//! The core data unit. An [`Item`] is a single entry in the
//! menu, either a plain-text string or a JSON object with
//! structured fields.

use serde_json::Value;

/// A menu entry wrapping a JSON value. Plain text is stored
/// as `Value::String`, structured entries as
/// `Value::Object`. The label is extracted and cached at
/// construction time so display calls are just a pointer
/// dereference. Sublabel, icon, and group are also cached
/// for structured items.
///
/// Serializes as the inner Value (transparent for output)
/// but construction always requires label extraction.
#[derive(Debug, Clone)]
pub struct Item {
    pub value: Value,
    label_cache: String,
    sublabel_cache: Option<String>,
    icon_cache: Option<String>,
    group_cache: Option<String>,
}

impl Item {
    /// Create an Item from a JSON value, extracting the display
    /// label from the given key. String values use the string
    /// itself. Object values look up the key. Also extracts
    /// sublabel, icon, and group from known keys on objects.
    pub fn new(value: Value, label_key: &str) -> Self {
        let label_cache = extract_label(&value, label_key).to_string();
        let sublabel_cache = extract_optional(&value, "sublabel");
        let icon_cache = extract_optional(&value, "icon");
        let group_cache = extract_optional(&value, "group");
        Self {
            value,
            label_cache,
            sublabel_cache,
            icon_cache,
            group_cache,
        }
    }

    /// Wrap a plain-text string as an Item. Stored internally
    /// as `Value::String` with the label cached. Optional
    /// fields are left as None.
    pub fn from_plain_text(line: &str) -> Self {
        Self {
            value: Value::String(line.to_string()),
            label_cache: line.to_string(),
            sublabel_cache: None,
            icon_cache: None,
            group_cache: None,
        }
    }

    /// Get the display label for this item. Cached at
    /// construction time, so this is just a borrow.
    pub fn label(&self) -> &str {
        &self.label_cache
    }

    /// Get the sublabel for this item, if present.
    pub fn sublabel(&self) -> Option<&str> {
        self.sublabel_cache.as_deref()
    }

    /// Get the icon for this item, if present.
    pub fn icon(&self) -> Option<&str> {
        self.icon_cache.as_deref()
    }

    /// Get the group for this item, if present.
    pub fn group(&self) -> Option<&str> {
        self.group_cache.as_deref()
    }

    /// Get the `meta` field from the underlying value, if it
    /// exists and the value is an object.
    pub fn meta(&self) -> Option<&Value> {
        match &self.value {
            Value::Object(map) => map.get("meta"),
            _ => None,
        }
    }

    /// Resolve a dotted field path against this item's value.
    /// For example, `field_value("meta.resolution")` on
    /// `{"meta": {"resolution": "1080p"}}` returns
    /// `Some(Value::String("1080p"))`.
    pub fn field_value(&self, path: &str) -> Option<&Value> {
        resolve_field_path(&self.value, path)
    }
}

/// Extract the display label from a JSON value.
fn extract_label<'a>(value: &'a Value, key: &str) -> &'a str {
    match value {
        Value::String(s) => s.as_str(),
        Value::Object(map) => map.get(key).and_then(|v| v.as_str()).unwrap_or(""),
        _ => "",
    }
}

/// Extract an optional string field from a JSON object value.
fn extract_optional(value: &Value, key: &str) -> Option<String> {
    match value {
        Value::Object(map) => map.get(key).and_then(|v| v.as_str()).map(|s| s.to_string()),
        _ => None,
    }
}

/// Walk a dotted path (e.g. `"meta.tags.0"`) through nested
/// JSON objects. Returns None if any intermediate is not an
/// object or the key is missing.
pub fn resolve_field_path<'a>(value: &'a Value, path: &str) -> Option<&'a Value> {
    let mut current = value;
    for segment in path.split('.') {
        match current {
            Value::Object(map) => {
                current = map.get(segment)?;
            }
            _ => return None,
        }
    }
    Some(current)
}

impl serde::Serialize for Item {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        self.value.serialize(serializer)
    }
}

impl<'de> serde::Deserialize<'de> for Item {
    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let value = Value::deserialize(deserializer)?;
        // Default to "label" key when deserializing. Callers that need
        // a different key should construct via Item::new() instead.
        Ok(Item::new(value, "label"))
    }
}

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

    #[test]
    fn label_from_string() {
        let item = Item::new(json!("hello"), "label");
        assert_eq!(item.label(), "hello");
    }

    #[test]
    fn label_from_object_with_key() {
        let item = Item::new(json!({"label": "foo", "value": 42}), "label");
        assert_eq!(item.label(), "foo");
    }

    #[test]
    fn label_from_object_missing_key() {
        let item = Item::new(json!({"name": "bar"}), "label");
        assert_eq!(item.label(), "");
    }

    #[test]
    fn label_from_object_custom_key() {
        let item = Item::new(json!({"name": "bar", "label": "ignored"}), "name");
        assert_eq!(item.label(), "bar");
    }

    #[test]
    fn label_from_number() {
        let item = Item::new(json!(42), "label");
        assert_eq!(item.label(), "");
    }

    #[test]
    fn label_from_null() {
        let item = Item::new(json!(null), "label");
        assert_eq!(item.label(), "");
    }

    #[test]
    fn from_plain_text() {
        let item = Item::from_plain_text("hello world");
        assert_eq!(item.label(), "hello world");
        assert!(item.value.is_string());
        assert!(item.sublabel().is_none());
        assert!(item.icon().is_none());
        assert!(item.group().is_none());
    }

    #[test]
    fn serialize_string_item() {
        let item = Item::from_plain_text("test");
        let json = serde_json::to_string(&item).unwrap_or_default();
        assert_eq!(json, "\"test\"");
    }

    #[test]
    fn serialize_object_item() {
        let item = Item::new(json!({"label": "foo"}), "label");
        let json = serde_json::to_string(&item).unwrap_or_default();
        assert_eq!(json, r#"{"label":"foo"}"#);
    }

    // -- New accessor tests --

    #[test]
    fn sublabel_from_object() {
        let item = Item::new(
            json!({"label": "Firefox", "sublabel": "Web Browser"}),
            "label",
        );
        assert_eq!(item.sublabel(), Some("Web Browser"));
    }

    #[test]
    fn sublabel_missing() {
        let item = Item::new(json!({"label": "Firefox"}), "label");
        assert!(item.sublabel().is_none());
    }

    #[test]
    fn icon_from_object() {
        let item = Item::new(
            json!({"label": "Firefox", "icon": "firefox.png"}),
            "label",
        );
        assert_eq!(item.icon(), Some("firefox.png"));
    }

    #[test]
    fn group_from_object() {
        let item = Item::new(
            json!({"label": "Firefox", "group": "browsers"}),
            "label",
        );
        assert_eq!(item.group(), Some("browsers"));
    }

    #[test]
    fn meta_from_object() {
        let item = Item::new(
            json!({"label": "test", "meta": {"res": 1080}}),
            "label",
        );
        let meta = item.meta();
        assert!(meta.is_some());
        assert_eq!(meta.and_then(|m| m.get("res")), Some(&json!(1080)));
    }

    #[test]
    fn meta_from_plain_text() {
        let item = Item::from_plain_text("hello");
        assert!(item.meta().is_none());
    }

    // -- Field path resolution tests --

    #[test]
    fn resolve_simple_path() {
        let value = json!({"label": "test"});
        assert_eq!(resolve_field_path(&value, "label"), Some(&json!("test")));
    }

    #[test]
    fn resolve_nested_path() {
        let value = json!({"meta": {"resolution": {"width": 3840}}});
        assert_eq!(
            resolve_field_path(&value, "meta.resolution.width"),
            Some(&json!(3840))
        );
    }

    #[test]
    fn resolve_missing_path() {
        let value = json!({"label": "test"});
        assert!(resolve_field_path(&value, "nope").is_none());
    }

    #[test]
    fn resolve_missing_nested() {
        let value = json!({"meta": {"a": 1}});
        assert!(resolve_field_path(&value, "meta.b").is_none());
    }

    #[test]
    fn resolve_non_object_intermediate() {
        let value = json!({"meta": "not an object"});
        assert!(resolve_field_path(&value, "meta.foo").is_none());
    }

    #[test]
    fn resolve_on_string_value() {
        let value = json!("hello");
        assert!(resolve_field_path(&value, "anything").is_none());
    }

    #[test]
    fn field_value_on_item() {
        let item = Item::new(
            json!({"label": "test", "meta": {"tags": ["a", "b"]}}),
            "label",
        );
        assert_eq!(item.field_value("meta.tags"), Some(&json!(["a", "b"])));
        assert!(item.field_value("meta.nope").is_none());
    }
}