package busstate

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"strings"

	stdio "git.novox.be/novox/mesh-sdk/go"
	"git.novox.be/novox/mesh-sdk/go/buscalls"
)

// The put and get sessions of a value larger than one chunk (design 47 G §518, §345, §490, A-21): a bundle sends and asks the
// chunks as calls on its channel to the tool runner, which holds the session; nothing of it is on the bus. The capability
// word put-sessions names the two calls, so a tool runner that does not state it refuses the session at once.

// callID is the bundle's id for one session: random, so two sessions never share one.
func callID() string {
	var b [12]byte
	_, _ = rand.Read(b[:])
	return hex.EncodeToString(b[:])
}

// put sends data as a put session: chunks of buscalls.ChunkBytes in order, each answered before the next is sent, the
// answer to the last being the put's.
func (o Objects) putSession(name string, data []byte, description string) (buscalls.ObjectInfo, error) {
	if err := stdio.RequireCapability(stdio.CapPutSessions); err != nil {
		return buscalls.ObjectInfo{}, fmt.Errorf("putting %s, larger than one call carries: %w", name, err)
	}
	id := callID()
	for seq, at := uint32(1), 0; ; seq++ {
		end := min(at+buscalls.ChunkBytes, len(data))
		last := end == len(data)
		req := buscalls.ObjectsPutChunkRequest{Objects: o.local, Name: name, Call: id, Seq: seq, Last: last, Data: data[at:end]}
		if seq == 1 {
			req.Description = description // the first chunk carries it (design 47 G A-25)
		}
		raw, err := stdio.BusState(buscalls.ObjectsPutChunk, req)
		if err != nil {
			return buscalls.ObjectInfo{}, fmt.Errorf("putting %s, chunk %d: %w", name, seq, err)
		}
		var taken buscalls.ObjectsChunkTaken
		if err := json.Unmarshal(raw, &taken); err != nil {
			return buscalls.ObjectInfo{}, fmt.Errorf("the runtime's answer to a chunk of %s: %w", name, err)
		}
		if taken.Error != "" {
			return buscalls.ObjectInfo{}, fmt.Errorf("putting %s, chunk %d: %s", name, seq, taken.Error)
		}
		if last {
			var info buscalls.ObjectInfo
			if err := json.Unmarshal(raw, &info); err != nil {
				return info, fmt.Errorf("the runtime's answer to the put of %s: %w", name, err)
			}
			return info, nil
		}
		if taken.Seq != seq {
			return buscalls.ObjectInfo{}, fmt.Errorf("putting %s: chunk %d was answered as chunk %d", name, seq, taken.Seq)
		}
		at = end
	}
}

// getSession reads the chunks of the session the runtime opened for name, and checks the whole against the digest and the
// size it answered.
func getSession(name string, c buscalls.ObjectsChunked) (buscalls.ObjectData, error) {
	if err := stdio.RequireCapability(stdio.CapPutSessions); err != nil {
		return buscalls.ObjectData{}, fmt.Errorf("getting %s, larger than one call carries: %w", name, err)
	}
	var whole []byte
	for seq := uint32(1); ; seq++ {
		raw, err := stdio.BusState(buscalls.ObjectsGetChunk, buscalls.ObjectsGetChunkRequest{Call: c.Call, Seq: seq})
		if err != nil {
			return buscalls.ObjectData{}, fmt.Errorf("getting %s, chunk %d: %w", name, seq, err)
		}
		var chunk buscalls.ObjectsChunk
		if err := json.Unmarshal(raw, &chunk); err != nil {
			return buscalls.ObjectData{}, fmt.Errorf("the runtime's chunk %d of %s: %w", seq, name, err)
		}
		if chunk.Error != "" {
			return buscalls.ObjectData{}, fmt.Errorf("getting %s, chunk %d: %s", name, seq, chunk.Error)
		}
		if chunk.Seq != seq {
			return buscalls.ObjectData{}, fmt.Errorf("getting %s: chunk %d was answered as chunk %d", name, seq, chunk.Seq)
		}
		whole = append(whole, chunk.Data...)
		if chunk.Last {
			break
		}
	}
	sum := sha256.Sum256(whole)
	if c.Digest != "" && !strings.EqualFold(c.Digest, "sha256:"+hex.EncodeToString(sum[:])) {
		return buscalls.ObjectData{}, fmt.Errorf("getting %s: what was read is not the value the runtime named by %s", name, c.Digest)
	}
	if c.Size != 0 && c.Size != uint64(len(whole)) {
		return buscalls.ObjectData{}, fmt.Errorf("getting %s: %d bytes were read, the runtime said %d", name, len(whole), c.Size)
	}
	return buscalls.ObjectData{Info: buscalls.ObjectInfo{Name: name, Size: uint64(len(whole)), Digest: c.Digest}, Data: whole}, nil
}

// chunkedAnswer is the session an answer to a get opens, if it is not the value itself.
func chunkedAnswer(raw json.RawMessage) (buscalls.ObjectsChunked, bool) {
	var c buscalls.ObjectsChunked
	if json.Unmarshal(raw, &c) != nil {
		return c, false
	}
	switch strings.TrimSpace(string(c.Chunked)) {
	case "", "null", "0", "false":
		return c, false
	}
	return c, c.Call != ""
}