package subex

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

// A part of an insertion, either a datum or a slot from which to load
// TODO rename this
type TransducerOutput interface {
	// Given the current store, return the []Datum produced by the TransducerOutput
	build(Store) []walk.Datum
}

// A TransducerOutput which is just a datum literal
type TransducerReplacementRune struct {
	datum walk.Datum
}
func (replacement TransducerReplacementRune) build(store Store) []walk.Datum {
	return []walk.Datum{replacement.datum}
}

// A TransducerOutput which is a slot that is loaded from
type TransducerReplacementLoad struct {
	datum walk.Datum
}
func (replacement TransducerReplacementLoad) build(store Store) []walk.Datum {
	return store[replacement.datum]
}

// Where slots are stored
type Store map[walk.Datum][]walk.Datum
// 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 walk.Datum, value []walk.Datum) 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{})
}

// One branch of subex execution
type SubexBranch struct {
	// Content of slots in this branch
	store Store
	// State in this branch
	state SubexState
	// Output so far in this branch
	output []walk.Datum
}
// Read a single character and return all the branches resulting from this branch consuming it
func (pair SubexBranch) eat(char walk.Datum) []SubexBranch {
	states := pair.state.eat(pair.store, char)
	for i := range states {
		states[i].output = append(pair.output, states[i].output...)
	}
	return states
}
func (pair SubexBranch) accepting() [][]walk.Datum {
	return pair.state.accepting(pair.store)
}

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.Datum) (output []walk.Datum, err bool) {
	states := []SubexBranch{{
		state: transducer,
		output: 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 {
		outputEnds := state.accepting()
		for _, outputEnd := range outputEnds {
			return append(state.output, outputEnd...), false
		}
	}
	return nil, true
}

func Main() {
	if len(os.Args) != 2 {
		panic("Expected: program [subex]")
	}
	stdin := bufio.NewReader(os.Stdin);
	jsonStream := walk.Json(stdin);
	var tokens []walk.WalkValue;
	for token := range jsonStream {
		tokens = append(tokens, token.Value);
	}
	program := os.Args[1]
	ast := Parse(program)
	transducer := CompileTransducer(ast)
	pieces := make(chan walk.Datum)
	go func(out chan<- walk.Datum, input []walk.WalkValue) {
		for _, value := range input {
			value.Pieces(out)
		}
		close(out)
	}(pieces, tokens)
	output, err := RunTransducer(transducer, pieces)
	// TODO recombine data into values and then convert into items with empty paths
	if !err {
		fmt.Print(output)
	} else {
		fmt.Print("Error")
	}
}