use crate::instructions::{
    stack::{Stack, Stackable},
    wasm, Instruction,
};
use std::{
    convert::{TryFrom, TryInto},
    marker::PhantomData,
};

struct Runtime<'invocation, 'instance, Instance, Export>
where
    Export: wasm::Export + 'instance,
    Instance: wasm::Instance<Export> + 'instance,
{
    invocation_inputs: &'invocation Vec<u64>,
    stack: Stack<u64>,
    wasm_instance: &'instance Instance,
    wasm_exports: PhantomData<Export>,
}

pub struct Interpreter<Instance, Export>
where
    Export: wasm::Export,
    Instance: wasm::Instance<Export>,
{
    executable_instructions: Vec<Box<dyn Fn(&mut Runtime<Instance, Export>) -> Result<(), String>>>,
}

impl<Instance, Export> Interpreter<Instance, Export>
where
    Export: wasm::Export,
    Instance: wasm::Instance<Export>,
{
    fn iter(
        &self,
    ) -> impl Iterator<Item = &Box<dyn Fn(&mut Runtime<Instance, Export>) -> Result<(), String>>> + '_
    {
        self.executable_instructions.iter()
    }

    pub fn run(
        &self,
        invocation_inputs: &Vec<u64>,
        wasm_instance: &Instance,
    ) -> Result<Stack<u64>, String> {
        let mut runtime = Runtime {
            invocation_inputs,
            stack: Stack::new(),
            wasm_instance,
            wasm_exports: PhantomData,
        };

        for executable_instruction in self.iter() {
            match executable_instruction(&mut runtime) {
                Ok(_) => continue,
                Err(message) => return Err(message),
            }
        }

        Ok(runtime.stack)
    }
}

impl<'binary_input, Instance, Export> TryFrom<&Vec<Instruction<'binary_input>>>
    for Interpreter<Instance, Export>
where
    Export: wasm::Export,
    Instance: wasm::Instance<Export>,
{
    type Error = String;

    fn try_from(instructions: &Vec<Instruction>) -> Result<Self, Self::Error> {
        let executable_instructions = instructions
            .iter()
            .map(
                |instruction| -> Box<dyn Fn(&mut Runtime<Instance, Export>) -> Result<(), String>> {
                    match instruction {
                        Instruction::ArgumentGet(index) => {
                            let index = index.to_owned();
                            let instruction_name: String = instruction.into();

                            Box::new(move |runtime: &mut Runtime<Instance, Export>| -> Result<(), _> {
                                let invocation_inputs = runtime.invocation_inputs;

                                if index >= (invocation_inputs.len() as u64) {
                                    return Err(format!(
                                        "`{}` cannot access argument #{} because it doesn't exist.",
                                        instruction_name, index
                                    ));
                                }

                                runtime.stack.push(invocation_inputs[index as usize]);

                                Ok(())
                            })
                        }
                        Instruction::CallExport(export_name) => {
                            let export_name = (*export_name).to_owned();
                            let instruction_name: String = instruction.into();

                            Box::new(move |runtime: &mut Runtime<Instance, Export>| -> Result<(), _> {
                                let instance = runtime.wasm_instance;

                                match instance.export(&export_name) {
                                    Some(export) => {
                                        let inputs_cardinality = export.inputs_cardinality();

                                        match runtime.stack.pop(inputs_cardinality) {
                                            Some(inputs) =>  {
                                                let inputs: Vec<wasm::Value> = inputs.iter().map(|i| wasm::Value::I32(*i as i32)).collect();

                                                match export.call(&inputs) {
                                                    Ok(outputs) => {
                                                        for output in outputs.iter() {
                                                            let output: i32 = output.try_into().unwrap();

                                                            runtime.stack.push(output as u64);
                                                        }

                                                        Ok(())
                                                    },
                                                    Err(_) => Err("failed".into()),
                                                }
                                            }
                                            None => Err(format!(
                                                "`{}` cannot call the exported function `{}` because there is no enought data in the stack for the arguments (need {}).",
                                                instruction_name,
                                                export_name,
                                                inputs_cardinality,
                                            ))
                                        }
                                    },

                                    None => Err(format!(
                                        "`{}` cannot call the exported function `{}` because it doesn't exist.",
                                        instruction_name,
                                        export_name,
                                    ))
                                }
                            })
                        }
                        Instruction::ReadUtf8 => {
                            Box::new(|_runtime: &mut Runtime<Instance, Export>| -> Result<(), _> {
                                println!("read utf8");

                                Ok(())
                            })
                        }
                        Instruction::Call(index) => {
                            let index = index.to_owned();

                            Box::new(move |_runtime: &mut Runtime<Instance, Export>| -> Result<(), _> {
                                println!("call {}", index);

                                Ok(())
                            })
                        }
                        _ => unimplemented!(),
                    }
                },
            )
            .collect();

        Ok(Interpreter {
            executable_instructions,
        })
    }
}

#[cfg(test)]
mod tests {
    use super::Interpreter;
    use crate::instructions::{stack::Stackable, wasm, Instruction};
    use std::{collections::HashMap, convert::TryInto};

    struct Export {
        inputs: Vec<wasm::Type>,
        outputs: Vec<wasm::Type>,
        function: fn(arguments: &[wasm::Value]) -> Result<Vec<wasm::Value>, ()>,
    }

    impl wasm::Export for Export {
        fn inputs_cardinality(&self) -> usize {
            self.inputs.len() as usize
        }

        fn outputs_cardinality(&self) -> usize {
            self.outputs.len()
        }

        fn inputs(&self) -> &[wasm::Type] {
            &self.inputs
        }

        fn outputs(&self) -> &[wasm::Type] {
            &self.outputs
        }

        fn call(&self, arguments: &[wasm::Value]) -> Result<Vec<wasm::Value>, ()> {
            (self.function)(arguments)
        }
    }

    struct Instance {
        exports: HashMap<String, Export>,
    }

    impl Instance {
        fn new() -> Self {
            Self {
                exports: {
                    let mut hashmap = HashMap::new();
                    hashmap.insert(
                        "sum".into(),
                        Export {
                            inputs: vec![wasm::Type::I32, wasm::Type::I32],
                            outputs: vec![wasm::Type::I32],
                            function: |arguments: &[wasm::Value]| {
                                let a: i32 = (&arguments[0]).try_into().unwrap();
                                let b: i32 = (&arguments[1]).try_into().unwrap();

                                Ok(vec![wasm::Value::I32(a + b)])
                            },
                        },
                    );

                    hashmap
                },
            }
        }
    }

    impl wasm::Instance<Export> for Instance {
        fn export(&self, export_name: &str) -> Option<&Export> {
            self.exports.get(export_name)
        }
    }

    #[test]
    fn test_interpreter_from_instructions() {
        let instructions = vec![
            Instruction::ArgumentGet(0),
            Instruction::ArgumentGet(0),
            Instruction::CallExport("foo"),
            Instruction::ReadUtf8,
            Instruction::Call(7),
        ];
        let interpreter: Interpreter<(), ()> = (&instructions).try_into().unwrap();

        assert_eq!(interpreter.executable_instructions.len(), 5);
    }

    #[test]
    fn test_interpreter_argument_get() {
        let interpreter: Interpreter<Instance, Export> =
            (&vec![Instruction::ArgumentGet(0)]).try_into().unwrap();

        let invocation_inputs = vec![42];
        let instance = Instance::new();
        let run = interpreter.run(&invocation_inputs, &instance);

        assert!(run.is_ok());

        let stack = run.unwrap();

        assert_eq!(stack.as_slice(), &[42]);
    }

    #[test]
    fn test_interpreter_argument_get_invalid_index() {
        let interpreter: Interpreter<Instance, Export> =
            (&vec![Instruction::ArgumentGet(1)]).try_into().unwrap();

        let invocation_inputs = vec![42];
        let instance = Instance::new();
        let run = interpreter.run(&invocation_inputs, &instance);

        assert!(run.is_err());

        let error = run.unwrap_err();

        assert_eq!(
            error,
            String::from("`arg.get 1` cannot access argument #1 because it doesn't exist.")
        );
    }

    #[test]
    fn test_interpreter_argument_get_argument_get() {
        let interpreter: Interpreter<Instance, Export> =
            (&vec![Instruction::ArgumentGet(0), Instruction::ArgumentGet(1)])
                .try_into()
                .unwrap();

        let invocation_inputs = vec![7, 42];
        let instance = Instance::new();
        let run = interpreter.run(&invocation_inputs, &instance);

        assert!(run.is_ok());

        let stack = run.unwrap();

        assert_eq!(stack.as_slice(), &[7, 42]);
    }

    #[test]
    fn test_interpreter_call_export() {
        let interpreter: Interpreter<Instance, Export> = (&vec![
            Instruction::ArgumentGet(1),
            Instruction::ArgumentGet(0),
            Instruction::CallExport("sum"),
        ])
            .try_into()
            .unwrap();

        let invocation_inputs = vec![3, 4];
        let instance = Instance::new();
        let run = interpreter.run(&invocation_inputs, &instance);

        assert!(run.is_ok());

        let stack = run.unwrap();

        assert_eq!(stack.as_slice(), &[7]);
    }

    #[test]
    fn test_interpreter_call_export_invalid_export_name() {
        let interpreter: Interpreter<Instance, Export> =
            (&vec![Instruction::CallExport("bar")]).try_into().unwrap();

        let invocation_inputs = vec![];
        let instance = Instance::new();
        let run = interpreter.run(&invocation_inputs, &instance);

        assert!(run.is_err());

        let error = run.unwrap_err();

        assert_eq!(
            error,
            String::from(r#"`call-export "bar"` cannot call the exported function `bar` because it doesn't exist."#)
        );
    }
}