#ifndef TK_STRINGS_H
#define TK_STRINGS_H

/**
 * @file tk_strings.h
 * @brief Single-header string utilities.
 *
 * Define TK_STRINGS_IMPLEMENTATION in exactly one translation unit before
 * including this file to include the implementation.
 */

#include <stddef.h>
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @brief Count occurrences of a character in a C string.
 * @param str Null-terminated input string. Must not be NULL.
 * @param c Character to count.
 * @return Number of times c appears in str.
 */
size_t tk_str_count_occurrences(const char* str, char c);

/**
 * @brief Count occurrences of a substring in a C string.
 * @param str Null-terminated input string. Must not be NULL.
 * @param substr Null-terminated substring to count. Must not be NULL or empty.
 * @return Number of times substr appears in str.
 */
size_t tk_str_count_occurrences_of_substring(const char* str, const char* substr);

/**
 * @brief Split a string by a delimiter character.
 *
 * This copies all parts. The caller is responsible for freeing each string in
 * result and the result array itself.
 *
 * @param str Null-terminated input string. Must not be NULL.
 * @param delimiter Delimiter character.
 * @param[out] result On success, set to a malloc'd array of char* parts.
 * @return Number of parts. An empty string returns one empty part. If the
 * result array allocation fails, returns 0. If a part allocation fails, returns
 * the number of parts allocated so far and result points to that partial array.
 */
size_t tk_str_split_by_char(const char* str, char delimiter, char*** result);

/**
 * @brief Split a string by a delimiter substring.
 *
 * This copies all parts. The caller is responsible for freeing each string in
 * result and the result array itself.
 *
 * @param str Null-terminated input string. Must not be NULL.
 * @param substr Null-terminated delimiter substring. Must not be NULL or empty.
 * @param[out] result On success, set to a malloc'd array of char* parts.
 * @return Number of parts. If the result array allocation fails, returns 0. If
 * a part allocation fails, returns the number of parts allocated so far and
 * result points to that partial array.
 */
size_t tk_str_split_by_substring(const char* str, const char* substr, char*** result);

/**
 * @brief Convert all lowercase ASCII letters in a string to uppercase.
 * @param str Null-terminated string to modify in place. Must not be NULL.
 */
void tk_str_to_upper(char* str);

/**
 * @brief Convert all uppercase ASCII letters in a string to lowercase.
 * @param str Null-terminated string to modify in place. Must not be NULL.
 */
void tk_str_to_lower(char* str);

/**
 * @brief Concatenate two null-terminated strings into a newly allocated string.
 * @param str1 First input string. Must not be NULL.
 * @param str2 Second input string. Must not be NULL.
 * @return Newly allocated concatenated string, or NULL on allocation error.
 */
char* tk_str_concat(const char* str1, const char* str2);

/**
 * @brief Trim leading and trailing whitespace from a string.
 * @param str Null-terminated input string. Must not be NULL, empty, or all whitespace.
 * @return Newly allocated trimmed string, or NULL on allocation error.
 */
char* tk_str_trim(const char* str);

/**
 * @brief Check whether a string contains a substring.
 * @param str Null-terminated input string. Must not be NULL.
 * @param substr Null-terminated substring to search for. Must not be NULL.
 * @return 1 if str contains substr, 0 otherwise.
 */
uint8_t tk_str_contains(const char* str, const char* substr);

#ifdef __cplusplus
}
#endif

#endif /* TK_STRINGS_H */

#ifdef TK_STRINGS_IMPLEMENTATION

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

inline size_t tk_str_count_occurrences(const char* str, const char c) {
    size_t i = 0;
    size_t count = 0;
    while (str[i] != '\0') {
        if (str[i] == c) {
            count++;
        }
        i++;
    }

    return count;
}

inline size_t tk_str_count_occurrences_of_substring(const char* str, const char* substr) {
    size_t i = 0;
    size_t count = 0;
    while (str[i] != '\0') {
        if (strstr(&str[i], substr) == &str[i]) {
            count++;
        }
        i++;
    }
    return count;
}

inline size_t tk_str_split_by_char(const char* str, const char delimiter, char*** result) {
    const size_t size = tk_str_count_occurrences(str, delimiter);
    char** parts = malloc((size + 1) * sizeof(char*));
    if (parts == NULL) {
        *result = NULL;
        return 0;
    }

    size_t curr_part_idx = 0;
    size_t last_part_end = 0;
    size_t idx = 0;
    while (str[idx] != '\0') {
        if (str[idx] == delimiter) {
            const size_t len = idx - last_part_end;
            char* part = malloc(sizeof(char) * (len + 1));
            if (part == NULL) {
                *result = parts;
                return curr_part_idx;
            }
            memcpy(part, &str[last_part_end], len);
            part[idx - last_part_end] = '\0';

            parts[curr_part_idx++] = part;
            last_part_end = idx;
            last_part_end++;
        }
        idx++;
    }
    char* part = malloc(sizeof(char) * (idx - last_part_end + 1));
    if (part == NULL) {
        *result = parts;
        return curr_part_idx;
    }
    memcpy(part, &str[last_part_end], idx - last_part_end);
    part[idx - last_part_end] = '\0';
    parts[curr_part_idx++] = part;

    *result = parts;
    return curr_part_idx;
}

inline size_t tk_str_split_by_substring(const char* str, const char* substr, char*** result) {
    const size_t size = tk_str_count_occurrences_of_substring(str, substr);
    char** parts = malloc((size + 1) * sizeof(char*));
    if (parts == NULL) {
        *result = NULL;
        return 0;
    }

    size_t curr_part_idx = 0;
    size_t last_part_end = 0;
    size_t idx = 0;

    while (str[idx] != '\0') {
        if (strstr(&str[idx], substr) == &str[idx]) {
            const size_t len = idx - last_part_end;
            char* part = malloc(sizeof(char) * (len + 1));
            if (part == NULL) {
                *result = parts;
                return curr_part_idx;
            }
            memcpy(part, &str[last_part_end], len);
            part[len] = '\0';

            parts[curr_part_idx++] = part;
            last_part_end = idx;
            last_part_end += strlen(substr);
        }
        idx++;
    }
    const size_t len = idx - last_part_end;
    char* part = malloc(sizeof(char) * (len + 1));
    if (part == NULL) {
        *result = parts;
        return curr_part_idx;
    }
    memcpy(part, &str[last_part_end], len);
    part[len] = '\0';

    parts[curr_part_idx++] = part;

    *result = parts;
    return curr_part_idx;
}

inline void tk_str_to_upper(char* str) {
    for (size_t i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] -= 'a' - 'A';
        }
    }
}

inline void tk_str_to_lower(char* str) {
    for (size_t i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'A' && str[i] <= 'Z') {
            str[i] += 'a' - 'A';
        }
    }
}

inline char* tk_str_concat(const char* str1, const char* str2) {
    const size_t len1 = strlen(str1);
    const size_t len2 = strlen(str2);

    char* result = malloc(sizeof(char) * (len1 + len2 + 1));
    if (result == NULL) {
        return NULL;
    }
    memcpy(result, str1, len1);
    memcpy(&result[len1], str2, len2);
    result[len1 + len2] = '\0';
    return result;
}

static inline bool tk_internal_str_char_is_rubbish(const char c) {
    return c == ' ' || c == '\t' || c == '\n' || c == '\r';
}

inline char* tk_str_trim(const char* str) {
    size_t start = 0;
    size_t end = strlen(str) - 1;
    while (tk_internal_str_char_is_rubbish(str[start])) {
        start++;
    }
    while (tk_internal_str_char_is_rubbish(str[end])) {
        end--;
    }

    char* new_str = malloc(sizeof(char) * (end - start + 2));
    if (new_str == NULL) {
        return NULL;
    }
    memcpy(new_str, &str[start], end - start + 1);
    new_str[end - start + 1] = '\0';

    return new_str;
}

inline uint8_t tk_str_contains(const char* str, const char* substr) {
    return strstr(str, substr) != NULL;
}

#endif /* TK_STRINGS_IMPLEMENTATION */