core/server/handlers/tree.go

package handlers

import (
	"database/sql"
	"encoding/json"
	"fmt"

	"git.gobha.me/xcaliber/chat-switchboard/database"
)

// ── Tree Types ──────────────────────────────

// PathMessage represents a single message in an active path, enriched
// with sibling metadata for the frontend branch indicator.
type PathMessage struct {
	ID              string           `json:"id"`
	ParentID        *string          `json:"parent_id"`
	Role            string           `json:"role"`
	Content         string           `json:"content"`
	Model           *string          `json:"model"`
	TokensUsed      *int             `json:"tokens_used,omitempty"`
	ToolCalls       *json.RawMessage `json:"tool_calls,omitempty"`
	Metadata        *json.RawMessage `json:"metadata,omitempty"`
	SiblingCount    int              `json:"sibling_count"`
	SiblingIndex    int              `json:"sibling_index"`
	ParticipantType string           `json:"participant_type,omitempty"`
	ParticipantID   string           `json:"participant_id,omitempty"`
	CreatedAt       string           `json:"created_at"`
}

// SiblingInfo is a lightweight entry for the siblings listing endpoint.
type SiblingInfo struct {
	ID           string  `json:"id"`
	Role         string  `json:"role"`
	Model        *string `json:"model,omitempty"`
	SiblingIndex int     `json:"sibling_index"`
	Preview      string  `json:"preview"` // first ~80 chars of content
	CreatedAt    string  `json:"created_at"`
}

// ── Get Active Leaf ─────────────────────────

// getActiveLeaf returns the cursor's active_leaf_id for a user in a channel.
// Falls back to the chronologically latest live message if no cursor exists.
func getActiveLeaf(channelID, userID string) (*string, error) {
	var leafID *string

	// Try cursor first
	err := database.DB.QueryRow(`
		SELECT active_leaf_id FROM channel_cursors
		WHERE channel_id = $1 AND user_id = $2
	`, channelID, userID).Scan(&leafID)

	if err == nil && leafID != nil {
		// Verify the leaf still exists and isn't deleted
		var exists bool
		database.DB.QueryRow(`
			SELECT EXISTS(SELECT 1 FROM messages WHERE id = $1 AND deleted_at IS NULL)
		`, *leafID).Scan(&exists)
		if exists {
			return leafID, nil
		}
	}

	// Fallback: latest live message in channel
	var fallbackID string
	err = database.DB.QueryRow(`
		SELECT id FROM messages
		WHERE channel_id = $1 AND deleted_at IS NULL
		ORDER BY created_at DESC LIMIT 1
	`, channelID).Scan(&fallbackID)
	if err == sql.ErrNoRows {
		return nil, nil // empty channel
	}
	if err != nil {
		return nil, err
	}
	return &fallbackID, nil
}

// ── Get Active Path ─────────────────────────

// getActivePath walks from the active leaf up to the root via parent_id,
// returning messages in root-first order. This is what gets sent to the LLM.
func getActivePath(channelID, userID string) ([]PathMessage, error) {
	leafID, err := getActiveLeaf(channelID, userID)
	if err != nil {
		return nil, err
	}
	if leafID == nil {
		return []PathMessage{}, nil // empty channel
	}

	return getPathToLeaf(channelID, *leafID)
}

// getPathToLeaf walks from a specific leaf up to root, returning root-first.
func getPathToLeaf(channelID, leafID string) ([]PathMessage, error) {
	rows, err := database.DB.Query(`
		WITH RECURSIVE path AS (
			-- Anchor: start at the leaf
			SELECT id, parent_id, role, content, model, tokens_used, tool_calls, metadata,
			       participant_type, participant_id, sibling_index, created_at,
			       0 AS depth
			FROM messages
			WHERE id = $1 AND channel_id = $2 AND deleted_at IS NULL

			UNION ALL

			-- Walk up via parent_id
			SELECT m.id, m.parent_id, m.role, m.content, m.model, m.tokens_used, m.tool_calls, m.metadata,
			       m.participant_type, m.participant_id, m.sibling_index, m.created_at,
			       p.depth + 1
			FROM messages m
			JOIN path p ON m.id = p.parent_id
			WHERE m.deleted_at IS NULL
		)
		SELECT id, parent_id, role, content, model, tokens_used, tool_calls, metadata,
		       participant_type, participant_id, sibling_index, created_at
		FROM path
		ORDER BY depth DESC
	`, leafID, channelID)
	if err != nil {
		return nil, fmt.Errorf("getPathToLeaf: %w", err)
	}
	defer rows.Close()

	var path []PathMessage
	for rows.Next() {
		var m PathMessage
		var participantType, participantID sql.NullString
		var toolCallsJSON, metadataJSON []byte
		if err := rows.Scan(
			&m.ID, &m.ParentID, &m.Role, &m.Content, &m.Model, &m.TokensUsed,
			&toolCallsJSON, &metadataJSON,
			&participantType, &participantID, &m.SiblingIndex, &m.CreatedAt,
		); err != nil {
			return nil, fmt.Errorf("getPathToLeaf scan: %w", err)
		}
		if len(toolCallsJSON) > 0 && string(toolCallsJSON) != "null" {
			raw := json.RawMessage(toolCallsJSON)
			m.ToolCalls = &raw
		}
		if len(metadataJSON) > 0 && string(metadataJSON) != "null" && string(metadataJSON) != "{}" {
			raw := json.RawMessage(metadataJSON)
			m.Metadata = &raw
		}
		if participantType.Valid {
			m.ParticipantType = participantType.String
		}
		if participantID.Valid {
			m.ParticipantID = participantID.String
		}
		path = append(path, m)
	}

	// Enrich with sibling counts
	for i := range path {
		path[i].SiblingCount = getSiblingCount(channelID, path[i].ParentID)
	}

	return path, nil
}

// ── Sibling Queries ─────────────────────────

// getSiblingCount returns how many live siblings share the same parent_id.
// Root messages (parent_id IS NULL) count all roots in the same channel.
func getSiblingCount(channelID string, parentID *string) int {
	var count int
	if parentID == nil {
		database.DB.QueryRow(`
			SELECT COUNT(*) FROM messages
			WHERE channel_id = $1 AND parent_id IS NULL AND deleted_at IS NULL
		`, channelID).Scan(&count)
	} else {
		database.DB.QueryRow(`
			SELECT COUNT(*) FROM messages
			WHERE parent_id = $1 AND deleted_at IS NULL
		`, *parentID).Scan(&count)
	}
	if count == 0 {
		count = 1
	}
	return count
}

// getSiblings returns all live siblings of a given message (including itself),
// ordered by sibling_index.
func getSiblings(messageID string) ([]SiblingInfo, int, error) {
	// First get the parent_id of the target message
	var parentID *string
	var channelID string
	err := database.DB.QueryRow(`
		SELECT parent_id, channel_id FROM messages
		WHERE id = $1 AND deleted_at IS NULL
	`, messageID).Scan(&parentID, &channelID)
	if err != nil {
		return nil, 0, fmt.Errorf("message not found: %w", err)
	}

	var rows *sql.Rows
	if parentID == nil {
		// Root messages: siblings are other roots in the same channel
		rows, err = database.DB.Query(`
			SELECT id, role, model, sibling_index, LEFT(content, 80), created_at
			FROM messages
			WHERE channel_id = $1 AND parent_id IS NULL AND deleted_at IS NULL
			ORDER BY sibling_index, created_at
		`, channelID)
	} else {
		rows, err = database.DB.Query(`
			SELECT id, role, model, sibling_index, LEFT(content, 80), created_at
			FROM messages
			WHERE parent_id = $1 AND deleted_at IS NULL
			ORDER BY sibling_index, created_at
		`, *parentID)
	}
	if err != nil {
		return nil, 0, err
	}
	defer rows.Close()

	var siblings []SiblingInfo
	currentIdx := 0
	for i := 0; rows.Next(); i++ {
		var s SiblingInfo
		if err := rows.Scan(&s.ID, &s.Role, &s.Model, &s.SiblingIndex, &s.Preview, &s.CreatedAt); err != nil {
			return nil, 0, err
		}
		if s.ID == messageID {
			currentIdx = i
		}
		siblings = append(siblings, s)
	}

	return siblings, currentIdx, nil
}

// ── Find Leaf ───────────────────────────────

// findLeafFromMessage walks down from a message to find the deepest descendant.
// Follows the first child (lowest sibling_index) at each level.
// Used when switching branches: clicking a mid-tree sibling navigates to its leaf.
func findLeafFromMessage(messageID string) (string, error) {
	var leafID string
	err := database.DB.QueryRow(`
		WITH RECURSIVE descendants AS (
			SELECT id, 0 AS depth
			FROM messages
			WHERE id = $1 AND deleted_at IS NULL

			UNION ALL

			SELECT child.id, d.depth + 1
			FROM messages child
			JOIN descendants d ON child.parent_id = d.id
			WHERE child.deleted_at IS NULL
			  AND child.sibling_index = (
			      SELECT MIN(sibling_index) FROM messages
			      WHERE parent_id = d.id AND deleted_at IS NULL
			  )
		)
		SELECT id FROM descendants
		ORDER BY depth DESC
		LIMIT 1
	`, messageID).Scan(&leafID)

	if err != nil {
		return messageID, nil // if anything fails, just use the message itself
	}
	return leafID, nil
}

// ── Next Sibling Index ──────────────────────

// nextSiblingIndex returns the next sibling_index for a new child of parentID.
// For root messages (parentID is nil), counts existing roots in the channel.
func nextSiblingIndex(channelID string, parentID *string) int {
	var maxIdx sql.NullInt64
	if parentID == nil {
		database.DB.QueryRow(`
			SELECT MAX(sibling_index) FROM messages
			WHERE channel_id = $1 AND parent_id IS NULL AND deleted_at IS NULL
		`, channelID).Scan(&maxIdx)
	} else {
		database.DB.QueryRow(`
			SELECT MAX(sibling_index) FROM messages
			WHERE parent_id = $1 AND deleted_at IS NULL
		`, *parentID).Scan(&maxIdx)
	}
	if !maxIdx.Valid {
		return 0
	}
	return int(maxIdx.Int64) + 1
}

// ── Update Cursor ───────────────────────────

// updateCursor upserts the channel_cursors row for a user.
func updateCursor(channelID, userID, messageID string) error {
	_, err := database.DB.Exec(`
		INSERT INTO channel_cursors (channel_id, user_id, active_leaf_id)
		VALUES ($1, $2, $3)
		ON CONFLICT (channel_id, user_id) DO UPDATE SET
			active_leaf_id = $3, updated_at = NOW()
	`, channelID, userID, messageID)
	return err
}