/*
 * Tuxánci 2 - A first person shooter
 * Copyright (C) 2007-2011  Tuxánci Development Team
 * Copyright (C) 2025-2026  Connor Thomson
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <stdbool.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "obj.h"

typedef struct ta_obj_position {
    float value[3];
} ta_obj_position;

typedef struct ta_obj_face {
    int position_indices[3];
} ta_obj_face;

static bool ta_obj_push_vertex(ta_obj_mesh *mesh, size_t *capacity, const ta_obj_vertex *vertex) {
    if (mesh->vertex_count == *capacity) {
        size_t next_capacity = *capacity == 0 ? 1024 : *capacity * 2;
        ta_obj_vertex *vertices = realloc(mesh->vertices, next_capacity * sizeof(*vertices));
        if (!vertices) {
            return false;
        }
        mesh->vertices = vertices;
        *capacity = next_capacity;
    }
    mesh->vertices[mesh->vertex_count++] = *vertex;
    return true;
}

bool ta_obj_parse(const unsigned char *data, size_t size, ta_obj_mesh *mesh) {
    ta_obj_position *positions = NULL;
    ta_obj_face *faces = NULL;
    float *normal_accum = NULL;
    size_t position_count = 0;
    size_t face_count = 0;
    size_t position_capacity = 0;
    size_t face_capacity = 0;
    size_t vertex_capacity = 0;
    bool success = false;

    memset(mesh, 0, sizeof(*mesh));
    char *text = malloc(size + 1);
    if (!text) {
        return false;
    }
    memcpy(text, data, size);
    text[size] = '\0';

    char *line = text;
    while (line && *line) {
        char *next_line = strchr(line, '\n');
        if (next_line) {
            *next_line = '\0';
        }

        if (line[0] == 'v' && line[1] == ' ') {
            ta_obj_position position;
            if (sscanf(line + 2, "%f %f %f", &position.value[0], &position.value[1], &position.value[2]) != 3) {
                goto done;
            }
            if (position_count == position_capacity) {
                size_t next_capacity = position_capacity == 0 ? 1024 : position_capacity * 2;
                ta_obj_position *grown = realloc(positions, next_capacity * sizeof(*grown));
                if (!grown) {
                    goto done;
                }
                positions = grown;
                position_capacity = next_capacity;
            }
            positions[position_count++] = position;
        } else if (line[0] == 'f' && line[1] == ' ') {
            ta_obj_face face;
            int discarded_normal_indices[3];
            bool has_normals = sscanf(line + 2, "%d//%d %d//%d %d//%d",
                                      &face.position_indices[0], &discarded_normal_indices[0],
                                      &face.position_indices[1], &discarded_normal_indices[1],
                                      &face.position_indices[2], &discarded_normal_indices[2]) == 6;
            if (!has_normals && sscanf(line + 2, "%d %d %d",
                                       &face.position_indices[0], &face.position_indices[1], &face.position_indices[2]) != 3) {
                goto done;
            }
            for (int index = 0; index < 3; index++) {
                if (face.position_indices[index] <= 0 || (size_t)face.position_indices[index] > position_count) {
                    goto done;
                }
            }
            if (face_count == face_capacity) {
                size_t next_capacity = face_capacity == 0 ? 1024 : face_capacity * 2;
                ta_obj_face *grown = realloc(faces, next_capacity * sizeof(*grown));
                if (!grown) {
                    goto done;
                }
                faces = grown;
                face_capacity = next_capacity;
            }
            faces[face_count++] = face;
        }
      
        if (!next_line) {
            break;
        }
        line = next_line + 1;
    }

    if (position_count == 0 || face_count == 0) {
        goto done;
    }

    normal_accum = calloc(position_count * 3, sizeof(*normal_accum));
    if (!normal_accum) {
        goto done;
    }

    for (size_t index = 0; index < face_count; index++) {
        const float *first = positions[faces[index].position_indices[0] - 1].value;
        const float *second = positions[faces[index].position_indices[1] - 1].value;
        const float *third = positions[faces[index].position_indices[2] - 1].value;
        float edge_a[3] = {second[0] - first[0], second[1] - first[1], second[2] - first[2]};
        float edge_b[3] = {third[0] - first[0], third[1] - first[1], third[2] - first[2]};
        float face_normal[3] = {
            edge_a[1] * edge_b[2] - edge_a[2] * edge_b[1],
            edge_a[2] * edge_b[0] - edge_a[0] * edge_b[2],
            edge_a[0] * edge_b[1] - edge_a[1] * edge_b[0],
        };
        for (int corner = 0; corner < 3; corner++) {
            size_t position_index = (size_t)(faces[index].position_indices[corner] - 1);
            normal_accum[position_index * 3 + 0] += face_normal[0];
            normal_accum[position_index * 3 + 1] += face_normal[1];
            normal_accum[position_index * 3 + 2] += face_normal[2];
        }
    }

    for (size_t index = 0; index < position_count; index++) {
        float *normal = &normal_accum[index * 3];
        float length = sqrtf(normal[0] * normal[0] + normal[1] * normal[1] + normal[2] * normal[2]);
        if (length > 0.0f) {
            normal[0] /= length;
            normal[1] /= length;
            normal[2] /= length;
        } else {
            normal[0] = 0.0f;
            normal[1] = 0.0f;
            normal[2] = 1.0f;
        }
    }

    for (size_t index = 0; index < face_count; index++) {
        for (int corner = 0; corner < 3; corner++) {
            size_t position_index = (size_t)(faces[index].position_indices[corner] - 1);
            ta_obj_vertex vertex;
            memcpy(vertex.position, positions[position_index].value, sizeof(vertex.position));
            memcpy(vertex.normal, &normal_accum[position_index * 3], sizeof(vertex.normal));
            if (!ta_obj_push_vertex(mesh, &vertex_capacity, &vertex)) {
                goto done;
            }
        }
    }

    success = mesh->vertex_count > 0;
done:
    if (!success) {
        ta_obj_free(mesh);
    }
    free(positions);
    free(faces);
    free(normal_accum);
    free(text);
    return success;
}

void ta_obj_free(ta_obj_mesh *mesh) {
    free(mesh->vertices);
    mesh->vertices = NULL;
    mesh->vertex_count = 0;
}