package config

import (
	"fmt"
	"reflect"
	"sort"
	"strings"

	"github.com/hashicorp/go-multierror"
	"github.com/hashicorp/packer/template/interpolate"
	"github.com/mitchellh/mapstructure"
)

// DecodeOpts are the options for decoding configuration.
type DecodeOpts struct {
	// Metadata, if non-nil, will be set to the metadata post-decode
	Metadata *mapstructure.Metadata

	// Interpolate, if true, will automatically interpolate the
	// configuration with the given InterpolateContext. User variables
	// will be automatically detected and added in-place to the given
	// context.
	Interpolate        bool
	InterpolateContext *interpolate.Context
	InterpolateFilter  *interpolate.RenderFilter

	DecodeHooks []mapstructure.DecodeHookFunc
}

var DefaultDecodeHookFuncs = []mapstructure.DecodeHookFunc{
	uint8ToStringHook,
	stringToTrilean,
	mapstructure.StringToSliceHookFunc(","),
	mapstructure.StringToTimeDurationHookFunc(),
}

// Decode decodes the configuration into the target and optionally
// automatically interpolates all the configuration as it goes.
func Decode(target interface{}, config *DecodeOpts, raws ...interface{}) error {
	if config == nil {
		config = &DecodeOpts{Interpolate: true}
	}

	// Interpolate first
	if config.Interpolate {
		// Detect user variables from the raws and merge them into our context
		ctx, err := DetectContext(raws...)
		if err != nil {
			return err
		}
		if config.InterpolateContext == nil {
			config.InterpolateContext = ctx
		} else {
			config.InterpolateContext.BuildName = ctx.BuildName
			config.InterpolateContext.BuildType = ctx.BuildType
			config.InterpolateContext.TemplatePath = ctx.TemplatePath
			config.InterpolateContext.UserVariables = ctx.UserVariables
		}
		ctx = config.InterpolateContext

		// Render everything
		for i, raw := range raws {
			m, err := interpolate.RenderMap(raw, ctx, config.InterpolateFilter)
			if err != nil {
				return err
			}

			raws[i] = m
		}
	}

	decodeHookFuncs := DefaultDecodeHookFuncs
	if len(config.DecodeHooks) != 0 {
		decodeHookFuncs = config.DecodeHooks
	}

	// Build our decoder
	var md mapstructure.Metadata
	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
		Result:           target,
		Metadata:         &md,
		WeaklyTypedInput: true,
		DecodeHook:       mapstructure.ComposeDecodeHookFunc(decodeHookFuncs...),
	})
	if err != nil {
		return err
	}
	for _, raw := range raws {
		if err := decoder.Decode(raw); err != nil {
			return err
		}
	}

	// Set the metadata if it is set
	if config.Metadata != nil {
		*config.Metadata = md
	}

	// If we have unused keys, it is an error
	if len(md.Unused) > 0 {
		var err error
		sort.Strings(md.Unused)
		for _, unused := range md.Unused {
			if unused != "type" && !strings.HasPrefix(unused, "packer_") {
				err = multierror.Append(err, fmt.Errorf(
					"unknown configuration key: %q", unused))
			}
		}
		if err != nil {
			return err
		}
	}

	return nil
}

// DetectContext builds a base interpolate.Context, automatically
// detecting things like user variables from the raw configuration params.
func DetectContext(raws ...interface{}) (*interpolate.Context, error) {
	var s struct {
		BuildName     string            `mapstructure:"packer_build_name"`
		BuildType     string            `mapstructure:"packer_builder_type"`
		TemplatePath  string            `mapstructure:"packer_template_path"`
		Vars          map[string]string `mapstructure:"packer_user_variables"`
		SensitiveVars []string          `mapstructure:"packer_sensitive_variables"`
	}

	for _, r := range raws {
		if err := mapstructure.Decode(r, &s); err != nil {
			return nil, err
		}
	}

	return &interpolate.Context{
		BuildName:          s.BuildName,
		BuildType:          s.BuildType,
		TemplatePath:       s.TemplatePath,
		UserVariables:      s.Vars,
		SensitiveVariables: s.SensitiveVars,
	}, nil
}

func uint8ToStringHook(f reflect.Kind, t reflect.Kind, v interface{}) (interface{}, error) {
	// We need to convert []uint8 to string. We have to do this
	// because internally Packer uses MsgPack for RPC and the MsgPack
	// codec turns strings into []uint8
	if f == reflect.Slice && t == reflect.String {
		dataVal := reflect.ValueOf(v)
		dataType := dataVal.Type()
		elemKind := dataType.Elem().Kind()
		if elemKind == reflect.Uint8 {
			v = string(dataVal.Interface().([]uint8))
		}
	}

	return v, nil
}

func stringToTrilean(f reflect.Type, t reflect.Type, v interface{}) (interface{}, error) {
	// We have a custom data type, config, which we read from a string and
	// then cast to a *bool. Why? So that we can appropriately read "unset"
	// *bool values in order to intelligently default, even when the values are
	// being set by a template variable.

	testTril, _ := TrileanFromString("")
	if t == reflect.TypeOf(testTril) {
		// From value is string
		if f == reflect.TypeOf("") {
			tril, err := TrileanFromString(v.(string))
			if err != nil {
				return v, fmt.Errorf("Error parsing bool from given var: %s", err)
			}
			return tril, nil
		} else {
			// From value is boolean
			if f == reflect.TypeOf(true) {
				tril := TrileanFromBool(v.(bool))
				return tril, nil
			}
		}

	}
	return v, nil
}
