utility methods
  private match(expected: string): boolean {
    if (this.isAtEnd()) return false;
    if (this.state.source.charAt(this.state.current) !== expected) return false;
    this.state.current++;
    this.state.column++;
    return true;
  }

  private advance(): string {
    if (this.isAtEnd()) return '\0';
    const char = this.state.source.charAt(this.state.current);
    this.state.current++;
    this.state.column++;
    return char;
  }

  private peek(): string {
    if (this.isAtEnd()) return '\0';
    return this.state.source.charAt(this.state.current);
  }

  private peekNext(): string {
    if (this.state.current + 1 >= this.state.source.length) return '\0';
    return this.state.source.charAt(this.state.current + 1);
  }

  private isAtEnd(): boolean {
    return this.state.current >= this.state.source.length;
  }

  private addToken(type: TokenType, value: string, startPosition?: SourcePosition): void {
    const start = startPosition || this.getPosition();
    const end = this.getPosition();

    const token: Token = {
      type,
      value,
      position: start,
      range: { start, end }
    };

    this.tokens.push(token);
  }

  private getPosition(): SourcePosition {
    return {
      line: this.state.line,
      column: this.state.column,
      offset: this.state.current
    };
  }

  private throwError(message: string): never {
    const error = new LexicalError(
      message,
      this.getPosition(),
      this.peek(),
      this.state.filename
    );

    if (this.options.enableRecovery && this.state.errors.length < this.options.maxErrors) {
      this.state.errors.push(error);
      // Skip the problematic character and continue
      this.advance();
      throw error; // Still throw for proper error handling
    }

    throw error;
  }
}

/**
 * Default token processors
 */
export const defaultTokenProcessors: TokenProcessor[] = [
  {
    name: 'context-validator',
    handles: [TokenType.CLIENT, TokenType.SERVER, TokenType.MARKUP],
    process: (token: Token, context: LexicalContext): Token | null => {
      // Validate that block keywords are used in appropriate contexts
      if (context !== LexicalContext.COMPONENT &&
          [TokenType.CLIENT, TokenType.SERVER, TokenType.MARKUP].includes(token.type)) {
        // Could emit warning here
      }
      return token;
    }
  },
  {
    name: 'identifier-enhancer',
    handles: [TokenType.IDENTIFIER],
    process: (token: Token, context: LexicalContext): Token | null => {
      // Could enhance identifiers with additional metadata
      return token;
    }
  }
];