use std::collections::HashMap;

use anyhow::Context;
use log::error;
use rust_htslib::bam::{ext::BamRecordExtensions, record::Aux, IndexedReader, Read, Record};

use crate::io::bam::{primary_record, primary_records};

/// A genomic bin containing reads from a specific region.
///
/// This struct represents a segment of a BAM file, storing reads that overlap
/// a specific genomic region. It provides methods to analyze read distributions
/// and extract primary alignments for supplementary alignments.
#[derive(Debug)]
pub struct Bin {
    /// The contig/chromosome name
    pub contig: String,
    /// The 0-based inclusive start position
    pub start: u32,
    /// The 0-based inclusive end position
    pub end: u32,
    /// Map of read query names to their BAM records
    pub reads_store: HashMap<Vec<u8>, Record>,
    /// Indexed BAM reader for fetching additional records
    // pub bam_reader: IndexedReader,
    /// Average read length within this bin
    // pub reads_mean_len: u32,
    /// Number of reads filtered due to low mapping quality
    pub n_low_mapq: u32,
    /// Vec of depths
    pub depths: Vec<u32>,
}

impl Bin {
    /// Creates a new genomic bin from a BAM file.
    ///
    /// # Arguments
    ///
    /// * `bam_path` - Path to the BAM file
    /// * `contig` - Chromosome/contig name
    /// * `start` - 0-based inclusive start position
    /// * `length` - Length of the region to extract
    ///
    /// # Returns
    ///
    /// A Result containing the new Bin if successful, or an error if the BAM file
    /// couldn't be read or the region couldn't be fetched.
    ///
    /// # Examples
    ///
    /// ```
    /// let bin = Bin::new("sample.bam", "chr1", 1000000, 1000)?;
    /// println!("Loaded {} reads", bin.n_reads());
    /// ```
    pub fn new(
        bam_reader: &mut IndexedReader,
        contig: &str,
        start: u32,
        length: u32,
        min_mapq: u8,
    ) -> anyhow::Result<Self> {
        let end = start + length - 1;

        bam_reader
            .fetch((contig, start as i64, end as i64))
            .with_context(|| format!("Failed to fetch region {}:{}-{}", contig, start, end))?;

        let mut reads_store: HashMap<Vec<u8>, Record> = HashMap::new();
        let mut n_low_mapq = 0;
        let mut depths = vec![0u32; length as usize]; // Optional pseudo-depth

        for record_result in bam_reader.rc_records() {
            let rc_record = match record_result {
                Ok(rc) => rc,
                Err(e) => {
                    error!(
                        "Failed to parse record in {}:{}-{}: {}",
                        contig, start, end, e
                    );
                    continue;
                }
            };

            let record = rc_record.as_ref();

            if record.mapq() < min_mapq {
                n_low_mapq += 1;
                continue;
            }

            if let Some((read_start, read_end)) = read_range(record) {
                if read_end < start || read_start > end {
                    continue; // Not overlapping this bin
                }

                // Clone the underlying Record
                reads_store.insert(record.qname().to_vec(), record.clone());

                // Optional: depth accumulation
                let local_start = start.max(read_start);
                let local_end = end.min(read_end);
                for pos in local_start..=local_end {
                    let i = (pos - start) as usize;
                    if i < depths.len() {
                        depths[i] += 1;
                    }
                }
            }
        }

        Ok(Bin {
            contig: contig.to_string(),
            start,
            end,
            reads_store,
            n_low_mapq,
            depths,
        })
    }
    /// Returns the total number of reads in this bin.
    pub fn n_reads(&self) -> usize {
        self.reads_store.len()
    }

    /// Returns the number of reads with SA (supplementary alignment) tags.
    pub fn n_sa(&self) -> usize {
        self.reads_store
            .values()
            .filter(|record| matches!(record.aux(b"SA"), Ok(Aux::String(_))))
            .count()
    }

    /// Retrieves primary alignments for all reads with SA tags in this bin.
    ///
    /// # Returns
    ///
    /// A vector of primary alignment records for reads with supplementary alignments.
    pub fn sa_primary(&mut self, bam_reader: &mut IndexedReader) -> Vec<Record> {
        self.reads_store
            .values()
            .filter(|record| matches!(record.aux(b"SA"), Ok(Aux::String(_))))
            .map(|record| primary_record(bam_reader, record.clone()))
            .collect()
    }

    /// Finds the position with the highest concentration of read starts or ends.
    ///
    /// # Returns
    ///
    /// A tuple containing (position, count) of the position with the most read starts or ends.
    pub fn max_start_or_end(&self) -> (u32, usize) {
        let mut position_counts: HashMap<u32, usize> = HashMap::new();

        for record in self.reads_store.values() {
            let reference_start = record.reference_start() as u32;
            let reference_end = record.reference_end() as u32;

            // Count start positions within the bin
            if reference_start >= self.start && reference_start <= self.end {
                *position_counts.entry(reference_start).or_default() += 1;
            }

            // Count end positions within the bin
            if reference_end >= self.start && reference_end <= self.end {
                *position_counts.entry(reference_end).or_default() += 1;
            }
        }

        position_counts
            .into_iter()
            .max_by_key(|(_, count)| *count)
            .unwrap_or((0, 0))
    }

    /// Computes the number of reads with SA tags, and finds the highest
    /// counts of read starts and ends at the same position.
    ///
    /// # Returns
    ///
    /// A tuple containing:
    /// - Number of reads with SA tags
    /// - Highest count of reads starting at any single position
    /// - Highest count of reads ending at any single position
    pub fn count_reads_sa_start_end(&self) -> (usize, usize, usize) {
        let mut n_sa = 0;
        let mut start_counts: HashMap<u32, usize> = HashMap::new();
        let mut end_counts: HashMap<u32, usize> = HashMap::new();

        for record in self.reads_store.values() {
            // Count reads with SA tags
            if matches!(record.aux(b"SA"), Ok(Aux::String(_))) {
                n_sa += 1;
            }

            let reference_start = record.reference_start() as u32;
            let reference_end = record.reference_end() as u32;

            // Count start positions within the bin
            if reference_start >= self.start && reference_start <= self.end {
                *start_counts.entry(reference_start).or_default() += 1;
            }

            // Count end positions within the bin
            if reference_end >= self.start && reference_end <= self.end {
                *end_counts.entry(reference_end).or_default() += 1;
            }
        }

        let max_start_count = start_counts.values().max().copied().unwrap_or(0);
        let max_end_count = end_counts.values().max().copied().unwrap_or(0);

        (n_sa, max_start_count, max_end_count)
    }

    /// Finds the position with the highest concentration of read starts.
    ///
    /// # Returns
    ///
    /// A tuple containing (position, count) of the position with the most read starts.
    pub fn max_start(&self) -> (u32, usize) {
        let mut start_counts: HashMap<u32, usize> = HashMap::new();

        for record in self.reads_store.values() {
            let reference_start = record.reference_start() as u32;

            if reference_start >= self.start && reference_start <= self.end {
                *start_counts.entry(reference_start).or_default() += 1;
            }
        }

        start_counts
            .into_iter()
            .max_by_key(|(_, count)| *count)
            .unwrap_or((0, 0))
    }

    /// Finds the position with the highest concentration of read ends.
    ///
    /// # Returns
    ///
    /// A tuple containing (position, count) of the position with the most read ends.
    pub fn max_end(&self) -> (u32, usize) {
        let mut end_counts: HashMap<u32, usize> = HashMap::new();

        for record in self.reads_store.values() {
            let reference_end = record.reference_end() as u32;

            if reference_end >= self.start && reference_end <= self.end {
                *end_counts.entry(reference_end).or_default() += 1;
            }
        }

        end_counts
            .into_iter()
            .max_by_key(|(_, count)| *count)
            .unwrap_or((0, 0))
    }

    /// Gets primary alignments for reads that start or end at a specific position.
    ///
    /// # Arguments
    ///
    /// * `pos` - The position to check for read starts or ends
    ///
    /// # Returns
    ///
    /// A vector of primary alignment records.
    pub fn se_primary(&mut self, pos: u32, bam_reader: &mut IndexedReader) -> Vec<Record> {
        let records: Vec<Record> = self
            .reads_store
            .values()
            .filter(|record| {
                record.reference_start() as u32 == pos || record.reference_end() as u32 == pos
            })
            .cloned()
            .collect();

        primary_records(bam_reader, records)
    }

    /// Gets primary alignments for reads that start at a specific position.
    ///
    /// # Arguments
    ///
    /// * `pos` - The position to check for read starts
    ///
    /// # Returns
    ///
    /// A vector of primary alignment records.
    pub fn s_primary(&mut self, pos: u32, bam_reader: &mut IndexedReader) -> Vec<Record> {
        self.reads_store
            .values()
            .filter(|record| record.reference_start() as u32 == pos)
            .map(|record| primary_record(bam_reader, record.clone()))
            .collect()
    }

    /// Gets primary alignments for reads that end at a specific position.
    ///
    /// # Arguments
    ///
    /// * `pos` - The position to check for read ends
    ///
    /// # Returns
    ///
    /// A vector of primary alignment records.
    pub fn e_primary(&mut self, pos: u32, bam_reader: &mut IndexedReader) -> Vec<Record> {
        self.reads_store
            .values()
            .filter(|record| record.reference_end() as u32 == pos)
            .map(|record| primary_record(bam_reader, record.clone()))
            .collect()
    }

    /// Calculates the mean coverage by considering the actual
    /// span of each read in the bin.
    ///
    /// # Returns
    ///
    /// The mean bin coverage as a floating-point value.
    pub fn mean_coverage(&self) -> f64 {
        // If bin has no length or no reads, return 0
        if self.end <= self.start || self.reads_store.is_empty() {
            return 0.0;
        }

        // Calculate the total length of the bin
        let bin_length = (self.end - self.start + 1) as f64;

        // Calculate the total bases covered by all reads within the bin
        let mut total_bases_covered = 0.0;
        for record in self.reads_store.values() {
            let read_start = record.reference_start() as u32;
            let read_end = record.reference_end() as u32;

            // Skip reads that don't overlap with our bin
            if read_end < self.start || read_start > self.end {
                continue;
            }

            // Calculate the overlapping region
            let overlap_start = read_start.max(self.start);
            let overlap_end = read_end.min(self.end);

            // Add the number of bases this read covers within our bin
            total_bases_covered += (overlap_end - overlap_start + 1) as f64;
        }

        // Divide by the bin length to get average coverage
        total_bases_covered / bin_length
    }

    pub fn mean_coverage_from_depths(&self) -> f64 {
        self.depths.iter().sum::<u32>() as f64 / self.depths.len() as f64
    }
}

/// Helper: get start and end position of a read
fn read_range(record: &Record) -> Option<(u32, u32)> {
    let start = record.pos();
    let end = record.cigar().end_pos();
    if start >= 0 && end > start {
        Some((start as u32, end as u32 - 1))
    } else {
        None
    }
}