"use strict"

const atRuleParamIndex = require("../../utils/atRuleParamIndex")
const declarationValueIndex = require("../../utils/declarationValueIndex")
const report = require("../../utils/report")
const ruleMessages = require("../../utils/ruleMessages")
const validateOptions = require("../../utils/validateOptions")
const valueParser = require("postcss-value-parser")

const ruleName = "number-leading-zero"

const messages = ruleMessages(ruleName, {
  expected: "Expected a leading zero",
  rejected: "Unexpected leading zero",
})

const rule = function (expectation) {
  return (root, result) => {
    const validOptions = validateOptions(result, ruleName, {
      actual: expectation,
      possible: [
        "always",
        "never",
      ],
    })
    if (!validOptions) {
      return
    }

    root.walkAtRules(atRule => {
      if (atRule.name.toLowerCase() === "import") {
        return
      }

      check(atRule, atRule.params, atRuleParamIndex)
    })

    root.walkDecls(decl => check(decl, decl.value, declarationValueIndex))

    function check(node, value, getIndex) {
      // Get out quickly if there are no periods
      if (value.indexOf(".") === -1) {
        return
      }

      valueParser(value).walk(valueNode => {
        // Ignore `url` function
        if (valueNode.type === "function" && valueNode.value.toLowerCase() === "url") {
          return false
        }

        // Ignore strings, comments, etc
        if (valueNode.type !== "word") {
          return
        }

        // Check leading zero
        if (expectation === "always") {
          const match = /(?:\D|^)(\.\d+)/.exec(valueNode.value)

          if (match === null) {
            return
          }

          // The regexp above consists of 2 capturing groups (or capturing parentheses).
          // We need the index of the second group. This makes sanse when we have "-.5" as an input
          // for regex. And we need the index of ".5".
          const capturingGroupIndex = match[0].length - match[1].length
          complain(messages.expected, node, getIndex(node) + valueNode.sourceIndex + match.index + capturingGroupIndex)
        }

        if (expectation === "never") {
          const match = /(?:\D|^)(0+\.\d+)/.exec(valueNode.value)

          if (match === null) {
            return
          }

          const capturingGroupIndex = match[0].length - match[1].length
          complain(messages.rejected, node, getIndex(node) + valueNode.sourceIndex + match.index + capturingGroupIndex)
        }
      })
    }

    function complain(message, node, index) {
      report({
        result,
        ruleName,
        message,
        node,
        index,
      })
    }
  }
}

rule.ruleName = ruleName
rule.messages = messages
module.exports = rule