#include "core/rendering/lighting.hpp"

#include <algorithm>
#include <cmath>
#include <cstddef>
#include <vector>

#include "core/resources/resource_helper.hpp"
#include "external/fkyaml_node.hpp"
#include "utils/defaults.hpp"
#include "utils/log.hpp"

namespace Lighting {

    namespace {

        // Buffer de luminància compartit entre frames. Es redimensiona
        // només si canvia la mida del canvas (mai en un run normal: el
        // canvas del joc és 320×240 fix). El reusem perquè una `apply`
        // allotjant cada frame seria un cost evitable.
        auto luminanceBuffer() -> std::vector<std::uint8_t>& {
            static std::vector<std::uint8_t> buf_;
            return buf_;
        }

        // Configuració global, inicialitzada amb els defaults compilats.
        // loadConfig() la reemplaça si troba el fitxer.
        auto activeConfig() -> GradientConfig& {
            static GradientConfig cfg_{
                .inner_ratio = Defaults::Lighting::INNER_RATIO,
                .mid_ratio = Defaults::Lighting::MID_RATIO,
                .inner_intensity = Defaults::Lighting::INNER_INTENSITY,
                .mid_intensity = Defaults::Lighting::MID_INTENSITY,
                .outer_intensity = Defaults::Lighting::OUTER_INTENSITY,
            };
            return cfg_;
        }

        // Quantitza un factor 0..1 a 0..255. `clamp` per defensar-nos de
        // YAMLs que entreguen valors fora de rang sense forçar la mà.
        auto toByte(float v) -> std::uint8_t {
            const float CLAMPED = std::clamp(v, 0.0F, 1.0F);
            return static_cast<std::uint8_t>(std::lround(CLAMPED * 255.0F));
        }

        void readField(const fkyaml::node& node, const char* key, float& dst) {
            if (node.contains(key)) { dst = node[key].get_value<float>(); }
        }

        // Pre-calcula els 3 quadrats de radi i les intensitats que farem
        // servir dins del bucle per píxel. Es resol una sola vegada per
        // emissor i s'evita arrastrar 6 paràmetres a `rasterizeEmitter`.
        struct EmitterRings {
            int radius_sq{0};
            int mid_sq{0};
            int inner_sq{0};
            std::uint8_t inner{0};
            std::uint8_t mid{0};
            std::uint8_t outer{0};
        };

        auto computeRings(int radius, const GradientConfig& cfg) -> EmitterRings {
            const auto R_F = static_cast<float>(radius);
            const float R_INNER = R_F * cfg.inner_ratio;
            const float R_MID = R_F * cfg.mid_ratio;
            return EmitterRings{
                .radius_sq = radius * radius,
                .mid_sq = static_cast<int>(R_MID * R_MID),
                .inner_sq = static_cast<int>(R_INNER * R_INNER),
                .inner = toByte(cfg.inner_intensity),
                .mid = toByte(cfg.mid_intensity),
                .outer = toByte(cfg.outer_intensity),
            };
        }

        // Itera la bounding box de l'emissor clipada al canvas i actualitza
        // la fila de luminància corresponent amb `max(actual, ring)`. Es
        // crida un cop per emissor, així extreure-la deixa `apply` simple.
        void rasterizeEmitter(const Emitter& e, const EmitterRings& rings, std::uint8_t* lum, int width, int height) {
            const int R = e.radius;
            const int CX = static_cast<int>(e.cx);
            const int CY = static_cast<int>(e.cy);
            const int X0 = std::max(0, CX - R);
            const int Y0 = std::max(0, CY - R);
            const int X1 = std::min(width - 1, CX + R);
            const int Y1 = std::min(height - 1, CY + R);
            for (int y = Y0; y <= Y1; ++y) {
                const int DY = y - CY;
                const int DY_SQ = DY * DY;
                if (DY_SQ > rings.radius_sq) { continue; }
                std::uint8_t* row = lum + (static_cast<std::ptrdiff_t>(y) * width);
                for (int x = X0; x <= X1; ++x) {
                    const int DX = x - CX;
                    const int DIST_SQ = (DX * DX) + DY_SQ;
                    if (DIST_SQ > rings.radius_sq) { continue; }
                    std::uint8_t intensity = rings.outer;
                    if (DIST_SQ <= rings.inner_sq) {
                        intensity = rings.inner;
                    } else if (DIST_SQ <= rings.mid_sq) {
                        intensity = rings.mid;
                    }
                    row[x] = std::max(intensity, row[x]);
                }
            }
        }

        // Pasada final: pixel = pixel * lum / 255 per canal. El canal alpha
        // es preserva (la resta del pipeline assumeix opacitat total al
        // canvas; veure Rendering::OPAQUE_ALPHA).
        void modulateCanvas(std::uint32_t* canvas, const std::uint8_t* lum, int width, int height) {
            for (int y = 0; y < height; ++y) {
                std::uint32_t* px = canvas + (static_cast<std::ptrdiff_t>(y) * width);
                const std::uint8_t* lrow = lum + (static_cast<std::ptrdiff_t>(y) * width);
                for (int x = 0; x < width; ++x) {
                    const std::uint8_t L = lrow[x];
                    if (L == 255) { continue; }  // píxel intacte.
                    const std::uint32_t SRC = px[x];
                    const std::uint8_t SR = (SRC >> 16) & 0xFF;
                    const std::uint8_t SG = (SRC >> 8) & 0xFF;
                    const std::uint8_t SB = SRC & 0xFF;
                    const auto R = static_cast<std::uint8_t>((SR * L) / 255);
                    const auto G = static_cast<std::uint8_t>((SG * L) / 255);
                    const auto B = static_cast<std::uint8_t>((SB * L) / 255);
                    px[x] = (SRC & 0xFF000000U) |
                        (static_cast<std::uint32_t>(R) << 16) |
                        (static_cast<std::uint32_t>(G) << 8) |
                        static_cast<std::uint32_t>(B);
                }
            }
        }

    }  // namespace

    auto config() -> const GradientConfig& {
        return activeConfig();
    }

    void loadConfig(const std::string& yaml_path) {
        auto bytes = Resource::Helper::loadFile(yaml_path);
        if (bytes.empty()) {
            Log::warn("Lighting", "no s'ha pogut obrir {} — s'usaran els defaults compilats", yaml_path);
            return;
        }
        try {
            const auto* begin = reinterpret_cast<const char*>(bytes.data());
            const auto* end = begin + bytes.size();
            auto yaml = fkyaml::node::deserialize(begin, end);
            if (yaml.contains("gradient")) {
                const auto& g = yaml["gradient"];
                auto& cfg = activeConfig();
                readField(g, "inner_ratio", cfg.inner_ratio);
                readField(g, "mid_ratio", cfg.mid_ratio);
                readField(g, "inner_intensity", cfg.inner_intensity);
                readField(g, "mid_intensity", cfg.mid_intensity);
                readField(g, "outer_intensity", cfg.outer_intensity);
            }
        } catch (const std::exception& ex) {
            Log::warn("Lighting", "error parsejant {}: {} — s'usaran els defaults compilats", yaml_path, ex.what());
        }
    }

    void apply(std::uint32_t* canvas, int width, int height, float room_light, std::span<const Emitter> emitters) {
        if (canvas == nullptr || width <= 0 || height <= 0) { return; }

        // Atajo: si la sala està totalment il·luminada i no hi ha
        // emissors, la pasada seria un `pixel * 1.0` global — no cal
        // tocar res. És el camí curt habitual mentre no posem
        // `light_level` a les sales.
        const std::uint8_t ROOM = toByte(room_light);
        if (ROOM == 255 && emitters.empty()) { return; }

        auto& lum = luminanceBuffer();
        const std::size_t TOTAL = static_cast<std::size_t>(width) * static_cast<std::size_t>(height);
        if (lum.size() != TOTAL) { lum.resize(TOTAL); }
        std::ranges::fill(lum, ROOM);

        const auto& cfg = activeConfig();
        for (const auto& e : emitters) {
            if (e.radius <= 0) { continue; }
            const auto RINGS = computeRings(e.radius, cfg);
            rasterizeEmitter(e, RINGS, lum.data(), width, height);
        }

        modulateCanvas(canvas, lum.data(), width, height);
    }

}  // namespace Lighting