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// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package abi

import (
    "fmt"
    "reflect"
    "strings"

    "github.com/ethereum/go-ethereum/crypto"
)

// Callable method given a `Name` and whether the method is a constant.
// If the method is `Const` no transaction needs to be created for this
// particular Method call. It can easily be simulated using a local VM.
// For example a `Balance()` method only needs to retrieve something
// from the storage and therefor requires no Tx to be send to the
// network. A method such as `Transact` does require a Tx and thus will
// be flagged `true`.
// Input specifies the required input parameters for this gives method.
type Method struct {
    Name    string
    Const   bool
    Inputs  []Argument
    Outputs []Argument
}

func (m Method) pack(method Method, args ...interface{}) ([]byte, error) {
    // Make sure arguments match up and pack them
    if len(args) != len(method.Inputs) {
        return nil, fmt.Errorf("argument count mismatch: %d for %d", len(args), len(method.Inputs))
    }
    // variable input is the output appended at the end of packed
    // output. This is used for strings and bytes types input.
    var variableInput []byte

    var ret []byte
    for i, a := range args {
        input := method.Inputs[i]
        // pack the input
        packed, err := input.Type.pack(reflect.ValueOf(a))
        if err != nil {
            return nil, fmt.Errorf("`%s` %v", method.Name, err)
        }

        // check for a slice type (string, bytes, slice)
        if input.Type.requiresLengthPrefix() {
            // calculate the offset
            offset := len(method.Inputs)*32 + len(variableInput)
            // set the offset
            ret = append(ret, packNum(reflect.ValueOf(offset))...)
            // Append the packed output to the variable input. The variable input
            // will be appended at the end of the input.
            variableInput = append(variableInput, packed...)
        } else {
            // append the packed value to the input
            ret = append(ret, packed...)
        }
    }
    // append the variable input at the end of the packed input
    ret = append(ret, variableInput...)

    return ret, nil
}

// Sig returns the methods string signature according to the ABI spec.
//
// Example
//
//     function foo(uint32 a, int b)    =    "foo(uint32,int256)"
//
// Please note that "int" is substitute for its canonical representation "int256"
func (m Method) Sig() string {
    types := make([]string, len(m.Inputs))
    i := 0
    for _, input := range m.Inputs {
        types[i] = input.Type.String()
        i++
    }
    return fmt.Sprintf("%v(%v)", m.Name, strings.Join(types, ","))
}

func (m Method) String() string {
    inputs := make([]string, len(m.Inputs))
    for i, input := range m.Inputs {
        inputs[i] = fmt.Sprintf("%v %v", input.Name, input.Type)
    }
    outputs := make([]string, len(m.Outputs))
    for i, output := range m.Outputs {
        if len(output.Name) > 0 {
            outputs[i] = fmt.Sprintf("%v ", output.Name)
        }
        outputs[i] += output.Type.String()
    }
    constant := ""
    if m.Const {
        constant = "constant "
    }
    return fmt.Sprintf("function %v(%v) %sreturns(%v)", m.Name, strings.Join(inputs, ", "), constant, strings.Join(outputs, ", "))
}

func (m Method) Id() []byte {
    return crypto.Keccak256([]byte(m.Sig()))[:4]
}