// Copyright (c) 2025, Zak Fenton
// Zak Fenton's libc is licensed under the Mulan PSL v2. You can use this
// software according to the terms and conditions of the Mulan PSL v2.
// You may obtain a copy of Mulan PSL v2 at:
// http://license.coscl.org.cn/MulanPSL2
// THIS SOFTWARE IS PROVIDED ON AN “AS IS” BASIS, WITHOUT warranties of
// any kind, either express or implied, including but not limited to
// non-infringement, merchantability or fit for a particular purpose.
// See the Mulan PSL v2 for more details.
#include <stdlib.h>
#include <unistd.h>
#include "internal.h"

/* DESIGN NOTE: At program entry the environment variables are just an
 * array of "key=value" strings allocated on/near the stack by the
 * kernel. When actively modifying environment variables the structure
 * needs to be reallocated, so the system initially just uses the
 * preallocated copy but keeps a _libc_env_reallocated flag to tell it
 * if it's using a malloc'd copy so it can be freed properly. This means
 * the system is optimised for programs that don't use environment
 * variables much so it doesn't rely on memory allocation in those
 * cases but may be slightly inefficient in cases where you do make
 * heavy use of them (copying the whole table on every change instead of
 * just using an optimised structure from the start).
 */
const char** _libc_env_variable;
int _libc_env_count;
int _libc_env_reallocated;

void _libc_env_init(const char** envv) {
  _libc_env_variable = envv;
  _libc_env_count = 0;
  _libc_env_reallocated = 0;
  while (envv != NULL && envv[_libc_env_count] != NULL) {
    _libc_env_count++;
  }
}

const char* _libc_env_match(const char* env, const char* key) {
  int i;
  for (i = 0; key[i] != 0; i++) {
    if (env[i] != key[i]) {
      return 0; // false, env doesn't match given key
    }
  }
  if (env[i] != '=') {
    return 0; // false, env key is longer than given key
  }
  return env+i+1; // true, env string starts with key followed by "="
}

char* getenv(const char* key) {
  for (int i = 0; i < _libc_env_count; i++) {
    const char* tmp;
    if ((tmp = _libc_env_match(_libc_env_variable[i], key)) != NULL) {
      return tmp;
    }
  }
  return NULL;
}

int setenv(const char* key, const char* value, int overwrite) {
  int exists = -1;
  int i;
  for (i = 0; i < _libc_env_count; i++) {
    const char* tmp;
    if ((tmp = _libc_env_match(_libc_env_variable[i], key)) != NULL) {
      if (overwrite) {
        exists = i;
        break;
      } else {
        return 0;
      }
    }
  }
  int newsize;
  newsize = _libc_env_count + (exists >= 0 ? 1 : 0);
  char* newentry = malloc(strlen(key)+strlen(value)+2);
  sprintf(newentry, "%s=%s", key, value);
  const char** oldptr = _libc_env_variable;
  const char** newptr = malloc(newsize * sizeof(char*));
  for (i = 0; i < _libc_env_count; i++) {
    const char* tmp;
    if (i == exists) {
      newptr[i] = newentry;
    } else {
      newptr[i] = strdup(oldptr[i]);
    }
    if (_libc_env_reallocated) {
      free(oldptr[i]);
    }
  }
  if (i < newsize) {
    newptr[i] = newentry;
  }
  _libc_env_variable = newptr;
  if (_libc_env_reallocated) {
    free(oldptr);
  }
  _libc_env_reallocated = 1;
  return 0;
}

int unsetenv(const char* key) {
  int exists = -1;
  int i;
  for (i = 0; i < _libc_env_count; i++) {
    const char* tmp;
    if ((tmp = _libc_env_match(_libc_env_variable[i], key)) != NULL) {
      exists = i;
      break;
    }
  }
  if (exists < 0) {
    return 0; // Nothing to do, env var already doesn't exist
  }
  int newsize = _libc_env_count - 1;
  const char** oldptr = _libc_env_variable;
  const char** newptr = malloc(newsize * sizeof(char*));
  for (i = 0; i < _libc_env_count; i++) {
    const char* tmp;
    if (i >= exists) {
      newptr[i] = strdup(oldptr[i-1]);
    } else {
      newptr[i] = strdup(oldptr[i]);
    }
    if (_libc_env_reallocated) {
      free(oldptr[i]);
    }
  }
  _libc_env_variable = newptr;
  if (_libc_env_reallocated) {
    free(oldptr);
  }
  _libc_env_reallocated = 1;
  return 0;
}

int system(const char* cmd) {
  UNIMPLEMENTED();
}

void abort() {
  UNIMPLEMENTED();
}

double atof(const char* str) {
  UNIMPLEMENTED();
}

int _libc_charnum(char c, int base) {
  int n;
  if (c >= '0' && c <= '9') {
    n = c - '0';
  } else if (c >= 'A' && c <= 'F') {
    n = 10 + c - 'A';
  } else if (c >= 'a' && c <= 'f') {
    n = 10 + c - 'a';
  } else {
    return -1;
  }
  if (n < base) {
    return n;
  } else {
    return -1;
  }
}

long strtol(const char* str, char**endvar, int base) {
  UNIMPLEMENTED();
}

long long strtoll(const char* str, char**endvar, int base) {
  UNIMPLEMENTED();
}

unsigned long strtoul(const char* str, char**endvar, int base) {
  return strtoull(str, endvar, base);
}

unsigned long long strtoull(const char* str, char**endvar, int base) {
  UNIMPLEMENTED();
}

float strtof(const char* str, char**endvar) {
  UNIMPLEMENTED();
}

double strtod(const char* str, char**endvar) {
  UNIMPLEMENTED();
}

long double strtold(const char* str, char**endvar) {
  UNIMPLEMENTED();
}