#include <math.h>

#include "raylib.h"
#include "rlgl.h"
#include "rendering.h"
#include "world.h"
#include "vec_math.h"

// Rendering constants
#define LIGHT_CHECK_HEIGHT 240
#define LIGHT_CHECK_RANGE 30
#define LIGHT_LEVEL_SHADOWED 0.6f
#define LIGHT_LEVEL_MIN 0.25f
#define LIGHT_BRIGHTNESS_TOP 1.0f
#define LIGHT_BRIGHTNESS_BOTTOM 0.8f
#define LIGHT_BRIGHTNESS_SIDE 0.95f
#define BLOCK_NEAR_EXEMPTION_DIST_SQ 225.0f  // 15^2
#define BLOCK_MIN_DIST 0.1f
#define BLOCK_RADIUS 0.5f
#define WORLD_HEIGHT_MAX 256

// Calculate light level for a block - check for unobstructed access to sunlight
// Uses early termination and limited search to avoid expensive iteration
float get_block_light_level(World* world, int x, int y, int z)
{
    // Quick check: if we're at height threshold or above, assume fully lit
    if (y >= LIGHT_CHECK_HEIGHT) return 1.0f;

    // Check limited range above (most light is blocked within this range)
    int check_limit = (y + LIGHT_CHECK_RANGE < WORLD_HEIGHT_MAX) ? y + LIGHT_CHECK_RANGE : WORLD_HEIGHT_MAX;

    for (int check_y = y + 1; check_y < check_limit; check_y++) {
        BlockType above = world_get_block(world, x, check_y, z);
        if (above != BLOCK_AIR) {
            // Hit a solid block - this position is shadowed
            return LIGHT_LEVEL_SHADOWED;
        }
    }

    // Made it all the way up without hitting obstruction
    return 1.0f;  // Fully lit - direct sky access
}

// Apply lighting to a face based on direction and adjacent air block's sky access
// face_index: 0=+X, 1=-X, 2=+Y(top), 3=-Y(bottom), 4=+Z, 5=-Z
// neighbor_x/y/z: coordinates of the adjacent air block this face is exposed to
Color apply_face_lighting(Color base_color, int face_index, World* world, int neighbor_x, int neighbor_y, int neighbor_z)
{
    // Get face brightness based on orientation
    float face_brightness = (face_index == 2) ? LIGHT_BRIGHTNESS_TOP :
                           (face_index == 3) ? LIGHT_BRIGHTNESS_BOTTOM :
                           LIGHT_BRIGHTNESS_SIDE;

    // Check if the adjacent air block has direct sky access
    // This determines if the face should be shadowed
    float adjacent_light = get_block_light_level(world, neighbor_x, neighbor_y, neighbor_z);

    // Apply both face brightness and adjacent block's light level, with clamping
    float final_brightness = face_brightness * adjacent_light;
    if (final_brightness < LIGHT_LEVEL_MIN) final_brightness = LIGHT_LEVEL_MIN;
    if (final_brightness > 1.0f) final_brightness = 1.0f;

    // Apply brightness to color
    Color lit_color;
    lit_color.r = (unsigned char)(base_color.r * final_brightness);
    lit_color.g = (unsigned char)(base_color.g * final_brightness);
    lit_color.b = (unsigned char)(base_color.b * final_brightness);
    lit_color.a = base_color.a;

    return lit_color;
}

// check if a block has any face visible (exposed to air)
bool has_visible_face(World* world, int x, int y, int z, Vector3 block_pos, Vector3 cam_pos)
{
    // Check all 6 neighbors - if any is air, this block has an exposed face
    if (world_get_block(world, x+1, y, z) == BLOCK_AIR ||
        world_get_block(world, x-1, y, z) == BLOCK_AIR ||
        world_get_block(world, x, y+1, z) == BLOCK_AIR ||
        world_get_block(world, x, y-1, z) == BLOCK_AIR ||
        world_get_block(world, x, y, z+1) == BLOCK_AIR ||
        world_get_block(world, x, y, z-1) == BLOCK_AIR) {
        return true;  // has at least one exposed face
    }

    return false;  // completely surrounded by solid blocks
}

// check if a block is occluded (completely surrounded by other blocks)
bool is_block_occluded(World* world, int x, int y, int z)
{
    // check all 6 neighbors - if all are stone, this block is completely hidden
    if (world_get_block(world, x+1, y, z) != BLOCK_AIR &&
        world_get_block(world, x-1, y, z) != BLOCK_AIR &&
        world_get_block(world, x, y+1, z) != BLOCK_AIR &&
        world_get_block(world, x, y-1, z) != BLOCK_AIR &&
        world_get_block(world, x, y, z+1) != BLOCK_AIR &&
        world_get_block(world, x, y, z-1) != BLOCK_AIR) {
        return true;  // block is completely surrounded, don't render
    }
    return false;
}

// Check if a block is visible in the camera frustum
// Uses precomputed FOV tangent values if provided for performance
bool is_block_visible_fast(Vector3 block_pos, Vector3 cam_pos, Vector3 cam_forward,
                           Vector3 cam_right, Vector3 cam_up, float render_distance,
                           float half_vert_tan, float half_horiz_tan)
{
    Vector3 to_block = vec3_sub(block_pos, cam_pos);
    float dist_sq = to_block.x*to_block.x + to_block.y*to_block.y + to_block.z*to_block.z;
    float render_dist_sq = render_distance * render_distance;

    if (dist_sq > render_dist_sq) {
        return false;
    }

    // Always render blocks within exemption distance (exempt from FOV culling)
    if (dist_sq < BLOCK_NEAR_EXEMPTION_DIST_SQ) return true;

    // Normalize direction to block
    float dist = sqrtf(dist_sq);
    if (dist < BLOCK_MIN_DIST) return true;

    float inv_dist = 1.0f / dist;
    to_block.x *= inv_dist;
    to_block.y *= inv_dist;
    to_block.z *= inv_dist;

    // Check if block is in front of camera
    float depth = to_block.x * cam_forward.x + to_block.y * cam_forward.y + to_block.z * cam_forward.z;
    if (depth <= 0) return false;

    // Block angular size for margin
    float block_angular_size = atanf(BLOCK_RADIUS / (dist > BLOCK_RADIUS ? dist : BLOCK_RADIUS));

    // Project block direction onto right and up vectors
    float right_proj = to_block.x * cam_right.x + to_block.y * cam_right.y + to_block.z * cam_right.z;
    float up_proj = to_block.x * cam_up.x + to_block.y * cam_up.y + to_block.z * cam_up.z;

    // Check if angles are within FOV bounds using pre-computed tangent values
    if (fabsf(right_proj / depth) > (half_horiz_tan + block_angular_size)) return false;
    if (fabsf(up_proj / depth) > (half_vert_tan + block_angular_size)) return false;

    return true;
}

// draw only the visible faces of a cube (faces pointing toward camera and not occluded by neighbors)
void draw_cube_faces(Vector3 pos, float size, Color color, Vector3 cam_pos, Color wire_color, World* world, int block_x, int block_y, int block_z, BlockType block_type, uint8_t exposed_faces, uint8_t face_light[6], bool show_wireframe)
{
    Vector3 to_cam = vec3_sub(cam_pos, pos);
    float h = size / 2.0f;

    // Get texture for this block type
    Texture2D texture = world_get_block_texture(world, block_type);
    bool has_texture = texture.id > 0;

    // Face normals for backface culling (pointing outward)
    Vector3 face_normals[6] = {
        {1, 0, 0},    // +X (right)
        {-1, 0, 0},   // -X (left)
        {0, 1, 0},    // +Y (top)
        {0, -1, 0},   // -Y (bottom)
        {0, 0, 1},    // +Z (front)
        {0, 0, -1}    // -Z (back)
    };

    Vector3 face_positions[6][4] = {
        // right (+X)
        {{pos.x + h, pos.y - h, pos.z - h}, {pos.x + h, pos.y + h, pos.z - h}, {pos.x + h, pos.y + h, pos.z + h}, {pos.x + h, pos.y - h, pos.z + h}},
        // left (-X)
        {{pos.x - h, pos.y - h, pos.z + h}, {pos.x - h, pos.y + h, pos.z + h}, {pos.x - h, pos.y + h, pos.z - h}, {pos.x - h, pos.y - h, pos.z - h}},
        // top (+Y)
        {{pos.x - h, pos.y + h, pos.z + h}, {pos.x + h, pos.y + h, pos.z + h}, {pos.x + h, pos.y + h, pos.z - h}, {pos.x - h, pos.y + h, pos.z - h}},
        // bottom (-Y)
        {{pos.x + h, pos.y - h, pos.z + h}, {pos.x - h, pos.y - h, pos.z + h}, {pos.x - h, pos.y - h, pos.z - h}, {pos.x + h, pos.y - h, pos.z - h}},
        // front (+Z)
        {{pos.x - h, pos.y - h, pos.z + h}, {pos.x + h, pos.y - h, pos.z + h}, {pos.x + h, pos.y + h, pos.z + h}, {pos.x - h, pos.y + h, pos.z + h}},
        // back (-Z)
        {{pos.x + h, pos.y - h, pos.z - h}, {pos.x - h, pos.y - h, pos.z - h}, {pos.x - h, pos.y + h, pos.z - h}, {pos.x + h, pos.y + h, pos.z - h}}
    };

    Vector2 face_uv[6][4] = {
        {{0, 1}, {0, 0}, {1, 0}, {1, 1}},  // +X
        {{1, 1}, {1, 0}, {0, 0}, {0, 1}},  // -X
        {{0, 0}, {1, 0}, {1, 1}, {0, 1}},  // +Y
        {{1, 0}, {0, 0}, {0, 1}, {1, 1}},  // -Y
        {{0, 1}, {1, 1}, {1, 0}, {0, 0}},  // +Z
        {{1, 1}, {0, 1}, {0, 0}, {1, 0}}   // -Z
    };

    // Face shading: how bright each face appears based on orientation
    float face_shading[6] = {
        0.85f,   // +X (right side) - medium
        0.85f,   // -X (left side) - medium
        1.0f,    // +Y (top) - fully lit
        0.6f,    // -Y (bottom) - dark
        0.9f,    // +Z (front) - slightly brighter
        0.8f     // -Z (back) - slightly darker
    };

    // OPTIMIZED: Calculate per-face lighting based on adjacent air block skylight
    // Instead of averaging all faces, each face gets its own neighbor's light
    Color face_colors[6];
    for (int i = 0; i < 6; i++) {
        // Use pre-baked per-face light provided by meshing step
        uint8_t fl = face_light[i];
        // Convert to brightness: 0=dark(0.3), 15=bright(1.0)
        float face_brightness = face_shading[i] * (0.3f + (fl / 15.0f) * 0.7f);

        face_colors[i].r = (unsigned char)(color.r * face_brightness);
        face_colors[i].g = (unsigned char)(color.g * face_brightness);
        face_colors[i].b = (unsigned char)(color.b * face_brightness);
        face_colors[i].a = color.a;
    }

    if (has_texture) {
        rlSetTexture(texture.id);
    }

    rlDisableBackfaceCulling();

    for (int face = 0; face < 6; face++) {
        // Skip faces that are not exposed to air
        if (!(exposed_faces & (1 << face))) {
            continue;  // Face is occluded by neighbor
        }

        // Backface culling is disabled for block faces here to avoid transient terrain holes
        // when the camera passes near a block plane edge during jumps.

        if (has_texture) {
            rlBegin(RL_QUADS);
            rlColor4ub(face_colors[face].r, face_colors[face].g, face_colors[face].b, face_colors[face].a);

            for (int v = 0; v < 4; v++) {
                rlTexCoord2f(face_uv[face][v].x, face_uv[face][v].y);
                rlVertex3f(face_positions[face][v].x, face_positions[face][v].y, face_positions[face][v].z);
            }
            rlEnd();
        } else {
            DrawTriangle3D(face_positions[face][0], face_positions[face][1], face_positions[face][2], face_colors[face]);
            DrawTriangle3D(face_positions[face][0], face_positions[face][2], face_positions[face][3], face_colors[face]);
        }
    }

    if (has_texture) {
        rlSetTexture(0);
    }

    rlEnableBackfaceCulling();

    // Draw wireframe if enabled
    if (show_wireframe) {
        for (int face = 0; face < 6; face++) {
            // Skip faces that are not exposed or face away from camera
            if (!(exposed_faces & (1 << face))) {
                continue;  // Face is occluded by neighbor
            }

            // Backface culling: skip faces facing away from camera
            float dot = to_cam.x * face_normals[face].x + to_cam.y * face_normals[face].y + to_cam.z * face_normals[face].z;
            if (dot <= 0.0f) {
                continue;  // Face points away from camera
            }

            // Draw wireframe edges for this face (quad outline)
            // Draw 4 edges of the quad
            Vector3* verts = face_positions[face];
            // Edge 0-1
            DrawLine3D(verts[0], verts[1], wire_color);
            // Edge 1-2
            DrawLine3D(verts[1], verts[2], wire_color);
            // Edge 2-3
            DrawLine3D(verts[2], verts[3], wire_color);
            // Edge 3-0
            DrawLine3D(verts[3], verts[0], wire_color);
        }
    }
}

// Check if a chunk's bounding box is within the camera frustum
// This is the most efficient culling - eliminates entire chunks at once before iterating blocks
bool is_chunk_in_frustum(Chunk* chunk, Vector3 cam_pos, Vector3 cam_forward,
                         Vector3 cam_right, Vector3 cam_up, float render_distance,
                         float half_vert_tan, float half_horiz_tan, Vector3 camera_offset)
{
    // Chunk world bounds
    float chunk_min_x = chunk->chunk_x * CHUNK_WIDTH - camera_offset.x;
    float chunk_max_x = chunk_min_x + CHUNK_WIDTH;
    float chunk_min_y = chunk->chunk_y * CHUNK_HEIGHT - camera_offset.y;
    float chunk_max_y = chunk_min_y + CHUNK_HEIGHT;
    float chunk_min_z = chunk->chunk_z * CHUNK_DEPTH - camera_offset.z;
    float chunk_max_z = chunk_min_z + CHUNK_DEPTH;

    // Chunk center and radius for distance/back-plane checks
    float chunk_center_x = (chunk_min_x + chunk_max_x) * 0.5f;
    float chunk_center_y = (chunk_min_y + chunk_max_y) * 0.5f;
    float chunk_center_z = (chunk_min_z + chunk_max_z) * 0.5f;

    float dx = chunk_center_x - cam_pos.x;
    float dy = chunk_center_y - cam_pos.y;
    float dz = chunk_center_z - cam_pos.z;
    float dist_sq = dx*dx + dy*dy + dz*dz;

    // Hard distance limit
    float render_dist_sq = render_distance * render_distance;
    if (dist_sq > render_dist_sq) {
        return false;
    }

    float dist = sqrtf(dist_sq);

    // Back-plane culling: if chunk is behind camera, skip it
    float depth = dx * cam_forward.x + dy * cam_forward.y + dz * cam_forward.z;
    if (depth < -CHUNK_WIDTH) {  // Account for chunk size
        return false;
    }

    // If very close to camera, always render (inside frustum)
    if (dist < BLOCK_NEAR_EXEMPTION_DIST_SQ) {
        return true;
    }

    // Simple bounding sphere frustum test: check if chunk bounding sphere is within FOV
    float inv_dist = 1.0f / (dist > BLOCK_MIN_DIST ? dist : BLOCK_MIN_DIST);
    float norm_dx = dx * inv_dist;
    float norm_dy = dy * inv_dist;
    float norm_dz = dz * inv_dist;

    // Angular size of chunk (using diagonal for safety)
    float chunk_radius = sqrtf(CHUNK_WIDTH*CHUNK_WIDTH + CHUNK_HEIGHT*CHUNK_HEIGHT + CHUNK_DEPTH*CHUNK_DEPTH) * 0.5f;
    float chunk_angular_size = atanf(chunk_radius / dist);

    // Check horizontal FOV
    float right_proj = norm_dx * cam_right.x + norm_dy * cam_right.y + norm_dz * cam_right.z;
    if (fabsf(right_proj / depth) > (half_horiz_tan + chunk_angular_size)) {
        return false;
    }

    // Check vertical FOV
    float up_proj = norm_dx * cam_up.x + norm_dy * cam_up.y + norm_dz * cam_up.z;
    if (fabsf(up_proj / depth) > (half_vert_tan + chunk_angular_size)) {
        return false;
    }

    return true;  // Chunk is in frustum
}

// Raycast from camera to find the block being looked at
// Returns true if a block was hit, false otherwise
// out_block_x/y/z: the coordinates of the block hit
// out_adjacent_x/y/z: the coordinates where a new block would be placed (adjacent to hit block)
bool raycast_block(World* world, Camera3D camera, float max_distance,
                   int* out_block_x, int* out_block_y, int* out_block_z,
                   int* out_adjacent_x, int* out_adjacent_y, int* out_adjacent_z)
{
    Vector3 ray_origin = camera.position;
    Vector3 ray_dir = vec3_normalize(vec3_sub(camera.target, camera.position));

    const float step = 0.1f;  // Step size for raycast iterations
    float distance = 0.0f;

    Vector3 prev_pos = ray_origin;

    while (distance < max_distance) {
        Vector3 current_pos = vec3_add(ray_origin, vec3_scale(ray_dir, distance));

        // Use proper floor for negative coordinates
        int block_x = (int)floorf(current_pos.x);
        int block_y = (int)floorf(current_pos.y);
        int block_z = (int)floorf(current_pos.z);

        // Check if we're in a block
        BlockType block = world_get_block(world, block_x, block_y, block_z);
        if (block != BLOCK_AIR) {
            // We hit a block - the hit block is the current one
            *out_block_x = block_x;
            *out_block_y = block_y;
            *out_block_z = block_z;

            // Adjacent block is where we came from (previous block)
            int prev_block_x = (int)floorf(prev_pos.x);
            int prev_block_y = (int)floorf(prev_pos.y);
            int prev_block_z = (int)floorf(prev_pos.z);

            *out_adjacent_x = prev_block_x;
            *out_adjacent_y = prev_block_y;
            *out_adjacent_z = prev_block_z;

            return true;
        }

        prev_pos = current_pos;
        distance += step;
    }

    return false;  // No block hit
}