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

use thiserror::Error;
use offline_web_model::Reference;
use sqlx::{Pool, Row, Sqlite, SqlitePool};

// Schema version constants
const CURRENT_SCHEMA_VERSION: i32 = 1;
const INITIAL_SCHEMA_VERSION: i32 = 0;

pub struct SqliteReferenceStore {
    pool: Pool<Sqlite>,
}

#[derive(Error, Debug)]
pub enum StoreError {
    #[error("No such reference")]
    NoSuchReference,
    #[error("No such content address")]
    NoSuchContentAddress,
    #[error("Unknown Storage Error: {0:?}")]
    StorageError(Box<dyn std::error::Error>),
}

#[allow(async_fn_in_trait)]
pub trait ReferenceStore {
    async fn get_reference(&self, id: &str) -> Result<Reference, StoreError>;
    
    async fn get_content_for_reference(&self, reference: Reference) -> Result<String, StoreError>;

    async fn get_graph(&self, root_name: &str) -> Result<Vec<Reference>, StoreError>;
}

impl SqliteReferenceStore {
    pub async fn new(database_url: &str) -> Result<Self, StoreError> {
        let pool = SqlitePool::connect(database_url)
            .await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;
        
        let store = Self { pool };
        
        // Check current schema version and migrate if necessary
        let current_version = store.get_current_schema_version().await?;
        if current_version != CURRENT_SCHEMA_VERSION {
            store.migrate_schema(current_version, CURRENT_SCHEMA_VERSION).await?;
        }

        Ok(store)
    }

    async fn get_current_schema_version(&self) -> Result<i32, StoreError> {
        // First, ensure the schema_version table exists
        sqlx::query(
            r#"
            CREATE TABLE IF NOT EXISTS schema_version (
                version INTEGER PRIMARY KEY,
                applied_at DATETIME DEFAULT CURRENT_TIMESTAMP,
                description TEXT
            )
            "#,
        )
        .execute(&self.pool)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Get the current version
        let row = sqlx::query(
            r#"
            SELECT version FROM schema_version ORDER BY version DESC LIMIT 1
            "#,
        )
        .fetch_optional(&self.pool)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        match row {
            Some(row) => {
                let version: i32 = row.get("version");
                Ok(version)
            }
            None => {
                // No version found, this is a fresh database
                Ok(INITIAL_SCHEMA_VERSION)
            }
        }
    }

    async fn migrate_schema(&self, from_version: i32, to_version: i32) -> Result<(), StoreError> {
        if from_version == to_version {
            return Ok(());
        }

        if from_version > to_version {
            return Err(StoreError::StorageError(
                "Downward migrations not currently supported".into()
            ));
        }

        // Use a transaction for the entire migration process
        let mut tx = self.pool.begin().await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Apply migrations step by step
        let mut current_version = from_version;
        while current_version < to_version {
            match current_version {
                0 => {
                    // Migration from version 0 to 1: Initial schema setup
                    self.migrate_to_v1(&mut tx).await?;
                    current_version = 1;
                }
                _ => {
                    return Err(StoreError::StorageError(
                        format!("Unknown migration path from version {}", current_version).into()
                    ));
                }
            }
        }

        // Commit all migrations
        tx.commit().await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        Ok(())
    }

    async fn migrate_to_v1(&self, tx: &mut sqlx::Transaction<'_, Sqlite>) -> Result<(), StoreError> {
        // Create the main application tables
        sqlx::query(
            r#"
            CREATE TABLE IF NOT EXISTS ref_entries (
                id TEXT PRIMARY KEY,
                content_address TEXT,
                name TEXT NOT NULL UNIQUE
            )
            "#,
        )
        .execute(&mut **tx)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        sqlx::query(
            r#"
            CREATE TABLE IF NOT EXISTS ref_dependencies (
                parent_id TEXT NOT NULL,
                dependent_id TEXT NOT NULL,
                PRIMARY KEY (parent_id, dependent_id),
                FOREIGN KEY (parent_id) REFERENCES ref_entries(id),
                FOREIGN KEY (dependent_id) REFERENCES ref_entries(id)
            )
            "#,
        )
        .execute(&mut **tx)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        sqlx::query(
            r#"
            CREATE TABLE IF NOT EXISTS content_store (
                content_address TEXT PRIMARY KEY,
                content BLOB NOT NULL
            )
            "#,
        )
        .execute(&mut **tx)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Record the schema version
        sqlx::query(
            r#"
            INSERT OR REPLACE INTO schema_version (version, description)
            VALUES (?, ?)
            "#,
        )
        .bind(1)
        .bind("Initial schema with ref_entries, ref_dependencies, and content_store tables")
        .execute(&mut **tx)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        Ok(())
    }

    pub async fn store_reference(&self, reference: &Reference) -> Result<(), StoreError> {
        // Use a transaction to ensure atomicity
        let mut tx = self.pool.begin().await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Insert or update the reference
        sqlx::query(
            r#"
            INSERT OR REPLACE INTO ref_entries (id, content_address, name)
            VALUES (?, ?, ?)
            "#,
        )
        .bind(&reference.id)
        .bind(&reference.content_address)
        .bind(&reference.name)
        .execute(&mut *tx)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Delete existing dependencies for this reference
        sqlx::query(
            r#"
            DELETE FROM ref_dependencies 
            WHERE parent_id = ?
            "#,
        )
        .bind(&reference.id)
        .execute(&mut *tx)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Insert new dependencies
        for dependent in &reference.dependents {
            sqlx::query(
                r#"
                INSERT INTO ref_dependencies (parent_id, dependent_id)
                VALUES (?, ?)
                "#,
            )
            .bind(&reference.id)
            .bind(&dependent.id)
            .execute(&mut *tx)
            .await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;
        }

        // Commit the transaction
        tx.commit().await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        Ok(())
    }

    pub async fn store_content(&self, content_address: &str, content: &[u8]) -> Result<(), StoreError> {
        sqlx::query(
            r#"
            INSERT OR REPLACE INTO content_store (content_address, content)
            VALUES (?, ?)
            "#,
        )
        .bind(content_address)
        .bind(content)
        .execute(&self.pool)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        Ok(())
    }
}

impl ReferenceStore for SqliteReferenceStore {
    async fn get_reference(&self, id: &str) -> Result<Reference, StoreError> {
        // First, get the basic reference information
        let row = sqlx::query(
            r#"
            SELECT id, content_address, name
            FROM ref_entries
            WHERE id = ?
            "#,
        )
        .bind(id)
        .fetch_optional(&self.pool)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        match row {
            Some(row) => {
                let id: String = row.get("id");
                let content_address: Option<String> = row.get("content_address");
                let name: String = row.get("name");

                // Get the dependents by recursively fetching them
                let dependents = self.get_dependents(&id).await?;

                Ok(Reference {
                    id,
                    content_address,
                    name,
                    dependents,
                })
            }
            None => Err(StoreError::NoSuchReference),
        }
    }

    async fn get_content_for_reference(&self, reference: Reference) -> Result<String, StoreError> {
        if let Some(content_address) = &reference.content_address {
            let row = sqlx::query(
                r#"
                SELECT content
                FROM content_store
                WHERE content_address = ?
                "#,
            )
            .bind(content_address)
            .fetch_optional(&self.pool)
            .await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;

            match row {
                Some(row) => {
                    let content: Vec<u8> = row.get("content");
                    String::from_utf8(content)
                        .map_err(|e| StoreError::StorageError(Box::new(e)))
                }
                None => Err(StoreError::NoSuchContentAddress),
            }
        } else {
            Err(StoreError::NoSuchContentAddress)
        }
    }

    async fn get_graph(&self, root_name: &str) -> Result<Vec<Reference>, StoreError> {
        let mut visited = std::collections::HashSet::new();
        let mut result = Vec::new();
        let mut queue = std::collections::VecDeque::new();
        
        // Start with the root name
        queue.push_back(root_name.to_string());
        
        while let Some(current_name) = queue.pop_front() {
            if visited.contains(&current_name) {
                continue;
            }
            
            visited.insert(current_name.clone());
            
            // Get the reference by name
            let row = sqlx::query(
                r#"
                SELECT id, content_address, name
                FROM ref_entries
                WHERE name = ?
                "#,
            )
            .bind(&current_name)
            .fetch_optional(&self.pool)
            .await
            .map_err(|e| StoreError::StorageError(Box::new(e)))?;

            if let Some(row) = row {
                let id: String = row.get("id");
                let content_address: Option<String> = row.get("content_address");
                let name: String = row.get("name");

                // Get dependents for this reference
                let dependents = self.get_dependents(&id).await?;

                let reference = Reference {
                    id,
                    content_address,
                    name,
                    dependents: dependents.clone(),
                };

                result.push(reference);

                // Add all dependent names to the queue for processing
                for dependent in dependents {
                    if !visited.contains(&dependent.name) {
                        queue.push_back(dependent.name.clone());
                    }
                }
            }
        }

        Ok(result)
    }
}

impl SqliteReferenceStore {
    async fn get_dependents(&self, parent_id: &str) -> Result<Vec<Arc<Reference>>, StoreError> {
        // Use a CTE (Common Table Expression) to get the entire dependency tree in one query
        let rows = sqlx::query(
            r#"
            WITH RECURSIVE dependency_tree AS (
                -- Base case: direct dependents of the parent
                SELECT r.id, r.content_address, r.name, rd.parent_id, 0 as depth
                FROM ref_entries r
                JOIN ref_dependencies rd ON r.id = rd.dependent_id
                WHERE rd.parent_id = ?
                
                UNION ALL
                
                -- Recursive case: dependents of dependents
                SELECT r.id, r.content_address, r.name, rd.parent_id, dt.depth + 1
                FROM ref_entries r
                JOIN ref_dependencies rd ON r.id = rd.dependent_id
                JOIN dependency_tree dt ON rd.parent_id = dt.id
                WHERE dt.depth < 100  -- Prevent infinite recursion
            )
            SELECT id, content_address, name, parent_id, depth
            FROM dependency_tree
            ORDER BY depth, name
            "#,
        )
        .bind(parent_id)
        .fetch_all(&self.pool)
        .await
        .map_err(|e| StoreError::StorageError(Box::new(e)))?;

        // Build the dependency tree iteratively
        let mut reference_map: HashMap<String, Reference> = HashMap::new();
        let mut children_map: HashMap<String, Vec<String>> = HashMap::new();

        // First pass: create all references and build the children map
        for row in &rows {
            let id: String = row.get("id");
            let content_address: Option<String> = row.get("content_address");
            let name: String = row.get("name");
            let parent_id: String = row.get("parent_id");

            let reference = Reference {
                id: id.clone(),
                content_address,
                name,
                dependents: Vec::new(), // Will be filled in second pass
            };

            reference_map.insert(id.clone(), reference);
            children_map.entry(parent_id).or_default().push(id);
        }

        // Second pass: build the dependency tree from bottom up (highest depth first)
        let mut depth_groups: BTreeMap<i32, Vec<String>> = BTreeMap::new();
        for row in &rows {
            let id: String = row.get("id");
            let depth: i32 = row.get("depth");
            depth_groups.entry(depth).or_default().push(id);
        }

        // Process from highest depth to lowest (leaves to roots)
        for (_depth, ids) in depth_groups.iter().rev() {
            for id in ids {
                if let Some(children) = children_map.get(id).cloned() {
                    let child_references: Vec<Arc<Reference>> = children
                        .iter()
                        .filter_map(|child_id| reference_map.get(child_id).map(|r| Arc::new(r.clone())))
                        .collect();
                    
                    if let Some(reference) = reference_map.get_mut(id) {
                        reference.dependents = child_references;
                    }
                }
            }
        }

        // Return the direct children of the parent
        let empty_vec = Vec::new();
        let direct_children = children_map.get(parent_id).unwrap_or(&empty_vec);
        let result = direct_children
            .iter()
            .filter_map(|child_id| reference_map.get(child_id).map(|r| Arc::new(r.clone())))
            .collect();

        Ok(result)
    }

}

#[cfg(test)]
mod integration_tests;