/*
    This file is part of jellything (https://codeberg.org/metamuffin/jellything)
    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
    Copyright (C) 2025 metamuffin <metamuffin.org>
*/
use crate::{error::Error, matroska::MatroskaTag, size::EbmlSize, Master, Result};
use log::{debug, warn};
use std::{
    collections::VecDeque,
    io::{Read, Seek, SeekFrom},
};

trait ReadAndSeek: Read + Seek {}
impl<T: Read + Seek> ReadAndSeek for T {}

#[derive(Debug, Clone, Copy)]
pub struct StackTag {
    end: Option<u64>,
    id: u64,
}

pub struct EbmlReader {
    inner: Box<dyn ReadAndSeek>,
    stack: Vec<StackTag>,
    queue: VecDeque<(Option<u64>, MatroskaTag)>,
    position: u64,
}

impl Read for EbmlReader {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        let r = self.inner.read(buf)?;
        self.position += r as u64;
        Ok(r)
    }
}

impl EbmlReader {
    pub fn new<T: Seek + Read + 'static>(inner: T) -> Self {
        Self {
            queue: VecDeque::new(),
            inner: Box::new(inner),
            stack: vec![],
            position: 0,
        }
    }

    #[inline]
    pub fn read_byte(&mut self) -> Result<u8> {
        let mut b = [0u8];
        self.inner.read_exact(&mut b).map_err(Error::Io)?;
        self.position += 1;
        Ok(b[0])
    }

    pub fn read_buf(&mut self, size: impl Into<usize>) -> Result<Vec<u8>> {
        let size = size.into();
        let mut b = vec![0u8; size];
        self.inner.read_exact(&mut b).map_err(Error::Io)?;
        self.position += size as u64;
        Ok(b)
    }

    pub fn read_vint_len(&mut self) -> Result<(u64, usize)> {
        let s = self.read_byte()?;
        let len = s.leading_zeros() + 1;
        if len > 8 {
            Err(Error::VarintTooLong)?
        }
        let mut value = s as u64;
        value -= 1 << (8 - len);
        for _ in 1..len {
            value <<= 8;
            value += self.read_byte()? as u64;
        }
        Ok((value, len as usize))
    }

    #[inline]
    pub fn read_vint(&mut self) -> Result<u64> {
        Ok(self.read_vint_len()?.0)
    }

    #[inline]
    pub fn read_utf8(&mut self, size: impl Into<usize>) -> Result<String> {
        let b = self.read_buf(size)?;
        String::from_utf8(b).map_err(|_| Error::InvalidUTF8)
    }

    #[inline]
    pub fn read_tag_id(&mut self) -> Result<u64> {
        let (value, len) = self.read_vint_len()?;
        Ok(value + (1 << (7 * len)))
    }

    #[inline]
    pub fn read_tag_size(&mut self) -> Result<EbmlSize> {
        Ok(EbmlSize::from_vint(self.read_vint_len()?))
    }

    /// reads *some* amount of tags from the stream and pushes it to the queue.
    pub fn read_stuff(&mut self) -> Result<()> {
        while let Some(e) = self.stack.last().copied() {
            if let Some(end) = e.end {
                if self.position >= end {
                    if self.position != end {
                        warn!("we missed the end by {} bytes", self.position - end)
                    }
                    self.stack.pop();
                    self.queue
                        .push_back((None, MatroskaTag::construct_master(e.id, Master::End)?));
                } else {
                    break;
                }
            } else {
                break;
            }
        }

        let start_position = self.position;
        let id = self.read_tag_id()?;
        let size = self.read_tag_size()?;
        let is_master = MatroskaTag::is_master(id)?;
        let tag = if is_master {
            MatroskaTag::construct_master(id, Master::Start)?
        } else {
            let data = self.read_buf(size.some().unwrap())?;
            MatroskaTag::parse(id, &data)?
        };

        if let Some(path) = tag.path() {
            // we have slightly different rules for closing tags implicitly
            // this closes as many tags as needed to make the next tag a valid child
            while let Some(stag @ StackTag { end: None, .. }) = self.stack.last() {
                if path.last() == Some(&stag.id) {
                    break;
                } else {
                    let end =
                        MatroskaTag::construct_master(self.stack.pop().unwrap().id, Master::End)?;
                    self.queue.push_back((None, end));
                }
            }
        }

        if is_master {
            self.stack.push(StackTag {
                end: size.some().map(|s| s as u64 + self.position),
                id,
            });
        }
        self.queue.push_back((Some(start_position), tag));
        Ok(())
    }

    /// context should be the next expected tag, such that the stack can be derived from its path.
    pub fn seek(&mut self, position: u64, context: MatroskaTag) -> Result<()> {
        let path = context.path().ok_or(Error::GlobalTagsAsContext)?;
        debug!(
            "seeking to {position} with a context restored from path {:x?}",
            path
        );
        self.queue.clear();
        self.position = position;
        self.inner.seek(SeekFrom::Start(position))?;
        self.stack = path
            .iter()
            .map(|id| StackTag { id: *id, end: None })
            .collect();
        Ok(())
    }
}

impl Iterator for EbmlReader {
    type Item = Result<(Option<u64>, MatroskaTag)>;
    fn next(&mut self) -> Option<Self::Item> {
        if let Some(t) = self.queue.pop_front() {
            // match t {
            //     MatroskaTag::SimpleBlock(_) | MatroskaTag::Block(_) => (),
            //     _ => debug!("reader yield: {t:?}"),
            // };
            Some(Ok(t))
        } else {
            match self.read_stuff() {
                Ok(()) => self.next(),
                // in case we reached the end (error: failed to fill whole buffer),
                // return the rest in the queue and pop all items of the stack
                Err(e) => {
                    // TODO this is horrible, should use a custom error enum instead
                    if format!("{e}").as_str() == "failed to fill whole buffer" {
                        match self.queue.pop_front() {
                            Some(q) => Some(Ok(q)),
                            None => match self.stack.pop() {
                                Some(q) => Some(Ok((
                                    None,
                                    MatroskaTag::construct_master(q.id, Master::End).unwrap(),
                                ))),
                                None => Some(Err(e)),
                            },
                        }
                    } else {
                        Some(Err(e))
                    }
                }
            }
        }
    }
}

pub trait ReadValue: Sized {
    fn from_buf(buf: &[u8]) -> Result<Self>;
}

impl ReadValue for u64 {
    fn from_buf(buf: &[u8]) -> Result<Self> {
        if buf.len() > 8 {
            Err(Error::InvalidTypeLen)?
        }
        let mut val = 0u64;
        for byte in buf {
            val <<= 8;
            val |= *byte as u64;
        }
        Ok(val)
    }
}
impl ReadValue for i64 {
    fn from_buf(buf: &[u8]) -> Result<Self> {
        if buf.len() > 8 {
            Err(Error::InvalidTypeLen)?
        }
        Ok(if buf[0] > 127 {
            if buf.len() == 8 {
                i64::from_be_bytes(buf.try_into().unwrap())
            } else {
                -((1 << (buf.len() * 8)) - (u64::from_buf(buf)? as i64))
            }
        } else {
            u64::from_buf(buf)? as i64
        })
    }
}
impl ReadValue for f64 {
    fn from_buf(buf: &[u8]) -> Result<Self> {
        Ok(if buf.len() == 4 {
            f32::from_be_bytes(buf.try_into().unwrap()) as f64
        } else if buf.len() == 8 {
            f64::from_be_bytes(buf.try_into().unwrap())
        } else {
            Err(Error::InvalidTypeLen)?
        })
    }
}

impl ReadValue for Vec<u8> {
    fn from_buf(buf: &[u8]) -> Result<Self> {
        Ok(buf.to_vec())
    }
}
impl ReadValue for String {
    fn from_buf(buf: &[u8]) -> Result<Self> {
        String::from_utf8(Vec::from(buf)).map_err(|_| Error::InvalidUTF8)
    }
}
impl ReadValue for Master {
    fn from_buf(_: &[u8]) -> Result<Self> {
        panic!("master shall not be read like this")
    }
}

pub trait ReadExt: Read {
    fn read_byte(&mut self) -> Result<u8>;
    fn read_vint_len(&mut self) -> Result<(u64, usize)>;
    fn read_vint(&mut self) -> Result<u64>;
}
impl<T: Read> ReadExt for T {
    fn read_byte(&mut self) -> Result<u8> {
        let mut b = [0u8];
        self.read_exact(&mut b).map_err(Error::Io)?;
        Ok(b[0])
    }
    fn read_vint_len(&mut self) -> Result<(u64, usize)> {
        let s = self.read_byte()?;
        let len = s.leading_zeros() + 1;
        if len > 8 {
            Err(Error::VarintTooLong)?
        }
        let mut value = s as u64;
        value -= 1 << (8 - len);
        for _ in 1..len {
            value <<= 8;
            value += self.read_byte()? as u64;
        }
        Ok((value, len as usize))
    }
    #[inline]
    fn read_vint(&mut self) -> Result<u64> {
        Ok(self.read_vint_len()?.0)
    }
}