use super::operators::{Frame, OperatorValidator, OperatorValidatorAllocations};
use crate::{BinaryReader, Result, ValType, VisitOperator};
use crate::{FunctionBody, Operator, WasmFeatures, WasmModuleResources};

/// Resources necessary to perform validation of a function.
///
/// This structure is created by
/// [`Validator::code_section_entry`](crate::Validator::code_section_entry) and
/// is created per-function in a WebAssembly module. This structure is suitable
/// for sending to other threads while the original
/// [`Validator`](crate::Validator) continues processing other functions.
pub struct FuncToValidate<T> {
    /// The reusable heap allocated resources required for Wasm validation.
    pub resources: T,
    /// The function index within the Wasm module.
    pub index: u32,
    /// The type index of the function.
    pub ty: u32,
    /// The Wasm features used for validating the function.
    pub features: WasmFeatures,
}

impl<T: WasmModuleResources> FuncToValidate<T> {
    /// Creates a new function to validate which will have the specified
    /// configuration parameters:
    ///
    /// * `index` - the core wasm function index being validated
    /// * `ty` - the core wasm type index of the function being validated,
    ///   defining the results and parameters to the function.
    /// * `resources` - metadata and type information about the module that
    ///   this function is validated within.
    /// * `features` - enabled WebAssembly features.
    pub fn new(index: u32, ty: u32, resources: T, features: &WasmFeatures) -> FuncToValidate<T> {
        FuncToValidate {
            resources,
            index,
            ty,
            features: *features,
        }
    }

    /// Converts this [`FuncToValidate`] into a [`FuncValidator`] using the
    /// `allocs` provided.
    ///
    /// This method, in conjunction with [`FuncValidator::into_allocations`],
    /// provides a means to reuse allocations across validation of each
    /// individual function. Note that it is also sufficient to call this
    /// method with `Default::default()` if no prior allocations are
    /// available.
    ///
    /// # Panics
    ///
    /// If a `FuncToValidate` was created with an invalid `ty` index then this
    /// function will panic.
    pub fn into_validator(self, allocs: FuncValidatorAllocations) -> FuncValidator<T> {
        let FuncToValidate {
            resources,
            index,
            ty,
            features,
        } = self;
        let validator =
            OperatorValidator::new_func(ty, 0, &features, &resources, allocs.0).unwrap();
        FuncValidator {
            validator,
            resources,
            index,
        }
    }
}

/// Validation context for a WebAssembly function.
///
/// This is a finalized validator which is ready to process a [`FunctionBody`].
/// This is created from the [`FuncToValidate::into_validator`] method.
pub struct FuncValidator<T> {
    validator: OperatorValidator,
    resources: T,
    index: u32,
}

/// External handle to the internal allocations used during function validation.
///
/// This is created with either the `Default` implementation or with
/// [`FuncValidator::into_allocations`]. It is then passed as an argument to
/// [`FuncToValidate::into_validator`] to provide a means of reusing allocations
/// between each function.
#[derive(Default)]
pub struct FuncValidatorAllocations(OperatorValidatorAllocations);

impl<T: WasmModuleResources> FuncValidator<T> {
    /// Convenience function to validate an entire function's body.
    ///
    /// You may not end up using this in final implementations because you'll
    /// often want to interleave validation with parsing.
    pub fn validate(&mut self, body: &FunctionBody<'_>) -> Result<()> {
        let mut reader = body.get_binary_reader();
        self.read_locals(&mut reader)?;
        reader.allow_memarg64(self.validator.features.memory64);
        while !reader.eof() {
            reader.visit_operator(&mut self.visitor(reader.original_position()))??;
        }
        self.finish(reader.original_position())
    }

    /// Reads the local definitions from the given `BinaryReader`, often sourced
    /// from a `FunctionBody`.
    ///
    /// This function will automatically advance the `BinaryReader` forward,
    /// leaving reading operators up to the caller afterwards.
    pub fn read_locals(&mut self, reader: &mut BinaryReader<'_>) -> Result<()> {
        for _ in 0..reader.read_var_u32()? {
            let offset = reader.original_position();
            let cnt = reader.read()?;
            let ty = reader.read()?;
            self.define_locals(offset, cnt, ty)?;
        }
        Ok(())
    }

    /// Defines locals into this validator.
    ///
    /// This should be used if the application is already reading local
    /// definitions and there's no need to re-parse the function again.
    pub fn define_locals(&mut self, offset: usize, count: u32, ty: ValType) -> Result<()> {
        self.validator.define_locals(offset, count, ty)
    }

    /// Validates the next operator in a function.
    ///
    /// This functions is expected to be called once-per-operator in a
    /// WebAssembly function. Each operator's offset in the original binary and
    /// the operator itself are passed to this function to provide more useful
    /// error messages.
    pub fn op(&mut self, offset: usize, operator: &Operator<'_>) -> Result<()> {
        self.visitor(offset).visit_operator(operator)
    }

    /// Get the operator visitor for the next operator in the function.
    ///
    /// The returned visitor is intended to visit just one instruction at the `offset`.
    ///
    /// # Example
    ///
    /// ```
    /// # use wasmparser_nostd::{WasmModuleResources, FuncValidator, FunctionBody, Result};
    /// pub fn validate<R>(validator: &mut FuncValidator<R>, body: &FunctionBody<'_>) -> Result<()>
    /// where R: WasmModuleResources
    /// {
    ///     let mut operator_reader = body.get_binary_reader();
    ///     while !operator_reader.eof() {
    ///         let mut visitor = validator.visitor(operator_reader.original_position());
    ///         operator_reader.visit_operator(&mut visitor)??;
    ///     }
    ///     validator.finish(operator_reader.original_position())
    /// }
    /// ```
    pub fn visitor<'this, 'a: 'this>(
        &'this mut self,
        offset: usize,
    ) -> impl VisitOperator<'a, Output = Result<()>> + 'this {
        self.validator.with_resources(&self.resources, offset)
    }

    /// Function that must be called after the last opcode has been processed.
    ///
    /// This will validate that the function was properly terminated with the
    /// `end` opcode. If this function is not called then the function will not
    /// be properly validated.
    ///
    /// The `offset` provided to this function will be used as a position for an
    /// error if validation fails.
    pub fn finish(&mut self, offset: usize) -> Result<()> {
        self.validator.finish(offset)
    }

    /// Returns the underlying module resources that this validator is using.
    pub fn resources(&self) -> &T {
        &self.resources
    }

    /// The index of the function within the module's function index space that
    /// is being validated.
    pub fn index(&self) -> u32 {
        self.index
    }

    /// Returns the number of defined local variables in the function.
    pub fn len_locals(&self) -> u32 {
        self.validator.locals.len_locals()
    }

    /// Returns the type of the local variable at the given `index` if any.
    pub fn get_local_type(&self, index: u32) -> Option<ValType> {
        self.validator.locals.get(index)
    }

    /// Get the current height of the operand stack.
    ///
    /// This returns the height of the whole operand stack for this function,
    /// not just for the current control frame.
    pub fn operand_stack_height(&self) -> u32 {
        self.validator.operand_stack_height() as u32
    }

    /// Returns the optional value type of the value operand at the given
    /// `depth` from the top of the operand stack.
    ///
    /// - Returns `None` if the `depth` is out of bounds.
    /// - Returns `Some(None)` if there is a value with unknown type
    /// at the given `depth`.
    ///
    /// # Note
    ///
    /// A `depth` of 0 will refer to the last operand on the stack.
    pub fn get_operand_type(&self, depth: usize) -> Option<Option<ValType>> {
        self.validator.peek_operand_at(depth)
    }

    /// Returns the number of frames on the control flow stack.
    ///
    /// This returns the height of the whole control stack for this function,
    /// not just for the current control frame.
    pub fn control_stack_height(&self) -> u32 {
        self.validator.control_stack_height() as u32
    }

    /// Returns a shared reference to the control flow [`Frame`] of the
    /// control flow stack at the given `depth` if any.
    ///
    /// Returns `None` if the `depth` is out of bounds.
    ///
    /// # Note
    ///
    /// A `depth` of 0 will refer to the last frame on the stack.
    pub fn get_control_frame(&self, depth: usize) -> Option<&Frame> {
        self.validator.get_frame(depth)
    }

    /// Consumes this validator and returns the underlying allocations that
    /// were used during the validation process.
    ///
    /// The returned value here can be paired with
    /// [`FuncToValidate::into_validator`] to reuse the allocations already
    /// created by this validator.
    pub fn into_allocations(self) -> FuncValidatorAllocations {
        FuncValidatorAllocations(self.validator.into_allocations())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::WasmFuncType;

    struct EmptyResources;

    impl WasmModuleResources for EmptyResources {
        type FuncType = EmptyFuncType;

        fn table_at(&self, _at: u32) -> Option<crate::TableType> {
            todo!()
        }
        fn memory_at(&self, _at: u32) -> Option<crate::MemoryType> {
            todo!()
        }
        fn tag_at(&self, _at: u32) -> Option<&Self::FuncType> {
            todo!()
        }
        fn global_at(&self, _at: u32) -> Option<crate::GlobalType> {
            todo!()
        }
        fn func_type_at(&self, _type_idx: u32) -> Option<&Self::FuncType> {
            Some(&EmptyFuncType)
        }
        fn type_of_function(&self, _func_idx: u32) -> Option<&Self::FuncType> {
            todo!()
        }
        fn element_type_at(&self, _at: u32) -> Option<ValType> {
            todo!()
        }
        fn element_count(&self) -> u32 {
            todo!()
        }
        fn data_count(&self) -> Option<u32> {
            todo!()
        }
        fn is_function_referenced(&self, _idx: u32) -> bool {
            todo!()
        }
    }

    struct EmptyFuncType;

    impl WasmFuncType for EmptyFuncType {
        fn len_inputs(&self) -> usize {
            0
        }
        fn len_outputs(&self) -> usize {
            0
        }
        fn input_at(&self, _at: u32) -> Option<ValType> {
            todo!()
        }
        fn output_at(&self, _at: u32) -> Option<ValType> {
            todo!()
        }
    }

    #[test]
    fn operand_stack_height() {
        let mut v = FuncToValidate::new(0, 0, EmptyResources, &Default::default())
            .into_validator(Default::default());

        // Initially zero values on the stack.
        assert_eq!(v.operand_stack_height(), 0);

        // Pushing a constant value makes use have one value on the stack.
        assert!(v.op(0, &Operator::I32Const { value: 0 }).is_ok());
        assert_eq!(v.operand_stack_height(), 1);

        // Entering a new control block does not affect the stack height.
        assert!(v
            .op(
                1,
                &Operator::Block {
                    blockty: crate::BlockType::Empty
                }
            )
            .is_ok());
        assert_eq!(v.operand_stack_height(), 1);

        // Pushing another constant value makes use have two values on the stack.
        assert!(v.op(2, &Operator::I32Const { value: 99 }).is_ok());
        assert_eq!(v.operand_stack_height(), 2);
    }
}