json-e 4.8.2

A data-structure parameterization system for embedding context in JSON objects
Documentation 
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#![allow(unused_variables)]
#![allow(dead_code)]

use crate::render::is_identifier;
use crate::value::Value;
use anyhow::{anyhow, Result};
use serde_json::Value as SerdeValue;
use std::collections::HashMap;

pub(crate) struct Context<'a> {
    content: HashMap<String, Value>,
    parent: Option<&'a Context<'a>>,
}

/// Context for expression evaluation.
impl<'a> Context<'a> {
    /// Create a new, empty context.
    pub(crate) fn new() -> Context<'a> {
        Context {
            content: HashMap::new(),
            parent: None,
        }
    }

    /// Create a child context, which will defer to the parent context when a value
    /// is not defined.
    pub(crate) fn child(&'a self) -> Context<'a> {
        Context {
            content: HashMap::new(),
            parent: Some(self),
        }
    }

    /// Create a context from a Serde JSON value, which must be an object.
    pub(crate) fn from_serde_value(
        value: &'_ SerdeValue,
        parent: Option<&'a Context>,
    ) -> Result<Context<'a>> {
        // TODO: this could be more efficient by converting only the values and not cloning
        let value: Value = value.into();
        Context::from_value(&value, parent)
    }

    /// Create a context from a json-e Value, which must be an object
    pub(crate) fn from_value(value: &'_ Value, parent: Option<&'a Context>) -> Result<Context<'a>> {
        let mut c = Context {
            content: HashMap::new(),
            parent,
        };

        if let Value::Object(o) = value {
            if o.keys().any(|k| !is_identifier(k)) {
                return Err(template_error!(
                    "top level keys of context must follow /[a-zA-Z_][a-zA-Z0-9_]"
                ));
            }
            for (k, v) in o.iter() {
                c.insert(k, v.clone());
            }
        } else {
            return Err(anyhow!("Context is not an Object"));
        }

        Ok(c)
    }

    /// Insert a value into this context.
    pub(crate) fn insert<K: Into<String>>(&mut self, k: K, v: Value) {
        self.content.insert(k.into(), v);
    }

    /// Get a value from this context (or its parents)
    pub(crate) fn get<'b>(&'b self, k: &'_ str) -> Option<&'b Value> {
        match self.content.get(k) {
            Some(v) => Some(v),
            None => match self.parent {
                Some(p) => p.get(k),
                None => None,
            },
        }
    }
}

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

    #[test]
    fn test_get_not_found() {
        let c = Context::new();
        assert_eq!(c.get("xyz"), None);
    }

    #[test]
    fn test_get_found() {
        let mut c = Context::new();
        c.insert("abc", Value::Null);
        assert_eq!(c.get("abc"), Some(&Value::Null))
    }

    #[test]
    fn test_get_parent() {
        let mut c1 = Context::new();
        c1.insert("abc", Value::Null);
        c1.insert("def", Value::Bool(true));
        let mut c2 = c1.child();
        c2.insert("def", Value::Bool(false));
        c2.insert("ghi", Value::String("hi".into()));
        assert_eq!(c2.get("abc"), Some(&Value::Null));
        assert_eq!(c2.get("def"), Some(&Value::Bool(false)));
        assert_eq!(c2.get("ghi"), Some(&Value::String("hi".into())));
    }
}