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use std::convert::TryFrom;

use crate::result::{decoding_error, IonError};
use crate::types::IonType;

/// Represents the type information found in the header byte of each binary Ion value.
/// While this value can be readily mapped to a user-level [`IonType`], it is a distinct concept.
/// The IonTypeCode enum captures system-level information that is not exposed to end users of the
/// library, including:
/// * Whether the cursor is positioned over whitespace that needs to be skipped.
/// * Whether the integer value being read is positive or negative.
/// * Whether the next type code is reserved.
///
/// See the
/// [Typed Value Formats](https://amazon-ion.github.io/ion-docs/docs/binary.html#typed-value-formats)
/// section of the spec for more information.
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum IonTypeCode {
    NullOrNop,       // 0
    Boolean,         // 1
    PositiveInteger, // 2
    NegativeInteger, // 3
    Float,           // 4
    Decimal,         // 5
    Timestamp,       // 6
    Symbol,          // 7
    String,          // 8
    Clob,            // 9
    Blob,            // 10
    List,            // 11
    SExpression,     // 12
    Struct,          // 13
    AnnotationOrIvm, // 14
    Reserved,        // 15
}

impl TryFrom<IonTypeCode> for IonType {
    type Error = IonError;

    /// Attempts to convert the system-level IonTypeCode into the corresponding user-level IonType.
    fn try_from(ion_type_code: IonTypeCode) -> Result<Self, Self::Error> {
        use IonTypeCode::*;
        let ion_type = match ion_type_code {
            NullOrNop => IonType::Null,
            Boolean => IonType::Bool,
            PositiveInteger | NegativeInteger => IonType::Int,
            Float => IonType::Float,
            Decimal => IonType::Decimal,
            Timestamp => IonType::Timestamp,
            Symbol => IonType::Symbol,
            String => IonType::String,
            Clob => IonType::Clob,
            Blob => IonType::Blob,
            List => IonType::List,
            SExpression => IonType::SExp,
            Struct => IonType::Struct,
            _ => {
                return decoding_error(format!(
                    "Attempted to make an IonType from an invalid type code: {ion_type_code:?}"
                ));
            }
        };
        Ok(ion_type)
    }
}

impl TryFrom<u8> for IonTypeCode {
    type Error = IonError;

    /// Attempts to convert the provided byte into an IonTypeCode. Any value greater than 15
    /// will result in an Error.
    fn try_from(type_code: u8) -> Result<Self, Self::Error> {
        use IonTypeCode::*;
        let ion_type_code = match type_code {
            0 => NullOrNop,
            1 => Boolean,
            2 => PositiveInteger,
            3 => NegativeInteger,
            4 => Float,
            5 => Decimal,
            6 => Timestamp,
            7 => Symbol,
            8 => String,
            9 => Clob,
            10 => Blob,
            11 => List,
            12 => SExpression,
            13 => Struct,
            14 => AnnotationOrIvm,
            15 => Reserved,
            _ => {
                return decoding_error(format!("{type_code:?} is not a valid header type code."));
            }
        };
        Ok(ion_type_code)
    }
}

impl IonTypeCode {
    /// Constant function to convert an [`IonTypeCode`] into a `u8`.
    pub const fn to_u8(self) -> u8 {
        use IonTypeCode::*;
        match self {
            NullOrNop => 0,
            Boolean => 1,
            PositiveInteger => 2,
            NegativeInteger => 3,
            Float => 4,
            Decimal => 5,
            Timestamp => 6,
            Symbol => 7,
            String => 8,
            Clob => 9,
            Blob => 10,
            List => 11,
            SExpression => 12,
            Struct => 13,
            AnnotationOrIvm => 14,
            Reserved => 15,
        }
    }
}