use super::Value;
use anyhow::{Context, Result, anyhow, bail};
use std::collections::BTreeMap;

pub trait FromValue: Sized {
    fn from_value(v: Value) -> Result<Self>;
}

impl Value {
    pub fn parse<T: FromValue>(self) -> Result<T> {
        T::from_value(self)
    }
    pub fn as_class(self, name: &'static str) -> Result<Fields> {
        if let Value::Object { class, fields } = self {
            if class == name {
                Ok(Fields {
                    class: name,
                    fields,
                })
            } else {
                bail!("expected class {name} but found {class}")
            }
        } else {
            bail!("expected class {name} but found something else")
        }
    }
}

pub struct Fields {
    class: &'static str,
    fields: BTreeMap<String, Value>,
}

impl Fields {
    pub fn field<T: FromValue>(&mut self, name: &str) -> Result<T> {
        self.fields
            .remove(name)
            .ok_or(anyhow!("expected {name} field in {}", self.class))?
            .parse()
            .context(anyhow!("in {}.{name} field", self.class))
    }
    pub fn remove(&mut self, key: &str) -> Option<Value> {
        self.fields.remove(key)
    }
}

impl FromValue for u8 {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_u8().ok_or(anyhow!("expected u8"))
    }
}
impl FromValue for u16 {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_u16().ok_or(anyhow!("expected u16"))
    }
}
impl FromValue for f32 {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_f32().ok_or(anyhow!("expected f32"))
    }
}
impl FromValue for u32 {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_u32().ok_or(anyhow!("expected u32"))
    }
}
impl FromValue for i32 {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_i32().ok_or(anyhow!("expected i32"))
    }
}
impl FromValue for u64 {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_u64().ok_or(anyhow!("expected u64"))
    }
}
impl FromValue for bool {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_bool().ok_or(anyhow!("expected bool"))
    }
}
impl FromValue for String {
    fn from_value(v: Value) -> anyhow::Result<Self> {
        v.as_string().ok_or(anyhow!("expected string"))
    }
}

impl Value {
    pub fn as_vector(self) -> Option<Vec<Value>> {
        self.as_class("vector").ok()?.remove("Array")?.as_array()
    }
}

impl<K: FromValue + Ord, V: FromValue> FromValue for BTreeMap<K, V> {
    fn from_value(v: Value) -> Result<Self> {
        v.as_class("map")?
            .remove("Array")
            .ok_or(anyhow!("map is missing Array field"))?
            .as_array()
            .ok_or(anyhow!("map Array field is not an array"))?
            .into_iter()
            .map(|e| {
                let mut fields = e.as_class("pair")?;
                Ok((fields.field("first")?, fields.field("second")?))
            })
            .collect::<Result<BTreeMap<_, _>>>()
    }
}