#!/usr/bin/env bash
# resolve-codec-patch — ffmpeg-based AAC→FLAC transcode helper.
#
# Used by aac_hybrid_shim.so as the fall-through path when an AAC file's
# esds box uses compact (1-byte) MPEG-4 descriptor lengths or a non-LC
# audioObjectType — cases the in-binary cave cannot safely decode in this
# Resolve version. Produces a FLAC-audio sibling in mp4 container that
# Resolve can decode natively (FLAC is one of the FOURCCs Resolve Linux's
# audio dispatch DOES handle).
#
# Pure ffmpeg, no root, no binary patches, no /opt/resolve modifications.
# Output cached in $AAC_REDIRECT_CACHE_DIR (defaults to
# ${XDG_CACHE_HOME:-$HOME/.cache}/resolve-aac/) and reused across runs.
#
# Usage:
#   resolve-codec-patch fix-file <source.mp4|.m4a|.mov>
#   resolve-codec-patch sibling-path <source.mp4|.m4a|.mov>   # print the cache path; no action

set -euo pipefail

CMD="${1:-}"
SRC="${2:-}"

if [ -z "$CMD" ] || [ -z "$SRC" ]; then
    cat <<EOF >&2
usage: $0 fix-file <source>           # transcode <source> to a FLAC-audio sibling in the cache dir
       $0 sibling-path <source>       # print the would-be sibling path, no transcode

env:
  AAC_REDIRECT_CACHE_DIR (default \${XDG_CACHE_HOME:-\$HOME/.cache}/resolve-aac)
      where cache siblings are written; the hybrid shim reads the same env var.
EOF
    exit 2
fi

CACHE_DIR="${AAC_REDIRECT_CACHE_DIR:-${XDG_CACHE_HOME:-$HOME/.cache}/resolve-aac}"

# resolve absolute path so the hash is stable across the user's cwd
SRC=$(readlink -f -- "$SRC" 2>/dev/null || echo "$SRC")
[ -r "$SRC" ] || { echo "source not readable: $SRC" >&2; exit 1; }

# AAC_FIX_OUT_PATH lets the in-process shim (aac_hybrid_shim.so) dictate the
# exact sibling path it will stat() after we exit — must be honored so the
# shim's lookup finds what we wrote. Otherwise compute a default cache path.
if [ -n "${AAC_FIX_OUT_PATH:-}" ]; then
    DEST="$AAC_FIX_OUT_PATH"
else
    # 8-hex of source absolute-path DJB2 (matches aac_hybrid_shim.so::path_hash
    # AND pre-backfill-aac _djb2 — single source of truth across the trio).
    # Direct CLI calls used to default to sha256 here, which created orphan
    # cache entries the shim couldn't find on import (caught 2026-05-26).
    HASH=$(python3 -c "
import sys
h = 5381
for c in sys.argv[1].encode():
    h = ((h << 5) + h + c) & 0xFFFFFFFFFFFFFFFF
print(f'{h & 0xFFFFFFFF:08x}')
" "$SRC")
    BASE=$(basename -- "${SRC%.*}")
    DEST="$CACHE_DIR/${HASH}-${BASE}.resolve.mp4"
fi

case "$CMD" in
    sibling-path)
        echo "$DEST"
        exit 0
        ;;
    fix-file)
        # already exists? respect the cache
        if [ -f "$DEST" ] && [ -s "$DEST" ]; then
            echo "$DEST  (cache hit)" >&2
            exit 0
        fi
        mkdir -p "$CACHE_DIR"
        command -v ffmpeg >/dev/null 2>&1 || { echo "ffmpeg not found in PATH" >&2; exit 1; }
        # flock the destination so concurrent imports of the same file serialize
        LOCK="$DEST.lock"
        exec 9>"$LOCK"
        if ! flock -w 60 9; then
            echo "could not obtain lock $LOCK after 60s" >&2
            exit 1
        fi
        # racy double-check after lock acquired
        if [ -f "$DEST" ] && [ -s "$DEST" ]; then
            echo "$DEST  (cache hit after lock)" >&2
            exit 0
        fi
        # ffmpeg picks the muxer from the EXTENSION; .tmp.$$ MUST go BEFORE
        # .mp4 so the filename still ends in .mp4 and ffmpeg writes ISO-BMFF.
        # (otherwise: "Unable to choose an output format for ...tmp.NNN".)
        TMP="${DEST%.mp4}.tmp.$$.mp4"
        # -map 0:v? — copy video stream if present (None for audio-only sources is fine)
        # -map 0:a:0 — first audio stream
        # -c:v copy — never recompress video
        # -c:a flac -compression_level 0 — fast lossless FLAC (Resolve decodes natively)
        # FLAC-in-mp4 is supported per ISO/IEC 14496-12 Annex E.2 (codingname 'fLaC').
        # 300s timeout — protects against malformed/malicious AAC that hangs
        # the decoder. 300s comfortably covers a 4-hour podcast on modern CPUs
        # at libavcodec AAC decode speed (~20-50× realtime).
        if timeout 300 ffmpeg -y -hide_banner -loglevel error \
                  -i "$SRC" \
                  -map 0:v? -c:v copy \
                  -map 0:a:0 -c:a flac -compression_level 0 \
                  -movflags +faststart \
                  "$TMP" </dev/null; then
            mv -f "$TMP" "$DEST"
            echo "$DEST" >&2
        else
            rm -f -- "$TMP"
            echo "ffmpeg transcode failed for $SRC" >&2
            exit 1
        fi
        # Self-prune cache to AAC_CACHE_CAP_GB (default 50 GB) by oldest atime.
        # Backgrounded + errors swallowed so import path is never affected.
        (
            set +e
            cap_gb="${AAC_CACHE_CAP_GB:-50}"
            cap_bytes=$((cap_gb * 1073741824))
            total=$(du -sb "$CACHE_DIR" 2>/dev/null | cut -f1)
            if [ -n "$total" ] && [ "$total" -gt "$cap_bytes" ]; then
                find "$CACHE_DIR" -type f -name '*.resolve.mp4' -printf '%A@\t%s\t%p\n' 2>/dev/null \
                  | sort -n \
                  | while IFS=$'\t' read -r _ sz f; do
                        [ "$total" -le "$cap_bytes" ] && break
                        rm -f -- "$f" 2>/dev/null && total=$((total - sz))
                    done
            fi
        ) >/dev/null 2>&1 &
        disown 2>/dev/null || true
        ;;
    *)
        echo "unknown command: $CMD" >&2
        exit 2
        ;;
esac