package runner

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"sync"

	"github.com/Sirupsen/logrus"
	"gitlab-odx.oracle.com/odx/functions/api/models"
	"gitlab-odx.oracle.com/odx/functions/api/runner/common"
)

// TODO kind of no reason to have FuncLogger interface... we can just do the thing.

type FuncLogger interface {
	Writer(ctx context.Context, appName, path, image, reqID string) io.WriteCloser
}

func NewFuncLogger(logDB models.FnLog) FuncLogger {
	// TODO we should probably make it somehow configurable to log to stderr and/or db but meh
	return &DefaultFuncLogger{
		logDB:   logDB,
		bufPool: &sync.Pool{New: func() interface{} { return new(bytes.Buffer) }},
		logPool: &sync.Pool{New: func() interface{} { return new(bytes.Buffer) }},
	}
}

// DefaultFuncLogger returns a WriteCloser that writes STDERR output from a
// container and outputs it in a parsed structured log format to attached
// STDERR as well as writing the log to the db when Close is called.
type DefaultFuncLogger struct {
	logDB   models.FnLog
	bufPool *sync.Pool // these are usually small, for buffering lines
	logPool *sync.Pool // these are usually large, for buffering whole logs
}

func (l *DefaultFuncLogger) Writer(ctx context.Context, appName, path, image, reqID string) io.WriteCloser {
	lbuf := l.bufPool.Get().(*bytes.Buffer)
	dbuf := l.logPool.Get().(*bytes.Buffer)

	close := func() error {
		// TODO we may want to toss out buffers that grow to grotesque size but meh they will prob get GC'd
		lbuf.Reset()
		dbuf.Reset()
		l.bufPool.Put(lbuf)
		l.logPool.Put(dbuf)
		return nil
	}

	// we don't need to limit the log writer, but we do need it to dispense lines
	linew := newLineWriterWithBuffer(lbuf, &logWriter{
		ctx:     ctx,
		appName: appName,
		path:    path,
		image:   image,
		reqID:   reqID,
	})

	const MB = 1 * 1024 * 1024 // pick a number any number.. TODO configurable ?

	// we don't need to log per line to db, but we do need to limit it
	limitw := newLimitWriter(MB, &dbWriter{
		Buffer: dbuf,
		db:     l.logDB,
		ctx:    ctx,
		reqID:  reqID,
	})

	// TODO / NOTE: we want linew to be first becauase limitw may error if limit
	// is reached but we still want to log. we should probably ignore hitting the
	// limit error since we really just want to not write too much to db and
	// that's handled as is. put buffers back last to avoid misuse, if there's
	// an error they won't get put back and that's really okay too.
	return multiWriteCloser{linew, limitw, &fCloser{close}}
}

// implements passthrough Write & arbitrary func close to have a seat at the cool kids lunch table
type fCloser struct {
	close func() error
}

func (f *fCloser) Write(b []byte) (int, error) { return len(b), nil }
func (f *fCloser) Close() error                { return f.close() }

// multiWriteCloser returns the first write or close that returns a non-nil
// err, if no non-nil err is returned, then the returned bytes written will be
// from the last call to write.
type multiWriteCloser []io.WriteCloser

func (m multiWriteCloser) Write(b []byte) (n int, err error) {
	for _, mw := range m {
		n, err = mw.Write(b)
		if err != nil {
			return n, err
		}
	}
	return n, err
}

func (m multiWriteCloser) Close() (err error) {
	for _, mw := range m {
		err = mw.Close()
		if err != nil {
			return err
		}
	}
	return err
}

// logWriter will log (to real stderr) every call to Write as a line. it should
// be wrapped with a lineWriter so that the output makes sense.
type logWriter struct {
	ctx     context.Context
	appName string
	path    string
	image   string
	reqID   string
}

func (l *logWriter) Write(b []byte) (int, error) {
	log := common.Logger(l.ctx)
	log = log.WithFields(logrus.Fields{"user_log": true, "app_name": l.appName, "path": l.path, "image": l.image, "call_id": l.reqID})
	log.Println(string(b))
	return len(b), nil
}

// lineWriter buffers all calls to Write and will call Write
// on the underlying writer once per new line. Close must
// be called to ensure that the buffer is flushed, and a newline
// will be appended in Close if none is present.
type lineWriter struct {
	b *bytes.Buffer
	w io.Writer
}

func newLineWriter(w io.Writer) io.WriteCloser {
	return &lineWriter{b: new(bytes.Buffer), w: w}
}

func newLineWriterWithBuffer(b *bytes.Buffer, w io.Writer) io.WriteCloser {
	return &lineWriter{b: b, w: w}
}

func (li *lineWriter) Write(ogb []byte) (int, error) {
	li.b.Write(ogb) // bytes.Buffer is guaranteed, read it!

	for {
		b := li.b.Bytes()
		i := bytes.IndexByte(b, '\n')
		if i < 0 {
			break // no more newlines in buffer
		}

		// write in this line and advance buffer past it
		l := b[:i+1]
		ns, err := li.w.Write(l)
		if err != nil {
			return ns, err
		}
		li.b.Next(len(l))
	}

	// technically we wrote all the bytes, so make things appear normal
	return len(ogb), nil
}

func (li *lineWriter) Close() error {
	// flush the remaining bytes in the buffer to underlying writer, adding a
	// newline if needed
	b := li.b.Bytes()
	if len(b) == 0 {
		return nil
	}

	if b[len(b)-1] != '\n' {
		b = append(b, '\n')
	}
	_, err := li.w.Write(b)
	return err
}

// dbWriter accumulates all calls to Write into an in memory buffer
// and writes them to the database when Close is called, returning
// any error from Close. it should be wrapped in a limitWriter to
// prevent blowing out the buffer and bloating the db.
type dbWriter struct {
	*bytes.Buffer

	db    models.FnLog
	ctx   context.Context
	reqID string
}

func (w *dbWriter) Close() error {
	return w.db.InsertLog(w.ctx, w.reqID, w.String())
}

func (w *dbWriter) Write(b []byte) (int, error) {
	return w.Buffer.Write(b)
}

// overrides Write, keeps Close
type limitWriter struct {
	n, max int
	io.WriteCloser
}

func newLimitWriter(max int, w io.WriteCloser) io.WriteCloser {
	return &limitWriter{max: max, WriteCloser: w}
}

func (l *limitWriter) Write(b []byte) (int, error) {
	if l.n >= l.max {
		return 0, errors.New("max log size exceeded, truncating log")
	}
	if l.n+len(b) >= l.max {
		// cut off to prevent gigantic line attack
		b = b[:l.max-l.n]
	}
	n, err := l.WriteCloser.Write(b)
	l.n += n
	if l.n >= l.max {
		// write in truncation message to log once
		l.WriteCloser.Write([]byte(fmt.Sprintf("\n-----max log size %d bytes exceeded, truncating log-----\n")))
	}
	return n, err
}