"""
Phase 1: Masked PPO on district_backlog_easy.
Phase 2: Curriculum Masked PPO across all 3 tasks.

Usage:
    python -m rl.train_ppo --phase 1 --timesteps 200000
    python -m rl.train_ppo --phase 2 --timesteps 500000
    python -m rl.train_ppo --phase 1 --task district_backlog_easy --n_envs 4
"""

from __future__ import annotations

import argparse
import os

import yaml
from stable_baselines3.common.vec_env import DummyVecEnv
from stable_baselines3.common.monitor import Monitor
from sb3_contrib import MaskablePPO

from rl.gov_workflow_env import GovWorkflowGymEnv
from rl.callbacks import GovWorkflowEvalCallback, CostMonitorCallback
from rl.curriculum import CurriculumScheduler, CurriculumConfig

os.makedirs("results/runs",       exist_ok=True)
os.makedirs("results/best_model", exist_ok=True)
os.makedirs("results/eval_logs",  exist_ok=True)

PHASE1_TASK_ID = "district_backlog_easy"


def _load_cfg(path: str) -> dict:
    if os.path.exists(path):
        # `utf-8-sig` safely handles files with/without UTF-8 BOM.
        with open(path, encoding="utf-8-sig") as f:
            return yaml.safe_load(f)
    return {}


def _resolve_checkpoint_path(path_like: str | None) -> str | None:
    if not path_like:
        return None
    if os.path.exists(path_like):
        return path_like
    zip_path = f"{path_like}.zip"
    if os.path.exists(zip_path):
        return zip_path
    return None


# ---------------------------------------------------------------------------
# Phase 1 — single task easy
# ---------------------------------------------------------------------------
def train_phase1(
    total_timesteps: int = 200_000,
    n_envs:          int = 4,
    seed:            int = 42,
    config_path:     str = "rl/configs/ppo_easy.yaml",
    eval_freq_override: int | None = None,
    n_eval_episodes_override: int | None = None,
    disable_eval_callback: bool = False,
    no_progress_bar: bool = False,
    grader_eval_freq_multiplier_override: int | None = None,
    resume_path: str | None = None,
) -> MaskablePPO:
    cfg = _load_cfg(config_path)
    hp  = cfg.get("hyperparameters", {})
    tr_c = cfg.get("training", {})

    def _make(rank: int):
        def _init():
            return Monitor(GovWorkflowGymEnv("district_backlog_easy", seed=seed + rank))
        return _init

    train_env = DummyVecEnv([_make(i) for i in range(n_envs)])
    eval_freq = int(eval_freq_override if eval_freq_override is not None else tr_c.get("eval_freq", max(16_384 // n_envs, 1)))
    n_eval_episodes = int(n_eval_episodes_override if n_eval_episodes_override is not None else tr_c.get("n_eval_episodes", 2))
    eval_callback_enabled = bool(tr_c.get("enable_eval_callback", True)) and (not disable_eval_callback)
    grader_eval_freq_multiplier = int(
        grader_eval_freq_multiplier_override
        if grader_eval_freq_multiplier_override is not None
        else tr_c.get("grader_eval_freq_multiplier", 4)
    )
    callback_verbose = int(tr_c.get("callback_verbose", 0))
    model_verbose = int(tr_c.get("model_verbose", 0))
    progress_bar_enabled = (not no_progress_bar) and bool(tr_c.get("progress_bar", False))

    callbacks = [CostMonitorCallback()]
    if eval_callback_enabled:
        eval_env = GovWorkflowGymEnv("district_backlog_easy", seed=seed + 1000, hard_action_mask=True)
        eval_cb = GovWorkflowEvalCallback(
            eval_env=eval_env,
            eval_freq=max(eval_freq, 1),
            n_eval_episodes=max(n_eval_episodes, 1),
            grader_eval_freq_multiplier=max(grader_eval_freq_multiplier, 1),
            best_model_save_path="results/best_model",
            log_path="results/eval_logs",
            task_id="district_backlog_easy",
            verbose=callback_verbose,
        )
        callbacks.insert(0, eval_cb)

    resolved_resume = _resolve_checkpoint_path(resume_path)
    if resume_path and resolved_resume is None:
        raise FileNotFoundError(
            f"Phase 1 resume checkpoint not found: {resume_path} (or {resume_path}.zip)"
        )

    if resolved_resume:
        print(f"[Phase 1] Resuming from {resolved_resume}")
        model = MaskablePPO.load(resolved_resume, env=train_env)
    else:
        model = MaskablePPO(
            policy="MlpPolicy",
            env=train_env,
            learning_rate=float(hp.get("learning_rate", 3e-4)),
            n_steps=int(hp.get("n_steps",     512)),
            batch_size=int(hp.get("batch_size", 64)),
            n_epochs=int(hp.get("n_epochs",   10)),
            gamma=float(hp.get("gamma",        0.99)),
            gae_lambda=float(hp.get("gae_lambda", 0.95)),
            clip_range=float(hp.get("clip_range", 0.2)),
            ent_coef=float(hp.get("ent_coef",     0.01)),
            vf_coef=float(hp.get("vf_coef",       0.5)),
            max_grad_norm=float(hp.get("max_grad_norm", 0.5)),
            policy_kwargs=dict(net_arch=hp.get("net_arch", [256, 256])),
            tensorboard_log="results/runs/phase1_masked_ppo",
            verbose=model_verbose,
            seed=seed,
        )

    print(
        f"\n[Phase 1] Masked PPO | timesteps={total_timesteps} | n_envs={n_envs} "
        f"| eval_cb={'on' if eval_callback_enabled else 'off'} "
        f"| eval_freq={max(eval_freq,1)} | n_eval_episodes={max(n_eval_episodes,1)} "
        f"| grader_eval_x{max(grader_eval_freq_multiplier, 1)}"
    )
    model.learn(
        total_timesteps=total_timesteps,
        callback=callbacks,
        tb_log_name="masked_ppo_easy",
        reset_num_timesteps=not bool(resolved_resume),
        progress_bar=progress_bar_enabled,
    )
    model.save("results/best_model/phase1_final")
    print("[Phase 1] Done -> results/best_model/phase1_final")
    return model


# ---------------------------------------------------------------------------
# Phase 2 — curriculum across all tasks
# ---------------------------------------------------------------------------
def train_phase2(
    total_timesteps: int = 500_000,
    n_envs:          int = 4,
    seed:            int = 42,
    config_path:     str = "rl/configs/curriculum.yaml",
) -> MaskablePPO:
    cfg = _load_cfg(config_path)
    if not cfg and config_path.endswith("curriculum.yaml"):
        # Backward compatibility with previous filename.
        cfg = _load_cfg("rl/configs/ppo_curriculum.yaml")
    hp    = cfg.get("hyperparameters", {})
    cur_c = cfg.get("curriculum", {})
    tr_c  = cfg.get("training", {})

    scheduler = CurriculumScheduler(
        total_timesteps=total_timesteps,
        config=CurriculumConfig(
            stage1_end_frac=float(cur_c.get("stage1_end_frac", 0.30)),
            stage2_end_frac=float(cur_c.get("stage2_end_frac", 0.70)),
            stage3_weights=tuple(cur_c.get("stage3_weights", [0.20, 0.40, 0.40])),
        ),
        rng_seed=seed,
    )

    global_step_counter = [0]

    def _sample_task() -> str:
        return scheduler.sample_task(global_step_counter[0])

    def _make_curr(rank: int):
        def _init():
            env = GovWorkflowGymEnv(
                task_id="district_backlog_easy",
                seed=seed + rank,
            )
            env.set_task_sampler(_sample_task, global_step_counter)
            return Monitor(env)
        return _init

    train_env = DummyVecEnv([_make_curr(i) for i in range(n_envs)])
    eval_task_id = str(tr_c.get("eval_task_id", "mixed_urgency_medium"))
    eval_env  = GovWorkflowGymEnv(eval_task_id, seed=seed + 999, hard_action_mask=True)

    eval_cb = GovWorkflowEvalCallback(
        eval_env=eval_env,
        eval_freq=int(tr_c.get("eval_freq", max(4096 // n_envs, 1))),
        n_eval_episodes=int(tr_c.get("n_eval_episodes", 3)),
        grader_eval_freq_multiplier=int(tr_c.get("grader_eval_freq_multiplier", 4)),
        best_model_save_path="results/best_model",
        log_path="results/eval_logs",
        task_id=eval_task_id,
        verbose=1,
    )

    warm_start_from = str(tr_c.get("warm_start_from", "results/best_model/phase1_final"))
    warm_start_path = _resolve_checkpoint_path(warm_start_from)

    if warm_start_path and os.path.exists(warm_start_path):
        print(f"[Phase 2] Warm-starting from {warm_start_path}")
        model = MaskablePPO.load(warm_start_path, env=train_env)
    else:
        model = MaskablePPO(
            policy="MlpPolicy",
            env=train_env,
            learning_rate=float(hp.get("learning_rate", 2e-4)),
            n_steps=int(hp.get("n_steps",     512)),
            batch_size=int(hp.get("batch_size", 64)),
            n_epochs=int(hp.get("n_epochs",    10)),
            gamma=float(hp.get("gamma",         0.99)),
            gae_lambda=float(hp.get("gae_lambda",  0.95)),
            clip_range=float(hp.get("clip_range",  0.2)),
            ent_coef=float(hp.get("ent_coef",      0.005)),
            policy_kwargs=dict(net_arch=hp.get("net_arch", [256, 256])),
            tensorboard_log="results/runs/phase2_curriculum_ppo",
            verbose=1,
            seed=seed,
        )

    print(f"\n[Phase 2] Curriculum PPO | timesteps={total_timesteps}")
    model.learn(
        total_timesteps=total_timesteps,
        callback=[eval_cb, CostMonitorCallback()],
        tb_log_name="curriculum_ppo",
        progress_bar=True,
    )
    model.save("results/best_model/phase2_final")
    print("[Phase 2] Done -> results/best_model/phase2_final")
    return model


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("--phase",     type=int, choices=[1, 2], default=1)
    parser.add_argument("--timesteps", type=int, default=200_000)
    parser.add_argument("--n-envs", "--n_envs", dest="n_envs", type=int, default=4)
    parser.add_argument("--seed",      type=int, default=42)
    parser.add_argument(
        "--task",
        default=None,
        help=(
            "CLI compatibility alias. Phase 1 supports only "
            f"'{PHASE1_TASK_ID}'. Phase 2 ignores this flag."
        ),
    )
    parser.add_argument(
        "--phase1-config",
        default="rl/configs/ppo_easy.yaml",
        help="Config file for Phase 1 training.",
    )
    parser.add_argument(
        "--phase1-eval-freq",
        type=int,
        default=None,
        help="Override Phase 1 eval callback frequency (in calls).",
    )
    parser.add_argument(
        "--phase1-n-eval-episodes",
        type=int,
        default=None,
        help="Override Phase 1 eval callback episodes per eval.",
    )
    parser.add_argument(
        "--phase1-disable-eval-callback",
        action="store_true",
        help="Disable Phase 1 evaluation callback to avoid pause-heavy eval blocks.",
    )
    parser.add_argument(
        "--phase1-no-progress-bar",
        action="store_true",
        help="Disable tqdm progress bar rendering for Phase 1.",
    )
    parser.add_argument(
        "--phase1-grader-eval-freq-multiplier",
        type=int,
        default=None,
        help="Run grader eval every N * eval_freq callback ticks for Phase 1.",
    )
    parser.add_argument(
        "--resume",
        default=None,
        help="Resume Phase 1 from checkpoint path (with or without .zip suffix).",
    )
    parser.add_argument(
        "--phase2-config",
        default="rl/configs/curriculum.yaml",
        help="Config file for Phase 2 curriculum training.",
    )
    args = parser.parse_args()

    if args.phase == 1 and args.task and args.task != PHASE1_TASK_ID:
        raise ValueError(
            f"Phase 1 currently supports only task '{PHASE1_TASK_ID}', got '{args.task}'."
        )
    if args.phase == 2 and args.task:
        print(f"[Phase 2] Ignoring --task={args.task}; curriculum scheduler controls task sampling.")

    if args.phase == 1:
        train_phase1(
            total_timesteps=args.timesteps,
            n_envs=args.n_envs,
            seed=args.seed,
            config_path=args.phase1_config,
            eval_freq_override=args.phase1_eval_freq,
            n_eval_episodes_override=args.phase1_n_eval_episodes,
            disable_eval_callback=args.phase1_disable_eval_callback,
            no_progress_bar=args.phase1_no_progress_bar,
            grader_eval_freq_multiplier_override=args.phase1_grader_eval_freq_multiplier,
            resume_path=args.resume,
        )
    else:
        train_phase2(
            total_timesteps=args.timesteps,
            n_envs=args.n_envs,
            seed=args.seed,
            config_path=args.phase2_config,
        )


if __name__ == "__main__":
    main()