package gitdiff

import (
	"bufio"
	"fmt"
	"io"
)

// Parse parses a patch with changes for one or more files. Any content
// preceding the first file header is ignored. If an error occurs while
// parsing, files will contain all files parsed before the error.
func Parse(r io.Reader) (files []*File, err error) {
	p := &parser{r: bufio.NewReader(r)}

	var file *File
	for {
		file, err = p.ParseNextFileHeader()
		if err != nil {
			return
		}
		if file == nil {
			break
		}

		err = p.ParseFileChanges(file)
		if err != nil {
			return
		}

		files = append(files, file)
	}

	return files, nil
}

type parser struct {
	r        *bufio.Reader
	lineno   int64
	nextLine string
}

// ParseNextFileHeader finds and parses the next file header in the stream. It
// returns nil if no headers are found before the end of the stream.
func (p *parser) ParseNextFileHeader() (*File, error) {
	panic("unimplemented")
}

// ParseFileChanges parses file changes until the next file header or the end
// of the stream and attaches them to the given file.
func (p *parser) ParseFileChanges(f *File) error {
	panic("unimplemented")
}

// Line reads and returns the next line.
func (p *parser) Line() (line string, err error) {
	if p.nextLine != "" {
		line = p.nextLine
		p.nextLine = ""
	} else {
		line, err = p.r.ReadString('\n')
	}
	p.lineno++
	return
}

// PeekLine reads and returns the next line without advancing the parser.
func (p *parser) PeekLine() (line string, err error) {
	if p.nextLine != "" {
		line = p.nextLine
	} else {
		line, err = p.r.ReadString('\n')
	}
	p.nextLine = line
	return
}

// Errorf generates an error and appends the current line information.
func (p *parser) Errorf(msg string, args ...interface{}) error {
	return fmt.Errorf("gitdiff: line %d: %s", p.lineno, fmt.Sprintf(msg, args...))
}