#!/usr/bin/env bash
jsonLoadFromStdIn="json.load(sys.stdin)"
loopOverItems=false
loopJsonOperation=""

__doJsonOperation() {
    json="$1"
    operation="$2"

    operationWithJsonLoad=${operation/__JSON__/$jsonLoadFromStdIn}

    echo "${json}" | python -c "import sys, json; print ${operationWithJsonLoad}"
}

__convertJsonPathToOperation() {
    jsonPath="$1"

    jsonPath="${jsonPath:1}"
    jsonPath="${jsonPath//[/.[}"

    IFS='.' read -ra jsonPathParts <<< "${jsonPath}"

    loopOverItems=false
    loopJsonOperation=""
    jsonOperation="__JSON__"

    for jsonPathPart in "${jsonPathParts[@]}"; do
        if [ "${jsonPathPart:0:1}" = "[" ] && [ "${jsonPathPart: -1}" = "]" ]; then
            # handle array lookups

            if [ "${jsonPathPart}" = "[*]" ]; then
                # act on all items in array
                loopOverItems=true
            else
                # get item at index in array
                if [ "${loopOverItems}" = false ]; then
                    jsonOperation="${jsonOperation}${jsonPathPart}"
                else
                    loopJsonOperation="${loopJsonOperation}${jsonPathPart}"
                fi
            fi
        elif [ "${jsonPathPart}" = "length()" ]; then
            # get length of array
            if [ "${loopOverItems}" = false ]; then
                jsonOperation="len(${jsonOperation})"
            else
                loopJsonOperation="${loopJsonOperation}.__len__()"
            fi
        elif [ ! -z "${jsonPathPart}" ]; then
            # get object property
            if [ "${loopOverItems}" = false ]; then
                jsonOperation="${jsonOperation}['${jsonPathPart}']"
            else
                loopJsonOperation="['${loopJsonOperation}${jsonPathPart}']"
            fi
        fi
    done

    echo "jsonOperation=\"${jsonOperation}\"; loopOverItems=${loopOverItems}; loopJsonOperation=\"${loopJsonOperation}\""
}

json-path-query() {
    json="$1"
    jsonPath="$2"

    if [ -z "${json}" ] || [ -z "${jsonPath}" ]; then
        >&2 echo "Usage: $0 json jsonPath"
        return 1
    fi

    eval $(__convertJsonPathToOperation "${jsonPath}")

    if [ "${loopOverItems}" = false ]; then
        __doJsonOperation "${json}" "${jsonOperation}"
    fi

    numItems="$(__doJsonOperation "${json}" "len(${jsonOperation})")"

    for ((i=0; i < ${numItems}; i++)); do
        __doJsonOperation "${json}" "${jsonOperation}[${i}]${loopJsonOperation}"
    done
}