package platform

import (
	"database/sql"
	"errors"
	"net/http"
)

type subgraphRelation struct {
	Parent   string `json:"parent_board_id"`
	Frame    string `json:"frame_id"`
	Child    string `json:"child_board_id"`
	Archived bool   `json:"archived"`
}
type subgraphRelationChange struct {
	Before subgraphRelation `json:"before"`
	After  subgraphRelation `json:"after"`
}

func readSubgraphRelation(r *http.Request, tx *sql.Tx, project, workspace, child string) (subgraphRelation, error) {
	result := subgraphRelation{Child: child}
	err := tx.QueryRowContext(r.Context(), `SELECT parent_board_id::text,frame_id,archived_at IS NOT NULL FROM canvas_subgraphs WHERE project=$1 AND workspace_id=$2 AND child_board_id=$3 FOR UPDATE`, project, workspace, child).Scan(&result.Parent, &result.Frame, &result.Archived)
	return result, err
}
func writeSubgraphRelation(r *http.Request, tx *sql.Tx, project, workspace string, relation subgraphRelation) error {
	before, err := readSubgraphRelation(r, tx, project, workspace, relation.Child)
	if err != nil {
		return err
	}
	if before != relation {
		if !relation.Archived {
			if err = validateSubgraphPlacement(r, tx, project, workspace, relation.Parent, relation.Child); err != nil {
				return err
			}
		}
		if err = invalidateCanvasAISubtree(r, tx, project, workspace, relation.Child); err != nil {
			return err
		}
	}

	_, err = tx.ExecContext(r.Context(), `UPDATE canvas_subgraphs SET parent_board_id=$4,frame_id=$5,archived_at=CASE WHEN $6 THEN COALESCE(archived_at,now()) ELSE NULL END WHERE project=$1 AND workspace_id=$2 AND child_board_id=$3`, project, workspace, relation.Child, relation.Parent, relation.Frame, relation.Archived)
	return err
}

var errSubgraphCycle = errors.New("subgraph_cycle")
var errSubgraphDepth = errors.New("subgraph_depth_exceeded")

func validateSubgraphPlacement(r *http.Request, tx *sql.Tx, project, workspace, parent, child string) error {
	var cycle bool
	var depth int
	err := tx.QueryRowContext(r.Context(), `WITH RECURSIVE ancestors(id,depth) AS(
 SELECT $3::uuid,0 UNION ALL SELECT s.parent_board_id,a.depth+1 FROM ancestors a JOIN canvas_subgraphs s ON s.project=$1 AND s.workspace_id=$2 AND s.child_board_id=a.id AND s.archived_at IS NULL WHERE a.depth<8
 ), descendants(id,depth) AS(
 SELECT $4::uuid,0 UNION ALL SELECT s.child_board_id,d.depth+1 FROM descendants d JOIN canvas_subgraphs s ON s.project=$1 AND s.workspace_id=$2 AND s.parent_board_id=d.id AND s.archived_at IS NULL WHERE d.depth<8
 ) SELECT EXISTS(SELECT 1 FROM ancestors WHERE id=$4::uuid), (SELECT max(depth) FROM ancestors)+1+(SELECT max(depth) FROM descendants)`, project, workspace, parent, child).Scan(&cycle, &depth)
	if err != nil {
		return err
	}
	if cycle {
		return errSubgraphCycle
	}
	if depth > 8 {
		return errSubgraphDepth
	}
	return nil
}