magellan 4.7.3

//! Go symbol extraction using tree-sitter-go.
//!
//! Extracts functions, methods, structs, and interfaces from Go source code.

use crate::common::safe_slice;
use crate::graph::canonical_fqn::FqnBuilder;
use crate::ingest::{ScopeSeparator, ScopeStack, SymbolFact, SymbolKind};
use crate::references::{CallFact, ReferenceFact};
use anyhow::Result;
use std::path::{Path, PathBuf};

/// Parser that extracts symbol facts from Go source code.
///
/// Pure function: Input (path, contents) → Output `Vec<SymbolFact>`
/// No filesystem access. No global state. No caching.
pub struct GoParser {
    pub(crate) parser: tree_sitter::Parser,
}

impl GoParser {
    /// Create a new parser for Go source code.
    pub fn new() -> Result<Self> {
        let mut parser = tree_sitter::Parser::new();
        parser.set_language(&tree_sitter_go::LANGUAGE.into())?;
        Ok(Self { parser })
    }

    /// Create parser wrapper from an existing tree-sitter parser
    pub(crate) fn from_parser(parser: tree_sitter::Parser) -> Self {
        Self { parser }
    }

    /// Extract symbol facts from Go source code.
    ///
    /// # Arguments
    /// * `file_path` - Path to the file (for context only, not accessed)
    /// * `source` - Source code content as bytes
    ///
    /// # Returns
    /// Vector of symbol facts found in the source
    ///
    /// # Guarantees
    /// - Pure function: same input → same output
    /// - No side effects
    /// - No filesystem access
    pub fn extract_symbols(&mut self, file_path: PathBuf, source: &[u8]) -> Vec<SymbolFact> {
        let tree = match self.parser.parse(source, None) {
            Some(t) => t,
            None => return Vec::new(), // Parse error: return empty
        };

        let root_node = tree.root_node();
        let mut facts = Vec::new();
        let mut scope_stack = ScopeStack::new(ScopeSeparator::Dot);

        // Find package declaration first
        let mut cursor = root_node.walk();
        for child in root_node.children(&mut cursor) {
            if child.kind() == "package_clause" {
                if let Some(name) = Self::extract_package_name(&child, source) {
                    scope_stack.push(&name);
                }
                break;
            }
        }

        // Walk tree with scope tracking
        Self::walk_tree_static(&root_node, source, &file_path, &mut facts, &mut scope_stack);

        facts
    }

    /// Extract package name from a package_clause node.
    fn extract_package_name(node: &tree_sitter::Node, source: &[u8]) -> Option<String> {
        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            if child.kind() == "package_identifier" {
                let name_bytes = safe_slice(source, child.start_byte(), child.end_byte())?;
                return std::str::from_utf8(name_bytes).ok().map(|s| s.to_string());
            }
        }
        None
    }

    /// Static walk tree for symbol extraction.
    fn walk_tree_static(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        facts: &mut Vec<SymbolFact>,
        scope_stack: &mut ScopeStack,
    ) {
        let kind = node.kind();

        // Skip package_clause (already handled)
        if kind == "package_clause" {
            return;
        }

        // Track type scope for method receivers
        let is_type_scope = kind == "type_declaration";

        if is_type_scope {
            // type_declaration may contain multiple type_spec children
            let mut cursor = node.walk();
            for child in node.children(&mut cursor) {
                if child.kind() == "type_spec" {
                    if let Some(fact) =
                        Self::extract_symbol_from_type_spec(&child, source, file_path, scope_stack)
                    {
                        facts.push(fact);
                    }
                }
            }
            return;
        }

        // Extract symbol from this node if applicable
        if let Some(fact) = Self::extract_symbol(node, source, file_path, scope_stack) {
            facts.push(fact);
        }

        // Recurse into children
        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            Self::walk_tree_static(&child, source, file_path, facts, scope_stack);
        }
    }

    /// Extract a symbol fact from a type_spec node.
    fn extract_symbol_from_type_spec(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        scope_stack: &ScopeStack,
    ) -> Option<SymbolFact> {
        let mut name: Option<String> = None;
        let mut symbol_kind = SymbolKind::Unknown;

        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            match child.kind() {
                "type_identifier" => {
                    let name_bytes = safe_slice(source, child.start_byte(), child.end_byte())?;
                    name = std::str::from_utf8(name_bytes).ok().map(|s| s.to_string());
                }
                "struct_type" => {
                    symbol_kind = SymbolKind::Class;
                }
                "interface_type" => {
                    symbol_kind = SymbolKind::Interface;
                }
                _ => {}
            }
        }

        let name = name?;
        if symbol_kind == SymbolKind::Unknown {
            // Default to Class for unknown type declarations
            symbol_kind = SymbolKind::Class;
        }

        let normalized_kind = symbol_kind.normalized_key().to_string();
        let fqn = scope_stack.fqn_for_symbol(&name);

        let builder = FqnBuilder::new(
            ".".to_string(),
            file_path.to_string_lossy().to_string(),
            ScopeSeparator::Dot,
        );
        let canonical_fqn = builder.canonical(scope_stack, symbol_kind.clone(), &name);
        let display_fqn = builder.display(scope_stack, symbol_kind.clone(), &name);

        Some(SymbolFact {
            file_path: file_path.to_path_buf(),
            kind: symbol_kind,
            kind_normalized: normalized_kind,
            name: Some(name),
            fqn: Some(fqn),
            canonical_fqn: Some(canonical_fqn),
            display_fqn: Some(display_fqn),
            byte_start: node.start_byte(),
            byte_end: node.end_byte(),
            start_line: node.start_position().row + 1,
            start_col: node.start_position().column,
            end_line: node.end_position().row + 1,
            end_col: node.end_position().column,
        })
    }

    /// Extract a symbol fact from a tree-sitter node, if applicable.
    fn extract_symbol(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        scope_stack: &ScopeStack,
    ) -> Option<SymbolFact> {
        let kind = node.kind();

        let symbol_kind = match kind {
            "function_declaration" => SymbolKind::Function,
            "method_declaration" => SymbolKind::Method,
            _ => return None,
        };

        let name = Self::extract_name(node, source)?;
        let normalized_kind = symbol_kind.normalized_key().to_string();
        let fqn = scope_stack.fqn_for_symbol(&name);

        let builder = FqnBuilder::new(
            ".".to_string(),
            file_path.to_string_lossy().to_string(),
            ScopeSeparator::Dot,
        );
        let canonical_fqn = builder.canonical(scope_stack, symbol_kind.clone(), &name);
        let display_fqn = builder.display(scope_stack, symbol_kind.clone(), &name);

        Some(SymbolFact {
            file_path: file_path.to_path_buf(),
            kind: symbol_kind,
            kind_normalized: normalized_kind,
            name: Some(name),
            fqn: Some(fqn),
            canonical_fqn: Some(canonical_fqn),
            display_fqn: Some(display_fqn),
            byte_start: node.start_byte(),
            byte_end: node.end_byte(),
            start_line: node.start_position().row + 1,
            start_col: node.start_position().column,
            end_line: node.end_position().row + 1,
            end_col: node.end_position().column,
        })
    }

    /// Extract name from a symbol node.
    fn extract_name(node: &tree_sitter::Node, source: &[u8]) -> Option<String> {
        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            match child.kind() {
                "identifier" | "field_identifier" => {
                    let name_bytes = safe_slice(source, child.start_byte(), child.end_byte())?;
                    return std::str::from_utf8(name_bytes).ok().map(|s| s.to_string());
                }
                _ => {}
            }
        }
        None
    }

    /// Extract symbol facts using an external parser (for parser pooling).
    pub fn extract_symbols_with_parser(
        parser: &mut tree_sitter::Parser,
        file_path: PathBuf,
        source: &[u8],
    ) -> Vec<SymbolFact> {
        let tree = match parser.parse(source, None) {
            Some(t) => t,
            None => return Vec::new(),
        };
        Self::extract_symbols_from_tree(&tree, file_path, source)
    }

    /// Extract symbol facts from a pre-parsed tree.
    pub fn extract_symbols_from_tree(
        tree: &tree_sitter::Tree,
        file_path: PathBuf,
        source: &[u8],
    ) -> Vec<SymbolFact> {
        let root_node = tree.root_node();
        let mut facts = Vec::new();
        let mut scope_stack = ScopeStack::new(ScopeSeparator::Dot);

        // Find package declaration first
        let mut cursor = root_node.walk();
        for child in root_node.children(&mut cursor) {
            if child.kind() == "package_clause" {
                if let Some(name) = Self::extract_package_name(&child, source) {
                    scope_stack.push(&name);
                }
                break;
            }
        }

        Self::walk_tree_static(&root_node, source, &file_path, &mut facts, &mut scope_stack);
        facts
    }

    /// Extract reference facts from Go source code.
    pub fn extract_references(
        &mut self,
        file_path: PathBuf,
        source: &[u8],
        symbols: &[SymbolFact],
    ) -> Vec<ReferenceFact> {
        let tree = match self.parser.parse(source, None) {
            Some(t) => t,
            None => return Vec::new(),
        };

        let root_node = tree.root_node();
        let mut references = Vec::new();
        Self::walk_tree_for_references(&root_node, source, &file_path, symbols, &mut references);
        references
    }

    fn walk_tree_for_references(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        symbols: &[SymbolFact],
        references: &mut Vec<ReferenceFact>,
    ) {
        if let Some(reference) = Self::extract_reference(node, source, file_path, symbols) {
            references.push(reference);
        }
        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            Self::walk_tree_for_references(&child, source, file_path, symbols, references);
        }
    }

    fn extract_reference(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        symbols: &[SymbolFact],
    ) -> Option<ReferenceFact> {
        if node.kind() != "identifier" && node.kind() != "type_identifier" {
            return None;
        }

        let text_bytes = &source[node.start_byte()..node.end_byte()];
        let text = std::str::from_utf8(text_bytes).ok()?;

        let referenced_symbol = symbols
            .iter()
            .find(|s| s.name.as_ref().map(|n| n == text).unwrap_or(false))?;

        let ref_start = node.start_byte();
        if ref_start < referenced_symbol.byte_end {
            return None;
        }

        Some(ReferenceFact {
            file_path: file_path.to_path_buf(),
            referenced_symbol: text.to_string(),
            byte_start: ref_start,
            byte_end: node.end_byte(),
            start_line: node.start_position().row + 1,
            start_col: node.start_position().column,
            end_line: node.end_position().row + 1,
            end_col: node.end_position().column,
        })
    }

    /// Extract function call facts from Go source code.
    pub fn extract_calls(
        &mut self,
        file_path: PathBuf,
        source: &[u8],
        symbols: &[SymbolFact],
    ) -> Vec<CallFact> {
        let tree = match self.parser.parse(source, None) {
            Some(t) => t,
            None => return Vec::new(),
        };
        Self::extract_calls_from_tree(&tree, file_path, source, symbols)
    }

    pub fn extract_calls_from_tree(
        tree: &tree_sitter::Tree,
        file_path: PathBuf,
        source: &[u8],
        symbols: &[SymbolFact],
    ) -> Vec<CallFact> {
        let root_node = tree.root_node();
        let mut calls = Vec::new();
        let symbol_map: std::collections::HashMap<String, &SymbolFact> = symbols
            .iter()
            .filter_map(|s| s.name.as_ref().map(|name| (name.clone(), s)))
            .collect();
        let functions: Vec<&SymbolFact> = symbols
            .iter()
            .filter(|s| s.kind == SymbolKind::Function || s.kind == SymbolKind::Method)
            .collect();
        Self::walk_tree_for_calls(
            &root_node,
            source,
            &file_path,
            &symbol_map,
            &functions,
            &mut calls,
        );
        calls
    }

    fn walk_tree_for_calls(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        symbol_map: &std::collections::HashMap<String, &SymbolFact>,
        _functions: &[&SymbolFact],
        calls: &mut Vec<CallFact>,
    ) {
        Self::walk_tree_for_calls_with_caller(node, source, file_path, symbol_map, None, calls);
    }

    fn walk_tree_for_calls_with_caller(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        symbol_map: &std::collections::HashMap<String, &SymbolFact>,
        current_caller: Option<&SymbolFact>,
        calls: &mut Vec<CallFact>,
    ) {
        let kind = node.kind();

        let caller: Option<&SymbolFact> =
            if kind == "function_declaration" || kind == "method_declaration" {
                Self::extract_function_name(node, source)
                    .and_then(|name| symbol_map.get(&name).copied())
            } else {
                current_caller
            };

        if kind == "call_expression" {
            if let Some(caller_fact) = caller {
                Self::extract_calls_in_node(
                    node,
                    source,
                    file_path,
                    caller_fact,
                    symbol_map,
                    calls,
                );
            }
        }

        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            Self::walk_tree_for_calls_with_caller(
                &child, source, file_path, symbol_map, caller, calls,
            );
        }
    }

    fn extract_function_name(node: &tree_sitter::Node, source: &[u8]) -> Option<String> {
        Self::extract_name(node, source)
    }

    fn extract_calls_in_node(
        node: &tree_sitter::Node,
        source: &[u8],
        file_path: &Path,
        caller: &SymbolFact,
        symbol_map: &std::collections::HashMap<String, &SymbolFact>,
        calls: &mut Vec<CallFact>,
    ) {
        if node.kind() == "call_expression" {
            if let Some(callee_name) = Self::extract_callee_from_call(node, source) {
                if symbol_map.contains_key(&callee_name) {
                    let node_start = node.start_byte();
                    let node_end = node.end_byte();
                    let call_fact = CallFact {
                        file_path: file_path.to_path_buf(),
                        caller: caller.name.clone().unwrap_or_default(),
                        callee: callee_name,
                        caller_symbol_id: None,
                        callee_symbol_id: None,
                        byte_start: node_start,
                        byte_end: node_end,
                        start_line: node.start_position().row + 1,
                        start_col: node.start_position().column,
                        end_line: node.end_position().row + 1,
                        end_col: node.end_position().column,
                    };
                    calls.push(call_fact);
                }
            }
        }
    }

    fn extract_callee_from_call(node: &tree_sitter::Node, source: &[u8]) -> Option<String> {
        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            if child.kind() == "identifier"
                || child.kind() == "field_identifier"
                || child.kind() == "selector_expression"
            {
                // For selector_expression (e.g., pkg.Func), extract the rightmost identifier
                if child.kind() == "selector_expression" {
                    return Self::extract_selector_name(&child, source);
                }
                let name_bytes = &source[child.start_byte()..child.end_byte()];
                return std::str::from_utf8(name_bytes).ok().map(|s| s.to_string());
            }
        }
        None
    }

    fn extract_selector_name(node: &tree_sitter::Node, source: &[u8]) -> Option<String> {
        let mut cursor = node.walk();
        for child in node.children(&mut cursor) {
            if child.kind() == "field_identifier" {
                let name_bytes = &source[child.start_byte()..child.end_byte()];
                return std::str::from_utf8(name_bytes).ok().map(|s| s.to_string());
            }
        }
        None
    }
}

impl Default for GoParser {
    fn default() -> Self {
        Self::new().expect("Failed to create Go parser") // M-UNWRAP: tree-sitter language is a build-time invariant
    }
}

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

    #[test]
    fn test_extract_simple_function() {
        let mut parser = GoParser::new().unwrap();
        let source = b"package main\n\nfunc main() {\n    println(\"hello\")\n}\n";
        let facts = parser.extract_symbols(PathBuf::from("main.go"), source);

        assert!(!facts.is_empty());
        let funcs: Vec<_> = facts
            .iter()
            .filter(|f| f.kind == SymbolKind::Function)
            .collect();
        assert_eq!(funcs.len(), 1);
        assert_eq!(funcs[0].name, Some("main".to_string()));
    }

    #[test]
    fn test_extract_struct() {
        let mut parser = GoParser::new().unwrap();
        let source = b"package main\n\ntype Person struct {\n    Name string\n}\n";
        let facts = parser.extract_symbols(PathBuf::from("main.go"), source);

        let structs: Vec<_> = facts
            .iter()
            .filter(|f| f.kind == SymbolKind::Class)
            .collect();
        assert_eq!(structs.len(), 1);
        assert_eq!(structs[0].name, Some("Person".to_string()));
    }

    #[test]
    fn test_extract_interface() {
        let mut parser = GoParser::new().unwrap();
        let source =
            b"package main\n\ntype Reader interface {\n    Read(p []byte) (n int, err error)\n}\n";
        let facts = parser.extract_symbols(PathBuf::from("main.go"), source);

        let interfaces: Vec<_> = facts
            .iter()
            .filter(|f| f.kind == SymbolKind::Interface)
            .collect();
        assert_eq!(interfaces.len(), 1);
        assert_eq!(interfaces[0].name, Some("Reader".to_string()));
    }

    #[test]
    fn test_extract_method() {
        let mut parser = GoParser::new().unwrap();
        let source =
            b"package main\n\nfunc (p *Person) Greet() string {\n    return \"hello\"\n}\n";
        let facts = parser.extract_symbols(PathBuf::from("main.go"), source);

        let methods: Vec<_> = facts
            .iter()
            .filter(|f| f.kind == SymbolKind::Method)
            .collect();
        assert_eq!(methods.len(), 1);
        assert_eq!(methods[0].name, Some("Greet".to_string()));
    }

    #[test]
    fn test_empty_file() {
        let mut parser = GoParser::new().unwrap();
        let source = b"";
        let facts = parser.extract_symbols(PathBuf::from("empty.go"), source);

        assert_eq!(facts.len(), 0);
    }

    #[test]
    fn test_byte_spans_within_bounds() {
        let mut parser = GoParser::new().unwrap();
        let source = b"package main\n\nfunc foo() {}";
        let facts = parser.extract_symbols(PathBuf::from("test.go"), source);

        assert!(!facts.is_empty());
        let fact = &facts[0];
        assert!(fact.byte_start < fact.byte_end);
        assert!(fact.byte_end <= source.len());
    }
}