use std::collections::BTreeMap;
use std::fmt::{Display, Formatter};
use std::fs;
use std::path::{Path, PathBuf};

use crate::json::JsonValue;

pub const CLAUDE_CODE_SETTINGS_SCHEMA_NAME: &str = "SettingsSchema";

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum ConfigSource {
    User,
    Project,
    Local,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ConfigEntry {
    pub source: ConfigSource,
    pub path: PathBuf,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct RuntimeConfig {
    merged: BTreeMap<String, JsonValue>,
    loaded_entries: Vec<ConfigEntry>,
    feature_config: RuntimeFeatureConfig,
}

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct RuntimeFeatureConfig {
    mcp: McpConfigCollection,
    oauth: Option<OAuthConfig>,
}

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct McpConfigCollection {
    servers: BTreeMap<String, ScopedMcpServerConfig>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ScopedMcpServerConfig {
    pub scope: ConfigSource,
    pub config: McpServerConfig,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum McpTransport {
    Stdio,
    Sse,
    Http,
    Ws,
    Sdk,
    ClaudeAiProxy,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum McpServerConfig {
    Stdio(McpStdioServerConfig),
    Sse(McpRemoteServerConfig),
    Http(McpRemoteServerConfig),
    Ws(McpWebSocketServerConfig),
    Sdk(McpSdkServerConfig),
    ClaudeAiProxy(McpClaudeAiProxyServerConfig),
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct McpStdioServerConfig {
    pub command: String,
    pub args: Vec<String>,
    pub env: BTreeMap<String, String>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct McpRemoteServerConfig {
    pub url: String,
    pub headers: BTreeMap<String, String>,
    pub headers_helper: Option<String>,
    pub oauth: Option<McpOAuthConfig>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct McpWebSocketServerConfig {
    pub url: String,
    pub headers: BTreeMap<String, String>,
    pub headers_helper: Option<String>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct McpSdkServerConfig {
    pub name: String,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct McpClaudeAiProxyServerConfig {
    pub url: String,
    pub id: String,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct McpOAuthConfig {
    pub client_id: Option<String>,
    pub callback_port: Option<u16>,
    pub auth_server_metadata_url: Option<String>,
    pub xaa: Option<bool>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OAuthConfig {
    pub client_id: String,
    pub authorize_url: String,
    pub token_url: String,
    pub callback_port: Option<u16>,
    pub manual_redirect_url: Option<String>,
    pub scopes: Vec<String>,
}

#[derive(Debug)]
pub enum ConfigError {
    Io(std::io::Error),
    Parse(String),
}

impl Display for ConfigError {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Io(error) => write!(f, "{error}"),
            Self::Parse(error) => write!(f, "{error}"),
        }
    }
}

impl std::error::Error for ConfigError {}

impl From<std::io::Error> for ConfigError {
    fn from(value: std::io::Error) -> Self {
        Self::Io(value)
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ConfigLoader {
    cwd: PathBuf,
    config_home: PathBuf,
}

impl ConfigLoader {
    #[must_use]
    pub fn new(cwd: impl Into<PathBuf>, config_home: impl Into<PathBuf>) -> Self {
        Self {
            cwd: cwd.into(),
            config_home: config_home.into(),
        }
    }

    #[must_use]
    pub fn default_for(cwd: impl Into<PathBuf>) -> Self {
        let cwd = cwd.into();
        let config_home = std::env::var_os("CLAUDE_CONFIG_HOME")
            .map(PathBuf::from)
            .or_else(|| std::env::var_os("HOME").map(|home| PathBuf::from(home).join(".claude")))
            .unwrap_or_else(|| PathBuf::from(".claude"));
        Self { cwd, config_home }
    }

    #[must_use]
    pub fn discover(&self) -> Vec<ConfigEntry> {
        vec![
            ConfigEntry {
                source: ConfigSource::User,
                path: self.config_home.join("settings.json"),
            },
            ConfigEntry {
                source: ConfigSource::Project,
                path: self.cwd.join(".claude").join("settings.json"),
            },
            ConfigEntry {
                source: ConfigSource::Local,
                path: self.cwd.join(".claude").join("settings.local.json"),
            },
        ]
    }

    pub fn load(&self) -> Result<RuntimeConfig, ConfigError> {
        let mut merged = BTreeMap::new();
        let mut loaded_entries = Vec::new();
        let mut mcp_servers = BTreeMap::new();

        for entry in self.discover() {
            let Some(value) = read_optional_json_object(&entry.path)? else {
                continue;
            };
            merge_mcp_servers(&mut mcp_servers, entry.source, &value, &entry.path)?;
            deep_merge_objects(&mut merged, &value);
            loaded_entries.push(entry);
        }

        let feature_config = RuntimeFeatureConfig {
            mcp: McpConfigCollection {
                servers: mcp_servers,
            },
            oauth: parse_optional_oauth_config(
                &JsonValue::Object(merged.clone()),
                "merged settings.oauth",
            )?,
        };

        Ok(RuntimeConfig {
            merged,
            loaded_entries,
            feature_config,
        })
    }
}

impl RuntimeConfig {
    #[must_use]
    pub fn empty() -> Self {
        Self {
            merged: BTreeMap::new(),
            loaded_entries: Vec::new(),
            feature_config: RuntimeFeatureConfig::default(),
        }
    }

    #[must_use]
    pub fn merged(&self) -> &BTreeMap<String, JsonValue> {
        &self.merged
    }

    #[must_use]
    pub fn loaded_entries(&self) -> &[ConfigEntry] {
        &self.loaded_entries
    }

    #[must_use]
    pub fn get(&self, key: &str) -> Option<&JsonValue> {
        self.merged.get(key)
    }

    #[must_use]
    pub fn as_json(&self) -> JsonValue {
        JsonValue::Object(self.merged.clone())
    }

    #[must_use]
    pub fn feature_config(&self) -> &RuntimeFeatureConfig {
        &self.feature_config
    }

    #[must_use]
    pub fn mcp(&self) -> &McpConfigCollection {
        &self.feature_config.mcp
    }

    #[must_use]
    pub fn oauth(&self) -> Option<&OAuthConfig> {
        self.feature_config.oauth.as_ref()
    }
}

impl RuntimeFeatureConfig {
    #[must_use]
    pub fn mcp(&self) -> &McpConfigCollection {
        &self.mcp
    }

    #[must_use]
    pub fn oauth(&self) -> Option<&OAuthConfig> {
        self.oauth.as_ref()
    }
}

impl McpConfigCollection {
    #[must_use]
    pub fn servers(&self) -> &BTreeMap<String, ScopedMcpServerConfig> {
        &self.servers
    }

    #[must_use]
    pub fn get(&self, name: &str) -> Option<&ScopedMcpServerConfig> {
        self.servers.get(name)
    }
}

impl ScopedMcpServerConfig {
    #[must_use]
    pub fn transport(&self) -> McpTransport {
        self.config.transport()
    }
}

impl McpServerConfig {
    #[must_use]
    pub fn transport(&self) -> McpTransport {
        match self {
            Self::Stdio(_) => McpTransport::Stdio,
            Self::Sse(_) => McpTransport::Sse,
            Self::Http(_) => McpTransport::Http,
            Self::Ws(_) => McpTransport::Ws,
            Self::Sdk(_) => McpTransport::Sdk,
            Self::ClaudeAiProxy(_) => McpTransport::ClaudeAiProxy,
        }
    }
}

fn read_optional_json_object(
    path: &Path,
) -> Result<Option<BTreeMap<String, JsonValue>>, ConfigError> {
    let contents = match fs::read_to_string(path) {
        Ok(contents) => contents,
        Err(error) if error.kind() == std::io::ErrorKind::NotFound => return Ok(None),
        Err(error) => return Err(ConfigError::Io(error)),
    };

    if contents.trim().is_empty() {
        return Ok(Some(BTreeMap::new()));
    }

    let parsed = JsonValue::parse(&contents)
        .map_err(|error| ConfigError::Parse(format!("{}: {error}", path.display())))?;
    let object = parsed.as_object().ok_or_else(|| {
        ConfigError::Parse(format!(
            "{}: top-level settings value must be a JSON object",
            path.display()
        ))
    })?;
    Ok(Some(object.clone()))
}

fn merge_mcp_servers(
    target: &mut BTreeMap<String, ScopedMcpServerConfig>,
    source: ConfigSource,
    root: &BTreeMap<String, JsonValue>,
    path: &Path,
) -> Result<(), ConfigError> {
    let Some(mcp_servers) = root.get("mcpServers") else {
        return Ok(());
    };
    let servers = expect_object(mcp_servers, &format!("{}: mcpServers", path.display()))?;
    for (name, value) in servers {
        let parsed = parse_mcp_server_config(
            name,
            value,
            &format!("{}: mcpServers.{name}", path.display()),
        )?;
        target.insert(
            name.clone(),
            ScopedMcpServerConfig {
                scope: source,
                config: parsed,
            },
        );
    }
    Ok(())
}

fn parse_optional_oauth_config(
    root: &JsonValue,
    context: &str,
) -> Result<Option<OAuthConfig>, ConfigError> {
    let Some(oauth_value) = root.as_object().and_then(|object| object.get("oauth")) else {
        return Ok(None);
    };
    let object = expect_object(oauth_value, context)?;
    let client_id = expect_string(object, "clientId", context)?.to_string();
    let authorize_url = expect_string(object, "authorizeUrl", context)?.to_string();
    let token_url = expect_string(object, "tokenUrl", context)?.to_string();
    let callback_port = optional_u16(object, "callbackPort", context)?;
    let manual_redirect_url =
        optional_string(object, "manualRedirectUrl", context)?.map(str::to_string);
    let scopes = optional_string_array(object, "scopes", context)?.unwrap_or_default();
    Ok(Some(OAuthConfig {
        client_id,
        authorize_url,
        token_url,
        callback_port,
        manual_redirect_url,
        scopes,
    }))
}

fn parse_mcp_server_config(
    server_name: &str,
    value: &JsonValue,
    context: &str,
) -> Result<McpServerConfig, ConfigError> {
    let object = expect_object(value, context)?;
    let server_type = optional_string(object, "type", context)?.unwrap_or("stdio");
    match server_type {
        "stdio" => Ok(McpServerConfig::Stdio(McpStdioServerConfig {
            command: expect_string(object, "command", context)?.to_string(),
            args: optional_string_array(object, "args", context)?.unwrap_or_default(),
            env: optional_string_map(object, "env", context)?.unwrap_or_default(),
        })),
        "sse" => Ok(McpServerConfig::Sse(parse_mcp_remote_server_config(
            object, context,
        )?)),
        "http" => Ok(McpServerConfig::Http(parse_mcp_remote_server_config(
            object, context,
        )?)),
        "ws" => Ok(McpServerConfig::Ws(McpWebSocketServerConfig {
            url: expect_string(object, "url", context)?.to_string(),
            headers: optional_string_map(object, "headers", context)?.unwrap_or_default(),
            headers_helper: optional_string(object, "headersHelper", context)?.map(str::to_string),
        })),
        "sdk" => Ok(McpServerConfig::Sdk(McpSdkServerConfig {
            name: expect_string(object, "name", context)?.to_string(),
        })),
        "claudeai-proxy" => Ok(McpServerConfig::ClaudeAiProxy(
            McpClaudeAiProxyServerConfig {
                url: expect_string(object, "url", context)?.to_string(),
                id: expect_string(object, "id", context)?.to_string(),
            },
        )),
        other => Err(ConfigError::Parse(format!(
            "{context}: unsupported MCP server type for {server_name}: {other}"
        ))),
    }
}

fn parse_mcp_remote_server_config(
    object: &BTreeMap<String, JsonValue>,
    context: &str,
) -> Result<McpRemoteServerConfig, ConfigError> {
    Ok(McpRemoteServerConfig {
        url: expect_string(object, "url", context)?.to_string(),
        headers: optional_string_map(object, "headers", context)?.unwrap_or_default(),
        headers_helper: optional_string(object, "headersHelper", context)?.map(str::to_string),
        oauth: parse_optional_mcp_oauth_config(object, context)?,
    })
}

fn parse_optional_mcp_oauth_config(
    object: &BTreeMap<String, JsonValue>,
    context: &str,
) -> Result<Option<McpOAuthConfig>, ConfigError> {
    let Some(value) = object.get("oauth") else {
        return Ok(None);
    };
    let oauth = expect_object(value, &format!("{context}.oauth"))?;
    Ok(Some(McpOAuthConfig {
        client_id: optional_string(oauth, "clientId", context)?.map(str::to_string),
        callback_port: optional_u16(oauth, "callbackPort", context)?,
        auth_server_metadata_url: optional_string(oauth, "authServerMetadataUrl", context)?
            .map(str::to_string),
        xaa: optional_bool(oauth, "xaa", context)?,
    }))
}

fn expect_object<'a>(
    value: &'a JsonValue,
    context: &str,
) -> Result<&'a BTreeMap<String, JsonValue>, ConfigError> {
    value
        .as_object()
        .ok_or_else(|| ConfigError::Parse(format!("{context}: expected JSON object")))
}

fn expect_string<'a>(
    object: &'a BTreeMap<String, JsonValue>,
    key: &str,
    context: &str,
) -> Result<&'a str, ConfigError> {
    object
        .get(key)
        .and_then(JsonValue::as_str)
        .ok_or_else(|| ConfigError::Parse(format!("{context}: missing string field {key}")))
}

fn optional_string<'a>(
    object: &'a BTreeMap<String, JsonValue>,
    key: &str,
    context: &str,
) -> Result<Option<&'a str>, ConfigError> {
    match object.get(key) {
        Some(value) => value
            .as_str()
            .map(Some)
            .ok_or_else(|| ConfigError::Parse(format!("{context}: field {key} must be a string"))),
        None => Ok(None),
    }
}

fn optional_bool(
    object: &BTreeMap<String, JsonValue>,
    key: &str,
    context: &str,
) -> Result<Option<bool>, ConfigError> {
    match object.get(key) {
        Some(value) => value
            .as_bool()
            .map(Some)
            .ok_or_else(|| ConfigError::Parse(format!("{context}: field {key} must be a boolean"))),
        None => Ok(None),
    }
}

fn optional_u16(
    object: &BTreeMap<String, JsonValue>,
    key: &str,
    context: &str,
) -> Result<Option<u16>, ConfigError> {
    match object.get(key) {
        Some(value) => {
            let Some(number) = value.as_i64() else {
                return Err(ConfigError::Parse(format!(
                    "{context}: field {key} must be an integer"
                )));
            };
            let number = u16::try_from(number).map_err(|_| {
                ConfigError::Parse(format!("{context}: field {key} is out of range"))
            })?;
            Ok(Some(number))
        }
        None => Ok(None),
    }
}

fn optional_string_array(
    object: &BTreeMap<String, JsonValue>,
    key: &str,
    context: &str,
) -> Result<Option<Vec<String>>, ConfigError> {
    match object.get(key) {
        Some(value) => {
            let Some(array) = value.as_array() else {
                return Err(ConfigError::Parse(format!(
                    "{context}: field {key} must be an array"
                )));
            };
            array
                .iter()
                .map(|item| {
                    item.as_str().map(ToOwned::to_owned).ok_or_else(|| {
                        ConfigError::Parse(format!(
                            "{context}: field {key} must contain only strings"
                        ))
                    })
                })
                .collect::<Result<Vec<_>, _>>()
                .map(Some)
        }
        None => Ok(None),
    }
}

fn optional_string_map(
    object: &BTreeMap<String, JsonValue>,
    key: &str,
    context: &str,
) -> Result<Option<BTreeMap<String, String>>, ConfigError> {
    match object.get(key) {
        Some(value) => {
            let Some(map) = value.as_object() else {
                return Err(ConfigError::Parse(format!(
                    "{context}: field {key} must be an object"
                )));
            };
            map.iter()
                .map(|(entry_key, entry_value)| {
                    entry_value
                        .as_str()
                        .map(|text| (entry_key.clone(), text.to_string()))
                        .ok_or_else(|| {
                            ConfigError::Parse(format!(
                                "{context}: field {key} must contain only string values"
                            ))
                        })
                })
                .collect::<Result<BTreeMap<_, _>, _>>()
                .map(Some)
        }
        None => Ok(None),
    }
}

fn deep_merge_objects(
    target: &mut BTreeMap<String, JsonValue>,
    source: &BTreeMap<String, JsonValue>,
) {
    for (key, value) in source {
        match (target.get_mut(key), value) {
            (Some(JsonValue::Object(existing)), JsonValue::Object(incoming)) => {
                deep_merge_objects(existing, incoming);
            }
            _ => {
                target.insert(key.clone(), value.clone());
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::{
        ConfigLoader, ConfigSource, McpServerConfig, McpTransport, CLAUDE_CODE_SETTINGS_SCHEMA_NAME,
    };
    use crate::json::JsonValue;
    use std::fs;
    use std::time::{SystemTime, UNIX_EPOCH};

    fn temp_dir() -> std::path::PathBuf {
        let nanos = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("time should be after epoch")
            .as_nanos();
        std::env::temp_dir().join(format!("runtime-config-{nanos}"))
    }

    #[test]
    fn rejects_non_object_settings_files() {
        let root = temp_dir();
        let cwd = root.join("project");
        let home = root.join("home").join(".claude");
        fs::create_dir_all(&home).expect("home config dir");
        fs::create_dir_all(&cwd).expect("project dir");
        fs::write(home.join("settings.json"), "[]").expect("write bad settings");

        let error = ConfigLoader::new(&cwd, &home)
            .load()
            .expect_err("config should fail");
        assert!(error
            .to_string()
            .contains("top-level settings value must be a JSON object"));

        fs::remove_dir_all(root).expect("cleanup temp dir");
    }

    #[test]
    fn loads_and_merges_claude_code_config_files_by_precedence() {
        let root = temp_dir();
        let cwd = root.join("project");
        let home = root.join("home").join(".claude");
        fs::create_dir_all(cwd.join(".claude")).expect("project config dir");
        fs::create_dir_all(&home).expect("home config dir");

        fs::write(
            home.join("settings.json"),
            r#"{"model":"sonnet","env":{"A":"1"},"hooks":{"PreToolUse":["base"]}}"#,
        )
        .expect("write user settings");
        fs::write(
            cwd.join(".claude").join("settings.json"),
            r#"{"env":{"B":"2"},"hooks":{"PostToolUse":["project"]}}"#,
        )
        .expect("write project settings");
        fs::write(
            cwd.join(".claude").join("settings.local.json"),
            r#"{"model":"opus","permissionMode":"acceptEdits"}"#,
        )
        .expect("write local settings");

        let loaded = ConfigLoader::new(&cwd, &home)
            .load()
            .expect("config should load");

        assert_eq!(CLAUDE_CODE_SETTINGS_SCHEMA_NAME, "SettingsSchema");
        assert_eq!(loaded.loaded_entries().len(), 3);
        assert_eq!(loaded.loaded_entries()[0].source, ConfigSource::User);
        assert_eq!(
            loaded.get("model"),
            Some(&JsonValue::String("opus".to_string()))
        );
        assert_eq!(
            loaded
                .get("env")
                .and_then(JsonValue::as_object)
                .expect("env object")
                .len(),
            2
        );
        assert!(loaded
            .get("hooks")
            .and_then(JsonValue::as_object)
            .expect("hooks object")
            .contains_key("PreToolUse"));

        fs::remove_dir_all(root).expect("cleanup temp dir");
    }

    #[test]
    fn parses_typed_mcp_and_oauth_config() {
        let root = temp_dir();
        let cwd = root.join("project");
        let home = root.join("home").join(".claude");
        fs::create_dir_all(cwd.join(".claude")).expect("project config dir");
        fs::create_dir_all(&home).expect("home config dir");

        fs::write(
            home.join("settings.json"),
            r#"{
              "mcpServers": {
                "stdio-server": {
                  "command": "uvx",
                  "args": ["mcp-server"],
                  "env": {"TOKEN": "secret"}
                },
                "remote-server": {
                  "type": "http",
                  "url": "https://example.test/mcp",
                  "headers": {"Authorization": "Bearer token"},
                  "headersHelper": "helper.sh",
                  "oauth": {
                    "clientId": "mcp-client",
                    "callbackPort": 7777,
                    "authServerMetadataUrl": "https://issuer.test/.well-known/oauth-authorization-server",
                    "xaa": true
                  }
                }
              },
              "oauth": {
                "clientId": "runtime-client",
                "authorizeUrl": "https://console.test/oauth/authorize",
                "tokenUrl": "https://console.test/oauth/token",
                "callbackPort": 54545,
                "manualRedirectUrl": "https://console.test/oauth/callback",
                "scopes": ["org:read", "user:write"]
              }
            }"#,
        )
        .expect("write user settings");
        fs::write(
            cwd.join(".claude").join("settings.local.json"),
            r#"{
              "mcpServers": {
                "remote-server": {
                  "type": "ws",
                  "url": "wss://override.test/mcp",
                  "headers": {"X-Env": "local"}
                }
              }
            }"#,
        )
        .expect("write local settings");

        let loaded = ConfigLoader::new(&cwd, &home)
            .load()
            .expect("config should load");

        let stdio_server = loaded
            .mcp()
            .get("stdio-server")
            .expect("stdio server should exist");
        assert_eq!(stdio_server.scope, ConfigSource::User);
        assert_eq!(stdio_server.transport(), McpTransport::Stdio);

        let remote_server = loaded
            .mcp()
            .get("remote-server")
            .expect("remote server should exist");
        assert_eq!(remote_server.scope, ConfigSource::Local);
        assert_eq!(remote_server.transport(), McpTransport::Ws);
        match &remote_server.config {
            McpServerConfig::Ws(config) => {
                assert_eq!(config.url, "wss://override.test/mcp");
                assert_eq!(
                    config.headers.get("X-Env").map(String::as_str),
                    Some("local")
                );
            }
            other => panic!("expected ws config, got {other:?}"),
        }

        let oauth = loaded.oauth().expect("oauth config should exist");
        assert_eq!(oauth.client_id, "runtime-client");
        assert_eq!(oauth.callback_port, Some(54_545));
        assert_eq!(oauth.scopes, vec!["org:read", "user:write"]);

        fs::remove_dir_all(root).expect("cleanup temp dir");
    }

    #[test]
    fn rejects_invalid_mcp_server_shapes() {
        let root = temp_dir();
        let cwd = root.join("project");
        let home = root.join("home").join(".claude");
        fs::create_dir_all(&home).expect("home config dir");
        fs::create_dir_all(&cwd).expect("project dir");
        fs::write(
            home.join("settings.json"),
            r#"{"mcpServers":{"broken":{"type":"http","url":123}}}"#,
        )
        .expect("write broken settings");

        let error = ConfigLoader::new(&cwd, &home)
            .load()
            .expect_err("config should fail");
        assert!(error
            .to_string()
            .contains("mcpServers.broken: missing string field url"));

        fs::remove_dir_all(root).expect("cleanup temp dir");
    }
}
