#ifndef UTIL_H
#define UTIL_H

#include <stdint.h>
#include <string.h>

typedef struct vector_t {
    uint8_t *data;
    int count;
    int capacity;
    int stride;
} vector_t;

/**
 * Zero-initialize a vector with the given element stride.
 *
 * @param v      vector to initialize
 * @param stride byte size of each element
 */
static void vec_init(vector_t *v, int stride) {
    memset(v, 0, sizeof(*v));
    v->stride = stride;
}

/**
 * Grow the vector's backing array to at least min_capacity elements.
 * Doubles capacity (starting at 8) or uses min_capacity, whichever is larger.
 *
 * @param v            vector to grow
 * @param min_capacity minimum element count required
 */
static void vec_grow(vector_t *v, int min_capacity) {
    int new_cap = v->capacity ? v->capacity * 2 : 8;
    if (new_cap < min_capacity) new_cap = min_capacity;
    uint8_t *new_data = (uint8_t*) ALLOC(new_cap * v->stride);
    if (!new_data) {
        EM_ASM({ console.error("vec_grow: ALLOC failed for %d elements of %d bytes", $0, $1); },
               new_cap, v->stride);
        return;
    }
    if (v->data) {
        memcpy(new_data, v->data, v->count * v->stride);
        FREE(v->data);
    }
    v->data = new_data;
    v->capacity = new_cap;
}

/**
 * Append an uninitialized element to the end of the vector. Grows if needed.
 *
 * @param v  vector to push into
 * @return   pointer to the new (uninitialized) element
 */
static void *vec_push(vector_t *v) {
    if (v->count >= v->capacity) vec_grow(v, v->count + 1);
    return v->data + (v->count++) * v->stride;
}

/**
 * Remove the last element from the vector (decrements count, no free).
 *
 * @param v  vector to pop from
 */
static void vec_pop(vector_t *v) {
    if (v->count > 0) v->count--;
}

static void vec_remove_ordered(vector_t *v, int index) {
    if (index < 0 || index >= v->count) return;
    if (index < v->count - 1) {
        memmove(v->data + index * v->stride,
                v->data + (index + 1) * v->stride,
                (v->count - index - 1) * v->stride);
    }
    v->count--;
}

// Remove `count` elements at given indices in a single compaction pass.
// Indices must be sorted in ascending order and must be valid.
static void vec_remove_ordered_bulk(vector_t *v, const int *indices, int count) {
    if (count <= 0) return;
    int write = indices[0];
    for (int k = 0; k < count; k++) {
        int gap_start = indices[k];
        int gap_end   = (k + 1 < count) ? indices[k + 1] : v->count;
        int keep = gap_end - gap_start - 1;
        if (keep > 0) {
            memmove(v->data + write * v->stride,
                    v->data + (gap_start + 1) * v->stride,
                    (size_t)keep * (size_t)v->stride);
            write += keep;
        }
    }
    v->count -= count;
}

static void *vec_insert(vector_t *v, int index) {
    if (index < 0 || index > v->count) return NULL;
    if (v->count >= v->capacity) vec_grow(v, v->count + 1);
    if (index < v->count) {
        memmove(v->data + (index + 1) * v->stride,
                v->data + index * v->stride,
                (v->count - index) * v->stride);
    }
    v->count++;
    return v->data + index * v->stride;
}

/**
 * Remove the element at index by swapping in the last element (O(1)).
 * Order is not preserved.
 *
 * @param v      vector to remove from
 * @param index  index of the element to remove
 */
static void vec_remove(vector_t *v, int index) {
    if (index < 0 || index >= v->count) return;
    if (index < v->count - 1) {
        memcpy(v->data + index * v->stride,
               v->data + (v->count - 1) * v->stride,
               v->stride);
    }
    v->count--;
}

/**
 * Return a pointer to the element at index (no bounds check).
 *
 * @param v      vector to access
 * @param index  element index
 * @return       pointer to the element
 */
static void *vec_get(vector_t *v, int index) {
    return v->data + index * v->stride;
}

/**
 * Free the backing array and reset the vector to empty.
 *
 * @param v  vector to free
 */
static void vec_free(vector_t *v) {
    if (v->data) FREE(v->data);
    v->data = NULL;
    v->count = 0;
    v->capacity = 0;
}

#endif