# Copyright 2022 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import argparse
import errno
import filecmp
import os
import sys
import plasa_differ
from enum import Enum


class Policy(Enum):
    # update_golden tells this script to overwrite the existing golden with
    # the current golden. This is useful for batch updates.
    update_golden = "update_golden"

    # ack_changes tells this script to fail if any changes are detected.
    # It will tell the user how to update the golden to acknowledge the
    # changes.
    ack_changes = "ack_changes"

    # no_breaking_changes tells this script to fail if breaking changes
    # are detected. If non-breaking changes are detected it will tell
    # the user how to update the golden to acknowledge the changes.
    no_breaking_changes = "no_breaking_changes"

    # no_changes tells this script to fail if any changes are detected.
    # It will not ask the user to update the golden.
    no_changes = "no_changes"

    def __str__(self):
        return self.value


FIDL_VERSIONING_DOCS_URL = (
    "https://fuchsia.dev/fuchsia-src/reference/fidl/language/versioning"
)

FIDL_AVAILABILITY_HINT = (
    f"Are you missing an @available annotation?\n"
    f"For more information see {FIDL_VERSIONING_DOCS_URL}\n"
)


class CompatibilityError(Exception):
    """Exception raised when breaking API changes are detected"""

    def __init__(self, api_level, breaking_changes, current, golden):
        self.api_level = api_level
        self.breaking_changes = breaking_changes
        self.current = current
        self.golden = golden

    def __str__(self):
        formatted_breaking_changes = "\n - ".join(self.breaking_changes)
        return (
            f"These changes are incompatible with API level {self.api_level}\n"
            f"{formatted_breaking_changes}\n\n"
            f"{FIDL_AVAILABILITY_HINT}"
        )


class GoldenMismatchError(Exception):
    """Exception raised when a stale golden file is detected."""

    def __init__(
        self,
        api_level,
        current,
        golden,
        show_update_hint=False,
        show_fidl_availability_hint=True,
    ):
        self.api_level = api_level
        self.current = current
        self.golden = golden
        self.show_update_hint = show_update_hint
        self.show_fidl_availability_hint = show_fidl_availability_hint

    def __str__(self):
        hints = []
        if self.show_fidl_availability_hint:
            hints.append(FIDL_AVAILABILITY_HINT)

        if self.show_update_hint:
            cmd = update_cmd(self.current, self.golden)
            hints.append(
                f"Please acknowledge this change by updating the golden.\n"
                f"To do this, please run:\n"
                f"  {cmd}\n"
            )

        hint_lines = "\n".join(hints)
        return f"Detected changes to API level {self.api_level}\n" + hint_lines


def golden_not_found_error(filename):
    message = (
        f"The golden file {filename} does not exist.\n"
        f"If this is a new FIDL API you must first create this file.\n"
        f"To do so, run:\n"
        f"  touch {os.path.abspath(filename)}\n"
    )
    return FileNotFoundError(errno.ENOENT, message, filename)


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--policy",
        help="How to handle failures",
        type=Policy,
        default=Policy.no_breaking_changes,
        choices=list(Policy),
    )
    parser.add_argument(
        "--depfile", help="Where to write the depfile", required=True
    )
    parser.add_argument(
        "--api-level", help="The API level being tested", required=True
    )
    parser.add_argument(
        "--golden", help="Path to the golden file", required=True
    )
    parser.add_argument(
        "--current", help="Path to the local file", required=True
    )
    parser.add_argument(
        "--stamp", help="Path to the victory file", required=True
    )
    parser.add_argument(
        "--fidl_api_diff_path",
        help="Path to the fidl_api_diff binary",
        required=True,
    )
    args = parser.parse_args()

    dependencies = [args.current, args.golden]

    if not os.path.exists(args.golden):
        if os.path.getsize(args.current) > 0:
            err = golden_not_found_error(args.golden)
        else:
            # Don't depend on files that don't exist.
            dependencies.remove(args.golden)

            # Skip testing if current is empty and golden is missing.
            # This prevents us from asking users to create empty golden files.
            err = None
    elif args.policy == Policy.update_golden:
        err = update_golden(args)
    elif args.policy == Policy.no_breaking_changes:
        err = fail_on_breaking_changes(args)
    elif args.policy == Policy.no_changes:
        err = fail_on_changes(args)
    elif args.policy == Policy.ack_changes:
        err = fail_on_unacknowledged_changes(args)
    else:
        raise ValueError("unknown policy: {}".format(args.policy))

    with open(args.depfile, "w") as f:
        f.write("{}: {}\n".format(args.stamp, " ".join(dependencies)))

    with open(args.stamp, "w") as stamp_file:
        stamp_file.write("Golden!\n")

    if not err:
        return 0

    print("\nERROR: ", err)
    return 1


def update_golden(args):
    import subprocess

    c = update_cmd(args.current, args.golden)
    if c is not None:
        subprocess.run(c.split())
    return None


def fail_on_breaking_changes(args):
    """Fails if current is not backward compatible with golden or if
    current and golden aren't identical.
    """
    differ = plasa_differ.PlasaDiffer(args.fidl_api_diff_path)
    breaking_changes = differ.find_breaking_changes_in_fragment_file(
        args.golden, args.current
    )

    if breaking_changes:
        return CompatibilityError(
            api_level=args.api_level,
            breaking_changes=breaking_changes,
            current=args.current,
            golden=args.golden,
        )

    if not filecmp.cmp(args.golden, args.current):
        return GoldenMismatchError(
            api_level=args.api_level,
            current=args.current,
            golden=args.golden,
            show_update_hint=True,
            # No breaking changes so the user must be using `@available` correctly.
            show_fidl_availability_hint=False,
        )

    return None


def fail_on_unacknowledged_changes(args):
    """Asks the user to fix the golden if current and golden aren't identical."""
    if not filecmp.cmp(args.golden, args.current):
        return GoldenMismatchError(
            api_level=args.api_level,
            current=args.current,
            golden=args.golden,
            show_update_hint=True,
        )
    return None


def fail_on_changes(args):
    """Fails if current and golden aren't identical."""
    if not filecmp.cmp(args.golden, args.current):
        return GoldenMismatchError(
            api_level=args.api_level,
            current=args.current,
            golden=args.golden,
        )
    return None


def update_cmd(current, golden):
    # Disable shallow comparison which doesn't prevent unnecessary writes. It
    # ignores file contents and only compares file type, size and mod time.
    if not filecmp.cmp(current, golden, shallow=False):
        return "cp {} {}".format(
            os.path.abspath(current), os.path.abspath(golden)
        )


if __name__ == "__main__":
    sys.exit(main())