#include "attribute_data.h"

#include <cstring>
#include <fstream>
#include <limits>

namespace fmt {

namespace {

constexpr char kHeader[] = "AttributeData";
constexpr std::size_t kHeaderSize = sizeof(kHeader); // include trailing NUL
constexpr std::uint32_t kMaxRecords = 1u << 20;
constexpr std::uint32_t kMaxHeightVertices = 1u << 24;

struct Reader {
    const std::uint8_t *data = nullptr;
    std::size_t size = 0;
    std::size_t offset = 0;
    std::string *error = nullptr;

    bool fail(const std::string &message) {
        if (error)
            *error = message + " at offset " + std::to_string(offset);
        return false;
    }

    bool require(std::size_t count) {
        if (count > size || offset > size - count)
            return fail("AttributeData truncated");
        return true;
    }

    template <typename T>
    bool read(T &value) {
        if (!require(sizeof(T)))
            return false;
        std::memcpy(&value, data + offset, sizeof(T));
        offset += sizeof(T);
        return true;
    }

    bool read_bytes(void *dst, std::size_t count) {
        if (!require(count))
            return false;
        std::memcpy(dst, data + offset, count);
        offset += count;
        return true;
    }
};

std::size_t dimension_count(std::uint32_t type) {
    switch (static_cast<AttributeCollisionType>(type)) {
    case AttributeCollisionType::Plane:
    case AttributeCollisionType::Cylinder:
        return 2;
    case AttributeCollisionType::Box:
    case AttributeCollisionType::Sphere:
    case AttributeCollisionType::Aabb:
    case AttributeCollisionType::Obb:
        return type == static_cast<std::uint32_t>(AttributeCollisionType::Sphere) ? 1 : 3;
    default:
        return 0;
    }
}

std::string fixed_name(const char (&raw)[32]) {
    const void *nul = std::memchr(raw, '\0', 32);
    const auto count = nul ? static_cast<const char *>(nul) - raw : 32;
    return std::string(raw, static_cast<std::size_t>(count));
}

} // namespace

bool parse_attribute_data(const std::uint8_t *data, std::size_t size,
                          AttributeData &out, std::string *err) {
    out = AttributeData{};
    if (data == nullptr)
        return err ? ((*err = "AttributeData buffer is null"), false) : false;

    Reader r{data, size, 0, err};
    char header[kHeaderSize] = {};
    if (!r.read_bytes(header, kHeaderSize))
        return false;
    if (std::memcmp(header, kHeader, kHeaderSize) != 0)
        return r.fail("AttributeData bad header");

    std::uint32_t collision_count = 0;
    std::uint32_t height_count = 0;
    if (!r.read(collision_count) || !r.read(height_count))
        return false;
    if (collision_count > kMaxRecords || height_count > kMaxRecords)
        return r.fail("AttributeData record count is unreasonable");

    out.collisions.reserve(collision_count);
    for (std::uint32_t i = 0; i < collision_count; ++i) {
        AttributeCollision collision;
        if (!r.read(collision.type))
            return false;
        const std::size_t dims = dimension_count(collision.type);
        if (dims == 0)
            return r.fail("AttributeData unknown collision type");

        char raw_name[32] = {};
        if (!r.read_bytes(raw_name, sizeof(raw_name)) ||
            !r.read_bytes(collision.position.data(), sizeof(float) * 3) ||
            !r.read_bytes(collision.dimensions.data(), sizeof(float) * dims) ||
            !r.read_bytes(collision.quaternion.data(), sizeof(float) * 4))
            return false;
        collision.name = fixed_name(raw_name);
        out.collisions.push_back(std::move(collision));
    }

    out.heights.reserve(height_count);
    for (std::uint32_t i = 0; i < height_count; ++i) {
        AttributeHeight height;
        char raw_name[32] = {};
        std::uint32_t vertex_count = 0;
        if (!r.read_bytes(raw_name, sizeof(raw_name)) || !r.read(vertex_count))
            return false;
        if (vertex_count > kMaxHeightVertices)
            return r.fail("AttributeData height vertex count is unreasonable");
        if (vertex_count > 0 && vertex_count > (std::numeric_limits<std::size_t>::max() / 12))
            return r.fail("AttributeData height size overflows");
        if (!r.require(static_cast<std::size_t>(vertex_count) * 12))
            return false;
        height.name = fixed_name(raw_name);
        height.vertices.resize(vertex_count);
        for (auto &vertex : height.vertices) {
            if (!r.read_bytes(vertex.data(), sizeof(float) * 3))
                return false;
        }
        out.heights.push_back(std::move(height));
    }

    if (r.offset != size)
        return r.fail("AttributeData trailing bytes");
    return true;
}

bool parse_attribute_data_file(const std::string &path, AttributeData &out,
                               std::string *err) {
    std::ifstream file(path, std::ios::binary | std::ios::ate);
    if (!file) {
        if (err)
            *err = "cannot open AttributeData: " + path;
        return false;
    }
    const std::streamoff end = file.tellg();
    if (end < 0) {
        if (err)
            *err = "cannot stat AttributeData: " + path;
        return false;
    }
    std::vector<std::uint8_t> bytes(static_cast<std::size_t>(end));
    file.seekg(0, std::ios::beg);
    if (!bytes.empty() && !file.read(reinterpret_cast<char *>(bytes.data()), static_cast<std::streamsize>(bytes.size()))) {
        if (err)
            *err = "cannot read AttributeData: " + path;
        return false;
    }
    return parse_attribute_data(bytes.data(), bytes.size(), out, err);
}

} // namespace fmt