use std::error::Error;
use std::fs;
use std::ops::Range;
use std::str;

use bio::io::fasta;
use bio::stats::{LogProb, PHREDProb};
use itertools::Itertools;
use ordered_float::NotNan;
use rust_htslib::bcf::Read;
use rust_htslib::{bam, bcf};

use model;
use utils;
use BCFError;
use Event;

pub const NUMERICAL_EPSILON: f64 = 1e-4;

/// Collect variants from a given ´bcf::Record`.
pub fn collect_variants(
    record: &mut bcf::Record,
    omit_snvs: bool,
    omit_indels: bool,
    indel_len_range: Option<Range<u32>>,
    exclusive_end: bool,
) -> Result<Vec<Option<model::Variant>>, Box<Error>> {
    let pos = record.pos();
    let svlen = match record.info(b"SVLEN").integer() {
        Ok(Some(svlen)) => Some(svlen[0].abs() as u32),
        _ => None,
    };
    let end = match record.info(b"END").integer() {
        Ok(Some(end)) => {
            let mut end = end[0] as u32 - 1;
            if exclusive_end {
                // this happens with DELLY
                debug!("fixing END tag");
                end -= 1;
            }
            Some(end)
        }
        _ => None,
    };
    // TODO avoid cloning svtype
    let svtype = match record.info(b"SVTYPE").string() {
        Ok(Some(svtype)) => Some(svtype[0].to_owned()),
        _ => None,
    };

    // check if len is within the given range
    let is_valid_len = |svlen| {
        if let Some(ref len_range) = indel_len_range {
            // TODO replace with Range::contains once stabilized
            if svlen < len_range.start || svlen >= len_range.end {
                return false;
            }
        }
        true
    };

    let is_valid_insertion_alleles = |ref_allele: &[u8], alt_allele: &[u8]| {
        alt_allele == b"<INS>"
            || (ref_allele.len() < alt_allele.len()
                && ref_allele == &alt_allele[..ref_allele.len()])
    };

    let is_valid_deletion_alleles = |ref_allele: &[u8], alt_allele: &[u8]| {
        alt_allele == b"<DEL>"
            || (ref_allele.len() > alt_allele.len()
                && &ref_allele[..alt_allele.len()] == alt_allele)
    };

    let variants = if let Some(svtype) = svtype {
        vec![if omit_indels {
            None
        } else if svtype == b"INS" {
            // get sequence
            let alleles = record.alleles();
            if alleles.len() > 2 {
                return Err(Box::new(BCFError::InvalidRecord(
                    "SVTYPE=INS but more than one ALT allele".to_owned(),
                )));
            }
            let ref_allele = alleles[0];
            let alt_allele = alleles[1];

            if alt_allele == b"<INS>" {
                // don't support insertions without exact sequence
                None
            } else {
                let len = alt_allele.len() - ref_allele.len();

                if is_valid_insertion_alleles(ref_allele, alt_allele) && is_valid_len(len as u32) {
                    Some(model::Variant::Insertion(
                        alt_allele[ref_allele.len()..].to_owned(),
                    ))
                } else {
                    None
                }
            }
        } else if svtype == b"DEL" {
            let svlen = match (svlen, end) {
                (Some(svlen), _) => svlen,
                (None, Some(end)) => end - pos,
                _ => {
                    return Err(Box::new(BCFError::MissingTag("SVLEN or END".to_owned())));
                }
            };
            let alleles = record.alleles();
            if alleles.len() > 2 {
                return Err(Box::new(BCFError::InvalidRecord(
                    "SVTYPE=DEL but more than one ALT allele".to_owned(),
                )));
            }
            let ref_allele = alleles[0];
            let alt_allele = alleles[1];

            if alt_allele == b"<DEL>" || is_valid_deletion_alleles(ref_allele, alt_allele) {
                if is_valid_len(svlen) {
                    Some(model::Variant::Deletion(svlen))
                } else {
                    None
                }
            } else {
                None
            }
        } else {
            None
        }]
    } else {
        let alleles = record.alleles();
        let ref_allele = alleles[0];

        alleles
            .iter()
            .skip(1)
            .map(|alt_allele| {
                if alt_allele == b"<*>" {
                    // dummy non-ref allele, signifying potential homozygous reference site
                    if omit_snvs {
                        None
                    } else {
                        Some(model::Variant::None)
                    }
                } else if alt_allele[0] == b'<' {
                    // skip allele if it is a special tag other than '<*>' (such alleles have been handled above)
                    None
                } else if alt_allele.len() == 1 && ref_allele.len() == 1 {
                    // SNV
                    if omit_snvs {
                        None
                    } else {
                        Some(model::Variant::SNV(alt_allele[0]))
                    }
                } else if alt_allele.len() == ref_allele.len() {
                    // neither indel nor SNV
                    None
                } else {
                    let indel_len =
                        (alt_allele.len() as i32 - ref_allele.len() as i32).abs() as u32;
                    // TODO fix position if variant is like this: cttt -> ct

                    if omit_indels {
                        None
                    } else if !is_valid_len(indel_len) {
                        None
                    } else if is_valid_deletion_alleles(ref_allele, alt_allele) {
                        Some(model::Variant::Deletion(
                            (ref_allele.len() - alt_allele.len()) as u32,
                        ))
                    } else if is_valid_insertion_alleles(ref_allele, alt_allele) {
                        Some(model::Variant::Insertion(
                            alt_allele[ref_allele.len()..].to_owned(),
                        ))
                    } else {
                        None
                    }
                }
            })
            .collect_vec()
    };

    Ok(variants)
}

/// A lazy buffer for reference sequences.
pub struct ReferenceBuffer {
    reader: fasta::IndexedReader<fs::File>,
    chrom: Option<Vec<u8>>,
    sequence: Vec<u8>,
}

impl ReferenceBuffer {
    pub fn new(fasta: fasta::IndexedReader<fs::File>) -> Self {
        ReferenceBuffer {
            reader: fasta,
            chrom: None,
            sequence: Vec::new(),
        }
    }

    /// Load given chromosome and return it as a slice. This is O(1) if chromosome was loaded before.
    pub fn seq(&mut self, chrom: &[u8]) -> Result<&[u8], Box<Error>> {
        if let Some(ref last_chrom) = self.chrom {
            if last_chrom == &chrom {
                return Ok(&self.sequence);
            }
        }
        self.reader.fetch_all(str::from_utf8(chrom)?)?;
        self.reader.read(&mut self.sequence)?;

        //try!(self.reader.read_all(try!(str::from_utf8(chrom)), &mut self.sequence));
        self.chrom = Some(chrom.to_owned());

        Ok(&self.sequence)
    }
}

/// Sum up in log space the probabilities of the given tags for all variants of
/// vartype in the given BCF record.
///
/// # Arguments
///
/// * `record` - BCF record
/// * `tags` - tags of the set of events to sum up for a particular site and variant
/// * `vartype` - the variant type to consider
fn tags_prob_sum(
    record: &mut bcf::Record,
    tags: &[String],
    vartype: &model::VariantType,
) -> Result<Vec<Option<LogProb>>, Box<Error>> {
    let variants = (utils::collect_variants(record, false, false, None, false))?;
    let mut tags_probs_out = vec![Vec::new(); variants.len()];

    for tag in tags {
        if let Some(tags_probs_in) = (record.info(tag.as_bytes()).float())? {
            //tag present
            for (i, (variant, tag_prob)) in
                variants.iter().zip(tags_probs_in.into_iter()).enumerate()
            {
                if let Some(ref variant) = *variant {
                    if !variant.is_type(vartype) || tag_prob.is_nan() {
                        continue;
                    }
                    tags_probs_out[i].push(LogProb::from(PHREDProb(*tag_prob as f64)));
                }
            }
        }
    }

    Ok(tags_probs_out
        .into_iter()
        .map(|probs| {
            if !probs.is_empty() {
                Some(LogProb::ln_sum_exp(&probs).cap_numerical_overshoot(NUMERICAL_EPSILON))
            } else {
                None
            }
        })
        .collect_vec())
}

/// Collect distribution of posterior probabilities from a VCF file that has been written by
/// libprosic.
///
/// # Arguments
///
/// * `calls` - BCF reader with libprosic calls
/// * `events` - the set of events to sum up for a particular site
/// * `vartype` - the variant type to consider
pub fn collect_prob_dist<E: Event>(
    calls: &mut bcf::Reader,
    events: &[E],
    vartype: &model::VariantType,
) -> Result<Vec<NotNan<f64>>, Box<Error>> {
    let mut record = calls.empty_record();
    let mut prob_dist = Vec::new();
    let tags = events.iter().map(|e| e.tag_name("PROB")).collect_vec();
    loop {
        if let Err(e) = calls.read(&mut record) {
            if e.is_eof() {
                break;
            } else {
                return Err(Box::new(e));
            }
        }

        for p in utils::tags_prob_sum(&mut record, &tags, &vartype)? {
            if let Some(p) = p {
                prob_dist.push(NotNan::new(*p)?);
            }
        }
    }
    prob_dist.sort();
    Ok(prob_dist)
}

/// Filter a VCF record stream by a minimum threshold on the sum of
/// posterior probabilities of a given set of Events. The threshold
/// should be an informative false discovery rate (FDR) threshold,
/// e.g. determined with the libprosic FDR control functionality.
///
/// # Arguments
///
/// * `calls` - BCF reader with libprosic calls
/// * `threshold` - minimum threshold for the sum of posterior probabilities of the set of Events considered
/// * `calls` - BCF writer for the filtered libprosic calls
/// * `events` - the set of Events to filter on
/// * `vartype` - the variant type to consider
pub fn filter_by_threshold<E: Event>(
    calls: &mut bcf::Reader,
    threshold: Option<LogProb>,
    out: &mut bcf::Writer,
    events: &[E],
    vartype: &model::VariantType,
) -> Result<(), Box<Error>> {
    let mut record = calls.empty_record();
    let tags = events.iter().map(|e| e.tag_name("PROB")).collect_vec();
    loop {
        if let Err(e) = calls.read(&mut record) {
            if e.is_eof() {
                return Ok(());
            } else {
                return Err(Box::new(e));
            }
        }

        let probs = utils::tags_prob_sum(&mut record, &tags, vartype)?;
        let mut remove = vec![false]; // don't remove the reference allele
        remove.extend(probs.into_iter().map(|p| {
            match (p, threshold) {
                // we allow some numerical instability in case of equality
                (Some(p), Some(threshold)) if p > threshold || relative_eq!(*p, *threshold) => {
                    false
                }
                (Some(_), None) => false,
                _ => true,
            }
        }));

        // Write trimmed record if any allele remains. Otherwise skip the record.
        if !remove[1..].iter().all(|r| *r) {
            record.remove_alleles(&remove)?;
            out.write(&record)?;
        }
    }
}

/// Describes whether read overlaps a variant in a valid or invalid (too large overlap) way.
#[derive(Debug)]
pub enum Overlap {
    Enclosing(u32),
    Left(u32),
    Right(u32),
    Some(u32),
    None,
}

impl Overlap {
    pub fn new(
        record: &bam::Record,
        cigar: &bam::record::CigarStringView,
        start: u32,
        variant: &model::Variant,
        consider_clips: bool,
    ) -> Result<Overlap, Box<Error>> {
        let mut pos = record.pos() as u32;
        let mut end_pos = cigar.end_pos()? as u32;

        if consider_clips {
            // consider soft clips for overlap detection
            pos = pos.saturating_sub(model::evidence::Clips::leading(&cigar).soft());
            end_pos = end_pos + model::evidence::Clips::trailing(&cigar).soft();
        }

        let overlap = match variant {
            &model::Variant::SNV(_) | &model::Variant::None => {
                if pos <= start && end_pos > start {
                    Overlap::Enclosing(1)
                } else {
                    Overlap::None
                }
            }
            &model::Variant::Deletion(l) => {
                let end = start + l;
                let enclosing = pos < start && end_pos > end;
                if enclosing {
                    Overlap::Enclosing(l)
                } else {
                    if end_pos <= end && end_pos > start {
                        Overlap::Right(end_pos - start)
                    } else if pos >= start && pos < end {
                        Overlap::Left(end - pos)
                    } else {
                        Overlap::None
                    }
                }
            }
            &model::Variant::Insertion(ref seq) => {
                let l = seq.len() as u32;

                let center_pos = (end_pos - pos) / 2 + pos;
                if pos < start && end_pos > start {
                    // TODO this does currently not reliably detect the side of the overlap.
                    // There can be cases where start is left of the center but clips are at the
                    // right side of the read. Also due to repeat structure, it is not possible to
                    // use relation of pos/end_pos with and without clips.
                    // Hence, we simply use this as a way to sample in a fair way.
                    // Since we might pick up fragments that overlap the insertion at the right
                    // side (with softclips), we disable insert size based probability computation
                    // for insertions. Instead, we rely exclusively on HMMs for insertions.
                    // The advantage is that this allows to consider far more fragments, in
                    // particular for the larger the insertions
                    // (e.g. exceeding insert size distribution).
                    if start > center_pos {
                        // right of alignment center
                        let overlap = end_pos - start;
                        if overlap > l {
                            // we overlap more than insertion len, hence we enclose it
                            Overlap::Enclosing(l)
                        } else {
                            // less overlap, hence it can be only partial
                            Overlap::Some(overlap)
                        }
                    } else {
                        // left of alignment center
                        let overlap = start - pos;
                        if overlap > l {
                            // we overlap more than insertion len, hence we enclose it
                            Overlap::Enclosing(l)
                        } else {
                            // less overlap, hence it can be only partial
                            Overlap::Some(overlap)
                        }
                    }
                } else {
                    Overlap::None
                }
            }
        };

        Ok(overlap)
    }

    pub fn is_enclosing(&self) -> bool {
        if let &Overlap::Enclosing(_) = self {
            true
        } else {
            false
        }
    }

    pub fn is_none(&self) -> bool {
        if let &Overlap::None = self {
            true
        } else {
            false
        }
    }

    pub fn len(&self) -> u32 {
        match self {
            &Overlap::Enclosing(l) => l,
            &Overlap::Left(l) => l,
            &Overlap::Right(l) => l,
            &Overlap::Some(l) => l,
            &Overlap::None => 0,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use bio::stats::{LogProb, Prob};
    use model::VariantType;
    use rust_htslib::bcf::{self, Read};
    use ComplementEvent;
    use SimpleEvent;

    #[test]
    fn test_tags_prob_sum() {
        // set up test input
        let test_file = "tests/resources/test_tags_prob_sum/overshoot.vcf";
        let mut overshoot_calls = bcf::Reader::from_path(test_file).unwrap();
        let mut record = overshoot_calls.empty_record();
        if let Err(e) = overshoot_calls.read(&mut record) {
            panic!("BCF reading error: {}", e);
        }

        // set up all alt events with names as in prosolo
        let alt_tags = [
            String::from("PROB_ADO_TO_REF"),
            String::from("PROB_ADO_TO_ALT"),
            String::from("PROB_HOM_ALT"),
            String::from("PROB_HET"),
            String::from("PROB_ERR_REF"),
        ];

        let snv = VariantType::SNV;

        if let Ok(prob_sum) = tags_prob_sum(&mut record, &alt_tags, &snv) {
            assert_eq!(LogProb::ln_one(), prob_sum[0].unwrap());
        } else {
            panic!("tags_prob_sum(&overshoot_calls, &alt_events, &snv) returned Error")
        }
    }

    #[test]
    fn test_collect_prob_dist() {
        // setup events with names as in prosic2
        let events = vec![
            SimpleEvent {
                name: "germline".to_owned(),
            },
            SimpleEvent {
                name: "somatic".to_owned(),
            },
        ];
        // setup absent event as the complement of the other events
        let absent_event = vec![ComplementEvent {
            name: "absent".to_owned(),
        }];

        let test_file = "tests/resources/test_collect_prob_dist/min.calls.vcf";

        //TESTS deletion
        let del = VariantType::Deletion(None);

        let mut del_calls_1 = bcf::Reader::from_path(test_file).unwrap();
        if let Ok(prob_del) = collect_prob_dist(&mut del_calls_1, &events, &del) {
            println!("prob_del[0]: {:?}", prob_del[0].into_inner());
            assert_eq!(prob_del.len(), 1);
            assert_relative_eq!(prob_del[0].into_inner(), Prob(0.8).ln(), epsilon = 0.000005);
        } else {
            panic!("collect_prob_dist(&calls, &events, &del) returned Error")
        }
        let mut del_calls_2 = bcf::Reader::from_path(test_file).unwrap();
        if let Ok(prob_del_abs) = collect_prob_dist(&mut del_calls_2, &absent_event, &del) {
            assert_eq!(prob_del_abs.len(), 1);
            assert_relative_eq!(
                prob_del_abs[0].into_inner(),
                Prob(0.2).ln(),
                epsilon = 0.000005
            );
        } else {
            panic!("collect_prob_dist(&calls, &absent_event, &del) returned Error")
        }

        //TESTS insertion
        let ins = VariantType::Insertion(None);

        let mut ins_calls_1 = bcf::Reader::from_path(test_file).unwrap();
        if let Ok(prob_ins) = collect_prob_dist(&mut ins_calls_1, &events, &ins) {
            assert_eq!(prob_ins.len(), 1);
            assert_relative_eq!(prob_ins[0].into_inner(), Prob(0.2).ln(), epsilon = 0.000005);
        } else {
            panic!("collect_prob_dist(&calls, &events, &ins) returned Error")
        }
        let mut ins_calls_2 = bcf::Reader::from_path(test_file).unwrap();
        if let Ok(prob_ins_abs) = collect_prob_dist(&mut ins_calls_2, &absent_event, &ins) {
            assert_eq!(prob_ins_abs.len(), 1);
            assert_relative_eq!(
                prob_ins_abs[0].into_inner(),
                Prob(0.8).ln(),
                epsilon = 0.000005
            );
        } else {
            panic!("collect_prob_dist(&calls, &absent_event, &ins) returned Error")
        }
    }

    #[test]
    fn test_filter_by_threshold() {
        // TODO: make this test work with both thresholds, testing against expected_output files
        /*
        // set up test input
        let test_file = "tests/resources/test_tags_prob_sum/overshoot.vcf";
        let mut calls = bcf::Reader::from_path( test_file ).unwrap();

        let threshold_1 = 0.1;
        let threshold_2 = 0.00000000001;

        let events = vec![
            SimpleEvent { name: "ADO_TO_REF".to_owned() },
            SimpleEvent { name: "ADO_TO_ALT".to_owned() },
            SimpleEvent { name: "HOM_ALT".to_owned() },
            SimpleEvent { name: "HET".to_owned() },
            SimpleEvent { name: "ERR_REF".to_owned() }
        ];

        let snv = VariantType::SNV;

        let header = bcf::Header::with_template(&calls.header());
        let mut out = bcf::Writer::from_stdout(&header, false, false).unwrap();

        filter_by_threshold(&mut calls, &threshold, &mut out, &events, &snv);

        panic!("Just checking");
        */
    }
}