/*
Copyright The ORAS Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package content

import (
	"context"
	"errors"
	"io"
	"time"

	"github.com/containerd/containerd/content"
	"github.com/opencontainers/go-digest"
)

// PassthroughWriter takes an input stream and passes it through to an underlying writer,
// while providing the ability to manipulate the stream before it gets passed through
type PassthroughWriter struct {
	writer           content.Writer
	pipew            *io.PipeWriter
	digester         digest.Digester
	size             int64
	underlyingWriter *underlyingWriter
	reader           *io.PipeReader
	hash             *digest.Digest
	done             chan error
}

// NewPassthroughWriter creates a pass-through writer that allows for processing
// the content via an arbitrary function. The function should do whatever processing it
// wants, reading from the Reader to the Writer. When done, it must indicate via
// sending an error or nil to the Done
func NewPassthroughWriter(writer content.Writer, f func(r io.Reader, w io.Writer, done chan<- error), opts ...WriterOpt) content.Writer {
	// process opts for default
	wOpts := DefaultWriterOpts()
	for _, opt := range opts {
		if err := opt(&wOpts); err != nil {
			return nil
		}
	}

	r, w := io.Pipe()
	pw := &PassthroughWriter{
		writer:   writer,
		pipew:    w,
		digester: digest.Canonical.Digester(),
		underlyingWriter: &underlyingWriter{
			writer:   writer,
			digester: digest.Canonical.Digester(),
			hash:     wOpts.OutputHash,
		},
		reader: r,
		hash:   wOpts.InputHash,
		done:   make(chan error, 1),
	}
	go f(r, pw.underlyingWriter, pw.done)
	return pw
}

func (pw *PassthroughWriter) Write(p []byte) (n int, err error) {
	n, err = pw.pipew.Write(p)
	if pw.hash == nil {
		pw.digester.Hash().Write(p[:n])
	}
	pw.size += int64(n)
	return
}

func (pw *PassthroughWriter) Close() error {
	if pw.pipew != nil {
		pw.pipew.Close()
	}
	pw.writer.Close()
	return nil
}

// Digest may return empty digest or panics until committed.
func (pw *PassthroughWriter) Digest() digest.Digest {
	if pw.hash != nil {
		return *pw.hash
	}
	return pw.digester.Digest()
}

// Commit commits the blob (but no roll-back is guaranteed on an error).
// size and expected can be zero-value when unknown.
// Commit always closes the writer, even on error.
// ErrAlreadyExists aborts the writer.
func (pw *PassthroughWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
	if pw.pipew != nil {
		pw.pipew.Close()
	}
	err := <-pw.done
	if pw.reader != nil {
		pw.reader.Close()
	}
	if err != nil && err != io.EOF {
		return err
	}

	// Some underlying writers will validate an expected digest, so we need the option to pass it
	// that digest. That is why we caluclate the digest of the underlying writer throughout the write process.
	return pw.writer.Commit(ctx, pw.underlyingWriter.size, pw.underlyingWriter.Digest(), opts...)
}

// Status returns the current state of write
func (pw *PassthroughWriter) Status() (content.Status, error) {
	return pw.writer.Status()
}

// Truncate updates the size of the target blob
func (pw *PassthroughWriter) Truncate(size int64) error {
	return pw.writer.Truncate(size)
}

// underlyingWriter implementation of io.Writer to write to the underlying
// io.Writer
type underlyingWriter struct {
	writer   content.Writer
	digester digest.Digester
	size     int64
	hash     *digest.Digest
}

// Write write to the underlying writer
func (u *underlyingWriter) Write(p []byte) (int, error) {
	n, err := u.writer.Write(p)
	if err != nil {
		return 0, err
	}

	if u.hash == nil {
		u.digester.Hash().Write(p)
	}
	u.size += int64(len(p))
	return n, nil
}

// Size get total size written
func (u *underlyingWriter) Size() int64 {
	return u.size
}

// Digest may return empty digest or panics until committed.
func (u *underlyingWriter) Digest() digest.Digest {
	if u.hash != nil {
		return *u.hash
	}
	return u.digester.Digest()
}

// PassthroughMultiWriter single writer that passes through to multiple writers, allowing the passthrough
// function to select which writer to use.
type PassthroughMultiWriter struct {
	writers   []*PassthroughWriter
	pipew     *io.PipeWriter
	digester  digest.Digester
	size      int64
	reader    *io.PipeReader
	hash      *digest.Digest
	done      chan error
	startedAt time.Time
	updatedAt time.Time
}

func NewPassthroughMultiWriter(writers func(name string) (content.Writer, error), f func(r io.Reader, getwriter func(name string) io.Writer, done chan<- error), opts ...WriterOpt) content.Writer {
	// process opts for default
	wOpts := DefaultWriterOpts()
	for _, opt := range opts {
		if err := opt(&wOpts); err != nil {
			return nil
		}
	}

	r, w := io.Pipe()

	pmw := &PassthroughMultiWriter{
		startedAt: time.Now(),
		updatedAt: time.Now(),
		done:      make(chan error, 1),
		digester: digest.Canonical.Digester(),
		hash:     wOpts.InputHash,
		pipew: w,
		reader: r,
	}

	// get our output writers
	getwriter := func(name string) io.Writer {
		writer, err := writers(name)
		if err != nil || writer == nil {
			return nil
		}
		pw := &PassthroughWriter{
			writer:   writer,
			digester: digest.Canonical.Digester(),
			underlyingWriter: &underlyingWriter{
				writer:   writer,
				digester: digest.Canonical.Digester(),
				hash:     wOpts.OutputHash,
			},
			done:   make(chan error, 1),
		}
		pmw.writers = append(pmw.writers, pw)
		return pw.underlyingWriter
	}
	go f(r, getwriter, pmw.done)
	return pmw
}

func (pmw *PassthroughMultiWriter) Write(p []byte) (n int, err error) {
	n, err = pmw.pipew.Write(p)
	if pmw.hash == nil {
		pmw.digester.Hash().Write(p[:n])
	}
	pmw.size += int64(n)
	pmw.updatedAt = time.Now()
	return
}

func (pmw *PassthroughMultiWriter) Close() error {
	pmw.pipew.Close()
	for _, w := range pmw.writers {
		w.Close()
	}
	return nil
}

// Digest may return empty digest or panics until committed.
func (pmw *PassthroughMultiWriter) Digest() digest.Digest {
	if pmw.hash != nil {
		return *pmw.hash
	}
	return pmw.digester.Digest()
}

// Commit commits the blob (but no roll-back is guaranteed on an error).
// size and expected can be zero-value when unknown.
// Commit always closes the writer, even on error.
// ErrAlreadyExists aborts the writer.
func (pmw *PassthroughMultiWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
	pmw.pipew.Close()
	err := <-pmw.done
	if pmw.reader != nil {
		pmw.reader.Close()
	}
	if err != nil && err != io.EOF {
		return err
	}

	// Some underlying writers will validate an expected digest, so we need the option to pass it
	// that digest. That is why we caluclate the digest of the underlying writer throughout the write process.
	for _, w := range pmw.writers {
		// maybe this should be Commit(ctx, pw.underlyingWriter.size, pw.underlyingWriter.Digest(), opts...)
		w.done <- err
		if err := w.Commit(ctx, size, expected, opts...); err != nil {
			return err
		}
	}
	return nil
}

// Status returns the current state of write
func (pmw *PassthroughMultiWriter) Status() (content.Status, error) {
	return content.Status{
		StartedAt: pmw.startedAt,
		UpdatedAt: pmw.updatedAt,
		Total:     pmw.size,
	}, nil
}

// Truncate updates the size of the target blob, but cannot do anything with a multiwriter
func (pmw *PassthroughMultiWriter) Truncate(size int64) error {
	return errors.New("truncate unavailable on multiwriter")
}