/// Validation constants for input field lengths.
pub const MAX_NAME_LENGTH: usize = 256;
pub const MAX_FOLDER_LENGTH: usize = 128;
pub const MAX_ENTRY_TYPE_LENGTH: usize = 64;
pub const MAX_NOTES_LENGTH: usize = 10000;
pub const MAX_TAG_LENGTH: usize = 64;
pub const MAX_TAG_COUNT: usize = 50;
pub const MAX_META_KEY_LENGTH: usize = 128;
pub const MAX_META_VALUE_LENGTH: usize = 4096;
pub const MAX_META_COUNT: usize = 100;

/// Validate input field lengths for MCP tools.
///
/// Returns an error if any field exceeds its maximum length.
pub fn validate_input_lengths(
    name: &str,
    folder: Option<&str>,
    entry_type: Option<&str>,
    notes: Option<&str>,
) -> Result<(), rmcp::ErrorData> {
    if name.chars().count() > MAX_NAME_LENGTH {
        return Err(rmcp::ErrorData::invalid_params(
            format!("name must be at most {} characters", MAX_NAME_LENGTH),
            None,
        ));
    }
    if let Some(folder) = folder
        && folder.chars().count() > MAX_FOLDER_LENGTH
    {
        return Err(rmcp::ErrorData::invalid_params(
            format!("folder must be at most {} characters", MAX_FOLDER_LENGTH),
            None,
        ));
    }
    if let Some(entry_type) = entry_type
        && entry_type.chars().count() > MAX_ENTRY_TYPE_LENGTH
    {
        return Err(rmcp::ErrorData::invalid_params(
            format!("type must be at most {} characters", MAX_ENTRY_TYPE_LENGTH),
            None,
        ));
    }
    if let Some(notes) = notes
        && notes.chars().count() > MAX_NOTES_LENGTH
    {
        return Err(rmcp::ErrorData::invalid_params(
            format!("notes must be at most {} characters", MAX_NOTES_LENGTH),
            None,
        ));
    }
    Ok(())
}

/// Validate the tags list.
///
/// Checks total count and per-tag character length.
pub fn validate_tags(tags: &[String]) -> Result<(), rmcp::ErrorData> {
    if tags.len() > MAX_TAG_COUNT {
        return Err(rmcp::ErrorData::invalid_params(
            format!("at most {} tags are allowed", MAX_TAG_COUNT),
            None,
        ));
    }
    for tag in tags {
        if tag.chars().count() > MAX_TAG_LENGTH {
            return Err(rmcp::ErrorData::invalid_params(
                format!(
                    "tag '{}' exceeds the maximum length of {} characters",
                    tag, MAX_TAG_LENGTH
                ),
                None,
            ));
        }
    }
    Ok(())
}

/// Validate metadata KV strings (key=value / key:=json format).
///
/// Checks total count and per-key/per-value character lengths.
/// This is a best-effort check on the raw KV strings before parsing;
/// keys containing `:` path separators are checked as a whole.
pub fn validate_meta_entries(entries: &[String]) -> Result<(), rmcp::ErrorData> {
    if entries.len() > MAX_META_COUNT {
        return Err(rmcp::ErrorData::invalid_params(
            format!("at most {} metadata entries are allowed", MAX_META_COUNT),
            None,
        ));
    }
    for entry in entries {
        // key:=json — check both key and JSON value length
        if let Some((key, value)) = entry.split_once(":=") {
            if key.chars().count() > MAX_META_KEY_LENGTH {
                return Err(rmcp::ErrorData::invalid_params(
                    format!(
                        "metadata key '{}' exceeds the maximum length of {} characters",
                        key, MAX_META_KEY_LENGTH
                    ),
                    None,
                ));
            }
            if value.chars().count() > MAX_META_VALUE_LENGTH {
                return Err(rmcp::ErrorData::invalid_params(
                    format!(
                        "metadata JSON value for key '{}' exceeds the maximum length of {} characters",
                        key, MAX_META_VALUE_LENGTH
                    ),
                    None,
                ));
            }
            continue;
        }
        // key=value or key@path
        if let Some((key, value)) = entry.split_once('=') {
            if key.chars().count() > MAX_META_KEY_LENGTH {
                return Err(rmcp::ErrorData::invalid_params(
                    format!(
                        "metadata key '{}' exceeds the maximum length of {} characters",
                        key, MAX_META_KEY_LENGTH
                    ),
                    None,
                ));
            }
            if value.chars().count() > MAX_META_VALUE_LENGTH {
                return Err(rmcp::ErrorData::invalid_params(
                    format!(
                        "metadata value for key '{}' exceeds the maximum length of {} characters",
                        key, MAX_META_VALUE_LENGTH
                    ),
                    None,
                ));
            }
        } else {
            // Fallback: entry without = or := — check total length
            let max_total = MAX_META_KEY_LENGTH + MAX_META_VALUE_LENGTH;
            if entry.chars().count() > max_total {
                let preview = entry.chars().take(50).collect::<String>();
                return Err(rmcp::ErrorData::invalid_params(
                    format!(
                        "metadata entry '{}' exceeds the maximum length of {} characters",
                        preview, max_total
                    ),
                    None,
                ));
            }
        }
    }
    Ok(())
}