package errs

import (
	"core/errs/stack"
	"fmt"
	"regexp"
)

const (
	// errCodePattern is the regular expression that defines a valid error code format.
	// The error code can optionally have a module, which is separated by "::".
	// The valid characters are alphanumeric characters and the symbols ":-_".
	errCodePattern string = "^[a-zA-Z0-9._-]+(::[a-zA-Z0-9._-]+)?$"
)

const (
	// ModuleSeparator is the separator used between the module and value parts of the error code.
	ModuleSeparator string = "::"
)

// Module configuration
const moduleName = "core.errs" + ModuleSeparator

// Error messages for internal use
const (
	errNilWrapMsg  string = "error trying to wrap % into a nil error"
	errNilCauseMsg string = "error trying to wrap % into a nil cause"
)

// Standard error codes for common error scenarios
const (
	CodePanicError           string = "panic"
	CodeMultiError           string = "multiple-errors"
	CodeParamError           string = "Param"
	CodeParamNilError        string = "Param-nil"
	CodeParamOutOfRangeError string = "Param-out-of-range"
)

// G provides a global access point for common errors and information
// This struct combines documentation links and pre-initialized error instances
var (
	G = struct {
		InfoHelp,
		InfoLink string

		ErrParam,
		ErrParamNil,
		ErrParamOutOfRange,
		ErrInvalidError,
		ErrInvalidNilError,
		ErrUnknownPanicError,
		ErrInvalidErrCode ErrCode
	}{
		InfoLink: "https://git.activething.com/go/active",
		InfoHelp: "https://doc.activething.com/go/active",

		ErrParam:             ErrCode(CodeParamError),
		ErrParamNil:          ErrCode(CodeParamNilError),
		ErrParamOutOfRange:   ErrCode(CodeParamOutOfRangeError),
		ErrUnknownPanicError: ErrCode(moduleName + "unknown-panic-error"),
		ErrInvalidNilError:   ErrCode(moduleName + "invalid-nil-error"),
		ErrInvalidError:      ErrCode(moduleName + "invalid-error"),
		ErrInvalidErrCode:    ErrCode(moduleName + "invalid-err-code"),
	}

	// g contains private package-level variables
	g = struct {
		panicErrNil *ErrPanic

		codeValidator *regexp.Regexp
	}{

		panicErrNil: NewErrPanic(G.ErrInvalidNilError),

		codeValidator: regexp.MustCompile(errCodePattern),
	}
)

// ToError converts any value to an error type
// Returns nil if the input is nil
// Converts []error to ErrMulti
// Uses fmt.Errorf for other types
func ToError(err any) error {
	if err == nil {
		return nil
	}
	switch e := err.(type) {
	case error:
		return e
	case []error:
		if len(e) == 0 {
			return nil
		}
		return NewErrMulti(e...)
	default:
		return fmt.Errorf("%v", err)
	}
}

// PanicRecoveredError creates an error from a recovered panic value
// Returns nil if the recovered value is nil
func PanicRecoveredError(rec any) error {
	if rec == nil {
		return nil
	}
	return *NewErrPanic(ToError(rec))
}

// Unwrap provides standard error unwrapping functionality
// Implements the unwrap interface for error chains
func Unwrap(err error) error {
	if err == nil {
		return nil
	}
	if cs, is := err.(Unwrapper); is {
		return cs.Unwrap()
	}
	return nil
}

// UnwrapCause retrieves the root cause of an error chain
// Traverses the error chain looking for Causer implementation
func UnwrapCause(err error) error {
	e := err
	for e != nil {
		cs, is := e.(Causer)
		if is {
			return cs.Cause()
		}
		e = Unwrap(e)
	}
	return nil
}

// UnwrapCauses retrieves all causes in an error chain
// Returns a slice of errors representing the cause chain
func UnwrapCauses(err error) []error {
	if err == nil {
		return nil
	}
	if al, is := err.(Causers); is {
		return al.Causes()
	}
	var l ErrorList
	e := err
	for e != nil {
		l = append(l, e)
		e = Unwrap(e)
	}
	return l
}

// UnwrapList retrieves all errors in an error chain as an ErrorList
// Handles both UnwrapperList implementations and standard error chains
func UnwrapList(err error) ErrorList {
	if err == nil {
		return nil
	}
	if al, is := err.(UnwrapperList); is {
		return al.Unwrap()
	}
	var l ErrorList
	e := err
	for e != nil {
		l = append(l, e)
		e = Unwrap(e)
	}
	return l
}

// UnwrapTrace retrieves the stack trace from an error
func UnwrapTrace(err error) stack.Stack {
	return stack.UnwrapStack(err, false)
}

// WrapError combines two errors into a single error, establishing a cause relationship.
// If either error is nil, the non-nil error is returned.
// Otherwise, a new error is returned that has the first error as the cause.
func WrapError(err, cause error) error {
	if err == nil {
		return cause
	}
	if cause == nil {
		return err
	}
	return *NewErrWithCause(err, cause)
}

// ValidateCode check if un err code is valid
func ValidateCode(code string) bool {
	return g.codeValidator.MatchString(code)
}