package internal

import (
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"runtime/debug"
)

// encode writes a JSON-encoded response to the provided http.ResponseWriter.
//
// Parameters:
// - w: The http.ResponseWriter where the response will be written.
// - r: The *http.Request associated with the response. (Unused in this function but could be relevant for context.)
// - status: The HTTP status code to send with the response.
// - v: The value to encode and send as the JSON response. Can be of any type.
//
// Returns:
// - An error if the JSON encoding or writing to the ResponseWriter fails, otherwise nil.
func encode[T any](w http.ResponseWriter, r *http.Request, status int, v T) error {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(v); err != nil {
		return fmt.Errorf("encode json: %w", err)
	}
	return nil
}

// decode reads and decodes a JSON-encoded request body into a value of the specified type.
//
// Parameters:
// - r: The *http.Request containing the JSON-encoded body to decode.
//
// Returns:
// - The decoded value of type T.
// - An error if decoding fails, or if the body contains invalid JSON.
func decode[T any](r *http.Request) (T, error) {
	var v T
	if err := json.NewDecoder(r.Body).Decode(&v); err != nil {
		return v, fmt.Errorf("decode json: %w", err)
	}
	return v, nil
}

// serverError logs an internal server error and sends a 500 Internal Server Error
// response to the client.
//
// Usage:
// This function is intended for use when handling unexpected server-side errors.
// It logs the error details along with the HTTP request method, URI, and a stack
// trace for debugging purposes. After logging, it sends a standardized 500 Internal
// Server Error response to the client.
//
// Parameters:
// - logger: The *slog.Logger instance used for logging error details.
// - w: The http.ResponseWriter to send the response to.
// - r: The *http.Request that triggered the error. Used to extract method and URI.
// - err: The error instance to log, providing context about the issue.
//
// Example:
//
//	func handler(w http.ResponseWriter, r *http.Request) {
//	    err := someOperation()
//	    if err != nil {
//	        serverError(logger, w, r, err)
//	        return
//	    }
//	    // Handle request normally
//	}
func serverError(logger *slog.Logger, w http.ResponseWriter, r *http.Request, err error) {
	var (
		method = r.Method
		uri    = r.URL.RequestURI()
		// Use debug.Stack() to get the stack trace. This returns a byte slice, which
		// we need to convert to a string so that it's readable in the log entry.
		trace = string(debug.Stack())
	)

	logger.Error(err.Error(), "method", method, "uri", uri, "trace", trace)
	http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
}

// clientError sends an HTTP error response to the client with the specified
// status code and its corresponding description.
//
// Usage:
// This function is useful for handling HTTP errors in a consistent manner.
// It sends the appropriate HTTP status text as the response body, along with
// the given status code as the response status. This is typically used in web
// applications to return standardized error messages for various client-side
// errors.
//
// Parameters:
//   - w: The http.ResponseWriter to send the response to.
//   - status: The HTTP status code to return. It should be a valid HTTP status
//     code as defined in the http package.
//
// Example:
//
//	func handler(w http.ResponseWriter, r *http.Request) {
//	    if !isAuthorized(r) {
//	        clientError(w, http.StatusForbidden) // Responds with "403 Forbidden"
//	        return
//	    }
//	    // Handle request normally
//	}
func clientError(w http.ResponseWriter, status int) {
	http.Error(w, http.StatusText(status), status)
}