#!/usr/bin/env bash
set -e

die() {
    echo "$0: error: $1" >&2
    exit 1
}

# Usage: update-source-hash <attr> <version> [<new-source-hash>]
attr=$1
newVersion=$2
newHash=$3

nixFile=$(nix-instantiate --eval --strict -A "$attr.meta.position" | sed -re 's/^"(.*):[0-9]+"$/\1/')
if [ ! -f "$nixFile" ]; then
    die "Couldn't evaluate '$attr.meta.position' to locate the .nix file!"
fi

oldHashAlgo=$(nix-instantiate --eval --strict -A "$attr.src.drvAttrs.outputHashAlgo" | tr -d '"')
oldHash=$(nix-instantiate --eval --strict -A "$attr.src.drvAttrs.outputHash" | tr -d '"')

if [ -z "$oldHashAlgo" -o -z "$oldHash" ]; then
    die "Couldn't evaluate old source hash from '$attr.src'!"
fi

if [ $(grep -c "$oldHash" "$nixFile") != 1 ]; then
    die "Couldn't locate old source hash '$oldHash' (or it appeared more than once) in '$nixFile'!"
fi

drvName=$(nix-instantiate --eval -E "with import ./. {}; (builtins.parseDrvName $attr.name).name" | tr -d '"')
oldVersion=$(nix-instantiate --eval -E "with import ./. {}; $attr.version or (builtins.parseDrvName $attr.name).version" | tr -d '"')

if [ -z "$drvName" -o -z "$oldVersion" ]; then
    die "Couldn't evaluate name and version from '$attr.name'!"
fi

if [ "$oldVersion" = "$newVersion" ]; then
    echo "$0: New version same as old version, nothing to do." >&2
    exit 0
fi

# Escape regex metacharacter that are allowed in store path names
oldVersion=$(echo "$oldVersion" | sed -re 's|[.+]|\\&|g')

if [ $(grep -c -E "^\s*(let\b)?\s*version\s+=\s+\"$oldVersion\"" "$nixFile") = 1 ]; then
    pattern="/\bversion\b\s*=/ s|\"$oldVersion\"|\"$newVersion\"|"
elif [ $(grep -c -E "^\s*(let\b)?\s*name\s+=\s+\"$drvName-$oldVersion\"" "$nixFile") = 1 ]; then
    pattern="/\bname\b\s*=/ s|\"$drvName-$oldVersion\"|\"$drvName-$newVersion\"|"
else
    die "Couldn't figure out where out where to patch in new version in '$attr'!"
fi

# Replace new version
sed -i.bak "$nixFile" -re "$pattern"
if cmp -s "$nixFile" "$nixFile.bak"; then
    die "Failed to replace version '$oldVersion' to '$newVersion' in '$attr'!"
fi

case "$oldHashAlgo" in
    sha256) hashLength=64 ;;
    sha512) hashLength=128 ;;
    *) die "Unhandled hash algorithm '$oldHashAlgo' in '$attr'!" ;;
esac

# Make a temporary all-zeroes hash of $hashLength characters
tempHash=$(printf '%0*d' "$hashLength" 0)

sed -i "$nixFile" -re "s|\"$oldHash\"|\"$tempHash\"|"
if cmp -s "$nixFile" "$nixFile.bak"; then
    die "Failed to replace source hash of '$attr' to a temporary hash!"
fi

# If new hash not given on the command line, recalculate it ourselves.
if [ -z "$newHash" ]; then
    nix-build --no-out-link -A "$attr.src" 2>"$attr.fetchlog" >/dev/null || true
    # FIXME: use nix-build --hash here once https://github.com/NixOS/nix/issues/1172 is fixed
    newHash=$(tail -n2 "$attr.fetchlog" | grep "output path .* has .* hash .* when .* was expected" | head -n1 | tr -dc '\040-\177' | awk '{ print $(NF-4) }')
fi

if [ -z "$newHash" ]; then
    cat "$attr.fetchlog" >&2
    die "Couldn't figure out new hash of '$attr.src'!"
fi

if [ "$oldVersion" != "$newVersion" ] && [ "$oldHash" = "$newHash" ]; then
    mv "$nixFile.bak" "$nixFile"
    die "Both the old and new source hashes of '$attr.src' were equivalent. Please fix the package's source URL to be dependent on '\${version}'!"
fi

sed -i "$nixFile" -re "s|\"$tempHash\"|\"$newHash\"|"
if cmp -s "$nixFile" "$nixFile.bak"; then
    die "Failed to replace temporary source hash of '$attr' to the final source hash!"
fi

rm -f "$nixFile.bak"
rm -f "$attr.fetchlog"