package envs

import (
	"math"
	"os"
	"reflect"
	"strings"

	"github.com/shirou/gopsutil/v4/process"
	"r00t2.io/sysutils/errs"
	"r00t2.io/sysutils/internal"
)

/*
Current returns a *copy* of the StaticEnv for this current process' environment.

It is set to dynamically refresh with strictRefresh mode set to false.
(see [NewEnvFromPid] docs for what these do/mean.)
Assuming permissions haven't wildly gone silly during runtime, it shouldn't ever
have issues with dynamic refreshing.
It will never panic regardless.
*/
func Current() (s *StaticEnv) {

	s = &StaticEnv{
		dynamic: defEnv.dynamic,
		envVars: defEnv.GetEnvMap(),
	}
	for k, v := range defEnv.envVars {
		s.envVars[k] = v
	}

	return
}

/*
NewEnvFromMap returns a [StaticEnv] from a fixed list of environment variables.
This is primarily useful for mocking and other tests.
*/
func NewEnvFromMap(envMap map[string]string) (s *StaticEnv, err error) {

	if envMap == nil {
		err = errs.ErrNilPtr
	}

	s = &StaticEnv{
		envVars: envMap,
	}

	return
}

/*
NewEnvFromPid returns a [StaticEnv] from a given PID.

If dynamicRefresh is true, the env vars will be refreshed from the process
on every method call.
Note that this will obviously cause errors/panics if the process it binds to disappears
during runtime,
or
*/
func NewEnvFromPid(pid uint, dynamicRefresh, strictRefresh bool) (s *StaticEnv, err error) {

	if pid > math.MaxInt32 {
		err = errs.ErrHighPid
		return
	}

	s = &StaticEnv{
		dynamic: dynamicRefresh,
	}

	if s.proc, err = process.NewProcess(int32(pid)); err != nil {
		return
	}
	if err = s.Refresh(); err != nil {
		return
	}
	// Test the ability to attach to procs.
	err = s.platChecks()
	s.strict = strictRefresh

	return
}

/*
DefEnv operates like Python's .get() method on dicts (maps);
if the environment variable specified by key does not exist/is not specified,
then the value specified by fallback will be returned instead
otherwise key's value is returned.
*/
func DefEnv(key, fallback string) (value string) {

	var exists bool

	if value, exists = os.LookupEnv(key); !exists {
		value = fallback
	}

	return
}

// DefEnvBlank is like [DefEnv] but will ADDITIONALLY/ALSO apply fallback if key is *defined/exists but is an empty string*.
func DefEnvBlank(key, fallback string) (value string) {

	value = DefEnv(key, fallback)
	if value == "" {
		value = fallback
	}

	return
}

// GetEnvErr returns the value of key if it exists. If it does not exist, err will be an [EnvErrNoVal].
func GetEnvErr(key string) (value string, err error) {

	var exists bool

	if value, exists = os.LookupEnv(key); !exists {
		err = &EnvErrNoVal{
			VarName: key,
		}
		return
	}

	return
}

/*
GetEnvErrNoBlank behaves exactly like [GetEnvErr] with the
additional stipulation that the value must not be empty.

An error for a value that is non-empty but whitespace only (e.g. VARNM="\t")
can be returned if ignoreWhitespace == true.

(If it is, an [EnvErrNoVal] will also be returned.)
*/
func GetEnvErrNoBlank(key string, ignoreWhitespace bool) (value string, err error) {

	var exists bool
	var e *EnvErrNoVal = &EnvErrNoVal{
		VarName:             key,
		WasRequiredNonEmpty: true,
		IgnoreWhitespace:    ignoreWhitespace,
	}

	if value, exists = os.LookupEnv(key); !exists {
		err = e
		return
	} else {
		e.WasFound = true
		e.WasWhitespace = (strings.TrimSpace(value) == "") && (value != "")
		if ignoreWhitespace && e.WasWhitespace {
			err = e
			return
		}
	}

	return
}

// GetEnvMap returns a map of all environment variables. All values are strings.
func GetEnvMap() (envVars map[string]string) {

	var envList []string = os.Environ()

	envVars = internal.EnvListToMap(envList)

	return
}

// GetEnvMust wraps GetEnvErr but will panic on error.
func GetEnvMust(key string) (value string) {

	var err error

	if value, err = GetEnvErr(key); err != nil {
		panic(err)
	}

	return
}

/*
GetEnvMapNative returns a map of all environment variables, but attempts to "nativize" them.
All values are interfaces. It is up to the caller to typeswitch them to proper types.

Note that the PATH/Path environment variable (for *Nix and Windows, respectively) will be
a []string (as per [GetPathEnv]). No other env vars, even if they contain [os.PathListSeparator],
will be transformed to a slice or the like.
If an error occurs during parsing the path env var, it will be rendered	as a string.

All number types will attempt to be their 64-bit version (i.e. int64, uint64, float64, etc.).

If a type cannot be determined for a value, its string form will be used
(as it would be found in [GetEnvMap]).
*/
func GetEnvMapNative() (envMap map[string]interface{}) {

	var stringMap map[string]string = GetEnvMap()

	envMap = internal.NativizeEnvMap(stringMap)

	return
}

/*
GetFirst gets the first instance if populated/set occurrence of varNames.

For example, if you have three potential env vars, FOO, FOOBAR, FOOBARBAZ,
and want to follow the logic flow of:

	1.) Check if FOO is set. If not,
	2.) Check if FOOBAR is set. If not,
	3.) Check if FOOBARBAZ is set.

Then this would be specified as:

	GetFirst([]string{"FOO", "FOOBAR", "FOOBARBAZ"})

If val is "" and ok is true, this means that one of the specified variable names IS
set but is set to an empty value. If ok is false, none of the specified variables
are set.

It is a thin wrapper around [GetFirstWithRef].
*/
func GetFirst(varNames []string) (val string, ok bool) {

	val, ok, _ = GetFirstWithRef(varNames)

	return
}

/*
GetFirstWithRef behaves exactly like [GetFirst], but with an additional returned value, idx,
which specifies the index in varNames in which a set variable was found. e.g. if:

	GetFirstWithRef([]string{"FOO", "FOOBAR", "FOOBAZ"})

is called and FOO is not set but FOOBAR is, idx will be 1.

If ok is false, idx will always be -1 and should be ignored.
*/
func GetFirstWithRef(varNames []string) (val string, ok bool, idx int) {

	idx = -1

	for i, vn := range varNames {
		if HasEnv(vn) {
			ok = true
			idx = i
			val = os.Getenv(vn)
			return
		}
	}

	return
}

// GetPathEnv returns a slice of the PATH variable's items.
func GetPathEnv() (pathList []string, err error) {

	if pathList, err = internal.GetPathEnv(); err != nil {
		return
	}

	return
}

/*
GetPidEnvMap will only work on *NIX-like systems with procfs.
It gets the environment variables of a given process' PID.
*/
func GetPidEnvMap(pid uint32) (envMap map[string]string, err error) {

	if envMap, err = internal.GetPidEnvMap(pid); err != nil {
		return
	}

	return
}

/*
GetPidEnvMapNative returns a map of all environment variables (like [GetEnvMapNative]), but attempts to "nativize" them.
All values are interfaces. It is up to the caller to typeswitch them to proper types.

See the documentation for [GetEnvMapNative] for details.
*/
func GetPidEnvMapNative(pid uint32) (envMap map[string]interface{}, err error) {

	var stringMap map[string]string

	if stringMap, err = internal.GetPidEnvMap(pid); err != nil {
		return
	}

	envMap = internal.NativizeEnvMap(stringMap)

	return
}

/*
HasEnv is much like [os.LookupEnv], but only returns a boolean indicating
if the environment variable key exists or not.

This is useful anywhere you may need to set a boolean in a func call
depending on the *presence* of an env var or not.
*/
func HasEnv(key string) (envIsSet bool) {

	_, envIsSet = os.LookupEnv(key)

	return
}

/*
Interpolate takes one of:

  - a string (pointer only)
  - a struct (pointer only)
  - a map (applied to both keys *and* values)
  - a slice

and performs variable substitution on strings from environment variables.

It supports both UNIX/Linux/POSIX syntax formats (e.g. $VARNAME, ${VARNAME}) and,
if on Windows, it *additionally* supports the EXPAND_SZ format (e.g. %VARNAME%).

For structs, the tag name used can be changed by setting the [StructTagInterpolate]
variable in this submodule; the default is `envsub`.
If the tag value is "-", the field will be skipped.
For map fields within structs etc., the default is to apply interpolation to both keys and values.
All other tag value(s) are ignored.

For maps and slices, Interpolate will recurse into values (e.g. [][]string will work as expected).

If s is nil, no interpolation will be performed. No error will be returned.
If s is not a valid/supported type, no interpolation will be performed. No error will be returned.
*/
func Interpolate[T any](s T) (err error) {

	var ptrVal reflect.Value
	var ptrType reflect.Type
	var ptrKind reflect.Kind
	var sVal reflect.Value = reflect.ValueOf(s)
	var sType reflect.Type = sVal.Type()
	var kind reflect.Kind = sType.Kind()

	switch kind {
	case reflect.Ptr:
		if sVal.IsNil() || sVal.IsZero() || !sVal.IsValid() {
			return
		}
		ptrVal = sVal.Elem()
		ptrType = ptrVal.Type()
		ptrKind = ptrType.Kind()
		if ptrKind == reflect.String {
			err = interpolateStringReflect(ptrVal)
		} else {
			// Otherwise, it should be a struct ptr.
			if ptrKind != reflect.Struct {
				return
			}
			err = interpolateStruct(ptrVal)
		}
	case reflect.Map:
		if sVal.IsNil() || sVal.IsZero() || !sVal.IsValid() {
			return
		}
		err = interpolateMap(sVal)
	case reflect.Slice:
		if sVal.IsNil() || sVal.IsZero() || !sVal.IsValid() {
			return
		}
		err = interpolateSlice(sVal)
		/*
			case reflect.Struct:
				if sVal.IsZero() || !sVal.IsValid() {
					return
				}
				err = interpolateStruct(sVal)

		*/
	}

	return
}

/*
InterpolateString takes (a pointer to) a struct or string and performs variable substitution on it
from environment variables.

It supports both UNIX/Linux/POSIX syntax formats (e.g. $VARNAME, ${VARNAME}) and,
if on Windows, it *additionally* supports the EXPAND_SZ format (e.g. %VARNAME%).

If s is nil, nothing will be done and err will be [errs.ErrNilPtr].

This is a standalone function that is much more performant than [Interpolate]
at the cost of rigidity.
*/
func InterpolateString(s *string) (err error) {

	var newStr string

	if s == nil {
		err = errs.ErrNilPtr
		return
	}

	if newStr, err = interpolateString(*s); err != nil {
		return
	}
	*s = newStr

	return
}