use std::time::{Instant, SystemTime, UNIX_EPOCH};

use tree_sitter::{Node as TsNode, Parser, Tree};

use crate::extraction::complexity::{count_complexity, ComplexityMetrics, FSHARP_COMPLEXITY};
use crate::types::{
    generate_node_id, Edge, EdgeKind, ExtractionResult, Node, NodeKind, UnresolvedRef, Visibility,
};

pub struct FSharpExtractor;

struct ExtractionState {
    nodes: Vec<Node>,
    edges: Vec<Edge>,
    unresolved_refs: Vec<UnresolvedRef>,
    errors: Vec<String>,
    node_stack: Vec<(String, String)>,
    file_path: String,
    source: Vec<u8>,
    timestamp: u64,
}

impl ExtractionState {
    fn new(file_path: &str, source: &str) -> Self {
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();
        Self {
            nodes: Vec::new(),
            edges: Vec::new(),
            unresolved_refs: Vec::new(),
            errors: Vec::new(),
            node_stack: Vec::new(),
            file_path: file_path.to_string(),
            source: source.as_bytes().to_vec(),
            timestamp,
        }
    }

    fn qualified_prefix(&self) -> String {
        let mut parts = vec![self.file_path.clone()];
        for (name, _) in &self.node_stack {
            parts.push(name.clone());
        }
        parts.join("::")
    }

    fn parent_node_id(&self) -> Option<&str> {
        self.node_stack.last().map(|(_, id)| id.as_str())
    }

    fn node_text(&self, node: TsNode<'_>) -> String {
        node.utf8_text(&self.source)
            .unwrap_or("<invalid utf8>")
            .to_string()
    }
}

impl FSharpExtractor {
    pub fn extract_fsharp(file_path: &str, source: &str) -> ExtractionResult {
        let start = Instant::now();
        let mut state = ExtractionState::new(file_path, source);

        let tree = match Self::parse_source(source) {
            Ok(t) => t,
            Err(msg) => {
                state.errors.push(msg);
                return Self::build_result(state, start);
            }
        };

        let file_node = Node {
            id: generate_node_id(file_path, &NodeKind::File, file_path, 0),
            kind: NodeKind::File,
            name: file_path.to_string(),
            qualified_name: file_path.to_string(),
            file_path: file_path.to_string(),
            start_line: 0,
            attrs_start_line: 0,
            end_line: source.lines().count().saturating_sub(1) as u32,
            start_column: 0,
            end_column: 0,
            signature: None,
            docstring: None,
            visibility: Visibility::Pub,
            is_async: false,
            branches: 0,
            loops: 0,
            returns: 0,
            max_nesting: 0,
            unsafe_blocks: 0,
            unchecked_calls: 0,
            assertions: 0,
            updated_at: state.timestamp,
            parent_id: None,
        };
        let file_node_id = file_node.id.clone();
        state.nodes.push(file_node);
        state.node_stack.push((file_path.to_string(), file_node_id));

        let root = tree.root_node();
        Self::visit_children(&mut state, root);

        state.node_stack.pop();
        Self::build_result(state, start)
    }

    fn parse_source(source: &str) -> Result<Tree, String> {
        let mut parser = Parser::new();
        let language = crate::extraction::ts_provider::language("fsharp");
        parser
            .set_language(&language)
            .map_err(|e| format!("failed to load F# grammar: {e}"))?;
        parser
            .parse(source, None)
            .ok_or_else(|| "tree-sitter parse returned None".to_string())
    }

    fn visit_children(state: &mut ExtractionState, node: TsNode<'_>) {
        let mut cursor = node.walk();
        if cursor.goto_first_child() {
            loop {
                Self::visit_node(state, cursor.node());
                if !cursor.goto_next_sibling() {
                    break;
                }
            }
        }
    }

    fn visit_node(state: &mut ExtractionState, node: TsNode<'_>) {
        match node.kind() {
            "function_or_value_defn" => Self::visit_function_or_value(state, node),
            "type_definition" => Self::visit_type_definition(state, node),
            "module_defn" | "named_module" => Self::visit_module(state, node),
            "namespace" => Self::visit_namespace(state, node),
            "open_decl" => Self::visit_open(state, node),
            _ => Self::visit_children(state, node),
        }
    }

    fn visit_function_or_value(state: &mut ExtractionState, node: TsNode<'_>) {
        // function_or_value_defn contains function_declaration_left or value_declaration_left.
        let name = Self::extract_binding_name(state, node);
        let Some(name) = name else { return };

        let is_fn = Self::has_params(node);
        let kind = if is_fn {
            NodeKind::Function
        } else {
            NodeKind::Const
        };
        let sig = Self::first_line(state, node);
        let docstring = Self::extract_docstring(state, node);
        let start_line = node.start_position().row as u32;
        let qualified_name = format!("{}::{}", state.qualified_prefix(), name);
        let id = generate_node_id(&state.file_path, &kind, &name, start_line);

        let metrics = if is_fn && node.child_count() > 0 {
            count_complexity(node, &FSHARP_COMPLEXITY, &state.source)
        } else {
            ComplexityMetrics::default()
        };

        let graph_node = Node {
            id: id.clone(),
            kind,
            name: name.clone(),
            qualified_name,
            file_path: state.file_path.clone(),
            start_line,
            attrs_start_line: start_line,
            end_line: node.end_position().row as u32,
            start_column: node.start_position().column as u32,
            end_column: node.end_position().column as u32,
            signature: sig,
            docstring,
            visibility: Visibility::Pub,
            is_async: false,
            branches: metrics.branches,
            loops: metrics.loops,
            returns: metrics.returns,
            max_nesting: metrics.max_nesting,
            unsafe_blocks: 0,
            unchecked_calls: metrics.unchecked_calls,
            assertions: metrics.assertions,
            updated_at: state.timestamp,
            parent_id: None,
        };
        state.nodes.push(graph_node);

        if let Some(parent_id) = state.parent_node_id() {
            state.edges.push(Edge {
                source: parent_id.to_string(),
                target: id.clone(),
                kind: EdgeKind::Contains,
                line: Some(start_line),
            });
        }

        Self::extract_calls(state, node, &id);
    }

    fn visit_type_definition(state: &mut ExtractionState, node: TsNode<'_>) {
        // type_definition contains type_name and the body.
        let name = Self::find_child_text(state, node, "type_name")
            .or_else(|| Self::find_child_text(state, node, "identifier"));
        let Some(name) = name else { return };

        let sig = Self::first_line(state, node);
        let start_line = node.start_position().row as u32;
        let qualified_name = format!("{}::{}", state.qualified_prefix(), name);
        let id = generate_node_id(&state.file_path, &NodeKind::Class, &name, start_line);

        let graph_node = Node {
            id: id.clone(),
            kind: NodeKind::Class,
            name,
            qualified_name,
            file_path: state.file_path.clone(),
            start_line,
            attrs_start_line: start_line,
            end_line: node.end_position().row as u32,
            start_column: node.start_position().column as u32,
            end_column: node.end_position().column as u32,
            signature: sig,
            docstring: None,
            visibility: Visibility::Pub,
            is_async: false,
            branches: 0,
            loops: 0,
            returns: 0,
            max_nesting: 0,
            unsafe_blocks: 0,
            unchecked_calls: 0,
            assertions: 0,
            updated_at: state.timestamp,
            parent_id: None,
        };
        state.nodes.push(graph_node);

        if let Some(parent_id) = state.parent_node_id() {
            state.edges.push(Edge {
                source: parent_id.to_string(),
                target: id,
                kind: EdgeKind::Contains,
                line: Some(start_line),
            });
        }
    }

    fn visit_module(state: &mut ExtractionState, node: TsNode<'_>) {
        let name = Self::find_child_text(state, node, "long_identifier")
            .or_else(|| Self::find_child_text(state, node, "identifier"));
        let Some(name) = name else { return };

        let start_line = node.start_position().row as u32;
        let qualified_name = format!("{}::{}", state.qualified_prefix(), name);
        let id = generate_node_id(&state.file_path, &NodeKind::Module, &name, start_line);

        let graph_node = Node {
            id: id.clone(),
            kind: NodeKind::Module,
            name: name.clone(),
            qualified_name,
            file_path: state.file_path.clone(),
            start_line,
            attrs_start_line: start_line,
            end_line: node.end_position().row as u32,
            start_column: node.start_position().column as u32,
            end_column: node.end_position().column as u32,
            signature: None,
            docstring: None,
            visibility: Visibility::Pub,
            is_async: false,
            branches: 0,
            loops: 0,
            returns: 0,
            max_nesting: 0,
            unsafe_blocks: 0,
            unchecked_calls: 0,
            assertions: 0,
            updated_at: state.timestamp,
            parent_id: None,
        };
        state.nodes.push(graph_node);

        if let Some(parent_id) = state.parent_node_id() {
            state.edges.push(Edge {
                source: parent_id.to_string(),
                target: id.clone(),
                kind: EdgeKind::Contains,
                line: Some(start_line),
            });
        }

        state.node_stack.push((name, id));
        Self::visit_children(state, node);
        state.node_stack.pop();
    }

    fn visit_namespace(state: &mut ExtractionState, node: TsNode<'_>) {
        let name = Self::find_child_text(state, node, "long_identifier")
            .or_else(|| Self::find_child_text(state, node, "identifier"))
            .unwrap_or_else(|| "?".to_string());

        let start_line = node.start_position().row as u32;
        let qualified_name = format!("{}::{}", state.file_path, name);
        let id = generate_node_id(&state.file_path, &NodeKind::Module, &name, start_line);

        let graph_node = Node {
            id: id.clone(),
            kind: NodeKind::Module,
            name: name.clone(),
            qualified_name,
            file_path: state.file_path.clone(),
            start_line,
            attrs_start_line: start_line,
            end_line: node.end_position().row as u32,
            start_column: 0,
            end_column: 0,
            signature: None,
            docstring: None,
            visibility: Visibility::Pub,
            is_async: false,
            branches: 0,
            loops: 0,
            returns: 0,
            max_nesting: 0,
            unsafe_blocks: 0,
            unchecked_calls: 0,
            assertions: 0,
            updated_at: state.timestamp,
            parent_id: None,
        };
        state.nodes.push(graph_node);

        if let Some(parent_id) = state.parent_node_id() {
            state.edges.push(Edge {
                source: parent_id.to_string(),
                target: id.clone(),
                kind: EdgeKind::Contains,
                line: Some(start_line),
            });
        }

        state.node_stack.push((name, id));
        Self::visit_children(state, node);
        state.node_stack.pop();
    }

    fn visit_open(state: &mut ExtractionState, node: TsNode<'_>) {
        let text = state.node_text(node);
        let name = text.trim_start_matches("open").trim().to_string();
        let start_line = node.start_position().row as u32;
        let id = generate_node_id(&state.file_path, &NodeKind::Use, &name, start_line);

        let graph_node = Node {
            id: id.clone(),
            kind: NodeKind::Use,
            name,
            qualified_name: format!("{}::open", state.file_path),
            file_path: state.file_path.clone(),
            start_line,
            attrs_start_line: start_line,
            end_line: node.end_position().row as u32,
            start_column: node.start_position().column as u32,
            end_column: node.end_position().column as u32,
            signature: Some(text.trim().to_string()),
            docstring: None,
            visibility: Visibility::Private,
            is_async: false,
            branches: 0,
            loops: 0,
            returns: 0,
            max_nesting: 0,
            unsafe_blocks: 0,
            unchecked_calls: 0,
            assertions: 0,
            updated_at: state.timestamp,
            parent_id: None,
        };
        state.nodes.push(graph_node);
        if let Some(parent_id) = state.parent_node_id() {
            state.edges.push(Edge {
                source: parent_id.to_string(),
                target: id,
                kind: EdgeKind::Contains,
                line: Some(start_line),
            });
        }
    }

    fn extract_binding_name(state: &ExtractionState, node: TsNode<'_>) -> Option<String> {
        // function_or_value_defn → function_declaration_left | value_declaration_left
        let mut cursor = node.walk();
        if cursor.goto_first_child() {
            loop {
                let child = cursor.node();
                match child.kind() {
                    "function_declaration_left" | "value_declaration_left" => {
                        // The first identifier or operator child is the name.
                        return Self::find_child_text(state, child, "identifier")
                            .or_else(|| Self::find_child_text(state, child, "operator_name"));
                    }
                    _ => {}
                }
                if !cursor.goto_next_sibling() {
                    break;
                }
            }
        }
        None
    }

    fn has_params(node: TsNode<'_>) -> bool {
        let mut cursor = node.walk();
        if cursor.goto_first_child() {
            loop {
                let child = cursor.node();
                if child.kind() == "function_declaration_left" {
                    // function_declaration_left has parameter children beyond the name.
                    return child.named_child_count() > 1;
                }
                if !cursor.goto_next_sibling() {
                    break;
                }
            }
        }
        false
    }

    fn find_child_text(state: &ExtractionState, node: TsNode<'_>, kind: &str) -> Option<String> {
        let mut cursor = node.walk();
        if cursor.goto_first_child() {
            loop {
                let child = cursor.node();
                if child.kind() == kind {
                    return Some(state.node_text(child));
                }
                if !cursor.goto_next_sibling() {
                    break;
                }
            }
        }
        None
    }

    fn extract_calls(state: &mut ExtractionState, node: TsNode<'_>, fn_id: &str) {
        let mut cursor = node.walk();
        if cursor.goto_first_child() {
            loop {
                let child = cursor.node();
                match child.kind() {
                    "application_expression" => {
                        if let Some(callee) = child.child(0) {
                            let name = state.node_text(callee);
                            state.unresolved_refs.push(UnresolvedRef {
                                from_node_id: fn_id.to_string(),
                                reference_name: name,
                                reference_kind: EdgeKind::Calls,
                                line: child.start_position().row as u32,
                                column: child.start_position().column as u32,
                                file_path: state.file_path.clone(),
                            });
                        }
                        Self::extract_calls(state, child, fn_id);
                    }
                    "function_or_value_defn" | "type_definition" => {}
                    _ => Self::extract_calls(state, child, fn_id),
                }
                if !cursor.goto_next_sibling() {
                    break;
                }
            }
        }
    }

    fn extract_docstring(state: &ExtractionState, node: TsNode<'_>) -> Option<String> {
        // F# XML doc comments: /// text
        let mut comments = Vec::new();
        let mut prev = node.prev_named_sibling();
        while let Some(p) = prev {
            if p.kind() == "xml_doc" || p.kind() == "line_comment" {
                let text = state.node_text(p);
                if text.starts_with("///") {
                    comments.push(text.trim_start_matches("///").trim().to_string());
                    prev = p.prev_named_sibling();
                } else {
                    break;
                }
            } else {
                break;
            }
        }
        if comments.is_empty() {
            return None;
        }
        comments.reverse();
        Some(comments.join("\n"))
    }

    fn first_line(state: &ExtractionState, node: TsNode<'_>) -> Option<String> {
        let text = state.node_text(node);
        text.lines().next().map(|l| l.trim().to_string())
    }

    fn build_result(state: ExtractionState, start: Instant) -> ExtractionResult {
        ExtractionResult {
            nodes: state.nodes,
            edges: state.edges,
            unresolved_refs: state.unresolved_refs,
            errors: state.errors,
            duration_ms: start.elapsed().as_millis() as u64,
        }
    }
}

impl crate::extraction::LanguageExtractor for FSharpExtractor {
    fn extensions(&self) -> &[&str] {
        &["fs", "fsi", "fsx"]
    }

    fn language_name(&self) -> &'static str {
        "F#"
    }

    fn extract(&self, file_path: &str, source: &str) -> ExtractionResult {
        Self::extract_fsharp(file_path, source)
    }
}
