#include "comdel_lexer.h"
#include "token.h"
#include "tokens_type.h"

#include <fstream>
#include <cctype>


/*************************************************************************
 *
 * Auxiliary functions - recognizing category of characters
 *
*************************************************************************/

inline bool identifierStart(char ch) {
    return isalpha(ch) || ch == '_';
}

inline bool identifierContinue(char ch) {
    return isalnum(ch) || ch == '_';
}

inline bool numberStart(char ch) {
    return isdigit(ch) || ch == '-';
}

inline bool isWhitespace(char ch) {
    return ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r';
}


/*************************************************************************
 *
 * ComdelLexer class public methods
 *
*************************************************************************/

ComdelLexer::ComdelLexer(std::string fileName, std::string source,
                         ParseContext *parseContext)
        : source(std::move(source)),
          parseContext(parseContext),
        // TODO Update this
          fileId(this->parseContext->addFile(fileName, this->source)),
          position(this->fileId, 1, 1, 0),
          ch(this->source[0]) {}


LexerResult ComdelLexer::tokenize() {
    while (!eof()) {
        tokenBegin = position;

        auto tokenType = nextTokenType();
        if (!tokenType) {
            errors.push_back(tokenType.error());
            continue;
        }
        if (tokenType == TokenType::WHITESPACE || tokenType == TokenType::COMMENT) {
            continue;
        }

        std::string text = source.substr(tokenBegin.offset,
                                         position.offset - tokenBegin.offset);

        tokenType = from_token(text, tokenType.value());

        tokens.emplace_back(*tokenType, Span(tokenBegin, position), text);
    }

    tokens.emplace_back(TokenType::END_OF_FILE, Span(position), "");

    return LexerResult{tokens, errors};
}


/*************************************************************************
 *
 * ComdelLexer class private methods
 *
*************************************************************************/


// Numbers are sequences of digits and underscores
// with AT LEAST ONE digit.

unsigned ComdelLexer::takeNumberInRadix(Radix radix) {
    unsigned digitsTaken = 0;

    while (true) {
        if (digitIsValid(ch, radix)) { // skip and count real digits
            bump();
            digitsTaken++;
        } else if (ch == '_') { // skip underscores
            bump();
        } else { // some other character => end of number
            return digitsTaken;
        }
    }
}


bool ComdelLexer::digitIsValid(char ch, Radix radix) {

    // Check valid digits
    // digit is 0..1
    if (ch == '1' || ch == '0') {
        // OK for all radixes
        return true;
    }
    //digit is 2..9
    if (isdigit(ch)) {
        // OK for decimal and hex radixes
        return (radix != Radix::BIN_NUMBER);
    }
        // digit is a..f A..F
    else if (isxdigit(ch)) {
        // OK only for hex radix
        return (radix == Radix::HEX_NUMBER);
    }
    // NOT 0..9 a..f A..F
    return false;
}


ComdelLexer::Radix ComdelLexer::takeRadix() {
    if (ch == '0') {
        char nextChar = peek();
        if (nextChar == 'x' || nextChar == 'X') {
            bump(2);
            return Radix::HEX_NUMBER;
        } else if (nextChar == 'b' || nextChar == 'B') {
            bump(2);
            return Radix::BIN_NUMBER;
        }
    }
    return Radix::DEC_NUMBER;
}


// color is sequence of hex-digits (preceded with # which is already consumed)
unsigned ComdelLexer::takeHexColor() {
    unsigned digitsTaken = 0;

    while (true) {
        if (digitIsValid(ch, Radix::HEX_NUMBER)) { // skip and count hex digits
            bump();
            digitsTaken++;
        } else { // some other character => end of number
            return digitsTaken;
        }
    }
}


PResult<TokenType> ComdelLexer::takeString() {
    Position lo = position;

    if (ch != '"')
        return PError({Span(lo), "expected string here"});
    bump(); // skip starting "

    // Check escape-sequences  \t  \n  \\  \"  but leave them in string.
    // They will be replaced in the constructor of StringLiteral AST-node.
    while (ch != '"' && ch != '\n' && !eof()) {
        if (ch == '"') {
            // possible start of escape-sequence
            char nextCh = peek();
            if (nextCh == '\\' || nextCh == '\"' || nextCh == 't' || nextCh == 'n')
                bump();   // legal escape-sequence: skip backslash
            else
                return PError({Span(lo, position), "illegal escape-sequence (allowed:  \\n  \\\"  \\\\  \\t"});
        }
        bump(); // skip normal char OR skip second char in escape-sequence
    }

    if (eof() || ch == '\n') {
        return PError({Span(lo, position), "unterminated string"});
    }
    bump(); // skip closing "
    return TokenType::STRING;
}


PResult<TokenType> ComdelLexer::takeRawString() {
    Position lo = position;

    if (ch != '`')
        return PError({Span(lo), "expected string here"});
    bump(); // skip starting '

    // Ignore escape-sequences - take all characters until closing '
    while (ch != '`' && !eof()) {
        bump(); // skip characters
    }

    if (eof() || ch == '\n') {
        return PError({Span(lo, position), "unterminated string"});
    }
    bump(); // skip closing '
    return TokenType::STRING;
}


void ComdelLexer::skipWhitespace() {
    while (!eof()) {
        if (isWhitespace(ch)) {
            bump();
        } else {
            break;
        }
    }
}


void ComdelLexer::skipComment() {
    while (!eof() && ch != '\n') {
        bump();
    }
}


// returns false if the comment is unterminated
bool ComdelLexer::skipMultilineComment() {
    while (!eof()) {
        if (ch == '*') {
            bump();
            if (ch == '/') {
                bump();
                return true;
            }
        }
        bump();
    }
    return false;
}


PResult<TokenType> ComdelLexer::nextTokenType() {
    if (isWhitespace(ch)) {
        skipWhitespace();
        return TokenType::WHITESPACE;
    } else if (identifierStart(ch)) {
        bump();
        while (identifierContinue(ch))
            bump();
        return TokenType::IDENTIFIER;
    } else if (numberStart(ch)) {
        if (ch == '-') {
            bump();
        }
        unsigned takenDigits;
        Radix radix = takeRadix();
        takenDigits = takeNumberInRadix(radix);
        if (takenDigits == 0) {
            return PError({Span(tokenBegin, position),
                           "no digits found for number, or misspelled number"});
        }
        if (isalnum(ch)) {
            return PError({Span(tokenBegin, position),
                           "illegal digit or letter found at the end of number"});
        }
        return TokenType::NUMBER;
    } else if (ch == '!') {
        bump();
        return TokenType::NOT;
    } else if (ch == '<') {
        bump();
        return TokenType::LT;
    } else if (ch == '>') {
        bump();
        return TokenType::GT;
    } else if (ch == '#') {
        bump();

        if (digitIsValid(ch, Radix::HEX_NUMBER)) {
            unsigned takenDigits = takeHexColor();
            if (takenDigits != 6 && takenDigits != 8) {
                return PError({Span(tokenBegin, position),
                               "hex-color must have 6 or 8 hex-digits"});
            }
            if (isalnum(ch)) {
                return PError({Span(tokenBegin, position),
                               "illegal letter found at the end of hex-color"});
            }
            return TokenType::COLOR;
        } else {
            return PError({Span(tokenBegin, position),
                           "unexpected #"});
        }
    } else if (ch == '@') {
        bump();
        while (identifierContinue(ch))
            bump();
        return TokenType::KEYWORD;
    } else if (ch == '"') {
        return takeString();
    } else if (ch == '`') {
        return takeRawString();
    } else if (ch == '(') {
        bump();
        return TokenType::LPAREN;
    } else if (ch == ')') {
        bump();
        return TokenType::RPAREN;
    } else if (ch == '[') {
        bump();
        return TokenType::LBRACKET;
    } else if (ch == ']') {
        bump();
        return TokenType::RBRACKET;
    } else if (ch == '{') {
        bump();
        return TokenType::LBRACE;
    } else if (ch == '}') {
        bump();
        return TokenType::RBRACE;
    } else if (ch == '/') {
        bump();
        if (ch == '/') {
            bump();
            skipComment();
            return TokenType::COMMENT;
        } else if (ch == '*') {
            bump();
            if (!skipMultilineComment()) {
                return PError({Span(tokenBegin, position),
                               "unterminated multiline comment"});
            }
            return TokenType::COMMENT;
        }
        return PError({Span(tokenBegin, position),
                       "unexpected /"});
    } else if (ch == '.') {
        bump();
        return TokenType::DOT;
    } else if (ch == ':') {
        bump();
        return TokenType::COLON;
    } else if (ch == ';') {
        bump();
        return TokenType::SEMICOLON;
    } else if (ch == ',') {
        bump();
        return TokenType::COMMA;
    } else if (ch == '=') {
        bump();
        return TokenType::EQUALS;
    } else {
        std::stringstream message;
        message << "unexpected character `" << ch << "`";
        bump();
        return PError({Span(tokenBegin, position), message.str()});
    }
}


// Move position to the new character in input file.
// Fetch the new character in 'ch'
void ComdelLexer::bump(unsigned count) {
    for (unsigned i = 0; i < count && !eof(); i++) {
        if (ch == '\n') {
            position.line += 1;
            position.col = 1;
            parseContext->getFile(fileId).addLineOffset(position.offset + 1);
        } else {
            position.col += 1;
        }
        position.offset += 1;
        ch = source[position.offset];
    }
}


// Fetch and return next character without moving position.
// Fetch does not cross line boundary.
// Returns \n when next char does not exist (end of line or end of file)
char ComdelLexer::peek() {
    if (position.offset + 1 == source.size()) // eof
        return '\n';

    return source[position.offset + 1];
}


bool ComdelLexer::eof() {
    return position.offset == source.size();
}