/**
 * @file Scanf.cpp
 * @author apio (cloudapio.eu)
 * @brief Scanf implementation.
 *
 * @copyright Copyright (c) 2023, the Luna authors.
 *
 */

#include <luna/CString.h>
#include <luna/CType.h>
#include <luna/DebugLog.h>
#include <luna/Heap.h>
#include <luna/NumberParsing.h>
#include <luna/SystemError.h>
#include <sys/types.h>

#define FLAG_DISCARD (1 << 0)
#define FLAG_ALLOC (1 << 1)
#define FLAG_WIDTH (1 << 2)
#define FLAG_LONG (1 << 3)
#define FLAG_LONG_LONG (1 << 4)
#define FLAG_SHORT (1 << 5)
#define FLAG_CHAR (1 << 6)

static int parse_flags(const char** format)
{
    int result = 0;

    while (true)
    {
        switch (**format)
        {
        case '*':
            result |= FLAG_DISCARD;
            (*format)++;
            break;
        case 'm':
            result |= FLAG_ALLOC;
            (*format)++;
            break;
        default: return result;
        }
    }
}

static size_t parse_width(const char** format, int& flags)
{
    size_t result = 0;

    if (_isdigit(**format))
    {
        result = scan_unsigned_integer(format);
        flags |= FLAG_WIDTH;
    }

    return result;
}

static void parse_type(const char** format, int& flags)
{
    // FIXME: Support %j (intmax_t/uintmax_t)
    switch (**format)
    {
    case 'h':
        flags |= FLAG_SHORT;
        (*format)++;
        if (**format == 'h')
        {
            flags |= FLAG_CHAR;
            (*format)++;
        }
        break;
    case 'l':
        flags |= FLAG_LONG;
        (*format)++;
        if (**format == 'l')
        {
            flags |= FLAG_LONG_LONG;
            (*format)++;
        }
        break;
    case 't':
        flags |= (sizeof(ptrdiff_t) == sizeof(long)) ? FLAG_LONG : FLAG_LONG_LONG;
        (*format)++;
        break;
    case 'z':
        flags |= (sizeof(size_t) == sizeof(long)) ? FLAG_LONG : FLAG_LONG_LONG;
        (*format)++;
        break;
    default: break;
    }
}

static void write_parsed_signed_integer(ssize_t value, int flags, va_list ap)
{
    if (flags & FLAG_LONG_LONG) *va_arg(ap, signed long long*) = (signed long long)value;
    else if (flags & FLAG_LONG)
        *va_arg(ap, signed long*) = (signed long)value;
    else if (flags & FLAG_SHORT)
        *va_arg(ap, signed int*) = (signed short)value;
    else if (flags & FLAG_CHAR)
        *va_arg(ap, signed int*) = (signed char)value;
    else
        *va_arg(ap, signed int*) = (signed int)value;
}

static void write_parsed_unsigned_integer(size_t value, int flags, va_list ap)
{
    if (flags & FLAG_LONG_LONG) *va_arg(ap, unsigned long long*) = (unsigned long long)value;
    else if (flags & FLAG_LONG)
        *va_arg(ap, unsigned long*) = (unsigned long)value;
    else if (flags & FLAG_SHORT)
        *va_arg(ap, unsigned int*) = (unsigned short)value;
    else if (flags & FLAG_CHAR)
        *va_arg(ap, unsigned int*) = (unsigned char)value;
    else
        *va_arg(ap, unsigned int*) = (unsigned int)value;
}

#define WHITESPACE_CHARACTERS " \t\f\r\n\v"

static void skip_whitespace(const char** str)
{
    *str += strspn(*str, WHITESPACE_CHARACTERS);
}

int scanf_impl(const char* str, const char* format, va_list ap)
{
    int parsed = 0;
    const char* s = str; // Keep a pointer to the beginning of the string for %n

    if (*str == 0) return -1;

    while (*format)
    {
        if (*format != '%')
        {
        normal:
            if (!_isspace(*format))
            {
                if (*str != *format) return parsed;
                str++;
                format++;
                if (*str == 0) return parsed;
                continue;
            }

            skip_whitespace(&format);
            skip_whitespace(&str);
            if (*str == 0) return parsed;
            continue;
        }
        else
        {
            format++;
            if (*format == '%')
            {
                skip_whitespace(&str);
                goto normal;
            }

            int flags = parse_flags(&format);
            size_t width = parse_width(&format, flags);
            parse_type(&format, flags);
            char specifier = *format++;
            if (!specifier) return parsed;

            switch (specifier)
            {
            case 's': {
                skip_whitespace(&str);
                size_t chars = strcspn(str, WHITESPACE_CHARACTERS);
                if (!chars) return parsed;
                if ((flags & FLAG_WIDTH) && chars > width) chars = width;
                if (!(flags & FLAG_DISCARD))
                {
                    char* ptr;
                    if (flags & FLAG_ALLOC)
                    {
                        ptr = (char*)malloc_impl(chars + 1).value_or(nullptr);
                        if (!ptr) return parsed;
                        *va_arg(ap, char**) = ptr;
                    }
                    else
                        ptr = va_arg(ap, char*);
                    memcpy(ptr, str, chars);
                    ptr[chars] = 0;
                }
                str += chars;
                parsed++;
                break;
            }
            case 'c': {
                if (strlen(str) < width) return parsed;
                if (!(flags & FLAG_WIDTH)) width = 1;
                if (!(flags & FLAG_DISCARD))
                {
                    char* ptr;
                    if (flags & FLAG_ALLOC)
                    {
                        ptr = (char*)malloc_impl(width).value_or(nullptr);
                        if (!ptr) return parsed;
                        *va_arg(ap, char**) = ptr;
                    }
                    else
                        ptr = va_arg(ap, char*);
                    memcpy(ptr, str, width);
                }
                str += width;
                parsed++;
                break;
            }
            case 'd': {
                skip_whitespace(&str);
                ssize_t value = scan_signed_integer(&str, 10);
                if (!(flags & FLAG_DISCARD)) write_parsed_signed_integer(value, flags, ap);
                parsed++;
                break;
            }
            case 'i': {
                skip_whitespace(&str);
                ssize_t value = scan_signed_integer(&str, 0);
                if (!(flags & FLAG_DISCARD)) write_parsed_signed_integer(value, flags, ap);
                parsed++;
                break;
            }
            case 'o': {
                skip_whitespace(&str);
                size_t value = scan_unsigned_integer(&str, 8);
                if (!(flags & FLAG_DISCARD)) write_parsed_unsigned_integer(value, flags, ap);
                parsed++;
                break;
            }
            case 'u': {
                skip_whitespace(&str);
                size_t value = scan_unsigned_integer(&str, 10);
                if (!(flags & FLAG_DISCARD)) write_parsed_unsigned_integer(value, flags, ap);
                parsed++;
                break;
            }
            case 'X':
            case 'x': {
                skip_whitespace(&str);
                size_t value = scan_unsigned_integer(&str, 16);
                if (!(flags & FLAG_DISCARD)) write_parsed_unsigned_integer(value, flags, ap);
                parsed++;
                break;
            }
            case 'p': {
                skip_whitespace(&str);
                size_t value = scan_unsigned_integer(&str, 16);
                if (!(flags & FLAG_DISCARD)) *va_arg(ap, void**) = (void*)value;
                parsed++;
                break;
            }
            case 'n': {
                if (!(flags & FLAG_DISCARD)) *va_arg(ap, int*) = (int)(str - s);
                break;
            }
            default: {
                dbgln("vsscanf: unknown conversion specifier: %%%c\n", specifier);
                return parsed;
            }
            }
        }
    }

    return parsed;
}