process BOWTIE2_ALIGN {
    tag "$meta.id"
    label "process_high"

    conda (params.enable_conda ? "bioconda::bowtie2=2.4.4 bioconda::samtools=1.15.1 conda-forge::pigz=2.6" : null)
    container "${ workflow.containerEngine == "singularity" && !task.ext.singularity_pull_docker_container ?
        "https://depot.galaxyproject.org/singularity/mulled-v2-ac74a7f02cebcfcc07d8e8d1d750af9c83b4d45a:1744f68fe955578c63054b55309e05b41c37a80d-0" :
        "quay.io/biocontainers/mulled-v2-ac74a7f02cebcfcc07d8e8d1d750af9c83b4d45a:1744f68fe955578c63054b55309e05b41c37a80d-0" }"

    input:
    tuple val(meta), path(reads)
    path  index
    val   save_unaligned

    output:
    tuple val(meta), path("*.bam")    , emit: bam
    tuple val(meta), path("*.log")    , emit: log
    tuple val(meta), path("*fastq.gz"), emit: fastq, optional:true
    path  "versions.yml"              , emit: versions

    when:
    task.ext.when == null || task.ext.when

    script:
    def args = task.ext.args ?: ""
    def args2 = task.ext.args2 ?: ""
    def prefix = task.ext.prefix ?: "${meta.id}"

    def unaligned = ""
    def reads_args = ""
    if (meta.single_end) {
        unaligned = save_unaligned ? "--un-gz ${prefix}.unmapped.fastq.gz" : ""
        reads_args = "-U ${reads}"
    } else {
        unaligned = save_unaligned ? "--un-conc-gz ${prefix}.unmapped.fastq.gz" : ""
        reads_args = "-1 ${reads[0]} -2 ${reads[1]}"
    }

    def samtools = "samtools view -@ $task.cpus --fast --with-header ${args2} > ${prefix}.bam"


    """
    INDEX=`find -L ./ -name "*.rev.1.bt2" | sed "s/.rev.1.bt2//"`
    [ -z "\$INDEX" ] && INDEX=`find -L ./ -name "*.rev.1.bt2l" | sed "s/.rev.1.bt2l//"`
    [ -z "\$INDEX" ] && echo "BT2 index files not found" 1>&2 && exit 1

    bowtie2 \\
        -x \$INDEX \\
        ${reads_args} \\
        --threads $task.cpus \\
        $unaligned \\
        $args \\
        2> ${prefix}.bowtie2.log \\
        | ${samtools}

    if [ -f ${prefix}.unmapped.fastq.1.gz ]; then
        mv ${prefix}.unmapped.fastq.1.gz ${prefix}.unmapped_1.fastq.gz
    fi

    if [ -f ${prefix}.unmapped.fastq.2.gz ]; then
        mv ${prefix}.unmapped.fastq.2.gz ${prefix}.unmapped_2.fastq.gz
    fi

    cat <<-END_VERSIONS > versions.yml
    "${task.process}":
        bowtie2: \$(echo \$(bowtie2 --version 2>&1) | sed 's/^.*bowtie2-align-s version //; s/ .*\$//')
        samtools: \$(echo \$(samtools --version 2>&1) | sed 's/^.*samtools //; s/Using.*\$//')
        pigz: \$( pigz --version 2>&1 | sed 's/pigz //g' )
    END_VERSIONS
    """
}