#if defined(GUF_STR_IMPL_STATIC)
    #define GUF_STR_KWRDS static
#else
    #define GUF_STR_KWRDS
#endif

#ifndef GUF_STR_H
#define GUF_STR_H
#include "guf_common.h"
#include "guf_alloc.h"
#include "guf_str_view_type.h"
#include "guf_utf8.h"
#include "guf_hash.h"

// cf. libc++ short-string optimisation: https://joellaity.com/2020/01/31/string.html (last-retrieved 2025-03-10)

typedef struct guf_str_internal_long_ { 
    size_t capacity; // If long string: capacity's least significant bit always set to 1 (or its most significant bit for big-endian platforms); the actual capacity must be even
    size_t size; 
    char *c_str;
} guf_str_internal_long_; 

#define GUF_STR_SSO_BUF_CAP (sizeof(guf_str_internal_long_) - sizeof(unsigned char)) /* 23 bytes on 64-bit platforms, 11 bytes on 32-bit platforms */

#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) || (defined(__cplusplus) && __cplusplus >= 201103L)
    static_assert(GUF_STR_SSO_BUF_CAP > 0, "GUF_STR_SSO_BUF_CAP < 0 (this is very weird)"); // Basically cannot fail. 
    static_assert(GUF_STR_SSO_BUF_CAP < 0x80, "GUF_STR_SSO_BUF_CAP >= 128 (no support for platforms with wordsize >= 512-bits)"); // Could fail on hypothetical platforms with 512-bit wordsize (and above).
#endif

typedef struct guf_str_internal_short_ { 
    unsigned char size; // size overlaps with the first byte of guf_str_internal_long_.capacity [1]
    char c_str[GUF_STR_SSO_BUF_CAP];
} guf_str_internal_short_; 

/*
    [1] The first byte of guf_str_internal_long_.capacity is its least-significant-byte on little-endian
        platforms, and its most-significant byte on big-endian platforms.
*/

typedef struct guf_str {
    union { 
        guf_str_internal_long_ lng; 
        guf_str_internal_short_ shrt;
    } data; // 24 bytes on 64-bit platforms, 12 bytes on 32-bit platforms.
    guf_allocator *allocator; // Wasteful (8 bytes on 64-bit platforms...), but keeping this pointer also allows us to have "read-only strings" (a string is read-only if allocator == NULL)
} guf_str; // Total: 32 bytes on 64-bit platforms, 16 bytes on 32-bit platforms.


#define GUF_CSTR_TO_VIEW(CSTR) ((guf_str_view){.str = (CSTR), .len = (ptrdiff_t)strlen((CSTR))})
#define GUF_CSTR_LIT_TO_VIEW(CSTR) ((guf_str_view){.str = (CSTR), .len = (ptrdiff_t)sizeof((CSTR)) - 1})
#define GUF_STR_TO_VIEW(GUF_STR_PTR) ((guf_str_view){.str = guf_str_const_cstr((GUF_STR_PTR)), .len = (ptrdiff_t)guf_str_len((GUF_STR_PTR))})
#define GUF_CSTR_TO_READONLY_STR(CSTR) ((guf_str){.allocator = NULL, .data.lng.c_str = (CSTR), .data.lng.size = strlen(CSTR) + 1, .data.lng.capacity = 0})
#ifdef __cplusplus
    // Standard C++ does not have compound literals like C99...
    #define GUF_CSTR_TO_VIEW_CPP(CSTR) guf_str_view{.str = (CSTR), .len = (ptrdiff_t)strlen(CSTR)}
    #define GUF_CSTR_LIT_TO_VIEW_CPP(CSTR) guf_str_view{.str = (CSTR), .len = (ptrdiff_t)sizeof(CSTR) - 1}
#endif

// guf_str_view:
GUF_STR_KWRDS bool guf_str_view_is_valid(guf_str_view sv);
GUF_STR_KWRDS guf_str guf_str_substr_cpy(guf_str_view str, ptrdiff_t pos, size_t count); // not necessary
GUF_STR_KWRDS guf_str_view guf_substr_view(guf_str_view str, ptrdiff_t pos, ptrdiff_t count);

GUF_STR_KWRDS guf_str_view guf_str_view_trim_left(guf_str_view str);
GUF_STR_KWRDS guf_str_view guf_str_view_trim_right(guf_str_view str);

GUF_STR_KWRDS guf_hash_size_t guf_str_view_hash(const guf_str_view *sv);
GUF_STR_KWRDS uint64_t guf_str_view_hash64(const guf_str_view *sv);
GUF_STR_KWRDS uint32_t guf_str_view_hash32(const guf_str_view *sv);

GUF_STR_KWRDS bool guf_str_view_equal(const guf_str_view* a, const guf_str_view* b);
GUF_STR_KWRDS bool guf_str_view_equal_val_arg(guf_str_view a_val, guf_str_view b_val);
GUF_STR_KWRDS int guf_str_view_cmp(const void *str_view_a, const void *str_view_b);  // For qsort etc.

GUF_STR_KWRDS guf_str_view guf_str_next_tok(guf_str_view *input, const guf_str_view *delims, ptrdiff_t num_delims, const guf_str_view *preserved_delims, ptrdiff_t num_preserved_delims);

// guf_str:

// DONE:
GUF_STR_KWRDS guf_str *guf_str_try_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc);

GUF_STR_KWRDS guf_str *guf_str_try_init_from_cstr(guf_str *str, const char* c_str, guf_allocator *alloc, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_init_from_cstr(guf_str *str, const char* c_str, guf_allocator *alloc);

GUF_STR_KWRDS guf_str guf_str_try_new(guf_str_view str_view, guf_allocator *alloc, guf_err *err);
GUF_STR_KWRDS guf_str guf_str_new(guf_str_view str_view, guf_allocator *alloc);

GUF_STR_KWRDS void guf_str_free(guf_str *str, void *ctx);
GUF_STR_KWRDS guf_str *guf_str_copy(guf_str *dst, const guf_str *src, void *ctx);
GUF_STR_KWRDS guf_str *guf_str_move(guf_str *dst, guf_str *src, void *ctx);

// TODO:
GUF_STR_KWRDS guf_str guf_str_try_new_substr(guf_str_view str_view, ptrdiff_t pos, ptrdiff_t len, guf_allocator *alloc, guf_err *err);
GUF_STR_KWRDS guf_str guf_str_new_substr(guf_str_view str_view, ptrdiff_t pos, ptrdiff_t len, guf_allocator *alloc);

// TODO:
GUF_STR_KWRDS bool guf_str_equal(const guf_str *a, const guf_str *b);
GUF_STR_KWRDS bool guf_str_equals_cstr(const guf_str *a, const char *c_str);
GUF_STR_KWRDS bool guf_str_equals_strview(const guf_str *a,  guf_str_view b);

// DONE: 
GUF_STR_KWRDS guf_str *guf_str_try_append_char(guf_str *str, char c, ptrdiff_t times, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_append_char(guf_str *str, char c, ptrdiff_t times);
GUF_STR_KWRDS guf_str *guf_str_try_append_one_char(guf_str *str, char c, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_append_one_char(guf_str *str, char c);

GUF_STR_KWRDS guf_str *guf_str_try_append(guf_str *str, guf_str_view sv, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_append(guf_str *str, guf_str_view sv);

GUF_STR_KWRDS guf_str *guf_str_try_append_cstr(guf_str *str, const char *c_str, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_append_cstr(guf_str *str, const char *c_str);


GUF_STR_KWRDS guf_str *guf_str_substr(guf_str* str, size_t pos, size_t count);

// DONE
GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t min_capacity, guf_err *err); 
GUF_STR_KWRDS guf_str *guf_str_reserve(guf_str *str, ptrdiff_t min_capacity); 

// TODO:
GUF_STR_KWRDS guf_str *guf_str_try_shrink_to_fit(guf_str *str, guf_err *err);
GUF_STR_KWRDS guf_str *guf_str_shrink_to_fit(guf_str *str);

// TODO:
GUF_STR_KWRDS char guf_str_pop_back(guf_str *str); 
GUF_STR_KWRDS char guf_str_pop_front(guf_str *str);

// TODO:
GUF_STR_KWRDS char *guf_str_at(guf_str *str, size_t idx);
GUF_STR_KWRDS char *guf_str_back(guf_str *str); 
GUF_STR_KWRDS char *guf_str_front(guf_str *str); 

// DONE: 
GUF_STR_KWRDS const char *guf_str_const_cstr(const guf_str *str);
GUF_STR_KWRDS char *guf_str_try_get_cstr(guf_str *str, guf_err *err); // Error if str is readonly.
GUF_STR_KWRDS char *guf_str_cstr(guf_str *str); // Panics if str is readonly.

GUF_STR_KWRDS ptrdiff_t guf_str_len(const guf_str *str);      // The length (in chars) without the final zero-terminator. 
GUF_STR_KWRDS ptrdiff_t guf_str_capacity(const guf_str *str); // The capacity (in chars) without the final zero-terminator. 

GUF_STR_KWRDS bool guf_str_is_short(const guf_str *str);
GUF_STR_KWRDS bool guf_str_is_readonly(const guf_str *str);
GUF_STR_KWRDS bool guf_str_is_valid(const guf_str *str);

GUF_STR_KWRDS guf_str guf_str_new_uninitialised(void);
GUF_STR_KWRDS bool guf_str_is_uninit(const guf_str *str);


#endif

// #define GUF_STR_IMPL_STATIC /* debug */

#if defined(GUF_STR_IMPL) || defined(GUF_STR_IMPL_STATIC)

#ifdef __cplusplus
    #error "Must compile guf_str as C99 (or above) because type-punning with unions is undefined behaviour in C++"
#endif

#include "guf_common.h"
#include "guf_math.h"
#include <string.h>

#ifdef GUF_STR_IMPL
    #define GUF_UTF8_IMPL
#else
    #define GUF_UTF8_IMPL_STATIC
#endif
#include "guf_utf8.h"

// TODO: find_first_of

// guf_str:
#if defined(GUF_PLATFORM_LITTLE_ENDIAN)
    #define GUF_STR_IS_LONG_MASK ((unsigned char)1)        /* binary 0000.0001 */
    #define GUF_STR_GET_CAP_MASK (~(size_t)1)              /* binary 1111.1111 (1111.1111)* 1111.1110 */

    static inline void guf_str_set_lng_cap_(guf_str *str, size_t cap_with_null)
    {
        GUF_ASSERT(cap_with_null % 2 == 0);
        GUF_ASSERT(cap_with_null <= PTRDIFF_MAX);
        GUF_ASSERT(cap_with_null > GUF_STR_SSO_BUF_CAP);
        str->data.lng.capacity = cap_with_null | ((size_t)1);
    }
    static inline void guf_str_set_shrt_size_(guf_str *str, unsigned char size_with_null)
    {
        GUF_ASSERT(size_with_null < GUF_STR_SSO_BUF_CAP && size_with_null < 0x80);
        str->data.shrt.size = (unsigned char)(size_with_null << 1);
    }
#elif defined(GUF_PLATFORM_BIG_ENDIAN)
    #define GUF_STR_IS_LONG_MASK ((unsigned char)0x80)      /* binary 1000 0000 */
    #define GUF_STR_GET_CAP_MASK ((size_t)SIZE_MAX >> 1u) /* binary 0111.1111 (1111.1111)* 1111.1111 */

    static inline void guf_str_set_lng_cap_(guf_str *str, size_t cap_with_null)
    {
        GUF_ASSERT(cap_with_null % 2 == 0);
        GUF_ASSERT(cap_with_null <= PTRDIFF_MAX);
        GUF_ASSERT(cap_with_null > GUF_STR_SSO_BUF_CAP);
        str->data.lng.capacity = ~GUF_STR_GET_CAP_MASK | (cap_with_null >> 1);
    }
    static inline void guf_str_set_shrt_size_(guf_str *str, unsigned char size_with_null)
    {
        GUF_ASSERT(size_with_null < GUF_STR_SSO_BUF_CAP && size_with_null < 0x80);
        str->data.shrt.size = size_with_null;
    }
#else
    #error "guf_str: neither GUF_PLATFORM_LITTLE_ENDIAN nor GUF_PLATFORM_BIG_ENDIAN is defined"
#endif

GUF_STR_KWRDS bool guf_str_is_readonly(const guf_str *str)
{
    GUF_ASSERT(str);
    return !str->allocator;
}

static bool guf_str_is_short_internal_(const guf_str *str)
{
    if (guf_str_is_readonly(str)) {
        return false;
    }
    const unsigned char first_byte = str->data.shrt.size; // union type-punning (only legal in C99 and above; undefined behaviour in C++ I think).
    return (first_byte & GUF_STR_IS_LONG_MASK) == 0;
}

// Returns the capacity without the final null-terminator
static size_t guf_str_cap_internal_(const guf_str *str)
{    
    if (guf_str_is_short_internal_(str)) {
        return GUF_STR_SSO_BUF_CAP - 1;
    } else if (guf_str_is_readonly(str)) {
        return 0;
    } else {
        // Precondition: all capacities for data.lng must be even.
        #if defined(GUF_PLATFORM_LITTLE_ENDIAN)
            GUF_ASSERT(str->data.lng.capacity & ~GUF_STR_GET_CAP_MASK); // Assert the is_long bit is actually set. 
            const size_t cap_with_null = str->data.lng.capacity & GUF_STR_GET_CAP_MASK; 
            GUF_ASSERT(cap_with_null % 2 == 0);
        #elif defined(GUF_PLATFORM_BIG_ENDIAN)
            GUF_ASSERT(str->data.lng.capacity & ~GUF_STR_GET_CAP_MASK); // Assert the is_long bit is actually set. 
            const size_t cap_with_null = (str->data.lng.capacity & GUF_STR_GET_CAP_MASK) << 1; 
            GUF_ASSERT(cap_with_null % 2 == 0);
        #endif
        GUF_ASSERT(cap_with_null > 0 && cap_with_null > GUF_STR_SSO_BUF_CAP);
        GUF_ASSERT(cap_with_null <= PTRDIFF_MAX);
        return cap_with_null - 1;
    }
}

static size_t guf_str_size_internal_(const guf_str *str)
{
    if (guf_str_is_short_internal_(str)) {
        GUF_ASSERT(str->data.shrt.size > 0);
        #if defined(GUF_PLATFORM_LITTLE_ENDIAN)
            const size_t size = (str->data.shrt.size >> 1);
        #elif defined(GUF_PLATFORM_BIG_ENDIAN)
            const size_t size = (str->data.shrt.size);
        #endif
        GUF_ASSERT(size > 0 && size <= GUF_STR_SSO_BUF_CAP);
        return size;
    } else {
        const size_t size = str->data.lng.size;
        GUF_ASSERT(size > 0 && size <= PTRDIFF_MAX);
        return size;
    }
}

static size_t guf_str_len_internal_(const guf_str *str)
{
    const size_t size = guf_str_size_internal_(str);
    GUF_ASSERT(size > 0);
    if (size == 0) {
        return 0;
    } else {
        return size - 1;
    }
}

GUF_STR_KWRDS bool guf_str_is_short(const guf_str *str)
{
    GUF_ASSERT(guf_str_is_valid(str));
    return guf_str_is_short_internal_(str);
}

GUF_STR_KWRDS ptrdiff_t guf_str_capacity(const guf_str *str)
{
    GUF_ASSERT(guf_str_is_valid(str));
    return (ptrdiff_t)guf_str_cap_internal_(str);
}

GUF_STR_KWRDS ptrdiff_t guf_str_len(const guf_str *str)
{
    GUF_ASSERT(guf_str_is_valid(str));
    return (ptrdiff_t)guf_str_len_internal_(str);
}

GUF_STR_KWRDS bool guf_str_is_valid(const guf_str *str)
{
    GUF_ASSERT(str);
    if (!str || guf_str_is_uninit(str)) {
        return false;
    }
    const bool is_readonly = !str->allocator;
    if (is_readonly) {
        bool valid_readonly = str->data.lng.c_str && str->data.lng.capacity == 0 && str->data.lng.size > 0;
        return valid_readonly;
    }
    const bool valid_allocator = str->allocator && str->allocator->alloc && str->allocator->free && str->allocator->realloc;
    if (!valid_allocator) {
        return false;
    }
    
    if (guf_str_is_short_internal_(str)) {
        const size_t size = guf_str_size_internal_(str); // len + 1
        return size > 0 && size <= GUF_STR_SSO_BUF_CAP && str->data.shrt.c_str[size - 1] == '\0';
    } else {
        const size_t cap_with_null = guf_str_cap_internal_(str) + 1;
        const bool valid_cap = cap_with_null > GUF_STR_SSO_BUF_CAP && cap_with_null <= PTRDIFF_MAX && (cap_with_null % 2 == 0);
        return valid_cap && str->data.lng.c_str && str->data.lng.size > 0 && str->data.lng.size <= cap_with_null;
    }
}

GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t new_cap_min, guf_err *err)
{
    GUF_ASSERT(guf_str_is_valid(str));
    GUF_ASSERT(!guf_str_is_readonly(str));

    const size_t old_cap_with_null = guf_str_cap_internal_(str) + 1;
    const size_t len_with_null = guf_str_len_internal_(str) + 1;

    if (new_cap_min <= (ptrdiff_t)old_cap_with_null) { // No need to grow.
        guf_err_set_if_not_null(err, GUF_ERR_NONE);
        return str;
    }

    if (new_cap_min >= PTRDIFF_MAX - 1) {
        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_reserve: new_cap_min >= PTRDIFF_MAX - 1");
        return NULL;
    }

    size_t new_cap_min_with_null = (size_t)new_cap_min + 1; 
    if (new_cap_min_with_null % 2 != 0) { // Only an even lng.capacity is allowed.
        new_cap_min_with_null += 1;
    }

    // Try if we can reach at least new_cap_min_with_null by doubling the capacity.
    const size_t GUF_STR_GROWTH_FAC = 2;
    size_t times_two_cap = old_cap_with_null * GUF_STR_GROWTH_FAC;
    if (guf_mul_is_overflow_size_t(old_cap_with_null, GUF_STR_GROWTH_FAC) || times_two_cap >= PTRDIFF_MAX) {
        times_two_cap = (PTRDIFF_MAX % 2 == 0) ? PTRDIFF_MAX : PTRDIFF_MAX - 1;
    }
    if (times_two_cap > new_cap_min_with_null) {
        new_cap_min_with_null = times_two_cap;
    } 
    GUF_ASSERT(new_cap_min_with_null >= len_with_null && new_cap_min_with_null <= PTRDIFF_MAX);

    const size_t space_remaining = (new_cap_min_with_null - len_with_null);
    if (new_cap_min_with_null < (PTRDIFF_MAX - 8) && space_remaining < 4) {
        new_cap_min_with_null += 4 - space_remaining; // Have some leeway.
    }

    GUF_ASSERT(new_cap_min_with_null % 2 == 0);

    if (guf_str_is_short_internal_(str)) { // a.) Was short string -> need initial allocation.
        char *c_str_new = str->allocator->alloc(new_cap_min_with_null, str->allocator->ctx);
        if (!c_str_new) {
            guf_err_set_or_panic(err, GUF_ERR_ALLOC_FAIL, "in guf_str_try_grow_if_necessary: Initial allocation failed.");
            return NULL;
        }
        memcpy(c_str_new, str->data.shrt.c_str, len_with_null);
        str->data.lng.c_str = c_str_new;
        guf_str_set_lng_cap_(str, new_cap_min_with_null);
    } else { // b) Was long string -> need re-allocation
        char *c_str_new = str->allocator->realloc(str->data.lng.c_str, old_cap_with_null, new_cap_min_with_null, str->allocator->ctx);
        if (!c_str_new) {
            guf_err_set_or_panic(err, GUF_ERR_ALLOC_FAIL, "in guf_str_try_grow_if_necessary: re-allocation failed.");
            return NULL;
        }
        str->data.lng.c_str = c_str_new;
        guf_str_set_lng_cap_(str, new_cap_min_with_null);
    }

    GUF_ASSERT(guf_str_is_valid(str));
    guf_err_set_if_not_null(err, GUF_ERR_NONE);
    return str;
}

static char *guf_str_get_cstr_internal_(guf_str *str)
{
    if (guf_str_is_short(str)) {
        return str->data.shrt.c_str;
    } else {
        return str->data.lng.c_str;
    }
}

static const char *guf_str_get_const_cstr_internal_(const guf_str *str)
{
    if (guf_str_is_short(str)) {
        return str->data.shrt.c_str;
    } else {
        return str->data.lng.c_str;
    }
}

GUF_STR_KWRDS const char *guf_str_const_cstr(const guf_str *str)
{
    GUF_ASSERT(guf_str_is_valid(str));
    const char* c_str = guf_str_get_const_cstr_internal_(str);
    GUF_ASSERT(c_str);
    return c_str;
}

GUF_STR_KWRDS char *guf_str_try_get_cstr(guf_str *str, guf_err *err)
{
    GUF_ASSERT(guf_str_is_valid(str));
    if (guf_str_is_readonly(str)) {
        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, "in guf_str_try_get_cstr: cannot return non-const char pointer because str is readonly");
        return NULL;
    }
    char *c_str = guf_str_get_cstr_internal_(str);
    GUF_ASSERT(c_str);
    return c_str;
}

GUF_STR_KWRDS char *guf_str_cstr(guf_str *str)
{
    return guf_str_try_get_cstr(str, NULL);
}


static void guf_str_set_len_internal_(guf_str *str, size_t len)
{
    GUF_ASSERT(len <= guf_str_cap_internal_(str));
    GUF_ASSERT(!guf_str_is_readonly(str));
    const size_t len_with_null = len + 1;
    if (guf_str_is_short_internal_(str)) {
        GUF_ASSERT(len_with_null <= UCHAR_MAX)
        guf_str_set_shrt_size_(str, (unsigned char)len_with_null);
    } else {
        str->data.lng.size = len_with_null;
    }
}

GUF_STR_KWRDS guf_str guf_str_new_uninitialised(void)
{
    guf_str str = {.allocator = NULL, .data.shrt.size = 0, .data.shrt.c_str[0] = '\0'};
    return str;
}

GUF_STR_KWRDS bool guf_str_is_uninit(const guf_str *str)
{
    GUF_ASSERT(str);
    return !str->allocator && !str->data.shrt.size && str->data.shrt.c_str[0] == '\0';
}


GUF_STR_KWRDS guf_str *guf_str_init_empty(guf_str *str, guf_allocator *allocator)
{
    GUF_ASSERT(str && allocator);
    str->allocator = allocator;
    guf_str_set_shrt_size_(str, 1);
    str->data.shrt.c_str[0] = '\0';
    return str;
}


GUF_STR_KWRDS guf_str *guf_str_try_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc, guf_err *err)
{
    if (!str) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_init: str is NULL");
        return NULL;
    } else if (!alloc || !alloc->alloc || !alloc->realloc || !alloc->free) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_init: alloc (or allocs function pointers) is/are NULL");
        return NULL;
    }

    if (!guf_str_view_is_valid(str_view)) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_init: invalid str_view");
        return NULL;
    }

    guf_str_init_empty(str, alloc);

    if (str_view.len == 0) {
        GUF_ASSERT(!guf_str_is_readonly(str));
        GUF_ASSERT(guf_str_is_valid(str));
        return str;
    }
    GUF_ASSERT(str_view.str && str_view.len > 0);

    guf_str_try_reserve(str, str_view.len, err);
    if (err && *err != GUF_ERR_NONE) {
        guf_panic(*err, "in guf_str_try_init: Initial allocation failed");
        return NULL;
    }
    GUF_ASSERT(guf_str_len_internal_(str) == 0);
    GUF_ASSERT(guf_str_cap_internal_(str) >= (size_t)str_view.len);
    GUF_ASSERT(!guf_str_is_readonly(str));

    char *c_str_dst = guf_str_get_cstr_internal_(str);
    GUF_ASSERT_RELEASE(c_str_dst);
    memcpy(c_str_dst, str_view.str, str_view.len);
    c_str_dst[str_view.len] = '\0';

    GUF_ASSERT(!guf_str_is_readonly(str));
    GUF_ASSERT(guf_str_is_valid(str));
    guf_err_set_if_not_null(err, GUF_ERR_NONE);
    return str;
}

GUF_STR_KWRDS guf_str *guf_str_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc)
{
    return guf_str_try_init(str, str_view, alloc, NULL);
}

GUF_STR_KWRDS guf_str guf_str_try_new(guf_str_view str_view, guf_allocator *alloc, guf_err *err)
{
    guf_str str = guf_str_new_uninitialised();
    guf_str_try_init(&str, str_view, alloc, err);
    if (err && *err != GUF_ERR_NONE) {
        guf_err_set_or_panic(err, *err, "in guf_str_try_new: failed init");
        return guf_str_new_uninitialised();
    } else {
        GUF_ASSERT(!guf_str_is_uninit(&str));
        return str;
    }
}

GUF_STR_KWRDS void guf_str_free(guf_str *str, void *ctx)
{
    (void)ctx;

    if (!str || guf_str_is_uninit(str)) {
        return;
    } else if (guf_str_is_readonly(str)) { // Don't need to de-allocate anything for read-only strings.
        *str = guf_str_new_uninitialised();
        return;
    } else if (!guf_str_is_short(str)) { // Need to de-allocate. 
        GUF_ASSERT(guf_str_capacity(str) < PTRDIFF_MAX);
        const ptrdiff_t cap_with_null = guf_str_capacity(str) + 1;
        GUF_ASSERT((cap_with_null % 2) == 0);
        char *c_str = guf_str_cstr(str); 
        GUF_ASSERT(str->allocator->free);
        if (str->allocator->free) {
            str->allocator->free(c_str, cap_with_null, str->allocator->ctx);
        }
        *str = guf_str_new_uninitialised();
        return;
    } else {
        GUF_ASSERT(guf_str_is_short(str));
        *str = guf_str_new_uninitialised();
    }
}

GUF_STR_KWRDS guf_str *guf_str_copy(guf_str *dst, const guf_str *src, void *ctx)
{
    (void)ctx;
    GUF_ASSERT_RELEASE(dst);
    GUF_ASSERT_RELEASE(guf_str_is_valid(src));

    guf_str_init_empty(dst, src->allocator);
    GUF_ASSERT(guf_str_is_short_internal_(dst));

    if (!guf_str_is_short_internal_(src)) {
        const size_t src_cap_with_null = guf_str_cap_internal_(src) + 1;
        char *dst_cstr = src->allocator->alloc(src_cap_with_null, src->allocator->ctx);
        if (!dst_cstr) {
            *dst = guf_str_new_uninitialised();
            return NULL;
        }
        dst->data.lng.c_str = dst_cstr;
        dst->data.lng.capacity = src->data.lng.capacity;
        dst->data.lng.size = src->data.lng.size;
    } else {
        dst->data.shrt.size = src->data.shrt.size;
    }
    
    const size_t src_len_with_null = guf_str_len_internal_(src) + 1;
    GUF_ASSERT(src_len_with_null == (guf_str_len_internal_(dst) + 1));
    GUF_ASSERT(guf_str_is_short(dst) == guf_str_is_short(src));

    const char *src_cstr = guf_str_const_cstr(src);
    char *dst_cstr = guf_str_cstr(dst);
    GUF_ASSERT(src_cstr && dst_cstr);
    memcpy(dst_cstr, src_cstr, src_len_with_null);

    GUF_ASSERT(guf_str_is_valid(dst));
    return dst;
}

GUF_STR_KWRDS guf_str *guf_str_move(guf_str *dst, guf_str *src, void *ctx)
{
    (void)ctx;
    GUF_ASSERT_RELEASE(dst);
    GUF_ASSERT_RELEASE(guf_str_is_valid(src));
    *dst = *src;
    *src = guf_str_new_uninitialised();
    return dst;
}




GUF_STR_KWRDS guf_str *guf_str_try_append_char(guf_str *str, char c, ptrdiff_t times, guf_err *err)
{
    GUF_ASSERT(guf_str_is_valid(str));

   if (guf_str_is_readonly(str)) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_append_char: str is readonly");
        return NULL;
    }

    if (times < 0) {
        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, "in guf_str_try_append_char: repeats < 0");
        return NULL;
    } else if (times == 0) {
        guf_err_set_if_not_null(err, GUF_ERR_NONE);
        return str;
    }

    GUF_ASSERT(guf_str_len_internal_(str) <= guf_str_cap_internal_(str));

    const size_t old_cap = guf_str_cap_internal_(str);
    const size_t old_len = guf_str_len_internal_(str);
    const size_t new_len = old_len + (size_t)times;
    if (new_len <= old_len || new_len > (size_t)PTRDIFF_MAX) { // Handle overflow.
        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_char: new length would overflow ptrdiff_t");
        return NULL;
    } else if (new_len > old_cap) { // Need to grow capacity.
        guf_str_try_reserve(str, new_len, err);
        if (err && *err != GUF_ERR_NONE) {
            guf_err_set_or_panic(err, *err, "in guf_str_try_append_char: failed to reserve capacity");
            return NULL;
        }
    }
    const size_t new_cap = guf_str_cap_internal_(str);
    GUF_ASSERT_RELEASE(new_cap >= new_len && new_cap >= old_cap);
    GUF_ASSERT(guf_str_len_internal_(str) == old_len);
    GUF_ASSERT(((ptrdiff_t)new_cap - (ptrdiff_t)old_len) >= times);

    char *c_str = guf_str_get_cstr_internal_(str);
    for (size_t i = old_len; i < new_len; ++i) {
        c_str[i] = c;
    }
    guf_str_set_len_internal_(str, new_len);
    c_str[new_len] = '\0';

    guf_err_set_if_not_null(err, GUF_ERR_NONE);
    return str;
}

GUF_STR_KWRDS guf_str *guf_str_append_char(guf_str *str, char c, ptrdiff_t times)
{
    return guf_str_try_append_char(str, c, times, NULL);
}

GUF_STR_KWRDS guf_str *guf_str_try_append_one_char(guf_str *str, char c, guf_err *err)
{
    return guf_str_try_append_char(str, c, 1, err);
}

GUF_STR_KWRDS guf_str *guf_str_append_one_char(guf_str *str, char c)
{
    return guf_str_try_append_one_char(str, c, NULL);
}


GUF_STR_KWRDS guf_str *guf_str_try_append(guf_str *str, guf_str_view sv, guf_err *err)
{
    GUF_ASSERT(guf_str_is_valid(str));

    if (!guf_str_view_is_valid(sv)) {
        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, "in guf_str_try_append_view: str_view is invalid");
        return NULL;
    } else if (guf_str_is_readonly(str)) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in in guf_str_try_append_view: str is readonly");
        return NULL;
    }

    if (sv.len == 0) {
        guf_err_set_if_not_null(err, GUF_ERR_NONE);
        return str;
    }
    GUF_ASSERT(sv.str && sv.len > 0);

    const size_t old_cap = guf_str_cap_internal_(str);
    const size_t old_len = guf_str_len_internal_(str);
    const size_t new_len = old_len + (size_t)sv.len;
    if (new_len <= old_len || new_len > (size_t)PTRDIFF_MAX) { // Handle overflow.
        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_view: new length would overflow ptrdiff_t");
        return NULL;
    }  else if (new_len > old_cap) { // Growth necessary.
        guf_str_try_reserve(str, new_len, err);
        if (err && *err != GUF_ERR_NONE) {
            guf_err_set_or_panic(err, *err, "in guf_str_try_append_view: failed to reserve capacity");
            return NULL;
        }
    }

    const size_t new_cap = guf_str_cap_internal_(str);
    GUF_ASSERT_RELEASE(new_cap >= old_cap && new_cap >= new_len);
    GUF_ASSERT(((ptrdiff_t)new_cap - (ptrdiff_t)old_len) >= sv.len);

    char *c_str_dst = guf_str_get_cstr_internal_(str);
    for (size_t dst_i = old_len, src_i = 0; dst_i < new_len; ++dst_i, ++src_i) {
        GUF_ASSERT(src_i < (size_t)sv.len);
        c_str_dst[dst_i] = sv.str[src_i];
    }
    c_str_dst[new_len] = '\0';
    guf_str_set_len_internal_(str, new_len);

    GUF_ASSERT(guf_str_is_valid(str));
    guf_err_set_if_not_null(err, GUF_ERR_NONE);
    return str;
}

GUF_STR_KWRDS guf_str *guf_str_append(guf_str *str, guf_str_view sv)
{
    return guf_str_try_append(str, sv, NULL);
}

GUF_STR_KWRDS guf_str *guf_str_try_append_cstr(guf_str *str, const char *c_str, guf_err *err)
{
    GUF_ASSERT(guf_str_is_valid(str));

    if (!c_str) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_append_cstr: c_str is NULL");
        return NULL;
    } else if (guf_str_is_readonly(str)) {
        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_append_cstr: str is readonly");
        return NULL;
    }

    char *dst_cstr = guf_str_get_cstr_internal_(str);
    size_t i = 0;
    do {
        size_t cap = guf_str_cap_internal_(str); 
        size_t len = guf_str_len_internal_(str);
        GUF_ASSERT(len <= cap);

        if (len == cap) { // Grow if necessary. 
            guf_str_try_reserve(str, cap < PTRDIFF_MAX ? cap + 1 : PTRDIFF_MAX, err);
            if (err && *err != GUF_ERR_NONE) {
                guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_cstr: failed to reserve");
                return NULL;
            }
            cap = guf_str_cap_internal_(str); 
            len = guf_str_len_internal_(str);
        }

        dst_cstr[len] = c_str[i];
        guf_str_set_len_internal_(str, len + 1);
    } while (c_str[i++] != '\0');

    GUF_ASSERT(guf_str_is_valid(str));
    GUF_ASSERT(dst_cstr[guf_str_len_internal_(str)] == '\0');

    guf_err_set_if_not_null(err, GUF_ERR_NONE);
    return str;
}

GUF_STR_KWRDS guf_str *guf_str_append_cstr(guf_str *str, const char *c_str)
{
    return guf_str_try_append_cstr(str, c_str, NULL);
}



// guf_str_view:

GUF_STR_KWRDS bool guf_str_view_is_valid(guf_str_view sv)
{
    if (sv.str) {
        return sv.len >= 0;
    } else {
        return sv.len == 0;
    }
}

GUF_STR_KWRDS guf_str_view guf_str_next_tok(guf_str_view *input, const guf_str_view *delims, ptrdiff_t num_delims, const guf_str_view *preserved_delims, ptrdiff_t num_preserved_delims)
{
    if (input->len <= 0 || input->str == NULL) {
        return (guf_str_view){.str = NULL, .len = 0};
    }

    ptrdiff_t max_delim_len = -1;
    for (ptrdiff_t i = 0; i < num_delims; ++i) {
        if (delims[i].len > max_delim_len) {
            max_delim_len = delims[i].len;
        }
    }

    guf_str_view tok = {.str = input->str, .len = 0};
    guf_str_view prev_input = *input;
    guf_utf8_char ch = {0};

    for (guf_utf8_stat stat = guf_utf8_char_next(&ch, input); stat != GUF_UTF8_READ_DONE; stat = guf_utf8_char_next(&ch, input)) {
        if (stat != GUF_UTF8_READ_VALID) {
            prev_input = *input;
            continue;
        }

        const int num_bytes = guf_utf8_char_num_bytes(&ch);

        for (ptrdiff_t delim_len = GUF_MIN(max_delim_len, prev_input.len); delim_len > 0; --delim_len) {
            guf_str_view delim_candidate = guf_substr_view(prev_input, 0, delim_len);
            for (ptrdiff_t delim_i = 0; delim_i < num_delims; ++delim_i) {
                if (guf_str_view_equal(&delim_candidate, delims + delim_i)) { // Found delim.
                    bool preserved = false; 
                    if (preserved_delims && num_preserved_delims > 0) {
                        for (ptrdiff_t preserved_i = 0; preserved_i < num_preserved_delims; ++preserved_i) {
                            if (guf_str_view_equal(&delim_candidate, preserved_delims + preserved_i)) { 
                                preserved = true;
                                break;
                            }
                        }
                    }
                    if (!preserved) {
                        input->len = prev_input.len - delim_len;
                        input->str = prev_input.len > 0 ? prev_input.str + delim_len : NULL;
                        GUF_ASSERT(input->len >= 0);
                    } else { 
                        input->str -= num_bytes;
                        input->len += num_bytes;
                    }
               
                    if (tok.len == 0) {
                        if (preserved) {
                            input->str += num_bytes;
                            input->len -= num_bytes;
                            return delim_candidate;
                        }
                        tok.str = input->str;
                        goto end;
                    } else {
                        return tok;
                    }
                }
            }
        }
        tok.len += num_bytes;

        end:;
        prev_input = *input;
    }

    return tok;
}

GUF_STR_KWRDS guf_str_view guf_str_view_trim_left_ascii(guf_str_view sv)
{
    if (sv.len <= 0 || sv.str == NULL) {
        return sv;
    }

    for (; sv.len > 0 && guf_char_isspace_ascii(*sv.str); --sv.len, ++sv.str)
    ;

    GUF_ASSERT(sv.len >= 0);
    GUF_ASSERT(sv.len == 0 || !guf_char_isspace_ascii(*sv.str));

    return sv;
}

GUF_STR_KWRDS guf_str_view guf_str_view_trim_right_ascii(guf_str_view sv)
{
    if (sv.len <= 0 || sv.str == NULL) {
        return sv;
    }

    for (; sv.len > 0 && guf_char_isspace_ascii(sv.str[sv.len - 1]); --sv.len)
    ;

    GUF_ASSERT(sv.len >= 0);
    GUF_ASSERT(sv.len == 0 || !guf_char_isspace_ascii(sv.str[sv.len - 1]));

    return sv;
}

GUF_STR_KWRDS guf_str_view guf_str_view_trim_right(guf_str_view sv)
{
    if (sv.len <= 0 || sv.str == NULL) {
        return sv;
    }
    char c = sv.str[sv.len - 1];
    while (sv.len > 0 && sv.str && c != ' ' && c != '\n' && c != '\t' && c != '\v' && c != '\f' && c != '\r') {
        --sv.len; 
        ++sv.str;
        c = sv.str[0];
    }
    return sv;
}

GUF_STR_KWRDS guf_str_view guf_substr_view(guf_str_view str, ptrdiff_t pos, ptrdiff_t count)
{
    GUF_ASSERT(str.str);
    GUF_ASSERT(pos >= 0);
    GUF_ASSERT(count >= 0);

    if (str.len == 0 || count == 0 || pos >= str.len || str.str == NULL) {
        return (guf_str_view){.str = str.str, .len = 0};
    }

    const ptrdiff_t substr_len = pos + count > str.len ? str.len - pos : count;
    GUF_ASSERT(substr_len >= 0);
    GUF_ASSERT(substr_len <= str.len);

    return (guf_str_view){.str = str.str + pos, .len = substr_len};
}  

GUF_STR_KWRDS guf_hash_size_t guf_str_view_hash(const guf_str_view *sv)
{
    GUF_ASSERT(sv);
    if (!sv->str || sv->len <= 0) {
        return GUF_HASH_INIT;
    }
    return guf_hash(sv->str, sv->len, GUF_HASH_INIT);
}

GUF_STR_KWRDS uint64_t guf_str_view_hash64(const guf_str_view *sv)
{
    GUF_ASSERT(sv);
    if (!sv->str || sv->len <= 0) {
        return GUF_HASH64_INIT;
    }
    return guf_hash64(sv->str, sv->len, GUF_HASH64_INIT);
}

GUF_STR_KWRDS uint32_t guf_str_view_hash32(const guf_str_view *sv)
{
    GUF_ASSERT(sv);
    if (!sv->str || sv->len <= 0) {
        return GUF_HASH32_INIT;
    }
    return guf_hash32(sv->str, sv->len, GUF_HASH32_INIT);
}

GUF_STR_KWRDS bool guf_str_view_equal(const guf_str_view* a, const guf_str_view* b)
{
    GUF_ASSERT(a && b);
    if (a->len != b->len) {
        return false;
    }

    if ((!a->str && b->str) || (!b->str && a->str)) {
        return false;
    } else if (!a->str && !b->str) {
        return a->len == b->len;
    }
    GUF_ASSERT(a->str && b->str);

    if (a->len <= 0) {
        return true;
    }
    
    return 0 == memcmp(a->str, b->str, a->len);
}

GUF_STR_KWRDS bool guf_str_view_equal_val_arg(guf_str_view a_val, guf_str_view b_val)
{
    return guf_str_view_equal(&a_val, &b_val);
}

#undef GUF_STR_IMPL
#undef GUF_STR_IMPL_STATIC
#endif /* end impl */

#undef GUF_STR_KWRDS