import torch
from torch.optim.lr_scheduler import _LRScheduler


# class CustomLambdaLR(_LRScheduler):
#     def __init__(self, optimizer, warmup_steps, last_epoch=-1):
#         self.warmup_steps = warmup_steps
#         super().__init__(optimizer, last_epoch)
#
#     def get_lr(self):
#         if self.last_epoch < self.warmup_steps:
#             return [
#                 base_lr * min(self.last_epoch / self.warmup_steps, 1) for base_lr in self.base_lrs
#             ]
#         else:
#             return [base_lr for base_lr in self.base_lrs]


class CustomLambdaLR(_LRScheduler):
    def __init__(
        self,
        optimizer,
        warmup_steps: int = 25000,
        total_steps: int = 500000,
        last_epoch=-1,
        verbose=False,
    ):
        self.warmup_steps = warmup_steps
        self.total_steps = total_steps
        super().__init__(optimizer, last_epoch, verbose)

    def get_lr(self):

        step = self.last_epoch + 1
        if step < self.warmup_steps:
            lr_scale = step / self.warmup_steps
        else:
            lr_scale = max(
                0.0, 1 - (step - self.warmup_steps) / (self.total_steps - self.warmup_steps)
            )
        return [base_lr * lr_scale for base_lr in self.base_lrs]