const postcss = require('postcss')

const defaults = {

rootSelector: ':root',

unit: 'lh',

lineHeight: 1.5

}

module.exports = postcss.plugin('lh', (opts = defaults) => {

const options = Object.assign(defaults, opts)

return css => {

const lineHeight = getLineHeight(css, options)

const lhReg = new RegExp('\\d*\\.?\\d+' + options.unit, 'gi')

css.replaceValues(lhReg, { fast: options.unit }, (val) => {

return lhToRem(parseFloat(val), lineHeight)

})

}

})

function getLineHeight (css, opts) {

// Start with the default line-height

let lineHeight = opts.lineHeight

// Walk over all the root selectors

css.walkRules(opts.rootSelector, rule => {

// Omit the process if the selector is inside a print media query

if (rule.parent && rule.parent.params === 'print') return

// Walk over all the font or line-height properties

rule.walkDecls(/font$|line-height/, decl => {

// Matches {$1:font-size}{$2:unit}/{$3:line-height} when the property is 'font'

const fontProps = decl.value.match(/(\d+|\d+?\.\d+)(r?em|px|%)(?:\s*\/\s*)(\d+|\d+?\.\d+)\s+/) || []

lineHeight = fontProps[3] || decl.value

})

})

return lineHeight

}

function lhToRem(val, lineHeight) {

return parseFloat((lineHeight * val).toFixed(3)) + 'rem'

}