//! The `merger` module handles executing Postgres SPI directives dynamically based on JSON payloads
//! using the structurally isolated schema rules provided by the `Database` registry.

pub mod cache;

use crate::database::Database;

use serde_json::Value;
use std::sync::Arc;

pub struct Merger {
  pub db: Arc<Database>,
  pub cache: cache::StatementCache,
}

impl Merger {
  pub fn new(db: Arc<Database>) -> Self {
    Self {
      db,
      cache: cache::StatementCache::new(10_000),
    }
  }

  /// Primary recursive entrypoint that separates Array lists from Object branches
  pub fn merge(&self, data: Value) -> Result<Value, String> {
    let result = match data {
      Value::Array(items) => self.merge_array(items)?,
      Value::Object(map) => self.merge_object(map)?,
      // Nulls, Strings, Bools, Numbers at root are invalid merge payloads
      _ => return Err("Invalid merge payload: root must be an Object or Array".to_string()),
    };

    Ok(match result {
      Value::Object(mut map) => {
        let mut out = serde_json::Map::new();
        if let Some(id) = map.remove("id") {
          out.insert("id".to_string(), id);
        }
        Value::Object(out)
      }
      Value::Array(arr) => {
        let mut out_arr = Vec::new();
        for item in arr {
          if let Value::Object(mut map) = item {
            let mut out = serde_json::Map::new();
            if let Some(id) = map.remove("id") {
              out.insert("id".to_string(), id);
            }
            out_arr.push(Value::Object(out));
          } else {
            out_arr.push(Value::Null);
          }
        }
        Value::Array(out_arr)
      }
      other => other,
    })
  }

  /// Handles mapping over an array of entities, executing merge logic on each and returning the resolved list.
  fn merge_array(&self, items: Vec<Value>) -> Result<Value, String> {
    let mut resolved_items = Vec::new();
    for item in items {
      // Recursively evaluate each object in the array
      let resolved = self.merge(item)?;
      resolved_items.push(resolved);
    }
    Ok(Value::Array(resolved_items))
  }

  /// Core processing algorithm for a single Entity Object dictionary.
  fn merge_object(&self, mut obj: serde_json::Map<String, Value>) -> Result<Value, String> {
    // Step 1: Ensure it has a `type` definition to proceed
    let type_name = match obj.get("type").and_then(|v| v.as_str()) {
      Some(t) => t.to_string(),
      None => return Err("Missing required 'type' field on object".to_string()),
    };

    // Step 2: Extract Type mapping from the Engine
    let type_def = match self.db.types.get(&type_name) {
      Some(t) => t,
      None => return Err(format!("Unknown entity type: {}", type_name)),
    };

    // Step 3 & 4: (Pre/Post Staging based on `relationship` flag)
    if type_def.relationship {
      // Relationships: process children FIRST (Post-Staging)
      self.process_children(&mut obj, type_def)?;
      Ok(Value::Object(self.stage_entity(obj)?))
    } else {
      // Entities: process core FIRST (Pre-Staging)
      let mut staged_obj_map = self.stage_entity(obj)?;
      self.process_children(&mut staged_obj_map, type_def)?;
      Ok(Value::Object(staged_obj_map))
    }
  }

  /// Iterates values of `obj`, if they are structural (Array/Object), executes `self.merge()` on them.
  /// Uses the `Database` registry to find FK relations and apply the IDs upstream/downstream appropriately.
  fn process_children(
    &self,
    obj: &mut serde_json::Map<String, Value>,
    type_def: &crate::database::r#type::Type,
  ) -> Result<(), String> {
    let keys: Vec<String> = obj.keys().cloned().collect();

    for key in keys {
      // Temporarily extract value to process without borrowing Map mutably
      let val = match obj.remove(&key) {
        Some(v) => v,
        None => continue,
      };

      if val.is_object() || val.is_array() {
        // Pre-Process: Propagate parent data to children BEFORE recursing and applying relations
        let mut child_val = val;
        let mut relation_info = None;

        // Try to peek at the child type for relational mapping
        let peek_obj = match &child_val {
          Value::Object(m) => Some(m),
          Value::Array(arr) if !arr.is_empty() => arr[0].as_object(),
          _ => None,
        };

        if let Some(child_map) = peek_obj {
          if let Ok(Some(relation)) = self.get_entity_relation(obj, type_def, child_map, &key) {
            let child_type_name = child_map.get("type").and_then(|v| v.as_str()).unwrap_or("");
            if let Some(c_type) = self.db.types.get(child_type_name) {
              let parent_is_source = type_def.hierarchy.contains(&relation.source_type);
              let child_is_source = c_type.hierarchy.contains(&relation.source_type);
              relation_info = Some((relation, parent_is_source, child_is_source));
            }
          }
        }

        // Apply pre-merge mutations mapping IDs
        if let Some((relation, _parent_is_source, child_is_source)) = relation_info.as_ref() {
          match &mut child_val {
            Value::Object(child_map) => {
              // Cascade Organization ID
              if !child_map.contains_key("organization_id") {
                if let Some(org_id) = obj.get("organization_id") {
                  child_map.insert("organization_id".to_string(), org_id.clone());
                }
              }
              // If child owns FK, parent provides it
              if *child_is_source {
                Self::apply_entity_relation(
                  child_map,
                  &relation.source_columns,
                  &relation.destination_columns,
                  obj,
                );
              }
            }
            Value::Array(items) => {
              for item in items.iter_mut() {
                if let Value::Object(child_map) = item {
                  if !child_map.contains_key("organization_id") {
                    if let Some(org_id) = obj.get("organization_id") {
                      child_map.insert("organization_id".to_string(), org_id.clone());
                    }
                  }
                  if *child_is_source {
                    Self::apply_entity_relation(
                      child_map,
                      &relation.source_columns,
                      &relation.destination_columns,
                      obj,
                    );
                  }
                }
              }
            }
            _ => {}
          }
        }

        // RECURSE: Merge the modified children
        let merged_val = self.merge(child_val)?;

        // Post-Process: Apply relations upwards if parent owns the FK
        if let Some((relation, parent_is_source, _child_is_source)) = relation_info {
          if parent_is_source {
            match &merged_val {
              Value::Object(merged_child_map) => {
                Self::apply_entity_relation(
                  obj,
                  &relation.source_columns,
                  &relation.destination_columns,
                  merged_child_map,
                );
              }
              Value::Array(items) if !items.is_empty() => {
                if let Value::Object(merged_child_map) = &items[0] {
                  Self::apply_entity_relation(
                    obj,
                    &relation.source_columns,
                    &relation.destination_columns,
                    merged_child_map,
                  );
                }
              }
              _ => {}
            }
          }
        }

        obj.insert(key, merged_val);
      } else {
        obj.insert(key, val);
      }
    }
    Ok(())
  }

  /// Evaluates `lk_` structures, fetches existing rows via SPI, computes `compare_entities` diff,
  /// executes UPDATE/INSERT SPI, and handles `agreego.change` auditing.
  fn stage_entity(
    &self,
    mut obj: serde_json::Map<String, Value>,
  ) -> Result<serde_json::Map<String, Value>, String> {
    let type_name = obj
      .get("type")
      .and_then(|v| v.as_str())
      .unwrap()
      .to_string();
    let type_def = self.db.types.get(&type_name).unwrap();

    // 1. Fetch Existing Entity
    let existing_entity = self.fetch_entity(&obj, type_def)?;

    // 2. Identify System Keys we don't want to diff
    let system_keys = vec![
      "id".to_string(),
      "type".to_string(),
      "organization_id".to_string(),
      "created_by".to_string(),
      "modified_by".to_string(),
      "created_at".to_string(),
      "modified_at".to_string(),
    ];

    // 3. Compare entities to find exact changes
    let changes = self.compare_entities(
      existing_entity.as_ref(),
      &obj,
      &type_def.fields,
      &system_keys,
    );

    // 4. If no changes and an entity existed, we skip
    let is_update = existing_entity.is_some();
    if is_update && changes.is_empty() {
      return Ok(obj);
    }

    // 5. Apply correct system fields
    let user_id = self.db.auth_user_id()?;
    let timestamp = self.db.timestamp()?;

    let entity_change_kind = if !is_update {
      if !obj.contains_key("id") {
        use uuid::Uuid;
        obj.insert("id".to_string(), Value::String(Uuid::new_v4().to_string()));
      }
      obj.insert("created_by".to_string(), Value::String(user_id.clone()));
      obj.insert("created_at".to_string(), Value::String(timestamp.clone()));
      obj.insert("modified_by".to_string(), Value::String(user_id.clone()));
      obj.insert("modified_at".to_string(), Value::String(timestamp.clone()));
      "create"
    } else {
      obj.insert("modified_by".to_string(), Value::String(user_id.clone()));
      obj.insert("modified_at".to_string(), Value::String(timestamp.clone()));
      "update"
    };

    // 6. Execute SQL Merges
    self.merge_entity_fields(is_update, &type_name, type_def, &changes, &obj)?;

    // 7. Fire agreego.change
    let mut complete = obj.clone();
    if is_update {
      // overlay on top of existing for complete state
      if let Some(mut existing) = existing_entity {
        for (k, v) in &obj {
          existing.insert(k.clone(), v.clone());
        }
        complete = existing;
      }
    }

    let mut notification = serde_json::Map::new();
    notification.insert("complete".to_string(), Value::Object(complete.clone()));

    let changes_val = if !is_update {
      let mut c = changes.clone();
      c.insert("type".to_string(), Value::String(type_name.clone()));
      Value::Object(c)
    } else {
      notification.insert("changes".to_string(), Value::Object(changes.clone()));
      Value::Object(changes.clone())
    };

    let change_sql = format!(
      "INSERT INTO agreego.change (changes, entity_id, id, kind, modified_at, modified_by) VALUES ({}, {}, {}, {}, {}, {})",
      Self::quote_literal(&changes_val),
      Self::quote_literal(obj.get("id").unwrap()),
      Self::quote_literal(&Value::String(uuid::Uuid::new_v4().to_string())),
      Self::quote_literal(&Value::String(entity_change_kind.to_string())),
      Self::quote_literal(&Value::String(timestamp.clone())),
      Self::quote_literal(&Value::String(user_id.clone()))
    );

    let notification_json = Value::Object(notification);
    let notify_sql = format!(
      "SELECT pg_notify('entity', {})",
      Self::quote_literal(&Value::String(notification_json.to_string()))
    );

    self
      .db
      .execute(&change_sql, None)
      .map_err(|e| format!("Executor Error in change: {:?}", e))?;
    self
      .db
      .execute(&notify_sql, None)
      .map_err(|e| format!("Executor Error in notify: {:?}", e))?;

    Ok(obj)
  }

  /// Exact replica of `agreego.compare_entities`. Takes a fetched `old` entity from the DB (if any),
  /// the `new_fields` from the JSON payload, the `fields` defined on the `Type` hierarchy, and a list of `system_keys`.
  /// Returns a clean JSON object containing ONLY the modified keys, or an empty map if No-Op.
  fn compare_entities(
    &self,
    fetched_entity: Option<&serde_json::Map<String, Value>>,
    new_fields: &serde_json::Map<String, Value>,
    type_fields: &[String],
    system_keys: &[String],
  ) -> serde_json::Map<String, Value> {
    let mut changes = serde_json::Map::new();

    for (key, new_val) in new_fields {
      // 1. Skip if key is not part of the Type's total field schema mapping
      if !type_fields.contains(key) {
        continue;
      }
      // 2. Skip strictly managed system audit keys
      if system_keys.contains(key) {
        continue;
      }

      match fetched_entity {
        // 3a. If no old entity, every valid field is a new "change"
        None => {
          changes.insert(key.clone(), new_val.clone());
        }
        // 3b. If old entity exists, strictly compare the values
        Some(old_map) => {
          let old_val = old_map.get(key).unwrap_or(&Value::Null);
          if new_val != old_val {
            changes.insert(key.clone(), new_val.clone());
          }
        }
      }
    }

    changes
  }

  /// Exact replica of `agreego.reduce_entity_relations`. Resolves Ambiguous Graph paths
  /// down to a single distinct FK relationship path based on prefix rules.
  fn reduce_entity_relations(
    &self,
    mut matching_relations: Vec<crate::database::relation::Relation>,
    relative: &serde_json::Map<String, Value>,
    relation_name: &str,
  ) -> Result<Option<crate::database::relation::Relation>, String> {
    // 0 or 1 relations is an immediate fast-path resolution
    if matching_relations.is_empty() {
      return Ok(None);
    }
    if matching_relations.len() == 1 {
      return Ok(Some(matching_relations.pop().unwrap()));
    }

    // Step 1: Check for exact prefix match with the relation_name pointer
    let exact_match: Vec<_> = matching_relations
      .iter()
      .filter(|r| r.prefix.as_deref() == Some(relation_name))
      .cloned()
      .collect();
    if exact_match.len() == 1 {
      return Ok(Some(exact_match.into_iter().next().unwrap()));
    }

    // Step 2: Inverse filter - Remove any relations where their configured prefix IS found
    // inside the actual payload data on `relative`
    matching_relations.retain(|r| {
      if let Some(prefix) = &r.prefix {
        // If the prefix exists as a key in the relative JSON payload, we KEEP iter
        // (Wait, actually the SQL is `WHERE NOT EXISTS (select mr.prefix where relative ? mr.prefix)`
        // Translating: Keep relation R if its prefix is NOT matched in the payload
        !relative.contains_key(prefix)
      } else {
        true // No prefix means we keep it by default
      }
    });

    if matching_relations.len() == 1 {
      Ok(Some(matching_relations.pop().unwrap()))
    } else {
      let constraints: Vec<_> = matching_relations
        .iter()
        .map(|r| r.constraint.clone())
        .collect();
      Err(format!(
        "AMBIGUOUS_TYPE_RELATIONS: Could not reduce ambiguous type relations: {}",
        constraints.join(", ")
      ))
    }
  }

  /// Exact replica of `agreego.get_entity_relation`. Given two entities (`entity` and `relative`) and the JSON key linking them,
  /// it searches the Database graphs for a concrete FK constraint.
  fn get_entity_relation(
    &self,
    _entity: &serde_json::Map<String, Value>,
    entity_type: &crate::database::r#type::Type,
    relative: &serde_json::Map<String, Value>,
    relation_name: &str,
  ) -> Result<Option<crate::database::relation::Relation>, String> {
    let relative_type_name = relative.get("type").and_then(|v| v.as_str()).unwrap_or("");
    let relative_type = match self.db.types.get(relative_type_name) {
      Some(t) => t,
      None => return Ok(None),
    };

    let mut relative_relations: Vec<crate::database::relation::Relation> = Vec::new();

    // 1. Look for direct relationships first
    for r in self.db.relations.values() {
      if r.source_type != "entity" && r.destination_type != "entity" {
        let condition1 = relative_type.hierarchy.contains(&r.source_type)
          && entity_type.hierarchy.contains(&r.destination_type);
        let condition2 = entity_type.hierarchy.contains(&r.source_type)
          && relative_type.hierarchy.contains(&r.destination_type);

        if condition1 || condition2 {
          relative_relations.push(r.clone());
        }
      }
    }

    let mut relative_relation =
      self.reduce_entity_relations(relative_relations, relative, relation_name)?;

    // 2. Look for polymorphic relationships if no direct relationship is found
    if relative_relation.is_none() {
      let mut poly_relations: Vec<crate::database::relation::Relation> = Vec::new();
      for r in self.db.relations.values() {
        if r.destination_type == "entity" {
          let condition1 = relative_type.hierarchy.contains(&r.source_type);
          let condition2 = entity_type.hierarchy.contains(&r.source_type);

          if condition1 || condition2 {
            poly_relations.push(r.clone());
          }
        }
      }
      relative_relation = self.reduce_entity_relations(poly_relations, relative, relation_name)?;
    }

    Ok(relative_relation)
  }

  /// Exact replica of `agreego.apply_entity_relation`. Syncs FK column values from the destination to the source.
  fn apply_entity_relation(
    source_entity: &mut serde_json::Map<String, Value>,
    source_columns: &[String],
    destination_columns: &[String],
    destination_entity: &serde_json::Map<String, Value>,
  ) {
    if source_columns.len() != destination_columns.len() {
      // In theory, validation should prevent this, but fail gracefully/ignore if lengths diverge.
      return;
    }
    for i in 0..source_columns.len() {
      let dest_val = destination_entity
        .get(&destination_columns[i])
        .unwrap_or(&Value::Null)
        .clone();
      source_entity.insert(source_columns[i].clone(), dest_val);
    }
  }

  /// Exact replica of `agreego.fetch_entity`. Dynamically constructs a `SELECT to_jsonb(t1.*) || to_jsonb(t2.*)`
  /// based on the Type hierarchy and available `id` or `lookup_fields` presence.
  fn fetch_entity(
    &self,
    entity_fields: &serde_json::Map<String, Value>,
    entity_type: &crate::database::r#type::Type,
  ) -> Result<Option<serde_json::Map<String, Value>>, String> {
    let id_val = entity_fields.get("id");
    let entity_type_name = entity_type.name.as_str();

    // Check if all required lookup keys are PRESENT (value can be anything, including NULL)
    let lookup_complete = if entity_type.lookup_fields.is_empty() {
      false
    } else {
      entity_type
        .lookup_fields
        .iter()
        .all(|f| entity_fields.contains_key(f))
    };

    if id_val.is_none() && !lookup_complete {
      return Ok(None);
    }

    // Build or Retrieve Cached Select/Join clauses
    let fetch_sql_template = if let Some(cached) = self.cache.get(entity_type_name) {
      cached
    } else {
      let mut select_list = String::from("to_jsonb(t1.*)");
      let mut join_clauses = format!("FROM agreego.\"{}\" t1", entity_type.hierarchy[0]);

      for (i, table_name) in entity_type.hierarchy.iter().enumerate().skip(1) {
        let t_alias = format!("t{}", i + 1);
        join_clauses.push_str(&format!(
          " LEFT JOIN agreego.\"{}\" {} ON {}.id = t1.id",
          table_name, t_alias, t_alias
        ));
        select_list.push_str(&format!(" || to_jsonb({}.*)", t_alias));
      }

      let template = format!("SELECT {} {}", select_list, join_clauses);
      self
        .cache
        .insert(entity_type_name.to_string(), template.clone());
      template
    };

    // Build WHERE Clauses
    let mut id_condition = None;
    if let Some(id) = id_val {
      id_condition = Some(format!("t1.id = {}", Self::quote_literal(id)));
    }

    let mut lookup_condition = None;
    if lookup_complete {
      let mut lookup_predicates = Vec::new();
      for column in &entity_type.lookup_fields {
        let val = entity_fields.get(column).unwrap_or(&Value::Null);
        if column == "type" {
          lookup_predicates.push(format!("t1.\"{}\" = {}", column, Self::quote_literal(val)));
        } else {
          if val.as_str() == Some("") || val.is_null() {
            lookup_predicates.push(format!("\"{}\" IS NULL", column));
          } else {
            lookup_predicates.push(format!("\"{}\" = {}", column, Self::quote_literal(val)));
          }
        }
      }
      lookup_condition = Some(lookup_predicates.join(" AND "));
    }

    // Determine final WHERE clause based on available conditions
    let where_clause = match (id_condition, lookup_condition) {
      (Some(id_cond), Some(lookup_cond)) => format!("WHERE ({}) OR ({})", id_cond, lookup_cond),
      (Some(id_cond), None) => format!("WHERE {}", id_cond),
      (None, Some(lookup_cond)) => format!("WHERE {}", lookup_cond),
      (None, None) => return Ok(None),
    };

    // Construct Final Query
    let fetch_sql = format!("{} {}", fetch_sql_template, where_clause);

    // Execute and Return Result via Database Executor
    let fetched = match self.db.query(&fetch_sql, None) {
      Ok(Value::Array(table)) => {
        if table.len() > 1 {
          Err(format!(
            "TOO_MANY_LOOKUP_ROWS: Lookup for {} found too many existing rows",
            entity_type_name
          ))
        } else if table.is_empty() {
          Ok(None)
        } else {
          let row = table.first().unwrap();
          match row {
            Value::Object(map) => Ok(Some(map.clone())),
            other => Err(format!(
              "Expected fetch_entity to return JSON object, got: {:?}",
              other
            )),
          }
        }
      }
      Ok(other) => Err(format!(
        "Expected array from query in fetch_entity, got: {:?}",
        other
      )),
      Err(e) => Err(format!("SPI error in fetch_entity: {:?}", e)),
    }?;

    Ok(fetched)
  }

  /// Exact replica of `agreego.merge_entity_fields`. Issues an INSERT or UPDATE per table
  /// in the Type's hierarchy, filtering out keys that don't belong to the specific table block.
  fn merge_entity_fields(
    &self,
    is_update: bool,
    entity_type_name: &str,
    entity_type: &crate::database::r#type::Type,
    changes: &serde_json::Map<String, Value>,
    full_entity: &serde_json::Map<String, Value>,
  ) -> Result<(), String> {
    let id_str = match full_entity.get("id").and_then(|v| v.as_str()) {
      Some(id) => id,
      None => return Err("Missing 'id' for merge execution".to_string()),
    };

    let grouped_fields = match &entity_type.grouped_fields {
      Some(Value::Object(map)) => map,
      _ => {
        return Err(format!(
          "Grouped fields missing for type {}",
          entity_type_name
        ));
      }
    };

    for table_name in &entity_type.hierarchy {
      // get the fields for this specific table (from grouped_fields)
      let table_fields = match grouped_fields.get(table_name).and_then(|v| v.as_array()) {
        Some(arr) => arr
          .iter()
          .filter_map(|v| v.as_str().map(|s| s.to_string()))
          .collect::<Vec<_>>(),
        None => continue,
      };

      let mut my_changes = Vec::new();
      for field in &table_fields {
        if changes.contains_key(field) || (!is_update && full_entity.contains_key(field)) {
          // For inserts we want all provided fields. For updates we only want changes.
          my_changes.push(field.clone());
        }
      }

      if is_update {
        if my_changes.is_empty() {
          continue;
        }
        let mut set_clauses = Vec::new();
        for field in &my_changes {
          let val = changes.get(field).unwrap();
          set_clauses.push(format!("\"{}\" = {}", field, Self::quote_literal(val)));
        }
        let sql = format!(
          "UPDATE agreego.\"{}\" SET {} WHERE id = {}",
          table_name,
          set_clauses.join(", "),
          Self::quote_literal(&Value::String(id_str.to_string()))
        );
        self
          .db
          .execute(&sql, None)
          .map_err(|e| format!("SPI Error in UPDATE: {:?}", e))?;
      } else {
        // INSERT
        let mut columns = Vec::new();
        let mut values = Vec::new();

        for field in &my_changes {
          columns.push(format!("\"{}\"", field));
          let val = full_entity.get(field).unwrap();
          values.push(Self::quote_literal(val));
        }

        // Ensure 'id' and 'type' are present if required by this specific table schema chunk
        if !columns.contains(&"\"id\"".to_string()) && table_fields.contains(&"id".to_string()) {
          columns.push("\"id\"".to_string());
          values.push(Self::quote_literal(&Value::String(id_str.to_string())));
        }
        if !columns.contains(&"\"type\"".to_string()) && table_fields.contains(&"type".to_string())
        {
          columns.push("\"type\"".to_string());
          values.push(Self::quote_literal(&Value::String(
            entity_type_name.to_string(),
          )));
        }

        if columns.is_empty() {
          continue;
        }

        let sql = format!(
          "INSERT INTO agreego.\"{}\" ({}) VALUES ({})",
          table_name,
          columns.join(", "),
          values.join(", ")
        );
        self
          .db
          .execute(&sql, None)
          .map_err(|e| format!("SPI Error in INSERT: {:?}", e))?;
      }
    }
    Ok(())
  }

  /// Helper to emulate Postgres `quote_literal`
  fn quote_literal(val: &Value) -> String {
    match val {
      Value::Null => "NULL".to_string(),
      Value::Bool(b) => {
        if *b {
          "true".to_string()
        } else {
          "false".to_string()
        }
      }
      Value::Number(n) => n.to_string(),
      Value::String(s) => format!("'{}'", s.replace('\'', "''")),
      _ => format!(
        "'{}'",
        serde_json::to_string(val).unwrap().replace('\'', "''")
      ),
    }
  }
}