package subex

import (
	"os"
	"fmt"
	"bufio"
	"main/walk"
)

// Where slots are stored
type Store map[rune][]walk.Atom
// Return a new store with all the data from this one
func (store Store) clone() Store {
	newStore := make(Store)
	for key, val := range store {
		newStore[key] = val
	}
	return newStore
}
// Return a copy of this store but with an additional slot set
func (store Store) withValue(key rune, value []walk.Atom) Store {
	newStore := store.clone()
	newStore[key] = value
	return newStore
}

// Compile the SubexAST into a transducer SubexState that can be run
func CompileTransducer(transducerAst SubexAST) SubexState {
	return transducerAst.compileWith(&SubexNoneState{})
}

// An immutable stack for outputting to
type OutputStack interface {
	pop() ([]walk.Atom, OutputStack)
	push(atoms []walk.Atom) OutputStack
}

type OutputStackNil struct {}
func (stack OutputStackNil) pop() ([]walk.Atom, OutputStack) {
	panic("Tried to pop from an empty OutputStack")
}
func (stack OutputStackNil) push(atoms []walk.Atom) OutputStack {
	return &OutputStackCons {
		head: atoms,
		tail: stack,
	}
}

type OutputStackCons struct {
	head []walk.Atom
	tail OutputStack
}
func (stack OutputStackCons) pop() ([]walk.Atom, OutputStack) {
	return stack.head, stack.tail
}
func (stack OutputStackCons) push(atoms []walk.Atom) OutputStack {
	return &OutputStackCons {
		head: atoms,
		tail: stack,
	}
}

func topAppend(outputStack OutputStack, atoms []walk.Atom) OutputStack {
	head, tail := outputStack.pop()
	return tail.push(walk.ConcatData(head, atoms))
}

// One branch of subex execution
type SubexBranch struct {
	// Content of slots in this branch
	store Store
	// State in this branch
	state SubexState
	// The output stack. At the end of the program, whatever is on top of this will be output
	// States may push or pop to the stack as they wish, creating sort of a call stack that allows states to capture the output of other states
	outputStack OutputStack
}
// Read a single character and return all the branches resulting from this branch consuming it
func (pair SubexBranch) eat(char walk.Atom) []SubexBranch {
	return pair.state.eat(pair.store, pair.outputStack, char)
}
func (pair SubexBranch) accepting() []OutputStack {
	return pair.state.accepting(pair.store, pair.outputStack)
}

func equalStates(left SubexBranch, right SubexBranch) bool {
	// Only care about if they are the same pointer
	return left.state == right.state
}

// If two branches have the same state, only the first has a chance of being successful
// This function removes all of the pointless execution branches to save execution time
func pruneStates(states []SubexBranch) (newStates []SubexBranch) {
	outer: for _, state := range states {
		for _, newState := range newStates {
			if equalStates(state, newState) {
				continue outer
			}
		}
		newStates = append(newStates, state)
	}
	return newStates
}

// Run the subex transducer
func RunTransducer(transducer SubexState, input <-chan walk.Atom) (output []walk.Atom, err bool) {
	states := []SubexBranch{{
		state: transducer,
		outputStack: OutputStackNil{}.push(nil),
		store: make(Store),
	}}
	for piece := range input {
		var newStates []SubexBranch
		for _, state := range states {
			newStates = append(newStates, state.eat(piece)...)
		}
		states = pruneStates(newStates)
	}
	for _, state := range states {
		acceptingStacks := state.accepting()
		for _, stack := range acceptingStacks {
			output, _ := stack.pop()
			return output, false
		}
	}
	return nil, true
}

func Main() {
	if len(os.Args) != 2 {
		panic("Expected: program [subex]")
	}
	program := os.Args[1]
	ast := Parse(program)
	transducer := CompileTransducer(ast)

	stdin := bufio.NewReader(os.Stdin);
	jsonStream := walk.Json(stdin);
	tokenStream := make(chan walk.WalkValue)
	go func(in <-chan walk.WalkItem, out chan<- walk.WalkValue) {
		for item := range in {
			out<-item.Value
		}
		close(out)
	}(jsonStream, tokenStream)

	atoms := walk.Atomise(tokenStream)

	output, err := RunTransducer(transducer, atoms)
	if err {
		fmt.Println("Error")
		return
	}

	valueOut, error := walk.MemoryCompound(output)
	if error != nil {
		fmt.Println(error.Error())
		return
	}
	for _, value := range valueOut {
		fmt.Println(value)
	}
}