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/*!
Contains the [Queryable](crate::queryable::Queryable) trait.
*/
use snafu::{ensure, Snafu};
use std::default::Default;
use std::sync::Arc;

use crate::codec::{build_codec, Codec};
use crate::descriptors::{Descriptor, TypePos};
use crate::errors::{self, DecodeError};
use edgedb_errors::{Error, ErrorKind, ProtocolEncodingError};

#[non_exhaustive]
#[derive(Default)]
pub struct Decoder {
    pub has_implicit_id: bool,
    pub has_implicit_tid: bool,
    pub has_implicit_tname: bool,
}

pub trait Queryable: Sized {
    fn decode(decoder: &Decoder, buf: &[u8]) -> Result<Self, DecodeError>;
    fn decode_optional(decoder: &Decoder, buf: Option<&[u8]>) -> Result<Self, DecodeError> {
        ensure!(buf.is_some(), errors::MissingRequiredElement);
        Self::decode(decoder, buf.unwrap())
    }
    fn check_descriptor(
        ctx: &DescriptorContext,
        type_pos: TypePos,
    ) -> Result<(), DescriptorMismatch>;
}

#[derive(Snafu, Debug)]
#[non_exhaustive]
pub enum DescriptorMismatch {
    #[snafu(display("unexpected type {}, expected {}", unexpected, expected))]
    WrongType {
        unexpected: String,
        expected: String,
    },
    #[snafu(display("unexpected field {}, expected {}", unexpected, expected))]
    WrongField {
        unexpected: String,
        expected: String,
    },
    #[snafu(display("expected {} fields, got {}", expected, unexpected))]
    FieldNumber { unexpected: usize, expected: usize },
    #[snafu(display("expected {}", expected))]
    Expected { expected: String },
    #[snafu(display("invalid type descriptor"))]
    InvalidDescriptor,
}

pub struct DescriptorContext<'a> {
    pub has_implicit_id: bool,
    pub has_implicit_tid: bool,
    pub has_implicit_tname: bool,
    descriptors: &'a [Descriptor],
}

impl DescriptorContext<'_> {
    pub(crate) fn new(descriptors: &[Descriptor]) -> DescriptorContext {
        DescriptorContext {
            descriptors,
            has_implicit_id: false,
            has_implicit_tid: false,
            has_implicit_tname: false,
        }
    }
    pub fn build_codec(&self, root_pos: TypePos) -> Result<Arc<dyn Codec>, Error> {
        build_codec(Some(root_pos), self.descriptors).map_err(ProtocolEncodingError::with_source)
    }
    pub fn get(&self, type_pos: TypePos) -> Result<&Descriptor, DescriptorMismatch> {
        self.descriptors
            .get(type_pos.0 as usize)
            .ok_or(DescriptorMismatch::InvalidDescriptor)
    }
    pub fn wrong_type(&self, descriptor: &Descriptor, expected: &str) -> DescriptorMismatch {
        DescriptorMismatch::WrongType {
            unexpected: format!("{descriptor:?}"),
            expected: expected.into(),
        }
    }
    pub fn field_number(&self, expected: usize, unexpected: usize) -> DescriptorMismatch {
        DescriptorMismatch::FieldNumber {
            expected,
            unexpected,
        }
    }
    pub fn wrong_field(&self, expected: &str, unexpected: &str) -> DescriptorMismatch {
        DescriptorMismatch::WrongField {
            expected: expected.into(),
            unexpected: unexpected.into(),
        }
    }
    pub fn expected(&self, expected: &str) -> DescriptorMismatch {
        DescriptorMismatch::Expected {
            expected: expected.into(),
        }
    }
}