package commands

import (
	"bytes"
	"context"
	"errors"
	"io"
	"strings"

	cmds "github.com/ipfs/go-ipfs/commands"
	"github.com/ipfs/go-ipfs/core"
	e "github.com/ipfs/go-ipfs/core/commands/e"

	cid "gx/ipfs/QmPSQnBKM9g7BaUcZCvswUJVscQ1ipjmwxN5PXCjkp9EQ7/go-cid"
	ipld "gx/ipfs/QmdDXJs4axxefSPgK6Y1QhpJWKuDPnGJiqgq4uncb4rFHL/go-ipld-format"
	cmdkit "gx/ipfs/Qmde5VP1qUkyQXKCfmEUA7bP64V2HAptbJ7phuPp7jXWwg/go-ipfs-cmdkit"
	path "gx/ipfs/QmdrpbDgeYH3VxkCciQCJY5LkDYdXtig6unDzQmMxFtWEw/go-path"
)

// KeyList is a general type for outputting lists of keys
type KeyList struct {
	Keys []cid.Cid
}

const (
	refsFormatOptionName    = "format"
	refsEdgesOptionName     = "edges"
	refsUniqueOptionName    = "unique"
	refsRecursiveOptionName = "recursive"
	refsMaxDepthOptionName  = "max-depth"
)

// KeyListTextMarshaler outputs a KeyList as plaintext, one key per line
func KeyListTextMarshaler(res cmds.Response) (io.Reader, error) {
	out, err := unwrapOutput(res.Output())
	if err != nil {
		return nil, err
	}

	output, ok := out.(*KeyList)
	if !ok {
		return nil, e.TypeErr(output, out)
	}

	buf := new(bytes.Buffer)
	for _, key := range output.Keys {
		buf.WriteString(key.String() + "\n")
	}
	return buf, nil
}

var RefsCmd = &cmds.Command{
	Helptext: cmdkit.HelpText{
		Tagline: "List links (references) from an object.",
		ShortDescription: `
Lists the hashes of all the links an IPFS or IPNS object(s) contains,
with the following format:

  <link base58 hash>

NOTE: List all references recursively by using the flag '-r'.
`,
	},
	Subcommands: map[string]*cmds.Command{
		"local": RefsLocalCmd,
	},
	Arguments: []cmdkit.Argument{
		cmdkit.StringArg("ipfs-path", true, true, "Path to the object(s) to list refs from.").EnableStdin(),
	},
	Options: []cmdkit.Option{
		cmdkit.StringOption(refsFormatOptionName, "Emit edges with given format. Available tokens: <src> <dst> <linkname>.").WithDefault("<dst>"),
		cmdkit.BoolOption(refsEdgesOptionName, "e", "Emit edge format: `<from> -> <to>`."),
		cmdkit.BoolOption(refsUniqueOptionName, "u", "Omit duplicate refs from output."),
		cmdkit.BoolOption(refsRecursiveOptionName, "r", "Recursively list links of child nodes."),
		cmdkit.IntOption(refsMaxDepthOptionName, "Only for recursive refs, limits fetch and listing to the given depth").WithDefault(-1),
	},
	Run: func(req cmds.Request, res cmds.Response) {
		ctx := req.Context()
		n, err := req.InvocContext().GetNode()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		unique, _, err := req.Option(refsUniqueOptionName).Bool()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		recursive, _, err := req.Option(refsRecursiveOptionName).Bool()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		maxDepth, _, err := req.Option(refsMaxDepthOptionName).Int()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		if !recursive {
			maxDepth = 1 // write only direct refs
		}

		format, _, err := req.Option(refsFormatOptionName).String()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		edges, _, err := req.Option(refsEdgesOptionName).Bool()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}
		if edges {
			if format != "<dst>" {
				res.SetError(errors.New("using format argument with edges is not allowed"),
					cmdkit.ErrClient)
				return
			}

			format = "<src> -> <dst>"
		}

		objs, err := objectsForPaths(ctx, n, req.Arguments())
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		out := make(chan interface{})
		res.SetOutput((<-chan interface{})(out))

		go func() {
			defer close(out)

			rw := RefWriter{
				out:      out,
				DAG:      n.DAG,
				Ctx:      ctx,
				Unique:   unique,
				PrintFmt: format,
				MaxDepth: maxDepth,
			}

			for _, o := range objs {
				if _, err := rw.WriteRefs(o); err != nil {
					select {
					case out <- &RefWrapper{Err: err.Error()}:
					case <-ctx.Done():
					}
					return
				}
			}
		}()
	},
	Marshalers: refsMarshallerMap,
	Type:       RefWrapper{},
}

var RefsLocalCmd = &cmds.Command{
	Helptext: cmdkit.HelpText{
		Tagline: "List all local references.",
		ShortDescription: `
Displays the hashes of all local objects.
`,
	},

	Run: func(req cmds.Request, res cmds.Response) {
		ctx := req.Context()
		n, err := req.InvocContext().GetNode()
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		// todo: make async
		allKeys, err := n.Blockstore.AllKeysChan(ctx)
		if err != nil {
			res.SetError(err, cmdkit.ErrNormal)
			return
		}

		out := make(chan interface{})
		res.SetOutput((<-chan interface{})(out))

		go func() {
			defer close(out)

			for k := range allKeys {
				select {
				case out <- &RefWrapper{Ref: k.String()}:
				case <-req.Context().Done():
					return
				}
			}
		}()
	},
	Marshalers: refsMarshallerMap,
	Type:       RefWrapper{},
}

var refsMarshallerMap = cmds.MarshalerMap{
	cmds.Text: func(res cmds.Response) (io.Reader, error) {
		v, err := unwrapOutput(res.Output())
		if err != nil {
			return nil, err
		}

		obj, ok := v.(*RefWrapper)
		if !ok {
			return nil, e.TypeErr(obj, v)
		}

		if obj.Err != "" {
			return nil, errors.New(obj.Err)
		}

		return strings.NewReader(obj.Ref + "\n"), nil
	},
}

func objectsForPaths(ctx context.Context, n *core.IpfsNode, paths []string) ([]ipld.Node, error) {
	objects := make([]ipld.Node, len(paths))
	for i, sp := range paths {
		p, err := path.ParsePath(sp)
		if err != nil {
			return nil, err
		}

		o, err := core.Resolve(ctx, n.Namesys, n.Resolver, p)
		if err != nil {
			return nil, err
		}
		objects[i] = o
	}
	return objects, nil
}

type RefWrapper struct {
	Ref string
	Err string
}

type RefWriter struct {
	out chan interface{}
	DAG ipld.DAGService
	Ctx context.Context

	Unique   bool
	MaxDepth int
	PrintFmt string

	seen map[string]int
}

// WriteRefs writes refs of the given object to the underlying writer.
func (rw *RefWriter) WriteRefs(n ipld.Node) (int, error) {
	return rw.writeRefsRecursive(n, 0)

}

func (rw *RefWriter) writeRefsRecursive(n ipld.Node, depth int) (int, error) {
	nc := n.Cid()

	var count int
	for i, ng := range ipld.GetDAG(rw.Ctx, rw.DAG, n) {
		lc := n.Links()[i].Cid
		goDeeper, shouldWrite := rw.visit(lc, depth+1) // The children are at depth+1

		// Avoid "Get()" on the node and continue with next Link.
		// We can do this if:
		// - We printed it before (thus it was already seen and
		//   fetched with Get()
		// - AND we must not go deeper.
		// This is an optimization for pruned branches which have been
		// visited before.
		if !shouldWrite && !goDeeper {
			continue
		}

		// We must Get() the node because:
		// - it is new (never written)
		// - OR we need to go deeper.
		// This ensures printed refs are always fetched.
		nd, err := ng.Get(rw.Ctx)
		if err != nil {
			return count, err
		}

		// Write this node if not done before (or !Unique)
		if shouldWrite {
			if err := rw.WriteEdge(nc, lc, n.Links()[i].Name); err != nil {
				return count, err
			}
			count++
		}

		// Keep going deeper. This happens:
		// - On unexplored branches
		// - On branches not explored deep enough
		// Note when !Unique, branches are always considered
		// unexplored and only depth limits apply.
		if goDeeper {
			c, err := rw.writeRefsRecursive(nd, depth+1)
			count += c
			if err != nil {
				return count, err
			}
		}
	}

	return count, nil
}

// visit returns two values:
// - the first boolean is true if we should keep traversing the DAG
// - the second boolean is true if we should print the CID
//
// visit will do branch pruning depending on rw.MaxDepth, previously visited
// cids and whether rw.Unique is set. i.e. rw.Unique = false and
// rw.MaxDepth = -1 disables any pruning. But setting rw.Unique to true will
// prune already visited branches at the cost of keeping as set of visited
// CIDs in memory.
func (rw *RefWriter) visit(c cid.Cid, depth int) (bool, bool) {
	atMaxDepth := rw.MaxDepth >= 0 && depth == rw.MaxDepth
	overMaxDepth := rw.MaxDepth >= 0 && depth > rw.MaxDepth

	// Shortcut when we are over max depth. In practice, this
	// only applies when calling refs with --maxDepth=0, as root's
	// children are already over max depth. Otherwise nothing should
	// hit this.
	if overMaxDepth {
		return false, false
	}

	// We can shortcut right away if we don't need unique output:
	//   - we keep traversing when not atMaxDepth
	//   - always print
	if !rw.Unique {
		return !atMaxDepth, true
	}

	// Unique == true from this point.
	// Thus, we keep track of seen Cids, and their depth.
	if rw.seen == nil {
		rw.seen = make(map[string]int)
	}
	key := string(c.Bytes())
	oldDepth, ok := rw.seen[key]

	// Unique == true && depth < MaxDepth (or unlimited) from this point

	// Branch pruning cases:
	// - We saw the Cid before and either:
	//   - Depth is unlimited (MaxDepth = -1)
	//   - We saw it higher (smaller depth) in the DAG (means we must have
	//     explored deep enough before)
	// Because we saw the CID, we don't print it again.
	if ok && (rw.MaxDepth < 0 || oldDepth <= depth) {
		return false, false
	}

	// Final case, we must keep exploring the DAG from this CID
	// (unless we hit the depth limit).
	// We note down its depth because it was either not seen
	// or is lower than last time.
	// We print if it was not seen.
	rw.seen[key] = depth
	return !atMaxDepth, !ok
}

// Write one edge
func (rw *RefWriter) WriteEdge(from, to cid.Cid, linkname string) error {
	if rw.Ctx != nil {
		select {
		case <-rw.Ctx.Done(): // just in case.
			return rw.Ctx.Err()
		default:
		}
	}

	var s string
	switch {
	case rw.PrintFmt != "":
		s = rw.PrintFmt
		s = strings.Replace(s, "<src>", from.String(), -1)
		s = strings.Replace(s, "<dst>", to.String(), -1)
		s = strings.Replace(s, "<linkname>", linkname, -1)
	default:
		s += to.String()
	}

	rw.out <- &RefWrapper{Ref: s}
	return nil
}