import { Token } from "./ast";
import { Source } from "./source";
import { syntaxError } from "../error";

/**
 * Given a Source object, this returns a Lexer for that source.
 * A Lexer is a stateful stream generator in that every time
 * it is advanced, it returns the next token in the Source. Assuming the
 * source lexes, the final Token emitted by the lexer will be of kind
 * EOF, after which the lexer will repeatedly return the same EOF token
 * whenever called.
 */
export function createLexer<TOptions>(source: Source, options: TOptions): Lexer<TOptions>;

/**
 * The return type of createLexer.
 */
export interface Lexer<TOptions> {
    source: Source;
    options: TOptions;

    /**
     * The previously focused non-ignored token.
     */
    lastToken: Token;

    /**
     * The currently focused non-ignored token.
     */
    token: Token;

    /**
     * The (1-indexed) line containing the current token.
     */
    line: number;

    /**
     * The character offset at which the current line begins.
     */
    lineStart: number;

    /**
     * Advances the token stream to the next non-ignored token.
     */
    advance(): Token;

    /**
     * Looks ahead and returns the next non-ignored token, but does not change
     * the Lexer's state.
     */
    lookahead(): Token;
}

/**
 * An exported enum describing the different kinds of tokens that the
 * lexer emits.
 */
export const TokenKind: _TokenKind;

// @internal
type _TokenKind = {
    SOF: "<SOF>";
    EOF: "<EOF>";
    BANG: "!";
    DOLLAR: "$";
    AMP: "&";
    PAREN_L: "(";
    PAREN_R: ")";
    SPREAD: "...";
    COLON: ":";
    EQUALS: "=";
    AT: "@";
    BRACKET_L: "[";
    BRACKET_R: "]";
    BRACE_L: "{";
    PIPE: "|";
    BRACE_R: "}";
    NAME: "Name";
    INT: "Int";
    FLOAT: "Float";
    STRING: "String";
    BLOCK_STRING: "BlockString";
    COMMENT: "Comment";
};

/**
 * The enum type representing the token kinds values.
 */
export type TokenKindEnum = _TokenKind[keyof _TokenKind];

/**
 * A helper function to describe a token as a string for debugging
 */
export function getTokenDesc(token: Token): string;