from dataclasses import dataclass

from django.utils import timezone

from apps.projects.models import Project, ProjectStage, ScriptVersion, VideoSegment


# 故事板已从流程中去掉:脚本 → 基础资产 → 视频 → 导出。
# ProjectStage.Stage.STORYBOARD 枚举保留(老项目的历史行还引用它),但不再出现在流水线里。
STAGE_ORDER = [
    ProjectStage.Stage.SCRIPT,
    ProjectStage.Stage.BASE_ASSETS,
    ProjectStage.Stage.VIDEO,
    ProjectStage.Stage.EXPORT,
]

# 老项目可能正停在已下线的 storyboard 阶段;按「基础资产之后」对待,让它们能正常进视频。
LEGACY_STAGE_FALLBACK = {ProjectStage.Stage.STORYBOARD: ProjectStage.Stage.BASE_ASSETS}


def normalize_stage(stage: str) -> str:
    """把已下线的阶段名归一到现役阶段,供索引/比较使用。"""
    return LEGACY_STAGE_FALLBACK.get(stage, stage)


@dataclass(frozen=True)
class StageTransition:
    current: str
    target: str
    allowed: bool
    reason: str = ""


def can_enter_stage(current_stage: str, target_stage: str) -> StageTransition:
    if target_stage not in STAGE_ORDER:
        return StageTransition(current_stage, target_stage, False, "unknown target stage")

    current = normalize_stage(current_stage)
    current_index = STAGE_ORDER.index(current) if current in STAGE_ORDER else -1
    target_index = STAGE_ORDER.index(target_stage)

    if target_index <= current_index + 1:
        return StageTransition(current_stage, target_stage, True)

    return StageTransition(current_stage, target_stage, False, "stage prerequisite is not satisfied")


def initialize_project_pipeline(project: Project, *, placeholder_segments: int = 4) -> None:
    """建立专业创作和一键成片共用的阶段、视频占位数据。幂等，可安全重试。"""
    for stage_name in STAGE_ORDER:
        ProjectStage.objects.get_or_create(project=project, stage=stage_name)
    for index in range(placeholder_segments):
        VideoSegment.objects.get_or_create(
            project=project,
            sort_order=index,
            defaults={"target_duration_seconds": 15},
        )


def sync_video_segments_to_script(project: Project, script: ScriptVersion) -> None:
    """把视频段数量和时长收口到采用脚本；已生成过的段绝不裁剪或改时长。"""
    if not script.is_adopted:
        return
    script_segments = list(script.segments.order_by("sort_order"))
    target = len(script_segments)
    segments = list(project.video_segments.order_by("sort_order"))
    while len(segments) > target:
        tail = segments[-1]
        if tail.status == VideoSegment.Status.NOT_STARTED and not tail.versions.exists():
            tail.delete()
            segments.pop()
        else:
            break

    next_order = (segments[-1].sort_order + 1) if segments else 0
    for _ in range(target - len(segments)):
        index = len(segments)
        seconds = script_segments[index].duration_seconds if index < target else 15
        segments.append(
            VideoSegment.objects.create(
                project=project,
                sort_order=next_order,
                target_duration_seconds=seconds,
            )
        )
        next_order += 1

    stale: list[VideoSegment] = []
    for index, video_segment in enumerate(segments):
        if index >= target:
            break
        seconds = script_segments[index].duration_seconds
        if not seconds or video_segment.target_duration_seconds == seconds:
            continue
        if video_segment.status == VideoSegment.Status.SUCCEEDED or video_segment.versions.exists():
            continue
        video_segment.target_duration_seconds = seconds
        stale.append(video_segment)
    if stale:
        VideoSegment.objects.bulk_update(stale, ["target_duration_seconds"])


def adopt_script_version(project: Project, script: ScriptVersion) -> None:
    """采用脚本并推进到资产阶段，供专业创作按钮和一键成片编排共同调用。"""
    ScriptVersion.objects.filter(project=project).exclude(id=script.id).update(is_adopted=False)
    if not script.is_adopted:
        script.is_adopted = True
        script.save(update_fields=["is_adopted", "updated_at"])
    sync_video_segments_to_script(project, script)
    stage, _ = ProjectStage.objects.get_or_create(project=project, stage=ProjectStage.Stage.SCRIPT)
    stage.status = ProjectStage.Status.SUCCEEDED
    stage.completed_at = timezone.now()
    stage.error_message = ""
    stage.save(update_fields=["status", "completed_at", "error_message", "updated_at"])
    project.current_stage = ProjectStage.Stage.BASE_ASSETS
    project.status = Project.Status.ASSETING
    project.failure_reason = ""
    project.save(update_fields=["current_stage", "status", "failure_reason", "updated_at"])


def finish_base_assets_stage(project: Project) -> None:
    """基础资产齐备后直接推进到视频阶段（故事板已下线），并再次校准片段数量。"""
    stage, _ = ProjectStage.objects.get_or_create(project=project, stage=ProjectStage.Stage.BASE_ASSETS)
    stage.status = ProjectStage.Status.SUCCEEDED
    stage.completed_at = timezone.now()
    stage.error_message = ""
    stage.save(update_fields=["status", "completed_at", "error_message", "updated_at"])
    adopted_script = project.script_versions.filter(is_adopted=True).order_by("-created_at").first()
    if adopted_script is not None:
        sync_video_segments_to_script(project, adopted_script)
    project.current_stage = ProjectStage.Stage.VIDEO
    project.status = Project.Status.VIDEOING
    project.save(update_fields=["current_stage", "status", "updated_at"])


def finish_video_stage(project: Project) -> bool:
    """全部片段成功即完成视频阶段。"""
    segments = list(project.video_segments.values_list("status", "adopted_version_id"))
    if not segments or not all(status == VideoSegment.Status.SUCCEEDED and adopted for status, adopted in segments):
        return False
    stage, _ = ProjectStage.objects.get_or_create(project=project, stage=ProjectStage.Stage.VIDEO)
    stage.status = ProjectStage.Status.SUCCEEDED
    stage.completed_at = timezone.now()
    stage.error_message = ""
    stage.save(update_fields=["status", "completed_at", "error_message", "updated_at"])
    project.current_stage = ProjectStage.Stage.VIDEO
    project.status = Project.Status.COMPLETED
    project.failure_reason = ""
    project.save(update_fields=["current_stage", "status", "failure_reason", "updated_at"])
    return True