//! Data fetching system for plugin UI pages
//!
//! Provides data fetching and caching for plugin data sources.

use std::{
  collections::{HashMap, HashSet},
  time::Duration,
};

use dioxus::prelude::*;
use dioxus_core::Task;
use pinakes_plugin_api::{DataSource, Expression, HttpMethod};

use super::expr::{evaluate_expression, value_to_display_string};
use crate::client::ApiClient;

/// Cached data for a plugin page
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct PluginPageData {
  data:    HashMap<String, serde_json::Value>,
  loading: HashSet<String>,
  errors:  HashMap<String, String>,
}

impl PluginPageData {
  /// Get data for a specific source
  #[must_use]
  pub fn get(&self, source: &str) -> Option<&serde_json::Value> {
    self.data.get(source)
  }

  /// Check if a source is currently loading
  #[must_use]
  pub fn is_loading(&self, source: &str) -> bool {
    self.loading.contains(source)
  }

  /// Get error for a specific source
  #[must_use]
  pub fn error(&self, source: &str) -> Option<&str> {
    self.errors.get(source).map(String::as_str)
  }

  /// Check if there is data for a specific source
  #[must_use]
  pub fn has_data(&self, source: &str) -> bool {
    self.data.contains_key(source)
  }

  /// Set data for a source
  pub fn set_data(&mut self, source: String, value: serde_json::Value) {
    self.data.insert(source, value);
  }

  /// Set loading state for a source
  pub fn set_loading(&mut self, source: &str, loading: bool) {
    if loading {
      self.loading.insert(source.to_string());
      self.errors.remove(source);
    } else {
      self.loading.remove(source);
    }
  }

  /// Set error for a source
  pub fn set_error(&mut self, source: String, error: String) {
    self.errors.insert(source, error);
  }

  /// Convert all resolved data to a single JSON object for expression
  /// evaluation
  #[must_use]
  pub fn as_json(&self) -> serde_json::Value {
    serde_json::Value::Object(
      self
        .data
        .iter()
        .map(|(k, v)| (k.clone(), v.clone()))
        .collect(),
    )
  }

  /// Clear all data
  pub fn clear(&mut self) {
    self.data.clear();
    self.loading.clear();
    self.errors.clear();
  }
}

/// Convert a plugin `HttpMethod` to a `reqwest::Method`.
pub(super) const fn to_reqwest_method(method: &HttpMethod) -> reqwest::Method {
  match method {
    HttpMethod::Get => reqwest::Method::GET,
    HttpMethod::Post => reqwest::Method::POST,
    HttpMethod::Put => reqwest::Method::PUT,
    HttpMethod::Patch => reqwest::Method::PATCH,
    HttpMethod::Delete => reqwest::Method::DELETE,
  }
}

/// Fetch data from an endpoint, evaluating any params expressions against
/// the given context.
async fn fetch_endpoint(
  client: &ApiClient,
  path: &str,
  method: HttpMethod,
  params: &HashMap<String, Expression>,
  ctx: &serde_json::Value,
  allowed_endpoints: &[String],
) -> Result<serde_json::Value, String> {
  if !allowed_endpoints.is_empty()
    && !allowed_endpoints.iter().any(|ep| path == ep.as_str())
  {
    return Err(format!(
      "Endpoint '{path}' is not in plugin's declared required_endpoints"
    ));
  }

  let reqwest_method = to_reqwest_method(&method);

  let mut request = client.raw_request(reqwest_method.clone(), path);

  if !params.is_empty() {
    if reqwest_method == reqwest::Method::GET {
      // Evaluate each param expression and add as query string
      let query_pairs: Vec<(String, String)> = params
        .iter()
        .map(|(k, expr)| {
          let v = evaluate_expression(expr, ctx);
          (k.clone(), value_to_display_string(&v))
        })
        .collect();
      request = request.query(&query_pairs);
    } else {
      // Evaluate params and send as JSON body
      let body: serde_json::Map<String, serde_json::Value> = params
        .iter()
        .map(|(k, expr)| (k.clone(), evaluate_expression(expr, ctx)))
        .collect();
      request = request.json(&body);
    }
  }

  // Send request and parse response
  let response = request
    .send()
    .await
    .map_err(|e| format!("Request failed: {e}"))?;

  if !response.status().is_success() {
    let status = response.status();
    let body = response.text().await.unwrap_or_default();
    return Err(format!("HTTP {status}: {body}"));
  }

  response
    .json::<serde_json::Value>()
    .await
    .map_err(|e| format!("Failed to parse JSON: {e}"))
}

/// Fetch all data sources for a page
///
/// Endpoint sources are deduplicated by `(path, method, params)`: if multiple
/// sources share the same triplet, a single HTTP request is made and the raw
/// response is shared, with each source's own `transform` applied
/// independently. All unique Endpoint and Static sources are fetched
/// concurrently. Transform sources are applied after, in iteration order,
/// against the full result set.
///
/// # Errors
///
/// Returns an error if any data source fails to fetch
pub async fn fetch_page_data(
  client: &ApiClient,
  data_sources: &HashMap<String, DataSource>,
  allowed_endpoints: &[String],
) -> Result<HashMap<String, serde_json::Value>, String> {
  // Group non-Transform sources into dedup groups.
  //
  // For Endpoint sources, two entries are in the same group when they share
  // the same (path, method, params) - i.e., they would produce an identical
  // HTTP request. The per-source `transform` expression is kept separate so
  // each name can apply its own transform to the shared raw response.
  //
  // Static sources never share an HTTP request so each becomes its own group.
  //
  // Each group is: (names_and_transforms, representative_source)
  // where names_and_transforms is Vec<(name, Option<Expression>)> for Endpoint,
  // or Vec<(name, ())> for Static (transform is baked in).
  struct Group {
    // (source name, per-name transform expression for Endpoint sources)
    members: Vec<(String, Option<Expression>)>,
    // The representative source used to fire the request (transform ignored
    // for Endpoint - we apply per-member transforms after fetching)
    source:  DataSource,
  }

  let mut groups: Vec<Group> = Vec::new();

  for (name, source) in data_sources {
    if matches!(source, DataSource::Transform { .. }) {
      continue;
    }

    match source {
      DataSource::Endpoint {
        path,
        method,
        params,
        transform,
        poll_interval,
      } => {
        // Find an existing group with the same (path, method, params).
        let existing = groups.iter_mut().find(|g| {
          matches!(
            &g.source,
            DataSource::Endpoint {
              path: ep,
              method: em,
              params: epa,
              ..
            } if ep == path && em == method && epa == params
          )
        });

        if let Some(group) = existing {
          group.members.push((name.clone(), transform.clone()));
        } else {
          groups.push(Group {
            members: vec![(name.clone(), transform.clone())],
            source:  DataSource::Endpoint {
              path:          path.clone(),
              method:        method.clone(),
              params:        params.clone(),
              poll_interval: *poll_interval,
              transform:     None,
            },
          });
        }
      },
      DataSource::Static { .. } => {
        // Static sources are trivially unique per name; no dedup needed.
        groups.push(Group {
          members: vec![(name.clone(), None)],
          source:  source.clone(),
        });
      },
      DataSource::Transform { .. } => unreachable!(),
    }
  }

  // Fire one future per group concurrently.
  let futs: Vec<_> = groups
    .into_iter()
    .map(|group| {
      let client = client.clone();
      let allowed = allowed_endpoints.to_vec();
      async move {
        // Fetch the raw value for this group.
        let raw = match &group.source {
          DataSource::Endpoint {
            path,
            method,
            params,
            ..
          } => {
            let empty_ctx = serde_json::json!({});
            fetch_endpoint(
              &client,
              path,
              method.clone(),
              params,
              &empty_ctx,
              &allowed,
            )
            .await?
          },
          DataSource::Static { value } => value.clone(),
          DataSource::Transform { .. } => unreachable!(),
        };

        // Apply per-member transforms and collect (name, value) pairs.
        let pairs: Vec<(String, serde_json::Value)> = group
          .members
          .into_iter()
          .map(|(name, transform)| {
            let value = if let Some(expr) = &transform {
              evaluate_expression(expr, &raw)
            } else {
              raw.clone()
            };
            (name, value)
          })
          .collect();

        Ok::<_, String>(pairs)
      }
    })
    .collect();

  let mut results: HashMap<String, serde_json::Value> = HashMap::new();
  for group_result in futures::future::join_all(futs).await {
    for (name, value) in group_result? {
      results.insert(name, value);
    }
  }

  // Process Transform sources in dependency order. HashMap iteration order is
  // non-deterministic, so a Transform referencing another Transform could see
  // null if the upstream was not yet resolved. The pending loop below defers
  // any Transform whose upstream is not yet in results, making progress on
  // each pass until all are resolved. UiPage::validate guarantees no cycles,
  // so the loop always terminates.
  let mut pending: Vec<(&String, &String, &Expression)> = data_sources
    .iter()
    .filter_map(|(name, source)| {
      match source {
        DataSource::Transform {
          source_name,
          expression,
        } => Some((name, source_name, expression)),
        _ => None,
      }
    })
    .collect();

  while !pending.is_empty() {
    let prev_len = pending.len();
    let mut i = 0;
    while i < pending.len() {
      let (name, source_name, expression) = pending[i];
      if results.contains_key(source_name.as_str()) {
        let ctx = serde_json::Value::Object(
          results
            .iter()
            .map(|(k, v)| (k.clone(), v.clone()))
            .collect(),
        );
        results.insert(name.clone(), evaluate_expression(expression, &ctx));
        pending.swap_remove(i);
      } else {
        i += 1;
      }
    }
    if pending.len() == prev_len {
      // No progress: upstream source is missing (should be caught by
      // UiPage::validate, but handled defensively here).
      tracing::warn!(
        "plugin transform dependency unresolvable; processing remaining in \
         iteration order"
      );
      for (name, _, expression) in pending {
        let ctx = serde_json::Value::Object(
          results
            .iter()
            .map(|(k, v)| (k.clone(), v.clone()))
            .collect(),
        );
        results.insert(name.clone(), evaluate_expression(expression, &ctx));
      }
      break;
    }
  }

  Ok(results)
}

/// Hook to fetch and cache plugin page data
///
/// Returns a signal containing the data state. If any data source has a
/// non-zero `poll_interval`, a background loop re-fetches automatically at the
/// minimum interval. The `refresh` counter can be incremented to trigger an
/// immediate re-fetch outside of the polling interval.
pub fn use_plugin_data(
  client: Signal<ApiClient>,
  data_sources: HashMap<String, DataSource>,
  refresh: Signal<u32>,
  allowed_endpoints: Vec<String>,
) -> Signal<PluginPageData> {
  let mut data = use_signal(PluginPageData::default);
  let mut poll_task: Signal<Option<Task>> = use_signal(|| None);

  use_effect(move || {
    // Subscribe to the refresh counter; incrementing it triggers a re-run.
    let _rev = refresh.read();
    let sources = data_sources.clone();
    let allowed = allowed_endpoints.clone();

    // Cancel the previous polling task before spawning a new one. Use
    // write() rather than read() so the effect does not subscribe to
    // poll_task and trigger an infinite re-run loop.
    if let Some(t) = poll_task.write().take() {
      t.cancel();
    }

    // Determine minimum poll interval (0 = no polling)
    let min_poll_secs: u64 = sources
      .values()
      .filter_map(|s| {
        if let DataSource::Endpoint { poll_interval, .. } = s {
          if *poll_interval > 0 {
            Some(*poll_interval)
          } else {
            None
          }
        } else {
          None
        }
      })
      .min()
      .unwrap_or(0);

    let handle = spawn(async move {
      // Clear previous data
      data.write().clear();

      // Mark all sources as loading
      for name in sources.keys() {
        data.write().set_loading(name, true);
      }

      // Initial fetch; clone to release the signal read borrow before await.
      let cl = client.peek().clone();
      match fetch_page_data(&cl, &sources, &allowed).await {
        Ok(results) => {
          for (name, value) in results {
            data.write().set_loading(&name, false);
            data.write().set_data(name, value);
          }
        },
        Err(e) => {
          for name in sources.keys() {
            data.write().set_loading(name, false);
            data.write().set_error(name.clone(), e.clone());
          }
        },
      }

      // Polling loop; only runs if at least one source has poll_interval > 0
      if min_poll_secs > 0 {
        loop {
          tokio::time::sleep(Duration::from_secs(min_poll_secs)).await;

          let cl = client.peek().clone();
          match fetch_page_data(&cl, &sources, &allowed).await {
            Ok(results) => {
              for (name, value) in results {
                // Only write if data is new or has changed to avoid spurious
                // signal updates that would force a re-render
                let changed = !data.read().has_data(&name)
                  || data.read().get(&name) != Some(&value);
                if changed {
                  data.write().set_data(name, value);
                }
              }
            },
            Err(e) => {
              tracing::warn!("Poll fetch failed: {e}");
            },
          }
        }
      }
    });

    *poll_task.write() = Some(handle);
  });

  data
}

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

  #[test]
  fn test_plugin_page_data() {
    let mut data = PluginPageData::default();

    // Test empty state
    assert!(!data.has_data("test"));
    assert!(!data.is_loading("test"));
    assert!(data.error("test").is_none());

    // Test setting data
    data.set_data("test".to_string(), serde_json::json!({"key": "value"}));
    assert!(data.has_data("test"));
    assert_eq!(data.get("test"), Some(&serde_json::json!({"key": "value"})));

    // Test loading state
    data.set_loading("loading", true);
    assert!(data.is_loading("loading"));
    data.set_loading("loading", false);
    assert!(!data.is_loading("loading"));

    // Test error state
    data.set_error("error".to_string(), "oops".to_string());
    assert_eq!(data.error("error"), Some("oops"));
  }

  #[test]
  fn test_as_json_empty() {
    let data = PluginPageData::default();
    assert_eq!(data.as_json(), serde_json::json!({}));
  }

  #[test]
  fn test_as_json_with_data() {
    let mut data = PluginPageData::default();
    data.set_data("users".to_string(), serde_json::json!([{"id": 1}]));
    data.set_data("count".to_string(), serde_json::json!(42));
    let json = data.as_json();
    assert_eq!(json["users"], serde_json::json!([{"id": 1}]));
    assert_eq!(json["count"], serde_json::json!(42));
  }

  #[test]
  fn test_set_loading_true_clears_error() {
    let mut data = PluginPageData::default();
    data.set_error("src".to_string(), "oops".to_string());
    assert!(data.error("src").is_some());
    data.set_loading("src", true);
    assert!(data.error("src").is_none());
    assert!(data.is_loading("src"));
  }

  #[test]
  fn test_set_loading_false_removes_flag() {
    let mut data = PluginPageData::default();
    data.set_loading("src", true);
    assert!(data.is_loading("src"));
    data.set_loading("src", false);
    assert!(!data.is_loading("src"));
  }

  #[test]
  fn test_clear_resets_all_state() {
    let mut data = PluginPageData::default();
    data.set_data("x".to_string(), serde_json::json!(1));
    data.set_loading("x", true);
    data.set_error("y".to_string(), "err".to_string());
    data.clear();
    assert!(!data.has_data("x"));
    assert!(!data.is_loading("x"));
    assert!(data.error("y").is_none());
  }

  #[test]
  fn test_partial_eq() {
    let mut a = PluginPageData::default();
    let mut b = PluginPageData::default();
    assert_eq!(a, b);
    a.set_data("k".to_string(), serde_json::json!(1));
    assert_ne!(a, b);
    b.set_data("k".to_string(), serde_json::json!(1));
    assert_eq!(a, b);
  }

  #[tokio::test]
  async fn test_fetch_page_data_static_only() {
    use pinakes_plugin_api::DataSource;

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    sources.insert("nums".to_string(), DataSource::Static {
      value: serde_json::json!([1, 2, 3]),
    });
    sources.insert("flag".to_string(), DataSource::Static {
      value: serde_json::json!(true),
    });

    let results = super::fetch_page_data(&client, &sources, &[])
      .await
      .unwrap();
    assert_eq!(results["nums"], serde_json::json!([1, 2, 3]));
    assert_eq!(results["flag"], serde_json::json!(true));
  }

  #[tokio::test]
  async fn test_fetch_page_data_transform_evaluates_expression() {
    use pinakes_plugin_api::{DataSource, Expression};

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    // The Transform expression accesses "raw" from the context
    sources.insert("derived".to_string(), DataSource::Transform {
      source_name: "raw".to_string(),
      expression:  Expression::Path("raw".to_string()),
    });
    sources.insert("raw".to_string(), DataSource::Static {
      value: serde_json::json!({"ok": true}),
    });

    let results = super::fetch_page_data(&client, &sources, &[])
      .await
      .unwrap();
    assert_eq!(results["raw"], serde_json::json!({"ok": true}));
    // derived should return the value of "raw" from context
    assert_eq!(results["derived"], serde_json::json!({"ok": true}));
  }

  #[tokio::test]
  async fn test_fetch_page_data_transform_literal_expression() {
    use pinakes_plugin_api::{DataSource, Expression};

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    sources.insert("raw".to_string(), DataSource::Static {
      value: serde_json::json!(42),
    });
    sources.insert("derived".to_string(), DataSource::Transform {
      source_name: "raw".to_string(),
      expression:  Expression::Literal(serde_json::json!("constant")),
    });

    let results = super::fetch_page_data(&client, &sources, &[])
      .await
      .unwrap();
    // A Literal expression returns the literal value, not the source data
    assert_eq!(results["derived"], serde_json::json!("constant"));
  }

  #[tokio::test]
  async fn test_fetch_page_data_deduplicates_identical_endpoints() {
    use pinakes_plugin_api::DataSource;

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    // Two Static sources with the same payload; dedup is for Endpoint sources,
    // but both names must appear in the output regardless.
    sources.insert("a".to_string(), DataSource::Static {
      value: serde_json::json!(1),
    });
    sources.insert("b".to_string(), DataSource::Static {
      value: serde_json::json!(1),
    });
    let results = super::fetch_page_data(&client, &sources, &[])
      .await
      .unwrap();
    assert_eq!(results["a"], serde_json::json!(1));
    assert_eq!(results["b"], serde_json::json!(1));
    assert_eq!(results.len(), 2);
  }

  // Verifies that endpoint sources with identical (path, method, params) are
  // deduplicated correctly. Because there is no real server, the allowlist
  // rejection fires before any network call; both names seeing the same error
  // proves they were grouped and that the single rejection propagated to all.
  #[tokio::test]
  async fn test_dedup_groups_endpoint_sources_with_same_key() {
    use pinakes_plugin_api::{DataSource, Expression, HttpMethod};

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    // Two endpoints with identical (path, method, params=empty) but different
    // transforms. Both should produce the same error when the path is blocked.
    sources.insert("x".to_string(), DataSource::Endpoint {
      path:          "/api/v1/media".to_string(),
      method:        HttpMethod::Get,
      params:        Default::default(),
      poll_interval: 0,
      transform:     Some(Expression::Literal(serde_json::json!("from_x"))),
    });
    sources.insert("y".to_string(), DataSource::Endpoint {
      path:          "/api/v1/media".to_string(),
      method:        HttpMethod::Get,
      params:        Default::default(),
      poll_interval: 0,
      transform:     Some(Expression::Literal(serde_json::json!("from_y"))),
    });

    // Both sources point to the same blocked endpoint; expect an error.
    let allowed = vec!["/api/v1/tags".to_string()];
    let result = super::fetch_page_data(&client, &sources, &allowed).await;
    assert!(
      result.is_err(),
      "fetch_page_data must return Err for blocked deduplicated endpoints"
    );
    let msg = result.unwrap_err();
    assert!(
      msg.contains("not in plugin's declared required_endpoints"),
      "unexpected error: {msg}"
    );
  }

  // Verifies the transform fan-out behavior: each member of a dedup group
  // applies its own transform to the shared raw value independently. This
  // mirrors what Endpoint dedup does after a single shared HTTP request.
  //
  // Testing Endpoint dedup with real per-member transforms requires a mock HTTP
  // server and belongs in an integration test.
  #[tokio::test]
  async fn test_dedup_transform_applied_per_source() {
    use pinakes_plugin_api::{DataSource, Expression};

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    sources.insert("raw_data".to_string(), DataSource::Static {
      value: serde_json::json!({"count": 42, "name": "test"}),
    });
    // Two Transform sources referencing "raw_data" with different expressions;
    // each must produce its own independently derived value.
    sources.insert("derived_count".to_string(), DataSource::Transform {
      source_name: "raw_data".to_string(),
      expression:  Expression::Path("raw_data.count".to_string()),
    });
    sources.insert("derived_name".to_string(), DataSource::Transform {
      source_name: "raw_data".to_string(),
      expression:  Expression::Path("raw_data.name".to_string()),
    });

    let results = super::fetch_page_data(&client, &sources, &[])
      .await
      .unwrap();
    assert_eq!(
      results["raw_data"],
      serde_json::json!({"count": 42, "name": "test"})
    );
    assert_eq!(results["derived_count"], serde_json::json!(42));
    assert_eq!(results["derived_name"], serde_json::json!("test"));
    assert_eq!(results.len(), 3);
  }

  #[tokio::test]
  async fn test_endpoint_blocked_when_not_in_allowlist() {
    use pinakes_plugin_api::{DataSource, HttpMethod};

    use crate::client::ApiClient;

    let client = ApiClient::default();
    let mut sources = HashMap::new();
    sources.insert("items".to_string(), DataSource::Endpoint {
      path:          "/api/v1/media".to_string(),
      method:        HttpMethod::Get,
      params:        Default::default(),
      poll_interval: 0,
      transform:     None,
    });

    // Provide a non-empty allowlist that does NOT include the endpoint path.
    let allowed = vec!["/api/v1/tags".to_string()];
    let result = super::fetch_page_data(&client, &sources, &allowed).await;

    assert!(
      result.is_err(),
      "fetch_page_data must return Err when endpoint is not in \
       allowed_endpoints"
    );
    let msg = result.unwrap_err();
    assert!(
      msg.contains("not in plugin's declared required_endpoints"),
      "error must explain that the endpoint is not declared, got: {msg}"
    );
  }
}