//! A module that contains the different rules that mutates a Lua block.

mod empty_do;
mod method_def;
mod rename_variables;

pub use empty_do::*;
pub use method_def::*;
pub use rename_variables::*;

use crate::nodes::Block;

use serde::{Serialize, Serializer, Deserialize, Deserializer};
use serde::ser::SerializeMap;
use serde::de::{self, MapAccess, Visitor};
use std::fmt;
use std::str::FromStr;
use std::collections::HashMap;

/// In order to be able to weakly-type the properties of any rule, this enum makes it possible to
/// easily use serde to gather the value associated with a property.
#[derive(Debug, Serialize, Deserialize)]
#[serde(untagged)]
pub enum RulePropertyValue {
    String(String),
    Usize(usize),
    StringList(Vec<String>),
}

/// When implementing the configure method of the Rule trait, the method returns a result
#[derive(Debug, Clone)]
pub enum RuleConfigurationError {
    /// When a rule gets an unknown property. The string should be the unknown field value.
    UnexpectedProperty(String),
    /// When a property is associated with something else than an expected string. The string is
    /// the property name.
    StringExpected(String),
    /// When a property is associated with something else than an expected unsigned number. The
    /// string is the property name.
    UsizeExpected(String),
    /// When a property is associated with something else than an expected list of strings. The
    /// string is the property name.
    StringListExpected(String),
}

impl fmt::Display for RuleConfigurationError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::UnexpectedProperty(property) => write!(f, "unexpected field '{}'", property),
            Self::StringExpected(property) => write!(f, "string value expected for field '{}'", property),
            Self::UsizeExpected(property) => write!(f, "unsigned integer expected for field '{}'", property),
            Self::StringListExpected(property) => write!(f, "list of string expected for field '{}'", property),
        }
    }
}

pub type RuleProperties = HashMap<String, RulePropertyValue>;

/// Defines an interface that will be used to mutate blocks and how to serialize and deserialize
/// the rule configuration.
pub trait Rule {
    /// This method should mutate the given block to apply the rule.
    fn process(&self, block: &mut Block);
    /// The rule deserializer will construct the default rule and then send the properties through
    /// this method to modify the behavior of the rule.
    fn configure(&mut self, properties: RuleProperties) -> Result<(), RuleConfigurationError>;
    /// This method should the unique name of the rule.
    fn get_name(&self) -> &'static str;
    /// For implementing the serialize trait on the Rule trait, this method should return all
    /// properties that differs from their default value.
    fn serialize_to_properties(&self) -> RuleProperties;
}

/// A function to get the default rule stack for darklua. All the rules here must preserve all the
/// functionalities of the original code after being applied. They must guarantee that the
/// processed block will work as much as the original one.
pub fn get_default_rules() -> Vec<Box<dyn Rule>> {
    vec![
        Box::new(RemoveEmptyDo::default()),
        Box::new(RemoveMethodDefinition::default()),
        Box::new(RenameVariables::default()),
    ]
}

impl FromStr for Box<dyn Rule> {
    type Err = String;

    fn from_str(string: &str) -> Result<Self, Self::Err> {
        let rule: Box<dyn Rule> = match string {
            REMOVE_EMPTY_DO_RULE_NAME => Box::new(RemoveEmptyDo::default()),
            REMOVE_METHOD_DEFINITION_RULE_NAME => Box::new(RemoveMethodDefinition::default()),
            RENAME_VARIABLES_RULE_NAME => Box::new(RenameVariables::default()),
            _ => return Err(format!("invalid rule name: {}", string)),
        };

        Ok(rule)
    }
}

impl Serialize for Box<dyn Rule> {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        let properties = self.serialize_to_properties();
        let property_count = properties.len();
        let rule_name = self.get_name();

        if property_count == 0 {
            serializer.serialize_str(rule_name)

        } else {
            let mut map = serializer.serialize_map(Some(property_count + 1))?;

            map.serialize_entry("rule", rule_name)?;

            for (key, value) in properties {
                map.serialize_entry(&key, &value)?;
            }

            map.end()
        }
    }
}

impl<'de> Deserialize<'de> for Box<dyn Rule> {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Box<dyn Rule>, D::Error> {

        struct StringOrStruct;

        impl<'de> Visitor<'de> for StringOrStruct {
            type Value = Box<dyn Rule>;

            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("rule name or rule object")
            }

            fn visit_str<E>(self, value: &str) -> Result<Self::Value, E> where E: de::Error {
                FromStr::from_str(value).map_err(de::Error::custom)
            }

            fn visit_map<M>(self, mut map: M) -> Result<Self::Value, M::Error> where M: MapAccess<'de> {
                let mut rule_name = None;
                let mut properties = HashMap::new();

                while let Some(key) = map.next_key::<String>()? {
                    match key.as_str() {
                        "rule" => if rule_name.is_none() {
                            rule_name.replace(map.next_value::<String>()?);
                        } else {
                            return Err(de::Error::duplicate_field("rule"))
                        }
                        property => {
                            let value = map.next_value::<RulePropertyValue>()?;

                            if properties.insert(property.to_owned(), value).is_some() {
                                return Err(de::Error::custom(format!("duplicate field {} in rule object", property)))
                            }
                        }
                    }
                }

                if let Some(rule_name) = rule_name {
                    let mut rule: Self::Value = FromStr::from_str(&rule_name)
                        .map_err(de::Error::custom)?;

                    rule.configure(properties).map_err(de::Error::custom)?;

                    Ok(rule)
                } else {
                    Err(de::Error::missing_field("rule"))
                }
            }
        }

        deserializer.deserialize_any(StringOrStruct)
    }
}

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

    use insta::assert_json_snapshot;

    #[test]
    fn snapshot_default_rules() {
        let rules = get_default_rules();

        assert_json_snapshot!("default_rules", rules);
    }
}