/*
 * Copyright (C) 2025 dwlr <dweller@cabin.digital>
 *
 * BSD 3-Clause License (BSD-3-Clause)
 * See LICENSE for details
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>


typedef   signed char s8;
typedef unsigned char u8;
typedef            s8 bool;

#define true  1
#define false 0


char* cstr_dup(const char* s)
{
    size_t sz = 0;
    char* r = NULL;

    if(!s) return NULL;

    sz = strlen(s);
    r = calloc(sz+1, 1);
    if(!r) return NULL;

    return memcpy(r, s, sz);
}

char* cstr_basename(const char* path)
{
    char*        dup = NULL;
    char*          c = NULL;
    char* last_slash = NULL;
    int    non_slash = 0;

    if(!path) return NULL;

    dup = cstr_dup(path);
    c = dup;
    last_slash = NULL;

    while(*c)
    {
        if(*c == '/')
        {
            if(*(c+1)) last_slash = c;
            else if(c != dup) *c = '\0';
        }
        else non_slash++;

        c++;
    }

    if(last_slash)
    {
        if(non_slash == 0)
        {
            dup[0] = '/';
            dup[1] = '\0';
        }
        else
            memmove(dup, last_slash + 1, strlen(last_slash + 1) + 1);
    }

    return dup;
}

ssize_t utf8_to_uri(const char* s, size_t size)
{
    ssize_t len = 0;
    size_t i = 0;

    while(i < size)
    {
        if(!(s[i] & 0x80))
        {
            if((s[i] >= '0' && s[i] <= '9')
            || (s[i] >= 'A' && s[i] <= 'Z')
            || (s[i] >= 'a' && s[i] <= 'z')
            || (s[i] == '-')
            || (s[i] == '.')
            || (s[i] == '_')
            || (s[i] == '~'))
                putchar(s[i]);
            else if(s[i] == ' ')
                putchar('+');
            else
                printf("%%%02x", (u8)s[i]);

            i++;
        }
        else if((s[i] & 0xF0) == 0xF0)
        {
            if(i + 4 >= size) return -1;

            printf("%%%02x", (u8)s[i  ]);
            printf("%%%02x", (u8)s[i+1]);
            printf("%%%02x", (u8)s[i+2]);
            printf("%%%02x", (u8)s[i+3]);

            i += 4;
        }
        else if((s[i] & 0xE0) == 0xE0)
        {
            if(i + 3 >= size) return -1;

            printf("%%%02x", (u8)s[i  ]);
            printf("%%%02x", (u8)s[i+1]);
            printf("%%%02x", (u8)s[i+2]);

            i += 3;
        }
        else if((s[i] & 0xC0) == 0xC0)
        {
            if(i + 2 >= size) return -1;

            printf("%%%02x", (u8)s[i  ]);
            printf("%%%02x", (u8)s[i+1]);

            i += 2;
        }
        else return -1;

        len++;
    }

    return len;
}

char ascii_lower(char c)
{
    if(c >= 'A' && c <= 'Z') return c + ('a' - 'A');
    else                     return c;
}

char* asciiz_lower(char* s)
{
    char* c;
    for(c = s; *c; c++) *c = ascii_lower(*c);

    return s;
}

typedef struct maybe_char maybe_char;
struct maybe_char
{
    bool ok;
    char c;
};

maybe_char hex_to_char(const char hex[2])
{
    int i;
    maybe_char ret = {0};

    for(i = 0; i < 2; i++)
    {
        char c = ascii_lower(hex[i]);
        char r = 0;

        if(c >= '0' && c <= '9')      r = c - '0';
        else if(c >= 'a' && c <= 'f') r = c - 'a' + 10;
        else return ret;

        ret.c |= r << 4 * (1 - i);
    }

    ret.ok = true;
    return ret;
}

ssize_t uri_to_utf8(const char* s, size_t size)
{
    ssize_t len = 0;
    size_t    i = 0;

    while(i < size)
    {
        if(s[i] == '+') putchar(' ');
        else if(s[i] == '%')
        {
            maybe_char c = {0};

            if(i + 1 >= size) return -1;

            c = hex_to_char(s + i + 1);
            i += 2;

            if(c.ok) putchar(c.c);
            else return -1;
        }
        else putchar(s[i]);

        i++;
        len++;
    }

    return len;
}


void usage(const char* name)
{
    fprintf(stderr, "%s - RFC3986 URI encoder/decoder\n"
                    "     2025 (C) dweller@cabin.digital\n"
                    "     All Wrongs Reserved\n\n"
                    "Usage: %s e|d [files...]\n"
                    "       e     - encode URI\n"
                    "       d     - decode URI\n"
                    "       files - optional list of files to read and encode/decode.\n"
                    "               If empty stdin is used\n",
                    name, name);

    exit(1);
}

void do_file(FILE* f, const char* name, bool context, ssize_t(*func)(const char*,size_t))
{
    char* line   = NULL;
    ssize_t read = 0;
    size_t len   = 0;

    clearerr(f);

    while((read = getline(&line, &len, f)) != -1)
    {
        if(context) putchar('\t');
        func(line, read - 1);
        putchar('\n');
    }

    if(line) free(line);

    if(ferror(f)) fprintf(stderr, "ERROR: failed to read '%s': %s\n", name, strerror(errno));
}

int main(int argc, char** argv)
{
    int r, i;
    char* base = cstr_basename(argv[0]);
    r = 0;

    if(strcmp(base, "urlenc") == 0)
    {
        for(i = 1; i < argc; i++)
        {
            utf8_to_uri(argv[i], strlen(argv[i]));
            putchar('\n');
        }
    }
    else if(strcmp(base, "urldec") == 0)
    {
        for(i = 1; i < argc; i++)
        {
            uri_to_utf8(argv[i], strlen(argv[i]));
            putchar('\n');
        }
    }
    else
    {
        bool encode = false;

        if(argc < 2) usage(base);

        if(strcmp(argv[1], "e") == 0) encode = true;
        else if(strcmp(argv[1], "d") == 0) encode = false;
        else usage(base);

        if(argc < 3)
        {
            if(encode) do_file(stdin, "stdin", false, utf8_to_uri);
            else       do_file(stdin, "stdin", false, uri_to_utf8);
        }
        else for(i = 2; i < argc; i++)
        {
            FILE* f =  NULL;
            const char* name = argv[i];

            errno = 0;
            f = fopen(name, "r");
            if(!f)
            {
                fprintf(stderr, "ERROR: could not open '%s': %s\n", name, strerror(errno));
                r = 1;
            }
            else
            {
                bool context = argc > 3;

                if(context) printf("%s:\n", name);
                if(encode) do_file(f, name, context, utf8_to_uri);
                else       do_file(f, name, context, uri_to_utf8);

                fclose(f);
            }
        }
    }

    free(base);
    return r;
}