//! LSP (Language Server Protocol) client registry for tool dispatch.
//!
//! Provides a stateful registry of LSP server connections, supporting
//! the LSP tool actions: diagnostics, hover, definition, references,
//! completion, symbols, and formatting.

use std::collections::HashMap;
use std::sync::{Arc, Mutex};

use serde::{Deserialize, Serialize};

/// Supported LSP actions.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum LspAction {
    Diagnostics,
    Hover,
    Definition,
    References,
    Completion,
    Symbols,
    Format,
}

impl LspAction {
    pub fn from_str(s: &str) -> Option<Self> {
        match s {
            "diagnostics" => Some(Self::Diagnostics),
            "hover" => Some(Self::Hover),
            "definition" | "goto_definition" => Some(Self::Definition),
            "references" | "find_references" => Some(Self::References),
            "completion" | "completions" => Some(Self::Completion),
            "symbols" | "document_symbols" => Some(Self::Symbols),
            "format" | "formatting" => Some(Self::Format),
            _ => None,
        }
    }
}

/// A diagnostic entry from an LSP server.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LspDiagnostic {
    pub path: String,
    pub line: u32,
    pub character: u32,
    pub severity: String,
    pub message: String,
    pub source: Option<String>,
}

/// A location result (definition, references).
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LspLocation {
    pub path: String,
    pub line: u32,
    pub character: u32,
    pub end_line: Option<u32>,
    pub end_character: Option<u32>,
    pub preview: Option<String>,
}

/// A hover result.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LspHoverResult {
    pub content: String,
    pub language: Option<String>,
}

/// A completion item.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LspCompletionItem {
    pub label: String,
    pub kind: Option<String>,
    pub detail: Option<String>,
    pub insert_text: Option<String>,
}

/// A document symbol.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LspSymbol {
    pub name: String,
    pub kind: String,
    pub path: String,
    pub line: u32,
    pub character: u32,
}

/// Connection status.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum LspServerStatus {
    Connected,
    Disconnected,
    Starting,
    Error,
}

impl std::fmt::Display for LspServerStatus {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Connected => write!(f, "connected"),
            Self::Disconnected => write!(f, "disconnected"),
            Self::Starting => write!(f, "starting"),
            Self::Error => write!(f, "error"),
        }
    }
}

/// Tracked state of an LSP server.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct LspServerState {
    pub language: String,
    pub status: LspServerStatus,
    pub root_path: Option<String>,
    pub capabilities: Vec<String>,
    pub diagnostics: Vec<LspDiagnostic>,
}

/// Thread-safe LSP server registry.
#[derive(Debug, Clone, Default)]
pub struct LspRegistry {
    inner: Arc<Mutex<RegistryInner>>,
}

#[derive(Debug, Default)]
struct RegistryInner {
    servers: HashMap<String, LspServerState>,
}

impl LspRegistry {
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Register an LSP server for a language.
    pub fn register(
        &self,
        language: &str,
        status: LspServerStatus,
        root_path: Option<&str>,
        capabilities: Vec<String>,
    ) {
        let mut inner = self.inner.lock().expect("lsp registry lock poisoned");
        inner.servers.insert(
            language.to_owned(),
            LspServerState {
                language: language.to_owned(),
                status,
                root_path: root_path.map(str::to_owned),
                capabilities,
                diagnostics: Vec::new(),
            },
        );
    }

    /// Get server state by language.
    pub fn get(&self, language: &str) -> Option<LspServerState> {
        let inner = self.inner.lock().expect("lsp registry lock poisoned");
        inner.servers.get(language).cloned()
    }

    /// Find the appropriate server for a file path based on extension.
    pub fn find_server_for_path(&self, path: &str) -> Option<LspServerState> {
        let ext = std::path::Path::new(path)
            .extension()
            .and_then(|e| e.to_str())
            .unwrap_or("");

        let language = match ext {
            "rs" => "rust",
            "ts" | "tsx" => "typescript",
            "js" | "jsx" => "javascript",
            "py" => "python",
            "go" => "go",
            "java" => "java",
            "c" | "h" => "c",
            "cpp" | "hpp" | "cc" => "cpp",
            "rb" => "ruby",
            "lua" => "lua",
            _ => return None,
        };

        self.get(language)
    }

    /// List all registered servers.
    pub fn list_servers(&self) -> Vec<LspServerState> {
        let inner = self.inner.lock().expect("lsp registry lock poisoned");
        inner.servers.values().cloned().collect()
    }

    /// Add diagnostics to a server.
    pub fn add_diagnostics(
        &self,
        language: &str,
        diagnostics: Vec<LspDiagnostic>,
    ) -> Result<(), String> {
        let mut inner = self.inner.lock().expect("lsp registry lock poisoned");
        let server = inner
            .servers
            .get_mut(language)
            .ok_or_else(|| format!("LSP server not found for language: {language}"))?;
        server.diagnostics.extend(diagnostics);
        Ok(())
    }

    /// Get diagnostics for a specific file path.
    pub fn get_diagnostics(&self, path: &str) -> Vec<LspDiagnostic> {
        let inner = self.inner.lock().expect("lsp registry lock poisoned");
        inner
            .servers
            .values()
            .flat_map(|s| &s.diagnostics)
            .filter(|d| d.path == path)
            .cloned()
            .collect()
    }

    /// Clear diagnostics for a language server.
    pub fn clear_diagnostics(&self, language: &str) -> Result<(), String> {
        let mut inner = self.inner.lock().expect("lsp registry lock poisoned");
        let server = inner
            .servers
            .get_mut(language)
            .ok_or_else(|| format!("LSP server not found for language: {language}"))?;
        server.diagnostics.clear();
        Ok(())
    }

    /// Disconnect a server.
    pub fn disconnect(&self, language: &str) -> Option<LspServerState> {
        let mut inner = self.inner.lock().expect("lsp registry lock poisoned");
        inner.servers.remove(language)
    }

    #[must_use]
    pub fn len(&self) -> usize {
        let inner = self.inner.lock().expect("lsp registry lock poisoned");
        inner.servers.len()
    }

    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Dispatch an LSP action and return a structured result.
    pub fn dispatch(
        &self,
        action: &str,
        path: Option<&str>,
        line: Option<u32>,
        character: Option<u32>,
        _query: Option<&str>,
    ) -> Result<serde_json::Value, String> {
        let lsp_action =
            LspAction::from_str(action).ok_or_else(|| format!("unknown LSP action: {action}"))?;

        // For diagnostics, we can check existing cached diagnostics
        if lsp_action == LspAction::Diagnostics {
            if let Some(path) = path {
                let diags = self.get_diagnostics(path);
                return Ok(serde_json::json!({
                    "action": "diagnostics",
                    "path": path,
                    "diagnostics": diags,
                    "count": diags.len()
                }));
            }
            // All diagnostics across all servers
            let inner = self.inner.lock().expect("lsp registry lock poisoned");
            let all_diags: Vec<_> = inner
                .servers
                .values()
                .flat_map(|s| &s.diagnostics)
                .collect();
            return Ok(serde_json::json!({
                "action": "diagnostics",
                "diagnostics": all_diags,
                "count": all_diags.len()
            }));
        }

        // For other actions, we need a connected server for the given file
        let path = path.ok_or("path is required for this LSP action")?;
        let server = self
            .find_server_for_path(path)
            .ok_or_else(|| format!("no LSP server available for path: {path}"))?;

        if server.status != LspServerStatus::Connected {
            return Err(format!(
                "LSP server for '{}' is not connected (status: {})",
                server.language, server.status
            ));
        }

        // Return structured placeholder — actual LSP JSON-RPC calls would
        // go through the real LSP process here.
        Ok(serde_json::json!({
            "action": action,
            "path": path,
            "line": line,
            "character": character,
            "language": server.language,
            "status": "dispatched",
            "message": format!("LSP {} dispatched to {} server", action, server.language)
        }))
    }
}

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

    #[test]
    fn registers_and_retrieves_server() {
        let registry = LspRegistry::new();
        registry.register(
            "rust",
            LspServerStatus::Connected,
            Some("/workspace"),
            vec!["hover".into(), "completion".into()],
        );

        let server = registry.get("rust").expect("should exist");
        assert_eq!(server.language, "rust");
        assert_eq!(server.status, LspServerStatus::Connected);
        assert_eq!(server.capabilities.len(), 2);
    }

    #[test]
    fn finds_server_by_file_extension() {
        let registry = LspRegistry::new();
        registry.register("rust", LspServerStatus::Connected, None, vec![]);
        registry.register("typescript", LspServerStatus::Connected, None, vec![]);

        let rs_server = registry.find_server_for_path("src/main.rs").unwrap();
        assert_eq!(rs_server.language, "rust");

        let ts_server = registry.find_server_for_path("src/index.ts").unwrap();
        assert_eq!(ts_server.language, "typescript");

        assert!(registry.find_server_for_path("data.csv").is_none());
    }

    #[test]
    fn manages_diagnostics() {
        let registry = LspRegistry::new();
        registry.register("rust", LspServerStatus::Connected, None, vec![]);

        registry
            .add_diagnostics(
                "rust",
                vec![LspDiagnostic {
                    path: "src/main.rs".into(),
                    line: 10,
                    character: 5,
                    severity: "error".into(),
                    message: "mismatched types".into(),
                    source: Some("rust-analyzer".into()),
                }],
            )
            .unwrap();

        let diags = registry.get_diagnostics("src/main.rs");
        assert_eq!(diags.len(), 1);
        assert_eq!(diags[0].message, "mismatched types");

        registry.clear_diagnostics("rust").unwrap();
        assert!(registry.get_diagnostics("src/main.rs").is_empty());
    }

    #[test]
    fn dispatches_diagnostics_action() {
        let registry = LspRegistry::new();
        registry.register("rust", LspServerStatus::Connected, None, vec![]);
        registry
            .add_diagnostics(
                "rust",
                vec![LspDiagnostic {
                    path: "src/lib.rs".into(),
                    line: 1,
                    character: 0,
                    severity: "warning".into(),
                    message: "unused import".into(),
                    source: None,
                }],
            )
            .unwrap();

        let result = registry
            .dispatch("diagnostics", Some("src/lib.rs"), None, None, None)
            .unwrap();
        assert_eq!(result["count"], 1);
    }

    #[test]
    fn dispatches_hover_action() {
        let registry = LspRegistry::new();
        registry.register("rust", LspServerStatus::Connected, None, vec![]);

        let result = registry
            .dispatch("hover", Some("src/main.rs"), Some(10), Some(5), None)
            .unwrap();
        assert_eq!(result["action"], "hover");
        assert_eq!(result["language"], "rust");
    }

    #[test]
    fn rejects_action_on_disconnected_server() {
        let registry = LspRegistry::new();
        registry.register("rust", LspServerStatus::Disconnected, None, vec![]);

        assert!(registry
            .dispatch("hover", Some("src/main.rs"), Some(1), Some(0), None)
            .is_err());
    }

    #[test]
    fn rejects_unknown_action() {
        let registry = LspRegistry::new();
        assert!(registry
            .dispatch("unknown_action", Some("file.rs"), None, None, None)
            .is_err());
    }

    #[test]
    fn disconnects_server() {
        let registry = LspRegistry::new();
        registry.register("rust", LspServerStatus::Connected, None, vec![]);
        assert_eq!(registry.len(), 1);

        let removed = registry.disconnect("rust");
        assert!(removed.is_some());
        assert!(registry.is_empty());
    }
}