AndroidRoomQueryBuilder.kt

internal class QueryBuilder(private val tableName: String) {
    private val columns = mutableListOf<String>()
    private val joins = mutableListOf<String>()
    private val filters = mutableListOf<String>()
    private val groupBy = mutableListOf<String>()
    private var orderBy = mutableListOf<String>()
    private var limit: Int? = null
    private var offset: Int? = null

    fun select(vararg columns: String) = apply {
        this.columns.addAll(columns)
    }

    fun join(joinClause: String) = apply {
        joins.add(joinClause)
    }

    fun bulkJoins(joinClauses: List<String>) = apply {
        joins.addAll(joinClauses)
    }

    fun where(condition: String) = apply {
        filters.add(condition)
    }

    fun orderBy(column: String, sortOrder: String) = apply {
        orderBy.add("$column $sortOrder")
    }

    fun groupBy(vararg columns: String) = apply {
        this.groupBy.addAll(columns)
    }

    fun paginate(page: Int, perPage: Int = PagingConsts.PERPAGE) = apply {
        this.limit = perPage
        this.offset = (page - 1) * perPage // so we don't get duplicate entries from old page
    }

    fun build(): String {
        val query = buildString {
            append("SELECT ")
            append(if (columns.isEmpty()) "*" else columns.joinToString(", "))
            append(" FROM $tableName")
            if (joins.isNotEmpty()) append(" ${joins.joinToString(" ")}")
            if (filters.isNotEmpty()) append(" WHERE ${filters.joinToString(" AND ")}")
            if (groupBy.isNotEmpty()) append(" GROUP BY ${groupBy.joinToString(", ")}")
            if (orderBy.isNotEmpty()) append(" ORDER BY ${orderBy.joinToString(", ")}")
            limit?.let { append(" LIMIT $it") }
            offset?.let { append(" OFFSET $it") }
        }
        Log.d("QueryBuilder", query)
        return query
    }
}

// DSL for query building
internal fun buildQuery(
    tableName: String,
    page: Int,
    builder: QueryBuilder.() -> Unit
): SimpleSQLiteQuery {
    return SimpleSQLiteQuery(
        QueryBuilder(tableName).apply(block = builder)
            .paginate(page = page).build()
    )
}

internal fun buildQuery(
    tableName: String,
    builder: QueryBuilder.() -> Unit
): SimpleSQLiteQuery {
    return SimpleSQLiteQuery(
        QueryBuilder(tableName).apply(block = builder).build()
    )
}