/*
 * 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_normal {
    float value[3];
} ta_obj_normal;

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_normal *normals = NULL;
    size_t position_count = 0;
    size_t normal_count = 0;
    size_t position_capacity = 0;
    size_t normal_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] == 'v' && line[1] == 'n' && line[2] == ' ') {
            ta_obj_normal normal;
            if (sscanf(line + 3, "%f %f %f", &normal.value[0], &normal.value[1], &normal.value[2]) != 3) {
                goto done;
            }
            if (normal_count == normal_capacity) {
                size_t next_capacity = normal_capacity == 0 ? 1024 : normal_capacity * 2;
                ta_obj_normal *grown = realloc(normals, next_capacity * sizeof(*grown));
                if (!grown) {
                    goto done;
                }
                normals = grown;
                normal_capacity = next_capacity;
            }
            normals[normal_count++] = normal;
        } else if (line[0] == 'f' && line[1] == ' ') {
            int position_indices[3];
            int normal_indices[3];
            bool has_normals = sscanf(line + 2, "%d//%d %d//%d %d//%d",
                                      &position_indices[0], &normal_indices[0],
                                      &position_indices[1], &normal_indices[1],
                                      &position_indices[2], &normal_indices[2]) == 6;
            if (!has_normals && sscanf(line + 2, "%d %d %d",
                                       &position_indices[0], &position_indices[1], &position_indices[2]) != 3) {
                goto done;
            }
            for (int index = 0; index < 3; index++) {
                if (position_indices[index] <= 0 ||
                    (size_t)position_indices[index] > position_count ||
                    (has_normals && (normal_indices[index] <= 0 ||
                                     (size_t)normal_indices[index] > normal_count))) {
                    goto done;
                }
            }
            float face_normal[3] = {0.0f, 0.0f, 1.0f};
            if (!has_normals) {
                const float *first = positions[position_indices[0] - 1].value;
                const float *second = positions[position_indices[1] - 1].value;
                const float *third = positions[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]};
                face_normal[0] = edge_a[1] * edge_b[2] - edge_a[2] * edge_b[1];
                face_normal[1] = edge_a[2] * edge_b[0] - edge_a[0] * edge_b[2];
                face_normal[2] = edge_a[0] * edge_b[1] - edge_a[1] * edge_b[0];
                float length = sqrtf(face_normal[0] * face_normal[0] + face_normal[1] * face_normal[1] + face_normal[2] * face_normal[2]);
                if (length > 0.0f) {
                    face_normal[0] /= length;
                    face_normal[1] /= length;
                    face_normal[2] /= length;
                }
            }
            for (int index = 0; index < 3; index++) {
                ta_obj_vertex vertex;
                memcpy(vertex.position, positions[position_indices[index] - 1].value, sizeof(vertex.position));
                if (has_normals) {
                    memcpy(vertex.normal, normals[normal_indices[index] - 1].value, sizeof(vertex.normal));
                } else {
                    memcpy(vertex.normal, face_normal, sizeof(vertex.normal));
                }
                if (!ta_obj_push_vertex(mesh, &vertex_capacity, &vertex)) {
                    goto done;
                }
            }
        }

        if (!next_line) {
            break;
        }
        line = next_line + 1;
    }

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

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