#include <assert.h>
#include <string.h>
#include <stdint.h>
#include <json.h>
#include "internal.h"

char *json_string_get_mut(struct json *str) {
	if (str->type != JSON_STRING)
		return NULL;
	return str->string;
}

const char *json_string_get_const(const struct json *string) {
	return json_string_get_mut((struct json *)string);
}

enum json_parse_result parse_string(struct json **json_out, struct raw_json *raw) {
	char *str;
	enum json_parse_result ret = parse_raw_string(&str, raw);
	if (ret != JSON_PARSE_OK) {
		return ret;
	}
	struct json *json = json_string_from(str);
	if (!json) {
		free(str);
		return JSON_OOM;
	}
	*json_out = json;
	return ret;
}

static inline
enum json_parse_result parse_octet(uint8_t *out, const char ch) {
	uint8_t value = ch;
	if (value >= '0' && value <= '9') {
		*out = value - '0';
		return JSON_PARSE_OK;
	}

	value |= 0x20; // set 6th bit to force lowercase.

	if (value >= 'a' && value <= 'f') {
		*out = 9 + (value & 0xF); // 'a' & 00001111 == 0001, but 0xA == 10, so +9
		return JSON_PARSE_OK;
	}

	return JSON_PARSE_STRING_INVALID_UNICODE_ERR;
}

static inline
enum json_parse_result parse_hex_pair(uint32_t *out, struct raw_json *raw) {
	if (raw->index + 4 > raw->size) {
		return JSON_PARSE_STRING_INVALID_UNICODE_ERR;
	}
	enum json_parse_result ret = JSON_PARSE_OK;
	uint8_t hihi = 0;
	uint8_t hilo = 0;

	ret = parse_octet(&hihi, raw->data[raw->index++]);
	if (ret != JSON_PARSE_OK)
		return ret;
	hihi <<= 4;
	ret = parse_octet(&hilo, raw->data[raw->index++]);
	if (ret != JSON_PARSE_OK)
		return ret;
	
	uint8_t hi = hihi | hilo;

	ret = parse_octet(&hihi, raw->data[raw->index++]);
	if (ret != JSON_PARSE_OK)
		return ret;
	hihi <<= 4;
	ret = parse_octet(&hilo, raw->data[raw->index++]);
	if (ret != JSON_PARSE_OK)
		return ret;

	uint8_t lo = hihi | hilo;

	*out = (hi << 8) | lo;
	return ret;
}

static inline
enum json_parse_result parse_unicode(char *str, size_t len, size_t i, struct raw_json *raw) {
	enum json_parse_result ret = JSON_PARSE_OK;
	uint32_t codepoint = 0;
	ret = parse_hex_pair(&codepoint, raw);
	if (ret != JSON_PARSE_OK) {
		return ret;
	}

	if (codepoint <= 0x1F || (codepoint >= 0x7F && codepoint <= 0x9F)) {
		if (i + 6 > len || i + 6 > raw->size) {
			return JSON_PARSE_STRING_INVALID_ERR;
		}

		/* unescaping the same codepoints as we do on ascii */
		switch (codepoint) {
			case 0x8:
				str[i++] = '\b';
				return JSON_PARSE_OK;
			case 0x9:
				str[i++] = '\t';
				return JSON_PARSE_OK;
			case 0xa:
				str[i++] = '\n';
				return JSON_PARSE_OK;
			case 0xc:
				str[i++] = '\f';
				return JSON_PARSE_OK;
			case 0xd:
				str[i++] = '\r';
				return JSON_PARSE_OK;
		}

		/* rolling back index so we can parse the codepoint again */
		raw->index -= 6;
		for (size_t limit = i + 6; i < limit; i++) {
			str[i] = raw->data[raw->index++];
		}
		/* the calling function expects to do the last advance */
		raw->index--;
		return ret;
	}

	/* here we're dealing with a utf-16 surrogate pair*/
	if (codepoint >= 0xD800 && codepoint <= 0xDFFF) {
		if (raw->index + 6 > raw->size
				|| (raw->data[raw->index++] != '\\' || raw->data[raw->index++] != 'u')
				|| codepoint < 0xD800 || codepoint > 0xDBFF) {
			ret = JSON_PARSE_STRING_INVALID_UNICODE_ERR;
			return ret;
		}
		uint32_t second_codepoint = 0;
		ret = parse_hex_pair(&second_codepoint, raw);
		if (ret != JSON_PARSE_OK) {
			return ret;
		}

		if (second_codepoint < 0xDC00 || second_codepoint > 0xDFFF) {
			return JSON_PARSE_STRING_INVALID_UNICODE_ERR;
		}
		/* 0x3FF = 00000011111111 - we mask the lower 10 bits of both,
		 * the first codepoint make up the high 10 bits of the result,
		 * the second makes up the low 10 bits */
		codepoint = ((codepoint & 0x3FF) << 10) | (second_codepoint & 0x3FF);
		codepoint += 0x10000;
		if (codepoint < 0x110000 && i + 4 < len) {
			str[i++] = 0xF0 | (codepoint >> 18);
			str[i++] = 0x80 | ((codepoint >> 12) & 0x3F);
			str[i++] = 0x80 | ((codepoint >> 6) & 0x3F);
			str[i] = 0x80 | (codepoint & 0x3F);
		} else {
			ret = JSON_PARSE_STRING_INVALID_UNICODE_ERR;
			return ret;
		}
	/* here it's utf-8 */
	} else {
		if (codepoint < 0x80) {
			str[i] = codepoint;
		} else if (codepoint < 0x800) {
			str[i++] = 0xC0 | (codepoint >> 6);
			str[i] = 0x80 | (codepoint & 0x3F);
		} else if (codepoint < 0x10000) {
			str[i++] = 0xE0 | (codepoint >> 12);
			str[i++] = 0x80 | ((codepoint >> 6) & 0x3F);
			str[i] = 0x80 | (codepoint & 0x3F);
		} else {
			ret = JSON_PARSE_STRING_INVALID_UNICODE_ERR;
			return ret;
		}
	}
	
	/* the calling function expects to do the last advance */
	raw->index--;
	return ret;
}

enum json_parse_result parse_raw_string(char **str_out, struct raw_json *raw) {
	assert(raw->data[raw->index] == '"');
	assert(str_out);
	assert(raw);

	char *str = NULL;
	enum json_parse_result ret = JSON_PARSE_OK;
	size_t end = raw->index + 1;
	size_t skipped = 0;
	for (; end < raw->size && raw->data[end] != '"'; end++) {
		switch (raw->data[end]) {
			case '\n':
			case '\f':
			case '\b':
			case '\r':
			case '\t':
			case 0:
				ret = JSON_PARSE_STRING_INVALID_ESCAPE_ERR;
				goto err;
			case '\\':
				/* for unicode escapes, we can't skip bytes, since control
				 * escape codes will not be parsed, and will be stored as is */
				if (++end < raw->size && raw->data[end] != 'u') {
					skipped++;
				}
				break;
		}
	}

	if (raw->data[end] != '"') {
		ret = JSON_PARSE_STRING_INVALID_ERR;
		goto err;
	}

	size_t len = end - raw->index - skipped;
	str = calloc(len + 1, sizeof(char));
	if (!str) {
		return JSON_OOM;
	}
	size_t i;
	for (i = 0, raw->index++; raw->index < raw->size && raw->data[raw->index] != '"' && i < len; raw->index++, i++) {
		if (raw->data[raw->index] == '\\' && raw->index + 1 < raw->size) {
			switch (raw->data[++raw->index]) {
				case '\\':
				case '\"':
				case '/':
					break;
				case 'n':
					str[i] = '\n';
					continue;
				case 'f':
					str[i] = '\f';
					continue;
				case 'b':
					str[i] = '\b';
					continue;
				case 'r':
					str[i] = '\r';
					continue;
				case 't':
					str[i] = '\t';
					continue;
				case 'u': {
					raw->index++;
					ret = parse_unicode(str, len, i, raw);
					if (ret != JSON_PARSE_OK)
						goto err;
					continue;
				}
				default:
					ret = JSON_PARSE_STRING_INVALID_ESCAPE_ERR;
					goto err;
			}
		}
		str[i] = raw->data[raw->index];
	}

	if (raw->data[raw->index++] != '"') {
		ret = JSON_PARSE_INVALID_STRING_ERR;
		goto err;
	}

	*str_out = str;
	goto end;
err:
	free(str);
end:
	return ret;
}

void json_string_set(struct json *dest, const char *string) {
	if (dest->type != JSON_STRING) {
		char *key = dest->key;
		dest->key = NULL;
		json_clear(dest);
		dest->key = key;
		dest->type = JSON_STRING;
		dest->string = strdup(string);
		return;
	}
	free(dest->string);
	dest->string = strdup(string);
}