package ots

import (
	"encoding/hex"
	"fmt"
	"slices"
	"strings"

	"git.intruders.space/public/opentimestamps/varn"
)

// Header magic bytes
// Designed to be give the user some information in a hexdump, while being identified as 'data' by the file utility.
// \x00OpenTimestamps\x00\x00Proof\x00\xbf\x89\xe2\xe8\x84\xe8\x92\x94
var (
	HeaderMagic  = []byte{0x00, 0x4f, 0x70, 0x65, 0x6e, 0x54, 0x69, 0x6d, 0x65, 0x73, 0x74, 0x61, 0x6d, 0x70, 0x73, 0x00, 0x00, 0x50, 0x72, 0x6f, 0x6f, 0x66, 0x00, 0xbf, 0x89, 0xe2, 0xe8, 0x84, 0xe8, 0x92, 0x94}
	PendingMagic = []byte{0x83, 0xdf, 0xe3, 0x0d, 0x2e, 0xf9, 0x0c, 0x8e}
	BitcoinMagic = []byte{0x05, 0x88, 0x96, 0x0d, 0x73, 0xd7, 0x19, 0x01}
)

// A File represents the parsed content of an .ots file: it has an initial digest and
// a series of sequences of instructions. Each sequence must be evaluated separately, applying the operations
// on top of each other, starting with the .Digest until they end on an attestation.
type File struct {
	Digest    []byte
	Sequences []Sequence
}

func (ts File) GetPendingSequences() []Sequence {
	bitcoin := ts.GetBitcoinAttestedSequences()

	results := make([]Sequence, 0, len(ts.Sequences))
	for _, seq := range ts.Sequences {
		if len(seq) > 0 && seq[len(seq)-1].Attestation != nil && seq[len(seq)-1].Attestation.CalendarServerURL != "" {
			// this is a calendar sequence, fine
			// now we check if this same sequence isn't contained in a bigger one that contains a bitcoin attestation
			cseq := seq
			for _, bseq := range bitcoin {
				if len(bseq) < len(cseq) {
					continue
				}

				if slices.EqualFunc(bseq[0:len(cseq)], cseq, func(a, b Instruction) bool { return CompareInstructions(a, b) == 0 }) {
					goto thisSequenceIsAlreadyConfirmed
				}
			}

			// sequence not confirmed, so add it to pending result
			results = append(results, seq)

		thisSequenceIsAlreadyConfirmed:
			// skip this
			continue
		}
	}
	return results
}

func (ts File) GetBitcoinAttestedSequences() []Sequence {
	results := make([]Sequence, 0, len(ts.Sequences))
	for _, seq := range ts.Sequences {
		if len(seq) > 0 && seq[len(seq)-1].Attestation != nil && seq[len(seq)-1].Attestation.BitcoinBlockHeight > 0 {
			results = append(results, seq)
		}
	}
	return results
}

func (ts File) Human(withPartials bool) string {
	strs := make([]string, 0, 100)
	strs = append(strs, fmt.Sprintf("file digest: %x", ts.Digest))
	strs = append(strs, fmt.Sprintf("hashed with: sha256"))
	strs = append(strs, "instruction sequences:")
	for _, seq := range ts.Sequences {
		curr := ts.Digest
		strs = append(strs, "~>")
		strs = append(strs, "  start "+hex.EncodeToString(curr))
		for _, inst := range seq {
			line := "  "
			if inst.Operation != nil {
				line += inst.Operation.Name
				curr = inst.Operation.Apply(curr, inst.Argument)
				if inst.Operation.Binary {
					line += " " + hex.EncodeToString(inst.Argument)
				}
				if withPartials {
					line += " = " + hex.EncodeToString(curr)
				}
			} else if inst.Attestation != nil {
				line += inst.Attestation.Human()
			} else {
				panic(fmt.Sprintf("invalid instruction timestamp: %v", inst))
			}
			strs = append(strs, line)
		}
	}
	return strings.Join(strs, "\n")
}

func (ts File) SerializeToFile() []byte {
	data := make([]byte, 0, 5050)
	data = append(data, HeaderMagic...)
	data = varn.AppendVarUint(data, 1)
	data = append(data, 0x08) // sha256
	data = append(data, ts.Digest...)
	data = append(data, ts.SerializeInstructionSequences()...)
	return data
}

func (ts File) SerializeInstructionSequences() []byte {
	sequences := make([]Sequence, len(ts.Sequences))
	copy(sequences, ts.Sequences)

	// first we sort everything so the checkpoint stuff makes sense
	slices.SortFunc(sequences, func(a, b Sequence) int { return slices.CompareFunc(a, b, CompareInstructions) })

	// checkpoints we may leave to the next people
	sequenceCheckpoints := make([][]int, len(sequences))
	for s1 := range sequences {
		// keep an ordered slice of all the checkpoints we will potentially leave during our write journey for this sequence
		checkpoints := make([]int, 0, len(sequences[s1]))
		for s2 := s1 + 1; s2 < len(sequences); s2++ {
			chp := GetCommonPrefixIndex(sequences[s1], sequences[s2])
			if pos, found := slices.BinarySearch(checkpoints, chp); !found {
				checkpoints = append(checkpoints, -1)        // make room
				copy(checkpoints[pos+1:], checkpoints[pos:]) // move elements to the right
				checkpoints[pos] = chp                       // insert this
			}
		}
		sequenceCheckpoints[s1] = checkpoints
	}

	// now actually go through the sequences writing them
	result := make([]byte, 0, 500)
	for s, seq := range sequences {
		startingAt := 0
		if s > 0 {
			// we will always start at the last checkpoint left by the previous sequence
			startingAt = sequenceCheckpoints[s-1][len(sequenceCheckpoints[s-1])-1]
		}

		for i := startingAt; i < len(seq); i++ {
			// before writing anything, decide if we wanna leave a checkpoint here
			for _, chk := range sequenceCheckpoints[s] {
				if chk == i {
					// leave a checkpoint
					result = append(result, 0xff)
				}
			}

			inst := seq[i]
			if inst.Operation != nil {
				// write normal operation
				result = append(result, inst.Operation.Tag)
				if inst.Operation.Binary {
					result = varn.AppendVarBytes(result, inst.Argument)
				}
			} else if inst.Attestation != nil {
				// write attestation record
				result = append(result, 0x00)
				{
					// will use a new buffer for the actual attestation result
					abuf := make([]byte, 0, 100)
					if inst.BitcoinBlockHeight != 0 {
						result = append(result, BitcoinMagic...) // this goes in the main result buffer
						abuf = varn.AppendVarUint(abuf, inst.BitcoinBlockHeight)
					} else if inst.CalendarServerURL != "" {
						result = append(result, PendingMagic...) // this goes in the main result buffer
						abuf = varn.AppendVarBytes(abuf, []byte(inst.CalendarServerURL))
					} else {
						panic(fmt.Sprintf("invalid attestation: %v", inst))
					}
					result = varn.AppendVarBytes(result, abuf) // we append that result as varbytes
				}
			} else {
				panic(fmt.Sprintf("invalid instruction: %v", inst))
			}
		}
	}
	return result
}

func ParseOTSFile(buf varn.Buffer) (*File, error) {
	// read magic
	// read version [1 byte]
	// read crypto operation for file digest [1 byte]
	// read file digest [32 byte (depends)]
	if magic, err := buf.ReadBytes(len(HeaderMagic)); err != nil || !slices.Equal(HeaderMagic, magic) {
		return nil, fmt.Errorf("invalid ots file header '%s': %w", magic, err)
	}

	if version, err := buf.ReadVarUint(); err != nil || version != 1 {
		return nil, fmt.Errorf("invalid ots file version '%v': %w", version, err)
	}

	tag, err := buf.ReadByte()
	if err != nil {
		return nil, fmt.Errorf("failed to read operation byte: %w", err)
	}

	if op, err := ReadInstruction(buf, tag); err != nil || op.Operation.Name != "sha256" {
		return nil, fmt.Errorf("invalid crypto operation '%v', only sha256 supported: %w", op, err)
	}

	// if we got here assume the digest is sha256
	digest, err := buf.ReadBytes(32)
	if err != nil {
		return nil, fmt.Errorf("failed to read 32-byte digest: %w", err)
	}

	ts := &File{
		Digest: digest,
	}

	if seqs, err := ParseTimestamp(buf); err != nil {
		return nil, err
	} else {
		ts.Sequences = seqs
	}

	return ts, nil
}