package server

import (
	"database/sql"
	"errors"
	"fmt"
	_ "github.com/mattn/go-sqlite3" // SQLite driver
	"log"
	"strings"
	"time"
)

// Messages cache
const (
	createMessagesTableQuery = `
		BEGIN;
		CREATE TABLE IF NOT EXISTS messages (
			id TEXT PRIMARY KEY,
			time INT NOT NULL,
			topic TEXT NOT NULL,
			message TEXT NOT NULL,
			title TEXT NOT NULL,
			priority INT NOT NULL,
			tags TEXT NOT NULL,
			published INT NOT NULL
		);
		CREATE INDEX IF NOT EXISTS idx_topic ON messages (topic);
		COMMIT;
	`
	insertMessageQuery           = `INSERT INTO messages (id, time, topic, message, title, priority, tags, published) VALUES (?, ?, ?, ?, ?, ?, ?, ?)`
	pruneMessagesQuery           = `DELETE FROM messages WHERE time < ? AND published = 1`
	selectMessagesSinceTimeQuery = `
		SELECT id, time, topic, message, title, priority, tags
		FROM messages 
		WHERE topic = ? AND time >= ? AND published = 1
		ORDER BY time ASC
	`
	selectMessagesSinceTimeIncludeScheduledQuery = `
		SELECT id, time, topic, message, title, priority, tags
		FROM messages 
		WHERE topic = ? AND time >= ?
		ORDER BY time ASC
	`
	selectMessagesDueQuery = `
		SELECT id, time, topic, message, title, priority, tags
		FROM messages 
		WHERE time <= ? AND published = 0
	`
	updateMessagePublishedQuery     = `UPDATE messages SET published = 1 WHERE id = ?`
	selectMessagesCountQuery        = `SELECT COUNT(*) FROM messages`
	selectMessageCountForTopicQuery = `SELECT COUNT(*) FROM messages WHERE topic = ?`
	selectTopicsQuery               = `SELECT topic FROM messages GROUP BY topic`
)

// Schema management queries
const (
	currentSchemaVersion          = 2
	createSchemaVersionTableQuery = `
		CREATE TABLE IF NOT EXISTS schemaVersion (
			id INT PRIMARY KEY,
			version INT NOT NULL
		);
	`
	insertSchemaVersion      = `INSERT INTO schemaVersion VALUES (1, ?)`
	updateSchemaVersion      = `UPDATE schemaVersion SET version = ? WHERE id = 1`
	selectSchemaVersionQuery = `SELECT version FROM schemaVersion WHERE id = 1`

	// 0 -> 1
	migrate0To1AlterMessagesTableQuery = `
		BEGIN;
		ALTER TABLE messages ADD COLUMN title TEXT NOT NULL DEFAULT('');
		ALTER TABLE messages ADD COLUMN priority INT NOT NULL DEFAULT(0);
		ALTER TABLE messages ADD COLUMN tags TEXT NOT NULL DEFAULT('');
		COMMIT;
	`

	// 1 -> 2
	migrate1To2AlterMessagesTableQuery = `
		ALTER TABLE messages ADD COLUMN published INT NOT NULL DEFAULT(1);
	`
)

type sqliteCache struct {
	db *sql.DB
}

var _ cache = (*sqliteCache)(nil)

func newSqliteCache(filename string) (*sqliteCache, error) {
	db, err := sql.Open("sqlite3", filename)
	if err != nil {
		return nil, err
	}
	if err := setupDB(db); err != nil {
		return nil, err
	}
	return &sqliteCache{
		db: db,
	}, nil
}

func (c *sqliteCache) AddMessage(m *message) error {
	if m.Event != messageEvent {
		return errUnexpectedMessageType
	}
	published := m.Time <= time.Now().Unix()
	_, err := c.db.Exec(insertMessageQuery, m.ID, m.Time, m.Topic, m.Message, m.Title, m.Priority, strings.Join(m.Tags, ","), published)
	return err
}

func (c *sqliteCache) Messages(topic string, since sinceTime, scheduled bool) ([]*message, error) {
	if since.IsNone() {
		return make([]*message, 0), nil
	}
	var rows *sql.Rows
	var err error
	if scheduled {
		rows, err = c.db.Query(selectMessagesSinceTimeIncludeScheduledQuery, topic, since.Time().Unix())
	} else {
		rows, err = c.db.Query(selectMessagesSinceTimeQuery, topic, since.Time().Unix())
	}
	if err != nil {
		return nil, err
	}
	return readMessages(rows)
}

func (c *sqliteCache) MessagesDue() ([]*message, error) {
	rows, err := c.db.Query(selectMessagesDueQuery, time.Now().Unix())
	if err != nil {
		return nil, err
	}
	return readMessages(rows)
}

func (c *sqliteCache) MarkPublished(m *message) error {
	_, err := c.db.Exec(updateMessagePublishedQuery, m.ID)
	return err
}

func (c *sqliteCache) MessageCount(topic string) (int, error) {
	rows, err := c.db.Query(selectMessageCountForTopicQuery, topic)
	if err != nil {
		return 0, err
	}
	defer rows.Close()
	var count int
	if !rows.Next() {
		return 0, errors.New("no rows found")
	}
	if err := rows.Scan(&count); err != nil {
		return 0, err
	} else if err := rows.Err(); err != nil {
		return 0, err
	}
	return count, nil
}

func (c *sqliteCache) Topics() (map[string]*topic, error) {
	rows, err := c.db.Query(selectTopicsQuery)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	topics := make(map[string]*topic)
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		topics[id] = newTopic(id)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return topics, nil
}

func (c *sqliteCache) Prune(olderThan time.Time) error {
	_, err := c.db.Exec(pruneMessagesQuery, olderThan.Unix())
	return err
}

func readMessages(rows *sql.Rows) ([]*message, error) {
	defer rows.Close()
	messages := make([]*message, 0)
	for rows.Next() {
		var timestamp int64
		var priority int
		var id, topic, msg, title, tagsStr string
		if err := rows.Scan(&id, &timestamp, &topic, &msg, &title, &priority, &tagsStr); err != nil {
			return nil, err
		}
		var tags []string
		if tagsStr != "" {
			tags = strings.Split(tagsStr, ",")
		}
		messages = append(messages, &message{
			ID:       id,
			Time:     timestamp,
			Event:    messageEvent,
			Topic:    topic,
			Message:  msg,
			Title:    title,
			Priority: priority,
			Tags:     tags,
		})
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return messages, nil
}

func setupDB(db *sql.DB) error {
	// If 'messages' table does not exist, this must be a new database
	rowsMC, err := db.Query(selectMessagesCountQuery)
	if err != nil {
		return setupNewDB(db)
	}
	rowsMC.Close()

	// If 'messages' table exists, check 'schemaVersion' table
	schemaVersion := 0
	rowsSV, err := db.Query(selectSchemaVersionQuery)
	if err == nil {
		defer rowsSV.Close()
		if !rowsSV.Next() {
			return errors.New("cannot determine schema version: cache file may be corrupt")
		}
		if err := rowsSV.Scan(&schemaVersion); err != nil {
			return err
		}
		rowsSV.Close()
	}

	// Do migrations
	if schemaVersion == currentSchemaVersion {
		return nil
	} else if schemaVersion == 0 {
		return migrateFrom0(db)
	} else if schemaVersion == 1 {
		return migrateFrom1(db)
	}
	return fmt.Errorf("unexpected schema version found: %d", schemaVersion)
}

func setupNewDB(db *sql.DB) error {
	if _, err := db.Exec(createMessagesTableQuery); err != nil {
		return err
	}
	if _, err := db.Exec(createSchemaVersionTableQuery); err != nil {
		return err
	}
	if _, err := db.Exec(insertSchemaVersion, currentSchemaVersion); err != nil {
		return err
	}
	return nil
}

func migrateFrom0(db *sql.DB) error {
	log.Print("Migrating cache database schema: from 0 to 1")
	if _, err := db.Exec(migrate0To1AlterMessagesTableQuery); err != nil {
		return err
	}
	if _, err := db.Exec(createSchemaVersionTableQuery); err != nil {
		return err
	}
	if _, err := db.Exec(insertSchemaVersion, 1); err != nil {
		return err
	}
	return migrateFrom1(db)
}

func migrateFrom1(db *sql.DB) error {
	log.Print("Migrating cache database schema: from 1 to 2")
	if _, err := db.Exec(migrate1To2AlterMessagesTableQuery); err != nil {
		return err
	}
	if _, err := db.Exec(updateSchemaVersion, 2); err != nil {
		return err
	}
	return nil // Update this when a new version is added
}