//! Code for applying replacement templates for matches that have previously been found.

use crate::matching::Var;
use crate::{resolving::ResolvedRule, Match, SsrMatches};
use ra_syntax::ast::{self, AstToken};
use ra_syntax::{SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken, TextRange, TextSize};
use rustc_hash::{FxHashMap, FxHashSet};
use text_edit::TextEdit;

/// Returns a text edit that will replace each match in `matches` with its corresponding replacement
/// template. Placeholders in the template will have been substituted with whatever they matched to
/// in the original code.
pub(crate) fn matches_to_edit(
    matches: &SsrMatches,
    file_src: &str,
    rules: &[ResolvedRule],
) -> TextEdit {
    matches_to_edit_at_offset(matches, file_src, 0.into(), rules)
}

fn matches_to_edit_at_offset(
    matches: &SsrMatches,
    file_src: &str,
    relative_start: TextSize,
    rules: &[ResolvedRule],
) -> TextEdit {
    let mut edit_builder = TextEdit::builder();
    for m in &matches.matches {
        edit_builder.replace(
            m.range.range.checked_sub(relative_start).unwrap(),
            render_replace(m, file_src, rules),
        );
    }
    edit_builder.finish()
}

struct ReplacementRenderer<'a> {
    match_info: &'a Match,
    file_src: &'a str,
    rules: &'a [ResolvedRule],
    rule: &'a ResolvedRule,
    out: String,
    // Map from a range within `out` to a token in `template` that represents a placeholder. This is
    // used to validate that the generated source code doesn't split any placeholder expansions (see
    // below).
    placeholder_tokens_by_range: FxHashMap<TextRange, SyntaxToken>,
    // Which placeholder tokens need to be wrapped in parenthesis in order to ensure that when `out`
    // is parsed, placeholders don't get split. e.g. if a template of `$a.to_string()` results in `1
    // + 2.to_string()` then the placeholder value `1 + 2` was split and needs parenthesis.
    placeholder_tokens_requiring_parenthesis: FxHashSet<SyntaxToken>,
}

fn render_replace(match_info: &Match, file_src: &str, rules: &[ResolvedRule]) -> String {
    let rule = &rules[match_info.rule_index];
    let template = rule
        .template
        .as_ref()
        .expect("You called MatchFinder::edits after calling MatchFinder::add_search_pattern");
    let mut renderer = ReplacementRenderer {
        match_info,
        file_src,
        rules,
        rule,
        out: String::new(),
        placeholder_tokens_requiring_parenthesis: FxHashSet::default(),
        placeholder_tokens_by_range: FxHashMap::default(),
    };
    renderer.render_node(&template.node);
    renderer.maybe_rerender_with_extra_parenthesis(&template.node);
    for comment in &match_info.ignored_comments {
        renderer.out.push_str(&comment.syntax().to_string());
    }
    renderer.out
}

impl ReplacementRenderer<'_> {
    fn render_node_children(&mut self, node: &SyntaxNode) {
        for node_or_token in node.children_with_tokens() {
            self.render_node_or_token(&node_or_token);
        }
    }

    fn render_node_or_token(&mut self, node_or_token: &SyntaxElement) {
        match node_or_token {
            SyntaxElement::Token(token) => {
                self.render_token(&token);
            }
            SyntaxElement::Node(child_node) => {
                self.render_node(&child_node);
            }
        }
    }

    fn render_node(&mut self, node: &SyntaxNode) {
        use ra_syntax::ast::AstNode;
        if let Some(mod_path) = self.match_info.rendered_template_paths.get(&node) {
            self.out.push_str(&mod_path.to_string());
            // Emit everything except for the segment's name-ref, since we already effectively
            // emitted that as part of `mod_path`.
            if let Some(path) = ast::Path::cast(node.clone()) {
                if let Some(segment) = path.segment() {
                    for node_or_token in segment.syntax().children_with_tokens() {
                        if node_or_token.kind() != SyntaxKind::NAME_REF {
                            self.render_node_or_token(&node_or_token);
                        }
                    }
                }
            }
        } else {
            self.render_node_children(&node);
        }
    }

    fn render_token(&mut self, token: &SyntaxToken) {
        if let Some(placeholder) = self.rule.get_placeholder(&token) {
            if let Some(placeholder_value) =
                self.match_info.placeholder_values.get(&Var(placeholder.ident.to_string()))
            {
                let range = &placeholder_value.range.range;
                let mut matched_text =
                    self.file_src[usize::from(range.start())..usize::from(range.end())].to_owned();
                let edit = matches_to_edit_at_offset(
                    &placeholder_value.inner_matches,
                    self.file_src,
                    range.start(),
                    self.rules,
                );
                let needs_parenthesis =
                    self.placeholder_tokens_requiring_parenthesis.contains(token);
                edit.apply(&mut matched_text);
                if needs_parenthesis {
                    self.out.push('(');
                }
                self.placeholder_tokens_by_range.insert(
                    TextRange::new(
                        TextSize::of(&self.out),
                        TextSize::of(&self.out) + TextSize::of(&matched_text),
                    ),
                    token.clone(),
                );
                self.out.push_str(&matched_text);
                if needs_parenthesis {
                    self.out.push(')');
                }
            } else {
                // We validated that all placeholder references were valid before we
                // started, so this shouldn't happen.
                panic!(
                    "Internal error: replacement referenced unknown placeholder {}",
                    placeholder.ident
                );
            }
        } else {
            self.out.push_str(token.text().as_str());
        }
    }

    // Checks if the resulting code, when parsed doesn't split any placeholders due to different
    // order of operations between the search pattern and the replacement template. If any do, then
    // we rerender the template and wrap the problematic placeholders with parenthesis.
    fn maybe_rerender_with_extra_parenthesis(&mut self, template: &SyntaxNode) {
        if let Some(node) = parse_as_kind(&self.out, template.kind()) {
            self.remove_node_ranges(node);
            if self.placeholder_tokens_by_range.is_empty() {
                return;
            }
            self.placeholder_tokens_requiring_parenthesis =
                self.placeholder_tokens_by_range.values().cloned().collect();
            self.out.clear();
            self.render_node(template);
        }
    }

    fn remove_node_ranges(&mut self, node: SyntaxNode) {
        self.placeholder_tokens_by_range.remove(&node.text_range());
        for child in node.children() {
            self.remove_node_ranges(child);
        }
    }
}

fn parse_as_kind(code: &str, kind: SyntaxKind) -> Option<SyntaxNode> {
    use ra_syntax::ast::AstNode;
    if ast::Expr::can_cast(kind) {
        if let Ok(expr) = ast::Expr::parse(code) {
            return Some(expr.syntax().clone());
        }
    } else if ast::Item::can_cast(kind) {
        if let Ok(item) = ast::Item::parse(code) {
            return Some(item.syntax().clone());
        }
    }
    None
}