package level

import (
	"encoding/json"
	"fmt"

	"git.kirsle.net/apps/doodle/render"
)

// Types of chunks.
const (
	MapType int = iota
	GridType
)

// Chunk holds a single portion of the pixel canvas.
type Chunk struct {
	Type int // map vs. 2D array.
	Accessor
}

// JSONChunk holds a lightweight (interface-free) copy of the Chunk for
// unmarshalling JSON files from disk.
type JSONChunk struct {
	Type int             `json:"type"`
	Data json.RawMessage `json:"data"`
}

// Accessor provides a high-level API to interact with absolute pixel coordinates
// while abstracting away the details of how they're stored.
type Accessor interface {
	Inflate(*Palette) error
	Iter() <-chan Pixel
	IterViewport(viewport render.Rect) <-chan Pixel
	Get(render.Point) (*Swatch, error)
	Set(render.Point, *Swatch) error
	Delete(render.Point) error
	Len() int
	MarshalJSON() ([]byte, error)
	UnmarshalJSON([]byte) error
}

// NewChunk creates a new chunk.
func NewChunk() *Chunk {
	return &Chunk{
		Type:     MapType,
		Accessor: NewMapAccessor(),
	}
}

// Usage returns the percent of free space vs. allocated pixels in the chunk.
func (c *Chunk) Usage(size int) float64 {
	return float64(c.Len()) / float64(size)
}

// MarshalJSON writes the chunk to JSON.
func (c *Chunk) MarshalJSON() ([]byte, error) {
	data, err := c.Accessor.MarshalJSON()
	if err != nil {
		return []byte{}, err
	}

	generic := &JSONChunk{
		Type: c.Type,
		Data: data,
	}
	b, err := json.Marshal(generic)
	return b, err
}

// UnmarshalJSON loads the chunk from JSON and uses the correct accessor to
// parse the inner details.
func (c *Chunk) UnmarshalJSON(b []byte) error {
	// Parse it generically so we can hand off the inner "data" object to the
	// right accessor for unmarshalling.
	generic := &JSONChunk{}
	err := json.Unmarshal(b, generic)
	if err != nil {
		return fmt.Errorf("Chunk.UnmarshalJSON: failed to unmarshal into generic JSONChunk type: %s", err)
	}

	switch c.Type {
	case MapType:
		c.Accessor = NewMapAccessor()
		return c.Accessor.UnmarshalJSON(generic.Data)
	default:
		return fmt.Errorf("Chunk.UnmarshalJSON: unsupported chunk type '%d'", c.Type)
	}
}