package ots

import (
	"fmt"
	"slices"
	"strings"

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

// a Instruction can be an operation like "append" or "prepend" (this will be the case when .Operation != nil)
// or an attestation (when .Attestation != nil).
// It will have a non-nil .Argument whenever the operation requires an argument.
type Instruction struct {
	*Operation
	Argument []byte
	*Attestation
}

func GetCommonPrefixIndex(s1 []Instruction, s2 []Instruction) int {
	n := min(len(s1), len(s2))
	for i := 0; i < n; i++ {
		if CompareInstructions(s1[i], s2[i]) != 0 {
			return i
		}
	}
	return n
}

// CompareInstructions returns negative if a<b, 0 if a=b and positive if a>b.
// It considers an operation smaller than an attestation, a pending attestation smaller than a Bitcoin attestation.
// It orders operations by their tag byte and then by their argument.
func CompareInstructions(a, b Instruction) int {
	if a.Operation != nil {
		if b.Attestation != nil {
			// a is an operation but b is an attestation, a is bigger
			return +1
		}
		if a.Operation == b.Operation {
			// if both are the same operation sort by the argument
			return slices.Compare(a.Argument, b.Argument)
		}

		// sort by the operation
		if a.Operation.Tag < b.Operation.Tag {
			return -1
		} else if a.Operation.Tag > b.Operation.Tag {
			return 1
		} else {
			return 0
		}
	} else if a.Attestation != nil && b.Attestation == nil {
		// a is an attestation but b is not, b is bigger
		return -1
	} else if a.Attestation != nil && b.Attestation != nil {
		// both are attestations
		if a.Attestation.BitcoinBlockHeight == 0 && b.Attestation.BitcoinBlockHeight == 0 {
			// none are bitcoin attestations
			return strings.Compare(a.Attestation.CalendarServerURL, b.Attestation.CalendarServerURL)
		}
		if a.Attestation.BitcoinBlockHeight != 0 && b.Attestation.BitcoinBlockHeight != 0 {
			// both are bitcoin attestations
			return int(b.Attestation.BitcoinBlockHeight - a.Attestation.BitcoinBlockHeight)
		}

		// one is bitcoin and the other is not -- compare by bitcoin block,
		// but reverse the result since the one with 0 should not be considered bigger
		return -1 * int(b.Attestation.BitcoinBlockHeight-a.Attestation.BitcoinBlockHeight)
	} else {
		// this shouldn't happen
		return 0
	}
}

func ReadInstruction(buf varn.Buffer, tag byte) (*Instruction, error) {
	op, ok := Tags[tag]
	if !ok {
		return nil, fmt.Errorf("unknown tag %v", tag)
	}

	inst := Instruction{
		Operation: op,
	}

	if op.Binary {
		val, err := buf.ReadVarBytes()
		if err != nil {
			return nil, fmt.Errorf("error reading argument: %w", err)
		}
		inst.Argument = val
	}

	return &inst, nil
}