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Ktor is a framework for quickly creating web applications in Kotlin with minimal effort.

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/*
* Copyright 2014-2021 JetBrains s.r.o and contributors. Use of this source code is governed by the Apache 2.0 license.
*/

package io.ktor.http

/**
 * Range specifier for partial content requests (RFC 2616 sec 14.35.1)
 * @property unit range units, usually bytes
 * @property ranges a list of requested ranges (could be open or closed ranges)
 */
public data class RangesSpecifier(val unit: String = RangeUnits.Bytes.unitToken, val ranges: List) {

    public constructor(unit: RangeUnits, ranges: List) : this(unit.unitToken, ranges)

    init {
        require(ranges.isNotEmpty()) { "It should be at least one range" }
    }

    /**
     * Verify ranges
     */
    public fun isValid(rangeUnitPredicate: (String) -> Boolean = { it == RangeUnits.Bytes.unitToken }): Boolean =
        rangeUnitPredicate(unit) && ranges.none {
            when (it) {
                is ContentRange.Bounded -> it.from < 0 || it.to < it.from
                is ContentRange.TailFrom -> it.from < 0
                is ContentRange.Suffix -> it.lastCount < 0
            }
        }

    /**
     * Resolve and merge all overlapping and neighbours ranges
     * @param length content length
     * @return a list of absolute long ranges
     */
    public fun merge(length: Long, maxRangeCount: Int = 50): List {
        if (ranges.size > maxRangeCount) {
            return mergeToSingle(length).toList()
        }

        // TODO rangeMergeMaxGap
        return merge(length)
    }

    /**
     * Merges all overlapping and neighbours ranges. Currently gaps collapse is not supported but should be, one day.
     */
    public fun merge(length: Long): List = ranges.toLongRanges(length).mergeRangesKeepOrder()

    /**
     * Merge all ranges into a single absolute long range
     * @param length content length
     */
    public fun mergeToSingle(length: Long): LongRange? {
        val mapped = ranges.toLongRanges(length)

        if (mapped.isEmpty()) {
            return null
        }

        val start = mapped.minByOrNull { it.first }!!.first
        val endInclusive = mapped.maxByOrNull { it.last }!!.last.coerceAtMost(length - 1)

        return start..endInclusive
    }

    override fun toString(): String = ranges.joinToString(",", prefix = "$unit=")

    private fun  T?.toList(): List = if (this == null) emptyList() else listOf(this)
}