package wand

import (
	"errors"
	"fmt"
	"reflect"
	"regexp"
	"slices"
)

var commandNameExpression = regexp.MustCompile("^[a-zA-Z_][a-zA-Z_0-9]*$")

func command(name string, impl any, subcmds ...Cmd) Cmd {
	return Cmd{
		name:        name,
		impl:        impl,
		subcommands: subcmds,
	}
}

func wrap(impl any) Cmd {
	cmd, ok := impl.(Cmd)
	if ok {
		return cmd
	}

	return Command("", impl)
}

func validateFields(f []field, conf Config) error {
	hasConfigFromOption := hasConfigFromOption(conf)
	mf := make(map[string]field)
	for _, fi := range f {
		if ef, ok := mf[fi.name]; ok && !compatibleTypes(fi.typ, ef.typ) {
			return fmt.Errorf("duplicate fields with different types: %s", fi.name)
		}

		if hasConfigFromOption && fi.name == "config" {
			return errors.New("option reserved for config file shadowed by struct field")
		}

		mf[fi.name] = fi
	}

	return nil
}

func validateParameter(visited map[reflect.Type]bool, t reflect.Type) error {
	switch t.Kind() {
	case reflect.Bool,
		reflect.Int,
		reflect.Int8,
		reflect.Int16,
		reflect.Int32,
		reflect.Int64,
		reflect.Uint,
		reflect.Uint8,
		reflect.Uint16,
		reflect.Uint32,
		reflect.Uint64,
		reflect.Float32,
		reflect.Float64,
		reflect.String:
		return nil
	case reflect.Pointer,
		reflect.Slice:
		if visited[t] {
			return fmt.Errorf("circular type definitions not supported: %s", t.Name())
		}

		if visited == nil {
			visited = make(map[reflect.Type]bool)
		}

		visited[t] = true
		t = unpack(t)
		return validateParameter(visited, t)
	case reflect.Interface:
		if t.NumMethod() > 0 {
			return errors.New("non-empty interface parameter")
		}

		return nil
	default:
		return fmt.Errorf("unsupported parameter type: %v", t)
	}
}

func validatePositional(t reflect.Type, min, max int) error {
	p := positionalParameters(t)
	ior, iow := ioParameters(p)
	if len(ior) > 1 || len(iow) > 1 {
		return errors.New("only zero or one reader and zero or one writer parameters is supported")
	}

	for i, pi := range p {
		if slices.Contains(ior, i) || slices.Contains(iow, i) {
			continue
		}

		if err := validateParameter(nil, pi); err != nil {
			return err
		}
	}

	last := t.NumIn() - 1
	lastVariadic := t.IsVariadic() &&
		!isStruct(t.In(last)) &&
		!slices.Contains(ior, last) &&
		!slices.Contains(iow, last)
	fixedPositional := len(p) - len(ior) - len(iow)
	if lastVariadic {
		fixedPositional--
	}

	if min > 0 && min < fixedPositional {
		return fmt.Errorf(
			"minimum positional defined as %d but the implementation expects minimum %d fixed parameters",
			min,
			fixedPositional,
		)
	}

	if min > 0 && min > fixedPositional && !lastVariadic {
		return fmt.Errorf(
			"minimum positional defined as %d but the implementation has only %d fixed parameters and no variadic parameter",
			min,
			fixedPositional,
		)
	}

	if max > 0 && max < fixedPositional {
		return fmt.Errorf(
			"maximum positional defined as %d but the implementation expects minimum %d fixed parameters",
			max,
			fixedPositional,
		)
	}

	if min > 0 && max > 0 && min > max {
		return fmt.Errorf(
			"minimum positional defined as larger then the maxmimum positional: %d > %d",
			min,
			max,
		)
	}

	return nil
}

func validateImpl(cmd Cmd, conf Config) error {
	v := reflect.ValueOf(cmd.impl)
	v = unpack(v)
	t := v.Type()
	if t.Kind() != reflect.Func {
		return errors.New("command implementation not a function")
	}

	s := structParameters(t)
	f, err := fieldsChecked(nil, s...)
	if err != nil {
		return err
	}

	if err := validateFields(f, conf); err != nil {
		return err
	}

	if err := validatePositional(t, cmd.minPositional, cmd.maxPositional); err != nil {
		return err
	}

	return nil
}

func validateShortForms(cmd Cmd, assignedShortForms map[string]string) error {
	mf := mapFields(cmd.impl)
	if len(cmd.shortForms)%2 != 0 {
		return fmt.Errorf(
			"undefined option short form: %s", cmd.shortForms[len(cmd.shortForms)-1],
		)
	}

	for i := 0; i < len(cmd.shortForms); i += 2 {
		fn := cmd.shortForms[i]
		sf := cmd.shortForms[i+1]
		if len(sf) != 1 && (sf[0] < 'a' || sf[0] > 'z') {
			return fmt.Errorf("invalid short form: %s", sf)
		}

		if _, ok := mf[sf]; ok {
			return fmt.Errorf("short form shadowing field name: %s", sf)
		}

		if _, ok := mf[fn]; !ok {
			continue
		}

		if lf, ok := assignedShortForms[sf]; ok && lf != fn {
			return fmt.Errorf("ambigous short form: %s", sf)
		}

		assignedShortForms[sf] = fn
	}

	return nil
}

func validateCommandTree(cmd Cmd, conf Config, assignedShortForms map[string]string, root bool) error {
	if cmd.isHelp {
		return nil
	}

	if cmd.version != "" {
		return nil
	}

	if !root && !commandNameExpression.MatchString(cmd.name) {
		return fmt.Errorf("command name is not a valid symbol: '%s'", cmd.name)
	}

	if cmd.impl != nil {
		if err := validateImpl(cmd, conf); err != nil {
			return fmt.Errorf("%s: %w", cmd.name, err)
		}
	}

	if cmd.impl == nil && len(cmd.subcommands) == 0 {
		return fmt.Errorf("empty command category: %s", cmd.name)
	}

	if cmd.impl != nil {
		if err := validateShortForms(cmd, assignedShortForms); err != nil {
			return fmt.Errorf("%s: %w", cmd.name, err)
		}
	}

	var hasDefault bool
	names := make(map[string]bool)
	for _, s := range cmd.subcommands {
		if s.name == "" {
			return fmt.Errorf("unnamed subcommand of: %s", cmd.name)
		}

		if names[s.name] {
			return fmt.Errorf("subcommand name conflict: %s", s.name)
		}

		names[s.name] = true
		if err := validateCommandTree(s, conf, assignedShortForms, false); err != nil {
			return fmt.Errorf("%s: %w", s.name, err)
		}

		if s.isDefault && cmd.impl != nil {
			return fmt.Errorf(
				"default subcommand defined for a command with explicit implementation: %s, %s",
				cmd.name,
				s.name,
			)
		}

		if s.isDefault && hasDefault {
			return fmt.Errorf("multiple default subcommands for: %s", cmd.name)
		}

		if s.isDefault {
			hasDefault = true
		}
	}

	return nil
}

func allShortForms(cmd Cmd) []string {
	var sf []string
	for _, sc := range cmd.subcommands {
		sf = append(sf, allShortForms(sc)...)
	}

	for i := 0; i < len(cmd.shortForms); i += 2 {
		sf = append(sf, cmd.shortForms[i])
	}

	return sf
}

func validateCommand(cmd Cmd, conf Config) error {
	assignedShortForms := make(map[string]string)
	if err := validateCommandTree(cmd, conf, assignedShortForms, true); err != nil {
		return err
	}

	asf := allShortForms(cmd)
	for _, sf := range asf {
		if _, ok := assignedShortForms[sf]; !ok {
			return fmt.Errorf("unassigned option short form: %s", sf)
		}
	}

	return nil
}