package buffer

import (
	"bytes"
	"fmt"
	"log/slog"
	"os"
	"time"

	"code.chimeric.al/dwrz/wen/internal/editor/buffer/line"
)

type Buffer struct {
	cursor *Cursor
	lines  []*line.Line
	log    *slog.Logger
	name   string
	offset *offset
	saved  time.Time
}

// offset is the 0-indexed first visible display column (glyph) and row (line)
// of the buffer viewport.
type offset struct {
	glyph int
	line  int
}

func (b *Buffer) CursorLine() *line.Line {
	return b.lines[b.cursor.line]
}

func (b *Buffer) Name() string {
	return b.name
}

type NewBufferParams struct {
	Name string
	Log  *slog.Logger
}

// Create creates or truncates the named file on disk.
// It returns a Buffer initialized with a single empty line,
// so CursorLine is always valid.
func Create(p NewBufferParams) (*Buffer, error) {
	var b = &Buffer{
		cursor: &Cursor{},
		lines:  []*line.Line{{}},
		log:    p.Log,
		name:   p.Name,
		offset: &offset{},
	}

	// Create the file.
	f, err := os.Create(b.name)
	if err != nil {
		return nil, fmt.Errorf("failed to create file: %w", err)
	}
	if err := f.Close(); err != nil {
		return nil, fmt.Errorf("failed to close file: %w", err)
	}

	return b, nil
}

// Open reads the named file into a Buffer. If the file is empty, the Buffer
// is initialized with a single empty line so CursorLine is always valid.
func Open(p NewBufferParams) (*Buffer, error) {
	var b = &Buffer{
		cursor: &Cursor{},
		lines:  []*line.Line{},
		log:    p.Log,
		name:   p.Name,
		offset: &offset{},
	}

	data, err := os.ReadFile(b.name)
	if err != nil {
		return nil, fmt.Errorf("failed to open file: %w", err)
	}

	// Trim a single trailing newline so saving doesn't add an extra blank line.
	data = bytes.TrimSuffix(data, []byte("\n"))
	data = bytes.TrimSuffix(data, []byte("\r"))

	if len(data) > 0 {
		for _, raw := range bytes.Split(data, []byte("\n")) {
			raw = bytes.TrimSuffix(raw, []byte("\r"))
			b.lines = append(b.lines, line.New(string(raw)))
		}
	}

	// Add a line to write in, if the file is empty.
	if len(b.lines) == 0 {
		b.lines = append(b.lines, &line.Line{})
	}

	return b, nil
}