package try

/*
try is a fork of lainio's err2 package
Copyright (c) 2019 Lainio, MIT License
https://github.com/lainio/err2
*/

import (
	"errors"
	"fmt"
	"os"
	"regexp"
	"runtime"
	"strings"
)

// Err is an interface for an error with extended stack info.
type Err interface {
	Error() string
	Unwrap() error
	CallStack() []call
	CallStackString() string
	PrintCallStack()
	GetData() *tryErrData
	Annotate(msg string)
}

// tryErr is an extended error struct.
type tryErr struct {
	err         error
	annotations []string
	callStack   []call
}

// tryErrData is exported error data. Can be converted to JSON.
type tryErrData struct {
	Msg         string   `json:"msg"`
	Annotations []string `json:"annotations"`
	CallStack   []call   `json:"call_stack"`
}

type call struct {
	File     string `json:"file"`
	Function string `json:"fn"`
	Line     int    `json:"l"`
}

// FromErr wraps a standard error into a try-compatible one with extended stack info.
func FromErr(err error) Err {
	// If the error is already try-compatible, return
	//nolint:errorlint
	cterr, ok := err.(Err)
	if ok {
		return cterr
	}

	terr := &tryErr{err: err, callStack: []call{}}

	pc, _, _, ok := runtime.Caller(0)
	if !ok {
		return terr
	}
	thisFnc := runtime.FuncForPC(pc)
	if thisFnc == nil {
		return terr
	}

	rexp := regexp.MustCompile(`.+\/`)
	thisPkg := rexp.FindString(thisFnc.Name())

	for i := 1; ; i++ {
		pc, f, l, ok := runtime.Caller(i)

		if !ok {
			break
		}

		fnc := runtime.FuncForPC(pc).Name()

		if strings.HasPrefix(fnc, thisPkg) && !strings.HasSuffix(f, "_test.go") {
			continue
		}

		terr.callStack = append(terr.callStack, call{File: f, Function: fnc, Line: l})
	}

	return terr
}

// NewErr creates a new try-compatible error with extended stack info.
func NewErr(msg string) Err {
	return FromErr(errors.New(msg))
}

// Error returns the standard go error message (initial message + annotations).
func (e *tryErr) Error() string {
	msgs := e.annotations
	msgs = append(msgs, e.err.Error())
	return strings.Join(msgs, ": ")
}

// Unwrap returns the standard go error.
func (e *tryErr) Unwrap() error {
	return e.err
}

// CallStack returns a slice of function calls leading to the error,
// with the most recent being first.
func (e *tryErr) CallStack() []call {
	return e.callStack
}

// CallStackString outputs the call stack as a printable multiline string.
func (e *tryErr) CallStackString() string {
	res := fmt.Sprintf("ERROR: %s\n", e.err.Error())
	for _, msg := range e.annotations {
		res += fmt.Sprintln(msg)
	}
	res += fmt.Sprintln("\nTraceback (most recent call first):")
	for _, c := range e.callStack {
		res += fmt.Sprintf("%s:%d\n", c.File, c.Line)
		res += fmt.Sprintf("  %s\n", c.Function)
	}
	return res
}

// PrintCallStack prints the call stack to stderr.
func (e *tryErr) PrintCallStack() {
	_, _ = fmt.Fprintln(os.Stderr, e.CallStackString())
}

// GetData returns a serializable error data object.
func (e *tryErr) GetData() *tryErrData {
	return &tryErrData{
		Msg:         e.err.Error(),
		CallStack:   e.callStack,
		Annotations: e.annotations,
	}
}

// Annotate adds additional text to the error message.
func (e *tryErr) Annotate(msg string) {
	e.annotations = append(e.annotations, msg)
}

// Empty is a helper method to handle errors of func() (string, error) functions.
func Empty(_ interface{}, err error) {
	Check(err)
}

// Any is as similar as proposed Go2 Try macro, but it's a function and it
// returns slice of interfaces. It has quite big performance penalty when
// compared to Check function.
func Any(args ...interface{}) []interface{} {
	check(args)
	return args
}

// Check performs the error check for the given argument. If the err is nil,
// it does nothing. According the measurements, it's as fast as if err != nil
// {return err} on happy path.
func Check(err error) {
	if err != nil {
		panic(FromErr(err))
	}
}

// Checks the error status of the last argument. It panics with "wrong
// signature" if the last calling parameter is not error. In case of error it
// delivers it by panicking.
func check(args []interface{}) {
	argCount := len(args)
	last := argCount - 1
	if args[last] != nil {
		err, ok := args[last].(error)
		if !ok {
			panic("wrong signature")
		}
		panic(FromErr(err))
	}
}

// Handle is for adding an error handler to a function by defer. It's for
// functions returning errors them self. For those functions that doesn't
// return errors there is a Catch function. Note! The handler function f is
// called only when err != nil.
func Handle(err *Err, f func()) {
	// We put real panic objects back and keep only those which are
	// carrying our errors. We must also call all of the handlers in defer
	// stack.
	switch r := recover(); r.(type) {
	case nil:
		// Defers are in the stack and the first from the stack gets the
		// opportunity to get panic object's error (below). We still must
		// call handler functions to the rest of the handlers if there is
		// an error.
		if *err != nil {
			f()
		}
	case Err:
		// We or someone did transport this error thru panic.
		*err = r.(Err)
		f()
	default:
		panic(r)
	}
}

// Catch is a convenient helper to those functions that doesn't return errors.
// Go's main function is a good example. Note! There can be only one deferred
// Catch function per non error returning function. See Handle for more
// information.
func Catch(f func(err Err)) {
	if r := recover(); r != nil {
		e, ok := r.(Err)
		if !ok {
			panic(r)
		}
		f(e)
	}
}

// CatchAll is a helper function to catch and write handlers for all errors and
// all panics thrown in the current go routine.
func CatchAll(errorHandler func(err Err), panicHandler func(v interface{})) {
	if r := recover(); r != nil {
		e, ok := r.(Err)
		if ok {
			errorHandler(e)
		} else {
			panicHandler(r)
		}
	}
}

// CatchTrace catches all errors and prints their call stack.
// Setting the exit parameter to a value above 0 will make the program
// exit in case of an error.
func CatchTrace(exit int) {
	if r := recover(); r != nil {
		e, ok := r.(Err)
		if !ok {
			panic(r)
		}
		e.PrintCallStack()
		if exit > 0 {
			os.Exit(exit)
		}
	}
}

// Return is same as Handle but it's for functions which don't wrap or annotate
// their errors. If you want to annotate errors see Annotate for more
// information.
func Return(err *Err) {
	if r := recover(); r != nil {
		e, ok := r.(Err)
		if !ok {
			panic(r) // Not ours, carry on panicking
		}
		*err = e
	}
}

// ReturnStd is like Return, but it returns the Go standard error type.
func ReturnStd(err *error) {
	if r := recover(); r != nil {
		e, ok := r.(Err)
		if !ok {
			panic(r) // Not ours, carry on panicking
		}
		*err = e.Unwrap()
	}
}

// Annotate adds additional messages to the error.
func Annotate(err *Err, msg string) {
	if r := recover(); r != nil {
		e, ok := r.(Err)
		if !ok {
			panic(r) // Not ours, carry on panicking
		}
		*err = e
		e.Annotate(msg)
	} else if *err != nil { // if other handlers call recovery() we still..
		(*err).Annotate(msg)
	}
}