package commands

import (
	"context"
	"errors"
	"fmt"
	"io"
	"strings"

	cmdenv "github.com/ipfs/kubo/core/commands/cmdenv"

	iface "github.com/ipfs/boxo/coreiface"
	path "github.com/ipfs/boxo/coreiface/path"
	merkledag "github.com/ipfs/boxo/ipld/merkledag"
	cid "github.com/ipfs/go-cid"
	cidenc "github.com/ipfs/go-cidutil/cidenc"
	cmds "github.com/ipfs/go-ipfs-cmds"
	ipld "github.com/ipfs/go-ipld-format"
)

var refsEncoderMap = cmds.EncoderMap{
	cmds.Text: cmds.MakeTypedEncoder(func(req *cmds.Request, w io.Writer, out *RefWrapper) error {
		if out.Err != "" {
			return fmt.Errorf(out.Err)
		}
		fmt.Fprintln(w, out.Ref)

		return nil
	}),
}

// 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"
)

// RefsCmd is the `ipfs refs` command
var RefsCmd = &cmds.Command{
	Helptext: cmds.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>

List all references recursively by using the flag '-r'.

NOTE: Like most other commands, Kubo will try to fetch the blocks of the passed path if they can't be found in the local store if it is running in online mode.
`,
	},
	Subcommands: map[string]*cmds.Command{
		"local": RefsLocalCmd,
	},
	Arguments: []cmds.Argument{
		cmds.StringArg("ipfs-path", true, true, "Path to the object(s) to list refs from.").EnableStdin(),
	},
	Options: []cmds.Option{
		cmds.StringOption(refsFormatOptionName, "Emit edges with given format. Available tokens: <src> <dst> <linkname>.").WithDefault("<dst>"),
		cmds.BoolOption(refsEdgesOptionName, "e", "Emit edge format: `<from> -> <to>`."),
		cmds.BoolOption(refsUniqueOptionName, "u", "Omit duplicate refs from output."),
		cmds.BoolOption(refsRecursiveOptionName, "r", "Recursively list links of child nodes."),
		cmds.IntOption(refsMaxDepthOptionName, "Only for recursive refs, limits fetch and listing to the given depth").WithDefault(-1),
	},
	Run: func(req *cmds.Request, res cmds.ResponseEmitter, env cmds.Environment) error {
		err := req.ParseBodyArgs()
		if err != nil {
			return err
		}

		ctx := req.Context
		api, err := cmdenv.GetApi(env, req)
		if err != nil {
			return err
		}

		enc, err := cmdenv.GetCidEncoder(req)
		if err != nil {
			return err
		}

		unique, _ := req.Options[refsUniqueOptionName].(bool)
		recursive, _ := req.Options[refsRecursiveOptionName].(bool)
		maxDepth, _ := req.Options[refsMaxDepthOptionName].(int)
		edges, _ := req.Options[refsEdgesOptionName].(bool)
		format, _ := req.Options[refsFormatOptionName].(string)

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

		if edges {
			if format != "<dst>" {
				return errors.New("using format argument with edges is not allowed")
			}

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

		// TODO: use session for resolving as well.
		objs, err := objectsForPaths(ctx, api, req.Arguments)
		if err != nil {
			return err
		}

		rw := RefWriter{
			res:      res,
			DAG:      merkledag.NewSession(ctx, api.Dag()),
			Ctx:      ctx,
			Unique:   unique,
			PrintFmt: format,
			MaxDepth: maxDepth,
		}

		for _, o := range objs {
			if _, err := rw.WriteRefs(o, enc); err != nil {
				if err := res.Emit(&RefWrapper{Err: err.Error()}); err != nil {
					return err
				}
			}
		}

		return nil
	},
	Encoders: refsEncoderMap,
	Type:     RefWrapper{},
}

var RefsLocalCmd = &cmds.Command{
	Helptext: cmds.HelpText{
		Tagline: "List all local references.",
		ShortDescription: `
Displays the hashes of all local objects. NOTE: This treats all local objects as "raw blocks" and returns CIDv1-Raw CIDs.
`,
	},

	Run: func(req *cmds.Request, res cmds.ResponseEmitter, env cmds.Environment) error {
		ctx := req.Context
		n, err := cmdenv.GetNode(env)
		if err != nil {
			return err
		}

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

		for k := range allKeys {
			err := res.Emit(&RefWrapper{Ref: k.String()})
			if err != nil {
				return err
			}
		}

		return nil
	},
	Encoders: refsEncoderMap,
	Type:     RefWrapper{},
}

func objectsForPaths(ctx context.Context, n iface.CoreAPI, paths []string) ([]cid.Cid, error) {
	roots := make([]cid.Cid, len(paths))
	for i, sp := range paths {
		o, err := n.ResolvePath(ctx, path.New(sp))
		if err != nil {
			return nil, err
		}
		roots[i] = o.Cid()
	}
	return roots, nil
}

type RefWrapper struct {
	Ref string
	Err string
}

type RefWriter struct {
	res cmds.ResponseEmitter
	DAG ipld.NodeGetter
	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(c cid.Cid, enc cidenc.Encoder) (int, error) {
	n, err := rw.DAG.Get(rw.Ctx, c)
	if err != nil {
		return 0, err
	}
	return rw.writeRefsRecursive(n, 0, enc)
}

func (rw *RefWriter) writeRefsRecursive(n ipld.Node, depth int, enc cidenc.Encoder) (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, enc); 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, enc)
			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, enc cidenc.Encoder) 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>", enc.Encode(from), -1)
		s = strings.Replace(s, "<dst>", enc.Encode(to), -1)
		s = strings.Replace(s, "<linkname>", linkname, -1)
	default:
		s += enc.Encode(to)
	}

	return rw.res.Emit(&RefWrapper{Ref: s})
}
