package paperformatter

import (
	"fmt"
	"strings"
)

// ValidationError represents an error that occurs when input validation fails.
// It includes the field name that failed validation and a descriptive message.
type ValidationError struct {
	Field   string
	Message string
}

func (e *ValidationError) Error() string {
	return fmt.Sprintf("validation error for %s: %s", e.Field, e.Message)
}

// FileError represents an error that occurs during file operations.
// It includes the file path, the operation that failed (e.g., "read" or "write"),
// and the underlying system error.
type FileError struct {
	Path    string
	Op      string
	Wrapped error
}

func (e *FileError) Error() string {
	return fmt.Sprintf("file operation '%s' failed for '%s': %v", e.Op, e.Path, e.Wrapped)
}

func (e *FileError) Unwrap() error {
	return e.Wrapped
}

// JSONError represents an error that occurs during JSON parsing.
// It wraps the underlying parsing error from the encoding/json package.
type JSONError struct {
	Wrapped error
}

func (e *JSONError) Error() string {
	return fmt.Sprintf("JSON parsing error: %v", e.Wrapped)
}

func (e *JSONError) Unwrap() error {
	return e.Wrapped
}

// validatePaper checks if a Paper has all required fields.
// Returns a ValidationError if any field is empty.
func validatePaper(paper Paper) error {
	if paper.Title == "" {
		return &ValidationError{
			Field:   "title",
			Message: "title cannot be empty",
		}
	}

	if paper.Abstract == "" {
		return &ValidationError{
			Field:   "abstract",
			Message: "abstract cannot be empty",
		}
	}

	if paper.ArxivID == "" {
		return &ValidationError{
			Field:   "arxiv_id",
			Message: "arxiv_id cannot be empty",
		}
	}

	return nil
}

// validateEntry performs validation on an entire Entry, including its Paper.
// It checks for required fields and valid decision values.
// Returns a ValidationError if validation fails.
func validateEntry(entry Entry) error {
	if err := validatePaper(entry.Paper); err != nil {
		return err
	}

	if entry.Decision == "" {
		return &ValidationError{
			Field:   "decision",
			Message: "decision cannot be empty",
		}
	}

	decision := strings.ToUpper(entry.Decision)
	if decision != "ACCEPT" && decision != "REJECT" {
		return &ValidationError{
			Field:   "decision",
			Message: "decision must be either 'accept' or 'reject'",
		}
	}

	if entry.Explanation == "" {
		return &ValidationError{
			Field:   "explanation",
			Message: "explanation cannot be empty",
		}
	}

	return nil
}