//! Persisted custom chat draft model.

use serde::{Deserialize, Serialize};
use thiserror::Error;

use crate::ids::{LayoutId, NodeId, ProjectId};

/// Maximum draft text size persisted by IdeA.
pub const CHAT_DRAFT_MAX_BYTES: usize = 100 * 1024;

/// Stable scope for one custom chat draft.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ChatDraftKey {
    /// Project owning the layout.
    pub project_id: ProjectId,
    /// Named layout containing the chat cell.
    pub layout_id: LayoutId,
    /// Layout node hosting the chat cell.
    pub node_id: NodeId,
}

impl ChatDraftKey {
    /// Builds a draft key.
    #[must_use]
    pub const fn new(project_id: ProjectId, layout_id: LayoutId, node_id: NodeId) -> Self {
        Self {
            project_id,
            layout_id,
            node_id,
        }
    }
}

/// Durable text draft for one custom chat composer.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ChatDraft {
    /// Stable draft scope.
    pub key: ChatDraftKey,
    /// Draft text. Attachments are deliberately excluded.
    pub text: String,
    /// Last update time, epoch milliseconds.
    pub updated_at_ms: u64,
}

impl ChatDraft {
    /// Builds validated draft metadata.
    ///
    /// # Errors
    /// Returns [`ChatDraftError::TooLarge`] when `text` exceeds the maximum
    /// persisted draft size.
    pub fn new(
        key: ChatDraftKey,
        text: impl Into<String>,
        updated_at_ms: u64,
    ) -> Result<Self, ChatDraftError> {
        let text = text.into();
        if text.len() > CHAT_DRAFT_MAX_BYTES {
            return Err(ChatDraftError::TooLarge {
                max: CHAT_DRAFT_MAX_BYTES,
                actual: text.len(),
            });
        }
        Ok(Self {
            key,
            text,
            updated_at_ms,
        })
    }
}

/// Chat draft validation errors.
#[derive(Debug, Clone, PartialEq, Eq, Error)]
pub enum ChatDraftError {
    /// Draft content exceeds the persisted size limit.
    #[error("chat draft exceeds {max} bytes: {actual}")]
    TooLarge {
        /// Maximum allowed bytes.
        max: usize,
        /// Actual text bytes.
        actual: usize,
    },
}