package subex

import (
	"main/walk"
)

// A state of execution for the transducer
type SubexState interface {
	// Eat a Atom and transition to any number of new states
	eat(store Store, char walk.Atom) []SubexBranch
	// Find accepting states reachable through epsilon transitions and return their outputs
	accepting(store Store) [][]walk.Atom
}

type SubexParentState interface {
	SubexState
	// Get the child
	child() SubexState
	// The child outputted output, what should be passed as accumulator data into the next version of the parent state
	nextAcc(output []walk.Atom) interface{}
	// Given the final accumulated data, run the next state after the parent, immutably borrows store
	feedNext(acc interface{}, store Store, char walk.Atom) []SubexBranch
	// Given the final accumulated data, get the accepted outputs from the next state, immutably borrows store
	acceptNext(acc interface{}, store Store) [][]walk.Atom
	// Given the next child and next accumulator data, generate the next parent
	nextParent(child SubexState, acc interface{}) SubexState
}

// Try first, if it fails then try second
type SubexGroupState struct {
	first, second SubexState
}
func (state SubexGroupState) eat(store Store, char walk.Atom) []SubexBranch {
	otherStore := store.clone()
	return append(state.first.eat(store, char), state.second.eat(otherStore, char)...)
}
func (state SubexGroupState) accepting(store Store) [][]walk.Atom {
	return append(state.first.accepting(store), state.second.accepting(store)...)
}

// Helper so states that are actually collections of states distinguished by a child state
// can pass eaten characters on to their children more easily
func feedChild(parent SubexParentState, store Store, char walk.Atom) (nextStates []SubexBranch) {
	child := parent.child()
	accepteds := child.accepting(store)
	for _, accepted := range accepteds {
		acc := parent.nextAcc(accepted)
		nextStates = append(nextStates, parent.feedNext(acc, store, char)...)
	}
	nextChildren := child.eat(store, char)
	for _, nextChild := range nextChildren {
		acc := parent.nextAcc(nextChild.output)
		nextStates = append(nextStates, SubexBranch{
			state: parent.nextParent(nextChild.state, acc),
			output: nil,
			store: nextChild.store,
		})
	}
	return nextStates
}

func acceptChild(parent SubexParentState, store Store) (outputs [][]walk.Atom) {
	child := parent.child()
	accepteds := child.accepting(store)
	for _, accepted := range accepteds {
		acc := parent.nextAcc(accepted)
		outputs = append(outputs, parent.acceptNext(acc, store)...)
	}
	return outputs
}

// Run the match machine and store the output in a slot for later use
// Output nothing
type SubexStoreState struct {
	match SubexState
	slot rune
	next SubexState
	toStore []walk.Atom
}
func (state SubexStoreState) child() SubexState {
	return state.match
}
func (state SubexStoreState) nextAcc(output []walk.Atom) interface{} {
	return walk.ConcatData(state.toStore, output)
}
func (state SubexStoreState) feedNext(acc interface{}, store Store, char walk.Atom) []SubexBranch {
	toStore := acc.([]walk.Atom)
	nextStore := store.withValue(state.slot, toStore)
	return state.next.eat(nextStore, char)
}
func (state SubexStoreState) acceptNext(acc interface{}, store Store) [][]walk.Atom {
	toStore := acc.([]walk.Atom)
	nextStore := store.withValue(state.slot, toStore)
	return state.next.accepting(nextStore)
}
func (state SubexStoreState) nextParent(match SubexState, acc interface{}) SubexState {
	toStore := acc.([]walk.Atom)
	return &SubexStoreState {
		match: match,
		slot: state.slot,
		next: state.next,
		toStore: toStore,
	}
}
func (state SubexStoreState) eat(store Store, char walk.Atom) (nextStates []SubexBranch) {
	return feedChild(state, store, char)
}
func (state SubexStoreState) accepting(store Store) (outputs [][]walk.Atom) {
	return acceptChild(state, store)
}

// A part of an output literal, either an Atom or a slot from which to load
type OutputContent interface {
	// Given the current store, return the []Atom produced by the TransducerOutput
	build(Store) []walk.Atom
}

// An OutputContent which is just an Atom literal
type OutputAtomLiteral struct {
	atom walk.Atom
}
func (replacement OutputAtomLiteral) build(store Store) []walk.Atom {
	return []walk.Atom{replacement.atom}
}

// An OutputContent which is a slot that is loaded from
type OutputLoad struct {
	slot rune
}
func (replacement OutputLoad) build(store Store) []walk.Atom {
	return store[replacement.slot]
}

// Don't read in anything, just output the series of data and slots specified
type SubexOutputState struct {
	content []OutputContent
	next SubexState
}
// Given a store, return what is outputted by an epsilon transition from this state
func (state SubexOutputState) build(store Store) []walk.Atom {
	var result []walk.Atom
	for _, part := range state.content {
		result = append(result, part.build(store)...)
	}
	return result
}
func (state SubexOutputState) eat(store Store, char walk.Atom) []SubexBranch {
	content := state.build(store)
	nextStates := state.next.eat(store, char)
	for i := range nextStates {
		nextStates[i].output = walk.ConcatData(content, nextStates[i].output)
	}
	return nextStates
}
func (state SubexOutputState) accepting(store Store) [][]walk.Atom {
	content := state.build(store)
	outputs := state.next.accepting(store)
	for i := range outputs {
		outputs[i] = walk.ConcatData(content, outputs[i])
	}
	return outputs
}

// A final state, transitions to nothing but is accepting
type SubexNoneState struct {}
func (state SubexNoneState) eat(store Store, char walk.Atom) []SubexBranch {
	return nil
}
func (state SubexNoneState) accepting(store Store) [][]walk.Atom {
	return [][]walk.Atom{nil}
}

// A dead end state, handy for making internals work nicer but technically redundant
type SubexDeadState struct {}
func (state SubexDeadState) eat(store Store, char walk.Atom) []SubexBranch {
	return nil
}
func (state SubexDeadState) accepting (store Store) [][]walk.Atom {
	return nil
}

// Read in a specific Atom and output it
type SubexCopyAtomState struct {
	atom walk.Atom
	next SubexState
}
func (state SubexCopyAtomState) eat(store Store, char walk.Atom) []SubexBranch {
	// TODO can I compare Atom values with == ?
	if char == state.atom {
		return []SubexBranch{{
			state: state.next,
			output: []walk.Atom{char},
			store: store,
		}}
	}
	return nil
}
func (state SubexCopyAtomState) accepting(store Store) [][]walk.Atom {
	return nil
}

// Read in any Atom and output it
type SubexCopyAnyState struct {
	next SubexState
}
func (state SubexCopyAnyState) eat(store Store, char walk.Atom) []SubexBranch {
	return []SubexBranch{{
		state: state.next,
		output: []walk.Atom{char},
		store: store,
	}}
}
func (state SubexCopyAnyState) accepting(store Store) [][]walk.Atom {
	return nil
}

// Read in an Atom and apply a map to generate an Atom to output
// If the input isn't in the map transition to nothing
type SubexRangeState struct {
	parts map[walk.Atom]walk.Atom
	next SubexState
}
func (state SubexRangeState) eat(store Store, char walk.Atom) []SubexBranch {
	out, exists := state.parts[char]
	if !exists {
		return nil
	} else {
		return []SubexBranch{{
			state: state.next,
			output: []walk.Atom{out},
			store: store,
		}}
	}
}
func (state SubexRangeState) accepting(store Store) [][]walk.Atom {
	return nil
}

func sumValues(values []walk.Atom) walk.ValueNumber {
	var sum float64 = 0
	for _, value := range values {
		switch v := value.(type) {
			case walk.ValueBool:
				if (bool(v)) {
					sum += 1
				}
			case walk.ValueNumber:
				sum += float64(v)
			case rune:
				if '0' <= v && v <= '9' {
					sum += float64(v - '0')
				}
			default:
		}
	}
	return walk.ValueNumber(sum)
}

// Run the inputState machine and sum any values output, output the sum
// Cast non numbers into numbers, ignore anything uncastable
type SubexSumState struct {
	inputState SubexState
	next SubexState
	sum walk.ValueNumber
}
func (state SubexSumState) child() SubexState {
	return state.inputState
}
func (state SubexSumState) nextAcc(output []walk.Atom) interface{} {
	return sumValues(append(output, state.sum))
}
func (state SubexSumState) feedNext(acc interface{}, store Store, char walk.Atom) []SubexBranch {
	total := acc.(walk.ValueNumber)
	output := []walk.Atom{total}
	nextStates := state.next.eat(store.clone(), char)
	for i := range nextStates {
		nextStates[i].output = walk.ConcatData(output, nextStates[i].output)
	}
	return nextStates
}
func (state SubexSumState) acceptNext(acc interface{}, store Store) [][]walk.Atom {
	total := acc.(walk.ValueNumber)
	output := []walk.Atom{total}
	outputs := state.next.accepting(store.clone())
	for i := range outputs {
		outputs[i] = walk.ConcatData(output, outputs[i])
	}
	return outputs
}
func (state SubexSumState) nextParent(child SubexState, acc interface{}) SubexState {
	sum := acc.(walk.ValueNumber)
	return &SubexSumState {
		inputState: child,
		next: state.next,
		sum: sum,
	}
}
func (state SubexSumState) eat(store Store, char walk.Atom) (nextStates []SubexBranch) {
	return feedChild(state, store, char)
}
func (state SubexSumState) accepting(store Store) (outputs [][]walk.Atom) {
	return acceptChild(state, store)
}