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
}

// 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)...)
}

// 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) eat(store Store, char walk.Atom) (nextStates []SubexBranch) {
	acceptedOutputs := state.match.accepting(store)
	for _, acceptedOutput := range acceptedOutputs {
		nextStore := store.withValue(state.slot, walk.ConcatData(state.toStore, acceptedOutput))
		nextStates = append(nextStates, state.next.eat(nextStore.clone(), char)...)
	}
	nextMatchStates := state.match.eat(store.clone(), char)
	for _, matchState := range nextMatchStates {
		nextStates = append(nextStates, SubexBranch {
			state: &SubexStoreState {
				match: matchState.state,
				slot: state.slot,
				next: state.next,
				toStore: walk.ConcatData(state.toStore, matchState.output),
			},
			output: nil,
			store: store.clone(),
		})
	}
	return nextStates
}
func (state SubexStoreState) accepting(store Store) (outputs [][]walk.Atom) {
	acceptedOutputs := state.match.accepting(store)
	for _, acceptedOutput := range acceptedOutputs {
		nextStore := store.withValue(state.slot, walk.ConcatData(state.toStore, acceptedOutput))
		outputs = append(outputs, state.next.accepting(nextStore)...)
	}
	return outputs
}

// 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}
}

// 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
}