import subprocess
import os
from typing import List, Tuple

def split_video(input_file: str, output_dir: str, timestamps: List[Tuple[float, float]], frame_perfect: bool = False) -> None:
    """
    Splits a video file into multiple segments based on specified time ranges.
    
    Args:
        input_file (str): The path to the video file to be split.
        output_dir (str): The directory where the split segments will be saved.
        timestamps (List[Tuple[float, float]]): A list of tuples representing (start_time, end_time).
        frame_perfect (bool): If True, skips fast-copy and forces high-quality re-encoding 
                              to ensure cuts happen exactly on the requested frame.
    """
    if not os.path.exists(input_file):
        print(f"Error: Input file not found at {input_file}")
        return

    os.makedirs(output_dir, exist_ok=True)
    print(f"Starting video split process for {input_file}...")

    for i, (start, end) in enumerate(timestamps):
        segment_name = f"segment_{i+1:02d}_{start:.2f}s_to_{end:.2f}s.mp4"
        output_file = os.path.join(output_dir, segment_name)

        print(f"\n-> Processing segment {i+1}/{len(timestamps)}: {segment_name}")
        
        # Method 1: Fast Copy (Lossless, no re-encoding)
        # Moving -ss BEFORE -i fixes the frozen/corrupted initial frames.
        fast_command = [
            "ffmpeg", "-y",
            "-ss", str(start),
            "-i", input_file,
            "-to", str(end),
            "-c", "copy",
            output_file
        ]
        
        # Method 2: High-Quality Re-encode (Frame-perfect fallback)
        # Used if fast copy fails or if frame-accuracy is explicitly requested.
        reencode_command = [
            "ffmpeg", "-y",
            "-ss", str(start),
            "-i", input_file,
            "-to", str(end),
            "-c:v", "libx264",
            "-crf", "18",         # High visual quality
            "-preset", "slow",    # Better compression efficiency
            "-c:a", "aac",
            "-b:a", "256k",       # High-fidelity audio
            output_file
        ]

        try:
            if frame_perfect:
                print("Running in frame-perfect mode (re-encoding)...")
                subprocess.run(reencode_command, check=True, capture_output=True, text=True)
            else:
                try:
                    print("Attempting lightning-fast stream copy...")
                    subprocess.run(fast_command, check=True, capture_output=True, text=True)
                except subprocess.CalledProcessError:
                    print("⚠️ Fast copy failed. Falling back to high-quality re-encode...")
                    subprocess.run(reencode_command, check=True, capture_output=True, text=True)
            
            print(f"Successfully created segment: {output_file}")

        except subprocess.CalledProcessError as e:
            print(f"❌ Error splitting video segment {i+1}:")
            print(f"Command failed with return code {e.returncode}")
            print(f"STDERR: {e.stderr}")
        except FileNotFoundError:
            print("-" * 50)
            print("CRITICAL ERROR: FFmpeg executable not found.")
            print("Please ensure 'ffmpeg' is installed and accessible in your system's PATH.")
            print("-" * 50)
            return

def main():
    """
    Example usage: 
    Assumes 'input.mp4' exists and a 'split_videos' directory is ready.
    """
    # --- CONFIGURATION ---
    INPUT_VIDEO_PATH = "path/to/your/input_video.mp4"  # <<< CHANGE THIS
    OUTPUT_SEGMENTS_DIR = "output_splits"              # <<< CHANGE THIS
    
    # Define time segments: [(start_time, end_time), ...]
    # Times should be floats representing seconds.
    # Example 1: 0s to 10s, then 10s to 20s
    TIMESTAMPS: List[Tuple[float, float]] = [
        (0.0, 10.0),
        (15.0, 25.0),
        (30.0, 35.0)
    ]
    # ---------------------

    if not os.path.exists(INPUT_VIDEO_PATH):
        print("!!! IMPORTANT !!!")
        print(f"Please update the 'INPUT_VIDEO_PATH' variable in the main() function with the correct path to your video.")
        print("!!! Script execution aborted. !!!")
        return

    split_video(
        input_file=INPUT_VIDEO_PATH,
        output_dir=OUTPUT_SEGMENTS_DIR,
        timestamps=TIMESTAMPS
    )

if __name__ == "__main__":
    main()