// vdm/net/content_disposition.cpp

#include "vdm/net/content_disposition.hpp"

#include <algorithm>
#include <string>
#include <utility>
#include <vector>

#include "net/text_codec.hpp"

namespace vdm::net {
namespace {

using detail::decode_rfc2047;
using detail::latin1_to_utf8;
using detail::percent_decode;
using detail::to_utf8_best_effort;

std::string_view trim(std::string_view s) {
    while (!s.empty() && (s.front() == ' ' || s.front() == '\t'))
        s.remove_prefix(1);
    while (!s.empty() &&
           (s.back() == ' ' || s.back() == '\t' || s.back() == '\r' || s.back() == '\n'))
        s.remove_suffix(1);
    return s;
}

std::string ascii_lower(std::string_view s) {
    std::string r(s);
    for (char &c : r)
        if (c >= 'A' && c <= 'Z')
            c = static_cast<char>(c - 'A' + 'a');
    return r;
}

// Split "type; a=b; c*=d; e=\"f;g\"" into the type and a param list, honouring quoted
// strings (a ';' inside quotes is not a separator). For quoted values the value stored is
// the *raw* inner text (quotes removed, escapes NOT yet resolved) with `quoted = true`;
// callers resolve escapes and strip path components together (order matters — see
// unquote_strip). Keys are lowercased.
struct Param {
    std::string key;
    std::string value;
    bool quoted = false;
};
struct Params {
    std::string type;
    std::vector<Param> kv;

    [[nodiscard]] const Param *find(std::string_view key) const {
        for (const auto &p : kv)
            if (p.key == key)
                return &p;
        return nullptr;
    }
};

Params tokenize(std::string_view h) {
    Params out;
    std::size_t i = 0;
    const std::size_t n = h.size();

    auto read_segment = [&]() -> std::string_view {
        std::size_t start = i;
        bool in_q = false;
        for (; i < n; ++i) {
            char c = h[i];
            if (c == '"') {
                in_q = !in_q;
            } else if (c == '\\' && in_q && i + 1 < n) {
                ++i;  // skip escaped char
            } else if (c == ';' && !in_q) {
                break;
            }
        }
        std::string_view seg = h.substr(start, i - start);
        if (i < n)
            ++i;  // consume ';'
        return seg;
    };

    out.type = ascii_lower(trim(read_segment()));

    while (i < n) {
        std::string_view seg = trim(read_segment());
        if (seg.empty())
            continue;
        auto eq = seg.find('=');
        if (eq == std::string_view::npos) {
            out.kv.emplace_back(ascii_lower(seg), std::string{});
            continue;
        }
        std::string key = ascii_lower(trim(seg.substr(0, eq)));
        std::string_view rawval = trim(seg.substr(eq + 1));

        Param param;
        param.key = std::move(key);
        if (rawval.size() >= 2 && rawval.front() == '"') {
            std::string_view inner = rawval.substr(1);
            auto close = inner.rfind('"');
            if (close != std::string_view::npos)
                inner = inner.substr(0, close);
            param.value.assign(inner);  // raw, escapes unresolved
            param.quoted = true;
        } else {
            param.value.assign(rawval);
        }
        out.kv.push_back(std::move(param));
    }
    return out;
}

std::string strip_path(std::string s) {
    auto slash = s.find_last_of("/\\");
    if (slash != std::string::npos)
        s.erase(0, slash + 1);
    return s;
}

// Resolve ONLY the `\"` escape (needed so a quote can appear mid-name). Every other
// backslash is kept literal and later treated as a path separator by strip_path — real
// Windows paths in the wild use `\` unescaped, and path-traversal defence matters more
// than supporting the vanishingly rare filename with a literal backslash.
std::string unescape_dquote(std::string_view raw) {
    std::string out;
    out.reserve(raw.size());
    for (std::size_t i = 0; i < raw.size(); ++i) {
        if (raw[i] == '\\' && i + 1 < raw.size() && raw[i + 1] == '"') {
            out.push_back('"');
            ++i;
        } else {
            out.push_back(raw[i]);
        }
    }
    return out;
}

// Decode an RFC 5987 ext-value: charset'lang'pct-encoded-octets
std::string decode_ext_value(std::string_view v) {
    auto q1 = v.find('\'');
    if (q1 == std::string_view::npos)
        return percent_decode(v);  // malformed: best effort
    auto q2 = v.find('\'', q1 + 1);
    if (q2 == std::string_view::npos)
        return percent_decode(v.substr(q1 + 1));

    std::string_view charset = v.substr(0, q1);
    std::string_view enc = v.substr(q2 + 1);
    std::string bytes = percent_decode(enc);

    std::string cs = ascii_lower(charset);
    if (cs == "iso-8859-1" || cs == "latin1")
        return latin1_to_utf8(bytes);
    return to_utf8_best_effort(bytes);  // utf-8 or unknown -> best effort
}

// Reassemble RFC 2231 continuations: name*0*, name*1, name*2* ... in order.
std::string join_continuations(const Params &p, std::string_view base, bool &is_ext) {
    std::vector<std::pair<int, std::string>> parts;
    is_ext = false;
    for (const auto &param : p.kv) {
        const std::string &k = param.key;
        const std::string &val = param.value;
        if (k.size() <= base.size() + 1 || k.compare(0, base.size(), base) != 0)
            continue;
        if (k[base.size()] != '*')
            continue;
        std::string_view rest(k);
        rest.remove_prefix(base.size() + 1);  // after "base*"
        bool star = false;
        if (!rest.empty() && rest.back() == '*') {
            star = true;
            rest.remove_suffix(1);
        }
        int idx = 0;
        for (char c : rest) {
            if (c < '0' || c > '9') {
                idx = -1;
                break;
            }
            idx = idx * 10 + (c - '0');
        }
        if (idx < 0)
            continue;
        if (star)
            is_ext = true;
        parts.emplace_back(idx, val);
    }
    if (parts.empty())
        return {};
    std::sort(parts.begin(), parts.end(),
              [](const auto &a, const auto &b) { return a.first < b.first; });

    // Piece 0 (if star-form) carries charset'lang' prefix; later pieces are raw
    // percent-encoded. Concatenate the percent-encoded text then decode once.
    std::string charset_prefix;
    std::string enc;
    bool first = true;
    for (auto &[idx, val] : parts) {
        if (first && is_ext) {
            auto q1 = val.find('\'');
            auto q2 = (q1 == std::string::npos) ? std::string::npos : val.find('\'', q1 + 1);
            if (q2 != std::string::npos) {
                charset_prefix = val.substr(0, q2 + 1);
                enc += val.substr(q2 + 1);
            } else {
                enc += val;
            }
        } else {
            enc += val;
        }
        first = false;
    }
    if (is_ext)
        return decode_ext_value(charset_prefix + enc);
    return to_utf8_best_effort(percent_decode(enc));
}

ContentDisposition::Type classify(std::string_view t) {
    if (t == "inline")
        return ContentDisposition::Type::inline_;
    if (t == "attachment")
        return ContentDisposition::Type::attachment;
    if (t == "form-data")
        return ContentDisposition::Type::form_data;
    if (t.empty())
        return ContentDisposition::Type::none;
    return ContentDisposition::Type::other;
}

}  // namespace

ContentDisposition parse_content_disposition(std::string_view header_value) {
    ContentDisposition cd;
    header_value = trim(header_value);
    if (header_value.empty())
        return cd;

    Params p = tokenize(header_value);
    cd.type = classify(p.type);

    // RFC 6266 §4.3: prefer filename* over filename.
    std::string ext_name;
    bool ext_is_ext = false;
    if (const Param *fstar = p.find("filename*")) {
        ext_name = decode_ext_value(fstar->value);
        ext_is_ext = true;
    } else {
        std::string joined = join_continuations(p, "filename", ext_is_ext);
        if (!joined.empty())
            ext_name = std::move(joined);
    }

    std::string plain_name;
    if (const Param *f = p.find("filename")) {
        // Resolve `\"`, then decode legacy encoded-words if present — BEFORE stripping
        // path components, since a base64 payload can legitimately contain '/'.
        std::string raw = f->quoted ? unescape_dquote(f->value) : f->value;
        bool had_ew = false;
        std::string decoded = decode_rfc2047(raw, &had_ew);
        plain_name = had_ew ? std::move(decoded) : to_utf8_best_effort(raw);
    }

    if (!ext_name.empty()) {
        cd.filename = strip_path(std::move(ext_name));
        cd.filename_from_ext = ext_is_ext;
    } else if (!plain_name.empty()) {
        cd.filename = strip_path(std::move(plain_name));
        cd.filename_from_ext = false;
    }

    // Trim ASCII whitespace the decoders may have left at the edges.
    std::string_view fv = trim(cd.filename);
    cd.filename.assign(fv);
    return cd;
}

}  // namespace vdm::net