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/*
 * Copyright (c) 2019. JetBrains s.r.o.
 * Use of this source code is governed by the MIT license that can be found in the LICENSE file.
 */

package jetbrains.datalore.base.function

object Functions {

    private val TRUE_PREDICATE: Predicate = {
        true
    }

    private val FALSE_PREDICATE: Predicate = {
        false
    }

    private val NULL_PREDICATE: Predicate = {
        it == null
    }

    private val NOT_NULL_PREDICATE: Predicate = {
        it != null
    }

    fun  constantSupplier(value: ItemT): Supplier {
        return object : Supplier {
            override fun get(): ItemT {
                return value
            }
        }
    }

    fun  memorize(supplier: Supplier): Supplier {
        return Memo(supplier)
    }

    fun  alwaysTrue(): Predicate {
        return TRUE_PREDICATE
    }

    fun  alwaysFalse(): Predicate {
        return FALSE_PREDICATE
    }

    fun  constant(result: ResultT): (ArgT) -> ResultT {
        return {
            result
        }
    }

    fun  isNull(): Predicate {
        return NULL_PREDICATE
    }

    fun  isNotNull(): Predicate {
        return NOT_NULL_PREDICATE
    }

    fun  identity(): (ValueT) -> ValueT {
        return { it }
    }

    fun  same(value: Any?): Predicate {
        return {
            it === value
        }
    }

    fun  funcOf(lambda: (ArgT) -> ResultT): Function {
        return object : Function {
            override fun apply(value: ArgT): ResultT {
                return lambda(value)
            }
        }
    }

    private class Memo internal constructor(private val mySupplier: Supplier) : Supplier {
        private var myCachedValue: ItemT? = null
        private var myCached = false

        override fun get(): ItemT {
            if (!myCached) {
                myCachedValue = mySupplier.get()
                myCached = true
            }
            return myCachedValue!!
        }
    }
}