package tind

import (
	"crypto/rand"
	"errors"
	"log"
)

// Config is a configuration for generating and working with TinD id's of
// possibly varying sizes and runesets
type Config struct {
	size     int
	runes    []rune
	runesize int
	mod      byte
}

const (
	defaultRunes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
	defaultSize  = 4
)

// New starts off a factory pattern to build a TinD
// with either the default values, or setting custom values
// using the `With` functions
// Example:
//
//		Get a default TinD id
//		`id := New().Gen()`
//
//		Get a TinD with 8 bytes but the default runeset
//		`id := New().WithSize(8).Gen()`
//
//	 Get a TinD of default size with a special runeset
//	 `id := New().WithRuneset("😃😡🕰️🧰BGD").Gen()`
//
// You can always define the configuration and create new TinD's
// using it.
// Example:
//
//	myNumberOnlyConfig := New().WithSize(8).WithRuneset("0123456789")
func New() *Config {
	c := &Config{
		size:     defaultSize,
		runes:    []rune(defaultRunes),
		runesize: len(defaultRunes),
	}
	c.calcMod()
	return c
}

// NewFrom will build a configuration from a byte slice. Because this is a
// byte slice, the provided input doesn't matter, it's more about the length,
func NewConfigFrom(in []byte) *Config {
func NewFrom(in []byte) *Config {
	c := New()
	c.size = len(in)
	c.calcMod()
	return c
}

// WithRuneset requires a string as input, where each character must be unique.
// The string can be comprised of any unique unicode character.
// Will filter out duplicate runes before storing it, meaning if you provide a
// runeset with duplicates, the size of the runeset will be reduced to ensure
// consistency. Dont' rely on len(runeset) of your custom runeset to be
// accurate.
//
// This does slow down initialization, but the final product still runs fast to
// generate ids
// When updating a runeset, the values of runesize and mod will be updated
func (c *Config) WithRuneset(r []rune) *Config {
	c.runes = ensureUniqueRunes(r)
	c.runesize = len(c.runes)
	c.calcMod()
	return c
}

func (c *Config) calcMod() {
	c.mod = byte(c.runesize - 1)
}

// ensureUniqueRunes loops through the provided runeset to make sure only unique
// runes are included. This ensures that, given the same runeset in the same
// order, a TinD can be decoded from a string.
func ensureUniqueRunes(r []rune) []rune {
	unq := make(map[rune]int)
	var index int
	// loop through the runes to find duplicates
	for _, v := range r {
		// if the current rune hasn't been seen yet, assign it
		if _, ok := unq[v]; !ok {
			unq[v] = index
			index++
		}
	}
	rr := make([]rune, len(unq))
	for k, n := range unq {
		rr[n] = k
	}
	return rr
}

// WithSize sets the number of bytes in the TinD ID
func (c *Config) WithSize(s int) *Config {
	c.size = s
	return c
}

// Zero returns a zero value TinD ID of the configured size
func (c *Config) Zero() TinD {
	t := TinD{
		bytes:  make([]byte, c.size),
		config: c,
	}
	return t
}

// Gen generates a TinD with the given configuration
func (c *Config) Gen() TinD {
	bytes := make([]byte, c.size)
	runes := make([]rune, c.size)
	_, err := rand.Read(bytes)
	if err != nil {
		log.Fatalln(err)
	}
	// Make sure each byte fits the rune so it can be encoded and decoded
	for i := 0; i < c.size; i++ {
		bytes[i] = bytes[i] & c.mod
		runes[i] = c.runes[bytes[i]]
	}
	t := TinD{
		bytes:  bytes,
		runes:  runes,
		config: c,
	}
	return t
}

// FromString takes a string representation of a TinD id and returns
// the actual TinD as bytes
func (c *Config) FromString(in string) (TinD, error) {
	// Make sure the number of characters matches what's needed
	if len(in) != c.size {
		return c.Zero(), errors.New("given id isn't the same size as the configuration")
	}
	t := TinD{
		bytes:  make([]byte, c.size),
		config: c,
	}
	r := []rune(in)
	for i := 0; i < c.size; i++ {
		for j := 0; j < c.runesize; j++ {
			if r[i] == c.runes[j] {
				t.bytes[i] = byte(j)
				break
			}
		}
	}
	return TinD(t), nil
}

// Load imports a TinD byte string, or really any byte string, that fits within
// the constraints of the configuration. You can't load an 8byte slice into a
// 4byte TinD configuration.
// To generate a configuration from a given byte slice, use NewConfigFrom.
func (c *Config) Load(in []byte) (TinD, error) {
	if len(in) != c.size {
		return c.Zero(), errors.New("given id isn't the same size as the configuration")
	}
	t := TinD{
		bytes:  in,
		config: c,
	}
	return t, nil
}