use std::{fs, io::{Read, BufRead}};
use bgzip::{BGZFReader, BGZFError};

#[derive(Debug)]
pub enum BamNucleotid {
    Equal, A, C, M, G, R, S, V, T, W, Y, H, K, D, B, N
}
#[derive(Debug)]
pub struct  BamSequence(Vec<BamNucleotid>);

impl BamSequence {
    pub fn new() -> BamSequence {
        BamSequence(Vec::new())
    }
    pub fn get_nt(e: &u8) -> BamNucleotid {
        match e {
            0  => BamNucleotid::Equal,
            1  => BamNucleotid::A,
            2  => BamNucleotid::C,
            3  => BamNucleotid::M,
            4  => BamNucleotid::G,
            5  => BamNucleotid::R,
            6  => BamNucleotid::S,
            7  => BamNucleotid::V,
            8  => BamNucleotid::T,
            9  => BamNucleotid::W,
            10 => BamNucleotid::Y,
            11 => BamNucleotid::H,
            12 => BamNucleotid::K,
            13 => BamNucleotid::D,
            14 => BamNucleotid::B,
            15 => BamNucleotid::N,
            _  => panic!("Parsing error")
        }
    }
    pub fn push(&mut self, e: &u8) {
        self.0.push(BamSequence::get_nt(e))
    }
}
#[derive(Debug, Clone)]
pub enum TagValue {
    Int(i8),
    U(u8),
    Int16(i16),
    U16(u16),
    Int32(i32),
    U32(u32),
    F32(f32),
    Str(String)
}

pub struct BamRead {
    ref_id: i32,                  // ref_id
    pos: i32,                     // pos
    mapq: u8,                     // mapq
    flag: u16,                    // flag
    read_name: String,            // read_name
    cigar: Vec<(String, u32)>,    // cigar
    sequence: BamSequence,        // sequence
    phred: Vec<u8>,               // phred
    tags: Vec<(String, TagValue)> // tags
}

pub struct BamReader {
    reader: BGZFReader<fs::File>,
    references: Vec<(String, u32)>
}

impl BamReader {
    pub fn new(bam_path: &str) -> Result<BamReader, BGZFError> {
        let bam = fs::File::open(bam_path).unwrap();
        let reader = BGZFReader::new(bam);
        let mut bam_reader = BamReader { reader, references: Vec::new() };
        bam_reader.read_header()?;
        Ok(bam_reader)
    }

    fn read_header(&mut self) -> Result<(), BGZFError> {
        let mut buffer_4 = [0u8; 4];
        let reader = &mut self.reader;
        
        // MAGIC
        reader.read_exact(&mut buffer_4)?;
        assert_eq!(buffer_4, [66, 65, 77, 1]);
    
        // l_text
        // size of the header
        reader.read_exact(&mut buffer_4)?;
        let l_text: u32 = u32::from_ne_bytes(buffer_4.clone().try_into().unwrap());
    
        // header
        let mut buffer_header = vec![0u8; l_text as usize];
        reader.read_exact(&mut buffer_header)?;
        // let header_txt = String::from_utf8(buffer_header).expect("Can't read the BAM header");
        // println!("{}", header_txt);
    
        // List of reference information (n=n_ref)
        // # reference sequences
        reader.read_exact(&mut buffer_4)?;
        let n_ref: u32 = u32::from_ne_bytes(buffer_4.try_into().unwrap());
        // println!("n_ref {}", n_ref);
    
        // reference vec: refrence_name refertence_size
        let mut references: Vec<(String, u32)> = Vec::new();
        for _ in 0..n_ref {
            // Length of the reference name plus 1 (including NUL)
            reader.read_exact(&mut buffer_4)?;
            let l_name: u32 = u32::from_ne_bytes(buffer_4.try_into().expect("Parse error"));
    
            // Reference sequence name; NUL-terminated
            let mut buffer_name = vec![0u8; l_name as usize];
            reader.read_exact(&mut buffer_name)?;
            let name = String::from_utf8(buffer_name).expect("Can't read the reference name");
    
            // Length of the reference sequence
            reader.read_exact(&mut buffer_4)?;
            let l_ref: u32 = u32::from_ne_bytes(buffer_4.clone().try_into().unwrap());
    
            references.push((name, l_ref));
        }
    
        self.references = references;
        Ok(())
    }

    fn parse_read(&mut self) -> Result<BamRead, BGZFError> {
        // buffers alloc
        let mut buffer_1 = [0u8; 1];
        let mut buffer_2 = [0u8; 2];
        let mut buffer_4 = [0u8; 4];
        // let mut reader = &self.reader;
        // Total length of the alignment record, excluding this field
        self.reader.read_exact(&mut buffer_4)?;
        // if r.is_err() { break; }; // triggered by eof
        let block_size: u32 = u32::from_ne_bytes(buffer_4.clone().try_into().unwrap());
        // println!("block size {}", block_size);

        let pos_start = self.reader.bgzf_pos();

        // Reference sequence ID, −1 ≤ refID < n ref; -1 for a read
        // without a mapping position
        self.reader.read_exact(&mut buffer_4)?;
        let ref_id: i32 = i32::from_ne_bytes(buffer_4.try_into().expect("Parse error"));
        // println!("ref_id {}", ref_id);
        // println!("ref_name {}", references[ref_id as usize].0);

        // 0-based leftmost coordinate (= POS − 1)
        self.reader.read_exact(&mut buffer_4)?;
        let pos: i32 = i32::from_ne_bytes(buffer_4.try_into().expect("Parse error"));
        // println!("pos {}", pos);

        // Length of read name below (= length(QNAME) + 1)
        self.reader.read_exact(&mut buffer_1)?;
        let l_read_name: u8 = u8::from_ne_bytes(buffer_1.try_into().expect("Parse error"));
        // println!("l_read_name {}", l_read_name);

        // Mapping quality (=MAPQ)
        self.reader.read_exact(&mut buffer_1)?;
        let mapq: u8 = u8::from_ne_bytes(buffer_1.try_into().expect("Parse error"));
        // println!("mapq {}", mapq);

        // BAI index bin
        self.reader.read_exact(&mut buffer_2)?;
        // let bin: u16 = u16::from_ne_bytes(buffer_2.try_into().expect("Parse error"));
        // println!("bin {}", bin);

        // Number of operations in CIGAR,
        self.reader.read_exact(&mut buffer_2)?;
        let n_cigar_op: u16 = u16::from_ne_bytes(buffer_2.try_into().expect("Parse error"));
        // println!("n_cigar_op {}", n_cigar_op);

        // Bitwise flags (= FLAG)^29
        self.reader.read_exact(&mut buffer_2)?;
        let flag: u16 = u16::from_ne_bytes(buffer_2.try_into().expect("Parse error"));
        
        // println!("flag {}", flag);

        // Length of SEQ 
        self.reader.read_exact(&mut buffer_4)?;
        let l_seq: u32 = u32::from_ne_bytes(buffer_4.try_into().unwrap());
        // println!("l_seq {}", l_seq);

        // Ref-ID of the next segment (−1 ≤ next refID < n ref) 
        self.reader.read_exact(&mut buffer_4)?;
        // let next_ref_id: i32 = i32::from_ne_bytes(buffer_4.try_into().unwrap());
        // println!("next_ref_id {}", next_ref_id);

        // 0-based leftmost pos of the next segment  (= PNEXT − 1)
        self.reader.read_exact(&mut buffer_4)?;
        // let next_pos: i32 = i32::from_ne_bytes(buffer_4.try_into().unwrap());
        // println!("next_pos {}", next_pos);

        // Template length (= TLEN)
        self.reader.read_exact(&mut buffer_4)?;
        // let tlen: i32 = i32::from_ne_bytes(buffer_4.try_into().unwrap());
        // println!("tlen {}", tlen);

        // Read name, NUL-terminated (QNAME with trailing ‘\0’)^30
        let mut buffer_read_name = vec![0u8; l_read_name as usize];
        self.reader.read_exact(&mut buffer_read_name)?;
        buffer_read_name.pop();
        let read_name = String::from_utf8(buffer_read_name).expect("Can't read the read name");
        // println!("read_name {}", read_name);

        // CIGAR: op len<<4|op. ‘MIDNSHP=X’→‘012345678’ 
        let l_buffer_cigar = (n_cigar_op as usize) * 4;
        let mut buffer_cigar = vec![0u8; l_buffer_cigar];
        self.reader.read_exact(&mut buffer_cigar)?;
        let cigar: Vec<(String, u32)> = buffer_cigar.chunks(4)
        .map(|c| { 
            let u = u32::from_ne_bytes(c.try_into().unwrap());
            let op = u << 28 >> 28;
            let n = u >> 4;
            match op {
                0 => ("M".to_string(), n),
                1 => ("I".to_string(), n),
                2 => ("D".to_string(), n),
                3 => ("N".to_string(), n),
                4 => ("S".to_string(), n),
                5 => ("H".to_string(), n),
                6 => ("P".to_string(), n),
                7 => ("=".to_string(), n),
                8 => ("X".to_string(), n),
                _ => panic!("Error parsing cigar")
            }
        })
        .collect();
        // println!("cigar {:?}", cigar);

        let l_buffer_seq = (l_seq as usize + 1) / 2;
        let mut buffer_seq = vec![0u8; l_buffer_seq];
        self.reader.read_exact(&mut buffer_seq)?;
        let mut sequence = BamSequence::new();
        for e in buffer_seq.into_iter() {
            let right = e << 4 >> 4;
            let left = e >> 4;
            sequence.push(&left);
            if right != 0 { sequence.push(&right) };
        }
        // println!("sequence {:?}", sequence);
        
        let mut phred = vec![0; l_seq as usize];
        self.reader.read_exact(&mut phred)?;

        let mut tags: Vec<(String, TagValue)> = Vec::new();
        loop {
            let mut tag_buffer = vec![0u8; 2];
            self.reader.read_exact(&mut tag_buffer)?;
            let tag = String::from_utf8(tag_buffer).unwrap();
            
            let mut tag_type = vec![0u8];
            self.reader.read_exact(&mut tag_type)?;

            let tag_v = match tag_type[0] {
                b'c' => {
                    self.reader.read_exact(&mut buffer_1)?;
                    TagValue::Int(buffer_1.clone()[0] as i8)
                },
                b'C' => {
                    self.reader.read_exact(&mut buffer_1)?;
                    TagValue::U(buffer_1.clone()[0])
                },
                b's' => {
                    self.reader.read_exact(&mut buffer_2)?;
                    TagValue::Int16(
                        i16::from_ne_bytes(buffer_2.try_into().expect("Parse error"))
                    )
                },
                b'S' => {
                    self.reader.read_exact(&mut buffer_2)?;
                    TagValue::U16(
                        u16::from_ne_bytes(buffer_2.try_into().expect("Parse error"))
                    )
                }
                b'i' => {
                    self.reader.read_exact(&mut buffer_4)?;
                    TagValue::Int32(
                        i32::from_ne_bytes(buffer_4.try_into().expect("Parse error"))
                    )
                },
                b'I' => {
                    self.reader.read_exact(&mut buffer_4)?;
                    TagValue::U32(
                        u32::from_ne_bytes(buffer_4.try_into().expect("Parse error"))
                    )
                },
                b'f' => {
                    self.reader.read_exact(&mut buffer_4)?;
                    TagValue::F32(
                        f32::from_ne_bytes(buffer_4.try_into().expect("Parse error"))
                    )
                },
                b'Z' => {
                    let mut buf: Vec<u8> = Vec::new();
                    self.reader.read_until(b'\0', &mut buf)?;
                    buf.pop();
                    TagValue::Str(String::from_utf8(buf).unwrap())
                }
                e => panic!("Error unknown tag type. {:?} tag: {:?}", e, tag)
            };
            tags.push((tag, tag_v));

            if self.reader.bgzf_pos() - pos_start >= block_size as u64 { break; }
        }
        Ok(BamRead {ref_id, pos, mapq, flag, read_name, cigar, sequence, phred, tags})
    }
}

impl Iterator for BamReader {
    type Item = BamRead;
    fn next(&mut self) -> Option<Self::Item> {
        match self.parse_read() {
            Ok(r) => Some(r),
            Err(err) => {
                println!("Error: {}", err);
                None
            }
        }
    }
}

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

    #[test]
    fn it_works() {
        let bam_path = "/Users/steimle/Documents/Programmes/sv-finder/betya.bam";
        let flags: Vec<u16> = vec![81, 161, 97, 145, 65, 129, 113, 177];
        
        let bam_reader = BamReader::new(bam_path).unwrap();
        
        let reads = bam_reader
        .filter(|br| flags.contains(&br.flag))
        .take(1000)
        .collect::<Vec<BamRead>>();

        assert_eq!(
            reads[0].read_name,
            "NB501645:337:HCCMVAFX2:3:11505:17842:2102_GATGGGACGG".to_string()
        );
    }
}