#include "tokens.h"

#include <string>
#include <cctype>
#include <vector>
#include <iostream>
#include <sstream>
#include <optional>

static bool iswhitespace(char& character) {
    return character == ' '
        || character == '\t'
        || character == '\n'
        || character == '\r';
}

static std::optional<char> get_escaped(std::string_view inspected) {
    if (inspected == "n")
        return '\n';
    if (inspected == "r")
        return '\r';
    if (inspected == "t")
        return '\t';
    if (inspected == "\\")
        return '\\';
    if (inspected.size() <= 3) {
        for (char c : inspected) {
            std::cout << c << std::endl;
            if (!std::isdigit(c))
                return {};
            if (std::stoi(std::string{ c }) > 8)
                return {};
        }
        unsigned int x;
        std::stringstream ss;
        ss << std::oct << inspected;
        ss >> x;

        return static_cast<char>(x);
    }
    return {};
}

namespace token {
    std::string type_name(Type& type) {
        switch (type) {
        case token::Type::Ident:
            return "Ident";
        case token::Type::Symbol:
            return "Symbol";
        case token::Type::LiteralInt:
            return "LiteralInt";
        case token::Type::LiteralStr:
            return "LiteralStr";

        case token::Type::ReturnKeyword:
            return "Return";
        case token::Type::IfKeyword:
            return "If";
        case token::Type::ElseKeyword:
            return "Else";

        case token::Type::Whitespace:
            return "Whitespace";

        case token::Type::Eof:
            return "EOF";

        default:
            return "Unknown";
        }
    }

    std::string Token::formatted() {
        std::stringstream out{ "" };
        out << type_name(this->type);
        out << "(" << this->content << ")";
        out << " at line " << this->metadata.start.line + 1
            << " col " << this->metadata.start.col + 1;

        return out.str();
    }

    std::ostream& operator<<(std::ostream& stream, Token& token) {
        stream << token.formatted();
        return stream;
    }

    Metadata operator+(Metadata meta, Metadata other) {
        return Metadata{
            Position {
                std::min(meta.start.line, other.start.line),
                std::min(meta.start.col, other.start.col),
            },
            Position {
                std::max(meta.start.line, other.start.line),
                std::max(meta.start.col, other.start.col),
            },
            meta.filename };
    }

    Metadata operator+(Metadata& meta, int length) {
        return Metadata{
            meta.start,
            Position {meta.end.line, meta.end.col + length},
            meta.filename,
        };
    }

    TokenStream::TokenStream(std::vector<Token>& tokens)
        : m_tokens{ tokens }, m_position{ 0 } {
    };

    Token TokenStream::peek(int length) {
        int new_pos = m_position + length;
        if (new_pos < 0 || new_pos > static_cast<int>(m_tokens.size())) {
            return Token{ Type::Eof, {}, {} };
        }
        return m_tokens[new_pos];
    }

    Token TokenStream::peek() {
        return this->peek(0);
    }

    Token TokenStream::next() {
        token::Token got = this->peek(0);
        m_position++;
        while (m_position < static_cast<int>(m_tokens.size()) && this->peek().type == Type::Whitespace) {
            m_position++;
        }
        return got;
    }

    Token TokenStream::expect(Type type) {
        auto next = this->next();
        if (next.type == type) {
            return next;
        }
        throw std::runtime_error("Expected " + type_name(type) + ", got " + next.formatted());
    }

    Token TokenStream::expect(Type type, std::string_view content) {
        auto next = this->next();
        if (next.type == type && next.content == content) {
            return next;
        }
        throw std::runtime_error("Expected " + type_name(type) + "(" + std::string{ content } + "), got " + next.formatted());
    }

    Metadata TokenStream::metadata() {
        return this->peek(0).metadata;
    }

    std::vector<token::Token> tokenize(std::string_view text, std::string filename) {
        std::vector<token::Token> tokens{};

        uint32_t line = 0;
        uint32_t line_start = 0;

        int text_length = static_cast<int>(text.length());

        for (int i = 0; i < text_length;) {
            Position position{ line, i - line_start };
            Metadata meta{ position, position, filename };

            char c = text[i];

            if (std::isdigit(c)) {
                std::string content{};
                do {
                    content += c;
                    if ((i + 1) >= text_length) break;
                    c = text[++i];
                } while (std::isdigit(c));
                tokens.push_back(token::Token{ token::Type::LiteralInt, content, meta + content.size() });
            }
            else if (c == '\"') {
                std::string content{};
                c = text[++i]; // Skip initial "
                do {
                    if (c == '\\') {
                        std::string escaped_content{};
                        if ((i + 1) >= text_length) break;
                        auto potential = get_escaped(escaped_content + text[++i]);
                        while (potential.has_value() && (i + 1) < text_length) {
                            escaped_content += text[i];
                            potential = get_escaped(escaped_content + text[++i]);
                        }
                        if (escaped_content.size() > 0) {
                            auto escaped = get_escaped(escaped_content);
                            if (escaped.has_value())
                                content += *escaped;
                        }

                        c = text[i];
                    }
                    else {
                        content += c;
                        if ((i + 1) >= text_length) break;
                        c = text[++i];
                    }
                } while (c != '\"');
                i++; // Skip second "
                tokens.push_back(token::Token{ token::Type::LiteralStr, content, meta + (content.size() + 2) });
            }
            else if (std::isalpha(c) || c == '_') {
                std::string content{};
                do {
                    content += c;
                    if ((i + 1) >= text_length) break;
                    c = text[++i];
                } while (std::isalnum(c) || c == '_');

                token::Type type = token::Type::Ident;
                if (content == "return") {
                    type = token::Type::ReturnKeyword;
                }
                else if (content == "if") {
                    type = token::Type::IfKeyword;
                }
                else if (content == "else") {
                    type = token::Type::ElseKeyword;
                }
                tokens.push_back(token::Token{ type, content, meta + content.size() });
            }
            else if (iswhitespace(c)) {
                std::string content{};
                do {
                    if (c == '\n') {
                        line++;
                        line_start = i + 1;
                    }
                    content += c;
                    if ((i + 1) >= text_length) break;
                    c = text[++i];
                } while (iswhitespace(c));
                tokens.push_back(token::Token{ token::Type::Whitespace, content, meta + content.size() });
            }
            else {
                tokens.push_back(token::Token{ token::Type::Symbol, std::string{c}, meta });
                i++;
            }
        }

        Position position{ line, static_cast<uint32_t>(text.length()) - line_start };
        Metadata meta{ position, position, filename };

        tokens.push_back(token::Token{ token::Type::Eof, {}, meta });

        return tokens;
    }
}