from __future__ import annotations

import dataclasses
import fractions
import functools

import generator.fretboard
import generator.solo.types
import generator.solo.profiles
import generator.solo.policy

def travel(previous: generator.solo.types.Note | None, current: generator.solo.types.Note, tempo: fractions.Fraction) -> int:
  if previous is None:
    return 0
  return transition(previous.position, current.position, current.start - previous.start, tempo)

@functools.lru_cache(maxsize=16384)
def transition(previous, current, duration, tempo):
  distance = abs(previous.fret - current.fret) + abs(previous.string_number - current.string_number)
  seconds = float(duration * 60 / tempo)
  # Movement is a preference, not an unsupported claim about a player's limits.
  return round(100 * distance / max(seconds, 0.05))

def hand_positions(position):
  return tuple(h for h in range(1, 10) if h <= position.fret <= h + 3)

@functools.lru_cache(maxsize=512)
def position_rank(position):
  return generator.solo.policy.stable_rank('guitar-position', position)

def stable_path(path):
  return tuple(position_rank(n.position) for n in path)

@functools.lru_cache(maxsize=4096)
def alternatives(notes, tempo, previous=None, limit=2, profile=generator.solo.profiles.UNRESTRICTED):
  """Phrase paths with a four-fret hand region and distinct endpoint choices."""
  states = [(0, (), h) for h in hand_positions(previous.position)] if previous and previous.position else [(0, (), None)]
  for note in notes:
    following = {}
    for position in positions(note.pitch.number(), profile):
      current = dataclasses.replace(note, position=position)
      for hand in hand_positions(position):
        best = None
        for cost, path, old_hand in states:
          prior = path[-1] if path else previous
          if note.continuation and (prior is None or prior.pitch != note.pitch or prior.position != position or prior.end != note.start):
            continue
          movement = 0
          if prior and not note.continuation:
            seconds = max(.05, float((note.start - prior.start) * 60 / tempo))
            distance = abs(hand - old_hand) if old_hand is not None else 0
            distance += .25 * abs(position.fret - prior.position.fret) + .5 * abs(position.string_number - prior.position.string_number)
            movement = round(100 * distance / seconds)
          candidate = (cost + movement, (*path, current), hand)
          if best is None or candidate[0] < best[0] or candidate[0] == best[0] and stable_path(candidate[1]) < stable_path(best[1]):
            best = candidate
        if best is not None:
          following[position, hand] = best
    if not following:
      return ()
    states = list(following.values())
  # Endpoints survive so the following phrase can choose a better transition.
  selected, seen = [], set()
  for cost, path, hand in sorted(states, key=lambda v: (v[0], stable_path(v[1]))):
    endpoint = path[-1].position if path else None
    if endpoint in seen:
      continue
    seen.add(endpoint)
    selected.append((cost, path))
    if len(selected) == limit:
      break
  return tuple(selected)

@functools.lru_cache(maxsize=4096)
def place(notes, tempo, previous=None, profile=generator.solo.profiles.UNRESTRICTED):
  result = alternatives(notes, tempo, previous, 1, profile)
  return result[0] if result else None

@functools.lru_cache(maxsize=2048)
def positions(number: int, profile=generator.solo.profiles.UNRESTRICTED):
  profile = profile or generator.solo.profiles.UNRESTRICTED
  return tuple(p for p in generator.fretboard.single_positions_for_pitch(fractions.Fraction(number)) if p.string_number in profile.strings)