package msc2836

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

	"github.com/matrix-org/dendrite/internal/config"
	"github.com/matrix-org/dendrite/internal/sqlutil"
	"github.com/matrix-org/gomatrixserverlib"
)

type Database interface {
	// StoreRelation stores the parent->child and child->parent relationship for later querying.
	StoreRelation(ctx context.Context, ev *gomatrixserverlib.HeaderedEvent) error
	ChildrenForParent(ctx context.Context, eventID, relType string) ([]string, error)
}

type DB struct {
	db                          *sql.DB
	writer                      sqlutil.Writer
	insertRelationStmt          *sql.Stmt
	selectChildrenForParentStmt *sql.Stmt
}

// NewDatabase loads the database for msc2836
func NewDatabase(dbOpts *config.DatabaseOptions) (Database, error) {
	if dbOpts.ConnectionString.IsPostgres() {
		return newPostgresDatabase(dbOpts)
	}
	return newSQLiteDatabase(dbOpts)
}

func newPostgresDatabase(dbOpts *config.DatabaseOptions) (Database, error) {
	d := DB{
		writer: sqlutil.NewDummyWriter(),
	}
	var err error
	if d.db, err = sqlutil.Open(dbOpts); err != nil {
		return nil, err
	}
	_, err = d.db.Exec(`
	CREATE TABLE IF NOT EXISTS msc2836_edges (
		parent_event_id TEXT NOT NULL,
		child_event_id TEXT NOT NULL,
		rel_type TEXT NOT NULL,
		CONSTRAINT msc2836_edges UNIQUE (parent_event_id, child_event_id, rel_type)
	);
	`)
	if err != nil {
		return nil, err
	}
	if d.insertRelationStmt, err = d.db.Prepare(`
		INSERT INTO msc2836_edges(parent_event_id, child_event_id, rel_type) VALUES($1, $2, $3) ON CONFLICT DO NOTHING
	`); err != nil {
		return nil, err
	}
	if d.selectChildrenForParentStmt, err = d.db.Prepare(`
		SELECT child_event_id FROM msc2836_edges WHERE parent_event_id = $1 AND rel_type = $2
	`); err != nil {
		return nil, err
	}
	return &d, err
}

func newSQLiteDatabase(dbOpts *config.DatabaseOptions) (Database, error) {
	d := DB{
		writer: sqlutil.NewExclusiveWriter(),
	}
	var err error
	if d.db, err = sqlutil.Open(dbOpts); err != nil {
		return nil, err
	}
	_, err = d.db.Exec(`
	CREATE TABLE IF NOT EXISTS msc2836_edges (
		parent_event_id TEXT NOT NULL,
		child_event_id TEXT NOT NULL,
		rel_type TEXT NOT NULL,
		UNIQUE (parent_event_id, child_event_id, rel_type)
	);
	`)
	if err != nil {
		return nil, err
	}
	if d.insertRelationStmt, err = d.db.Prepare(`
		INSERT INTO msc2836_edges(parent_event_id, child_event_id, rel_type) VALUES($1, $2, $3) ON CONFLICT (parent_event_id, child_event_id, rel_type) DO NOTHING
	`); err != nil {
		return nil, err
	}
	if d.selectChildrenForParentStmt, err = d.db.Prepare(`
		SELECT child_event_id FROM msc2836_edges WHERE parent_event_id = $1 AND rel_type = $2
	`); err != nil {
		return nil, err
	}
	return &d, nil
}

func (p *DB) StoreRelation(ctx context.Context, ev *gomatrixserverlib.HeaderedEvent) error {
	parent, child, relType := parentChildEventIDs(ev)
	if parent == "" || child == "" {
		return nil
	}
	_, err := p.insertRelationStmt.ExecContext(ctx, parent, child, relType)
	return err
}

func (p *DB) ChildrenForParent(ctx context.Context, eventID, relType string) ([]string, error) {
	rows, err := p.selectChildrenForParentStmt.QueryContext(ctx, eventID, relType)
	if err != nil {
		return nil, err
	}
	defer rows.Close() // nolint: errcheck
	var children []string
	for rows.Next() {
		var childID string
		if err := rows.Scan(&childID); err != nil {
			return nil, err
		}
		children = append(children, childID)
	}
	return children, nil
}

func parentChildEventIDs(ev *gomatrixserverlib.HeaderedEvent) (parent, child, relType string) {
	if ev == nil {
		return
	}
	body := struct {
		Relationship struct {
			RelType string `json:"rel_type"`
			EventID string `json:"event_id"`
		} `json:"m.relationship"`
	}{}
	if err := json.Unmarshal(ev.Content(), &body); err != nil {
		return
	}
	if body.Relationship.EventID == "" || body.Relationship.RelType == "" {
		return
	}
	return body.Relationship.EventID, ev.EventID(), body.Relationship.RelType
}