//! The `ResolveValue` trait resolves Fluent AST nodes to [`FluentValues`].
//!
//! This is an internal API used by [`MessageContext`] to evaluate Messages, Attributes and other
//! AST nodes to [`FluentValues`] which can be then formatted to strings.
//!
//! [`FluentValues`]: ../types/enum.FluentValue.html
//! [`MessageContext`]: ../context/struct.MessageContext.html

use std::collections::HashMap;
use std::str::FromStr;

use super::types::FluentValue;
use super::syntax::ast;
use super::context::MessageContext;

/// State for a single `ResolveValue::to_value` call.
pub struct Env<'env> {
    /// The current `MessageContext` instance.
    pub ctx: &'env MessageContext<'env>,
    /// The current arguments passed by the developer.
    pub args: Option<&'env HashMap<&'env str, FluentValue>>,
}

/// Converts an AST node to a `FluentValue`.
pub trait ResolveValue {
    fn to_value(&self, env: &Env) -> Option<FluentValue>;
}

impl ResolveValue for ast::Message {
    fn to_value(&self, env: &Env) -> Option<FluentValue> {
        self.value.as_ref().and_then(
            |pattern| pattern.to_value(env),
        )
    }
}

impl ResolveValue for ast::Attribute {
    fn to_value(&self, env: &Env) -> Option<FluentValue> {
        self.value.to_value(env)
    }
}

impl ResolveValue for ast::Pattern {
    fn to_value(&self, env: &Env) -> Option<FluentValue> {
        let string = self.elements
            .iter()
            .map(|elem| {
                elem.to_value(env).map_or(String::from("___"), |elem| {
                    elem.format(env.ctx)
                })
            })
            .collect::<String>();
        Some(FluentValue::from(string))
    }
}

impl ResolveValue for ast::PatternElement {
    fn to_value(&self, env: &Env) -> Option<FluentValue> {
        match *self {
            ast::PatternElement::TextElement(ref s) => Some(FluentValue::from(s.clone())),
            ast::PatternElement::Placeable(ref p) => p.to_value(env),
        }
    }
}

impl ResolveValue for ast::Placeable {
    fn to_value(&self, env: &Env) -> Option<FluentValue> {
        self.expression.to_value(env)
    }
}

impl ResolveValue for ast::Number {
    fn to_value(&self, _env: &Env) -> Option<FluentValue> {
        f32::from_str(&self.value).ok().map(FluentValue::from)
    }
}

impl ResolveValue for ast::Symbol {
    fn to_value(&self, _env: &Env) -> Option<FluentValue> {
        Some(FluentValue::from(self.name.clone()))
    }
}

impl ResolveValue for ast::Expression {
    fn to_value(&self, env: &Env) -> Option<FluentValue> {
        match *self {
            ast::Expression::StringExpression { ref value } => {
                Some(FluentValue::from(value.clone()))
            }
            ast::Expression::NumberExpression { ref value } => value.to_value(env),
            ast::Expression::MessageReference { ref id } => {
                env.ctx
                    .get_message(&id.name)
                    .and_then(|message| message.value.as_ref())
                    .and_then(|pattern| pattern.to_value(env))
            }
            ast::Expression::ExternalArgument { ref id } => {
                env.args
                    .and_then(|args| args.get(&id.name.as_ref()))
                    .cloned()
            }
            ast::Expression::SelectExpression {
                expression: None,
                ref variants,
            } => select_default(variants).and_then(|variant| variant.value.to_value(env)),
            ast::Expression::SelectExpression {
                expression: Some(box ast::Expression::MessageReference { ref id }),
                ref variants,
            } => {
                let tags = env.ctx.get_message(&id.name).and_then(
                    |message| message.tags.as_ref(),
                );

                if let Some(tags) = tags {
                    for variant in variants {
                        if let ast::VarKey::Symbol(ref symbol) = variant.key {
                            for tag in tags.iter() {
                                if symbol.name == tag.name.name {
                                    return variant.value.to_value(env);
                                }
                            }
                        }
                    }
                }

                select_default(variants).and_then(|variant| variant.value.to_value(env))
            }
            ast::Expression::SelectExpression {
                ref expression,
                ref variants,
            } => {
                let selector = expression.as_ref().and_then(|expr| expr.to_value(env));

                if let Some(ref selector) = selector {
                    for variant in variants {
                        match variant.key {
                            ast::VarKey::Symbol(ref symbol) => {
                                let key = FluentValue::from(symbol.name.clone());
                                if key.matches(env.ctx, selector) {
                                    return variant.value.to_value(env);
                                }
                            }
                            ast::VarKey::Number(ref number) => {
                                if let Some(key) = number.to_value(env) {
                                    if key.matches(env.ctx, selector) {
                                        return variant.value.to_value(env);
                                    }
                                }
                            }
                        }
                    }
                }

                select_default(variants).and_then(|variant| variant.value.to_value(env))
            }
            ast::Expression::AttributeExpression { ref id, ref name } => {
                let attributes = env.ctx.get_message(&id.name).as_ref().and_then(|message| {
                    message.attributes.as_ref()
                });
                if let Some(attributes) = attributes {
                    for attribute in attributes {
                        if attribute.id.name == name.name {
                            return attribute.to_value(env);
                        }
                    }
                }
                None
            }
            ast::Expression::VariantExpression { ref id, ref key } => {
                let message = env.ctx.get_message(&id.name);
                let variants = message
                    .as_ref()
                    .and_then(|message| message.value.as_ref())
                    .and_then(|pattern| {
                        if pattern.elements.len() > 1 {
                            return None;
                        }

                        match pattern.elements.first() {
                            Some(&ast::PatternElement::Placeable(ast::Placeable {
                           expression: ast::Expression::SelectExpression {
                               expression: None, ref variants
                           }
                       })) => Some(variants),
                            _ => None,
                        }
                    });

                if let Some(variants) = variants {
                    for variant in variants {
                        if variant.key == *key {
                            return variant.value.to_value(env);
                        }
                    }

                    return select_default(variants).and_then(|variant| variant.value.to_value(env));
                }

                message
                    .as_ref()
                    .and_then(|message| message.value.as_ref())
                    .and_then(|pattern| pattern.to_value(env))

            }
            _ => unimplemented!(),
        }
    }
}

fn select_default(variants: &[ast::Variant]) -> Option<&ast::Variant> {
    for variant in variants {
        if variant.default {
            return Some(variant);
        }
    }

    None
}