use std::io;
use super::{Deserialize, Serialize, Error, VarUint7, VarUint32};

/// Internal reference of the exported entry.
#[derive(Debug, Clone, Copy)]
pub enum Internal {
    /// Function reference.
    Function(u32),
    /// Table reference.
    Table(u32),
    /// Memory reference.
    Memory(u32),
    /// Global reference.
    Global(u32),
}

impl Deserialize for Internal {
    type Error = Error;

    fn deserialize<R: io::Read>(reader: &mut R) -> Result<Self, Self::Error> {
        let kind = VarUint7::deserialize(reader)?;
        match kind.into() {
            0x00 => Ok(Internal::Function(VarUint32::deserialize(reader)?.into())),
            0x01 => Ok(Internal::Table(VarUint32::deserialize(reader)?.into())),
            0x02 => Ok(Internal::Memory(VarUint32::deserialize(reader)?.into())),
            0x03 => Ok(Internal::Global(VarUint32::deserialize(reader)?.into())),
            _ => Err(Error::UnknownInternalKind(kind.into())),
        }
    }    
} 

impl Serialize for Internal {
    type Error = Error;
    
    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
        let (bt, arg) = match self {
            Internal::Function(arg) => (0x00, arg),
            Internal::Table(arg) => (0x01, arg),
            Internal::Memory(arg) => (0x02, arg),
            Internal::Global(arg) => (0x03, arg),
        };

        VarUint7::from(bt).serialize(writer)?;
        VarUint32::from(arg).serialize(writer)?;

        Ok(())
    }
}

/// Export entry.
#[derive(Debug)] 
pub struct ExportEntry {
    field_str: String,
    internal: Internal,
}

impl ExportEntry {
    /// New export entry
    pub fn new(field: String, internal: Internal) -> Self {
        ExportEntry {
            field_str: field,
            internal: internal
        }
    }

    /// Public name
    pub fn field(&self) -> &str { &self.field_str }

    /// Public name (mutable)
    pub fn field_mut(&mut self) -> &mut str { &mut self.field_str }

    /// Internal reference of the export entry.
    pub fn internal(&self) -> &Internal { &self.internal }

    /// Internal reference of the export entry (mutable).    
    pub fn internal_mut(&mut self) -> &mut Internal { &mut self.internal }
}

impl Deserialize for ExportEntry {
    type Error = Error;

    fn deserialize<R: io::Read>(reader: &mut R) -> Result<Self, Self::Error> {
        let field_str = String::deserialize(reader)?;
        let internal = Internal::deserialize(reader)?;

        Ok(ExportEntry {
            field_str: field_str,
            internal: internal,
        })
    }    
}

impl Serialize for ExportEntry {
    type Error = Error;
    
    fn serialize<W: io::Write>(self, writer: &mut W) -> Result<(), Self::Error> {
        self.field_str.serialize(writer)?;
        self.internal.serialize(writer)?;
        Ok(())
    }
}