package nomad

import (
	"database/sql"
	"fmt"

	_ "github.com/mattn/go-sqlite3"
)

type Executor interface {
	Exec(stmt string, args ...interface{}) (sql.Result, error)
	Query(stmt string, args ...interface{}) (*sql.Rows, error)
}

func buildArgs(n int) string {
	s := ""
	for i := 0; i < n; i++ {
		s += "?,"
	}

	return s[:len(s)-1]
}

type DB struct {
	path string
	db   *sql.DB
}

func NewDB(path string) *DB {
	return &DB{path: path}
}

func (db *DB) Connect() (err error) {
	if db.db != nil {
		return nil
	}
	db.db, err = sql.Open("sqlite3", db.path)
	return err
}

func (db *DB) Close() error {
	if db.db == nil {
		return nil
	}
	err := db.db.Close()
	db.db = nil
	return err
}

func (db *DB) Create() (err error) {
	err = db.Connect()
	if err != nil {
		return err
	}

	_, err = db.db.Exec(createSQL)
	return err
}

func (db *DB) Begin() (tx *sql.Tx, err error) {
	err = db.Connect()
	if err != nil {
		return tx, err
	}

	return db.db.Begin()
}

func (db *DB) executor(tx *sql.Tx) Executor {
	if tx != nil {
		return tx
	}

	return db.db
}

func (db *DB) Mark(tx *sql.Tx, item Item) (err error) {
	_, err = db.executor(tx).Exec(markSQL, item.URL.ID(), item.Title, item.PubDate)
	return err
}

func (db *DB) Filter(tx *sql.Tx, items []Item) (newItems []Item, err error) {
	seen := map[string]bool{}
	args := buildArgs(len(items))
	stmt := fmt.Sprintf(filterSQLTpl, args)
	urls := make([]interface{}, 0, len(items))
	for _, item := range items {
		urls = append(urls, item.URL.ID())
	}

	rows, err := db.executor(tx).Query(stmt, urls...)
	if err != nil {
		return nil, err
	}
	for rows.Next() {
		var url string
		err = rows.Scan(&url)
		if err != nil {
			return nil, err
		}
		seen[url] = true
	}

	for _, item := range items {
		if seen[item.URL.ID()] {
			continue
		}
		newItems = append(newItems, item)
	}

	// Reverse the list of items so that they are in reverse chronological order.
	nitems := len(items) - 1
	for i := range items {
		j := nitems - i
		items[i], items[j] = items[j], items[i]
	}

	return newItems, nil
}