package server

import (
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"

	"github.com/gin-gonic/gin"
)

// APIResponse represents the unified JSON structure for all API responses.
type APIResponse struct {
	Success bool        `json:"success"`
	Data    interface{} `json:"data,omitempty"`
	Error   string      `json:"error,omitempty"`
}

// OK responds with 200 and success data.
func OK(c *gin.Context, data interface{}) {
	c.JSON(http.StatusOK, APIResponse{Success: true, Data: data})
}

// Created responds with 201 and success data.
func Created(c *gin.Context, data interface{}) {
	c.JSON(http.StatusCreated, APIResponse{Success: true, Data: data})
}

// BadRequest responds with 400 and an error message.
func BadRequest(c *gin.Context, msg string) {
	c.JSON(http.StatusBadRequest, APIResponse{Success: false, Error: msg})
}

// NotFound responds with 404 and an error message.
func NotFound(c *gin.Context, msg string) {
	c.JSON(http.StatusNotFound, APIResponse{Success: false, Error: msg})
}

// InternalError responds with 500 and an error message.
func InternalError(c *gin.Context, msg string) {
	c.JSON(http.StatusInternalServerError, APIResponse{Success: false, Error: msg})
}

// ErrorWithStatus responds with a custom status code and an error message.
func ErrorWithStatus(c *gin.Context, code int, msg string) {
	c.JSON(code, APIResponse{Success: false, Error: msg})
}

// ParseRange parses an HTTP Range header (RFC 7233).
// Only single-part ranges are supported: bytes=start-end, bytes=start-, bytes=-suffix.
// Multi-part ranges (bytes=0-100,200-300) return an error.
func ParseRange(rangeHeader string, fileSize int64) (start, end int64, err error) {
	if rangeHeader == "" {
		return 0, 0, fmt.Errorf("empty range header")
	}

	if !strings.HasPrefix(rangeHeader, "bytes=") {
		return 0, 0, fmt.Errorf("invalid range unit: %s", rangeHeader)
	}

	rangeSpec := strings.TrimPrefix(rangeHeader, "bytes=")

	if strings.Contains(rangeSpec, ",") {
		return 0, 0, fmt.Errorf("multi-part ranges are not supported")
	}

	rangeSpec = strings.TrimSpace(rangeSpec)
	parts := strings.Split(rangeSpec, "-")
	if len(parts) != 2 {
		return 0, 0, fmt.Errorf("invalid range format: %s", rangeSpec)
	}

	if parts[0] == "" {
		suffix, parseErr := strconv.ParseInt(parts[1], 10, 64)
		if parseErr != nil {
			return 0, 0, fmt.Errorf("invalid suffix range: %s", parts[1])
		}
		if suffix <= 0 || suffix > fileSize {
			return 0, 0, fmt.Errorf("suffix range %d exceeds file size %d", suffix, fileSize)
		}
		start = fileSize - suffix
		end = fileSize - 1
	} else if parts[1] == "" {
		start, err = strconv.ParseInt(parts[0], 10, 64)
		if err != nil {
			return 0, 0, fmt.Errorf("invalid range start: %s", parts[0])
		}
		if start >= fileSize {
			return 0, 0, fmt.Errorf("range start %d exceeds file size %d", start, fileSize)
		}
		end = fileSize - 1
	} else {
		start, err = strconv.ParseInt(parts[0], 10, 64)
		if err != nil {
			return 0, 0, fmt.Errorf("invalid range start: %s", parts[0])
		}
		end, err = strconv.ParseInt(parts[1], 10, 64)
		if err != nil {
			return 0, 0, fmt.Errorf("invalid range end: %s", parts[1])
		}
		if start > end {
			return 0, 0, fmt.Errorf("range start %d > end %d", start, end)
		}
		if start >= fileSize {
			return 0, 0, fmt.Errorf("range start %d exceeds file size %d", start, fileSize)
		}
		if end >= fileSize {
			end = fileSize - 1
		}
	}

	return start, end, nil
}

// StreamFile sends a full file as an HTTP response with proper headers.
func StreamFile(c *gin.Context, reader io.ReadCloser, filename string, fileSize int64, contentType string) {
	defer reader.Close()

	c.Header("Content-Disposition", fmt.Sprintf(`attachment; filename="%s"`, filename))
	c.Header("Content-Type", contentType)
	c.Header("Content-Length", strconv.FormatInt(fileSize, 10))
	c.Header("Accept-Ranges", "bytes")

	c.Status(http.StatusOK)
	io.Copy(c.Writer, reader)
}

// StreamRange sends a partial content response (206) for a byte range.
func StreamRange(c *gin.Context, reader io.ReadCloser, start, end, totalSize int64, contentType string) {
	defer reader.Close()

	contentLength := end - start + 1

	c.Header("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, totalSize))
	c.Header("Content-Type", contentType)
	c.Header("Content-Length", strconv.FormatInt(contentLength, 10))
	c.Header("Accept-Ranges", "bytes")

	c.Status(http.StatusPartialContent)
	io.Copy(c.Writer, reader)
}