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use hcl_edit::{expr::Expression, structure::Body, visit_mut::VisitMut};

use crate::parser::Field;

struct HclEditor<'a> {
    fields: Vec<Field>,
    next: Option<Field>,
    value: &'a Expression,
}

impl<'a> HclEditor<'a> {
    fn new(fields: Vec<Field>, value: &'a Expression) -> Self {
        HclEditor {
            fields,
            next: None,
            value,
        }
    }

    fn next_field(&mut self) {
        if self.next.is_none() && !self.fields.is_empty() {
            self.next = Some(self.fields.remove(0));
        }
    }
}

impl<'a> VisitMut for HclEditor<'a> {
    fn visit_attr_mut(&mut self, mut node: hcl_edit::structure::AttributeMut) {
        self.next_field();
        // perform update if the attr key matches the field
        if let Some(ref next) = self.next {
            if node.key.as_str() == next.name {
                let value = node.value_mut();
                *value = self.value.clone();
            }
        }
    }

    fn visit_block_mut(&mut self, node: &mut hcl_edit::structure::Block) {
        self.next_field();
        // create a clone so that we can later mutate `self.next`
        let next = self.next.clone();
        if let Some(next) = next {
            if node.ident.as_str() == next.name {
                if next.labels.is_empty() {
                    // the block is a match if its name matches and there are no labels
                    // traverse to the next field
                    self.next = Some(self.fields.remove(0));
                    // then visit the body
                    self.visit_body_mut(&mut node.body);
                } else {
                    for filter_label in &next.labels {
                        for block_label in &node.labels {
                            if block_label.as_str() == filter_label {
                                // the block name and this label match the filters
                                // traverse to the next field
                                self.next = Some(self.fields.remove(0));
                                // then visit the body
                                self.visit_body_mut(&mut node.body);
                            }
                        }
                    }
                }
            }
        }
    }
}

pub fn write(fields: Vec<Field>, body: &mut Body, value: &Expression) {
    let mut visitor = HclEditor::new(fields, value);
    visitor.visit_body_mut(body);
}