// Copyright 2019 Google Inc.
//
// 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 axes

// value.go contains code dealing with values on the line chart.

import (
	"fmt"
	"math"

	"github.com/mum4k/termdash/internal/numbers"
)

// ValueOption is used to provide options to the NewValue function.
type ValueOption interface {
	// set sets the provided option.
	set(*valueOptions)
}

type valueOptions struct {
	formatter func(v float64) string
}

// valueOption implements ValueOption.
type valueOption func(opts *valueOptions)

// set implements ValueOption.set.
func (vo valueOption) set(opts *valueOptions) {
	vo(opts)
}

// ValueFormatter sets a custom formatter for the value.
func ValueFormatter(formatter func(float64) string) ValueOption {
	return valueOption(func(opts *valueOptions) {
		opts.formatter = formatter
	})
}

// Value represents one value.
type Value struct {
	// Value is the original unmodified value.
	Value float64
	// Rounded is the value rounded up to the nonZeroPlaces number of non-zero
	// decimal places.
	Rounded float64
	// ZeroDecimals indicates how many decimal places in Rounded have a value
	// of zero.
	ZeroDecimals int
	// NonZeroDecimals indicates the rounding precision used, it is provided on
	// a call to newValue.
	NonZeroDecimals int

	// formatter will format value to a string representation of the value,
	// if Formatter is not present it will fallback to default format.
	formatter func(float64) string
	// text value if this value was constructed using NewTextValue.
	text string
}

// String implements fmt.Stringer.
func (v *Value) String() string {
	return fmt.Sprintf("Value{Round(%v) => %v}", v.Value, v.Rounded)
}

// NewValue returns a new instance representing the provided value, rounding
// the value up to the specified number of non-zero decimal places.
func NewValue(v float64, nonZeroDecimals int, opts ...ValueOption) *Value {
	opt := &valueOptions{}
	for _, o := range opts {
		o.set(opt)
	}

	r, zd := numbers.RoundToNonZeroPlaces(v, nonZeroDecimals)
	return &Value{
		Value:           v,
		Rounded:         r,
		ZeroDecimals:    zd,
		NonZeroDecimals: nonZeroDecimals,
		formatter:       opt.formatter,
	}
}

// NewTextValue constructs a value out of the provided text.
func NewTextValue(text string) *Value {
	return &Value{
		Value:   math.NaN(),
		Rounded: math.NaN(),
		text:    text,
	}
}

// Text returns textual representation of the value.
func (v *Value) Text() string {
	if v.text != "" {
		return v.text
	}

	if v.formatter != nil {
		return v.formatter(v.Value)
	}

	return defaultFormatter(v.Rounded, v.NonZeroDecimals, v.ZeroDecimals)
}

func defaultFormatter(value float64, nonZeroDecimals, zeroDecimals int) string {
	if math.Ceil(value) == value {
		return fmt.Sprintf("%.0f", value)
	}

	format := fmt.Sprintf("%%.%df", nonZeroDecimals+zeroDecimals)
	t := fmt.Sprintf(format, value)
	if len(t) > 10 {
		t = fmt.Sprintf("%.2e", value)
	}

	return t
}