#include "http.h"
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    const char* message;
    size_t message_size;
    size_t i;
} HttpRequestParser;

#define PARSER_PANIC(message)                                                                      \
    (printf("error: http parser: %s\n    at %s:%d in '%s()'\n", message, __FILE__, __LINE__,       \
         __func__),                                                                                \
        exit(1))

HttpMethod parse_method(HttpRequestParser* parser)
{
    if (parser->i + 3 < parser->message_size && strncmp(&parser->message[0], "GET", 3) == 0) {
        parser->i += 3;
        return HttpMethodGet;
    } else if (parser->i + 4 < parser->message_size
        && strncmp(&parser->message[0], "POST", 4) == 0) {
        parser->i += 4;
        return HttpMethodPost;
    } else {
        PARSER_PANIC("failed to parse http method");
    }
}

void skip_char(HttpRequestParser* parser, char value)
{
    if (parser->i >= parser->message_size)
        PARSER_PANIC("unexpected end");
    if (parser->message[parser->i] != value)
        PARSER_PANIC("unexpected character, expected ' '");
    parser->i += 1;
}

typedef struct {
    size_t index, length;
} PathSpan;

PathSpan parse_path(HttpRequestParser* parser)
{
    size_t index = parser->i;
    while (parser->i < parser->message_size && parser->message[parser->i] != ' '
        && parser->message[parser->i] != '\r') {
        parser->i += 1;
    }
    if (parser->i >= parser->message_size)
        PARSER_PANIC("unexpected end");
    else if (parser->message[parser->i] != ' ')
        PARSER_PANIC("unexpected char, expected ' '");
    return (PathSpan) {
        .index = index,
        .length = parser->i - index,
    };
}

void skip_newline(HttpRequestParser* parser)
{
    skip_char(parser, '\r');
    skip_char(parser, '\n');
}

void skip_http_version_tag(HttpRequestParser* parser)
{
    skip_char(parser, 'H');
    skip_char(parser, 'T');
    skip_char(parser, 'T');
    skip_char(parser, 'P');
    skip_char(parser, '/');
    skip_char(parser, '1');
    skip_char(parser, '.');
    skip_char(parser, '1');
    skip_newline(parser);
}

typedef struct {
    size_t key_index, key_length;
    size_t value_index, value_length;
} HeaderPair;

HeaderPair parse_header_pair(HttpRequestParser* parser)
{
    size_t key_begin = parser->i;
    while (parser->i < parser->message_size && parser->message[parser->i] != ':'
        && parser->message[parser->i] != '\r') {
        parser->i += 1;
    }
    if (parser->i >= parser->message_size)
        PARSER_PANIC("unexpected end");
    size_t key_end = parser->i;
    skip_char(parser, ':');
    skip_char(parser, ' ');
    size_t value_begin = parser->i;
    while (parser->i < parser->message_size && parser->message[parser->i] != '\r') {
        parser->i += 1;
    }
    if (parser->i >= parser->message_size)
        PARSER_PANIC("unexpected end");
    return (HeaderPair) {
        .key_index = key_begin,
        .key_length = key_end - key_begin,
        .value_index = value_begin,
        .value_length = parser->i - value_begin,
    };
}

bool is_content_length_header(HttpRequestParser* parser, HeaderPair pair)
{
    return strncmp(&parser->message[pair.key_index], "Content-Length", pair.key_length) == 0;
}

size_t extract_content_length_value(HttpRequestParser* parser, HeaderPair pair)
{
    char string_value[21] = { 0 };
    strncpy(string_value, &parser->message[pair.value_index], pair.value_length);
    int64_t int_value = atoll(string_value);
    if (int_value < 0)
        PARSER_PANIC("Content-Length < 0");
    return (size_t)int_value;
}

HttpRequestHeader parse_http_request_header(const char* message, size_t message_size)
{
    HttpRequestParser parser = (HttpRequestParser) {
        .message = message,
        .message_size = message_size,
        .i = 0,
    };
    HttpMethod method = parse_method(&parser);
    skip_char(&parser, ' ');
    PathSpan path_span = parse_path(&parser);
    skip_char(&parser, ' ');
    skip_http_version_tag(&parser);
    size_t content_length = 0;
    while (parser.i < message_size && message[parser.i] != '\r') {
        HeaderPair pair = parse_header_pair(&parser);
        if (is_content_length_header(&parser, pair)) {
            content_length = extract_content_length_value(&parser, pair);
        }
        skip_newline(&parser);
    }
    skip_newline(&parser);
    return (HttpRequestHeader) {
        .method = method,
        .path_index = path_span.index,
        .path_length = path_span.length,
        .content_length = content_length,
        .body_index = parser.i,
    };
}