#include "json_scan.h"

namespace roro::release {

namespace {
bool space(char c) { return c == ' ' || c == '\t' || c == '\r' || c == '\n'; }
bool continuation(char c) { return (static_cast<uint8_t>(c) & 0xC0) == 0x80; }
}  // namespace

void JsonScanner::feed(const char* data, size_t len) {
    for (size_t i = 0; i < len && !failed_; i++) step(data[i]);
}

std::string JsonScanner::path() const {
    std::string p;
    for (const Frame& f : stack_) {
        if (f.isObject) {
            if (!p.empty()) p += '.';
            p += f.key;
        } else {
            p += '[' + std::to_string(f.index) + ']';
        }
    }
    return p;
}

void JsonScanner::append(const char* bytes, size_t n) {
    if (text_.size() + n > max_) {
        truncated_ = true;
        return;
    }
    text_.append(bytes, n);
}

void JsonScanner::appendCodePoint(uint32_t cp) {
    char b[4];
    size_t n;
    if (cp < 0x80) {
        b[0] = static_cast<char>(cp);
        n = 1;
    } else if (cp < 0x800) {
        b[0] = static_cast<char>(0xC0 | (cp >> 6));
        b[1] = static_cast<char>(0x80 | (cp & 0x3F));
        n = 2;
    } else if (cp < 0x10000) {
        b[0] = static_cast<char>(0xE0 | (cp >> 12));
        b[1] = static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
        b[2] = static_cast<char>(0x80 | (cp & 0x3F));
        n = 3;
    } else {
        b[0] = static_cast<char>(0xF0 | (cp >> 18));
        b[1] = static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
        b[2] = static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
        b[3] = static_cast<char>(0x80 | (cp & 0x3F));
        n = 4;
    }
    append(b, n);
}

void JsonScanner::startString(bool key) {
    inString_ = true;
    isKey_ = key;
    escape_ = false;
    unicodeLeft_ = 0;
    highSurrogate_ = 0;
    truncated_ = false;
    text_.clear();
}

void JsonScanner::stringChar(char c) {
    if (unicodeLeft_ > 0) {
        int digit = c >= '0' && c <= '9' ? c - '0' : c >= 'a' && c <= 'f' ? c - 'a' + 10 : c >= 'A' && c <= 'F' ? c - 'A' + 10 : -1;
        if (digit < 0) return fail();
        unicode_ = unicode_ * 16 + digit;
        if (--unicodeLeft_ == 0) {
            if (unicode_ >= 0xD800 && unicode_ < 0xDC00) {
                highSurrogate_ = unicode_;  // the low half comes next
            } else if (unicode_ >= 0xDC00 && unicode_ < 0xE000 && highSurrogate_) {
                appendCodePoint(0x10000 + ((highSurrogate_ - 0xD800) << 10) + (unicode_ - 0xDC00));
                highSurrogate_ = 0;
            } else {
                appendCodePoint(unicode_);
                highSurrogate_ = 0;
            }
        }
        return;
    }
    if (escape_) {
        escape_ = false;
        switch (c) {
            case 'n': append("\n", 1); break;
            case 't': append("\t", 1); break;
            case 'r': append("\r", 1); break;
            case 'b': append("\b", 1); break;
            case 'f': append("\f", 1); break;
            case 'u': unicodeLeft_ = 4; unicode_ = 0; break;
            default: append(&c, 1); break;  // \" \\ \/
        }
        return;
    }
    if (c == '\\') {
        escape_ = true;
    } else if (c == '"') {
        endString();
    } else {
        append(&c, 1);
    }
}

void JsonScanner::endString() {
    inString_ = false;
    // A cut can leave half a character at the end.
    while (truncated_ && !text_.empty()) {
        size_t k = text_.size();
        while (k > 0 && continuation(text_[k - 1])) k--;
        if (k == 0) break;
        uint8_t lead = static_cast<uint8_t>(text_[k - 1]);
        size_t want = lead >= 0xF0 ? 4 : lead >= 0xE0 ? 3 : lead >= 0xC0 ? 2 : 1;
        if (text_.size() - (k - 1) < want) text_.resize(k - 1);
        break;
    }
    if (isKey_) {
        stack_.back().key = text_;
        expect_ = Expect::Colon;
        return;
    }
    sink_(path(), text_, true, truncated_);
    valueDone();
}

void JsonScanner::endLiteral() {
    inLiteral_ = false;
    sink_(path(), text_, false, false);
    valueDone();
}

void JsonScanner::valueDone() {
    if (stack_.empty()) {
        done_ = true;
        return;
    }
    expect_ = Expect::CommaOrEnd;
}

void JsonScanner::step(char c) {
    if (inString_) return stringChar(c);
    if (inLiteral_) {
        if (space(c) || c == ',' || c == '}' || c == ']') {
            endLiteral();  // and the character that ended it is read again below
        } else {
            if (text_.size() < max_) text_ += c;
            return;
        }
    }
    if (space(c)) return;
    switch (expect_) {
        case Expect::Value:
            if (c == '{') {
                stack_.push_back({true, "", 0});
                expect_ = Expect::KeyOrEnd;
            } else if (c == '[') {
                stack_.push_back({false, "", 0});
                expect_ = Expect::Value;
            } else if (c == ']' && !stack_.empty() && !stack_.back().isObject && stack_.back().index == 0) {
                stack_.pop_back();  // an empty array
                valueDone();
            } else if (c == '"') {
                startString(false);
            } else if (c == '-' || (c >= '0' && c <= '9') || c == 't' || c == 'f' || c == 'n') {
                inLiteral_ = true;
                text_.assign(1, c);
            } else {
                fail();
            }
            return;
        case Expect::KeyOrEnd:
            if (c == '"') startString(true);
            else if (c == '}') {
                stack_.pop_back();
                valueDone();
            } else fail();
            return;
        case Expect::Colon:
            if (c == ':') expect_ = Expect::Value;
            else fail();
            return;
        case Expect::CommaOrEnd:
            if (c == ',') {
                if (stack_.back().isObject) expect_ = Expect::KeyOrEnd;
                else {
                    stack_.back().index++;
                    expect_ = Expect::Value;
                }
            } else if ((c == '}' && stack_.back().isObject) || (c == ']' && !stack_.back().isObject)) {
                stack_.pop_back();
                valueDone();
            } else fail();
            return;
    }
}

}  // namespace roro::release