//! Function for reading TIFF tags

use std::collections::HashMap;
use std::io::{self, Read, Seek};
use std::mem;

use super::stream::{ByteOrder, EndianReader, SmartReader};
use {TiffError, TiffFormatError, TiffResult, TiffUnsupportedError};

use self::Value::{Ascii, List, Rational, Unsigned, Signed, SRational};

macro_rules! tags {
    {
        // Permit arbitrary meta items, which include documentation.
        $( #[$enum_attr:meta] )*
        $vis:vis enum $name:ident($ty:ty) $(unknown($unknown_doc:literal))* {
            // Each of the `Name = Val,` permitting documentation.
            $($(#[$ident_attr:meta])* $tag:ident = $val:expr,)*
        }
    } => {
        $( #[$enum_attr] )*
        #[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
        pub enum $name {
            $($(#[$ident_attr])* $tag,)*
            // FIXME: switch to non_exhaustive once stabilized and compiler requirement new enough
            #[doc(hidden)]
            __NonExhaustive,
            $( 
                #[doc = $unknown_doc]
                Unknown($ty),
            )*
        }

        impl $name {
            #[inline(always)]
            fn __from_inner_type(n: $ty) -> Result<Self, $ty> {
                $(if n == $val { Ok($name::$tag) } else)* {
                    Err(n)
                }
            }

            #[inline(always)]
            fn __to_inner_type(&self) -> $ty {
                match *self {
                    $( $name::$tag => $val, )*
                    $( $name::Unknown(n) => { $unknown_doc; n }, )*
                    $name::__NonExhaustive => unreachable!(),
                }
            }
        }
    }
}

// Note: These tags appear in the order they are mentioned in the TIFF reference
tags! {
/// TIFF tags
pub enum Tag(u16) unknown("A private or extension tag") {
    // Baseline tags:
    Artist = 315,
    // grayscale images PhotometricInterpretation 1 or 3
    BitsPerSample = 258,
    CellLength = 265, // TODO add support
    CellWidth = 264, // TODO add support
    // palette-color images (PhotometricInterpretation 3)
    ColorMap = 320, // TODO add support
    Compression = 259, // TODO add support for 2 and 32773
    Copyright = 33_432,
    DateTime = 306,
    ExtraSamples = 338, // TODO add support
    FillOrder = 266, // TODO add support
    FreeByteCounts = 289, // TODO add support
    FreeOffsets = 288, // TODO add support
    GrayResponseCurve = 291, // TODO add support
    GrayResponseUnit = 290, // TODO add support
    HostComputer = 316,
    ImageDescription = 270,
    ImageLength = 257,
    ImageWidth = 256,
    Make = 271,
    MaxSampleValue = 281, // TODO add support
    MinSampleValue = 280, // TODO add support
    Model = 272,
    NewSubfileType = 254, // TODO add support
    Orientation = 274, // TODO add support
    PhotometricInterpretation = 262,
    PlanarConfiguration = 284,
    ResolutionUnit = 296, // TODO add support
    RowsPerStrip = 278,
    SamplesPerPixel = 277,
    Software = 305,
    StripByteCounts = 279,
    StripOffsets = 273,
    SubfileType = 255, // TODO add support
    Threshholding = 263, // TODO add support
    XResolution = 282,
    YResolution = 283,
    // Advanced tags
    Predictor = 317,
}
}

impl Tag {
    pub fn from_u16(val: u16) -> Self {
        Self::__from_inner_type(val).unwrap_or_else(Tag::Unknown)
    }

    pub fn to_u16(&self) -> u16 {
        Self::__to_inner_type(self)
    }
}

tags! {
/// The type of an IFD entry (a 2 byte field).
pub enum Type(u16) {
    BYTE = 1,
    ASCII = 2,
    SHORT = 3,
    LONG = 4,
    RATIONAL = 5,
    SBYTE = 6,
    SSHORT = 8,
    SLONG = 9,
    SRATIONAL = 10,
}
}

impl Type {
    pub fn from_u16(val: u16) -> Option<Self> {
        Self::__from_inner_type(val).ok()
    }

    pub fn to_u16(&self) -> u16 {
        Self::__to_inner_type(self)
    }
}


#[allow(unused_qualifications)]
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum Value {
    Signed(i32),
    Unsigned(u32),
    List(Vec<Value>),
    Rational(u32, u32),
    SRational(i32, i32),
    Ascii(String),
    #[doc(hidden)] // Do not match against this.
    __NonExhaustive,
}

impl Value {
    pub fn into_u32(self) -> TiffResult<u32> {
        match self {
            Unsigned(val) => Ok(val),
            val => Err(TiffError::FormatError(
                TiffFormatError::UnsignedIntegerExpected(val),
            )),
        }
    }

    pub fn into_i32(self) -> TiffResult<i32> {
        match self {
            Signed(val) => Ok(val),
            val => Err(TiffError::FormatError(
                TiffFormatError::SignedIntegerExpected(val),
            )),
        }
    }

    pub fn into_u32_vec(self) -> TiffResult<Vec<u32>> {
        match self {
            List(vec) => {
                let mut new_vec = Vec::with_capacity(vec.len());
                for v in vec {
                    new_vec.push(v.into_u32()?)
                }
                Ok(new_vec)
            }
            Unsigned(val) => Ok(vec![val]),
            Rational(numerator, denominator) => Ok(vec![numerator, denominator]),
            Ascii(val) => Ok(val.chars().map(|x| x as u32).collect()),
            val => Err(TiffError::FormatError(
                TiffFormatError::UnsignedIntegerExpected(val),
            )),
        }
    }

    pub fn into_i32_vec(self) -> TiffResult<Vec<i32>> {
        match self {
            List(vec) => {
                let mut new_vec = Vec::with_capacity(vec.len());
                for v in vec {
                    match v {
                        SRational(numerator, denominator) => {
                            new_vec.push(numerator);
                            new_vec.push(denominator);
                        }
                        _ => new_vec.push(v.into_i32()?)
                    }
                }
                Ok(new_vec)
            }
            Signed(val) => Ok(vec![val]),
            SRational(numerator, denominator) => Ok(vec![numerator, denominator]),
            val => Err(TiffError::FormatError(
                TiffFormatError::SignedIntegerExpected(val),
            )),
        }
    }
}

#[derive(Clone)]
pub struct Entry {
    type_: Type,
    count: u32,
    offset: [u8; 4],
}

impl ::std::fmt::Debug for Entry {
    fn fmt(&self, fmt: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
        fmt.write_str(&format!(
            "Entry {{ type_: {:?}, count: {:?}, offset: {:?} }}",
            self.type_, self.count, &self.offset
        ))
    }
}

impl Entry {
    pub fn new(type_: Type, count: u32, offset: [u8; 4]) -> Entry {
        Entry {
            type_,
            count,
            offset,
        }
    }

    /// Returns a mem_reader for the offset/value field
    fn r(&self, byte_order: ByteOrder) -> SmartReader<io::Cursor<Vec<u8>>> {
        SmartReader::wrap(io::Cursor::new(self.offset.to_vec()), byte_order)
    }

    pub fn val<R: Read + Seek>(
        &self,
        limits: &super::Limits,
        decoder: &mut super::Decoder<R>,
    ) -> TiffResult<Value> {
        let bo = decoder.byte_order();
        match (self.type_, self.count) {
            // TODO check if this could give wrong results
            // at a different endianess of file/computer.
            (Type::BYTE, 1) => Ok(Unsigned(u32::from(self.offset[0]))),
            (Type::BYTE, 2) => offset_to_bytes(2, self),
            (Type::BYTE, 3) => offset_to_bytes(3, self),
            (Type::BYTE, 4) => offset_to_bytes(4, self),
            (Type::BYTE, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Unsigned(u32::from(decoder.read_byte()?)))
            }),
            (Type::SBYTE, 1) => Ok(Signed(i32::from(self.offset[0] as i8))),
            (Type::SBYTE, 2) => offset_to_sbytes(2, self),
            (Type::SBYTE, 3) => offset_to_sbytes(3, self),
            (Type::SBYTE, 4) => offset_to_sbytes(4, self),
            (Type::SBYTE, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Signed(i32::from(decoder.read_byte()? as i8)))
            }),
            (Type::SHORT, 1) => Ok(Unsigned(u32::from(self.r(bo).read_u16()?))),
            (Type::SSHORT, 1) => Ok(Signed(i32::from(self.r(bo).read_i16()?))),
            (Type::SHORT, 2) => {
                let mut r = self.r(bo);
                Ok(List(vec![
                    Unsigned(u32::from(r.read_u16()?)),
                    Unsigned(u32::from(r.read_u16()?)),
                ]))
            }
            (Type::SSHORT, 2) => {
                let mut r = self.r(bo);
                Ok(List(vec![
                    Signed(i32::from(r.read_i16()?)),
                    Signed(i32::from(r.read_i16()?)),
                ]))
            }
            (Type::SHORT, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Unsigned(u32::from(decoder.read_short()?)))
            }),
            (Type::SSHORT, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Signed(i32::from(decoder.read_sshort()?)))
            }),
            (Type::LONG, 1) => Ok(Unsigned(self.r(bo).read_u32()?)),
            (Type::SLONG, 1) => Ok(Signed(self.r(bo).read_i32()?)),
            (Type::LONG, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Unsigned(decoder.read_long()?))
            }),
            (Type::SLONG, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Signed(decoder.read_slong()?))
            }),
            (Type::RATIONAL, 1) => {
                decoder.goto_offset(self.r(bo).read_u32()?)?;
                let numerator = decoder.read_long()?;
                let denominator = decoder.read_long()?;
                Ok(Rational(numerator, denominator))
            }
            (Type::SRATIONAL, 1) => {
                decoder.goto_offset(self.r(bo).read_u32()?)?;
                let numerator = decoder.read_slong()?;
                let denominator = decoder.read_slong()?;
                Ok(SRational(numerator, denominator))
            }
            (Type::RATIONAL, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(Rational(
                    decoder.read_long()?,
                    decoder.read_long()?,
                ))
            }),
            (Type::SRATIONAL, n) => self.decode_offset(n, bo, limits, decoder, |decoder| {
                Ok(SRational(
                    decoder.read_slong()?,
                    decoder.read_slong()?,
                ))
            }),
            (Type::ASCII, n) => {
                if n as usize > limits.decoding_buffer_size {
                    return Err(TiffError::LimitsExceeded);
                }
                decoder.goto_offset(self.r(bo).read_u32()?)?;
                let string = decoder.read_string(n as usize)?;
                Ok(Ascii(string))
            }
            _ => Err(TiffError::UnsupportedError(
                TiffUnsupportedError::UnsupportedDataType,
            )),
        }
    }

    #[inline]
    fn decode_offset<R, F>(&self, value_count: u32, bo: ByteOrder, limits: &super::Limits, decoder: &mut super::Decoder<R>, decode_fn: F) -> TiffResult<Value>
        where
            R: Read + Seek,
            F: Fn(&mut super::Decoder<R>) -> TiffResult<Value>,
    {
        if value_count as usize > limits.decoding_buffer_size / mem::size_of::<Value>() {
            return Err(TiffError::LimitsExceeded);
        }

        let mut v = Vec::with_capacity(value_count as usize);
        decoder.goto_offset(self.r(bo).read_u32()?)?;
        for _ in 0..value_count {
            v.push(decode_fn(decoder)?)
        }
        Ok(List(v))
    }
}

/// Extracts a list of BYTE tags stored in an offset
#[inline]
fn offset_to_bytes(n: usize, entry: &Entry) -> TiffResult<Value> {
    Ok(List(
        entry.offset[0..n]
            .iter()
            .map(|&e| Unsigned(u32::from(e)))
            .collect()
    ))
}

/// Extracts a list of SBYTE tags stored in an offset
#[inline]
fn offset_to_sbytes(n: usize, entry: &Entry) -> TiffResult<Value> {
    Ok(List(
        entry.offset[0..n]
            .iter()
            .map(|&e| Signed(i32::from(e as i8)))
            .collect()
    ))
}

/// Type representing an Image File Directory
pub type Directory = HashMap<Tag, Entry>;