/*
 * Copyright (c) 2020, Emanuel Sprung <emanuel.sprung@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include "RegexMatcher.h"
#include "RegexDebug.h"
#include "RegexParser.h"
#include <AK/Debug.h>
#include <AK/ScopedValueRollback.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>

namespace regex {

#if REGEX_DEBUG
static RegexDebug s_regex_dbg(stderr);
#endif

template<class Parser>
Regex<Parser>::Regex(StringView pattern, typename ParserTraits<Parser>::OptionsType regex_options)
{
    pattern_value = pattern.to_string();
    regex::Lexer lexer(pattern);

    Parser parser(lexer, regex_options);
    parser_result = parser.parse();

    if (parser_result.error == regex::Error::NoError)
        matcher = make<Matcher<Parser>>(*this, regex_options);
}

template<class Parser>
typename ParserTraits<Parser>::OptionsType Regex<Parser>::options() const
{
    if (parser_result.error != Error::NoError)
        return {};

    return matcher->options();
}

template<class Parser>
String Regex<Parser>::error_string(Optional<String> message) const
{
    StringBuilder eb;
    eb.append("Error during parsing of regular expression:\n");
    eb.appendff("    {}\n    ", pattern_value);
    for (size_t i = 0; i < parser_result.error_token.position(); ++i)
        eb.append(' ');

    eb.appendff("^---- {}", message.value_or(get_error_string(parser_result.error)));
    return eb.build();
}

template<typename Parser>
RegexResult Matcher<Parser>::match(const RegexStringView& view, Optional<typename ParserTraits<Parser>::OptionsType> regex_options) const
{
    AllOptions options = m_regex_options | regex_options.value_or({}).value();

    if (options.has_flag_set(AllFlags::Multiline))
        return match(view.lines(), regex_options); // FIXME: how do we know, which line ending a line has (1char or 2char)? This is needed to get the correct match offsets from start of string...

    Vector<RegexStringView> views;
    views.append(view);
    return match(views, regex_options);
}

template<typename Parser>
RegexResult Matcher<Parser>::match(const Vector<RegexStringView> views, Optional<typename ParserTraits<Parser>::OptionsType> regex_options) const
{
    // If the pattern *itself* isn't stateful, reset any changes to start_offset.
    if (!((AllFlags)m_regex_options.value() & AllFlags::Internal_Stateful))
        m_pattern.start_offset = 0;

    size_t match_count { 0 };

    MatchInput input;
    MatchState state;
    MatchOutput output;

    input.regex_options = m_regex_options | regex_options.value_or({}).value();
    input.start_offset = m_pattern.start_offset;
    output.operations = 0;
    size_t lines_to_skip = 0;

    if (input.regex_options.has_flag_set(AllFlags::Internal_Stateful)) {
        if (views.size() > 1 && input.start_offset > views.first().length()) {
            dbgln_if(REGEX_DEBUG, "Started with start={}, goff={}, skip={}", input.start_offset, input.global_offset, lines_to_skip);
            for (auto& view : views) {
                if (input.start_offset < view.length() + 1)
                    break;
                ++lines_to_skip;
                input.start_offset -= view.length() + 1;
                input.global_offset += view.length() + 1;
            }
            dbgln_if(REGEX_DEBUG, "Ended with start={}, goff={}, skip={}", input.start_offset, input.global_offset, lines_to_skip);
        }
    }

    if (c_match_preallocation_count) {
        output.matches.ensure_capacity(c_match_preallocation_count);
        output.capture_group_matches.ensure_capacity(c_match_preallocation_count);
        output.named_capture_group_matches.ensure_capacity(c_match_preallocation_count);

        auto& capture_groups_count = m_pattern.parser_result.capture_groups_count;
        auto& named_capture_groups_count = m_pattern.parser_result.named_capture_groups_count;

        for (size_t j = 0; j < c_match_preallocation_count; ++j) {
            output.matches.empend();
            output.capture_group_matches.unchecked_append({});
            output.capture_group_matches.at(j).ensure_capacity(capture_groups_count);
            for (size_t k = 0; k < capture_groups_count; ++k)
                output.capture_group_matches.at(j).unchecked_append({});

            output.named_capture_group_matches.unchecked_append({});
            output.named_capture_group_matches.at(j).ensure_capacity(named_capture_groups_count);
        }
    }

    auto append_match = [](auto& input, auto& state, auto& output, auto& start_position) {
        if (output.matches.size() == input.match_index)
            output.matches.empend();

        VERIFY(start_position + state.string_position - start_position <= input.view.length());
        if (input.regex_options.has_flag_set(AllFlags::StringCopyMatches)) {
            output.matches.at(input.match_index) = { input.view.substring_view(start_position, state.string_position - start_position).to_string(), input.line, start_position, input.global_offset + start_position };
        } else { // let the view point to the original string ...
            output.matches.at(input.match_index) = { input.view.substring_view(start_position, state.string_position - start_position), input.line, start_position, input.global_offset + start_position };
        }
    };

#if REGEX_DEBUG
    s_regex_dbg.print_header();
#endif

    bool continue_search = input.regex_options.has_flag_set(AllFlags::Global) || input.regex_options.has_flag_set(AllFlags::Multiline);
    if (input.regex_options.has_flag_set(AllFlags::Internal_Stateful))
        continue_search = false;

    for (auto& view : views) {
        if (lines_to_skip != 0) {
            ++input.line;
            --lines_to_skip;
            continue;
        }
        input.view = view;
        dbgln_if(REGEX_DEBUG, "[match] Starting match with view ({}): _{}_", view.length(), view);

        auto view_length = view.length();
        size_t view_index = m_pattern.start_offset;
        state.string_position = view_index;
        bool succeeded = false;

        if (view_index == view_length && m_pattern.parser_result.match_length_minimum == 0) {
            // Run the code until it tries to consume something.
            // This allows non-consuming code to run on empty strings, for instance
            // e.g. "Exit"
            MatchOutput temp_output { output };

            input.column = match_count;
            input.match_index = match_count;

            state.string_position = view_index;
            state.instruction_position = 0;

            auto success = execute(input, state, temp_output, 0);
            // This success is acceptable only if it doesn't read anything from the input (input length is 0).
            if (state.string_position <= view_index) {
                if (success.value()) {
                    output = move(temp_output);
                    if (!match_count) {
                        // Nothing was *actually* matched, so append an empty match.
                        append_match(input, state, output, view_index);
                        ++match_count;
                    }
                }
            }
        }

        for (; view_index < view_length; ++view_index) {
            auto& match_length_minimum = m_pattern.parser_result.match_length_minimum;
            // FIXME: More performant would be to know the remaining minimum string
            //        length needed to match from the current position onwards within
            //        the vm. Add new OpCode for MinMatchLengthFromSp with the value of
            //        the remaining string length from the current path. The value though
            //        has to be filled in reverse. That implies a second run over bytecode
            //        after generation has finished.
            if (match_length_minimum && match_length_minimum > view_length - view_index)
                break;

            input.column = match_count;
            input.match_index = match_count;

            state.string_position = view_index;
            state.instruction_position = 0;

            auto success = execute(input, state, output, 0);
            if (!success.has_value())
                return { false, 0, {}, {}, {}, output.operations };

            if (success.value()) {
                succeeded = true;

                if (input.regex_options.has_flag_set(AllFlags::MatchNotEndOfLine) && state.string_position == input.view.length()) {
                    if (!continue_search)
                        break;
                    continue;
                }
                if (input.regex_options.has_flag_set(AllFlags::MatchNotBeginOfLine) && view_index == 0) {
                    if (!continue_search)
                        break;
                    continue;
                }

                dbgln_if(REGEX_DEBUG, "state.string_position={}, view_index={}", state.string_position, view_index);
                dbgln_if(REGEX_DEBUG, "[match] Found a match (length={}): '{}'", state.string_position - view_index, input.view.substring_view(view_index, state.string_position - view_index));

                ++match_count;

                if (continue_search) {
                    append_match(input, state, output, view_index);

                    bool has_zero_length = state.string_position == view_index;
                    view_index = state.string_position - (has_zero_length ? 0 : 1);
                    continue;

                } else if (input.regex_options.has_flag_set(AllFlags::Internal_Stateful)) {
                    append_match(input, state, output, view_index);
                    break;

                } else if (state.string_position < view_length) {
                    return { false, 0, {}, {}, {}, output.operations };
                }

                append_match(input, state, output, view_index);
                break;
            }

            if (!continue_search && !input.regex_options.has_flag_set(AllFlags::Internal_Stateful))
                break;
        }

        ++input.line;
        input.global_offset += view.length() + 1; // +1 includes the line break character

        if (input.regex_options.has_flag_set(AllFlags::Internal_Stateful))
            m_pattern.start_offset = state.string_position;

        if (succeeded && !continue_search)
            break;
    }

    MatchOutput output_copy;
    if (match_count) {
        output_copy.capture_group_matches = output.capture_group_matches;
        // Make sure there are as many capture matches as there are actual matches.
        if (output_copy.capture_group_matches.size() < match_count)
            output_copy.capture_group_matches.resize(match_count);
        for (auto& matches : output_copy.capture_group_matches)
            matches.resize(m_pattern.parser_result.capture_groups_count + 1);
        if (!input.regex_options.has_flag_set(AllFlags::SkipTrimEmptyMatches)) {
            for (auto& matches : output_copy.capture_group_matches)
                matches.template remove_all_matching([](auto& match) { return match.view.is_null(); });
        }

        output_copy.named_capture_group_matches = output.named_capture_group_matches;
        // Make sure there are as many capture matches as there are actual matches.
        if (output_copy.named_capture_group_matches.size() < match_count)
            output_copy.named_capture_group_matches.resize(match_count);

        output_copy.matches = output.matches;
    } else {
        output_copy.capture_group_matches.clear_with_capacity();
        output_copy.named_capture_group_matches.clear_with_capacity();
    }

    return {
        match_count != 0,
        match_count,
        move(output_copy.matches),
        move(output_copy.capture_group_matches),
        move(output_copy.named_capture_group_matches),
        output.operations,
        m_pattern.parser_result.capture_groups_count,
        m_pattern.parser_result.named_capture_groups_count,
    };
}

template<class Parser>
Optional<bool> Matcher<Parser>::execute(const MatchInput& input, MatchState& state, MatchOutput& output, size_t recursion_level) const
{
    if (recursion_level > c_max_recursion)
        return false;

    Vector<MatchState, 64> reversed_fork_low_prio_states;
    MatchState fork_high_prio_state;
    Optional<bool> success;

    auto& bytecode = m_pattern.parser_result.bytecode;

    for (;;) {
        ++output.operations;
        auto& opcode = bytecode.get_opcode(state);

#if REGEX_DEBUG
        s_regex_dbg.print_opcode("VM", opcode, state, recursion_level, false);
#endif

        ExecutionResult result;
        if (input.fail_counter > 0) {
            --input.fail_counter;
            result = ExecutionResult::Failed_ExecuteLowPrioForks;
        } else {
            result = opcode.execute(input, state, output);
        }

#if REGEX_DEBUG
        s_regex_dbg.print_result(opcode, bytecode, input, state, result);
#endif

        state.instruction_position += opcode.size();

        switch (result) {
        case ExecutionResult::Fork_PrioLow:
            reversed_fork_low_prio_states.append(state);
            continue;
        case ExecutionResult::Fork_PrioHigh:
            fork_high_prio_state = state;
            fork_high_prio_state.instruction_position = fork_high_prio_state.fork_at_position;
            success = execute(input, fork_high_prio_state, output, ++recursion_level);
            if (!success.has_value())
                return {};

            if (success.value()) {
                state = fork_high_prio_state;
                return true;
            }

            continue;
        case ExecutionResult::Continue:
            continue;
        case ExecutionResult::Succeeded:
            return true;
        case ExecutionResult::Failed:
            return false;
        case ExecutionResult::Failed_ExecuteLowPrioForks: {
            Vector<MatchState> fork_low_prio_states;
            fork_low_prio_states.ensure_capacity(reversed_fork_low_prio_states.size());
            for (ssize_t i = reversed_fork_low_prio_states.size() - 1; i >= 0; i--)
                fork_low_prio_states.unchecked_append(move(reversed_fork_low_prio_states[i]));
            return execute_low_prio_forks(input, state, output, move(fork_low_prio_states), recursion_level + 1);
        }
        }
    }

    VERIFY_NOT_REACHED();
}

template<class Parser>
ALWAYS_INLINE Optional<bool> Matcher<Parser>::execute_low_prio_forks(const MatchInput& input, MatchState& original_state, MatchOutput& output, Vector<MatchState> states, size_t recursion_level) const
{
    for (auto& state : states) {

        state.instruction_position = state.fork_at_position;
        dbgln_if(REGEX_DEBUG, "Forkstay... ip = {}, sp = {}", state.instruction_position, state.string_position);
        auto success = execute(input, state, output, recursion_level);
        if (!success.has_value())
            return {};
        if (success.value()) {
            dbgln_if(REGEX_DEBUG, "Forkstay succeeded... ip = {}, sp = {}", state.instruction_position, state.string_position);
            original_state = state;
            return true;
        }
    }

    original_state.string_position = 0;
    return false;
}

template class Matcher<PosixExtendedParser>;
template class Regex<PosixExtendedParser>;

template class Matcher<ECMA262Parser>;
template class Regex<ECMA262Parser>;
}