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use std::path::{Path,PathBuf};
use std::fs::File;
use std::io::Seek;

use crate::merge::Merge;
use crate::record::OwnedRecord;
use crate::key_reader::*;
use crate::Wildcard;

use byteorder::ByteOrder;

pub struct DatabaseReader
{
  _dir: PathBuf,
  txes: Vec<(PathBuf,Reader)>,
}


impl DatabaseReader
{
  pub fn new(dir: &Path)
    -> std::io::Result<DatabaseReader>
  {
    Self::new_opts(dir, true)
  }

  pub fn without_main_db(dir: &Path)
    -> std::io::Result<DatabaseReader>
  {
    Self::new_opts(dir, false)
  }

  fn new_opts(dir: &Path, include_main_db: bool)
    -> std::io::Result<DatabaseReader>
  {
    let dir_reader = std::fs::read_dir(dir)?;

    let mut paths = vec!();

    for entry in dir_reader
    {
      let entry = entry?;
      if let Some(s) = entry.file_name().to_str()
      {
        if s.starts_with("tx.") && !s.ends_with(".tmp")
        {
          paths.push(entry.path());
        }
      }
    }

    paths.sort();
    let mut txes = Vec::with_capacity(paths.len());

    if include_main_db
    {
      let main_db_name = dir.join("main");
      let mut f = File::open(&main_db_name)?;
      let len = f.seek(std::io::SeekFrom::End(0))? as usize;
      if len == 0
      {
        eprintln!("disregarding main database, it is zero length");
      }
      else
      {
        let main_db = Reader::new(f)?;
        txes.push( (main_db_name, main_db) );
      }
    }

    for p in paths
    {
      let mut f = File::open(&p)?;
      let len = f.seek(std::io::SeekFrom::End(0))? as usize;
      if len == 0
      {
        eprintln!("disregarding {:?}, it is zero length", p);
        continue;
      }
      let r = Reader::new(f)?;
      txes.push( (p,r) );
    }

    Ok(DatabaseReader
    {
      txes,
      _dir: dir.to_owned(),
    })
  }

  pub fn transaction_paths(&self) -> Vec<PathBuf>
  {
    self.txes
      .iter()
      .map( |e| e.0.clone())
      .collect()
  }

  pub fn get<'rdr, 'k>(&'rdr self, key: &'k str)
    -> DatabaseKeyReader<'rdr, 'k, std::ops::RangeInclusive<&'k str>>
  {
    self.get_range( key ..= key )
  }

  pub fn get_range<'d, 'r, RB>(&'d self, range: RB)
    -> DatabaseKeyReader<'d, 'r, RB>
  where
    RB: std::ops::RangeBounds<&'r str> + Clone
  {
    let mut readers = Vec::with_capacity(self.txes.len());

    for tx in &self.txes
    {
      readers.push( tx.1.get_range(range.clone()) );
    }
    let merge = Merge::new(
      readers,
      |a, b|
      {
        a.key().cmp(b.key())
          .then_with(
            ||
              byteorder::BigEndian::read_u64(a.value())
                .cmp(&byteorder::BigEndian::read_u64(b.value()))
          )
      },
    );

    DatabaseKeyReader
    {
      _db: self,
      merge: Box::new(merge),
    }
  }
  pub fn get_filter<'d, 'k>(&'d self, wildcard: &'k Wildcard)
    -> DatabaseKeyReader<'d, 'k, std::ops::RangeFrom<&'k str>>
  {
    let mut readers = Vec::with_capacity(self.txes.len());

    for tx in &self.txes
    {
      readers.push( tx.1.get_filter(wildcard) );
    }
    let merge = Merge::new(
      readers,
      |a, b|
      {
        a.key().cmp(b.key())
          .then_with(
            ||
              byteorder::BigEndian::read_u64(a.value())
                .cmp(&byteorder::BigEndian::read_u64(b.value()))
          )
      },
    );

    DatabaseKeyReader
    {
      _db: self,
      merge: Box::new(merge),
    }
  }
}




pub struct DatabaseKeyReader<'d, 'r, RB>
where
  RB: std::ops::RangeBounds<&'r str>
{
  _db: &'d DatabaseReader,
  merge: Box<Merge<
    StringKeyRangeReader<'d, 'r, RB>, OwnedRecord,
  >>,
}

impl<'d, 'r, RB> Iterator for DatabaseKeyReader<'d, 'r, RB>
where
  RB: std::ops::RangeBounds<&'r str>
{
  type Item = OwnedRecord;

  fn next(&mut self) -> Option<Self::Item>
  {
    self.merge.next()
  }
}