// Copyright (c) 2023-present The Bitcoin Core developers

// Distributed under the MIT software license, see the accompanying

// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <test/fuzz/util/descriptor.h>

#include <ranges>

#include <stack>

void MockedDescriptorConverter::Init() {

    // The data to use as a private key or a seed for an xprv.

    std::array<std::byte, 32> key_data{std::byte{1}};

    // Generate keys of all kinds and store them in the keys array.

    for (size_t i{0}; i < TOTAL_KEYS_GENERATED; i++) {

        key_data[31] = std::byte(i);

        // If this is a "raw" key, generate a normal privkey. Otherwise generate

        // an extended one.

        if (IdIsCompPubKey(i) || IdIsUnCompPubKey(i) || IdIsXOnlyPubKey(i) || IdIsConstPrivKey(i)) {

            CKey privkey;

            privkey.Set(key_data.begin(), key_data.end(), !IdIsUnCompPubKey(i));

            if (IdIsCompPubKey(i) || IdIsUnCompPubKey(i)) {

                CPubKey pubkey{privkey.GetPubKey()};

                keys_str[i] = HexStr(pubkey);

            } else if (IdIsXOnlyPubKey(i)) {

                const XOnlyPubKey pubkey{privkey.GetPubKey()};

                keys_str[i] = HexStr(pubkey);

            } else {

                keys_str[i] = EncodeSecret(privkey);

            }

        } else {

            CExtKey ext_privkey;

            ext_privkey.SetSeed(key_data);

            if (IdIsXprv(i)) {

                keys_str[i] = EncodeExtKey(ext_privkey);

            } else {

                const CExtPubKey ext_pubkey{ext_privkey.Neuter()};

                keys_str[i] = EncodeExtPubKey(ext_pubkey);

            }

        }

    }

}

std::optional<uint8_t> MockedDescriptorConverter::IdxFromHex(std::string_view hex_characters) const {

    if (hex_characters.size() != 2) return {};

    auto idx = ParseHex(hex_characters);

    if (idx.size() != 1) return {};

    return idx[0];

}

std::optional<std::string> MockedDescriptorConverter::GetDescriptor(std::string_view mocked_desc) const {

    // The smallest fragment would be "pk(%00)"

    if (mocked_desc.size() < 7) return {};

    // The actual descriptor string to be returned.

    std::string desc;

    desc.reserve(mocked_desc.size());

    // Replace all occurrences of '%' followed by two hex characters with the corresponding key.

    for (size_t i = 0; i < mocked_desc.size();) {

        if (mocked_desc[i] == '%') {

            if (i + 3 >= mocked_desc.size()) return {};

            if (const auto idx = IdxFromHex(mocked_desc.substr(i + 1, 2))) {

                desc += keys_str[*idx];

                i += 3;

            } else {

                return {};

            }

        } else {

            desc += mocked_desc[i++];

        }

    }

    return desc;

}

bool HasDeepDerivPath(const FuzzBufferType& buff, const int max_depth)

{

    auto depth{0};

    for (const auto& ch: buff) {

        if (ch == ',') {

            // A comma is always present between two key expressions, so we use that as a delimiter.

            depth = 0;

        } else if (ch == '/') {

            if (++depth > max_depth) return true;

        }

    }

    return false;

}

bool HasTooManySubFrag(const FuzzBufferType& buff, const int max_subs, const size_t max_nested_subs)

{

    // We use a stack because there may be many nested sub-frags.

    std::stack<int> counts;

    for (const auto& ch: buff) {

        // The fuzzer may generate an input with a ton of parentheses. Rule out pathological cases.

        if (counts.size() > max_nested_subs) return true;

        if (ch == '(') {

            // A new fragment was opened, create a new sub-count for it and start as one since any fragment with

            // parentheses has at least one sub.

            counts.push(1);

        } else if (ch == ',' && !counts.empty()) {

            // When encountering a comma, account for an additional sub in the last opened fragment. If it exceeds the

            // limit, bail.

            if (++counts.top() > max_subs) return true;

        } else if (ch == ')' && !counts.empty()) {

            // Fragment closed! Drop its sub count and resume to counting the number of subs for its parent.

            counts.pop();

        }

    }

    return false;

}

bool HasTooManyWrappers(const FuzzBufferType& buff, const int max_wrappers)

{

    // The number of nested wrappers. Nested wrappers are always characters which follow each other so we don't have to

    // use a stack as we do above when counting the number of sub-fragments.

    std::optional<int> count;

    // We want to detect nested wrappers. A wrapper is a character prepended to a fragment, separated by a colon. There

    // may be more than one wrapper, in which case the colon is not repeated. For instance `jjjjj:pk()`.  To count

    // wrappers we iterate in reverse and use the colon to detect the end of a wrapper expression and count how many

    // characters there are since the beginning of the expression. We stop counting when we encounter a character

    // indicating the beginning of a new expression.

    for (const auto ch: buff | std::views::reverse) {

        // A colon, start counting.

        if (ch == ':') {

            // The colon itself is not a wrapper so we start at 0.

            count = 0;

        } else if (count) {

            // If we are counting wrappers, stop when we crossed the beginning of the wrapper expression. Otherwise keep

            // counting and bail if we reached the limit.

            // A wrapper may only ever occur as the first sub of a descriptor/miniscript expression ('('), as the

            // first Taproot leaf in a pair ('{') or as the nth sub in each case (',').

            if (ch == ',' || ch == '(' || ch == '{') {

                count.reset();

            } else if (++*count > max_wrappers) {

                return true;

            }

        }

    }

    return false;

}