#!/bin/sh
# som-provenance-f7 -- write the record som-mfg-f7 checks an STM32F7 SOM image
# against, read from the image itself: U-Boot's banner and the prompt it carries,
# or a uImage's name and size; with the file's sha256 and where it came from.

set -u

PROG=som-provenance-f7
F7_DIR="${SOM_FIRMWARE_DIR:-/usr/share/brintos-som/stm32f7}"

usage() {
    cat <<EOF
usage: $PROG [--origin TEXT] [--prompt PROMPT] FILE...

Writes, for each FILE, the record som-mfg-f7 reads, so an image of your own
needs no record written by hand:

  a uImage (the kernel)  FILE.PROVENANCE: the image name in its uImage header
                         as version:, and its size
  a U-Boot               PROVENANCE in FILE's directory: the "U-Boot 20..."
                         banner it carries as version:, and the prompt
                         som-mfg-f7 waits for

  --origin TEXT   where the image came from (default: when and where this ran)
  --prompt P      the U-Boot prompt, for a U-Boot that does not carry the
                  built-in one ($(sed -n 's/^prompt: *//p' "$F7_DIR/PROVENANCE" 2>/dev/null))

Each record also gives the file's sha256 and size. A U-Boot's record is named
PROVENANCE, one per directory, so keep one U-Boot per directory.

Exit status: 0 every record written, 1 a file refused, 2 usage.
EOF
}

origin=""
prompt=""
while [ $# -gt 0 ]; do
    case "$1" in
        --origin)  [ $# -ge 2 ] || { usage >&2; exit 2; }; origin=$2; shift 2 ;;
        --prompt)  [ $# -ge 2 ] || { usage >&2; exit 2; }; prompt=$2; shift 2 ;;
        -h|--help) usage; exit 0 ;;
        --)        shift; break ;;
        -*)        echo "$PROG: unknown argument: $1" >&2; usage >&2; exit 2 ;;
        *)         break ;;
    esac
done
[ $# -gt 0 ] || { usage >&2; exit 2; }
[ -n "$origin" ] || origin="recorded on this station by $PROG, $(date -u '+%Y-%m-%d %H:%M:%S UTC')"

rc=0
refuse() { echo "$PROG: $1: refused -- $2"; rc=1; }

# The printable runs of a binary, one a line, as strings(1) prints them. Spelled
# as a range: busybox tr has no [:print:] class.
runs() { LC_ALL=C tr -c ' -~' '\n' < "$1"; }

for f in "$@"; do
    if [ ! -f "$f" ] || [ ! -r "$f" ]; then
        refuse "$f" "not a readable file"; continue
    fi
    case "$(cd "$(dirname "$f")" && pwd -P)" in
        "$(cd "$F7_DIR" 2>/dev/null && pwd -P)")
            refuse "$f" "a built-in image: its record ships with it"; continue ;;
    esac
    size=$(stat -L -c %s "$f")
    sum=$(sha256sum "$f" | cut -d' ' -f1)
    # busybox's small od takes no -A, -t or -N.
    magic=$(dd if="$f" bs=4 count=1 2>/dev/null | od -b | sed -n '1{s/^[0-7]*//;s/ //g;p;}')
    if [ "$magic" = 047005031126 ]; then
        name=$(dd if="$f" bs=1 skip=32 count=32 2>/dev/null | tr '\000' '\n' | sed -n 1p)
        if [ -z "$name" ]; then
            refuse "$f" "its uImage header names no image"; continue
        fi
        rec=$f.PROVENANCE
        body="image:   $(basename "$f")
target:  Emcraft STM32F7 SOM, NOR, written by U-Boot's update over TFTP
version: $name
origin:  $origin
sha256:  $sum
size:    $size bytes"
    else
        banner=$(runs "$f" | sed -n '/^U-Boot 20[0-9][0-9]\./{p;q;}')
        if [ -z "$banner" ]; then
            refuse "$f" "neither a uImage nor a U-Boot: it carries no \"U-Boot 20...\" banner"; continue
        fi
        p=$prompt
        [ -n "$p" ] || p=$(sed -n 's/^prompt: *//p' "$F7_DIR/PROVENANCE" 2>/dev/null)
        if [ -z "$p" ]; then
            refuse "$f" "no prompt to record: give it with --prompt"; continue
        fi
        if ! runs "$f" | grep -q -F -- "$p"; then
            refuse "$f" "it does not carry the prompt '$p', so som-mfg-f7 would wait for it in vain: give its own with --prompt"; continue
        fi
        rec=$(dirname "$f")/PROVENANCE
        body="image:   $(basename "$f")
target:  Emcraft STM32F7 SOM (STM32F756), eNVM at 0x08000000
version: $banner
prompt:  $p
origin:  $origin
sha256:  $sum
size:    $size bytes"
    fi
    [ -e "$rec" ] && echo "$PROG: replacing $rec"
    if ! printf '%s\n' "$body" > "$rec"; then
        refuse "$f" "cannot write $rec"; continue
    fi
    echo "$PROG: $rec"
    sed 's/^/  | /' "$rec"
done
exit $rc