//! AWS Pricing CRUD Lambda
//!
//! This Lambda function provides centralized CRUD operations for AWS pricing data,
//! serving as the single source of truth for pricing operations across the Pathfinder
//! application. It handles both HTTP API Gateway requests and MCP (Model Context Protocol)
//! requests for pricing data stored in DynamoDB.
//!
//! # Operations
//! - Get: Retrieve pricing from cache
//! - Put: Store pricing data in cache
//! - ListCommon: Query most accessed instances for cache refresh
//! - IncrementAccess: Track instance access patterns
//!
//! # Data Flow
//! ```text
//! tool-pricing-query (MCP)        }
//! enrichment-server-pricing       } → crud-pricing → DynamoDB
//! tool-pricing-refresh            }
//! ```

mod db;
mod models;

use aws_config::BehaviorVersion;
use aws_sdk_dynamodb::Client as DynamoDbClient;
use lambda_runtime::{service_fn, Error, LambdaEvent};
use serde_json::Value;
use std::env;
use tracing::{error, info};

use crate::models::{PricingOperation, PricingRequest, PricingResponse, PricingType};

/// Main entry point for the Lambda function
///
/// Initializes logging and starts the Lambda runtime with the function handler.
///
/// # Returns
/// Returns Ok(()) on successful initialization, or Error if startup fails
#[tokio::main]
async fn main() -> Result<(), Error> {
    tracing_subscriber::fmt()
        .with_max_level(tracing::Level::INFO)
        .with_target(false)
        .without_time()
        .json()
        .init();

    lambda_runtime::run(service_fn(function_handler)).await
}

/// Lambda function handler
///
/// Routes incoming requests to either HTTP or MCP handlers based on request structure.
/// Determines request type by checking for API Gateway HTTP-specific fields.
///
/// # Arguments
/// * `event` - Lambda event containing the request payload and context
///
/// # Returns
/// Returns the serialized response as JSON Value
///
/// # Errors
/// Returns Error if request parsing or processing fails
async fn function_handler(event: LambdaEvent<Value>) -> Result<Value, Error> {
    let (payload, _context) = event.into_parts();

    info!("Received pricing request: {:?}", payload);

    // Load AWS config and create clients
    let config = aws_config::load_defaults(BehaviorVersion::latest()).await;
    let dynamodb_client = DynamoDbClient::new(&config);
    let table_name = env::var("TABLE_NAME").unwrap_or_else(|_| "pathfinder-dev-pricing".to_string());

    // Determine request source by checking for HTTP-specific fields
    let is_http_v2 = payload
        .get("requestContext")
        .and_then(|rc| rc.get("http"))
        .and_then(|http| http.get("method"))
        .is_some();

    if is_http_v2 {
        // Handle HTTP request from API Gateway
        handle_http_request(payload, &dynamodb_client, &table_name).await
    } else {
        // Handle MCP request
        handle_mcp_request(payload, &dynamodb_client, &table_name).await
    }
}

/// Handles HTTP requests from API Gateway
///
/// Processes HTTP GET requests for pricing data, extracting the instance type
/// from path parameters and returning formatted HTTP responses.
///
/// # Arguments
/// * `payload` - API Gateway HTTP request payload
/// * `dynamodb_client` - DynamoDB client for data access
/// * `table_name` - Name of the DynamoDB pricing table
///
/// # Returns
/// Returns HTTP response with status code, headers, and body
///
/// # Errors
/// Returns Error if instanceType path parameter is missing or DynamoDB query fails
async fn handle_http_request(
    payload: Value,
    dynamodb_client: &DynamoDbClient,
    table_name: &str,
) -> Result<Value, Error> {
    // Extract path parameters
    let instance_type = payload
        .get("pathParameters")
        .and_then(|p| p.get("instanceType"))
        .and_then(|it| it.as_str())
        .ok_or("Missing instanceType in path")?;

    info!("HTTP GET /pricing/{}", instance_type);

    // Fetch pricing for the instance type (use defaults for HTTP requests)
    let result = db::get_pricing(
        dynamodb_client,
        table_name,
        instance_type,
        "us-east-1",
        &PricingType::Retail,
        None
    ).await;

    match result {
        Ok(Some(pricing)) => {
            let response = serde_json::json!({
                "statusCode": 200,
                "headers": {
                    "Content-Type": "application/json"
                },
                "body": serde_json::to_string(&pricing)?
            });
            Ok(response)
        }
        Ok(None) => {
            info!("Pricing not found for: {}", instance_type);
            let response = serde_json::json!({
                "statusCode": 404,
                "headers": {
                    "Content-Type": "application/json"
                },
                "body": serde_json::to_string(&serde_json::json!({
                    "error": "Pricing not found"
                }))?
            });
            Ok(response)
        }
        Err(e) => {
            error!("Failed to fetch pricing: {}", e);
            let response = serde_json::json!({
                "statusCode": 500,
                "headers": {
                    "Content-Type": "application/json"
                },
                "body": serde_json::to_string(&serde_json::json!({
                    "error": e
                }))?
            });
            Ok(response)
        }
    }
}

/// Handles MCP (Model Context Protocol) requests
///
/// Processes structured MCP requests containing pricing operations,
/// routes to appropriate handler, and returns structured responses.
///
/// # Arguments
/// * `payload` - MCP request payload containing operation details
/// * `dynamodb_client` - DynamoDB client for data access
/// * `table_name` - Name of the DynamoDB pricing table
///
/// # Returns
/// Returns structured PricingResponse serialized as JSON Value
///
/// # Errors
/// Returns Error if request parsing fails or operation execution fails
async fn handle_mcp_request(
    payload: Value,
    dynamodb_client: &DynamoDbClient,
    table_name: &str,
) -> Result<Value, Error> {
    // Parse MCP request
    let request: PricingRequest = match serde_json::from_value(payload) {
        Ok(req) => req,
        Err(e) => {
            error!("Invalid request: {}", e);
            let response = PricingResponse::error(400, &format!("Invalid request: {}", e));
            return Ok(serde_json::to_value(response)?);
        }
    };

    // Route operation
    let result = handle_operation(
        request.operation,
        dynamodb_client,
        table_name,
    )
    .await;

    let response = match result {
        Ok(data) => PricingResponse::success(data),
        Err(e) => {
            error!("Operation failed: {}", e);
            PricingResponse::error(500, &e)
        }
    };

    Ok(serde_json::to_value(response)?)
}

/// Routes pricing operations to appropriate handlers
///
/// Dispatches each operation type (Get, Put, ListCommon, IncrementAccess) to its
/// specific handler function and returns the result as JSON.
///
/// # Arguments
/// * `operation` - The pricing operation to execute
/// * `dynamodb_client` - DynamoDB client for data access
/// * `table_name` - Name of the DynamoDB pricing table
///
/// # Returns
/// Returns operation result serialized as JSON Value
///
/// # Errors
/// Returns error message string if operation fails
async fn handle_operation(
    operation: PricingOperation,
    dynamodb_client: &DynamoDbClient,
    table_name: &str,
) -> Result<Value, String> {
    match operation {
        PricingOperation::Get {
            instance_type,
            region,
            pricing_type,
            aws_account_id,
            fetch_if_missing: _,
        } => {
            info!("Operation: Get (type={:?})", pricing_type);

            // Check cache
            let cached = db::get_pricing(
                dynamodb_client,
                table_name,
                &instance_type,
                &region,
                &pricing_type,
                aws_account_id.as_deref(),
            )
            .await?;

            match cached {
                Some(mut pricing) => {
                    // Cache hit - increment access count asynchronously
                    let client = dynamodb_client.clone();
                    let table = table_name.to_string();
                    let inst = instance_type.clone();
                    let reg = region.clone();
                    let pt = pricing_type.clone();
                    let acc_id = aws_account_id.clone();

                    tokio::spawn(async move {
                        let _ = db::increment_access_count(
                            &client,
                            &table,
                            &inst,
                            &reg,
                            &pt,
                            acc_id.as_deref(),
                        )
                        .await;
                    });

                    pricing.access_count += 1; // Show incremented count in response
                    Ok(serde_json::json!({
                        "pricing": pricing,
                        "cacheStatus": "hit"
                    }))
                }
                None => {
                    Err("Pricing not found in cache".to_string())
                }
            }
        }

        PricingOperation::Put {
            instance_type,
            region,
            pricing_type,
            pricing_data,
        } => {
            info!("Operation: Put ({} in {})", instance_type, region);

            db::put_pricing(dynamodb_client, table_name, &pricing_data).await?;

            Ok(serde_json::json!({
                "success": true,
                "instanceType": instance_type,
                "region": region,
                "pricingType": pricing_type
            }))
        }

        PricingOperation::ListCommon {
            limit,
            min_access_count,
        } => {
            info!("Operation: ListCommon (limit={}, min_access={})", limit, min_access_count.unwrap_or(0));

            let common = db::query_most_accessed(dynamodb_client, table_name, limit, min_access_count).await?;

            Ok(serde_json::json!({
                "instances": common,
                "count": common.len()
            }))
        }

        PricingOperation::IncrementAccess {
            instance_type,
            region,
        } => {
            info!("Operation: IncrementAccess ({} in {})", instance_type, region);

            // Default to retail for access counting
            db::increment_access_count(
                dynamodb_client,
                table_name,
                &instance_type,
                &region,
                &PricingType::Retail,
                None,
            )
            .await?;

            Ok(serde_json::json!({
                "success": true,
                "instanceType": instance_type,
                "region": region
            }))
        }
    }
}

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

    #[test]
    fn test_http_request_detection() {
        // Test that HTTP v2 request is detected correctly
        let http_payload = json!({
            "requestContext": {
                "http": {
                    "method": "GET",
                    "path": "/pricing/m6g.xlarge"
                }
            },
            "pathParameters": {
                "instanceType": "m6g.xlarge"
            }
        });

        let is_http = http_payload
            .get("requestContext")
            .and_then(|rc| rc.get("http"))
            .and_then(|http| http.get("method"))
            .is_some();

        assert!(is_http);
    }

    #[test]
    fn test_mcp_request_detection() {
        // Test that MCP request is detected correctly (no HTTP fields)
        let mcp_payload = json!({
            "operation": {
                "type": "get",
                "instanceType": "m6g.xlarge",
                "region": "us-east-1",
                "pricingType": "retail"
            }
        });

        let is_http = mcp_payload
            .get("requestContext")
            .and_then(|rc| rc.get("http"))
            .and_then(|http| http.get("method"))
            .is_some();

        assert!(!is_http);
    }

    #[test]
    fn test_path_parameter_extraction() {
        let payload = json!({
            "pathParameters": {
                "instanceType": "t3.medium"
            }
        });

        let instance_type = payload
            .get("pathParameters")
            .and_then(|p| p.get("instanceType"))
            .and_then(|it| it.as_str());

        assert_eq!(instance_type, Some("t3.medium"));
    }

    #[test]
    fn test_missing_path_parameter() {
        let payload = json!({
            "pathParameters": {}
        });

        let instance_type = payload
            .get("pathParameters")
            .and_then(|p| p.get("instanceType"))
            .and_then(|it| it.as_str());

        assert_eq!(instance_type, None);
    }

    #[test]
    fn test_mcp_request_parsing_valid() {
        let payload = json!({
            "operation": {
                "type": "get",
                "instanceType": "m6g.xlarge",
                "region": "us-east-1",
                "pricingType": "retail"
            }
        });

        let result: Result<PricingRequest, _> = serde_json::from_value(payload);
        assert!(result.is_ok());
    }

    #[test]
    fn test_mcp_request_parsing_invalid() {
        let payload = json!({
            "operation": {
                "type": "invalid_operation"
            }
        });

        let result: Result<PricingRequest, _> = serde_json::from_value(payload);
        assert!(result.is_err());
    }

    #[test]
    fn test_operation_type_extraction() {
        let get_op = json!({
            "operation": {
                "type": "get",
                "instanceType": "m6g.xlarge",
                "region": "us-east-1",
                "pricingType": "retail"
            }
        });

        let request: PricingRequest = serde_json::from_value(get_op).unwrap();
        assert!(matches!(request.operation, PricingOperation::Get { .. }));

        let list_op = json!({
            "operation": {
                "type": "listCommon",
                "limit": 100
            }
        });

        let request: PricingRequest = serde_json::from_value(list_op).unwrap();
        assert!(matches!(request.operation, PricingOperation::ListCommon { .. }));

        let inc_op = json!({
            "operation": {
                "type": "incrementAccess",
                "instanceType": "t3.medium",
                "region": "us-east-1"
            }
        });

        let request: PricingRequest = serde_json::from_value(inc_op).unwrap();
        assert!(matches!(request.operation, PricingOperation::IncrementAccess { .. }));
    }
}