# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========

from mirage.accessor.s3 import S3Accessor
from mirage.cache.index import IndexCacheStore
from mirage.core.s3.stat import stat as s3_stat
from mirage.provision.types import Precision, ProvisionResult
from mirage.types import PathSpec


async def _resolve_sizes(
    accessor: S3Accessor,
    paths: list[PathSpec],
    index: IndexCacheStore | None,
) -> tuple[list[tuple[str, int]], int]:
    """Walk paths, return (path, size) pairs. Self-heals via stat fallback.

    Order of resolution per path:
        1. Index lookup -- free, no network call.
        2. ``head_object`` via ``s3_stat`` -- one S3 metadata call (~50ms,
           ~100 bytes). Populates the index as a side effect, so the next
           provision is free.

    Returns:
        (resolved, missing): list of (path_str, size) for paths whose
            size could be determined, and the count of paths that
            could not be resolved (e.g. file not found).
    """
    resolved: list[tuple[str, int]] = []
    missing = 0
    for p in paths:
        path_str = p.original if isinstance(p, PathSpec) else p
        size = None
        if index is not None:
            lookup = await index.get(path_str)
            if lookup.entry is not None:
                size = lookup.entry.size
        if size is None:
            try:
                file_stat = await s3_stat(accessor, p, index)
                size = file_stat.size
            except (FileNotFoundError, ValueError):
                pass
        if size is not None:
            resolved.append((path_str, size))
        else:
            missing += 1
    return resolved, missing


async def file_read_provision(
    accessor: S3Accessor,
    paths: list[PathSpec],
    *_args: object,
    command: str = "",
    index: IndexCacheStore | None = None,
    **_extra: object,
) -> ProvisionResult:
    """Cost estimate for full file reads (cat, wc).

    Sums index-known file sizes. If any path is unknown, marks
    precision UNKNOWN for safety -- the caller might be reading a
    much larger file than we account for.
    """
    if not paths:
        return ProvisionResult(command=command, precision=Precision.UNKNOWN)
    resolved, missing = await _resolve_sizes(accessor, paths, index)
    if missing > 0 or not resolved:
        return ProvisionResult(command=command, precision=Precision.UNKNOWN)
    total = sum(size for _, size in resolved)
    return ProvisionResult(
        command=command,
        network_read_low=total,
        network_read_high=total,
        read_ops=len(resolved),
        precision=Precision.EXACT,
    )


async def head_tail_provision(
    accessor: S3Accessor,
    paths: list[PathSpec],
    *_args: object,
    command: str = "",
    n: str | int | None = None,
    c: str | int | None = None,
    index: IndexCacheStore | None = None,
    **_extra: object,
) -> ProvisionResult:
    """Cost estimate for partial reads (head, tail).

    With ``-c BYTES`` the byte count is exact: ``min(c, file_size)``
    per file. With ``-n LINES`` (the default) we cannot predict bytes
    without reading, so we mark precision RANGE with the full file
    size as the upper bound.
    """
    if not paths:
        return ProvisionResult(command=command, precision=Precision.UNKNOWN)
    resolved, missing = await _resolve_sizes(accessor, paths, index)
    if missing > 0 or not resolved:
        return ProvisionResult(command=command, precision=Precision.UNKNOWN)

    if c is not None:
        c_bytes = int(c)
        total = sum(min(c_bytes, size) for _, size in resolved)
        return ProvisionResult(
            command=command,
            network_read_low=total,
            network_read_high=total,
            read_ops=len(resolved),
            precision=Precision.EXACT,
        )

    full = sum(size for _, size in resolved)
    return ProvisionResult(
        command=command,
        network_read_low=0,
        network_read_high=full,
        read_ops=len(resolved),
        precision=Precision.RANGE,
    )


async def metadata_provision(
    accessor: S3Accessor,
    paths: list[PathSpec],
    *_args: object,
    command: str = "",
    index: IndexCacheStore | None = None,
    **_extra: object,
) -> ProvisionResult:
    """Cost estimate for metadata-only ops (stat, ls, find).

    These hit the S3 API but don't transfer bytes. We report
    ``read_ops`` so callers can multiply by the per-request cost.
    """
    n = max(1, len(paths) if paths else 1)
    return ProvisionResult(
        command=command,
        network_read_low=0,
        network_read_high=0,
        read_ops=n,
        precision=Precision.EXACT,
    )
