#!/usr/bin/env python3
"""Diffr — side-by-side file diff viewer with color."""
import argparse, difflib, os, sys


def color(text, code):
    return f"\033[{code}m{text}\033[0m" if sys.stdout.isatty() else text


def split_lines(text):
    return text.rstrip("\n").split("\n") if "\n" in text else [text.rstrip()]


def side_by_side(left_lines, right_lines, context=3, width=80):
    half = (width - 3) // 2
    result = []
    
    matcher = difflib.SequenceMatcher(None, left_lines, right_lines)
    
    for op, i1, i2, j1, j2 in matcher.get_opcodes():
        if op == "equal":
            # Show context around changes
            if context > 0 and result:
                # Check if we should show only context lines
                for k in range(i1, i2):
                    result.append((
                        left_lines[k],
                        right_lines[k - i1 + j1],
                        " ",
                    ))
            else:
                for k in range(i1, i2):
                    result.append((
                        left_lines[k],
                        right_lines[k - i1 + j1],
                        " ",
                    ))
        elif op == "replace":
            for k in range(i1, i2):
                r_idx = j1 + (k - i1)
                if r_idx < j2:
                    result.append((left_lines[k], right_lines[r_idx], "-"))
            for k in range(max(i1, i2 - (i2 - i1)), i2):
                pass
        elif op == "delete":
            for k in range(i1, i2):
                result.append((left_lines[k], "", "-"))
        elif op == "insert":
            for k in range(j1, j2):
                result.append(("", right_lines[k], "+"))
    
    return result


def color_diff_line(left, right, marker, half, use_color=True):
    if marker == " ":
        l = left[:half].ljust(half)
        r = right[:half].ljust(half)
        if use_color:
            return f" {color(l, '90')} │ {color(r, '90')}"
        return f" {l} │ {r}"
    elif marker == "-":
        l = left[:half].ljust(half)
        if use_color:
            return f"{color('<', '31')}{color(l, '31')} │ {color(''.ljust(half), '90')}"
        return f"<{l} │"
    elif marker == "+":
        r = right[:half].ljust(half)
        if use_color:
            return f" {color(''.ljust(half), '90')} │ {color('>', '32')}{color(r, '32')}"
        return f" │ >{r}"
    return f" {left[:half].ljust(half)} │ {right[:half].ljust(half)}"


def simple_diff(left_lines, right_lines, use_color=True):
    matcher = difflib.SequenceMatcher(None, left_lines, right_lines)
    result = []
    
    for op, i1, i2, j1, j2 in matcher.get_opcodes():
        if op == "equal":
            for k in range(i1, i2):
                result.append((" ", left_lines[k]))
        elif op == "replace":
            for k in range(i1, i2):
                result.append(("-", left_lines[k]))
            for k in range(j1, j2):
                result.append(("+", right_lines[k]))
        elif op == "delete":
            for k in range(i1, i2):
                result.append(("-", left_lines[k]))
        elif op == "insert":
            for k in range(j1, j2):
                result.append(("+", right_lines[k]))
    
    return result


def display_simple(diff_result, use_color=True, context=3):
    for i, (marker, line) in enumerate(diff_result):
        if marker == " ":
            if use_color:
                print(f"  {line}")
            else:
                print(f"  {line}")
        elif marker == "-":
            if use_color:
                print(f" {color('-' + line, '31')}")
            else:
                print(f" -{line}")
        elif marker == "+":
            if use_color:
                print(f" {color('+' + line, '32')}")
            else:
                print(f" +{line}")


def main():
    parser = argparse.ArgumentParser(
        description="Diffr — file diff viewer with color",
        formatter_class=argparse.RawDescriptionHelpFormatter,
        epilog=(
            "Examples:\n"
            "  diffr file1.txt file2.txt        # Side-by-side diff\n"
            "  diffr file1.txt file2.txt --simple  # Unified diff\n"
            "  diffr file1.txt file2.txt --context 5  # 5 lines context\n"
        ),
    )
    parser.add_argument("file1", help="First file")
    parser.add_argument("file2", help="Second file")
    parser.add_argument("--context", type=int, default=3,
                        help="Context lines (default: 3)")
    parser.add_argument("--simple", action="store_true",
                        help="Use unified diff format")
    parser.add_argument("--no-color", action="store_true",
                        help="Disable color output")
    parser.add_argument("--version", action="version",
                        version="diffr 1.0.0")
    
    args = parser.parse_args()
    
    try:
        with open(args.file1) as f:
            left = f.read().rstrip("\n").split("\n")
        with open(args.file2) as f:
            right = f.read().rstrip("\n").split("\n")
    except FileNotFoundError as e:
        print(f"Error: {e}", file=sys.stderr)
        sys.exit(1)
    
    use_color = sys.stdout.isatty() and not args.no_color
    
    print(f"\n  {color('Diffr: ', '1')}{args.file1}  {color('vs', '90')}  {args.file2}")
    print(f"  {color('─' * 60, '90')}\n")
    
    if args.simple:
        result = simple_diff(left, right, use_color)
        display_simple(result, use_color, args.context)
    else:
        # Basic line-by-line display with markers
        max_len = max(len(left), len(right))
        num_width = len(str(max_len))
        
        for i in range(max_len):
            l = left[i] if i < len(left) else ""
            r = right[i] if i < len(right) else ""
            
            if l == r:
                if use_color:
                    print(f"  {color(str(i+1).rjust(num_width), '90')} {l}")
                else:
                    print(f"  {str(i+1).rjust(num_width)} {l}")
            elif not l:
                if use_color:
                    print(f"  {color(str(i+1).rjust(num_width), '90')} {color('+' + r, '32')}")
                else:
                    print(f"  {str(i+1).rjust(num_width)} +{r}")
            elif not r:
                if use_color:
                    print(f"  {color(str(i+1).rjust(num_width), '90')} {color('-' + l, '31')}")
                else:
                    print(f"  {str(i+1).rjust(num_width)} -{l}")
            else:
                if use_color:
                    print(f"  {color(str(i+1).rjust(num_width), '90')} {color('-' + l, '31')}")
                    print(f"  {color(str(i+2).rjust(num_width), '90')} {color('+' + r, '32')}")
                else:
                    print(f"  {str(i+1).rjust(num_width)} -{l}")
                    print(f"  {str(i+2).rjust(num_width)} +{r}")
    
    print()


if __name__ == "__main__":
    main()