package api

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"log/slog"
	"net/http"

	"github.com/gin-gonic/gin"

	"github.com/dhao2001/mygo/internal/model"
)

// ErrorResponse is the standard JSON body for HTTP API errors.
type ErrorResponse struct {
	Error ErrorBody `json:"error"`
}

// ErrorBody contains human-readable error details.
type ErrorBody struct {
	Message string `json:"message"`
}

// Error writes a JSON error response.
func Error(c *gin.Context, status int, message string) {
	c.JSON(status, ErrorResponse{
		Error: ErrorBody{
			Message: message,
		},
	})
}

// RespondError unpacks an error from the service layer and writes a JSON
// error response. It expects *model.AppError; unexpected non-AppError
// values are treated as 500 with a safe message. For 500+ errors, a
// random reference hash is included in the response so operators can
// correlate it with server logs.
func RespondError(c *gin.Context, err error) {
	var ae *model.AppError
	if !errors.As(err, &ae) {
		ref := randomHex(8)
		slog.ErrorContext(c.Request.Context(), "non-AppError escaped to handler",
			"ref", ref, "error", err, "type", fmt.Sprintf("%T", err))
		Error(c, http.StatusInternalServerError, "internal server error (ref: "+ref+")")
		return
	}

	// 500+ errors: log full detail with a reference hash, return sanitized message.
	if ae.Status >= 500 {
		ref := randomHex(8)
		slog.ErrorContext(c.Request.Context(), "internal server error",
			"ref", ref, slog.Any("error", ae.Err), "message", ae.Message)
		Error(c, ae.Status, "internal server error (ref: "+ref+")")
		return
	}

	// 4xx errors with internal cause: log at WARN for diagnostics.
	if ae.Err != nil {
		slog.WarnContext(c.Request.Context(), ae.Message,
			"status", ae.Status, slog.Any("error", ae.Err))
	}

	Error(c, ae.Status, ae.Message)
}

func randomHex(n int) string {
	b := make([]byte, n)
	rand.Read(b)
	return hex.EncodeToString(b)
}