#define _POSIX_C_SOURCE 200809L

#include "exec/ast_exec_redirs.h"

#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include "ast/ast.h"
#include "ast/ast_accessors.h"
#include "ast/ast_redirect.h"
#include "utils/env.h"
#include "utils/libstring.h"

inline static long _get_open_max(void)
{
    return sysconf(_SC_OPEN_MAX);
}

static bool _file_exists(char *filename)
{
    struct stat s;
    return stat(filename, &s) == 0;
}

inline static bool _is_a_digit(char c)
{
    return c >= '0' && c <= '9';
}

static bool _is_a_number(struct string *s)
{
    size_t i = 0;
    while (i < s->length && _is_a_digit(s->data[i]))
    {
        i++;
    }
    return i == s->length;
}

/**
 * @brief Assigns the fd described by s to out_fd if s
 * describes an integer which is less than _SC_OPEN_MAX.
 */
static void _assign_if_valid_int_fd(struct string *s, int *out_fd)
{
    if (_is_a_number(s))
    {
        int fd = atoi(s->data);
        if (fd < _get_open_max())
        {
            *out_fd = fd;
            return;
        }
    }
    *out_fd = BAD_FD;
}

/**
 * @brief Assigns the fd described by s to out_fd if s
 * describes an integer which is less than _SC_OPEN_MAX.
 * s can also be exactly '-', in which case out_fd contains
 * the value CLOSE_FD.
 */
static void _assign_if_valid_fd_and(struct string *s, int *out_fd)
{
    if (_is_a_number(s))
    {
        int fd = atoi(s->data);
        int cpy_fd = dup(fd);
        *out_fd = cpy_fd;
        return;
    }
    if (s->length == 1 && s->data[0] == '-')
    {
        *out_fd = CLOSE_FD;
        return;
    }
    *out_fd = BAD_FD;
}

void find_fds(struct redirect r, int *left_fd, int *right_fd)
{
    char *rd = r.redir->data;
    static const int filemode = 0644;

    // Default value is no valid left fd is passed in `r`.
    *left_fd = BAD_FD;
    *right_fd = BAD_FD;

    if (STRINGS_ARE_EQUAL(rd, ">"))
    {
        // Sec. 2.7.2: noclobber must avoid overwritting on an existing file
        if (env_get("noclobber") != NULL && _file_exists(r.file->data))
        {
            fprintf(stderr, "redirection: Unable to overwrite on %s.\n",
                    r.file->data);
            return;
        }
        *right_fd = open(r.file->data, O_WRONLY | O_CREAT | O_TRUNC, filemode);
        _assign_if_valid_int_fd(r.fd, left_fd);
    }
    if (STRINGS_ARE_EQUAL(rd, ">>"))
    {
        *right_fd = open(r.file->data, O_WRONLY | O_CREAT | O_APPEND, filemode);
        _assign_if_valid_int_fd(r.fd, left_fd);
    }
    if (STRINGS_ARE_EQUAL(rd, ">|"))
    {
        // Sec. 2.7.2: this redir bypasses noclobber
        *right_fd = open(r.file->data, O_WRONLY | O_CREAT | O_TRUNC, filemode);
        _assign_if_valid_int_fd(r.fd, left_fd);
    }
    if (STRINGS_ARE_EQUAL(rd, ">&"))
    {
        _assign_if_valid_int_fd(r.fd, left_fd);
        _assign_if_valid_fd_and(r.file, right_fd);
        if (*right_fd == BAD_FD)
        {
            // Sure why not after all,
            // Because when it is about bash posix
            // 'undefined' in the SCL means:
            // OH <&{filename} is AMBIGUOUS
            // BUT >&{filename} is PERFECTLY FINE
            *right_fd =
                open(r.file->data, O_WRONLY | O_CREAT | O_TRUNC, filemode);
        }
    }
    if (STRINGS_ARE_EQUAL(rd, "<"))
    {
        *right_fd = open(r.file->data, O_RDONLY);
        _assign_if_valid_int_fd(r.fd, left_fd);
    }
    if (STRINGS_ARE_EQUAL(rd, "<&"))
    {
        _assign_if_valid_int_fd(r.fd, left_fd);
        _assign_if_valid_fd_and(r.file, right_fd);
    }
    if (STRINGS_ARE_EQUAL(rd, "<>"))
    {
        *right_fd = open(r.file->data, O_RDWR | O_CREAT, filemode);
        _assign_if_valid_int_fd(r.fd, left_fd);
    }
}