#include "maze32_protocol.h"

#include <limits.h>
#include <string.h>

typedef struct {
    const char* data;
    size_t length;
    size_t position;
} json_cursor_t;

static void skip_space(json_cursor_t* cursor) {
    while (cursor->position < cursor->length) {
        char character = cursor->data[cursor->position];
        if (character != ' ' && character != '\t' && character != '\r' && character != '\n') {
            return;
        }
        cursor->position++;
    }
}

static int consume(json_cursor_t* cursor, char expected) {
    skip_space(cursor);
    if (cursor->position >= cursor->length || cursor->data[cursor->position] != expected) {
        return 0;
    }
    cursor->position++;
    return 1;
}

static int parse_string(json_cursor_t* cursor, char* output, size_t capacity) {
    skip_space(cursor);
    if (cursor->position >= cursor->length || cursor->data[cursor->position++] != '"') {
        return 0;
    }
    size_t output_length = 0U;
    while (cursor->position < cursor->length) {
        unsigned char character = (unsigned char)cursor->data[cursor->position++];
        if (character == '"') {
            if (output_length >= capacity) {
                return 0;
            }
            output[output_length] = '\0';
            return 1;
        }
        if (character < 0x20U) {
            return 0;
        }
        if (character == '\\') {
            if (cursor->position >= cursor->length) {
                return 0;
            }
            character = (unsigned char)cursor->data[cursor->position++];
            if (character == '"' || character == '\\' || character == '/') {
                /* The escaped byte is copied below. */
            } else if (character == 'b') {
                character = '\b';
            } else if (character == 'f') {
                character = '\f';
            } else if (character == 'n') {
                character = '\n';
            } else if (character == 'r') {
                character = '\r';
            } else if (character == 't') {
                character = '\t';
            } else {
                return 0;
            }
        }
        if (output_length + 1U >= capacity) {
            return 0;
        }
        output[output_length++] = (char)character;
    }
    return 0;
}

static int parse_uint32(json_cursor_t* cursor, uint32_t* value) {
    skip_space(cursor);
    if (cursor->position >= cursor->length || cursor->data[cursor->position] < '0' ||
        cursor->data[cursor->position] > '9') {
        return 0;
    }
    uint64_t parsed = 0U;
    while (cursor->position < cursor->length && cursor->data[cursor->position] >= '0' &&
           cursor->data[cursor->position] <= '9') {
        parsed = parsed * 10U + (uint64_t)(cursor->data[cursor->position] - '0');
        if (parsed > UINT32_MAX) {
            return 0;
        }
        cursor->position++;
    }
    *value = (uint32_t)parsed;
    return 1;
}

static int payload_field_allowed(maze32_message_type_t type, const char* key, char* value,
                                 maze32_client_message_t* message, unsigned int* fields) {
    if (type == MAZE32_MESSAGE_JOIN && strcmp(key, "role") == 0 && !(*fields & 1U)) {
        if (strcmp(value, "player") == 0) {
            message->role = MAZE32_ROLE_PLAYER;
        } else if (strcmp(value, "observer") == 0) {
            message->role = MAZE32_ROLE_OBSERVER;
        } else {
            return 0;
        }
        *fields |= 1U;
        return 1;
    }
    if (type == MAZE32_MESSAGE_JOIN && strcmp(key, "name") == 0 && !(*fields & 2U)) {
        if (strlen(value) > MAZE32_PLAYER_NAME_MAX_BYTES) {
            return 0;
        }
        memcpy(message->name, value, strlen(value) + 1U);
        *fields |= 2U;
        return 1;
    }
    if (type == MAZE32_MESSAGE_RESTORE && strcmp(key, "token") == 0 && !(*fields & 1U)) {
        if (strlen(value) != MAZE32_SESSION_TOKEN_HEX_LENGTH) {
            return 0;
        }
        memcpy(message->token, value, MAZE32_SESSION_TOKEN_HEX_LENGTH + 1U);
        *fields |= 1U;
        return 1;
    }
    return 0;
}

static int parse_payload(json_cursor_t* cursor, maze32_client_message_t* message) {
    if (!consume(cursor, '{')) {
        return 0;
    }
    unsigned int fields = 0U;
    skip_space(cursor);
    if (cursor->position < cursor->length && cursor->data[cursor->position] == '}') {
        cursor->position++;
    } else {
        for (;;) {
            char key[16];
            char value[MAZE32_PLAYER_NAME_MAX_BYTES + 1U];
            if (!parse_string(cursor, key, sizeof(key)) || !consume(cursor, ':') ||
                !parse_string(cursor, value, sizeof(value)) ||
                !payload_field_allowed(message->type, key, value, message, &fields)) {
                return 0;
            }
            skip_space(cursor);
            if (consume(cursor, '}')) {
                break;
            }
            if (!consume(cursor, ',')) {
                return 0;
            }
        }
    }

    if (message->type == MAZE32_MESSAGE_JOIN) {
        return message->role == MAZE32_ROLE_PLAYER ? fields == 3U : fields == 1U;
    }
    if (message->type == MAZE32_MESSAGE_RESTORE) {
        return fields == 1U;
    }
    return fields == 0U;
}

static maze32_message_type_t message_type(const char* value) {
    if (strcmp(value, "join") == 0) {
        return MAZE32_MESSAGE_JOIN;
    }
    if (strcmp(value, "restore") == 0) {
        return MAZE32_MESSAGE_RESTORE;
    }
    if (strcmp(value, "start") == 0) {
        return MAZE32_MESSAGE_START;
    }
    if (strcmp(value, "heartbeat") == 0) {
        return MAZE32_MESSAGE_HEARTBEAT;
    }
    if (strcmp(value, "suggest_name") == 0) {
        return MAZE32_MESSAGE_SUGGEST_NAME;
    }
    return MAZE32_MESSAGE_INVALID;
}

maze32_protocol_result_t maze32_protocol_parse(const char* data, size_t length,
                                               maze32_client_message_t* message) {
    if (data == NULL || message == NULL || length == 0U) {
        return MAZE32_PROTOCOL_MALFORMED;
    }
    if (length > MAZE32_PROTOCOL_MESSAGE_LIMIT) {
        return MAZE32_PROTOCOL_TOO_LARGE;
    }
    memset(message, 0, sizeof(*message));
    json_cursor_t cursor = {.data = data, .length = length, .position = 0U};
    if (!consume(&cursor, '{')) {
        return MAZE32_PROTOCOL_MALFORMED;
    }

    unsigned int envelope_fields = 0U;
    uint32_t version = 0U;
    char type_value[24] = "";
    for (;;) {
        char key[24];
        if (!parse_string(&cursor, key, sizeof(key)) || !consume(&cursor, ':')) {
            return MAZE32_PROTOCOL_MALFORMED;
        }
        if (strcmp(key, "v") == 0 && !(envelope_fields & 1U)) {
            if (!parse_uint32(&cursor, &version)) {
                return MAZE32_PROTOCOL_MALFORMED;
            }
            envelope_fields |= 1U;
        } else if (strcmp(key, "type") == 0 && !(envelope_fields & 2U)) {
            if (!parse_string(&cursor, type_value, sizeof(type_value))) {
                return MAZE32_PROTOCOL_MALFORMED;
            }
            message->type = message_type(type_value);
            envelope_fields |= 2U;
        } else if (strcmp(key, "seq") == 0 && !(envelope_fields & 4U)) {
            if (!parse_uint32(&cursor, &message->sequence) || message->sequence == 0U) {
                return MAZE32_PROTOCOL_MALFORMED;
            }
            envelope_fields |= 4U;
        } else if (strcmp(key, "requestId") == 0 && !(envelope_fields & 8U)) {
            if (!parse_string(&cursor, message->request_id, sizeof(message->request_id))) {
                return MAZE32_PROTOCOL_MALFORMED;
            }
            envelope_fields |= 8U;
        } else if (strcmp(key, "payload") == 0 && !(envelope_fields & 16U)) {
            if (!(envelope_fields & 2U)) {
                return MAZE32_PROTOCOL_MALFORMED;
            }
            if (message->type == MAZE32_MESSAGE_INVALID) {
                return MAZE32_PROTOCOL_UNKNOWN_TYPE;
            }
            if (!parse_payload(&cursor, message)) {
                return MAZE32_PROTOCOL_INVALID_PAYLOAD;
            }
            envelope_fields |= 16U;
        } else {
            return MAZE32_PROTOCOL_MALFORMED;
        }
        skip_space(&cursor);
        if (consume(&cursor, '}')) {
            break;
        }
        if (!consume(&cursor, ',')) {
            return MAZE32_PROTOCOL_MALFORMED;
        }
    }
    skip_space(&cursor);
    if (cursor.position != cursor.length ||
        (envelope_fields & (1U | 2U | 4U | 16U)) != (1U | 2U | 4U | 16U)) {
        return MAZE32_PROTOCOL_MALFORMED;
    }
    if (version != MAZE32_PROTOCOL_VERSION) {
        return MAZE32_PROTOCOL_UNSUPPORTED_VERSION;
    }
    if (message->type == MAZE32_MESSAGE_INVALID) {
        return MAZE32_PROTOCOL_UNKNOWN_TYPE;
    }
    return MAZE32_PROTOCOL_OK;
}

const char* maze32_protocol_result_name(maze32_protocol_result_t result) {
    switch (result) {
        case MAZE32_PROTOCOL_OK:
            return "ok";
        case MAZE32_PROTOCOL_MALFORMED:
            return "malformed";
        case MAZE32_PROTOCOL_TOO_LARGE:
            return "too_large";
        case MAZE32_PROTOCOL_UNSUPPORTED_VERSION:
            return "unsupported_version";
        case MAZE32_PROTOCOL_UNKNOWN_TYPE:
            return "unknown_type";
        case MAZE32_PROTOCOL_INVALID_PAYLOAD:
            return "invalid_payload";
        default:
            return "unknown_error";
    }
}