/*
Copyright 2018 The Doctl Authors All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package displayers

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"reflect"
	"strings"
	"text/tabwriter"
)

// Displayable is a displable entity. These are used for printing results.
type Displayable interface {
	Cols() []string
	ColMap() map[string]string
	KV() []map[string]interface{}
	JSON(io.Writer) error
}

// Displayer has the display options, the item to display, and where to display to
type Displayer struct {
	OutputType string
	ColumnList string
	NoHeaders  bool

	Item Displayable
	Out  io.Writer
}

// Display ends up rendering the content in one of two formats (text|json)
func (d *Displayer) Display() error {
	switch d.OutputType {
	case "json":
		if containsOnlyNilSlice(d.Item) {
			_, err := d.Out.Write([]byte("[]"))
			return err
		}
		return d.Item.JSON(d.Out)
	case "text":
		var cols []string
		for _, c := range strings.Split(strings.Join(strings.Fields(d.ColumnList), ""), ",") {
			if c != "" {
				cols = append(cols, c)
			}
		}

		return DisplayText(d.Item, d.Out, d.NoHeaders, cols)
	default:
		return fmt.Errorf("unknown output type")
	}
}

// DisplayText writes tabbed content to the passed in io.Writer
// while potentially adding or removing headers.
func DisplayText(item Displayable, out io.Writer, noHeaders bool, includeCols []string) error {
	w := new(tabwriter.Writer)
	w.Init(out, 0, 0, 4, ' ', 0)

	cols := item.Cols()
	if len(includeCols) > 0 && includeCols[0] != "" {
		cols = includeCols
	}

	if !noHeaders {
		headers := []string{}
		for _, k := range cols {
			col := item.ColMap()[k]
			if col == "" {
				return fmt.Errorf("unknown column %q", k)
			}

			headers = append(headers, col)
		}
		fmt.Fprintln(w, strings.Join(headers, "\t"))
	}

	for _, r := range item.KV() {
		values := []interface{}{}
		formats := []string{}

		for _, col := range cols {
			v := r[col]

			values = append(values, v)

			switch v.(type) {
			case string:
				formats = append(formats, "%s")
			case int:
				formats = append(formats, "%d")
			case float64:
				formats = append(formats, "%f")
			case bool:
				formats = append(formats, "%v")
			default:
				formats = append(formats, "%v")
			}
		}
		format := strings.Join(formats, "\t")
		fmt.Fprintf(w, format+"\n", values...)
	}

	return w.Flush()
}

func writeJSON(item interface{}, w io.Writer) error {
	b, err := json.Marshal(item)
	if err != nil {
		return err
	}

	var out bytes.Buffer
	err = json.Indent(&out, b, "", "  ")
	if err != nil {
		return err
	}
	_, err = out.WriteTo(w)

	return err
}

// containsOnlyNiSlice returns true if the given interface's concrete type is
// a pointer to a struct that contains a single nil slice field.
func containsOnlyNilSlice(i interface{}) bool {
	if reflect.TypeOf(i).Kind() != reflect.Ptr {
		return false
	}

	element := reflect.ValueOf(i).Elem()
	if element.NumField() != 1 {
		return false
	}

	slice := element.Field(0)
	if slice.Kind() != reflect.Slice {
		return false
	}

	if slice.Cap() != 0 {
		return false
	}
	if slice.Len() != 0 {
		return false
	}
	if slice.Pointer() != 0 {
		return false
	}

	return true
}
